Transport and transformation of total reactive nitrogen over the east China sea

Abstract

Ground-based measurement of total reactive nitrogen (NO y), NO y(g) (gas phase NO x + HNO) an particulate NO 3 was carried out at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) in Okinawa, Japan, from spring to winter in 2006. The concentrations of NO y, NO y(g), and particulate NO 3 - were simultaneously high in spring but low in summer. This difference was mainly caused by air mass history, which was strongly associated with the typical weather pattern observed in the east Asian region for each season. The chemical transformation process of particulate NO 3 - during transport was examined using the data measured at Qingdao, China, in spring 2006. As the transport time of air masses increased, particulate NO 3 - continuously shifted from fine mode to coarse mode. It was found that the chemical transformation of particulate NO 3 - was mainly associated with the transport time of air masses, the geographical position of CHAAMS, and the transition from NH 4 NO 3 to gas phase HNO 3. In air masses from Qingdao, China, the ratio of NO y concentration observed at CHAAMS to that at Qingdao was about 0.1, which was lower than that of SO y (SO 2 + nss-SO 4 2-). Sulfate was found in fine particles at CHAAMS in contrast to particulate NO 3 2-. As the lifetimes of NO y and SO y depend on the particle size, the difference in chemical transformation process during transport largely influences the abundance of transported NO y. The variations of NO y(g) and particulate NO 3 - were analyzed when dust plumes reached CHAAMS. The presence of dust causes the formation of particulate NO 3 - in coarse mode from NO y(g) and an increase of its fraction in NO y. The effect of volcanic activity on particulate NO 3 - concentration was also analyzed. It is suggested that particulate NO 3 - escaped to gas phase HNO 3 through the uptake of abundant volcanic H 2 SO 4 by aerosols. Copyright 2008 by the American Geophysical Union.