Air pollution, including ozone, PM2.5, diesel PM, toxic releases, and traffic impacts, is correlated to risks to human health. California cities have the worst air pollution in the USA. Our study used a GIS approach to analyze air pollution, asthma, and cardiovascular disease in two California cities, Los Angeles and San Francisco. We determined the distribution of different air pollutants, generated an air pollution percentile measure, determined the top explanatory pollutant in each city, and analyzed the correlation between the top explanatory pollutant and the two diseases using different regression models.