Long-range transport of short-lived nitrogen dioxide in East Asia

This study explores the broader spatial influence of nitrogen dioxide (NO₂) over East Asia by integrating satellite and aircraft observations with chemical transport and trajectory model analyses. Tropospheric NO₂ column densities observed by the TROPOspheric Monitoring Instrument (TROPOMI) over the Yellow Sea-located between China and South Korea-are found to be 3.2 times higher in winter than the annual average, highlighting the role of prevailing westerlies in facilitating regional-scale transport during the cold season. Additional insights into the diurnal dynamics of NO₂ transport are provided by hourly observations from the Geostationary Environment Monitoring Spectrometer (GEMS). To further examine the mechanisms responsible for this transport, satellite-based evidence is complemented by in situ aircraft measurements and chemical transport model simulations. Aircraft profiles over the Yellow Sea confirm that NO₂ can be extensively transported at altitudes of 1-2 km under favorable meteorological conditions. Model results indicate that the lifetime of NOₓ in major urban areas-such as the Beijing-Tianjin-Hebei region and the Seoul Metropolitan Area-can be extended from several hours to 1-3 days, depending on meteorological conditions. Trajectory analyses further suggest that NOₓ originating from East Asia can reach downwind regions across adjacent seas within 12-24 h. These findings underscore the importance of accounting for the long-range transport of short-lived pollutants in the development of national air quality management strategies.