Where does PM2.5 come from?

Although natural processes also produce PM2.5, its main source is anthropogenic emissions. Humans emit both direct PM2.5 and certain gaseous pollutants that are converted in the air to PM2.5. Direct emissions are mainly from combustion processes, such as the burning of fossil fuels (coal, petrol, diesel), the burning of biomass (straw, firewood), and the incineration of rubbish. Other anthropogenic sources include: road dust, building construction dust, industrial dust, kitchen smoke. Natural sources include: wind-blown dust, volcanic ash, forest fires, floating sea salt, pollen, fungal spores, bacteria. 

It can be seen that volatile organic compounds (VOCs) generated in production and living are an important source of PM2.5. At present, the number of motor vehicles is growing rapidly, and vehicle emissions have become the number one source of PM2.5.