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Measurements of gaseous HONO, HNO3, SO2, HCl, NH3, particulate sulfate and PM2.5 in New York, NY
AE International – North America Atmospheric Environment 37 (2003) 2825–2835
Measurements of gaseous HONO, HNO3, SO2, HCl, NH3, particulate sulfate and PM2.5 in New York, NY Abdul Baria, Vincent Ferraroa, Lloyd R. Wilsonb, Dan Luttingerb, Liaquat Husaina,c,* a
Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA b New York State Department of Health, Center for Environmental Health, 547 River Street, Troy, NY, USA c Department of Environmental Health and Toxicology, School of Public Health Sciences, State University of New York, Albany, USA Received 2 June 2002; accepted 12 March 2003
Abstract Simultaneous measurements of gaseous HONO, HNO3, HCl, SO2, and NH3 for a period of 1 year from July 1999 to June 2000 and fine-fraction particulate (o2.5 mm) sulfate (SO2 4 ) from January 1999 to November 2000 were made at Bronx and Manhattan in New York City with an annular denuder system followed by ion chromatography. The hourly PM2.5 mass was measured with a Rupprecht and Patashnick TEOM Series 1400a real-time monitor for approximately 2 years (January 1999–November 2000) at the same sites. Concentrations at the two sites were highly correlated, with Manhattan being slightly higher than at the Bronx. The concentrations of HNO3, HCl, NH3 and SO2 4 were higher during summer than winter, the summer/winter ratios at Manhattan being 3.9, 3.1, 1.5, and 1.9, respectively. The concentrations of HONO and SO2 were lower during summer than winter, the summer/winter ratios at Manhattan being 0.48 and 0.44, respectively. Gaseous HONO concentrations were higher than that of HNO3 except in summer, when the HNO3 was higher. The annual mean concentration of PM2.5 was 15.2 mg/m3 at the Bronx, and 15.5 mg/m3 at Manhattan (based only on days when data were available from both sites). The monthly mean concentrations at Manhattan ranged from 13.2 to 21.7 mg/m3 and were highest in June and July 1999, and lowest in March and April. The monthly mean fraction of PM2.5 as SO2 ranged from 0.17 to 0.31, with the highest values observed during 4 June–September. The hourly mean concentrations of PM2.5 showed a bimodal pattern, with peaks at around 7–8 AM and 8–9 PM. In general, the second maximum is lower than the morning one, but during summer this is reversed. The contributions from regional and local emissions and the influence of atmospheric transport and chemical reactions on the observed concentrations are discussed in a compendium paper. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Acidic gases; Ammonia; Annular denuder system; Urban area; Aerosol
1. Introduction
*Corresponding author. Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA. Tel.: +1-518-4734854; fax: +1-518-473-2895. E-mail address: [email protected] (L. Husain).
The secondary pollutants HONO, HNO3, and SO2 4 in the atmosphere are produced from natural and manmade emissions of primary gas phase pollutants such as SO2 and NOx by photochemical reactions. HCl is mainly produced by coal combustion and refuse incineration (Lightowlers and Cape, 1988), municipal and industrial waste incineration (Kaneyasu et al., 1999)
1352-2310/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1352-2310(03)00199-7
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as primary pollutant, and by the reaction of HNO3 (g) with NaCl (s, aq) in sea-salt particles (Eldering et al., 1991) as a secondary pollutant. Much of the United States SO2 emissions are from the midwestern states, for example in 1998 emissions from WV, OH, IL, IN, MI, WI, KY, and western PA, represented 39% of the National SO2 inventory. The eastern United States and southern Ontario are exposed to SO2 and SO2 from 4 these sources by long distance transport. Space heating also contributes to SO2 emission, especially in large urban areas during the winter. In large urban areas, nearly half of NOx emissions are caused by automobile exhaust (Spengler et al., 1990; Mayer, 1999; Mage et al., 1996). A significant percentage of the observed HONO is produced from vehicular exhaust (Pitts et al., 1984; Matsumoto and Okita, 1998). During several episodes of extreme air pollution in various countries, an increase in morbidity and mortality was observed, suggesting that ambient air pollution adversely affect human health. Exposure to elevated concentrations, or long-continued exposure to low levels of ambient air pollutants has received increasing attention due to the wide range of adverse effects of air pollutants on ecological systems and human health (Dockery and Pope, 1994; Koenig, 2000; Pope et al., 2002). In a study measuring acidic aerosols in six cities, Speizer (1989) reported a correlation between the prevalence of chronic bronchitis among children 10–12 years of age and PM15; there was also a correlation with hydrogen ion concentration in the particles. Earlier, Kitagawa (1984) reported severe cases of lung disease near a plant emitting sulfuric acid aerosols; the number of incidences decreased with increasing distance from the plant. The incidence of lung diseases decreased sharply when the sulfuric acid was removed from the emissions. Bates and Sizto (1987, 1989) observed correlation between the concentration of SO2 4 and the number of admissions for respiratory disease in hospitals in Southern Ontario. Balmes et al. (1989) confirmed that inhaled SO2 3 aerosols were a stimulus to bronchoconstriction in subjects with asthma. Dockery et al. (1993) positively associated air pollution with death from lung cancer and cardiopulmonary disease, and also found a strong association of mortality with air pollution consisting of fine particulates, including SO2 4 . Pope et al. (2002) have provided strong evidence that long-term exposure to fine particulate air pollution common to many metropolitan areas is an important risk factor for cardiopulmonary mortality. Continuous development of various components of the annular denuder system (ADS), and stable and laminar air flow in the ADS, has provided an improved method by which to selectively collect the air pollutants of interest at a much higher flow rate, with greater efficiency, and with minimal artifacts. Numerous studies have been carried out for the simultaneous measurement
of acidic gases and SO2 4 , but most of these studies were of short duration or did not measure all of these components (HONO, HNO3, HCl, SO2, NH3 and SO2 4 ). In this work, we have simultaneously measured acidic gases, and SO2 for all seasons using the ADS 4 from 23 June 1999 to 11 July 2000. In addition, SO2 4 and PM2.5 were measured for the entire study period, January 1999–November 2000. The data will also be used to investigate the relationship between the observed daily concentrations of chemical species and asthma incidences, as indicated by area hospital emergency room visits and possibly admissions (results to be reported elsewhere). Here, we report on the daily concentrations of HONO, HNO3, HCl, SO2, NH3, SO2 4 , and PM2.5, seasonal variations, relationship between chemical species and suggest chemical reactions that may explain the observations. The data are also compared, when available, with the measurements from other urban centers.
2. Experimental The sampling systems were set up on the roof (fifth floor) of the Mabel Dean High School, located at 14th Street and 2nd Ave, in Manhattan, and at Intermediate School 155 (IS 155, third floor) located at Jackson Ave and St. Mary’s street in the Bronx. On 14 July 1999, IS 155 site was shut down, and monitoring resumed on 14 September 1999 on the roof (third floor) of Middle School 52 on Kelly Street in the Bronx. The two Bronx sites are of comparable height and are about 1 km apart so the sites are assumed to be equivalent. The Mabel Dean High School and Middle School 52 sites are very near sea level, about 11 km apart and in center city environments with high-density residential populations. The Manhattan site is also located near a commercial district. Although both sites are elevated above street level, the air monitoring system at Bronx site is the lowest (15 m above the ground) and is likely to have the greatest ‘‘neighborhood’’ influence. The air monitoring system at Manhattan site is 38 m above sea level and its height is comparable to the surrounding buildings, thus it should be strongly impacted by regional as well as ‘‘neighborhood’’ sources. Mabel Dean High School and Middle School 52 are also New York State Department of Environmental Conservation (NYSDEC) continuous monitoring sites. The air samples were collected using URG-2000-01L, Eight Channel Sequential Fine Particle Sampler, each with two 120 mm long glass-heavy wall Annular Denuders connected in series, followed by a 47 mm filter module. The first annular denuder was coated with Na2CO3 to collect acidic gases, and the second with citric acid to collect ammonia. The flushend of the citric acid coated annular denuder was attached directly to the filter module. The filters
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
(47-mm-diameter, 2 mm-pore Zefluor filter, Gelman Laboratory) were positioned on the Teflon-coated stainless-steel screen so that the air stream particulates were trapped on the Teflon-coated side of the filter. Two cyclones with cut points of 10 and 2.5 mm preceded the ADS. Air samples were collected for 24 h starting at midnight, at a flow rate of 10 l/min. The annular denuder tubes were coated with appropriate coating solutions (citric acid: 1% w/v in methanol; sodium carbonate: 1% w/v, 1% w/v glycerol in a 1:1 methanol/ water solution), and the coated tubes were dried with ‘‘zero’’ air at a rate of 3 l/min. The denuder trains were assembled and were leak-checked in clean laboratory conditions. With each batch of seven denuder assemblies (ADS+Filter) sent out in the field, a blank denuder assembly was included. It was left for 7 days inside the sampler but was not connected to the air flow. The coated annular denuders from the exposed assemblies and field blanks were extracted with 10 ml ultra-pure water (Millipore, Milli-Q UV Plus water system), and stored at 4 C for analysis. The water extract from sodium carbonate coated denuders was used for the determination of HONO, HNO3 and HCl. For SO2 analysis 5 ml of the water extracts from the sodium carbonate coated denuders were oxidized with 0.05 ml of 30% aqueous H2O2 solution to completely oxidize the collected SO2 to SO2 4 before analysis. The water extract from citric acid denuder was used to determine ammonia. The measurement of chloride, nitrite, nitrate, sulfate and ammonium was made with a DIONEX 500 ion chromatography system and the results were calculated for gaseous HCl, HONO, HNO3, SO2, and NH3. The separation of chloride, nitrite, nitrate, and sulfate was accomplished using an IonPac AS 14 (4 250 mm) analytical column, AG 14 guard column, with a 10 ml sample loop, and an anion self-regenerating suppressor-ultra A solution of 3.5 mM Na2CO3/1.0 mM NaHCO3 was used as eluent at a flow rate of 1 ml/min. The separation of ammonium was accomplished using an IonPac CS 14 (4 250 mm) analytical column, and a CG 14 guard column, with a 50 ml sample loop, and a cation self-regenerating suppressor-ultra A solution of 10 mM methanesulfonic acid was used as eluent at a flow rate of 1 ml/min. The Zefluor filters were ultrasonically extracted for 1 h in 5 ml ultra-pure water and stored at 4 C for analysis of particulate sulfate. The filter extracts were analyzed for SO2 by ion chromatography using 4 the DIONEX 100 ion chromatography system. Selenium was also determined in some of the filter extracts using inductively coupled plasma mass spectrometry (Richter et al., 1998). Concentrations in the field blanks for the target species were subtracted on a batch-to-batch basis. Accuracy of calibration curves was checked by analyzing the quality control samples, containing the analytes of interest at a concentration in the low- and highconcentration range provided by an independent QA/
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QC laboratory within the Wadsworth Center. For all the analytes the controls were within 710%. The percent standard deviation of measurements, evaluated on duplicate runs of several samples, was found to be better than 73.0%. PM2.5 measurements were made with a Rupprecht and Patashnick (R&P) TEOM Series 1400a real-time monitor. A 16.7 l/min airstream was pulled through the instrument. The air was pulled through a PM2.5 inlet, then isokinetically split into 3 l/min (lpm) and 13.7 lpm airstreams, sending the 3 lpm airstream to the instrument’s mass transducer. The flow was held at a constant volume by a mass flow controller and was corrected for local temperature and barometric pressure. Inside the mass transducer, the air stream was filtered by a Tefloncoated borosilicate glass filter located at the end of an oscillating tapered element. As mass collects on the filter the change in the oscillations were measured and converted to mass. A measure of the change in the mass concentration was made every 2 s and used to calculate hourly averages in particulate mass. The filter unit was held at 50 C to prevent condensation.
