Aerial observation of nitrogen compounds over the East China Sea in 2009 and 2010

Aerial observations of atmospheric pollutants were made over the East China Sea to analyze the transport of air pollutants, especially nitrogen oxides, from East Asia. Three flights each were conducted in October 2009 (autumn) and December 2010 (winter). Onboard measurements of gaseous total odd nitrogen species, gaseous nitric acid (HNO3(g)), O3, SO2, CO and black carbon were made and particles were collected on filters for ionic and metal component analyses. The NO3−(p)/T.NO3 (T.NO3 = HNO3(g) + NO3−(p); NO3−(p) indicates particulate nitrate) ratios were less than 0.5 in most cases. Exceptions were 17 October and 11 December, when high concentrations of dust particles (Kosa) were transported. The average T.NO3/NOy (NOy indicates total odd nitrogen species) ratio in winter was 0.59, and that in autumn was 0.71. In addition, positive and negative correlations between NOy − T.NO3 and ozone were observed in autumn and winter, respectively. These results indicate that the main components of NOy − T.NO3 are NOx and its descendant photochemical products, such as peroxyacyl nitrates and alkyl nitrates, in winter and autumn, respectively. Ratios of Na+ to Cl− + NO3− in particles were close to the seawater ratio for observations in both autumn and winter, save for the Kosa events. The main NO3−(p) formation process was the reaction of HNO3(g) with sea salt aerosols during autumn and winter. On the other hand, NO3−(p) was generated by the reaction of HNO3(g) with dust particles and sea salt during the Kosa events. The fraction of NH4NO3 in NO3−(p) was very small. •Aerial observations over the East China Sea were made.•Gaseous phase fraction was larger than that of particle phase for inorganic nitrate.•Sodium nitrate was a major component of aerosol nitrate over the East China Sea.•Aerosol nitrate originated from dust particles present during Kosa events.