State the symbol equation for the conversion of sulfur dioxide to sulfur trioxide in the Contact process, (2SO_2(g) + O_2(g) ightleftharpoons 2SO_3(g))
State the source of each of these air pollutants, limited to: (a) carbon dioxide from the complete combustion of carbon-containing fuels (b) carbon monoxide and particulates from the incomplete combustion of carbon-containing fuels (c) methane from the decomposition of vegetation and waste gases from digestion in animals (d) oxides of nitrogen from car engines (e) sulfur dioxide from the combustion of fossil fuels which contain sulfur compounds