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outdoor relationships of organic carbon (OC) and elemental carbon (EC) in PM2.5 in roadside environment of Hong Kong
ARTICLE IN PRESS AE International – Asia Atmospheric Environment 38 (2004) 6327–6335 www.elsevier.com/locate/atmosenv
Indoor/outdoor relationships of organic carbon (OC) and elemental carbon (EC) in PM2.5 in roadside environment of Hong Kong K.F. Hoa,b, J.J. Caob, Roy M. Harrisona,, S.C. Leeb, K.K. Baub a
Division of Environmental Health and Risk Management, School of Geography, Earth & Environmental Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK b Department of Civil and Structural Engineering, Research Center of Urban Environmental Technology and Management, The Hong Kong Polytechnic University, Hun Hom, Kowloon, Hong Kong Received 13 February 2004; received in revised form 22 July 2004; accepted 4 August 2004
Abstract Five buildings located near roadsides (an office and a classroom with mechanical ventilation (MV) and three residences with natural ventilation (NV)) were selected with a view to characterising indoor and outdoor concentrations of organic (OC) and elemental carbon (EC). PM2.5 samples were analysed using a thermal optical reflectance (TOR) method for OC and EC concentrations. The average 24-h PM2.5 outdoor concentration was 78.4 mg m3, whilst the average outdoor OC and EC concentrations were 12.6 and 6.4 mg m3, respectively, accounting for 17% and 9%, respectively of the outdoor PM2.5 mass. The average 24-h PM2.5 indoor concentration was 55.4 mg m3 of which indoor OC and EC were 11.3 and 4.8 mg m3, respectively, accounted for 22% and 9%, respectively. The mean value of indoor to outdoor ratios (I/O ratios) of PM2.5 was 0.80, with a close correlation between indoor and outdoor PM2.5 concentrations, especially in the NV residences. The average I/O ratios of OC and EC were 1.02 and 0.80, respectively. The higher ratio for OC reflects indoor sources of OC, which do not appear to occur for EC. The major source of indoor EC, OC and PM2.5, however, appears to be penetration of outdoor air, with a much greater attenuation in the MV buildings studied. r 2004 Elsevier Ltd. All rights reserved. Keywords: PM2.5; Organic carbon; Elemental carbon; Indoor air; Roadside
1. Introduction Particulate matter (PM) is one of the major air pollutants in urban areas (APEG, 1999) and has many sources such as automobile exhaust, industrial combustion processes and secondary conversion from gaseous Corresponding author.
E-mail address: [email protected] (R.M. Harrison).
pollutants (Gartrell and Friedlander, 1975). In the past few decades, attention has been focussed largely upon the study of exposure to outdoor air pollutants. However, the United States National Research Council (NRC) reports that people spend more than 80% of their time indoors. Hence, they are exposed to pollutants generated within the indoor environment, such as those arising from smoking and other indoor combustion sources, as well as those from the outdoors, which may lead to increased exposure relative to that outdoors.
1352-2310/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.08.007
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Frequently, the concentrations of air pollutants are much higher indoors than outdoors (Lee et al., 2001, 2002a, b; Spengler, 1995; Wallace, 1996). Therefore, indoor exposures may be more important than those occurring outdoors. Moreover, various epidemiological studies have shown strong associations between concentrations of PM and adverse health outcomes including cardiorespiratory hospital admissions and mortality (e.g. Pope et al., 1995, 2002; Anderson et al., 2001). To date, epidemiology has been based upon outdoor measurements and hence the observed effects relate to exposures to PM originating outdoors. Little is known with certainty of the health effects of PM generated indoors. There have been a number of studies in which indoor air in homes has been characterized and compared with outdoor air (e.g. Kamens et al., 1991; Clayton et al., 1993; Miguel et al., 1995; Chao et al., 1998). The concentration of airborne PM inside a home is governed by the generation of PM within the home, the concentration of PM outside the home, the rate of air exchange and the depositional characteristics of the PM (Kamens et al., 1991; Thatcher and Layton, 1995). However, most indoor–outdoor research has focused on the comparison of PM mass concentrations without chemical differentiation. Carbonaceous species, including organic carbon (OC) and elemental carbon (EC), are major components of PM. OC has both a primary and a secondary origin and includes polycyclic aromatic hydrocarbons and other components with possible mutagenic and carcinogenic effects. EC is graphitic carbon formed from incompletely combusted carbonbased fuels (Seinfeld and Pandis, 1998). Soot carbon which is predominantly EC and a major component of PM2.5 has been linked to significantly increased risk of death from lung cancer and other severe respiratory ailments. (Frazer, 2002.) To date, only limited studies of indoor/outdoor relationship of carbonaceous aerosols have been conducted (Li and Lin, 2003; Geller et al., 2002; Funasaka et al., 2000). Indoor/outdoor air studies in the USA have determined that smoking and cooking are the predominant activities associated with elevated concentrations of fine PM (Wallace, 1996). Indoor PM concentrations are influenced by cooking style (Kamens et al., 1991; Chao et al., 1998), especially frying. Moon et al. (1997) reported that indoor/outdoor ratios (I/O) were slightly higher in homes with gas cookers than in those without this source. The ratio between indoor and outdoor concentrations of PM and carbonaceous species gives an indication as to whether PM found indoors are the result of indoor generation or derive from the outdoor environment. In the absence of indoor sources, I/O ratios will be less than, or equal to one. Hong Kong is one of the most densely inhabited metropolitan areas in the world. The majority of the around 7 million population is crowded into only 15%
of the total area (about 1068 km2). There were 517,000 registered vehicles crowded into 1904 km of roads in 2000 (Census and Statistics Department of Hong Kong, 2001). Diesel trucks with high emissions of carbonaceous PM accounted for 30% of the total amount of motor vehicles. Motor vehicles are considered as one of the major contributors to air pollution in Hong Kong. Consequently, it is a good location in which to observe the impact of outdoor carbonaceous PM emissions on the indoor pollutant level in urban buildings. A preliminary monitoring programme for indoor and outdoor concentrations of PM2.5, OC and EC was conducted from 25th September, 2002 to 8th March, 2003 at five locations (two offices with mechanical ventilation (MV) and three residences with natural ventilation (NV)) in Hong Kong. The objectives of this study are (1) to provide quantitative information on the concentrations of PM2.5, OC and EC in the five selected indoor and outdoor roadside microenvironments, (2) to investigate the extent to which traffic pollution from outdoor sources infiltrates into the indoor environment, (3) to compare the indoor and outdoor concentrations and the I/O ratios of PM2.5 OC and EC, under NV and MV.
