C. Y. Chan

Urban roadside aromatic hydrocarbons in three cities of the Pearl River Delta, People's Republic of China

Urban roadside levels of benzene, toluene, ethylbenzene and xylenes (BTEX) were investigated in three typical cities (Guangzhou, Macau and Nanhai) in the Pearl River Delta Region of south China. Air samples were collected at typical ground level microenvironments by multi-bed adsorbent tubes. The BTEX concentrations were determined by thermal desorption–gas chromatography–mass selective detector (TD–GC–MSD) technique. The mean concentrations of benzene, toluene, ethylbenzene and xylenes were, respectively, 51.5, 77.3, 17.8 and 81.6mg/m 3 in Guangzhou, 34.9, 85.9, 24.1, 95.6mg/m 3 in Macau, and 20.0, 39.1, 3.0 and 14.2mg/m 3 in Nanhai. The relative concentration distribution pattern and mutual correlation analysis indicated that in Macau BTEX were predominantly traffic-related while in Guangzhou benzene had sources other than vehicle emission. In Nanhai, both benzene and toluene had different sources other than vehicle emission. The samples collected from Guangzhou showed that BTEX had significant higher concentrations in November than those in July. r 2002 Elsevier Science Ltd. All rights reserved.

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.

Characteristics of nonmethane hydrocarbons (NMHCs) in industrial, industrial-urban, and industrial-suburban atmospheres of the Pearl River Delta (PRD) region of south China

Author(s): Chan, LY; Chu, KW; Zou, SC; Chan, CY; Wang, XM; Barletta, B; Blake, DR; Guo, H; Tsai, WY | Abstract: In a study conducted in late summer 2000, a wide range of volatile organic compounds (VOCs) were measured throughout five target cities in the Pearl River Delta (PRD) region of south China. Twenty-eight nonmethane hydrocarbons (NMHCs; 13 saturated, 9 unsaturated, and 6 aromatic) are discussed. The effect of rapid industrialization was studied for three categories of landuse in the PRD: Industrial, industrial-urban, and industrial-suburban. The highest VOC mixing ratios were observed in industrial areas. Despite its relatively short atmospheric lifetime (2-3 days), toluene, which is largely emitted from industrial solvent use and vehicular emissions, was the most abundant NMHC quantified. Ethane, ethene, ethyne, propane, n-butane, i-pentane, benzene, and m-xylene were the next most abundant VOCs. Direct emissions from industrial activities were found to greatly impact the air quality in nearby neighborhoods. These emissions lead to large concentration variations for many VOCs in the five PRD study cities. Good correlations between isoprene and several short-lived combustion products were found in industrial areas, suggesting that in addition to biogenic sources, anthropogenic emissions may contribute to urban isoprene levels. This study provides a snapshot of industrial, industrial-urban, and industrial-suburban NMHCs in the five most industrially developed cities of the PRD. Increased impact of industrial activities on PRD air quality due to the rapid spread of industry from urban to suburban and rural areas, and the decrease of farmland, is expected to continue until effective emission standards are implemented. Copyright 2006 by the American Geophysical Union.

The effect of commuting microenvironment on commuter exposures to vehicular emission in Hong Kong

