CHINA PARTICUOLOGY Vol. 1, No. 1, 33-37, 2003

SPATIAL AND SEASONAL DISTRIBUTIONS OF ATMOSPHERIC CARBONACEOUS AEROSOLS IN DELTA REGION, Junji Cao 1, *, Shuncheng Lee 2, Kinfai Ho 2, Shichun Zou 3, Xiaoye Zhang 1 and Jianguo Pan 4 1 State Key Laboratory of Loess & Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710054, P. R. China 2 Research Center for Urban Environmental Technology and Management, Department of Civil and Structural Engineering, The Polytechnic University, Hong Kong, P. R. China 3 Department of Chemistry, University, 510275, P. R. China 4 Environmental Monitoring Station, Zhuhai 519000, P. R. China * Author to whom correspondence should be addressed. E-mail: [email protected]

Abstract Concentrations and spatial distributions of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured at 8 sites in four cities (Hong Kong, Guangzhou, and Zhuhai) of

Region (PRDR), China during 2001 winter period and 2002 summer period. PM2.5 (particle diameter smaller than 2.5 µm)

and PM10 (particle diameter smaller than 10 µm) samples were collected on pre-fired quartz filters with mini-volume

samplers and analyzed using thermal optical reflectance (TOR) method. The average PM2.5 and PM10 level were 60.1 –3 and 93.1 µg.m , respectively, with PM2.5 constituting 65.3% of the PM10 mass. The average OC and EC concentrations –3 –3 in PM2.5 were 12.0 and 5.1 µg.m , respectively, while those in PM10 were 16.0 and 6.5 µg.m , respectively. The carbo-

naceous aerosol accounted for 37.2% of the PM2.5 and 32.8% of the PM10. The highest concentrations of OC and EC

were observed at Guangzhou city in both winter and summer seasons. The average OC/EC ratios were 2.4 for PM2.5

and 2.5 for PM10, indicating the presence of secondary organic aerosols. The OC and EC in PRDR were found to be strongly correlated (correlation coefficients > 0.6), which implied that similar emission source contribute to the ambient carbon particles.

Keywords PM2.5, PM10, Organic carbon, Elemental carbon, OC/EC ratio, Pearl River Delta Region

1. Introduction The data on the concentrations, distributions, sources, and radiative properties of the carbonaceous components Atmospheric carbonaceous aerosols are responsible for of aerosols are much scarcer in China (He et al., 2001; public health, visibility reduction and climate changes Cao et al., 2003). The main objective of this paper was to (Penner, 1995). Carbon containing aerosols are com- determine the carbonaceous aerosol at 8 monitoring sites posed of organic (OC) and elemental (EC) carbon. OC, in four cities in Pearl River Delta Region (PRDR) in order containing polycyclic aromatic hydrocarbon and other to understand anthropogenic air pollutant levels and their components with possible mutagenic and carcinogenic fates in the region. Physicochemical characterization of effects, can be directly emitted from sources (primary OC) the OC and EC were summarized to obtain spatial and or produced from atmospheric reactions involving gaseous seasonal distributions of carbonaceous aerosol in PRDR organic precursors (secondary OC) (Turpin & Huntzicker, atmosphere. Information obtained in this study will also 1995). EC (often named black carbon or soot) may be the allow evaluation of the changes in air quality in PRDR and second most important component of global warming in help to set source emission control strategies for particu- terms of direct forcing, after CO2 (Jacobson, 2001). EC late matter reduction. heat the air, alter regional atmospheric stability and verti- cal motions, and affect the large-scale circulation and hy- 2. Methods and Materials drologic cycle with significant regional climate effects in China and India (Menon et al., 2002). Also, the “Asian 2.1 Sampling sites and descriptions Brown Cloud” mainly associated with carbonaceous aero- Sampling sites were selected for the particulate matter sol over South Asia, may be causing the premature deaths monitoring to obtain the spatial distributions information of a half-million people in India each year, deadly flooding according to their different land use categories, popula- in some areas and drought in others (http://www.fire.uni- tions and traffic densities. Eight sites were selected in four freiburg.de/media/news_08122002_sea.htm). Therefore, cities including 3 sites in Hong Kong, 3 sites in Guangzhou,

OC and EC are the next frontier for particle characteriza- 1 site in Shenzhen and 1 site in Zhuhai (Fig. 1). PM10 and tion and simulation (Turpin et al., 2000). PM2.5 samples were collected during the period from 34 CHINA PARTICUOLOGY Vol. 1, No. 1, 2003

-1 January to February 2001 (winter) and June to July 2002 flow rates of 5 L.min . Both PM2.5 and PM10 were collected (summer) to obtain the temporal variations information. on φ 47 mm Whatman quartz microfibre filters (QM/A).

