- Email: [email protected]
Characteristics of major secondary ions in typical polluted atmospheric aerosols during autumn in central Taiwan
Journal of Environmental Management 92 (2011) 1520e1527
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Characteristics of major secondary ions in typical polluted atmospheric aerosols during autumn in central Taiwan Guor-Cheng Fang a, Shih-Chieh Lin a, Shih-Yu Chang b, c, *, Chuan-Yao Lin d, Charles-C.K. Chou d, Yun-Jui Wu b, Yu-Chieh Chen b, Wei-Tzu Chen b, Tsai-Lin Wu b a
Air Toxic and Environmental Analysis, Hungkuang University, Taichung 433, Taiwan School of Public Health, Chung Shan Medical University, Taichung 402, Taiwan Department of Family and Community Medicine, Chung Shan Medical University Hospital, Taichung 402, Taiwan d Research Center for Environmental Changes, Academia Sinica, Taipei 105, Taiwan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 June 2010 Received in revised form 2 December 2010 Accepted 5 January 2011 Available online 12 February 2011
In autumn of 2008, the chemical characteristics of major secondary ionic aerosols at a suburban site in central Taiwan were measured during an annually occurring season of high pollution. The semicontinuous measurement system measured major soluble inorganic species, including NHþ 4 , NO3 , , in PM with a 15 min resolution time. The atmospheric conditions, except for the influences of and SO2 4 10 typhoons, were dominated by the local sea-land breeze with clear diurnal variations of meteorological parameters and air pollutant concentrations. To evaluate secondary aerosol formation at different ozone levels, daily ozone maximum concentration (O3,daily max) was used as an index of photochemical activity for dividing between the heavily polluted period (O3,daily max S80 ppb) and the lightly polluted period 2 þ (O3,daily max<80 ppb). The concentrations of PM10, NO 3 , SO4 , NH4 and total major ions during the heavily polluted period were 1.6, 1.9, 2.4, 2.7 and 2.3 times the concentrations during the lightly polluted period, respectively. Results showed that the daily maximum concentrations of PM10 occurred around midnight and the daily maximum ozone concentration occurred during daytime. The average concentration of SO2 was higher during daytime, which could be explained by the transportation of coastal industry emissions to the sampling site. In contrast, the high concentration of NO2 at night was due to the land breeze flow that transport inland urban air masses toward this site. The simulations of breeze circulations and transitions were reflected in transports and distributions of these pollutants. During heavily polluted þ periods, NO 3 and NH4 showed a clear diurnal variations with lower concentrations after midday, possibly due to the thermal volatilization of NH4NO3 during daytime and transport of inland urban þ plume at night. The diurnal variation of PM10 showed the similar pattern to that of NO 3 and NH4 aerosols. This indicated that the formatted secondary aerosols in the inland urban area could be transported to the coastal area by the weak land breeze and deteriorated the air quality in the coastal area at night. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: In situ IC Sea-land breeze Aerosol transport Diurnal variation Photochemical reaction Continuous measurement
1. Introduction In recent years, atmospheric aerosol has attracted much attention due to the roles it plays: as important species in climate and visibility reduction, as surfaces that can catalyze atmospheric chemical reactions, and as carriers for chemical species (IPCC, 2001; Lohmann and Feichter, 2005; Jacobson, 2002; Laden et al., 2000; Watson, 2002). Epidemiological studies have also shown that particulate matter can cause adverse health effects, such as respiratory and cardiovascular
* Corresponding author. School of Public Health, Chung Shan Medical University, Taichung 402, Taiwan. Tel.: þ886 4 2473 0022x11834; fax: þ886 4 2324 8179. E-mail address: [email protected] (S.-Y. Chang). 0301-4797/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2011.01.011
diseases, allergies, and lung cancer (Donaldson et al., 2003; Chow et al., 2006; Pope and Dockery, 2006). Atmospheric particles are usually classified in two main fractions with respect to their formation processes: primary and secondary aerosols. A primary aerosol is emitted directly from sources, such as road traffic or blown dust. Secondary aerosol is produced originally from gas-phase chemical reactions (Mysliwiec and Kleeman, 2002; Schlesinger and Cassee, 2003). For instance, SO2 and NOx can be oxidized in the atmo sphere and converted to SO2 4 and NO3 (Lin et al., 2009). In the last decade, the percentage of days with pollutant standard index (PSI) exceeding 100 in central Taiwan showed a decreasing trend from 4.77% in 2000 to 2.56% in 2008. However, PM10 and O3 are two main pollutant indexes that cause poor air quality (Hsieh et al., 2009). Chang and Lee (2006) indicated that even if concentrations
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
of primary pollutants decrease significantly, the average daily maximum ozone concentration still increases. Therefore, the production of secondary aerosol still cannot be ignored due to ozone formation (Chang and Lee, 2007, 2008). Various compositions of secondary aerosols can form, but most compositions are not large enough to contribute significantly to particulate pollution, except for ammonium, sulfate, and nitrate (Tsai and Chen, 2006). Lin (2002) found that sulfate, nitrate and ammonium dominated the identifiable compositions within both fine and coarse aerosols in Kaohsiung (a coastal urban city) in southern Taiwan and comprised 90.0% and 80.6% of total dissolved ionic concentrations for PM2.5 and PM10, respectively. In central Taiwan’s coastal regions, sulfate, nitrate, ammonium, and carbonaceous material combined represent 40e60% of the fine particle mass of highly polluted aerosols (Tsai and Cheng, 1999, 2004). Lin et al. (2007a) indicated that the mass ratio of NO 3 was higher than that of SO2 4 in all the sized particles at the traffic site. Aerosol chemical species can provide information about aerosol formation, conversion, transportation, and removal processes. These aerosol processes can vary rapidly over a wide range of different meteorological and topographic conditions. Central Taiwan can be divided into urban and coastal areas according to topographical characteristics. The urban area, a 163.4 km2 basin surrounded by the Central Mountain Range (CMR) and Tatu Hill, has a population of over 0.9 million people, giving a population density of over 5500 people km2. The number of vehicles exceeds 0.7 million. This high vehicle density leads to severe air pollution. The coastal area, located between the Taiwan Strait and Tatu Hill, extends to 95.1 km2 and has a population of 45,000 people, giving a population density of about 460 people km2 (Chio et al., 2004). This area has less than 840 motorized vehicles per square km, with <570 cars km2 and <1120 motorcycles km2. The sea-land breeze may be an important means of distributing air pollution between coastal areas and inland areas (Targino and Noone, 2006). Therefore, the interplay between emission from the coast and inland areas in central Taiwan and the transport pattern in the coastal boundary layer have caused the secondary aerosol formation of great complexity. The composition and reaction of secondary pollutants are very complex due to the various changes in aerosol characteristics. Understanding the temporal and spatial variations of physical and chemical characteristics for atmospheric aerosols is crucial (Kothai et al., 2008). However, most of the previous chemical analyses of aerosol source apportionment were based on the batch measurements’ relatively long sampling times, especially in Taiwan (Wang et al., 2008; Tseng et al., 2009). The long sampling intervals could dilute the temporal impact of pollutant sources, making it difficult to separate the individual sources. The time resolution of the batch measurement is also usually not sufficient to explain the complex characteristics and rapid changes of aerosols in real atmosphere. In Taiwan, the high time-resolved measurements of aerosol chemical compositions are limited, especially for central Taiwan. This study investigated the chemical composition distributions of watersoluble inorganic ions with the influence of sea-land breeze on air quality. The variation of the concentration and the diurnal variation of mainly secondary aerosol compositions (i.e., ammonium, nitrate, and sulfate) and precursor pollutants were also analyzed.