2. Methodology 2.1. Sampling sites Five urban locations (an office, a classroom and three residences) were selected for the PM2.5 monitoring programme near the roadside in Hong Kong. The classroom and office were MV while the residences were NV during the sampling periods. All the locations were selected so as to have no significant local pollution sources other than motor vehicles. The sampling locations were located within 1–10 m of a main road. All the indoor and outdoor samples were collected simultaneously. The characteristics of each sampling site are given in Table 1. 2.2. Sample collection Indoor and outdoor PM2.5 samples were collected simultaneously from September 2002 to February 2003 by using mini-volume samplers (Airmetrics, USA) operating with a flow rate of 5 l min1 for 24 h. The samplers were checked and calibrated in The Hong Kong Polytechnic University. A Partisol model 2000 sampler (Rupprecht & Patashnick, USA) with a 2.5 mm inlet was collocated with the mini-volume samplers. The difference between the mini-volume samplers and Partisol 2000 was less than 5% for the PM2.5 mass concentrations. All samples were collected on 47 mm Whatman quartz microfibre filters (QM/A). The filters
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Table 1 Characteristics of indoor/outdoor sampling locations in Hong Kong Locations
Area type
Abbreviation
Distance from the main traffic road (m)
Sampling height above ground level (m)
No. of occupants
Mechanical ventilation
No. of samples
PolyU, U-core
Urban outdoor, 17,000 vehicles/day Urban indoor, classroom
PUU-O
8
6
—
—
5
PUU-I
—
—
40–60
Yes
5
Urban outdoor, commercial area Urban indoor, office
PUA-O
10
6
—
—
5
PUA-I
—
—
80
Yes
5
PUS-O
3
6
—
—
5
PUS-I
—
—
2
No
5
Urban outdoor, residential area Urban indoor, apartment
TM-O
1
2
—
—
4
TM-I
—
—
4
No
4
Urban outdoor, mixed industrial and residential area Urban indoor, apartment
SPK-O
3
12
—
—
4
SPK-I
—
—
4
No
4
PolyU, A-core
PolyU Studenthostel
Tuen Mun
Sun Po Kong
Urban outdoor, residential area Urban indoor, hostel
were pre-heated before sampling at 900 1C for 3 h. After collection, loaded filters were stored in a refrigerator at about 4 1C before chemical analysis to prevent the evaporation of volatile components. Before and after the field sampling, quartz fibre filters were placed for 24-h in a room having a temperature 25 1C and relative humidity 40%. The total particulate mass was determined by weighing on an electronic microbalance with a 1 mg sensitivity (Sartorius, MC5, Germany). Each of the measured residences had an indoor PM2.5 sampler in the living room/bedroom, and an outdoor one located in the balcony/platform. The indoor and outdoor sampling heights were in the range of 1–1.5 m above ground in order to simulate the breathing zone and to avoid potential interferences from excessive resuspension of PM. A total of 23 paired filters were collected for the carbonaceous aerosol analysis, and 21 paired analyzed data were used for data analysis. 2.3. Carbonaceous aerosol analysis All the loaded filters were analyzed for OC and EC using a DRI Model 2001 Thermal/Optical Carbon Analyzer. The IMPROVE thermal/optical reflectance
(TOR) protocol (Chow and Watson, 2002) was used for the carbon analysis. The protocol heats a 0.526 cm2 punch aliquot of a sample quartz filter stepwise at temperatures of 120 1C (OC1), 250 1C (OC2), 450 1C (OC3), and 550 1C (OC4) in a non-oxidizing helium (He) atmosphere, and 550 1C (EC1), 700 1C (EC2), and 800 1C (EC3) in an oxidizing atmosphere of 2% oxygen in a balance of helium. The carbon that evolves at each temperature is oxidized to carbon dioxide (CO2), then reduced to methane (CH4) for quantification with a flame ionization detector. As the temperature increases in the inert helium, some of the OC pyrolyzes to black carbon, resulting in darkening of the filter deposit. This darkening is monitored by the reflectance of 633 nm light from a He–Ne laser. When oxygen is added, the original and pyrolyzed black carbon combusts and the reflectance increases. The amount of carbon measured after oxygen is added until the reflectance achieves its original value is reported as optically detected pyrolized carbon (OPC). The eight fractions OC1, OC2, OC3, OC4, EC1, EC2, EC3, and OPC are reported separately in the data sheet. The IMPROVE protocol defines OC as OC1+OC2+OC3+OC4+OPC and EC as EC1+EC2+EC3OPC. The analyzer was calibrated with
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known quantities of CH4 every day. Replicate analyses were performed at the rate of one per group of 10 samples. The detection limits for EC and OC were below 1.0 mg m3 (about 0.2 mg m3 for EC and 0.5 mg m3 for OC). The repeatability determined from replicate analyses was better than 5% for total carbon (TC), and 10% for OC and EC (Cao et al., 2003).
3. Results and discussion 3.1. Indoor and outdoor PM2.5 mass concentrations The indoor and outdoor PM2.5 concentrations measured in the urban areas of Hong Kong are summarized in Table 2. Individual indoor PM2.5 concentrations ranged from 15.3 to 108 mg m3, while the outdoor PM2.5 concentrations ranged from 27.8 to 197 mg m3. The average indoor and outdoor concentrations were found to be 55.4 and 78.4 mg m3 for PM2.5, respectively. High indoor and outdoor concentrations were observed at the TM site. The high traffic flow, and especially the
high flow of heavy-duty vehicles, was the main reason for the high concentrations in TM–O (however, no traffic data was available in this station). Also TM–O was the closer outdoor monitoring location to the road (1 m) than the others (3–10 m). Other than the penetration of outdoor pollutants, smoking and cooking activity in TM–I are likely to be the major sources for the PM2.5. Smoking can add 20 mg m3 (24-h mean) of fine PM per smoker to a household (Spengler et al., 1981). Chao et al. (2002) found that the average PM2.5 concentration of smoking homes was 18% higher that the average PM2.5 concentration of non-smoking homes. There was no obvious indoor source for PM2.5 in the offices. The results showed that the MV offices had lower PM2.5 concentrations than the NV residences although the outdoor PM2.5 concentrations were high. Comparative data for indoor and outdoor PM2.5 in different urban areas are presented in Table 3. It is clear that indoor and outdoor PM2.5 concentrations in Hong Kong are higher than those reported in other urban areas (Monn et al., 1997; Hak et al., 1997; Geller et al., 2002; Morawska et al., 2003; Li and Lin, 2003; Liu et al.,
Table 2 The average concentrations of PM2.5 in different indoor and outdoor roadside environments of Hong Kong Location
Average PM2.5 concentrations (mg m3)
PM2.5 concentrations ranges (mg m3)
Average I/O ratio
I/O ratio ranges
PUU-O PUU-I PUA-O PUA-I PUS-O PUS-I TM-O TM-I SPK-O SPK-I
89.5761.4 39.6725.8 91.4732.7 45.2712.4 51.5727.2 46.5731.0 108.372.0 97.976.9 76.7741.5 77.3718.6
42.0–197.2 15.3–83.3 59.7–109.7 30.3–58.3 27.8–104.2 27.0–108.3 106.9–109.7 93.1–102.8 37.5–125.0 59.7–98.6
0.570.2
0.2–0.7
0.570.1
0.4–0.7
0.970.2
0.6–1.1
0.970.1
0.8–0.9
1.270.4
0.8–1.6
Table 3 Intercomparison of indoor and outdoor PM2.5 mass concentrations in different urban areas Locations/sampling environment
PM2.5 concentrations (mg m3) Indoor
Hong Kong/urban area Brisbane, Australia/suburb Beijing, China/urban area Zurich, Switzerland/urban area Chongju, Korea/urban area Southern California, USA/desert area Taipei, Taiwan/urban area This study, Hong Kong/urban area, near roadside
50.4 15.5 28.1 (office) 26.0 25.3 15.5 Winter: 38.7, summer: 36.6 55.4
References Outdoor
21.0 26.3 15.0 Winter: 38.3, summer: 36.3 78.4
Chao and Wong (2002) Morawska et al. (2003) Liu et al. (2004) Monn et al. (1997) Hak et al. (1997) Geller et al. (2002) Li and Lin (2003)
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2004) but comparable to those observed previously at different sites in Hong Kong (Chao and Wong, 2002). The high outdoor concentrations in this study were due to all of the sampling sites being located in the urban area and near to heavily trafficked roads (1–10 m). Moreover, the northeast monsoon advects pollutants by long-range transport to Hong Kong from other Asian countries in winter (Qin et al., 1997; Fang et al., 1999). Over 50% of PM2.5 samples were observed to exceed the USEPA 24 h standard for PM2.5 concentrations (65 mg m3) in the outdoor locations. Chao et al. (1998) expressed the view that the high indoor PM concentrations in Hong Kong were due to the Chinese cooking styles and the high emission of oily fumes in the kitchen. It was found that I/O ratios of PM2.5 in this study ranged from 0.2 to 1.6. The MV office and classroom had I/O ratios for PM2.5 smaller than 0.7 which is comparable with the value (0.4–0.6) suggested to occur in the absence of indoor sources (Wallace, 1996). This was consistent with the stated view that no
Correlations of indoor PM2.5 and outdoor PM2.5
Indoor PM2.5 (µg m-3)
120
MV
100
NV
y = 0.80x + 9.92 R2 = 0.83
80 60
y = 0.38x + 8.1 R2 = 0.81
40 20 0 0
50
100
150
200
250
Outdoor PM2.5 (µg m-3)
Fig. 1. Scatterplot of outdoor PM2.5 vs. indoor PM2.5.
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potential source was present. For the NV residences, the I/O ratios ranged from 0.6 to 1.6. Monn et al. (1997) reported that I/O ratios of PM10 were within the range 0.7–1.2 except for the households of habitual smokers (all NV homes). Monn et al. (1997) also suggested that I/O ratios increase with human activities such as cleaning or daily working. The I/O ratios in this study were comparable to those found in Taipei, Taiwan (Li and Lin, 2003) and Osaka, Japan (Funasaka et al., 2000).
3.2. Indoor and outdoor correlation of PM2.5 As in previously published studies on the relationship between indoor and outdoor PM (Colome et al., 1992; Clayton et al., 1993), the value of the coefficient of determination (R2) between the indoor and outdoor data has been used as an indicator of the degree to which PM2.5 measured indoors can be attributed to infiltration from outdoors. It was found that the indoor PM2.5 levels were moderately correlated with the corresponding outdoor concentrations with an R2 of 0.42 (po0:01). However, if the data were classified into two groups, MV and NV, then good correlations were found in each group (Fig. 1). The correlations of MV and NV groups are R2=0.81 (po0:01) and R2=0.83 (po0:001), respectively. The strong indoor-to-outdoor PM2.5 association (especially in NV residences) suggested that these fine particulates were mainly from the outdoor environment but with different penetration efficiencies in the two ventilation groups. Chao and Wong, 2002 suggested that good correlations were found in indoor environments where frequent exchange of air occurs between the indoor and the outdoor environment. In this study, all the sampling sites appear to have had good infiltration and frequent exchange of air.
