Particulates, alternately referred to as Particulate Matter (PM), aerosols or fine particles are tiny particles of solid or liquid suspended in a gas. They range in size from less than 10 nanometres to more than 100 micrometres in diameter. This range of sizes represent scales from a gathering of a few molecules to the size where the particles no longer can be carried by the gas.
Sources of Particulate Matter
There are both natural and human sources of atmospheric particulates. The biggest natural sources are wind-blown dust, volcanoes, and forest fires. Sea spray is also a large source of particles though most of these fall back to the ocean close to where they were emitted. The biggest human sources of particles are combustion sources, mainly the burning of fossil fuel in internal combustion engines in automobiles and power plants, and wind blown dust from construction sites and other land areas where the water or vegetation has been removed. Some of these particles are emitted directly to the atmosphere (primary emissions) and some are emitted as gases and form particles in the atmosphere (secondary emissions).