(2) The gaseous air pollutantsof primary concern in urbansettings include sulfur dioxide,nitrogen dioxide, and carbonmonoxide; these are emitteddirectly into the air from thecombustion of fossilfuels.Smoke, a collection ofairborne solid and liquid particulatesand gases emittedSOLVED PAPER–08 SOLVED PAPER–08SSE-143when a material undergoescombustion, is also a pollutant.Hydrocarbon is an organiccompound consisting entirelyof hydrogen and carbon.