Table 4 The average concentrations of OC and EC as well as OC/EC and I/O ratios in different indoor and outdoor roadside environments of Hong Kong Locations
OC conc. (mg m1)
OC conc. range (mg m1)
EC conc. (mg m1)
EC conc. range (mg m1)
OC/EC
I/O ratios EC
I/O ratios OC
PUU-O PUU-I PUA-O PUA-I PUS-O PUS-I TM-O TM-I SPK-O SPK-I Average indoor Average outdoor
10.573.3 6.271.4 16.476.0 10.372.5 8.574.3 9.573.4 19.474.3 21.273.1 14.173.8 16.773.4 11.375.5 12.675.4
6.5–14.9 4.2–8.2 10.7–22.9 6.8–12.6 2.2–15.2 6.1–14.7 26.3–34.9 19.0–23.4 10.6–19.4 13.7–21.0
5.970.8 2.870.5 8.272.3 3.771.4 4.472.8 4.073.1 11.271.8 11.176.3 6.071.6 6.272.4 4.873.4 6.472.8
4.6–6.6 2.3–3.6 6.2–10.2 2.4–5.7 1.1–9.2 1.3–9.1 10.0–12.4 6.7–15.5 3.9–7.4 3.9–8.6
1.870.4 2.370.6 2.070.2 2.970.8 2.170.4 3.171.5 1.770.1 2.271.0 2.470.4 2.870.6 2.771.0 2.070.4
0.570.1
0.670.2
0.570.1
0.770.2
0.970.3
1.571.0
1.070.4
1.170.1
1.170.4
1.270.2
0.870.3
1.070.7
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Table 5 Statistical summary of the percentage of OC, EC, OM and TCA in PM2.5 Locations
% OC
% EC
% OM
% TCA
MV indoor environments NV indoor environments MV outdoor environments NV outdoor environments
21.076.0 22.676.6 16.075.0 18.576.3
8.573.0 8.873.9 8.672.2 9.174.1
33.679.5 36.2710.6 25.777.9 29.5710.8
42.1711.7 45.0713.3 34.379.8 38.6714.5
3.3. OC and EC concentrations in indoor and outdoor environments outdoor OC (µg m-3)
y = 1.76x + 1.23 2 R = 0.82
20 15 10 5 0 0
4
2
6 8 10 outdoor EC (µg m-3)
12
14
Fig. 2. Correlation of outdoor OC and EC.
Correlations of indoor OC and EC concentrations 30 indoor OC (µg m-3)
The average concentrations of OC and EC in PM2.5 as well as OC/EC and I/O ratios of OC and EC in indoor and outdoor environments are shown in Table 4 (the average I/O and OC/EC ratios were calculated by averaging the I/O or OC/EC values of all corresponding samples). The average indoor TC concentration was 16.1 mg m3, and the average outdoor TC was 19.2 mg m3. The overall average indoor and outdoor EC concentrations were found to be 4.8 and 6.4 mg m3, respectively. The indoor EC concentrations ranged from 1.3 to 15.6 mg m3 while the outdoor EC concentrations ranged from 1.1 to 12.4 mg m3. The overall average indoor and outdoor OC concentrations were found to be 11.3 and 12.6 mg m3, respectively. The indoor OC concentrations ranged from 4.2 to 23.4 mg m3 while the outdoor OC concentrations ranged from 2.2 to 22.9 mg m3. The highest average indoor and outdoor EC concentrations were observed in TM–I and TM–O (11.2 and 11.1 mg m3), respectively, which is consistent with the PM2.5 mass concentrations, and the high flow of heavy-duty vehicles (and short distance between the sampling site and the road) at this site. Table 5 shows the carbonaceous material as a percentage of PM2.5 mass. Clearly, OC is enriched in indoor, as compared to outdoor air. In order to convert the measured mass of OC to the total organic matter (OM) mass, the OC mass has to be multiplied by a factor that is an estimate of the average molecular weight per carbon weight for the organic aerosol (Kleefeld et al., 2002). According to Turpin and Lim (2001), the amount of urban OM may be estimated by multiplying the amount of OC by 1.6. Thus the total carbonaceous aerosol (TCA) mass was calculated from the sum of OM and EC. The average indoor OM and TCA concentrations were 18.1 and 22.9 mg m3, respectively, which accounted for 35.1% (OM) and 43.8% (TCA) of PM2.5 mass concentrations. The average outdoor OM and TCA concentrations were 20.1 and 26.5 mg m3, respectively, which accounted for 27.9% (OM) and 36.8% (TCA) of PM2.5 mass concentrations. In other words, the carbonaceous fraction accounted for more than onethird of the PM2.5 in both indoor and outdoor environments.
Correlations of outdoor OC and EC concentrations 25
y = 1.36x + 4.83 2 R = 0.71
25 20 15 10 5 0 0
2
4
6
8
10
12
14
16
18
indoor EC (µg m-3)
Fig. 3. Correlation of indoor OC and EC.
The OC to EC ratio has been used to study the emission and transformation characteristics of carbonaceous aerosols. OC/EC ratios exceeding 2.0 (Chow et al., 1996) or 1.1 (Castro et al., 1999) have been used to indicate the presence of secondary organic aerosols. The OC/EC ratios in PM2.5 are shown in Table 4, and in individual samples, varied between 1.41 and 2.70 (average 2.00) for outdoor environments; and the average OC/EC ratio was 2.7 for indoor environments. On average, all outdoor monitoring locations have OC/ EC ratios less than 2 except SPK where the traffic flow of heavy-duty vehicles was less than at the other locations. Also there may be industrial source influences at this outdoor sampling location. It seems likely, therefore, that there is a significant secondary OC contribution in the outdoor samples. An indoor
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enhancement of OC/EC ratios relative to outdoors is likely to be due to indoor sources of organic compounds. Graphs of OC versus EC (Figs. 2 and 3) show a much larger intercept for the indoor samples, indicative of an indoor source.
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OC, on the other hand appears to have indoor sources contributing of the order of 3 mg m3 in the NV buildings and 2 mg m3 in the MV ones.
4. Conclusion 3.4. Indoor and outdoor relationships of OC and EC The relationships between indoor and outdoor concentrations (separately for MV and NV conditions) of OC and EC are shown in Figs. 4 and 5, respectively. For the MV offices, fair correlations of OC (R2=0.66, po0:05) and EC (R2=0.42, po0:1) concentrations in indoor air to those in outdoor air were observed. However, when limited to NV residences, OC in indoor air was more highly correlated to that in outdoor air, R2=0.71 (po0:01). For fine EC, there was a good correlation between indoor and outdoor air of the NV residences, R2=0.76 (po0:001). These results suggest that indoor fine OC and EC are derived at least in part from outdoor air (especially the EC). This is consistent with results reported by Jones et al. (2000), who found that EC originates outdoors, mostly from vehicular emissions. The small intercepts in Fig. 5 suggest that virtually all indoor EC originates from outdoors, with very efficient penetration in the case of NV buildings. Correlations of indoor OC and outdoor OC Indoor OC (µg m-3)
25 20
MV
NV
y = 0.86x + 3.38 2 R = 0.71
15 10 y = 0.43x + 2.31 2 R = 0.66
5 0 0
5
10 15 Outdoor OC (µg m-3)
20
25
Acknowledgements
Fig. 4. Correlations of indoor OC and outdoor OC.
This project was supported by the Research Grants Council of Hong Kong (PolyU5038/01E, PolyU5145/ 03E).
Indoor EC (µg m-3)
Correlations of indoor EC and outdoor EC 18 16 14 12 10 8 6 4 2 0
MV
NV
y = 1.07x - 0.55 R2 = 0.76
References
y = 0.36x + 0.72 2 R = 0.42
0
2
4
6
8
This study has quantified the PM2.5 mass and concentrations of OC and EC in both indoor and outdoor air in five near-roadside locations in Hong Kong during the fall and winter from September 2002 to February 2003. The indoor-to-outdoor PM2.5 mass concentration ratios (I/O) ranged from 0.2 to 1.6. However, lower I/O ratios were observed for the MV offices, with higher ratios for NV residences. Good indoor–outdoor correlations were found for the MV and NV groups analysed separately, which suggested that the fine PM derived mainly from the outdoor environment, but with different penetration efficiencies in the two ventilation groups. Indoor PM2.5 consisted of 35% OM and 9% EC whilst outdoor PM2.5 comprised 28% OM and 9% EC. The average I/O ratios of OC and EC were 1.02 and 0.80, respectively. Again, higher I/O ratios of OC and EC were observed in NV residences than in the MV office and classroom due to higher infiltration rates in NV buildings. The average OC/EC ratio in PM2.5 was 2.0 for outdoor environments and 2.7 for indoor environments. Regression of indoor versus outdoor concentrations of OC and EC revealed an indoor source of OC, not present for EC, and presumably due to such activities as cooking, smoking and cleaning. The magnitude of the indoor source of OC, 2–3 mg m3, is generally less than the penetration of OC from outdoors. Much greater attenuation of indoor concentrations relative to outdoors was found for all analytes in the MV buildings when compared to the NV ones.
