Asian emissions of CO and NOx: Constraints from aircraft and Chinese station data

Observations of CO and NO y 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 NO x . 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 NO x , 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 NO x 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 NO x 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 NO x for different sectors indicates that emissions attributed to industry and transportation may be underestimated in the bottom‐up 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 low‐pressure systems in April in modulating concentrations of CO, with the latter most evident in the data from Lin An.