Which are the most important pollutants in contemporary urban environments?

In this century, the pollutants that we find in urban atmospheres are mainly emitted by the combustion of petroleum products, in the case of La Paz fuels such as fuel oil, diesel and gasoline are used; the two power generation plants located in this city (Punta Prieta and Central de Combustión Interna “CCI” Baja California Sur) burned significant amounts of fuel oil and diesel. Another contributing factor to environmental pollution of La Paz, are mobile sources, personal and public transportation vehicles, the vast majority of them, working with gasoline or diesel.
The pollutants emitted into the atmosphere of La Paz by the described sources, include carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), polyaromatic hydrocarbons and primary suspended particles. Once they are emitted to the atmosphere, a series of atmospheric chemical reactions happen between some of the compounds forming ozone (O3) and secondary suspended particles. Ozone and suspended particulate matter (PM), both primary and secondary, are the pollutants that appear to have the greatest adverse health impacts. Furthermore, they also are indicators of the complex mix of pollutants found in urban and industrial atmospheres of the contemporary world. The nature of these mixtures is potentially carcinogenic to humans, due to the presence of acids, hydrocarbons, metals and other reactive substances.