10
12
Outdoor EC (µg m-3)
Fig. 5. Correlations of indoor EC and outdoor EC.
14
Anderson, H.R., Bremner, S.A., Atkinson, R.W., Harrison, R.M., Walters, S., 2001. Particulate matter and daily mortality and hospital admissions in the West Midlands conurbation of the United Kingdom: associations with fine and coarse particles, black smoke and sulphate. Occupational Environmental Medicine 58, 504–510. APEG, 1999. Source Apportionment of Airborne Particulate Matter in the United Kingdom, R.M. Harrison et al. The
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First Report of the Airborne Particles Expert Group, Department of Environment, Transport and the Regions, London. Cao, J.J., Lee, S.C., Ho, K.F., Zhang, X.Y., Zou, S.C., Fung, Kochy, Chow, C., Watson, John, G., 2003. Characteristics of carbonaceous aerosol in Peral River Delta Region, China during 2001 winter period. Atmospheric Environment 37, 1451–1460. Castro, L.M., Pio, C.A., Harrison, R.M., Smith, D.J.T., 1999. Carbonaceous aerosol in urban and rural European atmospheres: estimation of secondary organic carbon concentrations. Atmospheric Environment 33, 2771–2781. Census and Statistics Department of Hong Kong (2001). Hong Kong Annual Digest of Statistics. Chao, C.Y., Tung, T.C.W., Burnett, J., 1998. Influence of different indoor activities on the indoor particulate levels in residential buildings. Indoor Built Environment 7, 110–121. Chao, C.Y., Wong, K., 2002. Residential indoor PM10 and PM2.5 in Hong Kong and the elemental composition. Atmospheric Environment 36, 265–277. Chow, J.C., Watson, J.G., Lu, Z., Lowenthal, D.H., Frazier, C.A., Solomon, P.A., Thuilier, R.H., Magliano, K., 1996. Descriptive analysis of PM2.5 and PM10 at regionally representative locations during SJVAQS/AUSPEX. Atmospheric Environment 30, 2079–2112. Chow, J.C., Watson, J.G., 2002. PM2.5 carbonate concentrations at regionally representative interagency monitoring of protected visual environment sites. Journal of Geophysical Research 107 (D21), ICC6-1–9ICC6-9. Clayton, C.A., Perritt, R.L., Pellizzari, E.D., Thomas, K.W., Whitmore, R.W., Wallace, L.A., Ozkaynak, H., Spengler, J.D., 1993. Particle total exposure assessment methodology (PTEAM) study: distributions of aerosol and elemental concentrations in personal, indoor and outdoor air samples in a Southern California community. Journal of Exposure Analysis and Environmental Epidemiology 3, 227–250. Colome, S., Kado, N., Jaques, P., Kleinman, M., 1992. Indoor–outdoor air pollution relations: particulate matter less than 10 mm in aerodynamic diameter (PM10) in homes of asthmatics. Atmospheric Environment 26A, 2173–2178. Fang, M., Zheng, M., Wang, F., Chim, K.S., Kot, S.C., 1999. The long-range transport of aerosols from northern China to Hong Kong—a multi-technique study. Atmospheric Environment 33, 1803–1817. Frazer, L., 2002. Seeing through soot. Environmental Health Perspectives 10, A470–A473. Funasaka, K., Miyazaki, T., Tsuruho, K., Tamura, K., Mizuno, T., Kuroda, K., 2000. Relationship between indoor and outdoor carbonaceous particulates in roadside households. Environmental Pollution 110, 127–134. Gartrell, G., Friedlander, S.K., 1975. Relating particulate pollution to source—the 1972 California aerosol characterization study. Atmospheric Environment 9, 279–289. Geller, M.D., Chang, M., Sioutas, C., Ostro, B.D., Lipsett, M.J., 2002. Indoor/outdoor relationship and chemical composition of fine and coarse particles in the southern
California deserts. Atmospheric Environment 36, 1099–1110. Hak, S.L., Kang, B.W., Cheong, J.P., Lee, S.W., 1997. Relationships between indoor and outdoor air quality during the summer season in Korea. Atmospheric Environment 31, 1689–1693. Jones, N.C., Thornton, C.A., Mark, D., Harrison, R.M., 2000. Indoor/outdoor relationships of particulate matter in domestic homes with roadside, urban and rural locations. Atmospheric Environment 34, 2603–2612. Kamens, R., Lee, C.T., Weiner, R., Leith, D., 1991. A study to characterize indoor particles in three non-smoking homes. Atmospheric Environment 25, 939–948. Kleefeld, S., Hoffer, A., Kriva´csy, Z., Jennings, S.G., 2002. Importance of organic and black carbon in atmospheric aerosols at Mace Head, on the West Coast of Ireland (531190 N, 91540 W). Atmospheric Environment 36, 4479–4490. Lee, S.C., Li, W.M., Chan, L.Y., 2001. Indoor air quality at restaurants with different styles of cooking in metropolitan Hong Kong. The Science of the Total Environment 279, 181–193. Lee, S.C., Guo, H., Li, W.M., Chan, L.Y., 2002a. Intercomparison of air pollutant concentrations in different indoor environment in Hong Kong. Atmospheric Environment 36, 1929–1940. Lee, S.C., Li, W.M., Ao, C.H., 2002b. Investigation of indoor air quality at residential homes in Hong Kong––case study. Atmospheric Environment 36, 225–237. Li, C.-S., Lin, C.-H., 2003. Carbon profile of residential indoor PM1 and PM2.5 in the subtropical region. Atmospheric Environment 37, 881–888. Liu, Y., Chen, R., Shen, X., Mao, X., 2004. Wintertime indoor air levels of PM10, PM2.5 and PM1 at public places and their contributions to TSP. Environment International 30, 189–197. Miguel, A.H., Neto, F.R., De, A., Cardoso, J.N., Vasconcellos, P., De, C., Pereira, A.S., Marquez, K.S.G., 1995. Characterization of indoor air quality in the cities of Sao Paulo and Rio de Janeiro, Brazil. Environmental Science and Technology 29, 338–345. Monn, Ch., Fuchs, A., Hogger, D., Junker, M., Kogelschatz, D., Roth, N., Wanner, H.U., 1997. Particulate matter less than 10 mm (PM10) and fine particles less than 2.5 mm (PM2.5): relationships between indoor, outdoor and personal concentrations. The Science of the Total Environment 208, 15–21. Morawska, L., He, C., Hitchins, J., Mengersen, K., Gilbert, D., 2003. Characteristics of particle number and mass concentrations in residential houses in Brisbane, Australia. Atmospheric Environment 37, 4195–4203. Pope, C.A., Thun, M.J., Namboodiri, M.M., Dockery, D.W., Evans, J.S., Speizer, F.E., Heath, C.W., 1995. Particulate air pollution as a predictor of mortality in a prospective study of US adults. American Journal of Respiratory and Critical Care Medicine 151, 669–674. Qin, Y., Chan, C.K., Chan, L.Y., 1997. Characteristics of chemical compositions of atmospheric aerosols in Hong Kong: spatial and seasonal distributions. The Science of the Total Environment 206, 25–37.
ARTICLE IN PRESS K.F. Ho et al. / Atmospheric Environment 38 (2004) 6327–6335 Spengler, J.D., Dockery, D.W., Turner, W.A., Wolfson, J.M., Ferris Jr., B.G., 1981. Long-term measurements of respirable sulfates and particles inside and outside homes. Atmospheric Environment 15, 23–30. Spengler, J.D., 1995. Indoor air quality––innovation and technology. In: Morawska, L., Bofinger, N.D., Maroni, M. (Eds.), Indoor Air: An Integrated Approach, 1st ed. Elsevier Science Ltd, Oxford, pp. 1–33.
6335
Thatcher, T.L., Layton, D.W., 1995. Deposition, re-suspension and penetration of particles within a residence. Atmospheric Environment 29, 1487–1497. Turpin, B.J., Lim, H.J., 2001. Species contributions to PM2.5 mass concentrations: revising common assumptions for estimating organic mass. Aerosol Science and Technology 35, 602–610. Wallace, L., 1996. Indoor particles: a review. Journal of the Air and Waste Management Association 46, 98–126.
