Emissions, Transport, and Evolution of Atmospheric Pollutants from China: An Observational Study

Abstract

China's air pollution issue, a byproduct of recent phenomenal economic growth, has received increasing attention in light of its local and large-scale impacts. I investigated the emissions, transport, and evolution of pollutants from China using measurements near some source regions in northern China in 2005. Surface pollution near Beijing in March was overall heavy but changed dramatically, as passing mid-latitude cyclones led to fast transitions between polluted prefrontal and clean postfrontal conditions. Large differences found between measurements and inventories suggest substantial uncertainties in emission estimates. Small, coal-fired boilers are shown unlikely to be the major source of inventory error; experiments measuring traffic emissions are called for. Ground-level aerosols absorb light and are from both wind-blown dust and anthropogenic emissions. Their effects on climate are to be further studied.

Pollutants at higher altitudes are more likely to have large-scale impact than pollutants that remain near the surface. The aircraft campaign in April was among the first efforts to measure the vertical distribution of pollutants over inland China. The largest pollutant levels observed in the free troposphere during the campaign were related to dry convective lofting over an industrial region. This differs from earlier experiments over the Pacific, which recognized the warm conveyor belt (WCB) as the main lofting mechanism. Dry convection over the continent may be followed by WCB lifting as the systems move out over the ocean. Their relative roles are yet to be determined.

Analyses of meteorological and satellite cloud data reveal the importance of in-cloud processing in oxidizing SO2 transported behind cold fronts. Through integration of satellite sensors, in-situ measurements, trajectory and chemical transport models, I tracked a pollution plume as it traveled away from source region. The decay of SO2 in the plume over three days was quantified, suggesting an SO2 lifetime of 1-4 d. Formation of sulfate and loss of dust together changed the aerosol loading of the plume. This analysis showcases the potential for employing satellites to trace transport events and pollutant evolution, and highlights the main uncertainties in quantitative application of satellite data.