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Theses Doctoral

Three essays on the environment and health in cities

Ngo, Nicole

In my dissertation, I examine the impacts of the local urban environment on health in the developed and developing world. By 2008, more than half the global population resided in urban areas, yet many questions regarding the health impact of urban environmental factors remain unanswered. I use large, unique micro data sets on fetal health in New York City, where 8 million people reside, to observe the impacts of air pollution and extreme weather events on birth outcomes. Previous work has shown that fetal health can affect long-run outcomes, like educational attainment or income, so it is necessary to understand how exposure to various environmental factors might affect fetal health. In contrast to the U.S. where air quality regulations have been implemented since the 1960's, I also observe air pollution in Nairobi, the capital of Kenya and home to 3.1 million residents. Currently, there are no air quality regulations enforced in Kenya, nor any long-term consistent pollution monitoring, though by 2020, more than half of Kenya's population is expected to reside in urban areas. Additionally, few studies have examine urban air pollution in sub-Saharan Africa. So in another chapter, I measure occupational exposure levels of fine particulate matter (PM2.5) for individuals who work by roadways and inside informal settlements. These chapters incorporate elements from economics, public health, and atmospheric science to better understand these issues and the potential policies needed to reconcile problems of urban development and sustainability. In my first chapter, "Transit buses and fetal health: Evaluating the impacts of bus pollution policies in New York City," I provide the first estimates of the impacts of diesel vehicles on fetal health using quasi-experimental analysis. The U.S. Environmental Protection Agency (EPA) re- duced emission standards for transit buses by 98% between 1988 and 2010. I exploit the variation induced by these policy changes over time to evaluate the impacts of transit bus pollution policies on fetal health in New York City (NYC). I use bus vintage as a proxy for street-level bus emis- sions and construct a novel panel data set for the NYC Transit bus fleet that allows me to assign maternal exposure to bus pollution at the census block level. Results show a 10% reduction in emission standards for particulate matter and nitrogen oxides during pregnancy increased infant Apgar 5 scores by 0.003 points and birth weight by 6.2 grams. While the impacts on fetal health are modest, the sensitivity of later-life outcomes to prenatal conditions suggests improved emission standards between 1990 and 2009 increased total earnings for the 2009 birth cohort by at least $51 million. In my second chapter, "Occupational exposure to PM2.5 from roadways and inside informal settlements in sub-Saharan Africa: A pilot study in Nairobi, Kenya," I observe the impacts of exposure to PM2.5 for at-risk populations. Few studies examine urban air pollution in sub-Saharan Africa (SSA), yet urbanization rates there are among the highest in the world. In this study, we measure 8-hr average occupational exposure levels of fine particulate matter (PM2.5), black carbon, UV-PM, and trace elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Se, Br, and Pb) for individuals who work along roadways in Nairobi, specifically bus drivers, garage workers, and street vendors. As a comparison group we also measured exposure levels for women who reside and work inside informal settlements in Nairobi and who may also be exposed to high levels of urban air pollution. First, we find strong correlations among sources of roadside dust and vehicle exhaust across all groups. Second, we find bus drivers in Nairobi experienced 2 to 5 times the PM2.5 levels as bus or truck drivers in U.S. or European cities. Additionally, exposure levels for garage workers, street vendors, and women in Mathare were not statistically different from each other, suggesting residents in informal settlements in SSA also experience high exposure levels. These results suggest major health benefits from regulations targeting diesel exhaust emissions and roadside dust for the large portion of Nairobi residents who walk and work along roadways. We also find that improved cook stove programs could reduce PM2.5 exposure levels for informal settlement residents, particularly women. This is the first study to measure occupational exposure to urban air pollution in SSA and results from this suggest that roadway emissions are a serious concern. In my third chapter, "The relationship between temperature and fetal health in cities," I observe the impact of extreme weather events on fetal health in New York City. Climate change is projected to increase the duration, intensity and frequency of heat waves, but few studies have examined this relationship, which is of particular concern in cities where the urban heat island effect could exacerbate impacts. In this study, I combine average daily temperature from 1985-2010 with detailed birth certificate data in New York City and flexibly estimate the impact of an increase in maternal exposure to moderate and extreme temperatures. I find exposure to a day where temperature is greater than 85 degrees F is associated with a 0.37 to 1.14 g reduction in birth weight. However, I find no effect on gestational age. The effect on birth weight is modest, but using projections on how climate change might affect future heat waves, I find birth weight could reduce by 8.5 to 26.2 grams in the future, or about six times the current impact.


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More About This Work

Academic Units
Sustainable Development
Thesis Advisors
Almond, Douglas V.
Ph.D., Columbia University
Published Here
May 30, 2013