1521
with a heavily traffic expressway approximately 2 km east from the station. The Shalu, Taiwan, EPA air-quality monitoring station is located roughly 10 m northwest of the Beishi sampling station. The observational campaign was carried out from 9 September to 3 October 2008. Hourly meteorological data, mass concentrations of PM10 and PM2.5, and concentrations of gaseous pollutants were obtained from the Shalu air-quality monitoring stations. Concentrations of water-soluble ions in PM10 were measured by the in situ ion chromatography (IC) system, with 15 min sampling intervals. þ 2 þ The eight water-soluble ions, such as Cl, NO 2 , NO3 , SO4 , Na , NH4 , þ 2þ K , and Ca were determined during the 2008 autumn campaign. All data discussed in this work were under the no-rain condition. 2.2. Instruments
2. Experimental methods
The particulate sampling apparatuses were placed on the roof of the Beishi junior high school, a four-story building (height is 15 m). The concentrations of water-soluble ions in PM10 were continuously measured by the in situ IC system at intervals of 15 min (Chang et al., 2006a, 2006b, 2007). The measuring system has three parts: (1) pre-impactor and gas removal denuders, (2) aerosol collecting device, and (3) IC (Ion Chromatography, Model ICS-90, Dionex Corp., Sunnyvale, CA, YSA). The in situ IC system was operated at a total flow rate of 16.7 l min1 for a PM10 sampling inlet. After leaving the pre-impactor, the sampling flow was split into a 10 l min1 main flow and 6.7 l min1 filter flow. The filter flow, which passes through the filter pack, was controlled by a mass flow controller. The ambient sample from the main flow line was drawn through the denuders to remove acidic and basic gases. After leaving the denuders, the main flow was turbulently mixed with saturated water vapor. The aerosol and water vapor were then passed through a growth chamber with a cool wall to form large droplets in a supersaturated condition. The growth chamber was actively air-cooled by fans. The airflow containing the droplets flowed through a single circular nozzle onto a flat quartz plate, where the droplets were collected. After impacting the plate, the air was drawn from a port on top of the impactor housing, and the liquid was transported by carrier water from the top of the quartz plate to the bottom of the impactor housing. The highly purified and deionized carrier water was regulated by a peristaltic pump. The final liquid sample, which contained the water-soluble ions of the collected aerosol and air bubbles, was introduced into the debubbler to remove the air bubbles before being injected into each IC (Ion Chromatography, ICS-90 Dionex Corporation). The IC for anions was equipped with an AG12A guard column, an AS-12A separator column, and a self-regenerating suppressor, which uses 9 mM Na2CO3/NaHCO3 as eluent. The retention time was 2 5.0, 6.0, 9.9, and 12.4 min for Cl, NO 2 , NO3 , and SO4 , respectively. The IC for cations was equipped with a CG-12A guard column, a CS12A separator column, and a self-regenerating suppressor, which employs 20 mM CH4O3S (MSA) as eluent. The retention time was 3.5, þ 2þ 4.0, 5.0 and 10.5 min for Naþ, NHþ 4 , K and Ca , respectively. Each soluble species was clearly separated and analyzed. The average drift of retention time was lower than 0.01 min after running for an extended period. The detection limits, calculated as three times the standard deviations of seven replicate blank samples, for Cl, NO 2, 2 þ þ þ 2þ were all lower than 0.1 mg m3. NO 3 , SO4 , Na , NH4 , K and Ca
2.1. Sampling program
3. Results
Fig. 1 presents the geographical location of the Beishi sampling station (2400130, 12000 340) in Shalu, Taichung, Taiwan. The sampling station is a suburban/coastal station on the western side of Tatu Hill and is about 9 km west of the Taiwan Strait. There is no obstruction around the sampling station. The immediate area is residential,
3.1. Overall of weather situation and air pollution level Taiwan is geographically within the western North Pacific monsoon region. The air quality in different parts of the island is strongly influenced by prevailing winds, especially in autumn
1522
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
Fig. 1. The geographical location of the sampling station.
and spring. During the autumn and spring months, interactions between the winter monsoon and the summer monsoon vary greatly and determine the local wind fields in Taiwan. The frontal zone is characterized by a strong temperature gradient and a shift in wind direction. After the frontal passage, the synoptic flow is easterly, with western Taiwan on the lee side of the CMR. In this circumstance, the atmospheric environment is sunny and is dominated by sea-land breeze in the coastal area of central Taiwan. Accumulations of local emissions are catalysts to the air pollution episodes. Previous studies have tried to indicate the relationships between synoptic weather pattern and air pollution in central Taiwan. For example, Lin et al. (2007b) examined the important role of local circulation in the formation of the secondary air pollution during the northeasterly monsoon. Kuo et al. (2008) founded the secondary air pollution depended strongly on the synoptic weather pattern especially for bringing easterly winds toward Taiwan. Tseng et al. (2009) also pointed out the secondary aerosols concentrations increased as the O3 concentrations increased, which typically occur during the sea-land breeze. Fig. 2(a)e(d) shows the meteorological parameters [i.e., ambient temperature, relative humidity (RH), wind speed (WS), wind direction (WD), and solar irradiation] and air pollutant concentrations (i.e., O3, PM10, and PM2.5) during the sampling period. On 9 and 10 September, the weather was heavily influenced by regional sea-land breeze with warm-strong sea wind and daily maximum radiation after midday. The daily maximum concentrations of O3, PM2.5, and PM10 were lower than the national ambient air quality standard (O3 < 80 ppb, PM2.5 < 65 mg m3, PM10 < 125 mg m3). Similar phenomena were observed between 23 and 26 September.
From 11 to 15 September and 27e29 September, central Taiwan was hit by typhoons Sinlaku and Jangmi. The diurnal variations of meteorological parameters and air pollutant concentrations disappeared. The weather was characterized by violent wind speed and low ambient temperature. The wind direction was determined by the location of the typhoon center. The bad air quality with higher PM10 concentration appeared in the front of the typhoon peripheral circumfluence (Fang et al., 2009). During 16 September through 23 September, the weather was influenced by the sea-land breeze with clear diurnal variations of meteorological parameters and air pollutant concentrations. The level of air pollutant was higher than the ambient air quality standard. The index of the daily maximum O3 concentration (O3, max) played an important role for understanding the formation of secondary aerosol (Na et al., 2004). Chang and Lee (2007) indicated that photochemical activities were low when O3, max was less than 60 ppb. In contrast, more secondary aerosols formed through photochemical reactions when O3, max exceeds 80 ppb. In this study, we excluded the influences of typhoons and differentiated the influence of photochemical activities on the secondary aerosol formation. Because O3, max of less than 60 ppb was almost observed during the typhoon influenced period, O3, max less than 80 ppb and greater than 80 ppb were defined as the lightly polluted period and the heavily polluted period respectively. 3.2. Solar irradiation and particulate matter Fig. 2(c) showed the time series of hourly solar irradiation during the sampling period. The average solar irradiation was 400 J m2
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
1523
Fig. 2. Hourly measurements of meteorological parameter and air pollutant concentrations during the sampling period. L: lightly polluted period; T: typhoon influenced period; H: heavily polluted period.
during the lightly polluted period and 330 J m2 during the heavily polluted period. The average concentration of PM10 was 65.7 mg m3 during the lightly polluted period and 108.3 mg m3 during the heavily polluted period. The proportion of PM2.5 in PM10 was 43% in the lightly polluted period and 61% in the heavily polluted period, which indicated that the increased range of concentration of fine particles was higher than that of coarse particles in the heavily polluted period. Most of the fine particles were connected with the secondary aerosols, especially the anthropogenic ones (Lun et al.,
2003; Tang et al., 2005). During the heavily polluted periods, the secondary aerosols were converted from the precursor gases by photochemical reactions in the troposphere. The formatted secondary aerosols can cause the solar irradiation decreases. In this study, the solar irradiation was measured by the ground base instrument. The secondary aerosols have depleted the solar irradiation before reaching to the ground. Results showed that the radiative forcing to the ground was negatively correlated to aerosol concentration, especially for the fine aerosol. Previous studies have
1524
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
shown that secondary aerosols, mainly emitted from anthropogenic pollution, can affect solar irradiation (Lee and Sequeira, 2002; Chang and Park, 2004; Latha and Badarinath, 2005). 3.3. Wind fields between heavily and lightly polluted periods Fig. 3 showed the daytime and nighttime wind fields between heavily and lightly polluted periods. When the dominant largescale meteorology was easterly over the sea to the east of Taiwan, the Taichung area was on the lee side of the CMR, and the prevalent easterly wind was shielded. At the same time, aerosol distribution was mainly controlled by local meteorological phenomena in the Taichung area. Among these processes, the sea-land breeze played an important role in the transport and derivation of aerosols. The sea breeze began to blow onshore progressively as the temperature difference between sea and land increased. The air pollutants, mainly emitted from Taichung harbor, industrial parks, and power plants, were transported from the coastal area to the inland area and reacted with urban pollutants to form secondary aerosols in the daytime during the lightly and heavily polluted periods (Fig. 3(a) and (c)). At night, the land surface temperature did not drop below sea temperature because of the heat-island effect, and the nocturnal winds were weaker than the daytime winds during the lightly and heavily polluted periods (Fig. 3(b) and (d)).
3.4. Hourly measurements of nitrate, sulfate, and ammonium The hourly variations of major soluble ions (Fig. 4) were very similar to those of PM10 (Fig. 2(d)), except during typhoons. Their concentrations were low on 9 and 10 September. On 11 September, when a typhoon moved into Taiwan, the hourly concentration of PM10 sharply increased. In contrast, the hourly concentrations of major soluble ions fell. The primary reason was the resuspension of the river sand during dry season (Fang et al., 2009). The concentrations of PM10 and the major soluble ions began to rise after the typhoon period. From midday of 23 September, central Taiwan was affected by the typhoon peripheral circumfluence. The concentrations of PM10 and major soluble ions decreased. When the typhoon arrived on 27 September, the phenomena of higher PM10 and lower major soluble ions were repeated. 2 þ The concentrations of PM10, NO 3 , SO4 , NH4 , and the total major ions during the heavily polluted period were 1.6, 1.9, 2.4, 2.7 and 2.3 times the concentrations during the lightly polluted period, respectively (Table 1). The weak intensity of sea-land transport and the high capacity of atmospheric oxidation contributed to the increased concentrations of these pollutants during the heavily polluted period. In many O3 chemistry studies, the total oxidant Ox (estimated by O3 þ NO2) is frequently used in data analysis because Ox is not affected by the rapid photodissociation of NO2 and the
Fig. 3. The wind field in Taiwan. (a) and (b) were the wind field in the daytime and nighttime respectively during the lightly polluted period. (c) and (d) were the wind field in the daytime and nighttime respectively during the heavily polluted period.
