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  • 1
    Publication Date: 2009-08-31
    Description: Tropospheric ozone is of great importance with regard to air quality, atmospheric chemistry, and climate change. In this paper we report the first continuous record of surface ozone in the background atmosphere of South China. The data were obtained from 1994 to 2007 at a coastal site in Hong Kong, which is strongly influenced by the outflow of Asian continental air during the winter and the inflow of maritime air from the subtropics in the summer. Three methods are used to derive the rate of change in ozone. A linear fit to the 14-year record shows that the ozone concentration increased by 0.58 ppbv/yr, whereas comparing means in years 1994–2000 and 2001–2007 gives an increase of 0.87 ppbv/yr for a 7-year period. The ozone changes in air masses from various source regions are also examined. Using local wind and carbon monoxide (CO) data to filter out local influence, we find that ozone increased by 0.94 ppbv/yr from 1994–2000 to 2001–2007 in air masses from Eastern China, with similar changes in the other two continent-influenced air-mass groups, but no statistically significant change in the marine air. An examination of the nitrogen dioxide (NO2) column obtained from GOME and SCIAMACHY reveals an increase in atmospheric NO2 in China's three fastest developing coastal regions, whereas NO2 in other parts of Asia decreased during the same period, and no obvious trend over the main shipping routes in the South China Sea was indicated. Thus the observed increase in background ozone in Hong Kong is most likely due to the increased emissions of NO2 (and possibly volatile organic compounds (VOCs) as well) in the upwind coastal regions of mainland China. The CO data at Hok Tsui showed less definitive changes compared to the satellite NO2 column. The increase in background ozone likely made a strong contribution (81%) to the rate of increase in "total ozone" at an urban site in Hong Kong, suggesting the need to consider distant sources when developing long-term strategies to mitigate local ozone pollution.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
    Publication Date: 2010-08-16
    Description: This paper presents the first results of the measurements of trace gases and aerosols at three surface sites in and outside Beijing before and during the 2008 Olympics. The official air pollution index near the Olympic Stadium and the data from our nearby site revealed an obvious association between air quality and meteorology and different responses of secondary and primary pollutants to the control measures. Ambient concentrations of vehicle-related nitrogen oxides (NOx) and volatile organic compounds (VOCs) at an urban site dropped by 25% and 20–45% in the first two weeks after full control was put in place, but the levels of ozone, sulfate and nitrate in PM2.5 increased by 16%, 64%, 37%, respectively, compared to the period prior to the full control; wind data and back trajectories indicated the contribution of regional pollution from the North China Plain. Air quality (for both primary and secondary pollutants) improved significantly during the Games, which were also associated with the changes in weather conditions (prolonged rainfall, decreased temperature, and more frequent air masses from clean regions). A comparison of the ozone data at three sites on eight ozone-pollution days, when the air masses were from the southeast-south-southwest sector, showed that regional pollution sources contributed 〉34–88% to the peak ozone concentrations at the urban site in Beijing. Regional sources also contributed significantly to the CO concentrations in urban Beijing. Ozone production efficiencies at two sites were low (~3 ppbv/ppbv), indicating that ozone formation was being controlled by VOCs. Compared with data collected in 2005 at a downwind site, the concentrations of ozone, sulfur dioxide (SO2), total sulfur (SO2+PM2.5 sulfate), carbon monoxide (CO), reactive aromatics (toluene and xylenes) sharply decreased (by 8–64%) in 2008, but no significant changes were observed for the concentrations of PM2.5, fine sulfate, total odd reactive nitrogen (NOy), and longer lived alkanes and benzene. We suggest that these results indicate the success of the government's efforts in reducing emissions of SO2, CO, and VOCs in Beijing, but increased regional emissions during 2005–2008. More stringent control of regional emissions will be needed for significant reductions of ozone and fine particulate pollution in Beijing.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
  • 4
    Publication Date: 2009-04-28
    Description: Tropospheric ozone is of great importance with regard to air quality, atmospheric chemistry, and climate change. In this paper we report the first continuous record of surface ozone in the background atmosphere of South China. The data were obtained from 1994 to 2007 at a coastal site in Hong Kong, which is strongly influenced by the outflow of Asian continental air during the winter and the inflow of maritime air from the subtropics in the summer. Overall, the ozone concentration increased by an averaged rate of 0.55 ppbv/yr, with a larger increase in autumn (0.68 ppbv/yr). We also examine the trend in air masses from various source regions in Asia. Using local wind and concurrently measured carbon monoxide (CO) data to filter out local emissions, the mean ozone in air masses from eastern China, using the pooled averaging method, increased by 0.64 ppbv/yr, while ozone levels in other air-mass groups showed a positive trend (0.29–0.67 ppbv/yr) but with lower levels of statistical significance. An examination of the nitrogen dioxide (NO2) column concentration data obtained from GOME and SCIAMACHY reveals an increase in atmospheric NO2 in the three fastest developing coastal regions of China, whereas NO2 in other parts of Asia decreased during the same period. It is believed that the observed increase in background ozone in Hong Kong is primarily due to the increased emissions of NO2 (and possibly volatile organic compounds (VOCs) as well) in the upwind coastal regions of mainland China, which is supported by the observed positive CO trend (5.23 ppbv/yr) at the site. The increase in background ozone contributed two thirds of the annual increase in ''total ozone'' in the downwind urban areas of Hong Kong, suggesting the need to consider distant sources when developing long-term strategies to mitigate local ozone pollution, although short-term strategies should be aimed at sources in Hong Kong and the adjacent Pearl River Delta.
    Electronic ISSN: 1680-7375
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 5
    Publication Date: 2010-05-12
    Description: This paper presents the first results of the atmospheric measurements of trace gases and aerosols at three surface sites in and around Beijing before and during the 2008 Olympics. We focus on secondary pollutants including ozone, fine sulfate and nitrate, and the contribution of regional sources in summer 2008. The results reveal different responses of secondary pollutants to the control measures from primary pollutants. Ambient concentrations of vehicle-related nitrogen oxides (NOx) and volatile organic compounds (VOCs) at an urban site dropped by 25% and 20–45% in the first two weeks after full control was put in place, but the levels of ozone, sulfate and nitrate in PM2.5 increased by 16%, 64%, 37%, respectively, compared to the period prior to the full control; wind data and back trajectories indicated the contribution of regional pollution from the North China Plain. Air quality (for both primary and secondary pollutants) improved significantly during the Games, which were also associated with the changes in weather conditions (prolonged rainfall, decreased temperature, and more frequent air masses from clean regions). A comparison of the ozone data at three sites on eight ozone-pollution days, when the air masses were from the southeast-south-southwest sector, showed that regional pollution sources contributed 34%–88% to the peak ozone concentrations in urban Beijing. Ozone production efficiencies at two sites were low (~3 ppbv/ppbv), indicating that ozone formation was being controlled by VOCs. Compared with data collected in 2005 at a downwind site, the concentrations of ozone, sulfur dioxide (SO2), total sulfur (SO2+PM2.5 sulfate), carbon monoxide (CO), reactive aromatics (toluene and xylenes) sharply decreased (by 8–64%) in 2008, but no significant changes were observed for the concentrations of PM2.5, fine sulfate, total odd reactive nitrogen (NOy), and longer lived alkanes and benzene. We suggest that these results indicate the success of the government's efforts in reducing emissions of SO2, CO, and VOCs in Beijing. However, further control of regional emissions is needed for significant reductions of ozone and fine particulate pollution in Beijing.
    Electronic ISSN: 1680-7375
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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