3. Results and discussion 3.1. Acidic gases Concentrations of acidic gases, HONO, HNO3, HCl, and SO2 were measured daily (midnight to midnight, local time) from 23 June 1999 to 11 July 2000 at both the Manhattan and Bronx sites. Table 1 gives a summary of the quarterly mean, median, and concentration range for all the species measured, for the period from 1 July 1999 to 30 June 2000. Summer season is defined as July– September, and winter as January–March. The daily HONO concentrations at Manhattan fluctuated widely, from the detection limit to about 9 ppb (Fig. 1a). Data at Bronx showed very similar variations and were highly correlated (r2 ¼ 0:81) with those from Manhattan. HNO3 concentrations at both sites showed less variation than for HONO. From the daily concentrations, we calculated the monthly mean concentrations. The data show a strong seasonal pattern. Since the data from both sampling sites show a similar pattern, only the Manhattan data are presented in Fig. 1b. A strong seasonal pattern is evident, with HNO3 concentrations being high during summer and low during the remaining months. These observations are in agreement with earlier studies (Danalatos and Glavas, 1999; Kasper and Puxbaum, 1998; Cadle, 1985; Keeler et al., 1991; Lee et al., 1993). The summer to winter ratio for HNO3 is 3.9. HNO3 concentrations approach or exceed 5 ppb only during May–August. The pattern for HONO shows the reverse. In Newton, a suburban Connecticut site, Keeler et al. (1991) observed much lower values for
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
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Table 1 Mean, median, and concentration range of HONO, HNO3, HCl, SO2, NH3, and SO2 4 at Manhattan and the Bronx in New York City SO2 (ppb)
NH3 (ppb)
SO2 4 (ppb)
B
M
B
M
B
M
B
0.32 0.34 360 0.2 0.01 1.98
0.28 0.27 299 0.2 0.01 1.83
10.2 7.3 359 8.5 1.2 59.8
10.0 7.2 300 8.3 0.6 50.6
5.0 2.7 182 5.0 0.9 15.5
3.1 2.6 148 2.4 0.1 9.9
1.08 0.96 359 0.79 0.07 6.08
0.9 0.76 300 0.69 0.04 4.96
0.76 0.7 34 0.6 0.04 2.49
0.62 0.47 90 0.51 0.01 1.98
0.45 0.38 34 0.35 0.04 1.55
6.7 3.9 90 5.7 1.2 17.4
5.0 4.3 34 3.9 0.6 20.1
6.1 1.3 47 6.2 2.2 8.7
1.61 1.44 90 1.04 0.07 6.08
1.28 1.34 34 0.66 0.04 4.96
0.24 0.2 91 0.18 0.02 1.1
0.18 0.14 90 0.15 0.01 0.68
0.17 0.11 91 0.14 0.02 0.51
0.19 0.12 90 0.16 0.01 0.56
12.3 7.1 90 10.4 2.3 37.8
11.4 6.5 90 10.2 0.6 35.9
0.75 0.5 90 0.56 0.16 2.45
0.7 0.47 90 0.55 0.05 2.19
January–March 2000 Mean 2.13 1.93 s.d. 1.39 1.35 Count 88 85 Median 1.72 1.49 Min 0.61 0.29 Max 8.76 6.5
0.36 0.27 88 0.28 0.04 1.15
0.2 0.12 85 0.18 0.05 0.58
0.2 0.14 88 0.165 0.01 0.6
0.27 0.17 85 0.23 0.02 0.7
15.5 8.9 88 13.3 2.2 59.8
14.7 8.4 85 12.5 2.6 50.6
4.1 2.6 88 3.4 0.9 11.9
2.1 2.1 87 1.6 0.1 9.6
0.86 0.5 88 0.745 0.23 2.4
0.79 0.47 85 0.68 0.22 1.98
April–June 2000 Mean 1.4 s.d. 1.03 Count 91 Median 1.19 Min 0.26 Max 6.11
0.6 0.59 91 0.37 0.04 2.66
0.58 0.61 91 0.32 0.05 2.79
0.3 0.31 91 0.18 0.01 1.32
0.33 0.36 90 0.19 0.02 1.83
6.7 3.5 91 5.9 1.5 16.9
6.1 3.4 91 5.0 1.6 19.3
5.9 3.4 44 5.0 1.6 15.5
4.2 2.6 46 3.3 0.7 9.9
1.11 0.84 91 0.82 0.13 3.88
1.06 0.84 91 0.77 0.17 4
HNO2 (ppb)
HNO3 (ppb)
HCl (ppb)
M
M
B
M
July 1999–June 2000 Mean 1.71 1.65 s.d. 1.22 1.24 Count 357 300 Median 1.49 1.32 Min 0.04 0.02 Max 8.76 6.58
0.64 0.82 357 0.33 0.02 5.69
0.37 0.48 300 0.21 0.01 2.79
July–September 1999 Mean 1 1.06 s.d. 0.76 0.83 Count 87 34 Median 0.83 0.92 Min 0.04 0.02 Max 3.32 2.76
1.39 1.21 87 0.97 0.04 5.69
October–December 1999 Mean 2.31 2.1 s.d. 1.13 1.33 Count 91 90 Median 2.17 1.76 Min 0.67 0.28 Max 5.41 6.58
B
1.16 0.91 91 1.04 0.19 6.14
M—Manhattan; and B—Bronx.
HONO (average value=0.4 ppb). The summer/winter ratio for HONO is 0.48. During winter, HONO concentrations are approximately 10-fold those of HNO3. The pattern of seasonal variation of HONO with a minimum in summer can be attributed to photolysis. The seasonal pattern for HNO3 can be assumed to be due to the reaction NO2+OH-HNO3. The production of HNO3 should be greater in summer due to the larger hydroxyl and O3 concentrations, and humidity. The seasonal variation can also be attributed to the reaction of HNO3 with ammonia, and to the dissociation
constant of NH4NO3, which increases with temperature (Stelson and Seinfeld, 1982). In summer, NH4NO3 will be mostly in the dissociated form, but mostly undissociated in winter, favoring a HNO3 minimum during winter. Fig. 2 shows the relationships between NO2 and HONO, HNO3, and [HONO+HNO3]. There is no correlation between NO2 and HONO (r2 ¼ 0:04), or between NO2 and HNO3 (r2 ¼ 0:21), but a trend is observed between NO2 and [HONO+HNO3] (r2 ¼ 0:44) concentrations. During a study in central urban, suburban, and rural environments, Harrison et al. (1996) observed that HONO was correlated with NO2 in
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
8
8
HONO (ppb)
HONO (ppb)
10
6 4 2 Jun-00
May-00
Apr-00
Mar-00
Feb-00
Jan-00
Dec-99
Nov-99
Oct-99
Sep-99
Aug-99
Jul-99
0
(a)
y = 0.029x + 0.666 R2 = 0.039
6 4 2 0 10
20
HONO (ppb)
2.5
40
50
60
50
60
50
60
HNO3 (ppb)
8
2.0 1.5
HNO3 (ppb)
(ppb)
30
NO2 (ppb)
3.0
1.0 0.5 0.0
(b)
2829
Jul-99
Sep-99
Nov-99
Jan-00
Mar-00
May-00
Fig. 1. (a) Daily concentrations of HONO at Manhattan; and (b) Monthly mean concentrations of HONO and HNO3 at Manhattan.
surface
2NO2 þ H2 O ! HONO þ HNO3 :
ð1Þ
Gaseous HNO3 produced by the above reaction is not observed in equivalent amounts to HONO due to its adsorption on surfaces (Finlayson-Pitts and Pitts, 2000). The formation of HONO by the heterogeneous reaction NO2 þ surface reduced site þ H2 O -HONO þ surface oxidized site þ OH
ð2Þ
has been proposed, and Gerecke et al. (1998) have reported large yields of HONO. This reaction can take place in parallel to the above reaction in polluted urban areas, as well as in the upper troposphere where soot from commercial aircraft is injected into the atmosphere (Finlayson-Pitts and Pitts, 2000). The observed trend between NO2 and the sum of HONO and HNO3 may be attributable to reaction (1), or reactions (1) and (2) taking place at the same time. HONO is also formed by the NO+OH reaction during daytime (Harrison et al., 1996). Other sources of HONO include auto exhaust, diesel exhaust (Kirchstetter et al., 1996; Arens et al., 2001). Use of gas stoves in the houses produces high concentrations of NO2 and significant amount of HONO, thus affecting the outdoor pollution in urban areas (Febo and Perrino, 1991).
y = 0.060x - 1.260 R2 = 0.212
4 2 0 10
20
30
40
NO2 (ppb) [HONO+HNO 3] (ppb)
suburban and rural areas, but not in central urban areas. They inferred that, although the formation of HONO in the central urban area was from NO2, the concentrations of HONO and NO2 were not highly correlated because of the relative proximity to motor traffic. HONO is also produced by the reaction
6
8 y = 0.088x - 0.594 2 R = 0.413
6 4 2 0 10
20
30
40
NO2 (ppb) Fig. 2. Relationship between NO2 versus HONO, HNO3, and [HONO+HNO3]. The NO2 values are averaged from hourly continuous chemiluminiscent measurements (TECO Model 42) obtained from the NYSDEC.