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
1525
Fig. 4. Hourly measurements of nitrate, sulfate and ammonium in PM10 during the sampling period.
titration of O3 with NO, being a better index of the real atmospheric oxidation capacity (Chou et al., 2006; Zhang et al., 2008). Table 1 also compares the weather situation and the atmospheric oxidation capacity between the heavily and lightly polluted periods. The lower average wind speed caused the accumulation of pollutants during the heavily polluted period. In addition, the total oxidant Ox was higher during the heavily polluted period, which contributed to the formation of secondary aerosol. 2 þ NO 3 , SO4 , and NH4 were the dominant ionic species according to the measurements of all soluble ions. The mass fraction of NO 3, þ SO2 4 and NH4 in PM10 aerosols all increased in the heavily polluted period compared with the lightly polluted period. The results show that the increased proportions of SO2 4 aerosols were higher than þ that of NO 3 and NH4 aerosols. NH4NO3 particles were likely to dissociate to gaseous HNO3 and NH3. Schaap et al. (2004) indicated that there is complete evaporation at temperatures exceeding 25 C and no significant evaporation is observed below 20 C. At temperatures between 20 and 25 C the retention is on average 50%, but with high variability. In this study, ambient temperatures were higher than 25 C during daytime, which caused mass fracþ tions of NO 3 and NH4 to slightly rose. 3.5. Average diurnal variation of PM10, nitrate, sulfate, and ammonium Fig. 5 shows the different average diurnal variation patterns of PM10 along with its components, gaseous pollutants, and meteorological parameters between the heavily and lightly polluted periods. Pronounced diurnal variations of PM10 concentrations were observed during the heavily polluted period (Fig. 5(a)). The highest concentration was usually occurred 1w2 h after midnight.
In contrast, diurnal variations of PM10 concentrations were no significant peaks during the lightly polluted period. The diurnal variations of the SO2 4 concentrations did not show significant peaks both during the heavily and lightly polluted periods (Fig. 5(b)). Because aerosol SO2 4 , unlike semi-volatile NH4NO3, does not evaporate from aerosol with increasing ambient temperature, the accumulations tend to dilute the diurnal variations of aerosol SO2 4 . Fig. 5(c) shows the diurnal variation of total oxidant Ox concentrations. The daily maximum total oxidant Ox concentrations were observed at 12:00 and 14:00 during the lightly and heavily polluted periods, respectively. Fig. 5(d) shows the diurnal variation of the SO2 concentration, which showed higher concentration in the morning and noon during the lightly and polluted periods, respectively. When the sea breeze developed, a substantial SO2 emitted from the upwind site of Taichung harbor, industrial parks, and power plants was brought to the downwind site of Shalu. The transport of these plumes strongly elevated the SO2 concentration during daytime. þ The NO 3 and NH4 took on different diurnal variation patterns during the heavily and lightly polluted periods (Fig. 5(e) and (f)). þ The diurnal cycles of NO 3 and NH4 demonstrated a single mode distribution during heavily polluted periods, with concentrations low during daytime and high at night. In contrast, the relatively þ unclear diurnal cycles of NO 3 and NH4 were observed during the lightly polluted periods, with concentrations low in the midday and high in the daily morning and evening rush hour. The lowest þ diurnal concentrations of NO 3 and NH4 were observed at noon both during the heavily and lightly polluted periods possibly because the evaporation of semi-volatile NH4NO3 was enhanced greatly under high temperature (Fig. 5(i)), and the development of the turbulence effect by sea breeze diluted the ambient pollutant concentrations.
Table 1 The concentrations and mass fractions of major soluble ions during the heavily and lightly polluted periods. Concentration (mg m3)
Atmospheric oxidation capacity
Weather situation
PM10 mg m3
3 NO 3 mg m
3 SO2 4 mg m
3 NHþ 4 mg m
Sum of three ions mg m3
O3 þ NO2 ppb
Temp C.
RH %
WS m s1
Heavily pollutant period (H)
108.3
14.2a (13.1)
22.7 (21.0)
8.9 (8.2)
45.8 (42.3)
62.1
29.3
77.2
1.6
Lightly pollutant period (L)
65.7
7.4 (11.3)
9.5 (14.5)
3.3 (5.0)
20.2 (30.7)
46.8
29.9
73.0
2.2
1.9
2.4
2.7
2.3
Ratio (H/L) a
1.6
the mass fraction of the ion in PM10, %.
1526
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
þ Fig. 5. Average diurnal variations of PM10, SO2 4 , O3, SO2, NO3 , NH4 , NO2, WS and PM2.5 between the heavily and lightly polluted periods from 9 to 30 September 2008.
þ The highest concentrations of NO 3 and NH4 were observed near midnight during the heavily polluted periods and in the rush hour during the lightly polluted periods. These differences depended not only on the evaporation of semi-volatile aerosols but also on the concentrations of precursor gases, the oxidation capacity in the atmosphere, and the transport of sea-land breeze. Previous study (Schaap et al., 2004) indicated that there is complete evaporation at temperatures exceeding 25 C and full retention at temperatures less than 20 C. At temperatures between 20 and 25 C the partial loss with high variability is observed. In addition, NH4NO3 is deliquescent and forms solution droplets at RH 62% (at 25 C) (Chang and Lee, 2002). Higher humidity increases the potential existence of external aerosols at night (Fig. 5(i)). Fig. 5(g) shows that the concentrations of the precursor gaseous NO2 at night were higher during the heavily polluted periods than during the lightly polluted periods. The total oxidant Ox concentration is an indicator to evaluating the oxidation capacity in the atmosphere. High concentrations of total oxidant Ox (Fig. 5(c)) led to a high potential for the oxidation of precursor gaseous NO2 to secondary aerosol NO 3 during the heavily polluted period. The predominant pollutants in the inland urban areas were characterized as vehicle emissions due to the large population and high density of vehicle exhaust. In contrast, the power plant and industrial areas could be an important source of VOC, SO2 and primary sulfates in the coastal area. The total oxidant (NO2 þ O3) and sulfate aerosols (primary and secondary sulfates) were transport from the coastal area into the urban area by the sea wind during the daytime. Comparing Fig. 5(b) and (c), the secondary sulfate aerosols were insignificantly converted from SO2. At the same time, a great amount of secondary nitrate aerosols have been converted from vehicle emissions (NOx) in the urban area. After sunset, lower ambient temperature is beneficial to form the secondary nitrate
aerosols. In addition, NH3 emitted from large population was reacted with the secondary nitrate in the urban area. When the land wind began to blow offshore, sulfate aerosols previously transþ ported from the coastal area and secondary aerosols (NO 3 and NH4 ) formed in the urban area were moved to the coastal area. Fig. 5(h) shows that the average diurnal wind speed was lower during nighttime than daytime. Consequently, the formatted secondary pollutants by photochemical reaction in the inland urban area could be accumulated and transported slowly to the coastal area, which would explain the high concentrations of NHþ 4 and NO3 was near 2 midnight and the diurnal variation of SO4 aerosol was small. 4. Conclusions Gaseous pollutants, particulate mass and water-soluble ions concentrations in PM10 were sampled and monitored between 9 September and 3 October 2008 in central Taiwan. Excluding the influences of typhoons, the pollution events were classified as heavily and lightly polluted periods according to the daily O3, max concentration S 80 ppb and <80 ppb, respectively. The concentrations of PM10 increased about 1.6 times during the heavily 2 þ polluted period. NO 3 , SO4 and NH4 were the dominant ions in PM10 and their concentrations increased by 1.9, 2.4 and 2.7 times, respectively, during the heavily polluted period compared with the lightly polluted period. The diurnal variations of pollutants transport and dispersion during the autumn months in this study area are dominated by the sea breeze dynamics formations. Breeze circulations and transitions are characterized by the enhanced sea breeze during the day and weak land breeze during the night. The O3 and SO2 concentrations increased as enhancing the sea breeze. The transportation of coastal industry emissions and urban traffic exhausts could explain the higher concentrations of SO2 and O3
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
during daytime and the rising concentrations of NO2 around midnight, respectively. During heavily polluted periods, particulate pollutants except for sulfate aerosols showed a clear diurnal variation with lower concentration around midday and higher concenþ tration around midnight. NO 3 and NH4 concentrations in PM10 are lower during the day, possibly due to the thermal volatilization on aerosols were more thermal NH4NO3. Because secondary SO2 4 stable and accumulated in the atmosphere, the SO2 4 diurnal variations was insignificant. The diurnal variation of PM10 showed the þ similar pattern to that of urban aerosols (NO 3 and NH4 ), suggesting the formatted secondary aerosols in the inland urban area were transported to the coastal area by the weak land breeze and deteriorated the air quality in the coastal area at night. Overall, the autumn pollution events in this study were characterized by the absence of synoptic-scale air mass advections, the development of breeze circulations and enhanced photochemistry.
