Nocturnal sink of NOx via NO3 and N2O5 in the outflow from a source area in Japan

To understand the nocturnal sink of NOx in the outflow from the Asian source area, simultaneous observations of NO3, N2O5, and related compounds were conducted utilizing an instrument based on laser-induced fluorescence at Izu-Oshima Island, Japan, during June 2004. Consequently, significant levels of NO3 and N2O5 were successfully observed, particularly in the polluted air mass originating from Tokyo. This observation concurred with the equilibrium among NO3, NO2, and N2O5 gases. As a result of steady-state analysis, nocturnal NOx losses were evaluated as 1.8 and 0.2 ppbv night−1 for polluted and maritime air, respectively. It was confirmed that the nocturnal NOx sink during the observation was promoted by the NO3 loss by VOC. DMS is significant for nocturnal loss of NOx over the sea.