N-containing species (such as NOx and Peroxyacetyl nitrate (PAN)) are potential interfering agents, and can produce NO 2 and NO3 inside the sodium carbonate coated denuder resulting in the overestimation of HONO and HNO3 concentrations. However, our data shows that the artifact is very small. If HONO and HNO3 are produced by the heterogeneous reaction of NO2 and water vapor, then equivalent amount of each will be produced on the denuder surface. Fig. 1b indicates that the contribution from the artifact is minimal. Comparing the daily concentrations of HONO and HNO3 also indicates the same. During winter, the concentrations of HNO3 is very small compared to HONO, for example during 1–4 January 2000 the
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
seasonal patterns. The concentration of SO2 is higher during winter than summer (summer/winter=0.44), while the SO2 4 concentration is higher during summer (summer/winter=1.9). Increased concentrations of SO2 in summer have been observed in many studies 4 (Parekh and Husain, 1982; Koutrakis et al., 1988b; Altshuller, 1984; Puxbaum et al., 1993; Kasper and Puxbaum, 1998; Danalatos and Glavas, 1999; Shaw and Paur, 1983). Higher concentration of SO2 4 in summer can be attributed to (a) the increased rate of oxidation of SO2 due to the higher concentrations of oxidizing species (Danalatos and Glavas, 1999; Calvert et al., 1978); and (b) longer reaction times during periods of meteorological stagnation (Shaw and Paur, 1983). The sum of gaseous SO2 and particulate SO2 shows a maximum 4 during winter. This could be due to the increased SO2 emissions in winter from space heating since this is a high-density area, or from seasonal differences in dispersion rates. Fig. 3b shows monthly mean percentage of total 2 sulfur present as SO2 fraction is much 4 . The SO4 higher during the warmer period (about 19%) compared to the colder part of the year (about 5–7%); a similar trend was observed by Altshuller (1984), Shaw and Paur (1983). Dutkiewicz et al. (2000) observed a similar trend over a number of years at Mayville and Whiteface Mountain, NY, where about 31% and 65–82%, respectively, of total sulfur was in the aerosol phase during the summer of 1998. The lower SO2 4 component in New York City suggests that the contribution from local or nearby sources to total S is more important than it is at Mayville or Whiteface Mountain. This suggestion 2 is also supported by the SO2 4 /Se ratios. Because SO4 is 20
3 SO2
Sulfate
2
12 8
1
Sulfate (ppb)
16 SO2 (ppb)
concentrations of HNO3 were 0.11, 0.12, 0.08, and 0.05 ppb, respectively, but during the same period concentrations of HONO were 4.47, 6.23, 5.5, and 4.13 ppb, respectively. During summer when the concentration of HONO is very small compared to HNO3, for example during 4–8 July 1999 the concentrations of HONO were 0.19, 0.15, 0.04, 0.08 and 0.11 ppb, respectively while that of HNO3 were 2.55, 2.42, 2.39, 1.08, and 1.13 ppb, respectively. We also did not see relationship between daily NO2 concentration and either HONO or HNO3 concentrations. On a number of occasions, we observe that when the concentration of NO2 is maximum, the concentration of HONO or HNO3 is minimum and vice versa. PAN thermally decomposes to peroxyacetyl radical and NO2, hence the artifact from it will be similar to NO2. This is also supported by the studies using sodium carbonate coated denuders in series. In rural and semirural sites, the artifact correction was typically around 20% (Massih et al., 1992). In suburban areas, the artifact correction was around 12710% for HONO and 675% HNO3 (Dasch et al., 1989). In urban areas, the artifact correction was observed to be less than that observed in rural, semirural and suburban areas, and in general ranged from 2% to 12.5% for HONO (Koutrakis et al., 1988a; Appel et al., 1990; Perrino et al., 1990; Harrison et al., 1996; Bai and Wen, 2000), and 3.4–13.2% for HNO3 (Koutrakis et al., 1988a; Perrino et al., 1990). Bai and Wen (2000) showed that the relative errors for HONO gas can be less than 10% as sampled with only one Na2CO3-coated denuder. The relative error due to artifact for the HONO and HNO3 measurements in urban areas will be less than about 13% when sampled with only one sodium carbonate coated denuder. SO2 concentrations were determined daily (midnight to midnight), from July 1999 to June 2000 using the ADS and ion chromatography. SO2 concentrations are routinely collected by the NYSDEC monitoring network at these sites, using a pulsed-fluorescence analyzer (TECO 43S). The data from the two techniques were in excellent agreement (r2 ; 0.92; slope, 1.01; intercept, 1.26). The denuder technique results in slightly lower values than pulsed-fluorescence analyzer. The daily SO2 concentrations varied nominally from B1 to 10 ppb except in winter, when concentrations as high as 60 ppb were observed. The daily SO2 4 concentrations were as high as 6 ppb during warmer months, but during the rest of the year the maximum values were around 2.5 ppb. While SO2 concentrations are usually expressed in 4 mass units comparison with SO2 are more meaningful when molar equivalents are used. Thus SO2 4 concentrations have been converted to ppb equivalents (1 ppb=3.96 mg/m3). Monthly mean concentrations at Manhattan were calculated from the daily concentrations for gaseous SO2 and fine particulate SO2 4 (Fig. 3a). SO2 and particulate sulfate show opposite
4 0
(a)
[SO 4/(SO2+SO4)]*100
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(b)
0 Jul-99
Sep-99 Nov-99 Jan-00
Mar-00 May-00
25 Manhattan
Bronx
20 15 10 5 0 Jul-99
Sep-99 Nov-99
Jan-00
Mar-00 May-00
Fig. 3. (a) Monthly mean concentrations of SO2 and SO2 4 ; and (b) Monthly mean percentage of total sulfur present as SO2 4 .
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
added by oxidation of SO2 during atmospheric transport, the SO2 4 /Se ratios increase as the air moves away from the source. Compared to the SO2 4 /Se ratios of about 9000 during summer at Whiteface Mountain, the ratios in New York City were observed to be about 4000. Lower SO2 4 /Se ratios in New York City compared to Mayville or Whiteface Mountain could be due to SO2 emission from local or nearby sources. However, the data were limited to 1 week of sampling, and hence must be taken as preliminary. Very few studies are available for the measurement of gaseous HCl, and most of these are of short duration. Fig. 4a and b shows the daily concentrations of gaseous HCl at Manhattan, and monthly means at the Bronx and Manhattan. The seasonal trend for HCl is similar to that observed for HNO3. The concentration of gaseous HCl is high during summer and low during winter; the summer/winter ratio is 3.1. During a study of the longterm HCl concentrations in the Southern California atmosphere by the denuder difference method, Eldering et al. (1991) also observed that HCl concentrations peak in the summer months, with peak single day concentrations of 4.02 ppb at Hawthorne and 3.02 ppb at downtown Los Angles. Their study also supported the hypothesis that the reaction of HNO3 gas with sea salt was the source of the HCl in the Los Angles atmosphere. Matsumoto and Okita (1998) also observed higher HCl in summer in Narra, Japan, a medium size city, and a
2.0
1.0 0.5
3.2. Ammonia Ammonia, a primary gas phase pollutant, is the major neutralizing agent in the atmosphere and plays an important role in the chemistry of the atmosphere. Major sources of ammonia emissions are live stock and ammonia-based chemical fertilizers. Other sources of ammonia emissions are human beings, sewage treatment plants and catalytic converter equipped vehicles. Most of the ammonia is emitted near the earth’s surface and may react with acidic constituents in the atmosphere. Ammonia reacts irreversibly with sulfuric acid containing aerosols, and reversibly with both nitric and hydrochloric acids to form relatively neutral ammonium salt aerosols, which can again dissociate, with the dissociation being dependent upon temperature and humidity. Fig. 5 shows the daily concentrations of ammonia at Manhattan. The concentration of ammonia varied considerably from day to day. The overall mean of all the values (n ¼ 182) measured was 5.0 ppb (range: 0.9–15.5 ppb; s.d.: 2.7). For comparison, the mean values of ammonia in various urban areas are given in Table 2. The monthly mean concentrations of ammonia ranged from 3.2 to 7.6 ppb, with lowest values observed during December 1999–February 2000 (3.2–3.8 ppb) and the highest during June–July 1999 and May 2000 (6.6–7.6 ppb). Similar seasonal trends were observed by Yamamoto et al. (1995), in urban Yokohama, Japan;
Jun-00
May-00
Apr-00
Mar-00
Jan-00
Feb-00
Dec-99
Oct-99
Nov-99
Sep-99
Aug-99
16 14
0.6 0.4
Bronx
Manhattan
0.2 0.0
12 NH 3 (ppb)
Monthly mean
10 8 6 4
May-00
Apr-00
0 Mar-00
Fig. 4. (a) Daily concentrations of HCl at Manhattan; and (b) monthly means at Bronx and Manhattan.
2 Dec-99
(b)
0.8
Jul-99 Aug-99 Sep-99 Oct-99 Nov-99 Dec-99 Jan-00 Feb-00 Mar-00 Apr-00 May-00 Jun-00
HCl (ppb)
1.0
Feb-00
(a)
Jul-99
0.0
summer/winter ratio of 1.6. Puxbaum et al. (1993), in a study at a rural site in northeastern Austria observed that the HCl values peaked during winter, with a summer/winter ratio of 0.4. As the primary source of HCl in Eastern Europe is coal combustion, the authors suggested that the winter peak may be due to the more effective transport in winter than summer due to the shallower boundary layer and smoother surface due to snow cover.
Jan-00
HCl (ppb)
1.5
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Fig. 5. Daily concentrations of ammonia at Manhattan.
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
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Table 2 Ammonia (ppb), concentrations in urban locations Site
Period
NH3
Reference
New York, NY Hamilton, Canada Windsor, Canada Yokohama, Japan Narra, Japan Seoul, South Korea Chicago, IL Philadelphia, PA Philadelphia, PA Deurne, Netherlands
1999–2000 1992–1994 1992–1994 5 years June 1994–May 1999 October 1996–September 1997 April 1990–March 1991 1992 1993 1996
5.1 6.24 2.48 6.85–10.2 3.54 6.32 2.38 1.18–5.54 2.04–5.68 16.9
This work Brook et al. (1997) Brook et al. (1997) Yamamoto et al. (1995) Matsumoto and Okita (1998) Lee et al. (1999) Lee et al. (1993) Suh et al. (1995) Suh et al. (1995) Hoek et al. (1996)
1:1
400
Linear (Series1)
26 PM 2.5 (µg/m3)
300
200
Manhattan
Bronx
18 14 10 Jan- Mar- May- Jul- Sep- Nov- Jan- Mar- May- Jul99 99 99 99 99 99 00 00 00 00
(a) y = 0.496x R2 = 0.084
100
22
Manhattan Bronx
20
0 0
200
400 3 NH3 (nmol/m )
600
800
Fig. 6. Correlation between the sum of nitric acid, nitrous acid, and hydrochloric acid versus ammonia. 1:1 line is drawn to indicate the excess of NH3 over acidic species.
