Formic acid measurements from space: Retrieval strategy, evaluation, and initial constraints on primary and secondary sources

Formic acid is a major contributor to acidity in the global atmosphere, and recent work suggests that its sources are significantly underestimated. New space-borne measurements from the Tropospheric Emission Spectrometer (TES), onboard EOS Aura, offer valuable global data for investigating this issue, and for quantifying primary and secondary formic acid sources to the atmosphere. In this presentation, we describe the TES formic acid retrieval strategy along with a series of sensitivity studies to test its reliability. We present initial global results showing the seasonal and spatial distribution of formic acid in the lower troposphere, and apply a 3D chemical transport model (GEOS-Chem) to i) evaluate the TES retrievals against a collection of airborne and ground-based observations, and ii) assess what constraints the satellite data can provide on the budget of atmospheric formic acid.