This study explored the nature of the health risk in the population of three municipalities of the Metropolitan Area of the Valley of Mexico (MAVM) by means of an empirical analysis of the health effects of air pollution and temperature variation. Based on the environmental justice theory, we asked whether, in unequal socioeconomic municipalities of the MAVM, the association between concentration and mortality depends on socioeconomic disparities. We differ from what has usually been done on these studies to establish the relationship between and mortality, by using a state-space model, instead of the Poisson regression model. The state-space model allows us to estimate the size of the unobserved at-risk population, its hazard rate, the life expectancy of individuals in that population, and the effect of changes in environmental conditions on that life expectancy. Our results show a lower hazard rate in the wealthy municipality, as compared to the higher hazard rate in the poor one. The lower hazard rate of the wealthy municipality extends life expectancy and enhances the likelihood of inhabitants staying long-lasting within the population at risk, thus increasing the size of that population, as compared to the population at risk in the poor municipality, whose members show a lower life expectancy. Thus, the smaller the at-risk population, the sicker its average member and, therefore, the smaller the impact on long-term mortality. Our study examines how health disparities play out regionally could provide information to propose public health policy initiatives that might improve living conditions among different communities.