Measurements and Modeling of Nitrogen Oxides: Tropospheric Transformations During Summer and Winter in Polluted Regions Across the U.S.

McDuffie, Erin Elizabeth

Graduate Thesis Or Dissertation

Measurements and Modeling of Nitrogen Oxides: Tropospheric Transformations During Summer and Winter in Polluted Regions Across the U.S. Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/h415p962w

Abstract

Atmospheric reactions of inorganic nitrogen oxides critically influence the composition of the troposphere, the lowest layer of the atmosphere that supports all terrestrial life on Earth. From controlling the global budget and distribution of tropospheric oxidants, to degrading local air quality through the production of ozone (O₃) and secondary particulate matter (PM), understanding the underlying chemistry of reactive nitrogen oxides is vital to both improving our predictive capabilities of global tropospheric chemistry and to developing effective mitigation strategies in regions with persistently poor air quality. Despite decades of research into their chemical mechanisms, significant uncertainties remain in the seasonally dependent lifetime and distribution of nitrogen oxides. Key remaining questions include: 1) the sensitivity of photochemical pollutant production to location-specific emission sectors, 2) factors influencing nocturnal inter-conversion processes, which involve multiphase reactions, and 3) the quantitative contribution of these heterogeneous reactions to wintertime air pollution.

In this thesis, I address these questions using observational and modeling-based analyses of data collected during three U.S. field campaigns in summer 2014 and the winters of 2015 and 2017. I first present observations from summer 2014 and results from an observationally-constrained, photochemical box model. This study was the first to quantify the contribution of oil and natural gas emissions to local O₃ pollution in the Colorado Front Range, a region that has been out of compliance with national air quality standards for O₃ since 2008. I next present the first wintertime aircraft determinations of aerosol uptake coefficients of dinitrogen pentoxide (N₂O₅) and production yields of nitryl chloride (ClNO₂). These parameters were derived from a custom, iterative, inorganic nocturnal nitrogen chemistry box model, fit to aircraft observations collected over the U.S. east coast in 2015. Field-determinations of these parameters are further compared to laboratory-based parameterizations to evaluate the current representation of these processes in global models. Lastly, I present results from the first aircraft observations in Salt Lake Valley, Utah. Observations and box model simulations are combined to assess the contribution of heterogeneous reactive nitrogen chemistry to wintertime PM formation in this region, which frequently violates PM air quality standards during wintertime pollution events.

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