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Particulate matter is small solids or liquids in the air, with primary particles directly from a source and secondary particles forming in the air. They range in size from 2-3 molecules to visible chunks and can cause breathing problems and changes in solar radiation. Sources include roads, fossil fuels, and natural events.
Particulate matter describes solids or liquids that are very small and usually present in the air, in which case they may also be referred to as particulate pollution. The size of a particle can range from just two or three molecules to chunks that are clearly visible to the human eye, albeit still small. There are two types of particulate matter, primary and secondary. Primary particles are created directly from a source and are somehow launched into the air, where they can remain suspended for hours or weeks, depending on their size. Secondary particles actually form in the air when different molecules and conditions create chemical reactions.
Most particulate matter is measured in micrometres. The smallest particles, called fine particles, are 2.5 micrometers or smaller. Coarse particles are larger, measuring 2.5 micrometers to 10 micrometers. Visually, the fine particles, if they can be seen, will appear as vapor or smoke. Larger coarse particles may be visible individually and can form grainy clouds of pollutants.
The atmosphere is not the only place where particulate matter can exist. It can also be found in liquids such as ocean water and chemical solutions. Particles in a liquid have the ability to become airborne through evaporation or types of agitation that can actually physically fling the particles into the air. An example of this is salt in the ocean that wind and evaporation can cause to become airborne. Evidence of this can be seen in metal structures near salty water bodies which can suffer from the corrosive effects of airborne particles carrying the salt onto the ground.
There are many sources of particulate matter, some man-made and some natural. One of the major sources of fine and coarse particulate pollution is airborne dust from roads. Other sources include the burning of fossil fuels such as coal, forest fires, volcanic eruptions, and emissions from car engines that use gasoline as fuel. The finer the particles, the longer they will remain in the atmosphere, allowing some to travel far enough before being washed down by rain or gravity.
One of the dangers of particulate matter, especially the fine kind, is that it can be inhaled. If the particles, which can be composed of any combination of hundreds of chemicals and elements, can pass through the defenses of the nose and mouth, then they can find their way into the lungs and possibly even the bloodstream. This can cause breathing problems and potentially contribute to a higher risk for certain types of cancer or heart disease.
Another problem caused by particulate matter is a change in the way the atmosphere absorbs solar radiation. A high enough concentration of particles in the atmosphere can change how heat passes through the atmosphere to the surface and how heat reflected from the surface returns to space. Some of the particles are able to scatter radiation, causing less heat to reach the ground, while also preventing radiation that reaches Earth from escaping into space as it normally would.
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