Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation and sea spray. Human activities, such as the burning of fossil fuels in vehicles, wood burning, stubble burning, power plants, road dust, wet cooling towers in cooling systems and various industrial processes, also generate significant amounts of particulates. Coal combustion in developing countries is the primary method for heating homes and supplying energy. Because salt spray over the oceans is the overwhelmingly most common form of particulate in the atmosphere, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total mass of aerosols in our atmosphere.
Microplastics are an emerging source of atmospheric pollution, particularly fine plastic fibers that are light enough to be carried by the wind. Microplastics traveling in the air cannot be traced back to their specific original sources, as the wind can blow the infinitesimal particles thousands of miles from where they were originally shed. Microplastics are being found in very remote regions of the Earth, where there are no apparent nearby sources of plastic. A common source of airborne microplastic fibers is plastic textiles. While most atmospheric microplastics tend to come from land, microplastics are also entering the atmosphere through ocean and sea mist.