Air Quality, Urban Form, And Environmental Justice

Abstract

Exposure to urban air pollution is the largest environmental risk factor for public health in the United States (US). Inequity in exposure to air pollution (environmental injustice) has been widely documented and has been linked with pervasive health disparities in the US: people with lower socioeconomic status and people of color are often more exposed to air pollution and more burdened by adverse health impacts related to air pollution exposure. Urban form (the physical design of a city) may influence both air pollution exposures and inequities in air pollution exposures. This dissertation quantifies and explores patterns in air quality, urban form, and environmental justice, on a national basis for the US. The goal of this dissertation is to provide new information on these topics that can inform action to reduce air pollution and to reduce pervasive health disparities related (at least in part) to air pollution exposure. This dissertation consists of four US-national empirical studies of air quality, urban form, and environmental justice (Chapters 2-5), plus an introduction to these topics (Chapter 1) and a summary of findings with potential implications for future research and for policy (Chapter 6). Chapter 1 introduces relevant background on the topics of air pollution, environmental justice, and urban form, and describes the objectives, approach, and structure of this dissertation. Chapter 2 presents a study of relationships between urban form characteristics and criteria air pollutant concentrations (focusing on fine particulate matter and ozone) using linear regression models in a cross-section of 111 US urban areas. Urban form attributes of population distributions are associated with concentrations of criteria air pollutants, with strongest associations for population density (associated with increased concentrations) and population centrality (associated with decreased concentrations). The magnitude of impact for these urban form characteristics on air pollution is comparable to the magnitude of impact for climate characteristics on air pollution. Chapter 3 presents a study of national and within-urban patterns of environmental justice for a transportation-related air pollutant, nitrogen dioxide (NO2), using a national satellite-based land use regression model for NO2, paired with census data at the block group (approximate “neighborhood”) scale. Within urban areas, on average, racial and ethnic minority groups experience higher levels of outdoor NO2, even after controlling for income. Based on a simple health-risk assessment calculation, national levels of environmental injustice for NO2 air pollution (measured as the average exposure disparity between people of color and whites) are associated with a substantial additional public health burden among people of color. Chapter 4 presents a study of changes over time in national and within-urban patterns of environmental justice for NO2, using annual land use regression model for NO2 paired with census data, for years 2000 and 2010. This study finds that environmental injustice decreased substantially on an absolute basis but persisted on a relative basis. Reductions in air pollution concentrations contributed to the absolute reduction in environmental injustice more so than changes in demographics or residential patterns (e.g., suburbs becoming more racially diverse). Chapter 5 presents an exploratory study of relationships between changes in urban characteristics (segregation, urban form, income inequality) and changes in NO2 air pollution environmental justice during 2000 to 2010 across 481 US urban areas. After controlling for urban area population, region, and urban form, changes in residential segregation are associated with changes in NO2 disparities by race, by poverty status, and by linguistic isolation. Chapter 6 summarizes the findings of the studies presented in Chapters 2-5 and discusses implications for future research and policy. Collectively, these studies provide national context for inequities in transportation-related air pollution exposures and suggest that urban form can potentially play a modest role in achieving air quality goals. This dissertation contributes to the literature documenting pervasive racial disparities in environmental risks by, for the first time, quantifying disparities in exposure to transportation-related air pollution in the US on a national basis and over time. Future research could explore in greater detail the public health implications of these inequities in air pollution exposure as well as potential policies, tools, and strategies to address environmental injustice in air pollution exposure.