 Experts cite coal mining, population growth, and the oil and gas industries as potential reasons for the Denver metro area becoming more polluted.In order to ensure safe ozone levels in an occupational setting, federal regulations are in place in order to enforce workplace exposure limits for all working men and women.These measures are not implemented as a response to Ozone Action Days but rather they are in place in order to reduce the levels of ozone and contribute to the overall reduction of ground ozone in the environment.