References Chang, L.S., Park, S.U., 2004. Direct radiative forcing due to anthropogenic aerosols in East Asia during April 2001. Atmospheric Environment 38, 4467e4482. Chang, S.C., Lee, C.T., 2006. Ozone variations through vehicle emissions reductions based on air quality monitoring data in Taipei City, Taiwan, from 1994 to 2003. Atmospheric Environment 40, 3513e3526. Chang, S.C., Lee, C.T., 2007. Secondary aerosol formation through photochemical reactions estimated by using air quality monitoring data in Taipei City from 1994 to 2003. Atmospheric Environment 41, 4002e4017. Chang, S.C., Lee, C.T., 2008. Evaluation of the temporal variations of air quality in Taipei City, Taiwan, from 1994 to 2003. Journal of Environmental Management 86, 627e635. Chang, S.Y., Fang, G.C., Chou, C.C.K., Chen, W.N., 2006a. Source identifications of PM10 aerosols depending on hourly measurements of soluble components characterization among different events in Taipei Basin during spring season of 2004. Chemosphere 65, 792e801. Chang, S.Y., Fang, G.C., Chou, C.C.K., Chen, W.N., 2006b. Chemical compositions and radiative properties of dust and anthropogenic air masses study in Taipei Basin, Taiwan, during Spring of 2004. Atmospheric Environment 40, 7796e7809. Chang, S.Y., Lee, C.T., 2002. Applying GC-TCD to investigate the hygroscopic characteristics of mixed aerosols. Atmospheric Environment 36, 1521e1530. Chang, S.Y., Lee, C.T., Chou, C.C.K., Liu, S.C., Wen, T.X., 2007. The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite, Taiwan. Atmospheric Environment 41, 1936e1949. Chio, C.P., Cheng, M.T., Wang, C.F., 2004. Source apportionment to PM10 in different air quality conditions for Taichung urban and coastal areas, Taiwan. Atmospheric Environment 38, 6893e6905. Chou, C.C.K., Liu, S.C., Lin, C.Y., Shiu, C.J., Chang, K.H., 2006. The trend of surface ozone in Taipei, Taiwan, and its causes: implications for ozone control strategies. Atmospheric Environment 40, 3898e3908. Chow, J.C., Watson, J.G., Mauderly, J.L., Costa, D.L., Wyzga, R.E., Vedal, S., Hidy, G.M., Altshuler, S.L., Marrack, D., Heuss, J.M., Wolff, G.T., Pope, C.A., Dockery, D.W., 2006. Health effects of fine particulate air pollution: lines that connect. Journal of Air and Waste Management Association 56, 1368e1380. Donaldson, K., Stone, V., Born, P.J.A., Jimenez, L.A., Gilmour, P.S., Schins, R.P.F., Knaapen, A.D.M., Rahman, I., Faux, S.P., Brown, D.M., MacNee, W., 2003. Oxidative stress and calcium signaling in the adverse effects of environmental particles (PM10). Free Radical Biology & Medicine 34, 1369e1382. Fang, G.C., Lin, S.J., Chang, S.Y., Chou, C.C.K., 2009. Effect of typhoon on atmospheric particulates in Autumn in central Taiwan. Atmospheric Environment 43, 6039e6048. Hsieh, L.Y., Kuo, S.C., Chen, C.L., Tsai, Y.I., 2009. Size distributions of nano/micron dicarboxylic acids and inorganic ions in suburban pm episode and non-episodic aerosol. Atmospheric Environment 43, 4396e4406. IPCC, 2001. Aerosols, their Direct and Indirect Effects. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, pp. 289e348.
1527
Jacobson, M.Z., 2002. Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming. Journal of Geophysical Research 107 (D19), 4410. doi:10.1029/2001JD001376. Kothai, P., Saradhi, I.V., Prathibha, P., Hopke, P.K., Pandit, G.G., Puranik, V.D., 2008. Source apportionment of coarse and fine particulate matter at Navi Mumbai, India. Aerosol and Air Quality Research 8, 423e436. Kuo, C.Y., Chen, P.T., Lin, Y.C., Lin, C.Y., Chen, H.H., Shih, J.F., 2008. Factors affecting the concentrations of PM10 in central Taiwan. Chemosphere 70, 1273e1279. Laden, F., Neas, L.M., Dockery, D.W., Schwartz, J., 2000. Association of fine particulate matter from different sources with daily mortality in six U.S. cities. Environmental Health Perspectives 108, 941e947. Latha, K.M., Badarinath, K., 2005. Shortwave radiative forcing efficiency of urban aerosols e a case study using ground based measurements. Chemosphere 58, 217e220. Lee, Y.L., Sequeira, R., 2002. Water-soluble aerosol and visibility degradation in Hong Knog during autumn and early winter, 1998. Environmental Pollution 116, 225e233. Lin, C.C., Huang, K.L., Chen, S.J., Liu, S.C., Tsai, J.H., Lin, Y.C., Lin, W.Y., 2009. NHþ 4 , NO3 , and SO2 4 in roadside and rural size-resolved particles and transformation of NO2/SO2 to nanoparticle-bound NO3/SO42. Atmospheric Environment 43, 2731e2736. Lin, C.C., Chen, S.J., Huang, K.L., Lee, W.J., Lin, W.Y., Liao, C.J., Chaung, H.C., Chiu, C.H., 2007a. Water-soluble ions in nano/ultrafine/fine/coarse particles collected near a busy road and at a rural site. Environmental Pollution 145, 562e570. Lin, C.Y., Wang, Z., Chou, C.C.K., Chang, C.C., Liu, S.C., 2007b. A numerical study of an autumn high ozone episode over southwestern Taiwan. Atmospheric Environment 41, 3684e3701. Lin, J.J., 2002. Characterization of water-soluble ion species in urban ambient particles. Environment International 28, 55e61. Lohmann, U., Feichter, J., 2005. Global indirect aerosol effects: a review. Atmospheric Chemistry and Physics 5, 715e737. Lun, X., Zhang, X., Mu, Y., Nang, A., Jiang, G., 2003. Size fractionated speciation of sulfate and nitrate in airborne particulates in Beijing, China. Atmospheric Environment 37, 2581e2588. Mysliwiec, M.J., Kleeman, M.J., 2002. Source apportionment of secondary airborne particulate matter in a polluted atmosphere. Environmental Science and Technology 36, 5376e5384. Na, K., Sawant, A.A., Song, C., Cocker III, D.R., 2004. Primary and secondary carbonaceous species in the atmosphere of Western Riverside County, California. Atmospheric Environment 39, 2011e2020. Pope, C.A., Dockery, D.W., 2006. Health effects of fine particulate air pollution: lines that connect. Journal of Air and Waste Management Association 56, 709e742. Schaap, M., Spindler, G., Schulz, M., Acker, K., Maenhaut, W., Berner, A., Wieprecht, W., Streit, N., Muller, K., Bruggemann, E., Chi, X., Putaud, J.P., Hitzenberger, R., Puxbaum, H., Baltensperger, U., ten Brink, J., 2004. Artefacts in the sampling of nitrate studied in the “INTERCOMP” campaigns of EUROTRACAEROSOL. Atmospheric Environment 38, 6487e6496. Schlesinger, R.B., Cassee, F., 2003. Atmospheric secondary inorganic particulate matter: the toxicological perspective as a basis for health effects risk assessment. Inhalation Toxicology 15, 197e235. Tang, A., Zhuang, G., Wang, Y., 2005. The chemistry of precipitation and its relation to aerosol in Beijing. Atmospheric Environment 39, 3397e3406. Targino, A.C., Noone, K.J., 2006. Airborne in situ characterization of dry urban aerosol optical properties around complex topography. Atmospheric Research 79, 148e174. Tsai, Y.I., Cheng, M.T., 1999. Visibility and aerosol chemical compositions near the coastal area in central Taiwan. Science of the Total Environment 231, 37e51. Tsai, Y.I., Cheng, M.T., 2004. Characterization of chemical species in atmospheric PM10 aerosols in a Metropolitan Basin. Chemosphere 54, 1171e1181. Tsai, Y.I., Chen, C.L., 2006. Atmospheric aerosol composition and source apportionments to aerosol in southern Taiwan. Atmospheric Environment 40, 4751e4763. Tseng, K.H., Wang, J.L., Cheng, M.T., Tsuang, B.J., 2009. Assessing the relationship between air mass age and summer ozone episodes based on photochemical indices. Aerosol and Air Quality Research 9, 149e171. Wang, W.C., Chen, K.S., Chen, S.J., Lin, C.C., Tsai, J.H., Lai, C.H., Wang, S.K., 2008. Characteristics and receptor modeling of atmospheric PM2.5 at urban and rural sites in Pingtung, Taiwan. Aerosol and Air Quality Research 8, 112e129. Watson, J.G., 2002. Visibility: science and regulation. Journal of Air and Waste Management Association 52, 628e713. Zhang, Y.H., Su, H., Zhong, L.J., Cheng, Y.F., Zeng, L.M., Wang, X.S., Xiang, Y.R., Wang, J.L., Gao, D.F., Shao, M., Fan, S.J., Liu, S.C., 2008. Regional ozone pollution and observation-based approach for analyzing ozone-precursor relationship during the PRIDE-PRD2004 campaign. Atmospheric Environment 42, 6203e6218.