Indoor/outdoor relationships of organic carbon (OC) and elemental carbon (EC) in PM2.5 in roadside environment of Hong Kong K.F. Hoa,b, J.J. Caob, Roy M. Harrisona,, S.C. Leeb, K.K. Baub a
Division of Environmental Health and Risk Management, School of Geography, Earth & Environmental Sciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK b Department of Civil and Structural Engineering, Research Center of Urban Environmental Technology and Management, The Hong Kong Polytechnic University, Hun Hom, Kowloon, Hong Kong Received 13 February 2004; received in revised form 22 July 2004; accepted 4 August 2004
Abstract Five buildings located near roadsides (an office and a classroom with mechanical ventilation (MV) and three residences with natural ventilation (NV)) were selected with a view to characterising indoor and outdoor concentrations of organic (OC) and elemental carbon (EC). PM2.5 samples were analysed using a thermal optical reflectance (TOR) method for OC and EC concentrations. The average 24-h PM2.5 outdoor concentration was 78.4 mg m3, whilst the average outdoor OC and EC concentrations were 12.6 and 6.4 mg m3, respectively, accounting for 17% and 9%, respectively of the outdoor PM2.5 mass. The average 24-h PM2.5 indoor concentration was 55.4 mg m3 of which indoor OC and EC were 11.3 and 4.8 mg m3, respectively, accounted for 22% and 9%, respectively. The mean value of indoor to outdoor ratios (I/O ratios) of PM2.5 was 0.80, with a close correlation between indoor and outdoor PM2.5 concentrations, especially in the NV residences. The average I/O ratios of OC and EC were 1.02 and 0.80, respectively. The higher ratio for OC reflects indoor sources of OC, which do not appear to occur for EC. The major source of indoor EC, OC and PM2.5, however, appears to be penetration of outdoor air, with a much greater attenuation in the MV buildings studied. r 2004 Elsevier Ltd. All rights reserved. Keywords: PM2.5; Organic carbon; Elemental carbon; Indoor air; Roadside
1. Introduction Particulate matter (PM) is one of the major air pollutants in urban areas (APEG, 1999) and has many sources such as automobile exhaust, industrial combustion processes and secondary conversion from gaseous Corresponding author.
E-mail address: [email protected] (R.M. Harrison).
pollutants (Gartrell and Friedlander, 1975). In the past few decades, attention has been focussed largely upon the study of exposure to outdoor air pollutants. However, the United States National Research Council (NRC) reports that people spend more than 80% of their time indoors. Hence, they are exposed to pollutants generated within the indoor environment, such as those arising from smoking and other indoor combustion sources, as well as those from the outdoors, which may lead to increased exposure relative to that outdoors.
1352-2310/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.08.007
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Frequently, the concentrations of air pollutants are much higher indoors than outdoors (Lee et al., 2001, 2002a, b; Spengler, 1995; Wallace, 1996). Therefore, indoor exposures may be more important than those occurring outdoors. Moreover, various epidemiological studies have shown strong associations between concentrations of PM and adverse health outcomes including cardiorespiratory hospital admissions and mortality (e.g. Pope et al., 1995, 2002; Anderson et al., 2001). To date, epidemiology has been based upon outdoor measurements and hence the observed effects relate to exposures to PM originating outdoors. Little is known with certainty of the health effects of PM generated indoors. There have been a number of studies in which indoor air in homes has been characterized and compared with outdoor air (e.g. Kamens et al., 1991; Clayton et al., 1993; Miguel et al., 1995; Chao et al., 1998). The concentration of airborne PM inside a home is governed by the generation of PM within the home, the concentration of PM outside the home, the rate of air exchange and the depositional characteristics of the PM (Kamens et al., 1991; Thatcher and Layton, 1995). However, most indoor–outdoor research has focused on the comparison of PM mass concentrations without chemical differentiation. Carbonaceous species, including organic carbon (OC) and elemental carbon (EC), are major components of PM. OC has both a primary and a secondary origin and includes polycyclic aromatic hydrocarbons and other components with possible mutagenic and carcinogenic effects. EC is graphitic carbon formed from incompletely combusted carbonbased fuels (Seinfeld and Pandis, 1998). Soot carbon which is predominantly EC and a major component of PM2.5 has been linked to significantly increased risk of death from lung cancer and other severe respiratory ailments. (Frazer, 2002.) To date, only limited studies of indoor/outdoor relationship of carbonaceous aerosols have been conducted (Li and Lin, 2003; Geller et al., 2002; Funasaka et al., 2000). Indoor/outdoor air studies in the USA have determined that smoking and cooking are the predominant activities associated with elevated concentrations of fine PM (Wallace, 1996). Indoor PM concentrations are influenced by cooking style (Kamens et al., 1991; Chao et al., 1998), especially frying. Moon et al. (1997) reported that indoor/outdoor ratios (I/O) were slightly higher in homes with gas cookers than in those without this source. The ratio between indoor and outdoor concentrations of PM and carbonaceous species gives an indication as to whether PM found indoors are the result of indoor generation or derive from the outdoor environment. In the absence of indoor sources, I/O ratios will be less than, or equal to one. Hong Kong is one of the most densely inhabited metropolitan areas in the world. The majority of the around 7 million population is crowded into only 15%
of the total area (about 1068 km2). There were 517,000 registered vehicles crowded into 1904 km of roads in 2000 (Census and Statistics Department of Hong Kong, 2001). Diesel trucks with high emissions of carbonaceous PM accounted for 30% of the total amount of motor vehicles. Motor vehicles are considered as one of the major contributors to air pollution in Hong Kong. Consequently, it is a good location in which to observe the impact of outdoor carbonaceous PM emissions on the indoor pollutant level in urban buildings. A preliminary monitoring programme for indoor and outdoor concentrations of PM2.5, OC and EC was conducted from 25th September, 2002 to 8th March, 2003 at five locations (two offices with mechanical ventilation (MV) and three residences with natural ventilation (NV)) in Hong Kong. The objectives of this study are (1) to provide quantitative information on the concentrations of PM2.5, OC and EC in the five selected indoor and outdoor roadside microenvironments, (2) to investigate the extent to which traffic pollution from outdoor sources infiltrates into the indoor environment, (3) to compare the indoor and outdoor concentrations and the I/O ratios of PM2.5 OC and EC, under NV and MV.
