The purpose of this study is to investigate the driving factors of population exposure to sources of environmental pollution and to determine if poor neighborhoods are disproportionately exposed to negative environmental externalities. This research also examines whether the concentration of polluting industries within neighborhoods of different socio-economic levels varies over time. To determine the causes of the spatial coincidence between population and industrial polluters, this study employs a mixed-methods approach. Quantitatively, this study uses an exploratory approach to capture the effects of poverty and segregation on the density of hazardous industries. This methodological approach models the spatial variation of the relationship between poverty and pollution. Qualitatively, a cross-case comparative analysis is conducted on two different socio-economic neighborhoods to trace the causes of continuity or change in industrial density. The study finds that polluting industries tend to be distributed homogenously across neighborhoods of different socio-economic backgrounds and that poverty and segregation are not mayor drivers of that distribution. On the contrary, the relationship between poor and segregated and industries presents spatial variation and it is localized in some specific areas. The case-studies comparison, moreover, indicates that the spatial concentration of hazardous industries varies over time, decreasing slightly in a middle-class neighborhood and increasing in a poor neighborhood. This is explained by: i) economic constraints and opportunities to the local economy determine the permanence of polluting activities; ii) middle-class collective actions to live in a better environment contribute to expel polluting activities from the neighborhood in the long run; and iii), local political practices and the lack of alternatives and resources to access the formal land market means that the poor face tremendous environmental burdens which traps them in a noxious environment. Several policy implications arise from this research; first, access to information, transparency, and environmental law enforcement must be strengthened in order to underpin equity and common standards across the city. Second, local governments should weigh and balance the need for housing and development, and the environmental consequences when establishing zoning ordinances. Third, policies and resources should be targeted towards residents, especially those poorer residents that are most at risk. / text