Vehicular exhaust emission has gradually become the major air pollution source in modern cities and traffic related exposure is found to contribute significantly to total human exposure level. A comprehensive survey was conducted from November 1995 to July 1996 in Hong Kong to assess the effect of traffic-induced air pollution inside different commuting microenvironments on commuter exposure. Microenvironmental monitoring is performed for six major public commuting modes (bus, light bus, MTR, railway, tram, ferry), plus private car and roadside pavement. Traffic-related pollutants, CO, NOx, THC and O3 were selected as the target pollutants. The results indicate that commuter exposure is highly influenced by the choice of commuting microenvironment. In general, the exposure level in decreasing order of measured pollutant level for respective commuting microenvironments are: private car, the group consisting light bus, bus, tram and pavement, MTR and train, and finally ferry. In private car, the CO level is several times higher than that in the other microenvironments with a trip averaged of 10.1 ppm and a maximum of 24.9 ppm. Factors such as the body position of the vehicle, intake point of the ventilation system, fuel used, ventilation, transport mode, road and driving conditions were used in the analysis. Inter-microenvironment, intra-microenvironment and temporal variation of CO concentrations were used as the major indicator. The low body position and low intake point of the ventilation system of the private car are believed to be the cause of higher intake of exhaust of other vehicles and thus result in high pollution level in this microenvironment. Compared with other metropolis around the world and the Hong Kong Air Quality Objectives (HKAQO), exposure levels of commuter to traffic-related air pollution in Hong Kong are relatively low for most pollutants measured. Only several cases of exceedence of HKAQO by NO2 were recorded. The strong prevailing wind plus the channeling effect created by the harbor, the fuel used, the relative abundance of new cars and the successful implementation of the vehicle emission control program are factors that compensate the effect of the emission source strength and thus lead to low exposure levels.

Spatial variation of mass concentration of roadside suspended particulate matter in metropolitan Hong Kong

Abstract This study conducted roadside particulate sampling to measure the total suspended particulate (TSP), PM10 (particles

Cyclic organosilicon compounds in ambient air in Guangzhou, Macau and Nanhai, Pearl River Delta

Silicon is present in the Earth’s atmosphere as a consequence of several processes including the release of Si compounds from anthropogenic sources, but little information is available on airborne Si compounds of anthropogenic origins. In this study ambient air samples from Guangzhou, Macau and Nanhai in the Pearl River Delta, South China were collected by sorbent tubes for the determination of concentrations of volatile organosilicon compounds. Samples were analysed by thermal desorption followed by a GC–MSD technique for compound identification and quantitative analysis. Hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasilo-xane (D4) were found to be the two dominant organosilicon compounds in the air. In Guangzhou, higher total D3 and D4 concentrations were observed in the industrial area, landfill and waste water treatment plant, while the lowest levels occurred in suburb forest. Two types of linear correlation between D3 and D4 were found in Guangzhou samples, indicating different sources of these organosilicon compounds. Samples in Macau and Nanhai showed different D3 and D4 relationships from the samples in Guangzhou. # 2001 Elsevier Science Ltd. All rights reserved.

The effects of Southeast Asia fire activities on tropospheric ozone, trace gases and aerosols at a remote site over the Tibetan Plateau of Southwest China

Tropospheric ozone (O3), carbon monoxide (CO), total reactive nitrogen (NOy) and aerosols (PM2.5 and PM10) were measured on the southeastern Tibetan Plateau at Tengchong (25.01◦N, 98.3◦E, 1960 m a.s.l.) in Southwest China, where observational data is scarce, during a field campaign of the TAPTO-China (Transport of Air Pollutants and Tropospheric O3 over China) in the spring of 2004. Fire maps derived from satellite data and backward air trajectories were used to trace the source regions and transport pathways of pollution. Ozone, CO, NOy, PM10 and PM2.5 had average concentrations of 26 ± 8 ppb, 179 ± 91 ppb, 2.7 ± 1.2 ppb and 34 ± 23 and 28 ± 19 μg/m3, respectively. The measured O3 level is low when compared with those reported for similar longitudinal sites in Southeast (SE) Asia and northeastern Tibetan Plateau in Northwest China suggesting that there exist complex O3 variations in the Tibetan Plateau and its neighbouring SE Asian region. High levels of pollution with hourly averages of O3, CO, NOy, PM10 and PM2.5 concentrations up to 59, 678 and 7.7 ppb and 158 and 137 μg/m-3, respectively, were observed. The increase of pollutants in the lower troposphere was caused by regional built-up and transport of pollution from active fire regions of the SE Asia subcontinent and from northern South Asia. Our results showed that pollution transport from SE Asia and South Asia had relatively stronger impacts than that from Central and South China on the abundance of O3, trace gases and aerosols in the background atmosphere of the Tibetan Plateau of Southwest China.

