Export of anthropogenic reactive nitrogen and sulfur compounds from the East Asia region in spring

Measurements of gaseous and particulate reactive nitrogen and sulfur species, as well as other chemical species, were made using the P‐3B and DC‐8 aircraft over the western Pacific during the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment, conducted between February and April 2001. These measurements provide a good opportunity to study the extent to which anthropogenic NO x and SO 2 emitted over the East Asian countries remain as NO y and SO x (=SO 2 + nssSO 4 2− ) in the form of gas or fine particles when an air mass is transported into the western Pacific region. In this paper a method to estimate transport efficiencies, ε(NO y ) and ε(SO x ), in an air mass that has experienced multiple injection, mixing, and loss processes is described. In this analysis, CO and CO 2 are used as passive tracers of transport, and the emission inventories of CO, CO 2 , NO x , and SO 2 over the East Asia region are used. Results from the P‐3B presented in this study indicate that 20–40% and 15% of NO x emitted over the northeastern part of China remained as NO y over the western Pacific in the boundary layer (BL) and free troposphere (FT), respectively. In the FT, PAN is found to have been the dominant form of NO y , while only 0.5% of emitted NO x remained as NO x . The transport efficiency of SO x is estimated to have been 25–45% and 15–20% in the BL and FT, respectively. Median values of the nssSO 4 2− /SO x ratio are 0.4–0.6 both in the BL and FT, however large variability is found in the FT. These results are generally consistent with those derived using DC‐8 data. The results obtained in this study indicate that more than half of NO y and SO x were lost over the continent and that the vertical transport from the BL to FT further reduced their amounts by a factor of 2, likely due to wet removal. Budgets of NO y and SO x were also studied for air masses, which we sampled during TRACE‐P and the flux out from the continent in these cases is estimated to be 20% of the emissions. Flux in the BL and FT is found to have a similar contribution.