PM2.5 (µg/m3)
[HNO 3+HONO+HCl] (nmol/m 3)
Monthly mean
22
16 14 12 10 0
(b)
Lee et al. (1999) in urban Seoul, South Korea; and Lee et al. (1993) in urban Chicago. The Manhattan summer to winter ratio was 1.5. Fig. 6 shows the correlation between the sum of nitric acid, nitrous acid, hydrochloric acid versus ammonia (in units of nmol/m3). It is obvious that in New York City the concentration of ammonia was in large excess compared to the concentrations of individual acids. So it is reasonable to expect that any H2SO4 present would be neutralized by forming NH4HSO4 and (NH4)2SO4. It is also observed that on 84% of the days during this study, the concentration of ammonia exceeded the sum of the concentrations of the three acids. 3.3. PM2.5 The mass of PM2.5 was measured hourly in both Manhattan and the Bronx from January 1999 through November 2000 with a Rupprecht and Patashnick
Time of day variation of PM2.5
18
300
600
900 1200 1500 Time of Day (hrs)
1800
2100
2400
Fig. 7. (a) Monthly mean concentrations of PM2.5 at Manhattan and Bronx; and (b) time of day variation of PM2.5 at Manhattan and Bronx.
TEOM Series 1400a real-time monitor. From the values of hourly mass of PM2.5, 24 h averages were calculated for both the sites. The PM2.5 concentration averaged 15.2 mg/m3 at the Bronx site and 16.1 mg/m3 at the Manhattan site. However, the PM2.5 concentration averaged 15.5 mg/m3 at Manhattan, if only days when Bronx data is also available are used. The PM2.5 concentrations varied greatly from day to day and throughout the day. The highest hourly concentrations and the daily mean were 94.8 and 51.6 mg/m3, respectively at Manhattan on 24 July 1999. The monthly means of PM2.5 at Manhattan and the Bronx are shown in Fig. 7a. The monthly mean concentrations of PM2.5 at Manhattan ranged from 13.2 to 21.7 ug/m3 with an
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
overall mean of 16.1 ug/m3, higher averages were found in June and July (18.1 and 21.7 ug/m3, respectively), and the lowest were found in March and April (13.2 and 13.7 ug/m3, respectively) in 1999. Brook and Dann (1999) have reported similar trends in Hamilton and Windsor, Ontario, and Parkhurst et al. (1999) have also observed high summer–low winter seasonality in the southeastern United States. In Manhattan, the monthly mean fraction of PM2.5 as SO2 4 ranged from 0.17 to 0.31. The highest fraction values were observed during the months of June to September with the maximum in July. This can be explained in terms of higher concentration of SO2 during summer as 4 discussed earlier. TEOM operates at 50 C, hence it can give lower values for PM2.5, by an average of more than 20–30% (Ayers et al., 1999; Allen et al., 1997), when compared with traditional filter-based gravimetric methods due to the loss of semivolatile material such as ammonium nitrate and semivolatile organic matter at this temperature. Since the NYDEC determined daily PM2.5 mass using a Federal Reference Method (FRM) at each of the sites, the daily values from the Bronx and Manhattan sites were compared with the DEC FRM PM2.5 values (available on the web site at http:// www.dec.state.ny.us/website/dar/baqs/pm25mon.html). The correlation for the combined data set was good, with an r2 of 0.92 and the slope of 0.95. The values from TEOM were only slightly lower than the FRM method. Concentrations of PM2.5 at Manhattan and the Bronx varied by time of day (Fig. 7b). The absolute value of the maxima and minima vary somewhat with season, but the bimodal pattern is clearly evident at both sites. Minimum mass occurs during the night; however, by 0500 h, the mass is increasing and peaks around 0700 h at Bronx and 0800 h at Manhattan. The peak at Manhattan is also around 1 mg/m3 higher. The PM2.5 concentration decreases by B4 mg/m3 at midday. A second peak is reached between 2000 and 2100 h. In general, the second peak is lower than that in the morning; however, during the third quarter this can be reversed, for example the highest concentration recorded was at Manhattan, 94.8 mg/m3 at 2200 h on 24 July 1999. The diurnal pattern of a pollutant depends on local emissions, chemistry, and the dynamics of the local meteorology. While the profile at Manhattan is around a mg/m3 higher between 0800 and 2200 h than that at Bronx, the shapes are very similar. Linear regression of the hourly data at the two sites has an r2 of only 0.62 but the slope is 0.97. However, if daily means are compared an r2 of 0.92 is obtained with a slope of 0.95. This suggests that at these sites PM2.5 mass has a significant regional component with only minor contributions due to very local sources. We have no specific information, however, to distinguish which process is controlling the mass at these sites.
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4. Summary Concentrations and seasonal variations of gaseous nitrous acid, nitric acid, hydrochloric acid, sulfur dioxide, ammonia, and SO2 4 , and PM2.5 were determined at monitoring sites in the Bronx and Manhattan in New York from 1999 to 2000. The inter-site (Bronx and Manhattan) correlations for nitrous acid, nitric acid, hydrochloric acid, sulfur dioxide, particulate sulfate and PM2.5 were very high, correlation coefficients were generally greater than or equal to 0.83 (0.83–0.96). Concentrations at Manhattan were, in general, slightly higher than at the Bronx for each of the species. The data showed marked seasonal variations. The concentrations of nitric acid, hydrochloric acid, ammonia, and SO2 were higher during summer than winter, the 4 summer/winter ratio for nitric acid, hydrochloric acid, and SO2 at Manhattan was 3.9, 3.1 and 1.9, 4 respectively. The concentrations of nitrous acid, and sulfur dioxide were higher during winter than summer; the summer/winter ratio at Manhattan was 0.48 and 0.44, respectively. Gaseous nitrous acid was the predominant form compared to nitric acid except in summer. The annual mean concentration of PM2.5 was 15.2 and 15.5 mg/m3 at the Bronx and at Manhattan, respectively. The monthly mean concentrations at Manhattan ranged from 13.2 to 21.7 mg/m3 and were highest in June and July, and lowest in March and April. The hourly mean concentrations of PM2.5 showed a bimodal pattern, with peaks at around 7–8 AM and 8– 9 PM. The monthly mean fraction of PM2.5 as SO2 4 ranged from 0.17 to 0.31; the highest fraction values were observed during June–September.
Acknowledgements The authors thank Bonnie Hall for assistance in chemical analysis, Stan House, Dan Lince, Dan Sharron and Pat Palmer for sampling. We also thank the staff of the NYSDEC, Division of Air Resources for providing NO2, O3 and SO2 hourly data, monitoring locations and the use of continuous PM2.5 instrument and assistance in its operation. The financial assistance provided by the Agency for Toxic Substances and Disease Registry, and New York State Energy Research and Development Authority is gratefully acknowledged.
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Dutkiewicz, V.A., Das, M., Husain, L., 2000. The relationship between regional SO2 emissions and downwind aerosol sulfate concentrations in the northeastern US. Atmospheric Environment 34, 1821–1832. Eldering, A., Solomon, P.A., Salmon, L.G., Fall, T., Cass, G.R., 1991. Hydrochloric Acid: a regional perspective on concentrations and formation in the atmosphere of Southern California. Atmospheric Environment 25A, 2091–2102. Febo, A., Perrino, C., 1991. Prediction and experimental evidence for high air concentration of nitrous acid in indoor environment. Atmospheric Environment 25A, 1055–1061. Finlayson-Pitts, B.J., Pitts Jr., J.N., 2000. Chemistry of the Upper and Lower Atmosphere. Academic Press, San diego, p. 847. Gerecke, A., Thielmann, A., Gutzwiller, L., Rossi, M.J., 1998. The chemical kinetics of HONO formation resulting from Heterogeneous interaction of NO2 with flame soot. Geophysical Research Letters 25, 2453–2456. Harrison, R.M., Peak, J.D., Collins, G.M., 1996. Tropospheric cycle of nitrous acid. Journal of Geophysical Research 101, 14429–14439. Hoek, G., Mennen, M.G., Allen, G.A., Hofschreuder, P., Meulen, T.V., 1996. Concentrations of acidic air pollutants in the Netherlands. Atmospheric Environment 30, 3141–3150. Kaneyasu, N., Yoshikado, H., Mizuno, T., Sakamoto, .K., Soufuku, M., 1999. Chemical forms and sources of extremely high nitrate and chloride in winter aerosol pollution in the Kanto plain of Japan. Atmospheric Environment 33, 1745–1756. Kasper, A., Puxbaum, H., 1998. Seasonal variation of SO2, HNO3, NH3 and selected aerosol compoents at Sonnblick (3106) m a.s.l.). Atmospheric Environment 32, 3925–3939. Keeler, G.J., Spengler, J.D., Castillo, R.A., 1991. Acid aerosol measurements at a suburban Connecticut site. Atmospheric Environment 25A, 681–690. Kirchstetter, T.W., Harley, R.A., Littlejohn, D., 1996. Measurement of nitrous acid in motor vehicle exhaust. Environmental Science and Technology 30, 2843–2849. Kitagawa, T., 1984. Cause analysis of the Yokkaichi asthma episode in Japan. Journal of Air Pollution Control Association 34, 743–746. Koenig, J.Q., 2000. Health Effects of Ambient Air Pollution. Kluwer Academic Publishers, Boston/Dordrecht/London. Koutrakis, P., Wolfson, J.M., Slater, J.L., Brauer, M., Spengler, J.D., Stevens R, K., Stone C, L., 1988a. Evaluation of an annular denuder/filter pack system to collect acidic aerosols and gases. Environmental Science and Technology 22, 1463–1468. Koutrakis, P., Wolfson, J.M., Spengler, J.D., 1988b. An improved method for measuring aerosol strong acidity: results from a nine-month study in St. Louis, Missouri and Kingston, Tennessee. Atmospheric Environment 22, 157–162. Lee, H.S., Wadden, R.A., Scheff, P.A., 1993. Measurement and evaluation of acid air pollutants in Chicago using an annular denuder system. Atmospheric Environment 27A, 543–553. Lee, H.S., Kang, C.-M., Kang, B.-W., Kim, H.-K., 1999. Seasonal variations of acidic air pollutants in Seoul, South Korea. Atmospheric Environment 33, 3143–3152.
