Latitudinal distribution and sources analysis of greenhouse gases and air pollutants observed during the 2021 Yellow Sea Air Quality campaign aboard a research vessel.

The Yellow Sea serves as a pathway for air pollution transport from the Asian continent into Korea and is annually monitored by the Korean Meteorological Administration (KMA) research vessel during the spring season. This study investigated the spatio-temporal variation of long-range transported greenhouse gases (CO 2 and CH 4) and air pollutants (CO, NO x , SO 2 , O 3) in the Yellow Sea during the Yellow Sea Air Quality (YES-AQ) campaign. Our analysis reveals that GHGs and air pollutants exhibit a clear latitudinal distribution. Lower concentrations are observed in the range of 31.2–34.5°N, primarily influenced by air masses traversing the ocean and the western part of Korean Peninsula. In contrast, higher concentrations occur more frequently at 34.5–37.8°N, primarily affected by continental air masses. The regression slopes of CO and CO 2 vary depending on regional characteristics, particularly in air originating from Korea and China. Regression slope analysis between CO, CO 2, and CH 4 , except for high plume of CH 4 (>2.05 ppm), indicates that fossil fuel sources play a significant role. A high plume of CH 4 (>2.05 ppm) was observed on April 22nd, coinciding with the maximum O 3 concentrations during the period of highest temperatures throughout the voyage. The potential source regions were identified in the west-southern coast of Korea, using footprint analysis from Stochastic Time-Inverted Lagrangian Transport (STILT) and column-averaged dry-air mole fraction of CH 4 (XCH 4) retrieval from the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite. The high CH 4 enhancements are most likely due to biogenic emissions triggered by favorable near-surface temperatures for microbial activities in soil. Furthermore, the high CH 4 enhancements were not correlated with CO and CO 2 , indicating that the source was not related to fossil fuel combustion. On March 29–30, a high plume of NO x was detected and is likely attributed to the Bohai Sea, which is located just above the Yellow Sea and surrounded by highly industrialized and semi-enclosed areas. • Yellow Sea Air Quality campaign studies greenhouse/air pollutants distribution. • Greenhouse/air pollutants show a clear latitudinal gradient over Yellow Sea. • CO, CO 2 , CH 4 correlation suggests fossil fuel-based sources mainly from China and Korea. • Highly elevated CH 4 linked to microbial-related biogenic emissions from Korean based on STILT analysis. [ABSTRACT FROM AUTHOR]