ultrafine

Ultrafine refers to particles with diameters typically less than 100 nanometers (0.1 micrometer). In aerosol science, ultrafine particles form a subset of nanoparticles, distinct from fine particles (about 0.1 to 2.5 micrometers) and coarse particles (2.5 to 10 micrometers).

Common sources include natural processes such as wildfire smoke, volcanic ash, sea spray, and dust, as well as human activities such as combustion (vehicle exhaust, industrial furnaces), welding, spray processes, and the production and use of engineered nanomaterials.

Due to their high surface area, ultrafine particles exhibit unique chemical reactivity and small mass per particle, affecting transport, agglomeration, and deposition. They diffuse readily in air, can remain suspended for long periods, and may coagulate to form larger particles or grow by condensation.

Inhalation is the primary exposure route. Ultrafine particles can reach deep lung regions and may translocate to other organs, potentially contributing to inflammation and cardiovascular or respiratory effects. Occupational exposure controls and air filtration are common mitigation measures; measurement typically centers on particle number concentration rather than mass.

Measurement uses instruments such as condensation particle counters and mobility analyzers (SMPS/DMA) to determine number concentration and size distribution. Regulatory focus varies by jurisdiction; many agencies regulate coarser fractions (PM2.5, PM10), while ultrafine-specific limits are not universal, and risk assessments are ongoing for consumer products and industrial processes.

Engineered ultrafine particles are used in medicine (drug delivery), catalysis, electronics, and materials science. Common materials include carbon black, titanium dioxide, silica, silver, and gold nanoparticles, among others. Environment and ecology considerations address fate, transport, and potential effects of nanoparticles in air and water.