Sources, distribution and partitioning of reactive nitrogen in the lower troposphere over western Pacific during TRACE-P

Measurements of NO, NO₂, PAN, PPN, HNO₃, particulate NO₃^-, total reactive nitrogen (NO_y), O₃, CO and nonmethane hydrocarbons (NMHCs) in the lower troposphere were conducted over the Pacific Ocean in March and April during the Transport and Chemical Evolution over the Pacific (TRACE-P) experiment. The measurements indicated that concentrations of reactive nitrogen species were largely enhanced below 3 km near Asian Continent, east of 150E. Based on the backward trajectories, five source regions (Japan, Korea, North China, South China, and Southeast Asia) of NO_y}{-enhanced air masses were identified to show the contribution of these regions to the observed distribution of reactive nitrogen. Contribution of emissions from North and South China was evident all latitude range between 15N and 40N. In the north of 30N, emissions from Japan and Korea contributed similarly with those from China. Correlation analyses among CO, NO_y, CH₃Cl, CS₂, COS, and C₂Cl₄ indicates that the emission source and combustion efficiency in each region were clearly different. In North and South China, coal burning was significant source, and the ratio of CO/NO_y was much higher than that in Japan or Korea. The partitioning of reactive nitrogen and its evolution were also discussed. Most of NO_x had already been converted to PAN, HNO₃ and particulate NO₃^- near the source region. During 5-day transport over Pacific, the PAN/NO_y ratio decreased significantly and the NO_x/NO_y ratio was nearly constant, suggesting that thermal decomposition of PAN maintained the NO_x/NO_y ratio. The percentage of HNO₃ and/or particulate NO₃^- gradually increased during the transport.