Aerosols

An aerosol is a suspension of fine solid or liquid particles in a gas, typically air. Particle sizes are commonly described by aerodynamic diameter, ranging from about 0.001 μm to over 100 μm, with most atmospheric aerosols in the 0.01–10 μm range. Aerosols can remain suspended for hours to weeks, depending on size and weather.

Aerosol composition includes mineral dust, sea salt, organic matter, soot (black carbon), sulfate, nitrate, and biological materials such as pollen and bacteria. They originate from natural sources (dust storms, sea spray, volcanic ash, wildfires, pollen) and human activities (fossil fuel combustion, biomasses, industry, agriculture).

Aerosols are classified as primary, emitted directly, and secondary, formed in the atmosphere from precursor gases (SO2, NOx, volatile organic compounds) through chemical reactions producing sulfates, nitrates, and secondary organic aerosols.

Impact: climate and weather, affecting Earth's radiation balance by scattering and absorbing sunlight and by acting as cloud condensation nuclei; health effects from inhalation, especially fine particles (PM2.5) linked to respiratory and cardiovascular diseases; indoor aerosols affecting air quality.

Transport and fate: aerosols can be transported long distances; removed by dry deposition, scavenging by rain (wet deposition). Measurement: mass concentration (μg/m3) for PM2.5 and PM10; number concentration; tool: air quality monitoring networks.

Research and regulation: studied by atmospheric science, environmental health; monitoring networks; guidelines by WHO and national agencies; applications in medicine and industry (aerosol therapies, spray drying).