PM2.5 has a wide range of sources and complex causes, including natural processes and man-made emission processes, mainly including
1. Anthropogenic emissions: anthropogenic emissions include particles directly emitted from fossil fuels (coal, gasoline, diesel, natural gas) and biomass (straw, firewood) combustion, road and building construction dust, industrial dust, catering oil smoke and other pollution sources, as well as secondary particles generated from the transformation of gaseous pollutants (mainly sulfur dioxide, nitrogen oxides, ammonia, volatile organic compounds, etc.) emitted at the first time.
Most of the residues discharged through combustion in the process of daily power generation, industrial production and automobile exhaust emission contain toxic substances such as heavy metals. Generally speaking, coarse particles with a particle size of 2.5 μ m to 10 μ m mainly come from road dust; Fine particles (PM2.5) below 2.5 μ m are mainly from the combustion of fossil fuels (such as motor vehicle exhaust, coal combustion), volatile organic compounds, etc.
The main sources of PM2.5 are natural sources and man-made sources, but the latter is more harmful.
2. Natural sources include soil dust, sea salt, plant pollen, spores, bacteria, etc. Disaster events in nature, such as volcanic eruptions that discharge a large amount of volcanic ash into the atmosphere, forest fires or naked coal fires and dust storms, will transport a large amount of fine particles into the atmosphere.
In addition to natural and man-made sources, gaseous precursor pollutants in the atmosphere will generate secondary particles through atmospheric chemical reactions, realizing the phase transition from gas to particle.
The main components of PM2.5 include organic carbon compounds, elemental carbon, sulfate, organic carbon compounds, sulfate and ammonium salt. Other common components include various metal elements, including sodium, magnesium, calcium, aluminum, iron and other elements rich in the earth's crust, as well as lead, zinc, arsenic, cadmium, copper and other heavy metal elements mainly from human pollution.