Atmospheric Nitrate Chemistry and Response to Emissions Reductions in the Northeastern USdissertationsKim, HeejeongcreatorHastings, MeredithAdvisorTsai, VictorReaderIbarra, DanielReaderWalters, WendellReaderPye, Havala Olson TaylorReaderBrown University. Department of Earth, Environmental, and Planetary Sciencessponsor202521, 222 p.born digitalThesis (Ph. D.)--Brown University, 2025thesesThe northeastern United States has historically experienced degraded air quality and acid rain due to dense urbanization and industrial activities. Over recent decades, federal regulations have substantially reduced emissions of nitrogen oxides (NOx), leading to improvements in air quality. However, predicting the responses in endpoints such as ozone, particulate matter, and deposition to emission reductions remains challenging due to complex chemical feedbacks. This dissertation investigates the impacts of emission regulations on atmospheric nitrate chemistry across urban and rural environments in the northeastern US, utilizing long-term and short-term isotope measurements with atmospheric chemistry models. Stable isotope analysis provides a higher-dimensional perspective on atmospheric chemistry, offering unique constraints on NOx emission sources and chemical processes that cannot be resolved by concentration measurements alone. This dissertation advances the scientific understanding of atmospheric nitrate chemistry by providing isotopic insights into NOx oxidation processes, thereby enhancing the evaluation of air quality models and supporting the development of more effective emission control strategies.Stable isotopesAir pollutionAtmospheric chemistryAtmospheric nitrogen oxidesNitrate formationEmission control policiesAir quality--U.S. statesAtmospheric Chemistry ModelingEnglishRPB20250707