The composition of fine particles depends on the source. Wind-blown dust tends to be made of mineral salts and other crustal earth material. Primary emissions from combustion sources are made primarily of unburned fuel (hydrocarbons), elemental carbon (soot), elemental sulfur, mineral salts, and often contain traces of toxic metals. Secondary emissions are a combination of ammonia with either sulfuric acid or nitric acid and water. Several classes of chemical compounds are known or believe to contribute to radiative forcing. These are sulfate, sea-salt, carbonaceous, and mineral dust aerosols. Sulfate aerosols consists of the sulfate anion existing in various chemical states: sulfuric acid, ammonium bisulfate, ammonium sulfate, or as a dissociated anion in aqueous solution. Sea-salt aerosol , the second largest contributor the global aerosol budget, consists mainly of sodium chloride salt from seawater.
Other components of seawater include magnesium chloride and organic compounds, which may influence its chemistry. The range of carbon-containing compounds that constitute the carbonaceous aerosol fraction are usually divided into two subclasses: organic carbon and elemental carbon. Elemental carbon is often referred to as black carbon or soot. The elemental portion of carbon aerosols are strongly light-absorbing while organic carbon consists of both light-scattering and light-absorbing compounds.Mineral dust refers to soil, dust and other windblown material from the earth’s surface.This makes up the majority of particulate matter less than 10 micrometers in size across the globe.