Airborne Measurements of Oxygenated Volatile Organic Compounds (OVOCs) during ATom: Implications for a Currently Unaccounted Source in the Remote Troposphere

Volatile organic compounds (VOCs) affect the oxidative capacity of the atmosphere, which largely controls the removal of short-lived climate forcers (e.g. methane and ozone). VOCs also leads to the formation of organic aerosols, which directly and indirectly affects the radiative balance of the atmosphere. Airborne observations of VOCs in the vastness of remote troposphere, especially oxygenated VOCs (OVOCs) such as acetaldehyde and acetone, are often underestimated by current chemistry-climate models. Ocean plays a key role in the budget of OVOCs in the remote regions, yet the air-sea exchange of OVOCs remains poorly understood.

In this work, we present an online air-sea exchange framework developed for the Community Earth System Model (CESM2). The module has been tested with previous ship-based measurements of seawater concentrations and fluxes for a number of species, including acetaldehyde and acetone. The modeling results have been evaluated using airborne measurements obtained during the recent NASA-sponsored, multi-year, nearly pole-to-pole campaign, Atmospheric Tomography Mission (ATom). We show that the air-sea exchange module greatly improves the model performance in the marine boundary layer, yet in the free troposphere a substantial fraction of the observed OVOCs still remain unexplained. We further show that this carbon pool in the atmosphere inferred from these measurements cannot be all explained by current knowledge of the chemical evolution of organic aerosols, of ocean or continental origin. The broader impacts of these OVOCs on the HOx radicals and halogen chemistry warrant further investigation.