K.F. Ho

Spatial and seasonal distributions of carbonaceous aerosols over China

[1]xa0Simultaneous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during winter and summer seasons at 2003 in 14 cities in China. Daily PM2.5 samples were analyzed for OC and EC by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance protocol. Average PM2.5 OC concentrations in the 14 cities were 38.1 μg m−3 and 13.8 μg m−3 for winter and summer periods, and the corresponding EC were 9.9 μg m−3 and 3.6 μg m−3, respectively. OC and EC concentrations had summer minima and winter maxima in all the cities. Carbonaceous matter (CM), the sum of organic matter (OM = 1.6 × OC) and EC, contributed 44.2% to PM2.5 in winter and 38.8% in summer. OC was correlated with EC (R2: 0.56–0.99) in winter, but correlation coefficients were lower in summer (R2: 0.003–0.90). Using OC/EC enrichment factors, the primary OC, secondary OC and EC accounted for 47.5%, 31.7% and 20.8%, respectively, of total carbon in Chinese urban environments. More than two thirds of Chinas urban carbon is derived from directly emitted particles. Average OC/EC ratios ranged from 2.0 to 4.7 among 14 cities during winter and from 2.1 to 5.9 during summer. OC/EC ratios in this study were consistent with a possible cooling effect of carbonaceous aerosols over China.

Characteristics of carbonaceous aerosol in Pearl River Delta Region, China during 2001 winter period

Abstract Concentrations and distributions of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured at 8 sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of Pearl River Delta Region (PRDR), China during two winter months (January and February, 2002). PM 2.5 and PM 10 samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed using thermal optical reflectance (TOR) method. Average PM 2.5 and PM 10 level were 72.6 and 111.5xa0μgxa0m −3 , respectively, with PM 2.5 constituting 70.4% of the PM 10 mass. The average OC and EC concentrations in PM 2.5 were 14.7 and 6.1xa0μgxa0m −3 , respectively, while those in PM 10 were 19.7 and 7.8xa0μgxa0m −3 , respectively. The carbonaceous aerosol accounted for 40.2% of the PM 2.5 and 35.9% of the PM 10 . The average OC/EC ratio was 2.4 for PM 2.5 and 2.5 for PM 10 , which are comparable with most urban cities in the world. The OC and EC in PRDR were found to be strongly correlated (correlation coefficients >0.7). Secondary organic carbon was found to constitute 42.6% and 38.4% of the total organic carbon in PM 2.5 and PM 10 , respectively.

Characterization of chemical species in PM2.5 and PM10 aerosols in Hong Kong

Aerosol samples for PM10 and PM2.5 were collected in wintertime from November 2000 to February 2001 at three different sampling locations in Hong Kong. PM10 and PM2.5 were collected by high-volume (hi-vol.) samplers and the concentrations of major elements, ions, organic and elemental carbons were quantified. The ratios of PM2.5/PM10 were 0.61 and 0.78 at the PolyU campus and Kwun Tong (KT), respectively. These results indicated that the concentrations of PM2.5 contribute the majority of the PM10 fraction. The concentrations of anthropogenic species (e.g. Pb and Cu) in PM10 and PM2.5measured at urban areas were generally higher than at an urban background site (Hok Tsui, HT). The major fractions of sulfate at three monitoring sites are non-sea-salts (nss) sulfates. Although HT is located in coastal areas, the contribution of sea salts to sulfate in fine particles was small, indicating a substantial anthropogenic origin. The OC/EC ratios were less than 2 in PolyU and KT monitoring stations for PM10 and PM2.5. However, the OC/EC ratios were over 3 at HT for both PM10 and PM2.5. This indicates the presence of secondary organic aerosols. Correlations between OC and EC as well as OC and sulfate in HT during both seasons were used to prove that atmospheric transport and transformation of anthropogenic organic species from northeastern area was the dominant source in winter. The chemical composition of the samples was reconstructed from the observed elemental composition. The contribution of the seven components, namely crustal matter, sea salt, ammonium, sulfate, nitrate, elemental carbon and organic matter accounted for 77–84% of the PM10 and PM2.5 mass in the urban area (PolyU and KT) and 74% for Hok Tsui (HT). Sulfate, organic matter and elemental carbon are the major constituents in particles especially in PM2.5 collected at PolyU and KT. The major constituents of PM10 in HT are sea salt and sulfate.

