Secondary Aerosol Particles and their Precursor Gases: Comparisons of Observations from OMI and MODIS Observations and GEOS-Chem Model Results

Abstract

Human activities around the globe cause the emission of gases such as SO2, NOx and VOCs. In the atmosphere, these gases are transformed to secondary fine mode aerosol particles. Understanding sources of anthropogenic aerosols and their precursor gases is relevant for climate change as well as for air quality. To predict how the aerosol load responds on changing emissions, knowledge of the chemical composition of aerosol particles is necessary. Over the last decade, accurate satellite data on aerosol optical thickness (AOT) and tropospheric NO2 and formaldehyde columns have become available. In this contribution we use AOT from MODIS on the NASA EOS Aqua satellite and NO2 and formaldehyde data from OMI on the NASA EOS Aura satellite, which are both part of the A-Train satellite constellation. Whereas tropospheric NO2 and formaldehyde are direct measures of the concentration of these gases, the AOT is an optical parameter and its positive correlation with aerosol mass concentration can be complicated by the physical and chemical properties of the aerosol particles. To establish the link between the AOT and its precursor gases, we have investigated the spatial correlation of AOT and precursor gases in multi-year averages for different regions and seasons. By comparing the measurements with GEOS-Chem chemistry transport model simulations, we show that the corresponding slope between the AOT and the NO2 and formaldehyde varies strongly between source regions and contains information on the chemical composition of the aerosol particles. A global comparison of OMI-MODIS observations with the GEOS-Chem model will be presented. Our analysis provides the first-ever global-scale evaluation a state-of-science chemistry transport model with the satellite-based paired observation of aerosol and their precursors.