aérosols

Aérosols are suspensions of fine solid or liquid particles in a gas. They originate from direct emission (primary aerosols) or form in the atmosphere through gas-to-particle conversion (secondary aerosols). Common examples include dust, smoke, sea spray, pollen, fog, and soot.

Particle sizes span roughly 0.001 to over 100 micrometres. Inhalable fractions are typically described by PM10 and PM2.5, representing particles with diameters up to 10 and 2.5 micrometres, respectively. Aerosols are classified by source (geogenic, biogenic, anthropogenic) and by phase (solid or liquid).

Primary aerosols are emitted directly from sources such as deserts, wildfires, seas, and industrial processes. Secondary aerosols form in the atmosphere from gases like sulfur dioxide, nitrogen oxides, and volatile organic compounds through chemical reactions and condensation, producing sulfates, nitrates, and organic aerosols.

Key properties include composition, particle size distribution, hygroscopicity (growth with humidity), and optical behavior. These properties determine how aerosols interact with light (scattering and absorption) and their ability to serve as cloud condensation nuclei, which can influence climate and weather patterns.

Health and environmental relevance: inhalation of fine aerosols is associated with respiratory and cardiovascular issues; aerosols also affect air quality, visibility, and climate forcing by altering the Earth's radiative balance and cloud properties.

Measurements and regulation: air-quality monitoring uses PM2.5/PM10, aerosol optical depth, and specialized instruments to assess concentration and properties. Policies target emission reductions and exposure limits to mitigate adverse health effects.

Applications: aerosols are used in medicine (inhalation therapies), agricultural sprays, and industrial processes such as coatings and material deposition.