The field descriptions were given as follows: PM10 and PM2.5 samples were collected every 24 hours simultaneously at eight sites. The filters were pre-heated before sampling at 900°C for 3 hours. After collection, loaded filters were stored in a refrigerator at about 4°C before chemical analysis to prevent the evaporation of volatile components. Also field blank filters were collected to subtract the positive artifacts due to adsorption of gas- phase organic components onto the filter during and/or after sampling. However, negative artifacts due to volatili- zation of particle-phase organics from particle sample were not quantified in this study. 2.3 Carbonaceous aerosols analysis The samples were analyzed for OC/EC using DRI Model 2001 (Thermal/Optical Carbon Analyzer). The IMPROVE (Interagency Monitoring of Protected Visual Environment) thermal/optical reflectance (TOR) protocol Fig. 1 Sampling map. (Chow et al., 2001) was used for the carbon analysis. The Hong Kong: protocol heats a 0.526 cm2 punch aliquot of a sample Polytechnic University (PU): The site was situated at about 6 quartz filter stepwise at temperatures of 120oC (OC1), m above ground level in The Hong Kong Polytechnic Univer- 250oC (OC2), 450oC (OC3), and 550oC (OC4) in a non- sity, and about 8 m away from the main traffic road that leads oxidizing helium (He) atmosphere, and 550oC (EC1), to the Cross Harbor Tunnel. The traffic volume on this road is o o extremely high with about 170,000 vehicles per day. 700 C (EC2), and 800 C (EC3) in an oxidizing atmosphere Baptist University (BU): The site was located about 30 m of 2% oxygen in a balance of helium. The carbon that above ground on the roof of a science building in Hong Kong evolves at each temperature is oxidized to carbon dioxide Baptist University. It represents a residential and commercial (CO2), and then reduced to methane (CH4) for quantifica- environment of urban area. tion with a flame ionization detector. As temperature in- Hok Tsui (HT): The site was situated at the southern tip of Hong Kong Island where the least anthrogenic pollution is creases in the inert helium, some of the organic carbon expected. It is about 10 m above ground level. This is consid- pyrolyzes to black carbon, resulting in darkening of the ered as a background monitoring station. filter deposit. This darkening is monitored by reflectance of Guangzhou: 633 nm light of a He-Ne laser. When oxygen is added, the Zhongshan University (ZU): The station was located on a 15 original and pyrolyzed black carbon combusts and the m-high rooftop at the campus of Zhongshan University. It reflectance increases. The amount of carbon measured represents an urban monitoring site. Huangpu (HP): The site was in an industrial of Guang- after oxygen is added until the reflectance achieves its zhou city. There are many industrial emission sources includ- original value is reported as optically-detected pyrolyzed ing chemical and metallurgical factories, power plants, etc. It carbon (OPC). The eight fractions OC1, OC2, OC3, OC4, is about 20 m above ground level. This station is regarded as EC1, EC2, EC3 and OPC are reported separately in the an industrial monitoring site. data sheet. The IMPROVE protocol defines OC as OC1 + Longgui (LG): This station was on the roof (10 m) of a build- ing in the Green Country Ecological Educational Center of OC2 +OC3 +OC4 + OPC and EC as EC1 + EC2 + EC3- Guangzhou city. It was selected as a background monitoring OPC. site because it is about 25 km, far away from Guangzhou ur- The detection limits for EC and OC were below 1.0 µg.m-3. ban district. The difference determined from replicate analyses was Shenzhen: smaller than 5% for TC (total carbon), and 10% for OC and Luohu (LH): This station is one of the existing monitoring sta- tions of Shenzhen Environmental Protection Bureau. It is on EC. the roof (8 m) of the monitoring station at the Honghu Park in the Luohu district. It is an urban monitoring site. 3. Results and Analyses Zhuhai: Xiangzhou (XZ): This station is one of monitoring stations of 3.1 PM2.5 and PM10 concentrations and ratios Zhuhai Environmental Protection Bureau, on the roof (20 m) of the monitoring station in the Xiangzhou district. It is an ur- Descriptive statistics for all valid observations of PM2.5 ban monitoring site. and PM10 concentrations from the 8 sites in PRDR are 2.2 Particulate matter collection summarized in Table 1. The average twenty-four-hour PM2.5 concentrations at the 8 sites were (72.6±49.0) -3 -3 PM10 and PM2.5 samples were collected using eight mini µg.m for winter period and (49.1±30.6) µg.m for summer volume (mini-vol.) samplers (Airmetrics, USA), operated at period, respectively. Among the 8 sites, average PM2.5 Cao, Lee, Ho, Zou, Zhang & Pan: Spatial and Seasonal Distributions of Atmospheric Carbonaceous Aerosols 35