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835 Lightowlers, P.J., Cape, J.N., 1988. Sources and fate of atmospheric HCl in the UK and Western Europe. Atmospheric Environment 22, 7–15. Mage, D., Ozolins, G., Peterson, P., Webster, A., Orthofer, R., Vandeweerd, V., Gwynne, M., 1996. Urban air pollution in megacities of the world. Atmospheric Environment 30, 681–686. Massih, A., Kitto, N., Harrison, R.M., 1992. Nitrous and nitric acid measurements at sites in south-east England. Atmospheric Environment 26A, 235–241. Matsumoto, M., Okita, T., 1998. Long term measurements of atmospheric gaseous and aerosol species using an annular denuder system in Nara, Japan. Atmospheric Environment 32, 1419–1425. Mayer, H., 1999. Air pollution in cities. Atmospheric Environment 33, 4029–4037. Parekh, P.P., Husain, L., 1982. Ambient sulfate concentrations and windflow patterns at whiteface mountain, New York. Geophysical Research Letters 9, 79–82. Parkhurst, W.J., Tanner, R.L., Weatherford, F.P., Valente, R.J., Meagher, J.F., 1999. Historic PM2.5/PM10 concentrations in the southeastern United States-Potential implications of the revised particulate matter standard. Journal of Air and Waste Management Association 49, 1060–1067. Perrino, C., Santis, F.D., Febo, A., 1990. Criteria for the choice of a denuder sampling technique devoted to the measurement of atmospheric nitrous and nitric acids. Atmospheric Environment 24A, 617–626. Pitts Jr., J.N., Biermann, H.W., Winer, A.M., Tauzon, E.C., 1984. Spectroscopic identification and measurement of gaseous nitrous acid in dilute auto exhaust. Atmospheric Environment 18, 847–854.
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Pope III, C.A., Burnett, R.T., Thun, M.J., Calle, E.E., Krewski, D., Ito, K., Thurston, G.D., 2002. Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution. Journal of American Medical Association 287, 1132–1141. Puxbaum, H., Haumer, G., Moser, K., Ellinger, R., 1993. Seasonal variation of HNO3, HCl, SO2, NH3 and particulate matter at a rural site in north eastern Austria (Wolkersdorf, 240 m a.s.l.). Atmospheric Environment 27A, 2445–2447. Richter, R.C., Swami, K., Chace, S., Husain, L., 1998. Determination of arsenic, selenium, and antimony in cloud water by inductively coupled plasma mass spectrometry. Fresenius Journal of Analytical Chemistry 361, 168–173. Shaw, R.W., Paur, R.J., 1983. Measurement of sulfur in gases and particles during sixteen months in the Ohio River valley. Atmospheric Environment 17, 1431–1438. Speizer, F.E., 1989. Studies of acid aerosols in six cities and in a new multi-city investigation: design issues. Environmental Health Perspectives 79, 61–67. Spengler, J.D., Brauer, M., Koutrakis, P., 1990. Acid air and health. Environmental Science and Technology 24, 946–956. Stelson, A.W., Seinfeld, J.H., 1982. Relative humidity and temperature dependence of the ammonium nitrate dissociation constant. Atmospheric Environment 16, 983–992. Suh, H.H., Allen, G.A., Koutrakis, P., Burton, R.M., 1995. Spatial Variation in acidic sulfate and ammonia concentrations within metropolitan Philadelphia. Journal of Air and Waste Management Association 45, 442–452. Yamamoto, N., Nishiura, H., Honjo, K., Ishikawa, Y., Suziki, K., 1995. A long term study of atmospheric ammonia and particulate ammonium concentrations in Yokohama, Japan. Atmospheric Environment 29, 97–103.
Measurements of gaseous HONO, HNO3, SO2, HCl, NH3, particulate sulfate and PM2.5 in New York, NY Abdul Baria, Vincent Ferraroa, Lloyd R. Wilsonb, Dan Luttingerb, Liaquat Husaina,c,* a
Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA b New York State Department of Health, Center for Environmental Health, 547 River Street, Troy, NY, USA c Department of Environmental Health and Toxicology, School of Public Health Sciences, State University of New York, Albany, USA Received 2 June 2002; accepted 12 March 2003
Abstract Simultaneous measurements of gaseous HONO, HNO3, HCl, SO2, and NH3 for a period of 1 year from July 1999 to June 2000 and fine-fraction particulate (o2.5 mm) sulfate (SO2 4 ) from January 1999 to November 2000 were made at Bronx and Manhattan in New York City with an annular denuder system followed by ion chromatography. The hourly PM2.5 mass was measured with a Rupprecht and Patashnick TEOM Series 1400a real-time monitor for approximately 2 years (January 1999–November 2000) at the same sites. Concentrations at the two sites were highly correlated, with Manhattan being slightly higher than at the Bronx. The concentrations of HNO3, HCl, NH3 and SO2 4 were higher during summer than winter, the summer/winter ratios at Manhattan being 3.9, 3.1, 1.5, and 1.9, respectively. The concentrations of HONO and SO2 were lower during summer than winter, the summer/winter ratios at Manhattan being 0.48 and 0.44, respectively. Gaseous HONO concentrations were higher than that of HNO3 except in summer, when the HNO3 was higher. The annual mean concentration of PM2.5 was 15.2 mg/m3 at the Bronx, and 15.5 mg/m3 at Manhattan (based only on days when data were available from both sites). The monthly mean concentrations at Manhattan ranged from 13.2 to 21.7 mg/m3 and were highest in June and July 1999, and lowest in March and April. The monthly mean fraction of PM2.5 as SO2 ranged from 0.17 to 0.31, with the highest values observed during 4 June–September. The hourly mean concentrations of PM2.5 showed a bimodal pattern, with peaks at around 7–8 AM and 8–9 PM. In general, the second maximum is lower than the morning one, but during summer this is reversed. The contributions from regional and local emissions and the influence of atmospheric transport and chemical reactions on the observed concentrations are discussed in a compendium paper. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Acidic gases; Ammonia; Annular denuder system; Urban area; Aerosol
1. Introduction
*Corresponding author. Wadsworth Center for Laboratories and Research, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA. Tel.: +1-518-4734854; fax: +1-518-473-2895. E-mail address: [email protected] (L. Husain).
The secondary pollutants HONO, HNO3, and SO2 4 in the atmosphere are produced from natural and manmade emissions of primary gas phase pollutants such as SO2 and NOx by photochemical reactions. HCl is mainly produced by coal combustion and refuse incineration (Lightowlers and Cape, 1988), municipal and industrial waste incineration (Kaneyasu et al., 1999)
1352-2310/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1352-2310(03)00199-7
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as primary pollutant, and by the reaction of HNO3 (g) with NaCl (s, aq) in sea-salt particles (Eldering et al., 1991) as a secondary pollutant. Much of the United States SO2 emissions are from the midwestern states, for example in 1998 emissions from WV, OH, IL, IN, MI, WI, KY, and western PA, represented 39% of the National SO2 inventory. The eastern United States and southern Ontario are exposed to SO2 and SO2 from 4 these sources by long distance transport. Space heating also contributes to SO2 emission, especially in large urban areas during the winter. In large urban areas, nearly half of NOx emissions are caused by automobile exhaust (Spengler et al., 1990; Mayer, 1999; Mage et al., 1996). A significant percentage of the observed HONO is produced from vehicular exhaust (Pitts et al., 1984; Matsumoto and Okita, 1998). During several episodes of extreme air pollution in various countries, an increase in morbidity and mortality was observed, suggesting that ambient air pollution adversely affect human health. Exposure to elevated concentrations, or long-continued exposure to low levels of ambient air pollutants has received increasing attention due to the wide range of adverse effects of air pollutants on ecological systems and human health (Dockery and Pope, 1994; Koenig, 2000; Pope et al., 2002). In a study measuring acidic aerosols in six cities, Speizer (1989) reported a correlation between the prevalence of chronic bronchitis among children 10–12 years of age and PM15; there was also a correlation with hydrogen ion concentration in the particles. Earlier, Kitagawa (1984) reported severe cases of lung disease near a plant emitting sulfuric acid aerosols; the number of incidences decreased with increasing distance from the plant. The incidence of lung diseases decreased sharply when the sulfuric acid was removed from the emissions. Bates and Sizto (1987, 1989) observed correlation between the concentration of SO2 4 and the number of admissions for respiratory disease in hospitals in Southern Ontario. Balmes et al. (1989) confirmed that inhaled SO2 3 aerosols were a stimulus to bronchoconstriction in subjects with asthma. Dockery et al. (1993) positively associated air pollution with death from lung cancer and cardiopulmonary disease, and also found a strong association of mortality with air pollution consisting of fine particulates, including SO2 4 . Pope et al. (2002) have provided strong evidence that long-term exposure to fine particulate air pollution common to many metropolitan areas is an important risk factor for cardiopulmonary mortality. Continuous development of various components of the annular denuder system (ADS), and stable and laminar air flow in the ADS, has provided an improved method by which to selectively collect the air pollutants of interest at a much higher flow rate, with greater efficiency, and with minimal artifacts. Numerous studies have been carried out for the simultaneous measurement
of acidic gases and SO2 4 , but most of these studies were of short duration or did not measure all of these components (HONO, HNO3, HCl, SO2, NH3 and SO2 4 ). In this work, we have simultaneously measured acidic gases, and SO2 for all seasons using the ADS 4 from 23 June 1999 to 11 July 2000. In addition, SO2 4 and PM2.5 were measured for the entire study period, January 1999–November 2000. The data will also be used to investigate the relationship between the observed daily concentrations of chemical species and asthma incidences, as indicated by area hospital emergency room visits and possibly admissions (results to be reported elsewhere). Here, we report on the daily concentrations of HONO, HNO3, HCl, SO2, NH3, SO2 4 , and PM2.5, seasonal variations, relationship between chemical species and suggest chemical reactions that may explain the observations. The data are also compared, when available, with the measurements from other urban centers.