2. Methodology 2.1. Sampling sites Five urban locations (an office, a classroom and three residences) were selected for the PM2.5 monitoring programme near the roadside in Hong Kong. The classroom and office were MV while the residences were NV during the sampling periods. All the locations were selected so as to have no significant local pollution sources other than motor vehicles. The sampling locations were located within 1–10 m of a main road. All the indoor and outdoor samples were collected simultaneously. The characteristics of each sampling site are given in Table 1. 2.2. Sample collection Indoor and outdoor PM2.5 samples were collected simultaneously from September 2002 to February 2003 by using mini-volume samplers (Airmetrics, USA) operating with a flow rate of 5 l min1 for 24 h. The samplers were checked and calibrated in The Hong Kong Polytechnic University. A Partisol model 2000 sampler (Rupprecht & Patashnick, USA) with a 2.5 mm inlet was collocated with the mini-volume samplers. The difference between the mini-volume samplers and Partisol 2000 was less than 5% for the PM2.5 mass concentrations. All samples were collected on 47 mm Whatman quartz microfibre filters (QM/A). The filters
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Table 1 Characteristics of indoor/outdoor sampling locations in Hong Kong Locations
Area type
Abbreviation
Distance from the main traffic road (m)
Sampling height above ground level (m)
No. of occupants
Mechanical ventilation
No. of samples
PolyU, U-core
Urban outdoor, 17,000 vehicles/day Urban indoor, classroom
PUU-O
8
6
—
—
5
PUU-I
—
—
40–60
Yes
5
Urban outdoor, commercial area Urban indoor, office
PUA-O
10
6
—
—
5
PUA-I
—
—
80
Yes
5
PUS-O
3
6
—
—
5
PUS-I
—
—
2
No
5
Urban outdoor, residential area Urban indoor, apartment
TM-O
1
2
—
—
4
TM-I
—
—
4
No
4
Urban outdoor, mixed industrial and residential area Urban indoor, apartment
SPK-O
3
12
—
—
4
SPK-I
—
—
4
No
4
PolyU, A-core
PolyU Studenthostel
Tuen Mun
Sun Po Kong
Urban outdoor, residential area Urban indoor, hostel
were pre-heated before sampling at 900 1C for 3 h. After collection, loaded filters were stored in a refrigerator at about 4 1C before chemical analysis to prevent the evaporation of volatile components. Before and after the field sampling, quartz fibre filters were placed for 24-h in a room having a temperature 25 1C and relative humidity 40%. The total particulate mass was determined by weighing on an electronic microbalance with a 1 mg sensitivity (Sartorius, MC5, Germany). Each of the measured residences had an indoor PM2.5 sampler in the living room/bedroom, and an outdoor one located in the balcony/platform. The indoor and outdoor sampling heights were in the range of 1–1.5 m above ground in order to simulate the breathing zone and to avoid potential interferences from excessive resuspension of PM. A total of 23 paired filters were collected for the carbonaceous aerosol analysis, and 21 paired analyzed data were used for data analysis. 2.3. Carbonaceous aerosol analysis All the loaded filters were analyzed for OC and EC using a DRI Model 2001 Thermal/Optical Carbon Analyzer. The IMPROVE thermal/optical reflectance
(TOR) protocol (Chow and Watson, 2002) was used for the carbon analysis. The protocol heats a 0.526 cm2 punch aliquot of a sample quartz filter stepwise at temperatures of 120 1C (OC1), 250 1C (OC2), 450 1C (OC3), and 550 1C (OC4) in a non-oxidizing helium (He) atmosphere, and 550 1C (EC1), 700 1C (EC2), and 800 1C (EC3) in an oxidizing atmosphere of 2% oxygen in a balance of helium. The carbon that evolves at each temperature is oxidized to carbon dioxide (CO2), then reduced to methane (CH4) for quantification with a flame ionization detector. As the temperature increases in the inert helium, some of the OC pyrolyzes to black carbon, resulting in darkening of the filter deposit. This darkening is monitored by the reflectance of 633 nm light from a He–Ne laser. When oxygen is added, the original and pyrolyzed black carbon combusts and the reflectance increases. The amount of carbon measured after oxygen is added until the reflectance achieves its original value is reported as optically detected pyrolized carbon (OPC). The eight fractions OC1, OC2, OC3, OC4, EC1, EC2, EC3, and OPC are reported separately in the data sheet. The IMPROVE protocol defines OC as OC1+OC2+OC3+OC4+OPC and EC as EC1+EC2+EC3OPC. The analyzer was calibrated with
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known quantities of CH4 every day. Replicate analyses were performed at the rate of one per group of 10 samples. The detection limits for EC and OC were below 1.0 mg m3 (about 0.2 mg m3 for EC and 0.5 mg m3 for OC). The repeatability determined from replicate analyses was better than 5% for total carbon (TC), and 10% for OC and EC (Cao et al., 2003).
3. Results and discussion 3.1. Indoor and outdoor PM2.5 mass concentrations The indoor and outdoor PM2.5 concentrations measured in the urban areas of Hong Kong are summarized in Table 2. Individual indoor PM2.5 concentrations ranged from 15.3 to 108 mg m3, while the outdoor PM2.5 concentrations ranged from 27.8 to 197 mg m3. The average indoor and outdoor concentrations were found to be 55.4 and 78.4 mg m3 for PM2.5, respectively. High indoor and outdoor concentrations were observed at the TM site. The high traffic flow, and especially the
high flow of heavy-duty vehicles, was the main reason for the high concentrations in TM–O (however, no traffic data was available in this station). Also TM–O was the closer outdoor monitoring location to the road (1 m) than the others (3–10 m). Other than the penetration of outdoor pollutants, smoking and cooking activity in TM–I are likely to be the major sources for the PM2.5. Smoking can add 20 mg m3 (24-h mean) of fine PM per smoker to a household (Spengler et al., 1981). Chao et al. (2002) found that the average PM2.5 concentration of smoking homes was 18% higher that the average PM2.5 concentration of non-smoking homes. There was no obvious indoor source for PM2.5 in the offices. The results showed that the MV offices had lower PM2.5 concentrations than the NV residences although the outdoor PM2.5 concentrations were high. Comparative data for indoor and outdoor PM2.5 in different urban areas are presented in Table 3. It is clear that indoor and outdoor PM2.5 concentrations in Hong Kong are higher than those reported in other urban areas (Monn et al., 1997; Hak et al., 1997; Geller et al., 2002; Morawska et al., 2003; Li and Lin, 2003; Liu et al.,
Table 2 The average concentrations of PM2.5 in different indoor and outdoor roadside environments of Hong Kong Location
Average PM2.5 concentrations (mg m3)
PM2.5 concentrations ranges (mg m3)
Average I/O ratio
I/O ratio ranges
PUU-O PUU-I PUA-O PUA-I PUS-O PUS-I TM-O TM-I SPK-O SPK-I
89.5761.4 39.6725.8 91.4732.7 45.2712.4 51.5727.2 46.5731.0 108.372.0 97.976.9 76.7741.5 77.3718.6
42.0–197.2 15.3–83.3 59.7–109.7 30.3–58.3 27.8–104.2 27.0–108.3 106.9–109.7 93.1–102.8 37.5–125.0 59.7–98.6
0.570.2
0.2–0.7
0.570.1
0.4–0.7
0.970.2
0.6–1.1
0.970.1
0.8–0.9
1.270.4
0.8–1.6
Table 3 Intercomparison of indoor and outdoor PM2.5 mass concentrations in different urban areas Locations/sampling environment
PM2.5 concentrations (mg m3) Indoor
Hong Kong/urban area Brisbane, Australia/suburb Beijing, China/urban area Zurich, Switzerland/urban area Chongju, Korea/urban area Southern California, USA/desert area Taipei, Taiwan/urban area This study, Hong Kong/urban area, near roadside
50.4 15.5 28.1 (office) 26.0 25.3 15.5 Winter: 38.7, summer: 36.6 55.4
References Outdoor
21.0 26.3 15.0 Winter: 38.3, summer: 36.3 78.4
Chao and Wong (2002) Morawska et al. (2003) Liu et al. (2004) Monn et al. (1997) Hak et al. (1997) Geller et al. (2002) Li and Lin (2003)
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2004) but comparable to those observed previously at different sites in Hong Kong (Chao and Wong, 2002). The high outdoor concentrations in this study were due to all of the sampling sites being located in the urban area and near to heavily trafficked roads (1–10 m). Moreover, the northeast monsoon advects pollutants by long-range transport to Hong Kong from other Asian countries in winter (Qin et al., 1997; Fang et al., 1999). Over 50% of PM2.5 samples were observed to exceed the USEPA 24 h standard for PM2.5 concentrations (65 mg m3) in the outdoor locations. Chao et al. (1998) expressed the view that the high indoor PM concentrations in Hong Kong were due to the Chinese cooking styles and the high emission of oily fumes in the kitchen. It was found that I/O ratios of PM2.5 in this study ranged from 0.2 to 1.6. The MV office and classroom had I/O ratios for PM2.5 smaller than 0.7 which is comparable with the value (0.4–0.6) suggested to occur in the absence of indoor sources (Wallace, 1996). This was consistent with the stated view that no
Correlations of indoor PM2.5 and outdoor PM2.5
Indoor PM2.5 (µg m-3)
120
MV
100
NV
y = 0.80x + 9.92 R2 = 0.83
80 60
y = 0.38x + 8.1 R2 = 0.81
40 20 0 0
50
100
150
200
250
Outdoor PM2.5 (µg m-3)
Fig. 1. Scatterplot of outdoor PM2.5 vs. indoor PM2.5.
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potential source was present. For the NV residences, the I/O ratios ranged from 0.6 to 1.6. Monn et al. (1997) reported that I/O ratios of PM10 were within the range 0.7–1.2 except for the households of habitual smokers (all NV homes). Monn et al. (1997) also suggested that I/O ratios increase with human activities such as cleaning or daily working. The I/O ratios in this study were comparable to those found in Taipei, Taiwan (Li and Lin, 2003) and Osaka, Japan (Funasaka et al., 2000).
3.2. Indoor and outdoor correlation of PM2.5 As in previously published studies on the relationship between indoor and outdoor PM (Colome et al., 1992; Clayton et al., 1993), the value of the coefficient of determination (R2) between the indoor and outdoor data has been used as an indicator of the degree to which PM2.5 measured indoors can be attributed to infiltration from outdoors. It was found that the indoor PM2.5 levels were moderately correlated with the corresponding outdoor concentrations with an R2 of 0.42 (po0:01). However, if the data were classified into two groups, MV and NV, then good correlations were found in each group (Fig. 1). The correlations of MV and NV groups are R2=0.81 (po0:01) and R2=0.83 (po0:001), respectively. The strong indoor-to-outdoor PM2.5 association (especially in NV residences) suggested that these fine particulates were mainly from the outdoor environment but with different penetration efficiencies in the two ventilation groups. Chao and Wong, 2002 suggested that good correlations were found in indoor environments where frequent exchange of air occurs between the indoor and the outdoor environment. In this study, all the sampling sites appear to have had good infiltration and frequent exchange of air.