mass at LG (Guangzhou city) reached the highest for win- Among the four cities, PM2.5 levels in Hong Kong were the ter period and another site HP in Guangzhou city has the lowest for both seasons ((54.5±22.9) µg.m-3 for winter pe- highest level for PM2.5 for summer period. The PM2.5 at HT riod and (31.0±16.9) µg.m-3 for summer period). The av- . -3 ((41.3±20.0) µg m ) were lower than the other sites for erage PM2.5 concentration in Guangzhou was high for both both seasons, as it lies far away from the urban district of seasons indicating serious fine particulate pollution and Hong Kong. High dispersion from sea wind rendered the multi-source contribution to airborne PM2.5 in this city. particulate concentration at this site being the lowest.

Table 1 Ambient PM2.5 and PM10 concentrations at 8 sites in PRDR

-3 a -3 City Site PM2.5 /µg.m Concentration PM10 /µg.m Concentration Average PM2.5/PM10 / % Winter Nb Summer N Winter N Summer N Winter Summer PU 60.4±22.9 14 40.1±19.7 10 78.4±34.1 6 40.8±15.6 10 79.9 83.0 Hong Kong BU 48.5±24.7 5 30.8±7.6 6 55.7±19.3 3 38.6±12.8 6 68.9 71.2 HT 41.3±20.0 4 15.8±2.4 682.9±17.9 331.9±4.9 6 58.1 50.3 Average 54.5±22.9 23 31±16.9 2273.9±27.9 1241.4±14.2 22 71.7 70.9

HP 104.0±77.8 5 101.7±11.4 5 167.0±146.1 5 164.2±17.4 5 66.5 62.1 Guangzhou ZU 90.5±41.0 10 66.3±18.9 10 138.2±70.1 10102.7±32.5 10 67.9 65.1 LG 138.6±111.6 5 78.2±46.9 5 203.4±161.7 5 129.5±93.5 5 69.3 64.1 Average 105.9± 71.4 20 78.1±29.7 20 161.7±114.4 20 124.7±55.5 20 67.9 64.1

Shenzhen LH 60.8±18.0 9 47.1±16.7 9 83.7±27.4 975.1±23.0 9 73.3 62.6

Zhuhai XZ 59.3±23.7 9 31.0±20.0 9 84.1±31.6 944.0±24.8 9 70.8 68.9

PRDR Average 72.6±49.0 63 49.1±30.6 60 111.5±83.5 52 74.6±51.2 60 70.4 68.7

a Values represent average ± standard deviation. b Numbers of samples.

