Global and regional trends of atmospheric carbon monoxide – a background ozone precursor

Carbon monoxide (CO) plays an important role in both air quality and climate. Photochemical oxidation of CO produces ozone (O3) and carbon dioxide (CO2) while also affecting the lifetime of methane (CH4) through reactions with the hydroxyl radical (OH). Because CO2, CH4 and O3 are greenhouse gases, emissions of CO have an indirect radiative forcing, estimated at 0.22 W/m2. Ground-level O3 and CO are also air pollutants that affect human and ecosystem health. Quantifying trends in carbon monoxide is essential for understanding trends in tropospheric ozone, especially in background regions. Using the 22-year data record from MOPITT (Measurements of Pollution In The Troposphere), we show global and regional trends from satellite observations of atmospheric CO. We also examine trends in CO emissions based on model inversions for CO emitted by biomass burning (BB) and fossil fuels (FF) and from chemical production from emissions of biogenic (BG) VOCs (volatile organic compounds). We find that CO concentrations and CO emissions from BB and FF have been mostly decreasing globally, with some notable regional exceptions.