2. Experimental The sampling systems were set up on the roof (fifth floor) of the Mabel Dean High School, located at 14th Street and 2nd Ave, in Manhattan, and at Intermediate School 155 (IS 155, third floor) located at Jackson Ave and St. Mary’s street in the Bronx. On 14 July 1999, IS 155 site was shut down, and monitoring resumed on 14 September 1999 on the roof (third floor) of Middle School 52 on Kelly Street in the Bronx. The two Bronx sites are of comparable height and are about 1 km apart so the sites are assumed to be equivalent. The Mabel Dean High School and Middle School 52 sites are very near sea level, about 11 km apart and in center city environments with high-density residential populations. The Manhattan site is also located near a commercial district. Although both sites are elevated above street level, the air monitoring system at Bronx site is the lowest (15 m above the ground) and is likely to have the greatest ‘‘neighborhood’’ influence. The air monitoring system at Manhattan site is 38 m above sea level and its height is comparable to the surrounding buildings, thus it should be strongly impacted by regional as well as ‘‘neighborhood’’ sources. Mabel Dean High School and Middle School 52 are also New York State Department of Environmental Conservation (NYSDEC) continuous monitoring sites. The air samples were collected using URG-2000-01L, Eight Channel Sequential Fine Particle Sampler, each with two 120 mm long glass-heavy wall Annular Denuders connected in series, followed by a 47 mm filter module. The first annular denuder was coated with Na2CO3 to collect acidic gases, and the second with citric acid to collect ammonia. The flushend of the citric acid coated annular denuder was attached directly to the filter module. The filters
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
(47-mm-diameter, 2 mm-pore Zefluor filter, Gelman Laboratory) were positioned on the Teflon-coated stainless-steel screen so that the air stream particulates were trapped on the Teflon-coated side of the filter. Two cyclones with cut points of 10 and 2.5 mm preceded the ADS. Air samples were collected for 24 h starting at midnight, at a flow rate of 10 l/min. The annular denuder tubes were coated with appropriate coating solutions (citric acid: 1% w/v in methanol; sodium carbonate: 1% w/v, 1% w/v glycerol in a 1:1 methanol/ water solution), and the coated tubes were dried with ‘‘zero’’ air at a rate of 3 l/min. The denuder trains were assembled and were leak-checked in clean laboratory conditions. With each batch of seven denuder assemblies (ADS+Filter) sent out in the field, a blank denuder assembly was included. It was left for 7 days inside the sampler but was not connected to the air flow. The coated annular denuders from the exposed assemblies and field blanks were extracted with 10 ml ultra-pure water (Millipore, Milli-Q UV Plus water system), and stored at 4 C for analysis. The water extract from sodium carbonate coated denuders was used for the determination of HONO, HNO3 and HCl. For SO2 analysis 5 ml of the water extracts from the sodium carbonate coated denuders were oxidized with 0.05 ml of 30% aqueous H2O2 solution to completely oxidize the collected SO2 to SO2 4 before analysis. The water extract from citric acid denuder was used to determine ammonia. The measurement of chloride, nitrite, nitrate, sulfate and ammonium was made with a DIONEX 500 ion chromatography system and the results were calculated for gaseous HCl, HONO, HNO3, SO2, and NH3. The separation of chloride, nitrite, nitrate, and sulfate was accomplished using an IonPac AS 14 (4 250 mm) analytical column, AG 14 guard column, with a 10 ml sample loop, and an anion self-regenerating suppressor-ultra A solution of 3.5 mM Na2CO3/1.0 mM NaHCO3 was used as eluent at a flow rate of 1 ml/min. The separation of ammonium was accomplished using an IonPac CS 14 (4 250 mm) analytical column, and a CG 14 guard column, with a 50 ml sample loop, and a cation self-regenerating suppressor-ultra A solution of 10 mM methanesulfonic acid was used as eluent at a flow rate of 1 ml/min. The Zefluor filters were ultrasonically extracted for 1 h in 5 ml ultra-pure water and stored at 4 C for analysis of particulate sulfate. The filter extracts were analyzed for SO2 by ion chromatography using 4 the DIONEX 100 ion chromatography system. Selenium was also determined in some of the filter extracts using inductively coupled plasma mass spectrometry (Richter et al., 1998). Concentrations in the field blanks for the target species were subtracted on a batch-to-batch basis. Accuracy of calibration curves was checked by analyzing the quality control samples, containing the analytes of interest at a concentration in the low- and highconcentration range provided by an independent QA/
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QC laboratory within the Wadsworth Center. For all the analytes the controls were within 710%. The percent standard deviation of measurements, evaluated on duplicate runs of several samples, was found to be better than 73.0%. PM2.5 measurements were made with a Rupprecht and Patashnick (R&P) TEOM Series 1400a real-time monitor. A 16.7 l/min airstream was pulled through the instrument. The air was pulled through a PM2.5 inlet, then isokinetically split into 3 l/min (lpm) and 13.7 lpm airstreams, sending the 3 lpm airstream to the instrument’s mass transducer. The flow was held at a constant volume by a mass flow controller and was corrected for local temperature and barometric pressure. Inside the mass transducer, the air stream was filtered by a Tefloncoated borosilicate glass filter located at the end of an oscillating tapered element. As mass collects on the filter the change in the oscillations were measured and converted to mass. A measure of the change in the mass concentration was made every 2 s and used to calculate hourly averages in particulate mass. The filter unit was held at 50 C to prevent condensation.
3. Results and discussion 3.1. Acidic gases Concentrations of acidic gases, HONO, HNO3, HCl, and SO2 were measured daily (midnight to midnight, local time) from 23 June 1999 to 11 July 2000 at both the Manhattan and Bronx sites. Table 1 gives a summary of the quarterly mean, median, and concentration range for all the species measured, for the period from 1 July 1999 to 30 June 2000. Summer season is defined as July– September, and winter as January–March. The daily HONO concentrations at Manhattan fluctuated widely, from the detection limit to about 9 ppb (Fig. 1a). Data at Bronx showed very similar variations and were highly correlated (r2 ¼ 0:81) with those from Manhattan. HNO3 concentrations at both sites showed less variation than for HONO. From the daily concentrations, we calculated the monthly mean concentrations. The data show a strong seasonal pattern. Since the data from both sampling sites show a similar pattern, only the Manhattan data are presented in Fig. 1b. A strong seasonal pattern is evident, with HNO3 concentrations being high during summer and low during the remaining months. These observations are in agreement with earlier studies (Danalatos and Glavas, 1999; Kasper and Puxbaum, 1998; Cadle, 1985; Keeler et al., 1991; Lee et al., 1993). The summer to winter ratio for HNO3 is 3.9. HNO3 concentrations approach or exceed 5 ppb only during May–August. The pattern for HONO shows the reverse. In Newton, a suburban Connecticut site, Keeler et al. (1991) observed much lower values for
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
2828
Table 1 Mean, median, and concentration range of HONO, HNO3, HCl, SO2, NH3, and SO2 4 at Manhattan and the Bronx in New York City SO2 (ppb)
NH3 (ppb)
SO2 4 (ppb)
B
M
B
M
B
M
B
0.32 0.34 360 0.2 0.01 1.98
0.28 0.27 299 0.2 0.01 1.83
10.2 7.3 359 8.5 1.2 59.8
10.0 7.2 300 8.3 0.6 50.6
5.0 2.7 182 5.0 0.9 15.5
3.1 2.6 148 2.4 0.1 9.9
1.08 0.96 359 0.79 0.07 6.08
0.9 0.76 300 0.69 0.04 4.96
0.76 0.7 34 0.6 0.04 2.49
0.62 0.47 90 0.51 0.01 1.98
0.45 0.38 34 0.35 0.04 1.55
6.7 3.9 90 5.7 1.2 17.4
5.0 4.3 34 3.9 0.6 20.1
6.1 1.3 47 6.2 2.2 8.7
1.61 1.44 90 1.04 0.07 6.08
1.28 1.34 34 0.66 0.04 4.96
0.24 0.2 91 0.18 0.02 1.1
0.18 0.14 90 0.15 0.01 0.68
0.17 0.11 91 0.14 0.02 0.51
0.19 0.12 90 0.16 0.01 0.56
12.3 7.1 90 10.4 2.3 37.8
11.4 6.5 90 10.2 0.6 35.9
0.75 0.5 90 0.56 0.16 2.45
0.7 0.47 90 0.55 0.05 2.19
January–March 2000 Mean 2.13 1.93 s.d. 1.39 1.35 Count 88 85 Median 1.72 1.49 Min 0.61 0.29 Max 8.76 6.5
0.36 0.27 88 0.28 0.04 1.15
0.2 0.12 85 0.18 0.05 0.58
0.2 0.14 88 0.165 0.01 0.6
0.27 0.17 85 0.23 0.02 0.7
15.5 8.9 88 13.3 2.2 59.8
14.7 8.4 85 12.5 2.6 50.6
4.1 2.6 88 3.4 0.9 11.9
2.1 2.1 87 1.6 0.1 9.6
0.86 0.5 88 0.745 0.23 2.4
0.79 0.47 85 0.68 0.22 1.98
April–June 2000 Mean 1.4 s.d. 1.03 Count 91 Median 1.19 Min 0.26 Max 6.11
0.6 0.59 91 0.37 0.04 2.66
0.58 0.61 91 0.32 0.05 2.79
0.3 0.31 91 0.18 0.01 1.32
0.33 0.36 90 0.19 0.02 1.83
6.7 3.5 91 5.9 1.5 16.9
6.1 3.4 91 5.0 1.6 19.3
5.9 3.4 44 5.0 1.6 15.5
4.2 2.6 46 3.3 0.7 9.9
1.11 0.84 91 0.82 0.13 3.88
1.06 0.84 91 0.77 0.17 4
HNO2 (ppb)
HNO3 (ppb)
HCl (ppb)
M
M
B
M
July 1999–June 2000 Mean 1.71 1.65 s.d. 1.22 1.24 Count 357 300 Median 1.49 1.32 Min 0.04 0.02 Max 8.76 6.58
0.64 0.82 357 0.33 0.02 5.69
0.37 0.48 300 0.21 0.01 2.79
July–September 1999 Mean 1 1.06 s.d. 0.76 0.83 Count 87 34 Median 0.83 0.92 Min 0.04 0.02 Max 3.32 2.76
1.39 1.21 87 0.97 0.04 5.69
October–December 1999 Mean 2.31 2.1 s.d. 1.13 1.33 Count 91 90 Median 2.17 1.76 Min 0.67 0.28 Max 5.41 6.58
B
1.16 0.91 91 1.04 0.19 6.14
M—Manhattan; and B—Bronx.
