Outdoor air pollution is a combination of different harmful substances, but the exact components vary depending on the sources of pollution nearby your location and weather. Air pollution is separated into indoor and outdoor pollution. Both indoor and outdoor air pollutants have been found as the causes of cancer, it is important to keep the risk in mind and take necessary precautions. Sources of outdoor air pollution can be man-made, such as vehicular emission, smoke from burning fuels. While dust, radon gas are natural sources of air pollution.