Urban and background ozone trend in 1984-1999 at subtropical Hong Kong, South China

There has been a growing concern for the impact of increasing Asian pollutant emissions on climate, atmospheric chemistry and air quality of the downwind region. In this study, we examined the long-term records of surface ozone (O3) and its precursors (NO and NO2) measured in Hong Kong from the early 1980s to 2000. The urban O3 concentration has shown more than two-fold increase since the early 1980s and the increase was especially apparent after the late 1980s. The O3 increases led to frequent O3 pollution episodes and caused deterioration of local air quality. Such increases were not accompanied by local NO and NO2 concentration changes in Hong Kong but coincided with the increase of NOx emissions from Asia. We derived the background O3 concentration for the South China region using the early morning (1:00–5:00 a.m. local standard time) data and linked the transport of Asian emissions and background O3 change using back air trajectory and local meteorology. The derived background O3 concentration shows an increase rate of 1.5% per year over the 15-year period from 1984 to 1999, which is close to that in the midlatitudes of East Asia at Japan. The sharp O3 increase is related to the regional O3 built-up in South China and the East Asia region due to the increases in the pollutant emissions as a result of rapid urban and industrial development in the region.

Carbon monoxide levels measured in major commuting corridors covering different landuse and roadway microenvironments in Hong Kong

Abstract Vehicle exhaust is the major source of pollutant in modern cities. About half of Hong Kong residents are living in suburban or rural areas. They need to traverse through tunnels, highways, urban street canyons and other road conditions in different landuse areas when they traverse to work in urban centres or new towns. Also, there is increasing traffic, especially trucks across the border between Hong Kong and mainland China via several border highways. This study helps us in assessing the exposure level of suburban and cross border commuters. Carbon monoxide (CO) is used as a tracer for traffic emission. An experimental vehicle traversing major commuting corridors were used to measure CO levels in different landuse and roadway microenvironments including tunnels and highways. The air samples were taken simultaneously at the outside and inside of a travelling vehicle. Result indicates that the pattern of fluctuation of the out-vehicle and in-vehicle CO level vary with different landuse areas. The variation pattern of in-vehicle CO level is closely related to that of out-vehicle level. The effects of the out-vehicle CO concentration on the in-vehicle CO concentration under different roadway conditions in various landuse categories are examined. There is an indication that external air pollutants penetrated into the in-vehicle compartment through car body cracks, ventilation system. From our observation, the exhaust of a nearby petrol vehicle contributed significantly to the in-vehicle CO level. The use of low standard of diesel fuel from Shenzhen in mainland China leads to higher CO level near border area.

Effects of 1997 Indonesian forest fires on tropospheric ozone enhancement, radiative forcing, and temperature change over the Hong Kong region

Tropospheric ozone enhancements were measured over Hong Kong (22.2°N, 114.3°E) by electrochemical concentration cell ozonesondes during the 1997 period when many forest fires were burning in Indonesia. The enhancements have a maximum ozone concentration of up to 130 ppbv and an ozone-enhanced layer depth of 10 km. We used Total Ozone Mapping Spectrometer, advanced very high resolution radiometer satellite image, and back air trajectory to identify the source region and the transport pattern of ozone. The strong tropospheric ozone enhancements covered all of tropical Southeast Asia and subtropical south China. They were due to photochemical ozone buildup from the biomass burning emissions from the Indonesian fires. The ozone-rich air mass was transported to Hong Kong following the east Asia local Hadley circulation and an abnormal anticyclonic flow related to the El Nino phenomenon in the tropical western Pacific. A rough estimation of the radiative forcing due to the ozone enhancement was carried out for two cases in October and December in 1997 using a normalized tropospheric ozone radiative forcing parameter derived from the Unified Chemistry-Climate model [Mickley et al., 1999]. The ozone enhancements induced an additional radiative forcing of 0.26 and 0.48 Wm−2 compared to the normal total forcing of 0.48 and 0.39 Wm−2 in October and December over the Hong Kong region. Estimation of the associated surface temperature change suggests that enhanced ozone from biomass burning on the scale of the 1997 Indonesian fires may have significant impact on regional surface temperature change.