The average 24-h PM10 concentrations were (111.5±83.5) spatial and seasonal distributions of OC/EC were illus- µg.m-3 for winter period and (74.6±51.2) µg.m-3 for sum- trated in Fig. 2. OC from both primary anthropogenic mer period. Among the 8 sites, PM10 at three sites in sources and formation by chemical reactions in the at- Guangzhou (LG, ZU and HP) for both seasons were more mosphere rendered the concentrations of OC higher than -3 EC at eight sampling sites. The average PM2.5 OC con- than 100 µg.m , exceeding the Class 2 of Chinese PM10 . -3 standard of 100 µg.m-3. The high PM concentrations in centrations in PRDR were (14.7±11.9) µg m and (9.2±6.5) -3 Guangzhou could be attributed to a large number of indus- µg.m for winter and summer period, respectively, and the -3 trial and motor vehicular emissions within the city. Unlike average EC concentrations in PM2.5 were (6.1±4.0) µg.m -3 the distribution of PM2.5 concentrations, the lowest levels and (4.1±2.7) µg.m , respectively. Obviously, the OC and of PM10 appeared at the BU site during winter period, but EC for both PM2.5 and PM10 fractions have high levels in the PM10 in HT has low level during summer period. the winter period. In general, there were several factors Among all the sites, the PM2.5 and PM10 concentrations in that could affect the concentrations of OC in the winter winter period have higher level than those in summer pe- and in the summer. Dilution due to the increased mixing riod, which implied that there is serious particle pollution in depth was found in summer. More rainy days in the sum- winter period in PRDR. mer cause the particulate matters to be washed out in the The ratios of average 24-h PM2.5 to PM10 concentrations atmosphere. Also physical dispersion may be the reason at the 8 sites varied from site to site, ranging from 50.3% for higher concentrations in winter. to 83.0%, with an average of 70.4% during the winter pe- The average OC and EC concentrations in PM2.5 and riod. The average PM2.5/PM10 in summer period has simi- PM10 for the four cities were all in the order of Hong Kong lar value (68.7%) with that in winter period. This study < Zhuhai < Shenzhen < Guangzhou in the winter period. showed that in PRDR, PM2.5 concentrations tend to be The average OC and EC concentrations in PM2.5 for the higher than the coarse particle (PM2.5-10) concentrations, four cities were also the same order, but the OC and EC with the average PM2.5 that is around 2 times higher for concentrations in PM10 were in the order of Zhuhai < Hong both seasons. Therefore, it is more important to control the Kong < Shenzhen < Guangzhou in the summer period. fine particles in the PRDR. The high loadings of carbonaceous aerosol observed in 3.2 Spatial and seasonal distributions of OC Guangzhou may be due to: firstly, there are more than 1 and EC million motor vehicles in the city; secondly, a large number of industrial emission sources are located in the city; Statistics for OC and EC concentration at eight sampling thirdly, coal-combustion is used occasionally by residents sites in winter and summer were shown in Table 2 and during the winter. But for other three cities, exhaust from 36 CHINA PARTICUOLOGY Vol. 1, No. 1, 2003 motor vehicles is the only dominant source contributing to atmospheric carbon particles.

Table 2 Statistical description of the concentrations of organic carbon (OC) and elemental carbon (EC) at 8 sites in PRDR a

. -3 b . -3 OC/EC City Site Season OC/µg m EC/µg m PM2.5 PM10 PM2.5 PM10 PM2.5 PM10

PU Winter 10.6±3.7 12.7±4.7 6.1±1.8 7.0±2.6 1.7 1.8 Summer 6.3±2.3 7.4±2.9 3.9±1.6 4.7±2.1 1.7 1.6 Hong Kong BU Winter 8.4±6.3 7.6±1.3 4.4±4.7 3.4±0.7 2.3 2.2 Summer 5.6±0.8 6.7±1.1 3.2±0.4 3.9±0.5 1.8 1.7 HT Winter 6.3±2.6 9.1±1.0 1.9±0.9 3.0±1.0 3.3 3.2 Summer 3.4±0.3 4.1±0.6 0.7±0.1 1.1±0.1 4.7 3.8 Average Winter 9.6±4.5 10.5±4.0 4.7±2.9 5.1±2.7 2.3 2.3 Summer 5.3±2.1 6.3±2.5 3.2±2.6 3.9±2.9 1.9 1.8

HP Winter 23.3±16.6 32.6±26.6 11.0±6.3 12.1±6.6 2.1 2.4 Summer 20.0±2.8 28.5±5.2 7.9±1.1 10.5±1.9 2.5 2.7 Guangzhou ZU Winter 17.8±10.2 23.3±12.0 6.0±3.2 8.1±3.8 2.9 2.9 Summer 13.1±3.9 17.8±6.9 4.6±1.2 5.9±1.8 2.8 3.0 LG Winter 31.7±29.4 38.4±33.3 10.4±7.5 13.3±10.7 2.8 2.8 Summer 17.0±10.6 24.7±18.9 6.5±2.5 8.8±4.0 2.6 2.8 Average Winter 22.6±18.0 29.4±22.2 8.3±5.6 10.4±6.8 2.7 2.7 Summer 15.8±6.4 22.2±11.2 5.9±2.1 7.8±3.1 2.7 2.9

