The progress of the study on the estimation and forecast of air pollution in Lima-Peru is presented and discussed. This work presents the study of the reduction of atmospheric pollutants (PM10, MP2.5, CO, SO2 and NOx), reduction of patients, cost reduction due to health, due to the use of natural gas in Metropolitan Lima by 2040. A detailed study of the vehicle fleet considering the entry of natural gas into the energy matrix since 2004, of patients due to atmospheric pollution, expenses associated with people's health, then emission calculations were carried out using the emission factors as the main tool in this study and forecasts were made by statistical calculations to 2040. It was concluded with an investment proposal to the conversion of the automotive fleet to natural gas getting favorably the reduction of patients, cost for health for the state, and reduction of air pollution.