By means of a single-bounded, referendum format contingent valuation, this paper estimates willingness to pay (WTP) for improved air quality among residents of Mexico City Metropolitan Area (MCMA). Findings from this paper illustrate heterogeneity in WTP associated with environmental and social attitudes, and family concerns. For instance, WTP is higher than average if respondents state a very high priority to air pollution but smaller than average if respondent's household contains more adults than the sample median. This contingent valuation exercise provides elements to carry out cost-benefit analysis of environmental policies both recently implemented and currently under discussion in the MCMA context. For instance, a cost-benefit analysis using estimates from this paper suggests benefits from improved air quality surpass the costs of investing in hybrid buses. Usefulness of this study is underscored by pointing out recent evidence suggesting that (1) air pollution in MCMA has larger health impacts than in similar cities located in developed countries, and (2) policies tackling air pollution in MCMA have had no impact on pollution levels.