CHARACTERIZATION OF SELECTED VOLATILE ORGANIC COMPOUNDS, POLYCYCLIC AROMATIC HYDROCARBONS AND CARBONYL COMPOUNDS AT A ROADSIDE MONITORING STATION

Abstract Volatile organic compounds (VOCs), PAHs and carbonyl compounds are the major toxic components in Hong Kong. Emissions from motor vehicles have been one of the primary pollution sources in the metropolitan areas throughout Hong Kong for a long time. A 1-yr monitoring program for VOCs, PAHs and carbonyl compounds had been performed at a roadside urban station at Hong Kong Polytechnic University in order to determine the variations and correlations of each selected species (VOCs, PAHs and carbonyl compounds). This study is aimed to analyze toxic volatile organic compounds (benzene, toluene, ethylbenzene and xylene), two carbonyl compounds (formaldehyde, acetaldehyde), and selective polycyclic aromatic hydrocarbons. The monitoring program started from 16 April 1999 to 30 March 2000. Ambient VOC concentrations, many of which originate from the same sources as particulate PAHs and carbonyls compounds, show significant quantities of benzene, toluene and xylenes. Correlations and multivariate analysis of selected gaseous and particulate phase organic pollutants were performed. Source identification by principle component analysis and hierarchical cluster analysis allowed the identification of four sources (factors) for the roadside monitoring station. Factor 1 represents the effect of diesel vehicle exhaust. Factor 2 shows the contribution of aromatic compounds. Factor 3 explains photochemical products—formaldehyde and acetaldehyde. Factor 4 explains the effect of gasoline vehicle exhaust.

Characterization of PM10 and PM2.5 source profiles for fugitive dust in Hong Kong

Abstract PM 10 and PM 2.5 chemical source profiles from Hong Kong were investigated for paved road dust and soil. These profiles are needed for urban-scale speciated emissions inventories and for source apportionment by receptor modeling. Five urban soil and five paved road dust samples were collected, dried and sieved, resuspended in a laboratory chamber, air drawn through PM 10 and PM 2.5 inlet onto Teflon and quartz filters. The filter samples were submitted for both gravimetric and chemical analyses. Chemical analyses included X-ray fluorescence for elemental composition, ion chromatography for water soluble chloride, nitrate, sulfate, atomic absorption spectrophotometry for water soluble sodium and potassium, automated colorimetric analysis for ammonium and thermal/optical reflectance analysis for carbon species. The PM 2.5 constituted 11–30% of the PM 10 in all geological samples. Al, Si and organic carbon (OC) are abundant constituents in all paved road dust and soil samples. The chemical abundances of PM 2.5 and PM 10 for a given source type were similar for most species. In addition, results from resuspended soil (three sets), paved road dust (five sets), aggregate (three sets) and cement (two sets) were obtained from Hong Kong Environmental Protection Department (HKEPD) for comparison as well as mass closure analysis.

Polycyclic aromatic hydrocarbons (PAHs) and carbonyl compounds in urban atmosphere of Hong Kong

Polycyclic aromatic hydrocarbons (PAHs) and carbonyls compounds are becoming a major component of atmospheric toxic air pollutants (TAPs) in Hong Kong. Many studies in Hong Kong show that traffic emission is one of the most significant contributors in urban area of Hong Kong. A twelve months monitoring program for PAHs and carbonyl compounds started on 10 April 1999 including a two weeks intensive sampling in winter had been performed at a roadside urban station at Hong Kong Polytechnic University in order to determine the monthly and seasonal variations of PAHs and carbonyl concentrations. The objective of this study is to characterize the roadside concentrations of selected TAPs (PAHs and carbonyl compounds) and to compare with the long-term compliance monitoring data acquired by Hong Kong Environmental Protection Department (EPD). Monthly variations, seasonal variations and winter/summer ratios at the monitoring station are discussed.

Characterization of ambient volatile organic compounds at a landfill site in Guangzhou, South China.