HONO (average value=0.4 ppb). The summer/winter ratio for HONO is 0.48. During winter, HONO concentrations are approximately 10-fold those of HNO3. The pattern of seasonal variation of HONO with a minimum in summer can be attributed to photolysis. The seasonal pattern for HNO3 can be assumed to be due to the reaction NO2+OH-HNO3. The production of HNO3 should be greater in summer due to the larger hydroxyl and O3 concentrations, and humidity. The seasonal variation can also be attributed to the reaction of HNO3 with ammonia, and to the dissociation
constant of NH4NO3, which increases with temperature (Stelson and Seinfeld, 1982). In summer, NH4NO3 will be mostly in the dissociated form, but mostly undissociated in winter, favoring a HNO3 minimum during winter. Fig. 2 shows the relationships between NO2 and HONO, HNO3, and [HONO+HNO3]. There is no correlation between NO2 and HONO (r2 ¼ 0:04), or between NO2 and HNO3 (r2 ¼ 0:21), but a trend is observed between NO2 and [HONO+HNO3] (r2 ¼ 0:44) concentrations. During a study in central urban, suburban, and rural environments, Harrison et al. (1996) observed that HONO was correlated with NO2 in
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
8
8
HONO (ppb)
HONO (ppb)
10
6 4 2 Jun-00
May-00
Apr-00
Mar-00
Feb-00
Jan-00
Dec-99
Nov-99
Oct-99
Sep-99
Aug-99
Jul-99
0
(a)
y = 0.029x + 0.666 R2 = 0.039
6 4 2 0 10
20
HONO (ppb)
2.5
40
50
60
50
60
50
60
HNO3 (ppb)
8
2.0 1.5
HNO3 (ppb)
(ppb)
30
NO2 (ppb)
3.0
1.0 0.5 0.0
(b)
2829
Jul-99
Sep-99
Nov-99
Jan-00
Mar-00
May-00
Fig. 1. (a) Daily concentrations of HONO at Manhattan; and (b) Monthly mean concentrations of HONO and HNO3 at Manhattan.
surface
2NO2 þ H2 O ! HONO þ HNO3 :
ð1Þ
Gaseous HNO3 produced by the above reaction is not observed in equivalent amounts to HONO due to its adsorption on surfaces (Finlayson-Pitts and Pitts, 2000). The formation of HONO by the heterogeneous reaction NO2 þ surface reduced site þ H2 O -HONO þ surface oxidized site þ OH
ð2Þ
has been proposed, and Gerecke et al. (1998) have reported large yields of HONO. This reaction can take place in parallel to the above reaction in polluted urban areas, as well as in the upper troposphere where soot from commercial aircraft is injected into the atmosphere (Finlayson-Pitts and Pitts, 2000). The observed trend between NO2 and the sum of HONO and HNO3 may be attributable to reaction (1), or reactions (1) and (2) taking place at the same time. HONO is also formed by the NO+OH reaction during daytime (Harrison et al., 1996). Other sources of HONO include auto exhaust, diesel exhaust (Kirchstetter et al., 1996; Arens et al., 2001). Use of gas stoves in the houses produces high concentrations of NO2 and significant amount of HONO, thus affecting the outdoor pollution in urban areas (Febo and Perrino, 1991).
y = 0.060x - 1.260 R2 = 0.212
4 2 0 10
20
30
40
NO2 (ppb) [HONO+HNO 3] (ppb)
suburban and rural areas, but not in central urban areas. They inferred that, although the formation of HONO in the central urban area was from NO2, the concentrations of HONO and NO2 were not highly correlated because of the relative proximity to motor traffic. HONO is also produced by the reaction
6
8 y = 0.088x - 0.594 2 R = 0.413
6 4 2 0 10
20
30
40
NO2 (ppb) Fig. 2. Relationship between NO2 versus HONO, HNO3, and [HONO+HNO3]. The NO2 values are averaged from hourly continuous chemiluminiscent measurements (TECO Model 42) obtained from the NYSDEC.
N-containing species (such as NOx and Peroxyacetyl nitrate (PAN)) are potential interfering agents, and can produce NO 2 and NO3 inside the sodium carbonate coated denuder resulting in the overestimation of HONO and HNO3 concentrations. However, our data shows that the artifact is very small. If HONO and HNO3 are produced by the heterogeneous reaction of NO2 and water vapor, then equivalent amount of each will be produced on the denuder surface. Fig. 1b indicates that the contribution from the artifact is minimal. Comparing the daily concentrations of HONO and HNO3 also indicates the same. During winter, the concentrations of HNO3 is very small compared to HONO, for example during 1–4 January 2000 the
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
seasonal patterns. The concentration of SO2 is higher during winter than summer (summer/winter=0.44), while the SO2 4 concentration is higher during summer (summer/winter=1.9). Increased concentrations of SO2 in summer have been observed in many studies 4 (Parekh and Husain, 1982; Koutrakis et al., 1988b; Altshuller, 1984; Puxbaum et al., 1993; Kasper and Puxbaum, 1998; Danalatos and Glavas, 1999; Shaw and Paur, 1983). Higher concentration of SO2 4 in summer can be attributed to (a) the increased rate of oxidation of SO2 due to the higher concentrations of oxidizing species (Danalatos and Glavas, 1999; Calvert et al., 1978); and (b) longer reaction times during periods of meteorological stagnation (Shaw and Paur, 1983). The sum of gaseous SO2 and particulate SO2 shows a maximum 4 during winter. This could be due to the increased SO2 emissions in winter from space heating since this is a high-density area, or from seasonal differences in dispersion rates. Fig. 3b shows monthly mean percentage of total 2 sulfur present as SO2 fraction is much 4 . The SO4 higher during the warmer period (about 19%) compared to the colder part of the year (about 5–7%); a similar trend was observed by Altshuller (1984), Shaw and Paur (1983). Dutkiewicz et al. (2000) observed a similar trend over a number of years at Mayville and Whiteface Mountain, NY, where about 31% and 65–82%, respectively, of total sulfur was in the aerosol phase during the summer of 1998. The lower SO2 4 component in New York City suggests that the contribution from local or nearby sources to total S is more important than it is at Mayville or Whiteface Mountain. This suggestion 2 is also supported by the SO2 4 /Se ratios. Because SO4 is 20
3 SO2
Sulfate
2
12 8
1
Sulfate (ppb)
16 SO2 (ppb)
concentrations of HNO3 were 0.11, 0.12, 0.08, and 0.05 ppb, respectively, but during the same period concentrations of HONO were 4.47, 6.23, 5.5, and 4.13 ppb, respectively. During summer when the concentration of HONO is very small compared to HNO3, for example during 4–8 July 1999 the concentrations of HONO were 0.19, 0.15, 0.04, 0.08 and 0.11 ppb, respectively while that of HNO3 were 2.55, 2.42, 2.39, 1.08, and 1.13 ppb, respectively. We also did not see relationship between daily NO2 concentration and either HONO or HNO3 concentrations. On a number of occasions, we observe that when the concentration of NO2 is maximum, the concentration of HONO or HNO3 is minimum and vice versa. PAN thermally decomposes to peroxyacetyl radical and NO2, hence the artifact from it will be similar to NO2. This is also supported by the studies using sodium carbonate coated denuders in series. In rural and semirural sites, the artifact correction was typically around 20% (Massih et al., 1992). In suburban areas, the artifact correction was around 12710% for HONO and 675% HNO3 (Dasch et al., 1989). In urban areas, the artifact correction was observed to be less than that observed in rural, semirural and suburban areas, and in general ranged from 2% to 12.5% for HONO (Koutrakis et al., 1988a; Appel et al., 1990; Perrino et al., 1990; Harrison et al., 1996; Bai and Wen, 2000), and 3.4–13.2% for HNO3 (Koutrakis et al., 1988a; Perrino et al., 1990). Bai and Wen (2000) showed that the relative errors for HONO gas can be less than 10% as sampled with only one Na2CO3-coated denuder. The relative error due to artifact for the HONO and HNO3 measurements in urban areas will be less than about 13% when sampled with only one sodium carbonate coated denuder. SO2 concentrations were determined daily (midnight to midnight), from July 1999 to June 2000 using the ADS and ion chromatography. SO2 concentrations are routinely collected by the NYSDEC monitoring network at these sites, using a pulsed-fluorescence analyzer (TECO 43S). The data from the two techniques were in excellent agreement (r2 ; 0.92; slope, 1.01; intercept, 1.26). The denuder technique results in slightly lower values than pulsed-fluorescence analyzer. The daily SO2 concentrations varied nominally from B1 to 10 ppb except in winter, when concentrations as high as 60 ppb were observed. The daily SO2 4 concentrations were as high as 6 ppb during warmer months, but during the rest of the year the maximum values were around 2.5 ppb. While SO2 concentrations are usually expressed in 4 mass units comparison with SO2 are more meaningful when molar equivalents are used. Thus SO2 4 concentrations have been converted to ppb equivalents (1 ppb=3.96 mg/m3). Monthly mean concentrations at Manhattan were calculated from the daily concentrations for gaseous SO2 and fine particulate SO2 4 (Fig. 3a). SO2 and particulate sulfate show opposite
4 0
(a)
[SO 4/(SO2+SO4)]*100
2830
(b)
0 Jul-99
Sep-99 Nov-99 Jan-00
Mar-00 May-00
25 Manhattan
Bronx
20 15 10 5 0 Jul-99
Sep-99 Nov-99
Jan-00
Mar-00 May-00
Fig. 3. (a) Monthly mean concentrations of SO2 and SO2 4 ; and (b) Monthly mean percentage of total sulfur present as SO2 4 .
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
added by oxidation of SO2 during atmospheric transport, the SO2 4 /Se ratios increase as the air moves away from the source. Compared to the SO2 4 /Se ratios of about 9000 during summer at Whiteface Mountain, the ratios in New York City were observed to be about 4000. Lower SO2 4 /Se ratios in New York City compared to Mayville or Whiteface Mountain could be due to SO2 emission from local or nearby sources. However, the data were limited to 1 week of sampling, and hence must be taken as preliminary. Very few studies are available for the measurement of gaseous HCl, and most of these are of short duration. Fig. 4a and b shows the daily concentrations of gaseous HCl at Manhattan, and monthly means at the Bronx and Manhattan. The seasonal trend for HCl is similar to that observed for HNO3. The concentration of gaseous HCl is high during summer and low during winter; the summer/winter ratio is 3.1. During a study of the longterm HCl concentrations in the Southern California atmosphere by the denuder difference method, Eldering et al. (1991) also observed that HCl concentrations peak in the summer months, with peak single day concentrations of 4.02 ppb at Hawthorne and 3.02 ppb at downtown Los Angles. Their study also supported the hypothesis that the reaction of HNO3 gas with sea salt was the source of the HCl in the Los Angles atmosphere. Matsumoto and Okita (1998) also observed higher HCl in summer in Narra, Japan, a medium size city, and a
2.0
1.0 0.5
3.2. Ammonia Ammonia, a primary gas phase pollutant, is the major neutralizing agent in the atmosphere and plays an important role in the chemistry of the atmosphere. Major sources of ammonia emissions are live stock and ammonia-based chemical fertilizers. Other sources of ammonia emissions are human beings, sewage treatment plants and catalytic converter equipped vehicles. Most of the ammonia is emitted near the earth’s surface and may react with acidic constituents in the atmosphere. Ammonia reacts irreversibly with sulfuric acid containing aerosols, and reversibly with both nitric and hydrochloric acids to form relatively neutral ammonium salt aerosols, which can again dissociate, with the dissociation being dependent upon temperature and humidity. Fig. 5 shows the daily concentrations of ammonia at Manhattan. The concentration of ammonia varied considerably from day to day. The overall mean of all the values (n ¼ 182) measured was 5.0 ppb (range: 0.9–15.5 ppb; s.d.: 2.7). For comparison, the mean values of ammonia in various urban areas are given in Table 2. The monthly mean concentrations of ammonia ranged from 3.2 to 7.6 ppb, with lowest values observed during December 1999–February 2000 (3.2–3.8 ppb) and the highest during June–July 1999 and May 2000 (6.6–7.6 ppb). Similar seasonal trends were observed by Yamamoto et al. (1995), in urban Yokohama, Japan;
Jun-00
May-00
Apr-00
Mar-00
Jan-00
Feb-00
Dec-99
Oct-99
Nov-99
Sep-99
Aug-99
16 14
0.6 0.4
Bronx
Manhattan
0.2 0.0
12 NH 3 (ppb)
Monthly mean
10 8 6 4
May-00
Apr-00
0 Mar-00
Fig. 4. (a) Daily concentrations of HCl at Manhattan; and (b) monthly means at Bronx and Manhattan.
