Assessing Mass Balance Approach in Deriving Ammonia Emissions from Space
Ammonia emission inventory is a crucial component in chemical transport modeling of aerosols and could be constrained from satellite observations. Two inversion methods are tested by synthetic experiments using GEOS-Chem and its adjoint at coarse (2˚ × 2.5˚) and fine (0.25˚ × 0.3125˚) resolutions. Comparing to the more rigorous 4D-Var method, the iterative finite difference mass balance (IFDMB) approach requires 3-4 times lower computational cost, and yields top-down inventories with smaller errors (12-17% vs. 17-26%) at coarse resolution, yet larger errors (44-69% vs. 30-45%) at fine resolution. The larger errors of IFDMB at fine resolution are attributable to enhanced transport and spatial smearing based on adjoint calculation over emission source (Paper for more details).
Space-Borne Estimation of Volcanic Sulfate Aerosol Lifetime
Processes that remove aerosols from the atmosphere are difficult to evaluate with observations in isolation from aerosol sources. As a result, a quantitative assessment of uncertainties in our understanding of aerosols is limited and narrowing of those uncertainties is difficult to demonstrate. In this study, we use satellite observations of sulfur dioxide (SO2) and aerosols downwind of the Kīlauea volcano during May–September 2008. We derive the SO2 emission rate, the loss rate of SO2 that is indicative of the production rate of sulfate aerosols, and the subsequent removal rate of the formed sulfate. The result is the first determination of volcanic sulfate aerosol lifetime, 40–64 h, directly from satellite observations. The derived sulfate lifetime is significantly lower than the global average (3–5.5 days) and reflects the rapid wet scavenging of this plume (Paper).