Abstract
Nitrogen oxides (NOx ≡ NO + NO2) play a critical role in controlling the oxidative capacity of the atmosphere, adversely affect our health, drive the production of other harmful pollutants, e.g., ozone and particulate matter, and influence climate and ecosystem nutrient cycling. NO is emitted by a variety of sources and is rapidly converted to NO2. Because NO2 is short-lived, NO2 concentrations are highly variable spatiotemporally. Satellite instruments produce spatially-comprehensive observations, including in locations where there are no surface measurements; however, there are uncertainties in their application that require examination. In this dissertation, I generate and analyze new observational constraints on intraurban NO2 spatial patterns and NOx emissions in three different environments: U.S. urban areas where NO2 is distributed unequally at neighborhood-scales; cities in West Africa, where there is almost no routine surface monitoring; and an agricultural field in Nebraska, where soil NOx emissions potentially affect regional air quality and are highly uncertain. I use satellite and surface measurements to advance our ability to describe and understand NOx sources and NO2 impacts and use satellites for this purpose. Specifically, I develop an approach to calculating enhancements in satellite NO2 columns above the tropospheric background that I apply to reduce a substantial low bias in census tract-scale NO2 inequality estimates. I show that this approach produces inequality estimates that are, on average, ~50% larger than those from tropospheric vertical columns and discuss the politically relevant implications of the column enhancements. Second, I use satellite and vehicle measurements to estimate NOx emissions in 21 West Africa cities, showing that the current methodology has a low bias when applied to West African cities, and describe new approaches to disaggregating overlapping plumes within cities that are not isolated from surrounding sources. Lastly, I present the first multi-month eddy-covariance NO and NOx flux record over a U.S. agricultural field, with which I investigate, but ultimately find no evidence of, NO freeze-thaw pulses. To conclude, I provide commentary on areas for future work.