2 Dec-99
(b)
0.8
Jul-99 Aug-99 Sep-99 Oct-99 Nov-99 Dec-99 Jan-00 Feb-00 Mar-00 Apr-00 May-00 Jun-00
HCl (ppb)
1.0
Feb-00
(a)
Jul-99
0.0
summer/winter ratio of 1.6. Puxbaum et al. (1993), in a study at a rural site in northeastern Austria observed that the HCl values peaked during winter, with a summer/winter ratio of 0.4. As the primary source of HCl in Eastern Europe is coal combustion, the authors suggested that the winter peak may be due to the more effective transport in winter than summer due to the shallower boundary layer and smoother surface due to snow cover.
Jan-00
HCl (ppb)
1.5
2831
Fig. 5. Daily concentrations of ammonia at Manhattan.
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
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Table 2 Ammonia (ppb), concentrations in urban locations Site
Period
NH3
Reference
New York, NY Hamilton, Canada Windsor, Canada Yokohama, Japan Narra, Japan Seoul, South Korea Chicago, IL Philadelphia, PA Philadelphia, PA Deurne, Netherlands
1999–2000 1992–1994 1992–1994 5 years June 1994–May 1999 October 1996–September 1997 April 1990–March 1991 1992 1993 1996
5.1 6.24 2.48 6.85–10.2 3.54 6.32 2.38 1.18–5.54 2.04–5.68 16.9
This work Brook et al. (1997) Brook et al. (1997) Yamamoto et al. (1995) Matsumoto and Okita (1998) Lee et al. (1999) Lee et al. (1993) Suh et al. (1995) Suh et al. (1995) Hoek et al. (1996)
1:1
400
Linear (Series1)
26 PM 2.5 (µg/m3)
300
200
Manhattan
Bronx
18 14 10 Jan- Mar- May- Jul- Sep- Nov- Jan- Mar- May- Jul99 99 99 99 99 99 00 00 00 00
(a) y = 0.496x R2 = 0.084
100
22
Manhattan Bronx
20
0 0
200
400 3 NH3 (nmol/m )
600
800
Fig. 6. Correlation between the sum of nitric acid, nitrous acid, and hydrochloric acid versus ammonia. 1:1 line is drawn to indicate the excess of NH3 over acidic species.
PM2.5 (µg/m3)
[HNO 3+HONO+HCl] (nmol/m 3)
Monthly mean
22
16 14 12 10 0
(b)
Lee et al. (1999) in urban Seoul, South Korea; and Lee et al. (1993) in urban Chicago. The Manhattan summer to winter ratio was 1.5. Fig. 6 shows the correlation between the sum of nitric acid, nitrous acid, hydrochloric acid versus ammonia (in units of nmol/m3). It is obvious that in New York City the concentration of ammonia was in large excess compared to the concentrations of individual acids. So it is reasonable to expect that any H2SO4 present would be neutralized by forming NH4HSO4 and (NH4)2SO4. It is also observed that on 84% of the days during this study, the concentration of ammonia exceeded the sum of the concentrations of the three acids. 3.3. PM2.5 The mass of PM2.5 was measured hourly in both Manhattan and the Bronx from January 1999 through November 2000 with a Rupprecht and Patashnick
Time of day variation of PM2.5
18
300
600
900 1200 1500 Time of Day (hrs)
1800
2100
2400
Fig. 7. (a) Monthly mean concentrations of PM2.5 at Manhattan and Bronx; and (b) time of day variation of PM2.5 at Manhattan and Bronx.
TEOM Series 1400a real-time monitor. From the values of hourly mass of PM2.5, 24 h averages were calculated for both the sites. The PM2.5 concentration averaged 15.2 mg/m3 at the Bronx site and 16.1 mg/m3 at the Manhattan site. However, the PM2.5 concentration averaged 15.5 mg/m3 at Manhattan, if only days when Bronx data is also available are used. The PM2.5 concentrations varied greatly from day to day and throughout the day. The highest hourly concentrations and the daily mean were 94.8 and 51.6 mg/m3, respectively at Manhattan on 24 July 1999. The monthly means of PM2.5 at Manhattan and the Bronx are shown in Fig. 7a. The monthly mean concentrations of PM2.5 at Manhattan ranged from 13.2 to 21.7 ug/m3 with an
A. Bari et al. / Atmospheric Environment 37 (2003) 2825–2835
overall mean of 16.1 ug/m3, higher averages were found in June and July (18.1 and 21.7 ug/m3, respectively), and the lowest were found in March and April (13.2 and 13.7 ug/m3, respectively) in 1999. Brook and Dann (1999) have reported similar trends in Hamilton and Windsor, Ontario, and Parkhurst et al. (1999) have also observed high summer–low winter seasonality in the southeastern United States. In Manhattan, the monthly mean fraction of PM2.5 as SO2 4 ranged from 0.17 to 0.31. The highest fraction values were observed during the months of June to September with the maximum in July. This can be explained in terms of higher concentration of SO2 during summer as 4 discussed earlier. TEOM operates at 50 C, hence it can give lower values for PM2.5, by an average of more than 20–30% (Ayers et al., 1999; Allen et al., 1997), when compared with traditional filter-based gravimetric methods due to the loss of semivolatile material such as ammonium nitrate and semivolatile organic matter at this temperature. Since the NYDEC determined daily PM2.5 mass using a Federal Reference Method (FRM) at each of the sites, the daily values from the Bronx and Manhattan sites were compared with the DEC FRM PM2.5 values (available on the web site at http:// www.dec.state.ny.us/website/dar/baqs/pm25mon.html). The correlation for the combined data set was good, with an r2 of 0.92 and the slope of 0.95. The values from TEOM were only slightly lower than the FRM method. Concentrations of PM2.5 at Manhattan and the Bronx varied by time of day (Fig. 7b). The absolute value of the maxima and minima vary somewhat with season, but the bimodal pattern is clearly evident at both sites. Minimum mass occurs during the night; however, by 0500 h, the mass is increasing and peaks around 0700 h at Bronx and 0800 h at Manhattan. The peak at Manhattan is also around 1 mg/m3 higher. The PM2.5 concentration decreases by B4 mg/m3 at midday. A second peak is reached between 2000 and 2100 h. In general, the second peak is lower than that in the morning; however, during the third quarter this can be reversed, for example the highest concentration recorded was at Manhattan, 94.8 mg/m3 at 2200 h on 24 July 1999. The diurnal pattern of a pollutant depends on local emissions, chemistry, and the dynamics of the local meteorology. While the profile at Manhattan is around a mg/m3 higher between 0800 and 2200 h than that at Bronx, the shapes are very similar. Linear regression of the hourly data at the two sites has an r2 of only 0.62 but the slope is 0.97. However, if daily means are compared an r2 of 0.92 is obtained with a slope of 0.95. This suggests that at these sites PM2.5 mass has a significant regional component with only minor contributions due to very local sources. We have no specific information, however, to distinguish which process is controlling the mass at these sites.
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4. Summary Concentrations and seasonal variations of gaseous nitrous acid, nitric acid, hydrochloric acid, sulfur dioxide, ammonia, and SO2 4 , and PM2.5 were determined at monitoring sites in the Bronx and Manhattan in New York from 1999 to 2000. The inter-site (Bronx and Manhattan) correlations for nitrous acid, nitric acid, hydrochloric acid, sulfur dioxide, particulate sulfate and PM2.5 were very high, correlation coefficients were generally greater than or equal to 0.83 (0.83–0.96). Concentrations at Manhattan were, in general, slightly higher than at the Bronx for each of the species. The data showed marked seasonal variations. The concentrations of nitric acid, hydrochloric acid, ammonia, and SO2 were higher during summer than winter, the 4 summer/winter ratio for nitric acid, hydrochloric acid, and SO2 at Manhattan was 3.9, 3.1 and 1.9, 4 respectively. The concentrations of nitrous acid, and sulfur dioxide were higher during winter than summer; the summer/winter ratio at Manhattan was 0.48 and 0.44, respectively. Gaseous nitrous acid was the predominant form compared to nitric acid except in summer. The annual mean concentration of PM2.5 was 15.2 and 15.5 mg/m3 at the Bronx and at Manhattan, respectively. The monthly mean concentrations at Manhattan ranged from 13.2 to 21.7 mg/m3 and were highest in June and July, and lowest in March and April. The hourly mean concentrations of PM2.5 showed a bimodal pattern, with peaks at around 7–8 AM and 8– 9 PM. The monthly mean fraction of PM2.5 as SO2 4 ranged from 0.17 to 0.31; the highest fraction values were observed during June–September.
Acknowledgements The authors thank Bonnie Hall for assistance in chemical analysis, Stan House, Dan Lince, Dan Sharron and Pat Palmer for sampling. We also thank the staff of the NYSDEC, Division of Air Resources for providing NO2, O3 and SO2 hourly data, monitoring locations and the use of continuous PM2.5 instrument and assistance in its operation. The financial assistance provided by the Agency for Toxic Substances and Disease Registry, and New York State Energy Research and Development Authority is gratefully acknowledged.
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