Ammonia and Aerosol Emission Impacts: New Insights with Open-path Measurements

Abstract

Atmospheric aerosols and their precursors have significant influences on Earth's climate and tropospheric air quality. Aerosol direct and indirect radiative forcing currently constitute the largest uncertainties for future climate change predictions. Anthropogenic aerosols degrade regional air quality, with implications for human health. Aerosol and precursor observations on multiple spatial scales are necessary to understand primary emissions, secondary formation, long-range transport and nitrogen deposition. Ammonia (NH3) is an important gas-phase precursor to fine particulate matter. Recent air quality model simulations show large discrepancies with NH3 observations due to significant emission inventory uncertainties, especially for increasing, highly variable agricultural NH3 emissions. Gas-phase NH3 measurement challenges due to surface adsorption and partitioning in closed-path NH3 sensors have led to a lack of widespread NH3 observations. To improve our understanding of aerosol and NH3 precursor emissions, my dissertation focuses on synthesizing new observations from continental to individual emission plume scales. First, I synthesized multiple aerosol datasets to track the physical and chemical evolution of biomass burning smoke aerosols and quantified how

their long-range transport influenced U.S. air quality. Next, I developed and performed rigorous field testing of a quantum cascade laser-based, open-path NH3 instrument capable of high precision (0.15 ppbv NH3), high time resolution (10 Hz) field measurements with minimal sampling biases. Upon validating its field performance, I applied this sensor to perform open-path, mobile measurements of NH3 dairy emission ratios in the Central Valley, California during the NASA DISCOVER-AQ field campaign. Ammonia emission ratios were quantified from individual dairy farms to regional scales through syntheses with aircraft measurements. The final part of my dissertation involved the development and field deployment of a quantum cascade laser-based, open path-integrated methane sensor, which achieved long path length, high precision (0.5% at 1 Hz) measurements in an Arctic field environment. The path-integrated configuration is applicable for future NH3 measurements on comparable spatial scales to regional model simulations. Ultimately, these efforts have implications for understanding aerosol long-range transport and provide new high resolution, in-situ NH3 measurement capabilities applicable for validating NH3 emission inventories and air quality modeling efforts to constrain NH3 emission influences on air quality.