Yu Song, Wei Dai, Xuesong Wang,* Mingming Cui, Hang Su, Shaodong Xie, and Yuanhang Zhang, Department of Environmental Sciences, Peking University – January 1, 2008
Abstract
Respirable suspended particulates (RSP, i.e., particles with an aerodynamic diameter of 10 μm or less) were measured in 2004 and 2005 at seven sites in the rapidly developing Guangzhou area of China. The average RSP concentration was 126 μg m-3, a high level that could be very harmful to human health. The chemical species composition of the RSP, including organic and elemental carbon, water-soluble ions, and elemental compositions, was also analyzed. The organics and sulfate may be the major components of RSP mass concentrations. Positive matrix factorization (PMF) was used to identify the sources of RSP as secondary sulfates (32%), secondary nitrates (6%), biomass burning (15%), coal fly ash/cement (18%), sea salt (3%), crustal dust (5%), vehicle exhaust (6%), and coal-fired power plants (3%). Reducing coal combustion and controlling vehicle emissions would alleviate RSP pollution, as most of the precursors were components of coal burning emissions and vehicular exhaust.
Conclusions
Guangzhou, a rapidly developing megacity in China, suffers from a high level of RSP pollution. Our results show that organics and sulfate were dominant in RSP mass concentrations. Climatologic conditions, that is, high temperature, high RH, and strong solar radiation, determined by the geographic location of Guangzhou (low latitude and proximity to the sea), resulted in high rates of VOC transformation to secondary organics and SO2 transformation to secondary sulfate. However, ammonium nitrate was unstable at high temperatures. These results also demonstrated the spatial
variability of RSP levels. Urban and industrial areas often had higher levels of RSP pollution. Source apportionment identified three major sources contributing to RSP pollution: secondary products, coal fly ash/cement, and biomass burning.
To alleviate RSP pollution in Guangzhou, some control measures should be implemented. First, reducing or replacing coal-fired power stations with advanced coal gasification technologies and desulfurizing the smoke emitted by coal-fired manufacturing plants could be important pathways to control SO2 and coal fly ash emission. These methods could help abate the secondary sulfate and coal fly ash in RSP. Second, public transportation such as subways and buses should be improved to limit the further increase in the number of automobiles, given that more than 80% of vehicles in Guangzhou were private cars. The gaseous precursors of NOx and VOCs emitted mostly from motor vehicles could be transformed to SOC and secondary nitrate. Third, growing grass or paving bare surfaces may limit the amount of cement dust entering the air. Construction projects should be well managed. Finally, the contribution of biomass burning was high in Guangzhou, especially in suburban areas. Some measures should be implemented to control these cultivation activities in farmlands. It is important to note, however, that atmospheric pollution is a regional problem, and the government of Guangzhou will need to negotiate with other administrations to control RSP levels in the study area.
The factor analysis method is only one way to apportion the sources of RSP; other methods, such as the bottom-up approach, should be implemented to obtain the source inventory in the future. Accurate source profiles should also be measured to better represent the conditions in Guangzhou and may be better applied in the multivariate method. Although seven sampling locations were used in this study, the number of sites is insufficient for evaluation of RSP pollution across Guangzhou; dispersion models, for example, MODEL-3 and CAMx, that include physical and chemical
processes, could solve this problem.
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