Importance of Long-Range Nitrate Transport Based on Long-Term Observation and Modeling of Dust and Pollutants over East Asia

ABSTRACT

Long-term synergetic fine and coarse mode aerosol observations were analyzed at 1-h intervals at Fukuoka, Japan, from January to June 2015. The GEOS-Chem chemical transport model, including dust and sea-salt acid uptake processes, was used for detailed analysis of observation data. Several Asian dust events and long-range anthropogenic aerosol transport events were observed during our analysis period, and the numerical model generally explained the observed time variation for both fine and coarse mode aerosols. We found that (i) the majority of fine mode NO₃^– can be considered as long-range transport (LRT) outside of Japan during the cold season, and (ii) the peak timing of fine mode NO₃^– coincided with that of SO₄^–, indicating that both aerosols are controlled by LRT. Also, an observed mass concentration ratio of NO₃^–/SO₄^2– > 0.9 occurred during the cold season, indicating the importance of NO₃^– as a major contributor to the PM_2.5 mass fraction. Finally, we clearly showed that large-scale dust-nitrate outflow from China to Fukuoka was confirmed in all cases of dust events, indicating that the anthropogenic NO_x is converted to dust-nitrate and transported to Japan with dust. These results demonstrate the importance of anthropogenic NO₃^– LRT during the cold season and dust-nitrate LRT for all dust events (even in June).