Transport and transformation of total reactive nitrogen over the East China Sea



[1] Ground-based measurement of total reactive nitrogen (NOy), NOy(g) (gas phase NOx + HNO3), and particulate NO3 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 NOy, NOy(g), and particulate NO3 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 NO3 during transport was examined using the data measured at Qingdao, China, in spring 2006. As the transport time of air masses increased, particulate NO3 continuously shifted from fine mode to coarse mode. It was found that the chemical transformation of particulate NO3 was mainly associated with the transport time of air masses, the geographical position of CHAAMS, and the transition from NH4NO3 to gas phase HNO3. In air masses from Qingdao, China, the ratio of NOy concentration observed at CHAAMS to that at Qingdao was about 0.1, which was lower than that of SOy (SO2 + nss-SO42−). Sulfate was found in fine particles at CHAAMS in contrast to particulate NO3. As the lifetimes of NOy and SOy depend on the particle size, the difference in chemical transformation process during transport largely influences the abundance of transported NOy. The variations of NOy(g) and particulate NO3 were analyzed when dust plumes reached CHAAMS. The presence of dust causes the formation of particulate NO3 in coarse mode from NOy(g) and an increase of its fraction in NOy. The effect of volcanic activity on particulate NO3 concentration was also analyzed. It is suggested that particulate NO3 escaped to gas phase HNO3 through the uptake of abundant volcanic H2SO4 by aerosols.