Ambient air monitoring was conducted at Datianshan landfill, Guangzhou, South China in 1998 to investigate the seasonal and horizontal variations of trace volatile organic compounds (VOCs). Twelve sampling points over the Datianshan landfill were selected and samples were collected simultaneously using Carbontrap(TM) adsorption tubes. Thirty eight VOCs were detected in the winter, whereas 60 were detected in the summer. The VOC levels measured in summer were alkanes, 0.5-6.5 microg/m(3); aromatics, 2.3-1667 microg/m(3); chlorinated species, 0.2-31 microg/m(3); terpines, 0.1-34 microg/m(3); carbonyl species, 0.3-5.6 microg/m(3) and naphthalene and its derivatives, 0.4-27 microg/m(3). Compared to the summer samples the VOC levels in winter were much lower (mostly 1-2 orders of magnitude lower). The aromatics are dominant VOCs in landfill air both in winter and summer. High levels of alkylbenzene and terpines such as methyl-isopropylbenzene (max 1667 microg/m(3)) and limonene (max 162 microg/m(3)) cause undesirable odor. The similar correlation coefficients of BTEX in summer and winter suggest VOCs emissions were from landfill site sources. The variation of BTEX ratio at landfill site is different from that in the urban area of Guangzhou. It shows that the ambient VOCs at landfill site were different from the urban areas.

Dicarboxylic acids；ketocarboxylic acids；and dicarbonyls in the urban atmosphere of China

[1]xa0PM2.5 samples from 14 Chinese cities during winter and summer of 2003 were analyzed for 29 water-soluble organic species including diacids, ketoacids and dicarbonyls using a capillary GC and GC/MS. Homologous series of α,ω-dicarboxylic acids (C2–C12) and ω-oxocarboxylic acids (C2–C9) were detected as well as aromatic (phthalic) acid, α-ketoacid (pyruvic acid) and α-dicarbonyls (C2–C3). Molecular distributions of diacids demonstrated that oxalic (C2) acid was the most abundant species followed by C3 or C4 diacids. Higher carbon number diacids were less abundant. C2 diacid constituted 42–74% of total diacids (211–2162 ng m−3), corresponding to 0.15–2.83% of PM2.5 mass. In winter, the highest concentrations were observed in the southern city of Guangzhou (1886 ng m−3), while the lowest concentrations were observed in the northwest city of Jinchang (388 ng m−3). In summer, the highest concentrations were found in the northern city of Beijing (1598 ng m−3), whereas the lowest concentrations were found in Jinchang (223 ng m−3). Spatial variations of water-soluble diacids were characterized by higher concentrations in the south and lower concentrations in the north during winter whereas highest concentrations were observed in the north and midwest during summer. These spatial and seasonal distributions are consistent with photochemical production and the subsequent accumulation under different meteorological conditions.

Characterization of airborne carbonate over a site near Asian dust source regions during spring 2002 and its climatic and environmental significance

[1]xa0During spring 2002, three dust storm events were monitored by filter sampling in Xian near an Asian dust source region of northwest China. The carbonate (CO32−) fraction was determined by sample acidification and thermal evolution. The CO32− accounted for 8.0 ± 0.8% of particles with aerodynamic diameter ≤2.5 μm (PM2.5) during dust storms and 4.7 ± 3.0% of PM2.5 between storms. The ratios of calcium to carbonate carbon were consistent with those of calcite (CaCO3). The δ13C and δ18O abundances in dust storm samples were −2.7 ± 0.7‰ and −5.8 ± 1.5‰, which differed from −8.3 ± 1.9‰ for δ13C and −10.8 ± 2.0‰ for δ18O during normal conditions. The δ13C is positively correlated with δ18O values (r = 0.78). This first measurement of isotopic abundance in Asian dust indicates the potential to quantify its contribution at distant locations using receptor models. By increasing the alkalinity of ocean water in the Pacific Ocean and buffering the atmospheric acidity of east Asia, the large amounts of airborne CO32− (as high as 44.8 Tg yr−1) entrained by Asian dust may provide an important atmospheric alkaline carbon reservoir for large-scale climatic and environmental changes.

Black carbon measurement in a coastal area of South China

Aethalometer, hourly BC concentrations ranged from 63.0 ng/m 3 to 17.3 mg/m 3 , showing a clear seasonal pattern with high concentrations in winter, spring, and fall and low values in summer. During the winter, high BC concentrations occurred frequently as a result of southward long-range transport of polluted air masses in the boundary layer over the Asian continent. Anthropogenic emissions in coastal areas of southeastern China were the major potential sources for the observed pollutants. During the summer, high BC concentrations were measured occasionally when the air masses came from the northwest. These anthropogenic pollutants were found to be regional in nature, originating from sources in the Pearl River Delta (PRD) region, which included emissions from residential and agricultural combustion, industry, power plants, motor vehicles, and ships.