Shenzhen LH Winter 13.2±4.1 16.4±5.3 6.1±1.8 7.3±2.0 2.2 2.2 Summer 7.6±4.9 10.4±6.5 4.2±3.1 5.0±3.5 1.8 2.1

Zhuhai XZ Winter 12.2±4.4 14.5±4.6 5.0±1.6 6.0±1.8 2.5 2.4 Summer 5.4±3.4 6.9±4.3 1.9±0.9 2.5±1.0 2.9 2.7

PRDR Average Winter 14.7±11.9 19.7±16.1 6.1±4.0 7.8±5.0 2.4 2.5 Summer 9.2±6.5 12.3±10.1 4.1±2.7 5.2±3.4 2.5 2.5 a Values represent average ± standard deviation. b The numbers of samples are shown in Table 1.

ing the summer period. In other words, the carbonaceous fraction accounted for more than one-third of the PM2.5 and PM10 mass in the PRDR. 3.3 The ratios and correlation of OC to EC

Based on the relationship between organic and elemen- tal carbon, the origin of carbonaceous particles can be estimated (Turpin & Huntzicker, 1995). Chow et al. (1996) used the value of 2 for the ratio of OC to EC to identify secondary organic aerosol formation (SOA). The OC/EC ratios shown in Table 2 were less than 2 at PU monitoring stations for PM10 and PM2.5 in winter and summer. This site is adjacent to the main road leading to a cross harbor tunnel to Hong Kong Island. Direct vehicular emission of primary OC and EC accounts for the major compositions in the PM2.5 and PM10. For other sites (except HT), most of the OC/EC ratios had similar levels between 2 and 3. For urban sites, most monitoring stations are located at . -3 Fig. 2 Box plots of OC and EC concentration (µg m ) in PM2.5 and ground-level and by design not close to any major primary PM10 samples during the winter period and summer period at OC/EC emission sources such as motor vehicles, indus- four cities (HK, GZ, SZ and ZH) in Pearl River Delta Region. trial sources, etc. to avoid being unduly influenced by them. According to Turpin & Lim (2001), the amount of urban However, the OC/EC ratios were over 3 at HT for both organic matter can be estimated by multiplying the amount PM10 and PM2.5. This indicated that the presence of sec- of OC by 1.6. Thus the total carbonaceous aerosol (TCA) ondary organic aerosols and confirmed that one of the was calculated by the sum of organic matter and elemental major sources of OC at HT was SOA. The average OC/EC carbon. At the 8 sampling sites, total carbonaceous aerosol ratios for PRDR in winter (PM2.5=2.4, PM10=2.5) were (TCA) accounted for an average 40.2% of PM2.5 mass and close to those in summer (PM2.5=2.5, PM10=2.5), which 35.9% of PM10 during the winter period and accounted for indicated that the dominant emission source of carbona- an average 38.0% of PM2.5 mass and 32.9% of PM10 dur- ceous particles was motor vehicular exhaust. Cao, Lee, Ho, Zou, Zhang & Pan: Spatial and Seasonal Distributions of Atmospheric Carbonaceous Aerosols 37

