fineparticle

Fine particles are small solid or liquid particles. In aerosol science, they are typically defined as particles with an aerodynamic diameter of 2.5 micrometers or smaller (PM2.5). This category is distinguished from coarse particles (2.5–10 μm) and ultrafine particles (below about 0.1 μm).

Their small size yields high surface area to mass, affecting reactivity, transport, and health impacts. They are characterized by aerodynamic diameter, mobility diameter, or geometric diameter. Instruments include cascade impactors, optical particle counters, and differential mobility analyzers.

Fine particles originate from combustion (vehicles, industry) and from gas-to-particle conversion in the atmosphere, producing sulfates, nitrates, and organic aerosols. They can be emitted directly or formed in situ.

Health effects include deposition in the alveolar region and potential systemic exposure. Climate and air chemistry effects include scattering and absorption of radiation and participation in cloud formation. In industry, fine powders are used as pigments, catalysts, and carriers but require safety controls due to inhalation hazards.

Monitoring PM2.5 is common in air quality programs, with exposure limits varying by country. Measurement uses filtration-based samplers and real-time sensors.