Table 4 The average concentrations of OC and EC as well as OC/EC and I/O ratios in different indoor and outdoor roadside environments of Hong Kong Locations
OC conc. (mg m1)
OC conc. range (mg m1)
EC conc. (mg m1)
EC conc. range (mg m1)
OC/EC
I/O ratios EC
I/O ratios OC
PUU-O PUU-I PUA-O PUA-I PUS-O PUS-I TM-O TM-I SPK-O SPK-I Average indoor Average outdoor
10.573.3 6.271.4 16.476.0 10.372.5 8.574.3 9.573.4 19.474.3 21.273.1 14.173.8 16.773.4 11.375.5 12.675.4
6.5–14.9 4.2–8.2 10.7–22.9 6.8–12.6 2.2–15.2 6.1–14.7 26.3–34.9 19.0–23.4 10.6–19.4 13.7–21.0
5.970.8 2.870.5 8.272.3 3.771.4 4.472.8 4.073.1 11.271.8 11.176.3 6.071.6 6.272.4 4.873.4 6.472.8
4.6–6.6 2.3–3.6 6.2–10.2 2.4–5.7 1.1–9.2 1.3–9.1 10.0–12.4 6.7–15.5 3.9–7.4 3.9–8.6
1.870.4 2.370.6 2.070.2 2.970.8 2.170.4 3.171.5 1.770.1 2.271.0 2.470.4 2.870.6 2.771.0 2.070.4
0.570.1
0.670.2
0.570.1
0.770.2
0.970.3
1.571.0
1.070.4
1.170.1
1.170.4
1.270.2
0.870.3
1.070.7
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Table 5 Statistical summary of the percentage of OC, EC, OM and TCA in PM2.5 Locations
% OC
% EC
% OM
% TCA
MV indoor environments NV indoor environments MV outdoor environments NV outdoor environments
21.076.0 22.676.6 16.075.0 18.576.3
8.573.0 8.873.9 8.672.2 9.174.1
33.679.5 36.2710.6 25.777.9 29.5710.8
42.1711.7 45.0713.3 34.379.8 38.6714.5
3.3. OC and EC concentrations in indoor and outdoor environments outdoor OC (µg m-3)
y = 1.76x + 1.23 2 R = 0.82
20 15 10 5 0 0
4
2
6 8 10 outdoor EC (µg m-3)
12
14
Fig. 2. Correlation of outdoor OC and EC.
Correlations of indoor OC and EC concentrations 30 indoor OC (µg m-3)
The average concentrations of OC and EC in PM2.5 as well as OC/EC and I/O ratios of OC and EC in indoor and outdoor environments are shown in Table 4 (the average I/O and OC/EC ratios were calculated by averaging the I/O or OC/EC values of all corresponding samples). The average indoor TC concentration was 16.1 mg m3, and the average outdoor TC was 19.2 mg m3. The overall average indoor and outdoor EC concentrations were found to be 4.8 and 6.4 mg m3, respectively. The indoor EC concentrations ranged from 1.3 to 15.6 mg m3 while the outdoor EC concentrations ranged from 1.1 to 12.4 mg m3. The overall average indoor and outdoor OC concentrations were found to be 11.3 and 12.6 mg m3, respectively. The indoor OC concentrations ranged from 4.2 to 23.4 mg m3 while the outdoor OC concentrations ranged from 2.2 to 22.9 mg m3. The highest average indoor and outdoor EC concentrations were observed in TM–I and TM–O (11.2 and 11.1 mg m3), respectively, which is consistent with the PM2.5 mass concentrations, and the high flow of heavy-duty vehicles (and short distance between the sampling site and the road) at this site. Table 5 shows the carbonaceous material as a percentage of PM2.5 mass. Clearly, OC is enriched in indoor, as compared to outdoor air. In order to convert the measured mass of OC to the total organic matter (OM) mass, the OC mass has to be multiplied by a factor that is an estimate of the average molecular weight per carbon weight for the organic aerosol (Kleefeld et al., 2002). According to Turpin and Lim (2001), the amount of urban OM may be estimated by multiplying the amount of OC by 1.6. Thus the total carbonaceous aerosol (TCA) mass was calculated from the sum of OM and EC. The average indoor OM and TCA concentrations were 18.1 and 22.9 mg m3, respectively, which accounted for 35.1% (OM) and 43.8% (TCA) of PM2.5 mass concentrations. The average outdoor OM and TCA concentrations were 20.1 and 26.5 mg m3, respectively, which accounted for 27.9% (OM) and 36.8% (TCA) of PM2.5 mass concentrations. In other words, the carbonaceous fraction accounted for more than onethird of the PM2.5 in both indoor and outdoor environments.
Correlations of outdoor OC and EC concentrations 25
y = 1.36x + 4.83 2 R = 0.71
25 20 15 10 5 0 0
2
4
6
8
10
12
14
16
18
indoor EC (µg m-3)
Fig. 3. Correlation of indoor OC and EC.
The OC to EC ratio has been used to study the emission and transformation characteristics of carbonaceous aerosols. OC/EC ratios exceeding 2.0 (Chow et al., 1996) or 1.1 (Castro et al., 1999) have been used to indicate the presence of secondary organic aerosols. The OC/EC ratios in PM2.5 are shown in Table 4, and in individual samples, varied between 1.41 and 2.70 (average 2.00) for outdoor environments; and the average OC/EC ratio was 2.7 for indoor environments. On average, all outdoor monitoring locations have OC/ EC ratios less than 2 except SPK where the traffic flow of heavy-duty vehicles was less than at the other locations. Also there may be industrial source influences at this outdoor sampling location. It seems likely, therefore, that there is a significant secondary OC contribution in the outdoor samples. An indoor
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enhancement of OC/EC ratios relative to outdoors is likely to be due to indoor sources of organic compounds. Graphs of OC versus EC (Figs. 2 and 3) show a much larger intercept for the indoor samples, indicative of an indoor source.
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OC, on the other hand appears to have indoor sources contributing of the order of 3 mg m3 in the NV buildings and 2 mg m3 in the MV ones.
4. Conclusion 3.4. Indoor and outdoor relationships of OC and EC The relationships between indoor and outdoor concentrations (separately for MV and NV conditions) of OC and EC are shown in Figs. 4 and 5, respectively. For the MV offices, fair correlations of OC (R2=0.66, po0:05) and EC (R2=0.42, po0:1) concentrations in indoor air to those in outdoor air were observed. However, when limited to NV residences, OC in indoor air was more highly correlated to that in outdoor air, R2=0.71 (po0:01). For fine EC, there was a good correlation between indoor and outdoor air of the NV residences, R2=0.76 (po0:001). These results suggest that indoor fine OC and EC are derived at least in part from outdoor air (especially the EC). This is consistent with results reported by Jones et al. (2000), who found that EC originates outdoors, mostly from vehicular emissions. The small intercepts in Fig. 5 suggest that virtually all indoor EC originates from outdoors, with very efficient penetration in the case of NV buildings. Correlations of indoor OC and outdoor OC Indoor OC (µg m-3)
25 20
MV
NV
y = 0.86x + 3.38 2 R = 0.71
15 10 y = 0.43x + 2.31 2 R = 0.66
5 0 0
5
10 15 Outdoor OC (µg m-3)
20
25
Acknowledgements
Fig. 4. Correlations of indoor OC and outdoor OC.
This project was supported by the Research Grants Council of Hong Kong (PolyU5038/01E, PolyU5145/ 03E).
Indoor EC (µg m-3)
Correlations of indoor EC and outdoor EC 18 16 14 12 10 8 6 4 2 0
MV
NV
y = 1.07x - 0.55 R2 = 0.76
References
y = 0.36x + 0.72 2 R = 0.42
0
2
4
6
8
This study has quantified the PM2.5 mass and concentrations of OC and EC in both indoor and outdoor air in five near-roadside locations in Hong Kong during the fall and winter from September 2002 to February 2003. The indoor-to-outdoor PM2.5 mass concentration ratios (I/O) ranged from 0.2 to 1.6. However, lower I/O ratios were observed for the MV offices, with higher ratios for NV residences. Good indoor–outdoor correlations were found for the MV and NV groups analysed separately, which suggested that the fine PM derived mainly from the outdoor environment, but with different penetration efficiencies in the two ventilation groups. Indoor PM2.5 consisted of 35% OM and 9% EC whilst outdoor PM2.5 comprised 28% OM and 9% EC. The average I/O ratios of OC and EC were 1.02 and 0.80, respectively. Again, higher I/O ratios of OC and EC were observed in NV residences than in the MV office and classroom due to higher infiltration rates in NV buildings. The average OC/EC ratio in PM2.5 was 2.0 for outdoor environments and 2.7 for indoor environments. Regression of indoor versus outdoor concentrations of OC and EC revealed an indoor source of OC, not present for EC, and presumably due to such activities as cooking, smoking and cleaning. The magnitude of the indoor source of OC, 2–3 mg m3, is generally less than the penetration of OC from outdoors. Much greater attenuation of indoor concentrations relative to outdoors was found for all analytes in the MV buildings when compared to the NV ones.
