Improved HCOOH retrieval from IASI measurements: Comparison with ground-based measurements

Abstract : Formic acid (HCOOH) is one among the most abundant volatile organic compounds (VOCs) present in the atmosphere. HCOOH sources include emissions from vegetation, soil and biomass burning. To a lesser extent, it is also produced by motor vehicles. It is mainly a secondary product from organic precursors. HCOOH plays a role in the oxidizing capacity of the troposphere and on the global budget of tropospheric ozone (O3), and it is also a source of rain acidity in remote areas. There are however large uncertainties on sources and sinks and HCOOH is misrepresented in the global emissions inventories. In this work, we retrieve concentrations from spectra recorded by the IASI (Infrared Atmospheric Sounding Interferometer) instrument launched onboard the MetOp-A satellite in 2006. IASI is a nadir looking Fourier transform spectrometer, sounding the atmosphere with a global coverage twice per day. The HCOOH global distributions are derived using a new retrieval approach, based on conversion factors between brightness temperature differences and representative retrieved total columns. We present global distributions and comparisons with FTIR measurements obtained at La Reunion, Wollongong and Jungfraujoch from 2008 to 2013. The IASI instrument provides a 6-year record for different regions, highlighting the signatures from biomass burning events and allowing the study of seasonal and interannual variations