The primary goal of the project is to investigate the sources, formation, and direct radiative impacts of ammonium nitrate and ammonium sulfate aerosols that are important elements of the terrestrial nitrogen cycle. The project will substantially reduce the currently large uncertainties in the emissions of the precursor gas ammonia that lead to large uncertainties in the formation, vertical distribution, and radiative impacts of ammonium nitrate and ammonium sulfate aerosol, which in turn lead to significant uncertainties in predictions of future climate. The project will employ in situ surface and aircraft measurements from the recent NOAA CalNex field campaign in May to July 2010, along with satellite retrievals of ammonia from the Tropospheric Emission Spectrometer (TES) aboard the NASA Aura satellite and the NOAA Cross-track Infrared Sounder (CrIS) aboard the joint NOAA, NASA, and DOD Suomi National Polar-orbiting Partnership (NPP) satellite. CalNex measurements and TES retrievals will first be used, along with the recently updated adjoint of the Community Multiscale Air Quality (CMAQ) model, to improve estimates of the emissions of ammonia during the CalNex campaign. The NOAA CalNex field campaign is uniquely suited for this work as,not only did TES make special observations with high spectral sampling during CalNex, but gas-phase ammonia was also measured at the Bakersfield, CA, and Los Angeles, CA, surface sites and aboard the NOAA WP-3 aircraft (providing in situ vertical profile measurements of ammonia) during the campaign. Next, an NH3 retrieval algorithm for the NOAA CrIS instrument will be developed and validated, and the ability of these retrievals will be assessed, along with the CMAQ adjoint and special observations made by TES, to reduce uncertainties in ammonia emissions in California between May and July 2012. Finally, the CMAQ model will be used and the fast radiation code RRTM developed to estimate the regional radiative and air quality impacts of these aerosols and the sensitivity of these impacts to emission control strategies.