Formation and transport of oxidized reactive nitrogen, ozone, and secondary organic aerosol in Tokyo

Measurements of the major reactive nitrogen species (NO y ) i (NO x , peroxyacyl nitrates, HNO 3 , and particulate nitrate (NO 3 − )), total reactive nitrogen (NO y ), volatile organic compounds, OH and HO 2 , and organic aerosol were made near the urban center of Tokyo in different seasons of 2003–2004 to study the processes involving oxidized forms of reactive nitrogen and O 3 . Generally, NO x constituted the dominant fraction of NO y throughout the seasons. The NO x /NO y and HNO 3 /NO y ratios were lowest and highest, respectively, in summer, owing to the seasonally high OH concentration. The fraction of NO y that remained in the atmosphere after emission (R NOy ) decreased with the decrease in the NO x /NO y ratio in summer and fall. It is likely that the median seasonal‐diurnal variations of O x = O 3 + NO 2 were controlled by those of the background O 3 levels, photochemical O 3 formation, and vertical transport. O x showed large increases during midday under stagnant conditions in mid‐August 2004. Their in situ production rates calculated by a box model were too slow to explain the observed increases. The high O x was likely due to the accumulation of O x from previous days in the upper part of the boundary layer (BL) followed by transport down to near the surface by mixing after sunrise. Considering the tight correlation between O x and secondary organic aerosol (SOA), it is likely that SOA also accumulated during the course of sea‐land breeze circulation in the BL.