10
12
Outdoor EC (µg m-3)
Fig. 5. Correlations of indoor EC and outdoor EC.
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Anderson, H.R., Bremner, S.A., Atkinson, R.W., Harrison, R.M., Walters, S., 2001. Particulate matter and daily mortality and hospital admissions in the West Midlands conurbation of the United Kingdom: associations with fine and coarse particles, black smoke and sulphate. Occupational Environmental Medicine 58, 504–510. APEG, 1999. Source Apportionment of Airborne Particulate Matter in the United Kingdom, R.M. Harrison et al. The
ARTICLE IN PRESS 6334
K.F. Ho et al. / Atmospheric Environment 38 (2004) 6327–6335
First Report of the Airborne Particles Expert Group, Department of Environment, Transport and the Regions, London. Cao, J.J., Lee, S.C., Ho, K.F., Zhang, X.Y., Zou, S.C., Fung, Kochy, Chow, C., Watson, John, G., 2003. Characteristics of carbonaceous aerosol in Peral River Delta Region, China during 2001 winter period. Atmospheric Environment 37, 1451–1460. Castro, L.M., Pio, C.A., Harrison, R.M., Smith, D.J.T., 1999. Carbonaceous aerosol in urban and rural European atmospheres: estimation of secondary organic carbon concentrations. Atmospheric Environment 33, 2771–2781. Census and Statistics Department of Hong Kong (2001). Hong Kong Annual Digest of Statistics. Chao, C.Y., Tung, T.C.W., Burnett, J., 1998. Influence of different indoor activities on the indoor particulate levels in residential buildings. Indoor Built Environment 7, 110–121. Chao, C.Y., Wong, K., 2002. Residential indoor PM10 and PM2.5 in Hong Kong and the elemental composition. Atmospheric Environment 36, 265–277. Chow, J.C., Watson, J.G., Lu, Z., Lowenthal, D.H., Frazier, C.A., Solomon, P.A., Thuilier, R.H., Magliano, K., 1996. Descriptive analysis of PM2.5 and PM10 at regionally representative locations during SJVAQS/AUSPEX. Atmospheric Environment 30, 2079–2112. Chow, J.C., Watson, J.G., 2002. PM2.5 carbonate concentrations at regionally representative interagency monitoring of protected visual environment sites. Journal of Geophysical Research 107 (D21), ICC6-1–9ICC6-9. Clayton, C.A., Perritt, R.L., Pellizzari, E.D., Thomas, K.W., Whitmore, R.W., Wallace, L.A., Ozkaynak, H., Spengler, J.D., 1993. Particle total exposure assessment methodology (PTEAM) study: distributions of aerosol and elemental concentrations in personal, indoor and outdoor air samples in a Southern California community. Journal of Exposure Analysis and Environmental Epidemiology 3, 227–250. Colome, S., Kado, N., Jaques, P., Kleinman, M., 1992. Indoor–outdoor air pollution relations: particulate matter less than 10 mm in aerodynamic diameter (PM10) in homes of asthmatics. Atmospheric Environment 26A, 2173–2178. Fang, M., Zheng, M., Wang, F., Chim, K.S., Kot, S.C., 1999. The long-range transport of aerosols from northern China to Hong Kong—a multi-technique study. Atmospheric Environment 33, 1803–1817. Frazer, L., 2002. Seeing through soot. Environmental Health Perspectives 10, A470–A473. Funasaka, K., Miyazaki, T., Tsuruho, K., Tamura, K., Mizuno, T., Kuroda, K., 2000. Relationship between indoor and outdoor carbonaceous particulates in roadside households. Environmental Pollution 110, 127–134. Gartrell, G., Friedlander, S.K., 1975. Relating particulate pollution to source—the 1972 California aerosol characterization study. Atmospheric Environment 9, 279–289. Geller, M.D., Chang, M., Sioutas, C., Ostro, B.D., Lipsett, M.J., 2002. Indoor/outdoor relationship and chemical composition of fine and coarse particles in the southern
California deserts. Atmospheric Environment 36, 1099–1110. Hak, S.L., Kang, B.W., Cheong, J.P., Lee, S.W., 1997. Relationships between indoor and outdoor air quality during the summer season in Korea. Atmospheric Environment 31, 1689–1693. Jones, N.C., Thornton, C.A., Mark, D., Harrison, R.M., 2000. Indoor/outdoor relationships of particulate matter in domestic homes with roadside, urban and rural locations. Atmospheric Environment 34, 2603–2612. Kamens, R., Lee, C.T., Weiner, R., Leith, D., 1991. A study to characterize indoor particles in three non-smoking homes. Atmospheric Environment 25, 939–948. Kleefeld, S., Hoffer, A., Kriva´csy, Z., Jennings, S.G., 2002. Importance of organic and black carbon in atmospheric aerosols at Mace Head, on the West Coast of Ireland (531190 N, 91540 W). Atmospheric Environment 36, 4479–4490. Lee, S.C., Li, W.M., Chan, L.Y., 2001. Indoor air quality at restaurants with different styles of cooking in metropolitan Hong Kong. The Science of the Total Environment 279, 181–193. Lee, S.C., Guo, H., Li, W.M., Chan, L.Y., 2002a. Intercomparison of air pollutant concentrations in different indoor environment in Hong Kong. Atmospheric Environment 36, 1929–1940. Lee, S.C., Li, W.M., Ao, C.H., 2002b. Investigation of indoor air quality at residential homes in Hong Kong––case study. Atmospheric Environment 36, 225–237. Li, C.-S., Lin, C.-H., 2003. Carbon profile of residential indoor PM1 and PM2.5 in the subtropical region. Atmospheric Environment 37, 881–888. Liu, Y., Chen, R., Shen, X., Mao, X., 2004. Wintertime indoor air levels of PM10, PM2.5 and PM1 at public places and their contributions to TSP. Environment International 30, 189–197. Miguel, A.H., Neto, F.R., De, A., Cardoso, J.N., Vasconcellos, P., De, C., Pereira, A.S., Marquez, K.S.G., 1995. Characterization of indoor air quality in the cities of Sao Paulo and Rio de Janeiro, Brazil. Environmental Science and Technology 29, 338–345. Monn, Ch., Fuchs, A., Hogger, D., Junker, M., Kogelschatz, D., Roth, N., Wanner, H.U., 1997. Particulate matter less than 10 mm (PM10) and fine particles less than 2.5 mm (PM2.5): relationships between indoor, outdoor and personal concentrations. The Science of the Total Environment 208, 15–21. Morawska, L., He, C., Hitchins, J., Mengersen, K., Gilbert, D., 2003. Characteristics of particle number and mass concentrations in residential houses in Brisbane, Australia. Atmospheric Environment 37, 4195–4203. Pope, C.A., Thun, M.J., Namboodiri, M.M., Dockery, D.W., Evans, J.S., Speizer, F.E., Heath, C.W., 1995. Particulate air pollution as a predictor of mortality in a prospective study of US adults. American Journal of Respiratory and Critical Care Medicine 151, 669–674. Qin, Y., Chan, C.K., Chan, L.Y., 1997. Characteristics of chemical compositions of atmospheric aerosols in Hong Kong: spatial and seasonal distributions. The Science of the Total Environment 206, 25–37.
ARTICLE IN PRESS K.F. Ho et al. / Atmospheric Environment 38 (2004) 6327–6335 Spengler, J.D., Dockery, D.W., Turner, W.A., Wolfson, J.M., Ferris Jr., B.G., 1981. Long-term measurements of respirable sulfates and particles inside and outside homes. Atmospheric Environment 15, 23–30. Spengler, J.D., 1995. Indoor air quality––innovation and technology. In: Morawska, L., Bofinger, N.D., Maroni, M. (Eds.), Indoor Air: An Integrated Approach, 1st ed. Elsevier Science Ltd, Oxford, pp. 1–33.
6335
Thatcher, T.L., Layton, D.W., 1995. Deposition, re-suspension and penetration of particles within a residence. Atmospheric Environment 29, 1487–1497. Turpin, B.J., Lim, H.J., 2001. Species contributions to PM2.5 mass concentrations: revising common assumptions for estimating organic mass. Aerosol Science and Technology 35, 602–610. Wallace, L., 1996. Indoor particles: a review. Journal of the Air and Waste Management Association 46, 98–126.