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Characteristics of major secondary ions in typical polluted atmospheric aerosols during autumn in central Taiwan Guor-Cheng Fang a, Shih-Chieh Lin a, Shih-Yu Chang b, c, *, Chuan-Yao Lin d, Charles-C.K. Chou d, Yun-Jui Wu b, Yu-Chieh Chen b, Wei-Tzu Chen b, Tsai-Lin Wu b a
Air Toxic and Environmental Analysis, Hungkuang University, Taichung 433, Taiwan School of Public Health, Chung Shan Medical University, Taichung 402, Taiwan Department of Family and Community Medicine, Chung Shan Medical University Hospital, Taichung 402, Taiwan d Research Center for Environmental Changes, Academia Sinica, Taipei 105, Taiwan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 June 2010 Received in revised form 2 December 2010 Accepted 5 January 2011 Available online 12 February 2011
In autumn of 2008, the chemical characteristics of major secondary ionic aerosols at a suburban site in central Taiwan were measured during an annually occurring season of high pollution. The semicontinuous measurement system measured major soluble inorganic species, including NHþ 4 , NO3 , , in PM with a 15 min resolution time. The atmospheric conditions, except for the influences of and SO2 4 10 typhoons, were dominated by the local sea-land breeze with clear diurnal variations of meteorological parameters and air pollutant concentrations. To evaluate secondary aerosol formation at different ozone levels, daily ozone maximum concentration (O3,daily max) was used as an index of photochemical activity for dividing between the heavily polluted period (O3,daily max S80 ppb) and the lightly polluted period 2 þ (O3,daily max<80 ppb). The concentrations of PM10, NO 3 , SO4 , NH4 and total major ions during the heavily polluted period were 1.6, 1.9, 2.4, 2.7 and 2.3 times the concentrations during the lightly polluted period, respectively. Results showed that the daily maximum concentrations of PM10 occurred around midnight and the daily maximum ozone concentration occurred during daytime. The average concentration of SO2 was higher during daytime, which could be explained by the transportation of coastal industry emissions to the sampling site. In contrast, the high concentration of NO2 at night was due to the land breeze flow that transport inland urban air masses toward this site. The simulations of breeze circulations and transitions were reflected in transports and distributions of these pollutants. During heavily polluted þ periods, NO 3 and NH4 showed a clear diurnal variations with lower concentrations after midday, possibly due to the thermal volatilization of NH4NO3 during daytime and transport of inland urban þ plume at night. The diurnal variation of PM10 showed the similar pattern to that of NO 3 and NH4 aerosols. This indicated that the formatted secondary aerosols in the inland urban area could be transported to the coastal area by the weak land breeze and deteriorated the air quality in the coastal area at night. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: In situ IC Sea-land breeze Aerosol transport Diurnal variation Photochemical reaction Continuous measurement
1. Introduction In recent years, atmospheric aerosol has attracted much attention due to the roles it plays: as important species in climate and visibility reduction, as surfaces that can catalyze atmospheric chemical reactions, and as carriers for chemical species (IPCC, 2001; Lohmann and Feichter, 2005; Jacobson, 2002; Laden et al., 2000; Watson, 2002). Epidemiological studies have also shown that particulate matter can cause adverse health effects, such as respiratory and cardiovascular
* Corresponding author. School of Public Health, Chung Shan Medical University, Taichung 402, Taiwan. Tel.: þ886 4 2473 0022x11834; fax: þ886 4 2324 8179. E-mail address: [email protected] (S.-Y. Chang). 0301-4797/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2011.01.011
diseases, allergies, and lung cancer (Donaldson et al., 2003; Chow et al., 2006; Pope and Dockery, 2006). Atmospheric particles are usually classified in two main fractions with respect to their formation processes: primary and secondary aerosols. A primary aerosol is emitted directly from sources, such as road traffic or blown dust. Secondary aerosol is produced originally from gas-phase chemical reactions (Mysliwiec and Kleeman, 2002; Schlesinger and Cassee, 2003). For instance, SO2 and NOx can be oxidized in the atmo sphere and converted to SO2 4 and NO3 (Lin et al., 2009). In the last decade, the percentage of days with pollutant standard index (PSI) exceeding 100 in central Taiwan showed a decreasing trend from 4.77% in 2000 to 2.56% in 2008. However, PM10 and O3 are two main pollutant indexes that cause poor air quality (Hsieh et al., 2009). Chang and Lee (2006) indicated that even if concentrations
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
of primary pollutants decrease significantly, the average daily maximum ozone concentration still increases. Therefore, the production of secondary aerosol still cannot be ignored due to ozone formation (Chang and Lee, 2007, 2008). Various compositions of secondary aerosols can form, but most compositions are not large enough to contribute significantly to particulate pollution, except for ammonium, sulfate, and nitrate (Tsai and Chen, 2006). Lin (2002) found that sulfate, nitrate and ammonium dominated the identifiable compositions within both fine and coarse aerosols in Kaohsiung (a coastal urban city) in southern Taiwan and comprised 90.0% and 80.6% of total dissolved ionic concentrations for PM2.5 and PM10, respectively. In central Taiwan’s coastal regions, sulfate, nitrate, ammonium, and carbonaceous material combined represent 40e60% of the fine particle mass of highly polluted aerosols (Tsai and Cheng, 1999, 2004). Lin et al. (2007a) indicated that the mass ratio of NO 3 was higher than that of SO2 4 in all the sized particles at the traffic site. Aerosol chemical species can provide information about aerosol formation, conversion, transportation, and removal processes. These aerosol processes can vary rapidly over a wide range of different meteorological and topographic conditions. Central Taiwan can be divided into urban and coastal areas according to topographical characteristics. The urban area, a 163.4 km2 basin surrounded by the Central Mountain Range (CMR) and Tatu Hill, has a population of over 0.9 million people, giving a population density of over 5500 people km2. The number of vehicles exceeds 0.7 million. This high vehicle density leads to severe air pollution. The coastal area, located between the Taiwan Strait and Tatu Hill, extends to 95.1 km2 and has a population of 45,000 people, giving a population density of about 460 people km2 (Chio et al., 2004). This area has less than 840 motorized vehicles per square km, with <570 cars km2 and <1120 motorcycles km2. The sea-land breeze may be an important means of distributing air pollution between coastal areas and inland areas (Targino and Noone, 2006). Therefore, the interplay between emission from the coast and inland areas in central Taiwan and the transport pattern in the coastal boundary layer have caused the secondary aerosol formation of great complexity. The composition and reaction of secondary pollutants are very complex due to the various changes in aerosol characteristics. Understanding the temporal and spatial variations of physical and chemical characteristics for atmospheric aerosols is crucial (Kothai et al., 2008). However, most of the previous chemical analyses of aerosol source apportionment were based on the batch measurements’ relatively long sampling times, especially in Taiwan (Wang et al., 2008; Tseng et al., 2009). The long sampling intervals could dilute the temporal impact of pollutant sources, making it difficult to separate the individual sources. The time resolution of the batch measurement is also usually not sufficient to explain the complex characteristics and rapid changes of aerosols in real atmosphere. In Taiwan, the high time-resolved measurements of aerosol chemical compositions are limited, especially for central Taiwan. This study investigated the chemical composition distributions of watersoluble inorganic ions with the influence of sea-land breeze on air quality. The variation of the concentration and the diurnal variation of mainly secondary aerosol compositions (i.e., ammonium, nitrate, and sulfate) and precursor pollutants were also analyzed.
