Impact of Air Quality on the Composition and Degradability of Atmospheric Organic Matter in Coastal Regions

Atmospheric deposition contributes approximately 90 million tons of dissolved organic carbon (DOC) to the oceans and 400 million tons to the land surface each year. Natural organic matter (OM) is composed of tens of thousands of distinct molecules, making its characterization a significant challenge. This complexity is particularly evident in atmospheric OM, which is more dynamic than its aquatic counterpart. Due to analytical difficulties, the cycling of atmospheric OM in receiving waters is not well understood and is not currently represented in global carbon cycling models. To address these knowledge gaps, we conducted seasonal aerosol sampling in two major coastal cities in China—Xiamen and Qingdao—each representing different air quality levels. Using ultra-high resolution mass spectrometry, we characterized the OM composition and conducted laboratory experiments to assess its potential degradability. We also investigated the relationship between molecular composition and air quality parameters. Preliminary results indicate that as air quality worsens (as reflected by an increasing Air Quality Index, or AQI), atmospheric OM becomes more aromatic, and the fraction of DOC that can be utilized by microbes decreases. These findings suggest that during periods of higher AQI, atmospheric OM is primarily derived from fossil fuel combustion, potentially persisting in the ocean for extended periods. Future research will focus on the biogeochemical impacts of these changes