Comparison of Near-Surface NO₂ Pollution With Pandora Total Column NO₂ During the Korea-United States Ocean Color (KORUS OC) Campaign

Abstract

Near‐surface air quality (AQ) observations over coastal waters are scarce, a situation that limitsour capacity to monitor pollution events at land‐water interfaces. Satellite measurements of total column(TC) nitrogen dioxide (NO₂) observations are a useful proxy for combustion sources, but the once dailysnapshots available from most sensors are insufficient for tracking the diurnal evolution and transport ofpollution. Ground‐based remote sensors like the Pandora Spectrometer Instrument (PSI) that have beendeveloped to verify space‐based TC NO₂and other trace gases are being tested for routine use as certifiedAQ monitors. The KORUS‐OC (Korea‐United States Ocean Color) cruise aboard the R/VOnnuriinMay–June 2016 represented an opportunity to study AQ near the South Korean coast, a region affected byboth local/regional and long‐distance pollution sources. Using PSI data in direct‐Sun mode and in situsensors for shipboard ozone, CO, and NO₂, we explore, for thefirst time, relationships between TC NO₂andsurface AQ in this coastal region. Three case studies illustrate the value of the PSI and complexities in thesurface‐column NO₂relationship caused by varying meteorological conditions. Case Study 1(25–26 May 2016) exhibited a high correlation of surface NO₂to TC NO₂measured by both PSI and Aura'sOzone Monitoring Instrument, but two other cases displayed poor relationships between in situ andTC NO₂due to decoupling of pollution layers from the surface. With suitable interpretation the PSI TC NO₂measurement demonstrates good potential for working with upcoming geostationary satellites toadvance diurnal tracking of pollution.