Air Pollution as a Climate Forcing: A Workshop
Day 1 Presentations
Aerosol Pollution and its Sources in Major Cities of China
Yuanhang Zhang*, Shaodong Xie*, Min Shao*, Limin Zeng*, Min Hu*,
* Center for Environmental Sciences, Peking University, Beijing, China
+ Chinese Research Academy of Environmental Sciences, Beijing, China
° School of Earth and Atmospheric Sciences, Georgia Institute of Technology
|Figure 1: PM10 and PM2.5 emission inventory in Beijing urban area|
|Figure 2: PM10 and PM2.5 emission inventory in Pearl River Delta|
While air pollution due to coal burning is not effectively controlled, the most rapid growth is from rapid increase of vehicular population in most cities of China, especially in mega-cities and economically developed regions, such as Beijing, Shanghai, Guangzhou, Pearl River Delta and the Yangtze Delta. Coal smog and traffic exhaust problems coexist to form serious photochemical smog and particulate pollution. Air pollution in those areas is characterized by enhanced atmospheric oxidation capacity, a high level of fine particles with impact on urban visibility, and regional air quality degradation. Transformation and transport of air pollutants results in unique characteristics and high levels of O3 and particulates. Atmospheric chemistry is complicated due to coupling between primary emissions and photochemical processes, coupling between gaseous and aerosol phase interactions, and coupling between local and regional air pollution. As a result, traditional control policy focused on a single city is not effective in abating urban air pollution, and efforts to reduce emission in one mega-city cannot significantly improve regional air quality.
A number of projects have been set up since 1999 to study emission inventory, air pollution status, formation mechanism and control policy in Beijing city, Guangzhou city, Pearl River Delta, and Yangtze Delta. This paper gives an overview of results obtained in those projects with a focus on aerosol pollution.
Emission inventory of PM10, PM2.5, SO2, NOx and VOC was developed by using emission factors from the literature, which were partly validated by limited measurements on boilers in power plants and industry, vehicles, and dust emission. PM10 and PM2.5 emission in Beijing urban and Pearl River Delta are shown in Figures 1 and 2.
|Figure 3: Chemical composition of PM2.5 in Beijing and Guangzhou urban.|
Integrated experiments were conducted to understand chemistry of photochemical smog and particulate pollution. Ambient PM10 and PM2.5 samples were collected in different functional areas of Beijing and the Pearl River Delta. Elements, ions, organic carbon and elemental carbon were analyzed by various methods. Averaged chemical characteristics of PM2.5 are shown in Figure 3 for Beijing and Guangzhou city as an example. Concentrations of fine particulates were high on both the urban and regional scales. Organic carbon and sulfate had high percentages, the sum of which was more than 50% of the PM2.5 mass.
As Table 1 shows, fine particle pollution was a common problem in major cities and regions in China. Sulfate and organic carbon were major components in PM2.5. The EC concentration was also high compared with that in remote areas. Concentration of nitrate was relative low, with high uncertainty because of sampling interference without a denuder in front of filter. On-line measurements by steam jet aerosol collector showed that nitrate had almost the same concentration level as sulfate in Beijing summer.
|Pearl River Delta||2000_11||19.2||1.7||14.4||2.3||2.4||84.3|
|Yangtze Delta: Li_an||1999_11||27.7||2.8||15.8||6.7||7.1||73.1|
|Yangtze Delta: Changsu||1999_11||40.5||3.0||20.0||11.3||9.4||111.9|
|Yangtze Delta: Sheshan||1999_11||33.2||2.0||16.2||9.3||6.6||83.8|
|(Jie Tang et al., Meteorology, 27(11) 3-7, 2001)|
|Figure 4: Source apportionment of ambient PM2.5 in Beijing|
Sources of PM2.5 in Beijing were identified by chemical mass balance. The main sources having significant contribution to PM2.5 included vehicle exhaust, coal burning, secondary sulfate and nitrate, organics, traffic road dust, soil dust, construction, biomass burning, and unknown sources, as shown in Figure 4.