Using CrIS Ammonia Observations to Improve Decision Making on PM2.5 Control Policies

Abstract:

Air quality managers and forecasters need accurate emissions estimates of PM_2.5 precursors, such as ammonia (NH₃), to forecast how these emissions will impact human health and air quality. However, current emission inventories are too uncertain to provide reliable estimates of the health effects of NH₃. Observations from the Cross-track Infrared Spectrometer (CrIS) provide an opportunity to address this problem and improve NH₃ emissions estimates using inversion-based modeling techniques. Moreover, as new CrIS instruments are expected to be launched over the next two decades as part of the JPSS series, designing an infrastructure and methodology to use these observations in operational air quality policymaking and forecasting will provide benefits extending through 2030 and possibly beyond. In the current study, CrIS NH₃ observations are used in a finite-difference mass-balance approach to constrain NH₃ emissions in the Community Multiscale Air Quality (CMAQ) model. CMAQ is run over the continental United States using 12 km grid spacing for June 2015. A baseline simulation is made with unperturbed NH3 emissions. Then, a second simulation is performed with NH₃ emissions perturbed by 20%. The resulting total column concentrations of NH₃ are compared to CrIS observations to derive a monthly-mean scaling factor for the a priori NH₃ emissions. This scaling factor accounts for the relationship of NH₃ concentrations to NH₃ emissions in the baseline model run and is used to derive updated emissions, which are utilized in a final CMAQ simulation. This finite-difference inversion method has been incorporated into Amazon Web Services, and the data will be made publicly available. It will ultimately allow air quality managers and other stakeholders to obtain more accurate NH₃ emissions estimates that can be implemented directly into their air quality modeling.