[snopercod]

Would you mind telling me specifically what "pollution" you are concerned about.

[dufekin]

The main air pollution problems of concern today are (tropospheric) ozone and particulates (soot and dust). Ozone is one of the major hazardous components of photochemical smog. As a secondary pollutant, ozone is not emitted directly from sources; rather, it forms in chemical reactions between various pollutants and non-pollutants in the atmosphere under certain conditions. Therefore, ozone is not easy to control because we must control the myriad source chemicals. And the chemistry isn't simple; cutting some precursor pollutants (e.g. nitrates) can enhance ozone production before reducing it. In addition, the demise of the chestnut tree and the changing composition and extent of American forests has changed the biogenic emissions profile of volatile organic compounds.

Sulfurous smog is also of concern and can be fatal, especially in some of the concentrations commonplace in the nineteenth and early twentieth centuries and in the developing world. It rarely presents an issue in America today.