2 As shown in Fig. 3, strong OC-EC correlations (R > 0.6) PRDR were (14.7±11.9) and (9.2±6.5) µg.m-3 for winter in PM2.5 and PM10 (the figure is omitted) at the four cities and summer period, respectively, and the average EC were observed. This suggests that the emission of OC and -3 concentration in PM2.5 were (6.1±4.0) and (4.1±2.7) µg.m , EC at the four cities was likely attributed to a common respectively. On average, carbonaceous aerosol ac- source, such as motor vehicular emission. The slope of counted for more than one-third of PM2.5 and PM10. The regression line in winter was very close to that in summer, OC and EC for both PM2.5 and PM10 fractions have high which indicated that there are similar emission sources levels in the winter period. The average OC/EC ratios for contributing to ambient carbonaceous particles in PRDR. PM2.5 and PM10 in the PRDR were 2.4 and 2.5. OC and Over the past 20 years, Hong Kong’s annual GDP growth EC in PRDR were found to be strongly correlated, which rate has been about 5% in real terms. Guangzhou, indicates that the dominant source of OC and EC is motor Shenzhen and Zhuhai’s economy grew continuously at a vehicular emission. To formulate effective control strate- rate of more than 10%. The usage of motor vehicle has gies for regional air pollutant in Pearl River Delta Region, increased substantially in PRDR. For example, the total further studies of the origin and composition of the primary vehicle kilometers traveled grew by 133%, from 73,200 and secondary particles will be needed. million km in 1997 to 97,900 million km in 2000 in Hong Kong (Hong Kong Environment Protection Department, 2002). Thus in PRDR, motor vehicular emission has be- Acknowledgement come the major air pollution source replacing coal- This project is supported by China NSFC project (40205018), combustion. Consequently, in order to control the air- Research Grants Council of Hong Kong (BQ-500) and G-V951 of borne carbon pollution, it is critical to control emissions the Hong Kong Polytechnic University. from the large number of motor vehicles within the region. With the fast growth of the Chinese economy after References ’s entry into the World Trade Organization, more cities will likely experience similar increase in par- Cao, J. J., Lee, S. C., Ho, K. F., Zhang, X. Y., Zou, S. C., Fung, ticulate pollution due to increasing number of motor vehi- K., Chow, J. C. & Watson, J. G. (2003). Characteristics of car- cles. bonaceous aerosol in Pearl River Delta Region, China during 2001 winter period. Atmos. Environ., in press. Chow, J. C., Watson, J. G., Crow, D., Lowenthal, D. H. & Merri- field, T. (2001). Comparison of IMPROVE and NIOSH carbon measurements. Aerosol Sci. Technol., 34, 23-34. Chow, J. C., Watson, J. G., Lu, Z., Lowenthal, D. H., Frazier, C. A., Solomon, P. A., Thuillier, R. H. & Magliano, K. (1996). De-

scriptive analysis of PM2.5 and PM10 at regionally representative locations during SJVAQS/AUSPEX. Atmos. Environ., 30, 2079- 2112. He, K. B., Yang, F. M., Ma, Y. L., Zhang, Q., Yao, X. H., Chan, C. K., Cadle, S., Chan, T. & Mulawa, P. (2001). The characteris-

tics of PM2.5 in Beijing, China. Atmos. Environ., 35, 4959-4970. Hong Kong Environment Protection Department. (2002). Study of air quality in the Pearl River Delta Region. Final report, Agree- ment No. CE 106/98. Jacobson, M. Z. (2001). Strong radiative heating due to the mix- ing state of black carbon in atmospheric aerosols. Nature, 409, Fig. 3 Relationship between organic carbon and elemental carbon 695-697.

concentration in PM2.5 samples during the winter and summer Menon, S., Hansen, J., Nazarenko, L. & Luo, Y. F. (2002). Cli- period in Pearl River Delta Region. mate effects of black carbon aerosols in China and India. Sci- ence, 297, 2250-2253. Penner, J. E. (1995). Carbonaceous aerosols influencing atmos- 4. Conclusion phere radiation: black and organic carbon. In Charlson, R. J. & Heintzenberg, J. (Eds.), Aerosol Forcing of Climate (pp.91-107). PM2.5, PM10 and carbonaceous aerosol were investi- Chichester: Wiley. gated at eight ambient air quality monitoring sites in four Turpin, B. J. & Huntzicker, J. J. (1995). Identification of secondary cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) in aerosol episodes and quantification of primary and secondary Pearl River Delta Region during the winter and summer organic aerosol concentrations during SCAQS. Atmos. Environ., 29, 3527-3544. period. The average 24-h PM2.5 concentrations at the 8 . -3 Turpin, B. J. & Lim, H. J. (2001). Species contributions to PM2.5 sites were (72.6±49.0) µg m for winter period and mass concentrations: revisiting common assumptions for esti- -3 (49.1±30.6) µg.m for summer period, respectively. The mating organic mass. Aerosol Sci. Technol., 35, 602-610. average 24-h PM10 concentrations were (111.5±83.5) Turpin, B. J., Saxena, P. & Andrews, E. (2000). Measuring and . -3 . -3 simulating particulate organics in the atmosphere: problems µg m for winter period and (74.6±51.2) µg m for sum- and prospects. Atmos. Environ., 34, 2983-3013. mer period. On average, PM2.5 constituted around 70% of PM10 mass. The average PM2.5 OC concentrations in Manuscript received March 17, 2003 and accepted March 31, 2003 CHINA PARTICUOLOGY Vol. 1, No. 1, 33-37, 2003