1521
with a heavily traffic expressway approximately 2 km east from the station. The Shalu, Taiwan, EPA air-quality monitoring station is located roughly 10 m northwest of the Beishi sampling station. The observational campaign was carried out from 9 September to 3 October 2008. Hourly meteorological data, mass concentrations of PM10 and PM2.5, and concentrations of gaseous pollutants were obtained from the Shalu air-quality monitoring stations. Concentrations of water-soluble ions in PM10 were measured by the in situ ion chromatography (IC) system, with 15 min sampling intervals. þ 2 þ The eight water-soluble ions, such as Cl, NO 2 , NO3 , SO4 , Na , NH4 , þ 2þ K , and Ca were determined during the 2008 autumn campaign. All data discussed in this work were under the no-rain condition. 2.2. Instruments
2. Experimental methods
The particulate sampling apparatuses were placed on the roof of the Beishi junior high school, a four-story building (height is 15 m). The concentrations of water-soluble ions in PM10 were continuously measured by the in situ IC system at intervals of 15 min (Chang et al., 2006a, 2006b, 2007). The measuring system has three parts: (1) pre-impactor and gas removal denuders, (2) aerosol collecting device, and (3) IC (Ion Chromatography, Model ICS-90, Dionex Corp., Sunnyvale, CA, YSA). The in situ IC system was operated at a total flow rate of 16.7 l min1 for a PM10 sampling inlet. After leaving the pre-impactor, the sampling flow was split into a 10 l min1 main flow and 6.7 l min1 filter flow. The filter flow, which passes through the filter pack, was controlled by a mass flow controller. The ambient sample from the main flow line was drawn through the denuders to remove acidic and basic gases. After leaving the denuders, the main flow was turbulently mixed with saturated water vapor. The aerosol and water vapor were then passed through a growth chamber with a cool wall to form large droplets in a supersaturated condition. The growth chamber was actively air-cooled by fans. The airflow containing the droplets flowed through a single circular nozzle onto a flat quartz plate, where the droplets were collected. After impacting the plate, the air was drawn from a port on top of the impactor housing, and the liquid was transported by carrier water from the top of the quartz plate to the bottom of the impactor housing. The highly purified and deionized carrier water was regulated by a peristaltic pump. The final liquid sample, which contained the water-soluble ions of the collected aerosol and air bubbles, was introduced into the debubbler to remove the air bubbles before being injected into each IC (Ion Chromatography, ICS-90 Dionex Corporation). The IC for anions was equipped with an AG12A guard column, an AS-12A separator column, and a self-regenerating suppressor, which uses 9 mM Na2CO3/NaHCO3 as eluent. The retention time was 2 5.0, 6.0, 9.9, and 12.4 min for Cl, NO 2 , NO3 , and SO4 , respectively. The IC for cations was equipped with a CG-12A guard column, a CS12A separator column, and a self-regenerating suppressor, which employs 20 mM CH4O3S (MSA) as eluent. The retention time was 3.5, þ 2þ 4.0, 5.0 and 10.5 min for Naþ, NHþ 4 , K and Ca , respectively. Each soluble species was clearly separated and analyzed. The average drift of retention time was lower than 0.01 min after running for an extended period. The detection limits, calculated as three times the standard deviations of seven replicate blank samples, for Cl, NO 2, 2 þ þ þ 2þ were all lower than 0.1 mg m3. NO 3 , SO4 , Na , NH4 , K and Ca
2.1. Sampling program
3. Results
Fig. 1 presents the geographical location of the Beishi sampling station (2400130, 12000 340) in Shalu, Taichung, Taiwan. The sampling station is a suburban/coastal station on the western side of Tatu Hill and is about 9 km west of the Taiwan Strait. There is no obstruction around the sampling station. The immediate area is residential,
3.1. Overall of weather situation and air pollution level Taiwan is geographically within the western North Pacific monsoon region. The air quality in different parts of the island is strongly influenced by prevailing winds, especially in autumn
1522
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
Fig. 1. The geographical location of the sampling station.
and spring. During the autumn and spring months, interactions between the winter monsoon and the summer monsoon vary greatly and determine the local wind fields in Taiwan. The frontal zone is characterized by a strong temperature gradient and a shift in wind direction. After the frontal passage, the synoptic flow is easterly, with western Taiwan on the lee side of the CMR. In this circumstance, the atmospheric environment is sunny and is dominated by sea-land breeze in the coastal area of central Taiwan. Accumulations of local emissions are catalysts to the air pollution episodes. Previous studies have tried to indicate the relationships between synoptic weather pattern and air pollution in central Taiwan. For example, Lin et al. (2007b) examined the important role of local circulation in the formation of the secondary air pollution during the northeasterly monsoon. Kuo et al. (2008) founded the secondary air pollution depended strongly on the synoptic weather pattern especially for bringing easterly winds toward Taiwan. Tseng et al. (2009) also pointed out the secondary aerosols concentrations increased as the O3 concentrations increased, which typically occur during the sea-land breeze. Fig. 2(a)e(d) shows the meteorological parameters [i.e., ambient temperature, relative humidity (RH), wind speed (WS), wind direction (WD), and solar irradiation] and air pollutant concentrations (i.e., O3, PM10, and PM2.5) during the sampling period. On 9 and 10 September, the weather was heavily influenced by regional sea-land breeze with warm-strong sea wind and daily maximum radiation after midday. The daily maximum concentrations of O3, PM2.5, and PM10 were lower than the national ambient air quality standard (O3 < 80 ppb, PM2.5 < 65 mg m3, PM10 < 125 mg m3). Similar phenomena were observed between 23 and 26 September.
From 11 to 15 September and 27e29 September, central Taiwan was hit by typhoons Sinlaku and Jangmi. The diurnal variations of meteorological parameters and air pollutant concentrations disappeared. The weather was characterized by violent wind speed and low ambient temperature. The wind direction was determined by the location of the typhoon center. The bad air quality with higher PM10 concentration appeared in the front of the typhoon peripheral circumfluence (Fang et al., 2009). During 16 September through 23 September, the weather was influenced by the sea-land breeze with clear diurnal variations of meteorological parameters and air pollutant concentrations. The level of air pollutant was higher than the ambient air quality standard. The index of the daily maximum O3 concentration (O3, max) played an important role for understanding the formation of secondary aerosol (Na et al., 2004). Chang and Lee (2007) indicated that photochemical activities were low when O3, max was less than 60 ppb. In contrast, more secondary aerosols formed through photochemical reactions when O3, max exceeds 80 ppb. In this study, we excluded the influences of typhoons and differentiated the influence of photochemical activities on the secondary aerosol formation. Because O3, max of less than 60 ppb was almost observed during the typhoon influenced period, O3, max less than 80 ppb and greater than 80 ppb were defined as the lightly polluted period and the heavily polluted period respectively. 3.2. Solar irradiation and particulate matter Fig. 2(c) showed the time series of hourly solar irradiation during the sampling period. The average solar irradiation was 400 J m2
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
1523
Fig. 2. Hourly measurements of meteorological parameter and air pollutant concentrations during the sampling period. L: lightly polluted period; T: typhoon influenced period; H: heavily polluted period.
during the lightly polluted period and 330 J m2 during the heavily polluted period. The average concentration of PM10 was 65.7 mg m3 during the lightly polluted period and 108.3 mg m3 during the heavily polluted period. The proportion of PM2.5 in PM10 was 43% in the lightly polluted period and 61% in the heavily polluted period, which indicated that the increased range of concentration of fine particles was higher than that of coarse particles in the heavily polluted period. Most of the fine particles were connected with the secondary aerosols, especially the anthropogenic ones (Lun et al.,
2003; Tang et al., 2005). During the heavily polluted periods, the secondary aerosols were converted from the precursor gases by photochemical reactions in the troposphere. The formatted secondary aerosols can cause the solar irradiation decreases. In this study, the solar irradiation was measured by the ground base instrument. The secondary aerosols have depleted the solar irradiation before reaching to the ground. Results showed that the radiative forcing to the ground was negatively correlated to aerosol concentration, especially for the fine aerosol. Previous studies have
1524
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
shown that secondary aerosols, mainly emitted from anthropogenic pollution, can affect solar irradiation (Lee and Sequeira, 2002; Chang and Park, 2004; Latha and Badarinath, 2005). 3.3. Wind fields between heavily and lightly polluted periods Fig. 3 showed the daytime and nighttime wind fields between heavily and lightly polluted periods. When the dominant largescale meteorology was easterly over the sea to the east of Taiwan, the Taichung area was on the lee side of the CMR, and the prevalent easterly wind was shielded. At the same time, aerosol distribution was mainly controlled by local meteorological phenomena in the Taichung area. Among these processes, the sea-land breeze played an important role in the transport and derivation of aerosols. The sea breeze began to blow onshore progressively as the temperature difference between sea and land increased. The air pollutants, mainly emitted from Taichung harbor, industrial parks, and power plants, were transported from the coastal area to the inland area and reacted with urban pollutants to form secondary aerosols in the daytime during the lightly and heavily polluted periods (Fig. 3(a) and (c)). At night, the land surface temperature did not drop below sea temperature because of the heat-island effect, and the nocturnal winds were weaker than the daytime winds during the lightly and heavily polluted periods (Fig. 3(b) and (d)).
3.4. Hourly measurements of nitrate, sulfate, and ammonium The hourly variations of major soluble ions (Fig. 4) were very similar to those of PM10 (Fig. 2(d)), except during typhoons. Their concentrations were low on 9 and 10 September. On 11 September, when a typhoon moved into Taiwan, the hourly concentration of PM10 sharply increased. In contrast, the hourly concentrations of major soluble ions fell. The primary reason was the resuspension of the river sand during dry season (Fang et al., 2009). The concentrations of PM10 and the major soluble ions began to rise after the typhoon period. From midday of 23 September, central Taiwan was affected by the typhoon peripheral circumfluence. The concentrations of PM10 and major soluble ions decreased. When the typhoon arrived on 27 September, the phenomena of higher PM10 and lower major soluble ions were repeated. 2 þ The concentrations of PM10, NO 3 , SO4 , NH4 , and the total major ions during the heavily polluted period were 1.6, 1.9, 2.4, 2.7 and 2.3 times the concentrations during the lightly polluted period, respectively (Table 1). The weak intensity of sea-land transport and the high capacity of atmospheric oxidation contributed to the increased concentrations of these pollutants during the heavily polluted period. In many O3 chemistry studies, the total oxidant Ox (estimated by O3 þ NO2) is frequently used in data analysis because Ox is not affected by the rapid photodissociation of NO2 and the
Fig. 3. The wind field in Taiwan. (a) and (b) were the wind field in the daytime and nighttime respectively during the lightly polluted period. (c) and (d) were the wind field in the daytime and nighttime respectively during the heavily polluted period.
