FAS Harvard-China Project

Observations of CO and NOy from the Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission over the northwest Pacific and from two Chinese ground stations (Hong Kong and Lin An) during spring 2001 are used in conjunction with an optimal estimation inverse model to constrain estimates of Asian emissions of CO and NOx. A priori emissions are based on a detailed bottom-up inventory for the observation period. The inversion analysis requires 43% and 47% increases in Chinese emissions of CO and NOx, respectively, distributed heterogeneously, with the largest adjustments required for central China. A posteriori estimates of emissions from biomass burning in Southeast Asia are much lower than a priori values. Inversion results for NOx emissions are consistent with CO emissions in terms of the sense of the adjustments. Inclusion of the station data in the inversion analysis significantly improves estimates for emissions from central and south China. A large increase in NOx emissions inferred for central China (a factor of 3) is attributed to decomposition of organic wastes associated with the human-animal food chain and extensive applications of chemical fertilizer. An analysis of emission ratios for CO relative to NOx for different sectors indicates that emissions attributed to industry and transportation may be underestimated in the bottomup inventory for central China, while emissions from the domestic sector may be underestimated for south China. An increase in emission factors could help reconcile results from the inversion analysis with the ‘‘bottom-up’’ approach. Detailed analysis of the surface observations using a posteriori emissions indicates the importance of meteorological phenomena, notably cold fronts in March and small-scale high- and lowpressure systems in April in modulating concentrations of CO, with the latter most evident in the data from Lin An.

Large intra-season differences in mixing ratios of CO and (O_3) were detected at Miyun, a rural site north of Beijing, in summer 2006. Despite an increase in mean daytime mixing ratio of CO from 500 ppbv in June to 700 ppbv in July, mean daytime (O_3) dropped from 67 ppbv in June to 50 ppbv in July and August. The observed changes in CO and (O_3) are attributed to the influence of the summer monsoonal circulation that develops over the North China Plain in July. Photochemical production of (O_3) is reduced as a consequence of increased cloudiness during July and August, as indicated by the strong negative correlation observed between (O_3) and satellite observations of cloud optical depth, with cloudiness having little effect on CO. The analysis suggests a strategy for emission controls that could be implemented in an economically efficient manner to minimize the frequency of high levels of (O_3) during summer in Beijing.