Air pollution is an emerging environmental issue in the big cities of Pakistan. Dust and smoke particles in Pakistan are generally twice the world average and five times higher than in the developed world. Though some of the pollution comes from natural sources, most is the result of human activities. The biggest causes are fossil fuel-burning power plants and cars. Combined, these two sources are responsible for about 90% of all air pollution. The most serious issue relating to air pollution in Pakistan is the presence of excessive suspended particulates matter (SPM).