Sources, Transport, and Chemistry

The China Project's atmospheric research is committed to building observationally validated, fundamental research on the physical and chemical dimensions of China’s atmospheric environment and the emissions that influence it, at local, regional, continental, and global scales. In addition to the model-based research described below, it includes observational research described here.

The primary tool is the GEOS-CHEM global chemical transport model developed at Harvard, and a nested higher resolution window over China developed by WANG Yuxuan and China Project faculty chair Michael B. McElroy (Harvard School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences). Validated by agreement of modeled concentrations with measurements made by ground stations and offshore aircraft, the model differentiates air transport mechanisms for individual sub-regions of China on a finer scale than previously possible (Wang et al. 2004a) and captures critical seasonal effects of meteorology—notably cold fronts in winter and monsoonal patterns in summer—on regional and urban air quality.

Applied in inverse mode—in which atmospheric concentrations observed by ground stations, aircraft, and satellites are use to derive optimized emissions—the model provides independent checks on “bottom-up” inventories of carbon monoxide (CO), nitrogen oxides (NO_X), other pollutants, and greenhouse gases. Collaborating with WANG Tao (Hong Kong Polytechnic University, Department of Civil and Structural Engineering; Chinese Research Academy of Environmental Sciences, Beijing), the team has estimated that official estimates of emissions of CO and NO_X in 2001 should be raised as much as 43% and 47%, respectively, to explain the levels observed in the atmosphere (Wang et al. 2004b).

Another paper proposes that the discrepancy for NO_X may be explained by processes largely overlooked previously: the mobilization of nitrogen though the management of human and animal wastes and the use of chemical fertilizers, oxidized in part to NO_X by bacterial action (McElroy and Wang 2005). This proposition of a large biological source of NO_X over rural areas in China is supported also by satellite observations of column NO₂ (Wang et al. 2007a).

These capabilities can inform emission control policies. For a given region, if biological sources of NO_X—a main precursor of health-endangering secondary pollutants including fine particles and ozone—approach the total contribution from fossil fuel combustion, pollution control strategies may need to be broadened in directions unanticipated by experience in the differing conditions of western countries: waste management and agricultural practices.

A newer inverse application to near-real-time satellite observations of atmospheric concentrations yields encouraging evidence to officials preparing for the Beijing Olympics in 2008. It shows that measures to restrict vehicular traffic in Beijing during the Sino-African Summit of November of 2006 had the intended effect: a large reduction of NO_X emissions, as much as 40%, during the period in which the restrictions were in place (Wang et al. 2007b). Click on the figure above for comparison of model estimates and observations, illustrating the capability of the GEOS-CHEM China model to capture local variation in NO₂ column concentrations. The natural experiment of the Sino-African summit thus has had both practical and scientific value, serving to validate the efficacy of emission control policies and the Project's atmospheric model itself.

The results of the Sino-African summit paper have been reported recently on the online news of Science and in other science and general news media.