Comparison of Near-surface NO Pollution with Pandora Total Column NO during the Korea-United States Ocean Color (KORUS OC) Campaign.

Near-surface air quality (AQ) observations over coastal waters are scarce, a situation that limits our capacity to monitor pollution events at land-water interfaces. Satellite measurements of total column (TC) nitrogen dioxide (NO) observations are a useful proxy for combustion sources but the once daily snapshots available from most sensors are insufficient for tracking the diurnal evolution and transport of pollution. Ground-based remote sensors like the Pandora Spectrometer Instrument (PSI) that have been developed to verify space-based total column NO and other trace gases are being tested for routine use as certified AQ monitors. The KORUS-OC (Korea-United States Ocean Color) cruise aboard the R/V in May-June 2016 represented an opportunity to study AQ near the South Korean coast, a region affected by both local/regional and long-distance pollution sources. Using PSI data in direct-sun mode and sensors for shipboard ozone, CO and NO, we explore, for the first time, relationships between TC NO and surface AQ in this coastal region. Three case studies illustrate the value of the PSI as well as complexities in the surface-column NO relationship caused by varying meteorological conditions. Case Study 1 (25-26 May 2016) exhibited a high correlation of surface NO to TC NO measured by both PSI and Aura's Ozone Monitoring Instrument (OMI) but two other cases displayed poor relationships between and TC NO due to decoupling of pollution layers from the surface. With suitable interpretation the PSI TC NO measurement demonstrates good potential for working with upcoming geostationary satellites to advance diurnal tracking of pollution.