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
1525
Fig. 4. Hourly measurements of nitrate, sulfate and ammonium in PM10 during the sampling period.
titration of O3 with NO, being a better index of the real atmospheric oxidation capacity (Chou et al., 2006; Zhang et al., 2008). Table 1 also compares the weather situation and the atmospheric oxidation capacity between the heavily and lightly polluted periods. The lower average wind speed caused the accumulation of pollutants during the heavily polluted period. In addition, the total oxidant Ox was higher during the heavily polluted period, which contributed to the formation of secondary aerosol. 2 þ NO 3 , SO4 , and NH4 were the dominant ionic species according to the measurements of all soluble ions. The mass fraction of NO 3, þ SO2 4 and NH4 in PM10 aerosols all increased in the heavily polluted period compared with the lightly polluted period. The results show that the increased proportions of SO2 4 aerosols were higher than þ that of NO 3 and NH4 aerosols. NH4NO3 particles were likely to dissociate to gaseous HNO3 and NH3. Schaap et al. (2004) indicated that there is complete evaporation at temperatures exceeding 25 C and no significant evaporation is observed below 20 C. At temperatures between 20 and 25 C the retention is on average 50%, but with high variability. In this study, ambient temperatures were higher than 25 C during daytime, which caused mass fracþ tions of NO 3 and NH4 to slightly rose. 3.5. Average diurnal variation of PM10, nitrate, sulfate, and ammonium Fig. 5 shows the different average diurnal variation patterns of PM10 along with its components, gaseous pollutants, and meteorological parameters between the heavily and lightly polluted periods. Pronounced diurnal variations of PM10 concentrations were observed during the heavily polluted period (Fig. 5(a)). The highest concentration was usually occurred 1w2 h after midnight.
In contrast, diurnal variations of PM10 concentrations were no significant peaks during the lightly polluted period. The diurnal variations of the SO2 4 concentrations did not show significant peaks both during the heavily and lightly polluted periods (Fig. 5(b)). Because aerosol SO2 4 , unlike semi-volatile NH4NO3, does not evaporate from aerosol with increasing ambient temperature, the accumulations tend to dilute the diurnal variations of aerosol SO2 4 . Fig. 5(c) shows the diurnal variation of total oxidant Ox concentrations. The daily maximum total oxidant Ox concentrations were observed at 12:00 and 14:00 during the lightly and heavily polluted periods, respectively. Fig. 5(d) shows the diurnal variation of the SO2 concentration, which showed higher concentration in the morning and noon during the lightly and polluted periods, respectively. When the sea breeze developed, a substantial SO2 emitted from the upwind site of Taichung harbor, industrial parks, and power plants was brought to the downwind site of Shalu. The transport of these plumes strongly elevated the SO2 concentration during daytime. þ The NO 3 and NH4 took on different diurnal variation patterns during the heavily and lightly polluted periods (Fig. 5(e) and (f)). þ The diurnal cycles of NO 3 and NH4 demonstrated a single mode distribution during heavily polluted periods, with concentrations low during daytime and high at night. In contrast, the relatively þ unclear diurnal cycles of NO 3 and NH4 were observed during the lightly polluted periods, with concentrations low in the midday and high in the daily morning and evening rush hour. The lowest þ diurnal concentrations of NO 3 and NH4 were observed at noon both during the heavily and lightly polluted periods possibly because the evaporation of semi-volatile NH4NO3 was enhanced greatly under high temperature (Fig. 5(i)), and the development of the turbulence effect by sea breeze diluted the ambient pollutant concentrations.
Table 1 The concentrations and mass fractions of major soluble ions during the heavily and lightly polluted periods. Concentration (mg m3)
Atmospheric oxidation capacity
Weather situation
PM10 mg m3
3 NO 3 mg m
3 SO2 4 mg m
3 NHþ 4 mg m
Sum of three ions mg m3
O3 þ NO2 ppb
Temp C.
RH %
WS m s1
Heavily pollutant period (H)
108.3
14.2a (13.1)
22.7 (21.0)
8.9 (8.2)
45.8 (42.3)
62.1
29.3
77.2
1.6
Lightly pollutant period (L)
65.7
7.4 (11.3)
9.5 (14.5)
3.3 (5.0)
20.2 (30.7)
46.8
29.9
73.0
2.2
1.9
2.4
2.7
2.3
Ratio (H/L) a
1.6
the mass fraction of the ion in PM10, %.
1526
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
þ Fig. 5. Average diurnal variations of PM10, SO2 4 , O3, SO2, NO3 , NH4 , NO2, WS and PM2.5 between the heavily and lightly polluted periods from 9 to 30 September 2008.
þ The highest concentrations of NO 3 and NH4 were observed near midnight during the heavily polluted periods and in the rush hour during the lightly polluted periods. These differences depended not only on the evaporation of semi-volatile aerosols but also on the concentrations of precursor gases, the oxidation capacity in the atmosphere, and the transport of sea-land breeze. Previous study (Schaap et al., 2004) indicated that there is complete evaporation at temperatures exceeding 25 C and full retention at temperatures less than 20 C. At temperatures between 20 and 25 C the partial loss with high variability is observed. In addition, NH4NO3 is deliquescent and forms solution droplets at RH 62% (at 25 C) (Chang and Lee, 2002). Higher humidity increases the potential existence of external aerosols at night (Fig. 5(i)). Fig. 5(g) shows that the concentrations of the precursor gaseous NO2 at night were higher during the heavily polluted periods than during the lightly polluted periods. The total oxidant Ox concentration is an indicator to evaluating the oxidation capacity in the atmosphere. High concentrations of total oxidant Ox (Fig. 5(c)) led to a high potential for the oxidation of precursor gaseous NO2 to secondary aerosol NO 3 during the heavily polluted period. The predominant pollutants in the inland urban areas were characterized as vehicle emissions due to the large population and high density of vehicle exhaust. In contrast, the power plant and industrial areas could be an important source of VOC, SO2 and primary sulfates in the coastal area. The total oxidant (NO2 þ O3) and sulfate aerosols (primary and secondary sulfates) were transport from the coastal area into the urban area by the sea wind during the daytime. Comparing Fig. 5(b) and (c), the secondary sulfate aerosols were insignificantly converted from SO2. At the same time, a great amount of secondary nitrate aerosols have been converted from vehicle emissions (NOx) in the urban area. After sunset, lower ambient temperature is beneficial to form the secondary nitrate
aerosols. In addition, NH3 emitted from large population was reacted with the secondary nitrate in the urban area. When the land wind began to blow offshore, sulfate aerosols previously transþ ported from the coastal area and secondary aerosols (NO 3 and NH4 ) formed in the urban area were moved to the coastal area. Fig. 5(h) shows that the average diurnal wind speed was lower during nighttime than daytime. Consequently, the formatted secondary pollutants by photochemical reaction in the inland urban area could be accumulated and transported slowly to the coastal area, which would explain the high concentrations of NHþ 4 and NO3 was near 2 midnight and the diurnal variation of SO4 aerosol was small. 4. Conclusions Gaseous pollutants, particulate mass and water-soluble ions concentrations in PM10 were sampled and monitored between 9 September and 3 October 2008 in central Taiwan. Excluding the influences of typhoons, the pollution events were classified as heavily and lightly polluted periods according to the daily O3, max concentration S 80 ppb and <80 ppb, respectively. The concentrations of PM10 increased about 1.6 times during the heavily 2 þ polluted period. NO 3 , SO4 and NH4 were the dominant ions in PM10 and their concentrations increased by 1.9, 2.4 and 2.7 times, respectively, during the heavily polluted period compared with the lightly polluted period. The diurnal variations of pollutants transport and dispersion during the autumn months in this study area are dominated by the sea breeze dynamics formations. Breeze circulations and transitions are characterized by the enhanced sea breeze during the day and weak land breeze during the night. The O3 and SO2 concentrations increased as enhancing the sea breeze. The transportation of coastal industry emissions and urban traffic exhausts could explain the higher concentrations of SO2 and O3
G.-C. Fang et al. / Journal of Environmental Management 92 (2011) 1520e1527
during daytime and the rising concentrations of NO2 around midnight, respectively. During heavily polluted periods, particulate pollutants except for sulfate aerosols showed a clear diurnal variation with lower concentration around midday and higher concenþ tration around midnight. NO 3 and NH4 concentrations in PM10 are lower during the day, possibly due to the thermal volatilization on aerosols were more thermal NH4NO3. Because secondary SO2 4 stable and accumulated in the atmosphere, the SO2 4 diurnal variations was insignificant. The diurnal variation of PM10 showed the þ similar pattern to that of urban aerosols (NO 3 and NH4 ), suggesting the formatted secondary aerosols in the inland urban area were transported to the coastal area by the weak land breeze and deteriorated the air quality in the coastal area at night. Overall, the autumn pollution events in this study were characterized by the absence of synoptic-scale air mass advections, the development of breeze circulations and enhanced photochemistry.
