| Atmospheric particles are one of the major air pollutants in China. They can affect human health, reduce visibility, alter the chemistry and the radiation balance of the atmosphere, and influence the globalclimate change. In the present study, several filed studies were conducted at Beijing, Jinan (Shandong Province) and Mount Heng (Hunan Province). A long term records on particle compositions and acid rain in Hong Kong were also analyzed. The targets of this study are to evaluate the performances of several PM2.5measuringtechniques in the ambient of heavy particle pollution in China, to study the long term trends of particle compositions and rain acidity, and to understand the particle size distribution in the typical regions of China.Base on two filed studies, which were conducted at an urban site in Jinan, Shandong province, during the winter of2007and at a rural site near Beijing in the summer of2008, a comparison was aided to evaluate the performances of two filter-based samplers, including a Thermo Anderson Chemical Speciation Monitor (RAAS) and a honeycomb denuder filter-pack system (HCD), a Micro Orifice Uniform Deposit Impactor (MOUDI) and a real-time ambient ion monitor (AIM, URG9000B) in measuring atmospheric concentrations of PM2.5sulfate and nitrate. The AIM was first compared with the honeycomb denuder filter-pack system which was considered to have minimal sampling artifacts. After some modifications made to it, the AIM showed good performance for both sulfate and nitrate measurement at the two sites and was then used to evaluate other instruments. For the un-denuded RAAS, the extent of sampling artifacts for nitrate on quartz filters was negligible, while that on Teflon filters was also minimal at high nitrate concentrations (>10μgm-3); however, lossthrough evaporation was significant (～75%) at low nitrate concentrations under hot summer conditions. The MOUDI using aluminum substrates suffered a significant loss of nitrate (50-70%) under summer conditions due to evaporation. Considering that the aluminum substrates are still being widely used to obtain size-resolved aerosol compositions because of their low cost and accurate mass weighed, caution should be taken about the potential significant under determination of semi-volatile components such as ammonium nitrate.A14-year records (1995-2008) of PM10compositions and acid rain in the subtropical city of Hong Kong were analyzed, with the aim to study the long term trends and seasonal variations of particle compositions and rain acidity. A linear regression method and a Regional Kendall test are employed for trend calculations. There are increasing overall trends in ambient concentrations of PM10sulfate, nitrate, As, Cd, Cr and Zn, with the change rates of0.25μg/m3/yr,0.064μg/m3/yr,0.14ng/m3/yr,0.04ng/m3/yr,0.054ng/m3/yr and9.0ng/m3/yr. Rain acidity also showed a significant increase trend, with the change rate of pH of-0.013/yr. Typical seasonal variations were observed for all the PM species and rain acidity, largely in relation to the Asian monsoon, that the highest values appeared in winter (Dec or Jan), and the lowest values appeared in summer (Jun or Jul). Backward trajectories were computed to help identify the origin of large-scale air masses arriving in Hong Kong. By comparing the trends of PM10sulfate and PM10nitrate concentrations in the air masses originating from eastern China and the changes in emissions of their precursors in eastern China, we found the trend of PM10sulfate in Hong Kong was mainly determined by the long range transport from eastern China; while the trend of PM10nitrate was contributed by both the local and long distance sources. In addition, the rain acidity and atmospheric heavy metals in Hong Kong were also largely influenced by the emissions from mainland China. These results demonstrate the important impact exerted by long-distance sources and suggest a need to consider the impact of super-regional transport when formulating air-quality management strategy in Hong Kong in future.Two filed campaigns were conducted at an urban site in Beijing during the summer of2008, and at a mountain top site of Mt. Heng, Hunan province, to investigate the particle number concentrations, size distributions, particle formation rates and particle growth rates at the two typical regions of China. Urban Beijing showed a high number concentrations (6012±3218#/cm-3) with the peaks mostly appearing at the Aitken mode, while the particle number concentrations at Mt. Heng were much lower (1170±1075#/cm-3) with the peaks usually appearing at the Aitken and/or accumulation modes. The pattern of mean particle number concentrations in the free troposphere (night time) at Mt. Heng showed an obvious single peak in the accumulation mode (100-200nm). Air masses played a role on the particle size distribution in the free troposphere at Mt. Heng. In the continental air masses, particle number concentrations showed a bimodal size distribution, with the two peaks in the Aitken (40-60nm) and accumulation (100-200nm) modes, respectively; however, there were only single peaks in the accumulation mode (100-200nm) in the regional air masses. New particle formation and growth events were often observed at the both sites, which approximatelyaccounted for40%of the sampling days at the Beijing site and27%at Mt. Heng. At Beijing site, the formation rates of Class I nucleation events were between0.48#/cm3/s and2.47#/cm3/s, with the mean value of1.01#/cm3/s; the growth rates were between4.9nm/h and19.8nm/h, with the mean value of7.7nm/h. While at Mt. Heng, the formation rates of Class I nucleation events were between0.11#/cm3/s and0.55#/cm3/s, with the mean value of0.34#/cm3/s; the growth rates were between2.7nm/h and16.7nm/h, with the mean value of7.7nm/h.During the2008Olympics, we conducted an intensive field campaign at three surface sites suited at the upwind, urban and downwind regions of Beijing, to investigate the impact of emission control measures and regional transport on the air quality of Beijing. The results reveal different responses of secondary pollutants to the control measures from primary pollutants. Ambient concentrations of the primary pollutants, especially the vehicle-related nitrogen oxides (NOX) and volatile organic compounds (VOCs) at an urban sitedropped significantly after full control was put in place, but the levels of ozone, sulfate and nitrate in PM2.5increasedcompared to the period prior to the full control. Air quality (for both primary and secondary pollutants) improved significantly during the Games, which were associated with the changes in weather conditions (prolonged rainfall, decreased temperature, and more frequent air masses from clean regions). Wind data and back trajectories indicated the contribution of regional pollution from the North China Plain. In the ozone episode days, regional transport contributed34%-88%of the ozone peak concentrations, and69%-91%of the CO peak concentrations. The acid rain pollution became more serious after the full control put into effect, indicating the control measures targeting on other air pollutants (such as coarse particles) may bring some negative effect on the acid rain problem, especially in northern China. These results suggest that the implemented control measures are not enough to improve the air quality under the adverse weather conditions, especially for the secondary pollutants, such as ozone, sulfate and nitrate. This study demonstrated the importance of simultaneity of pollution control on multi-pollutants at multi-regions to improve the regional air pollution problems (such as haze and acid rain). |
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