Spaceborne Measurements of Formic and Acetic Acid: A Global View of the Regional Sources

Formic (HCOOH) and acetic acids (CH3COOH) are the most abundant carboxylic acids inthe Earth's atmosphere and key compounds to aqueous-phase chemistry. Here we present the firstdistributions of CH3COOH retrieved from the 2007–2018 satellite observations of the nadir-lookinginfrared atmospheric sounding interferometer (IASI), using a neural network-based retrieval approach. Ajoint analysis with the IASI HCOOH product reveals that the two species exhibit similar distributions,seasonality, and atmospheric burden, pointing to major common sources. We show that their abundance ishighly correlated to isoprene and monoterpenes emissions, as well as to biomass burning. Over Africa,evidence is provided that residual smoldering combustion might be a major driver of the HCOOH andCH3COOH seasonality. Earlier seasonal enhancement of HCOOH at Northern Hemisphere middle andhigh latitudes and late seasonal secondary peaks of CH3COOH in the tropics suggest that sources andproduction pathways specific to each species are also at play.