References Chang, L.S., Park, S.U., 2004. Direct radiative forcing due to anthropogenic aerosols in East Asia during April 2001. Atmospheric Environment 38, 4467e4482. Chang, S.C., Lee, C.T., 2006. Ozone variations through vehicle emissions reductions based on air quality monitoring data in Taipei City, Taiwan, from 1994 to 2003. Atmospheric Environment 40, 3513e3526. Chang, S.C., Lee, C.T., 2007. Secondary aerosol formation through photochemical reactions estimated by using air quality monitoring data in Taipei City from 1994 to 2003. Atmospheric Environment 41, 4002e4017. Chang, S.C., Lee, C.T., 2008. Evaluation of the temporal variations of air quality in Taipei City, Taiwan, from 1994 to 2003. Journal of Environmental Management 86, 627e635. Chang, S.Y., Fang, G.C., Chou, C.C.K., Chen, W.N., 2006a. Source identifications of PM10 aerosols depending on hourly measurements of soluble components characterization among different events in Taipei Basin during spring season of 2004. Chemosphere 65, 792e801. Chang, S.Y., Fang, G.C., Chou, C.C.K., Chen, W.N., 2006b. Chemical compositions and radiative properties of dust and anthropogenic air masses study in Taipei Basin, Taiwan, during Spring of 2004. Atmospheric Environment 40, 7796e7809. Chang, S.Y., Lee, C.T., 2002. Applying GC-TCD to investigate the hygroscopic characteristics of mixed aerosols. Atmospheric Environment 36, 1521e1530. Chang, S.Y., Lee, C.T., Chou, C.C.K., Liu, S.C., Wen, T.X., 2007. The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite, Taiwan. Atmospheric Environment 41, 1936e1949. Chio, C.P., Cheng, M.T., Wang, C.F., 2004. Source apportionment to PM10 in different air quality conditions for Taichung urban and coastal areas, Taiwan. Atmospheric Environment 38, 6893e6905. Chou, C.C.K., Liu, S.C., Lin, C.Y., Shiu, C.J., Chang, K.H., 2006. The trend of surface ozone in Taipei, Taiwan, and its causes: implications for ozone control strategies. Atmospheric Environment 40, 3898e3908. Chow, J.C., Watson, J.G., Mauderly, J.L., Costa, D.L., Wyzga, R.E., Vedal, S., Hidy, G.M., Altshuler, S.L., Marrack, D., Heuss, J.M., Wolff, G.T., Pope, C.A., Dockery, D.W., 2006. Health effects of fine particulate air pollution: lines that connect. Journal of Air and Waste Management Association 56, 1368e1380. Donaldson, K., Stone, V., Born, P.J.A., Jimenez, L.A., Gilmour, P.S., Schins, R.P.F., Knaapen, A.D.M., Rahman, I., Faux, S.P., Brown, D.M., MacNee, W., 2003. Oxidative stress and calcium signaling in the adverse effects of environmental particles (PM10). Free Radical Biology & Medicine 34, 1369e1382. Fang, G.C., Lin, S.J., Chang, S.Y., Chou, C.C.K., 2009. Effect of typhoon on atmospheric particulates in Autumn in central Taiwan. Atmospheric Environment 43, 6039e6048. Hsieh, L.Y., Kuo, S.C., Chen, C.L., Tsai, Y.I., 2009. Size distributions of nano/micron dicarboxylic acids and inorganic ions in suburban pm episode and non-episodic aerosol. Atmospheric Environment 43, 4396e4406. IPCC, 2001. Aerosols, their Direct and Indirect Effects. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, pp. 289e348.
1527
Jacobson, M.Z., 2002. Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming. Journal of Geophysical Research 107 (D19), 4410. doi:10.1029/2001JD001376. Kothai, P., Saradhi, I.V., Prathibha, P., Hopke, P.K., Pandit, G.G., Puranik, V.D., 2008. Source apportionment of coarse and fine particulate matter at Navi Mumbai, India. Aerosol and Air Quality Research 8, 423e436. Kuo, C.Y., Chen, P.T., Lin, Y.C., Lin, C.Y., Chen, H.H., Shih, J.F., 2008. Factors affecting the concentrations of PM10 in central Taiwan. Chemosphere 70, 1273e1279. Laden, F., Neas, L.M., Dockery, D.W., Schwartz, J., 2000. Association of fine particulate matter from different sources with daily mortality in six U.S. cities. Environmental Health Perspectives 108, 941e947. Latha, K.M., Badarinath, K., 2005. Shortwave radiative forcing efficiency of urban aerosols e a case study using ground based measurements. Chemosphere 58, 217e220. Lee, Y.L., Sequeira, R., 2002. Water-soluble aerosol and visibility degradation in Hong Knog during autumn and early winter, 1998. Environmental Pollution 116, 225e233. Lin, C.C., Huang, K.L., Chen, S.J., Liu, S.C., Tsai, J.H., Lin, Y.C., Lin, W.Y., 2009. NHþ 4 , NO3 , and SO2 4 in roadside and rural size-resolved particles and transformation of NO2/SO2 to nanoparticle-bound NO3/SO42. Atmospheric Environment 43, 2731e2736. Lin, C.C., Chen, S.J., Huang, K.L., Lee, W.J., Lin, W.Y., Liao, C.J., Chaung, H.C., Chiu, C.H., 2007a. Water-soluble ions in nano/ultrafine/fine/coarse particles collected near a busy road and at a rural site. Environmental Pollution 145, 562e570. Lin, C.Y., Wang, Z., Chou, C.C.K., Chang, C.C., Liu, S.C., 2007b. A numerical study of an autumn high ozone episode over southwestern Taiwan. Atmospheric Environment 41, 3684e3701. Lin, J.J., 2002. Characterization of water-soluble ion species in urban ambient particles. Environment International 28, 55e61. Lohmann, U., Feichter, J., 2005. Global indirect aerosol effects: a review. Atmospheric Chemistry and Physics 5, 715e737. Lun, X., Zhang, X., Mu, Y., Nang, A., Jiang, G., 2003. Size fractionated speciation of sulfate and nitrate in airborne particulates in Beijing, China. Atmospheric Environment 37, 2581e2588. Mysliwiec, M.J., Kleeman, M.J., 2002. Source apportionment of secondary airborne particulate matter in a polluted atmosphere. Environmental Science and Technology 36, 5376e5384. Na, K., Sawant, A.A., Song, C., Cocker III, D.R., 2004. Primary and secondary carbonaceous species in the atmosphere of Western Riverside County, California. Atmospheric Environment 39, 2011e2020. Pope, C.A., Dockery, D.W., 2006. Health effects of fine particulate air pollution: lines that connect. Journal of Air and Waste Management Association 56, 709e742. Schaap, M., Spindler, G., Schulz, M., Acker, K., Maenhaut, W., Berner, A., Wieprecht, W., Streit, N., Muller, K., Bruggemann, E., Chi, X., Putaud, J.P., Hitzenberger, R., Puxbaum, H., Baltensperger, U., ten Brink, J., 2004. Artefacts in the sampling of nitrate studied in the “INTERCOMP” campaigns of EUROTRACAEROSOL. Atmospheric Environment 38, 6487e6496. Schlesinger, R.B., Cassee, F., 2003. Atmospheric secondary inorganic particulate matter: the toxicological perspective as a basis for health effects risk assessment. Inhalation Toxicology 15, 197e235. Tang, A., Zhuang, G., Wang, Y., 2005. The chemistry of precipitation and its relation to aerosol in Beijing. Atmospheric Environment 39, 3397e3406. Targino, A.C., Noone, K.J., 2006. Airborne in situ characterization of dry urban aerosol optical properties around complex topography. Atmospheric Research 79, 148e174. Tsai, Y.I., Cheng, M.T., 1999. Visibility and aerosol chemical compositions near the coastal area in central Taiwan. Science of the Total Environment 231, 37e51. Tsai, Y.I., Cheng, M.T., 2004. Characterization of chemical species in atmospheric PM10 aerosols in a Metropolitan Basin. Chemosphere 54, 1171e1181. Tsai, Y.I., Chen, C.L., 2006. Atmospheric aerosol composition and source apportionments to aerosol in southern Taiwan. Atmospheric Environment 40, 4751e4763. Tseng, K.H., Wang, J.L., Cheng, M.T., Tsuang, B.J., 2009. Assessing the relationship between air mass age and summer ozone episodes based on photochemical indices. Aerosol and Air Quality Research 9, 149e171. Wang, W.C., Chen, K.S., Chen, S.J., Lin, C.C., Tsai, J.H., Lai, C.H., Wang, S.K., 2008. Characteristics and receptor modeling of atmospheric PM2.5 at urban and rural sites in Pingtung, Taiwan. Aerosol and Air Quality Research 8, 112e129. Watson, J.G., 2002. Visibility: science and regulation. Journal of Air and Waste Management Association 52, 628e713. Zhang, Y.H., Su, H., Zhong, L.J., Cheng, Y.F., Zeng, L.M., Wang, X.S., Xiang, Y.R., Wang, J.L., Gao, D.F., Shao, M., Fan, S.J., Liu, S.C., 2008. Regional ozone pollution and observation-based approach for analyzing ozone-precursor relationship during the PRIDE-PRD2004 campaign. Atmospheric Environment 42, 6203e6218.