smoke

Smoke is a visible aerosol produced by the incomplete combustion of materials. It comprises a mixture of solid particles, liquid droplets, and gases that are suspended in air.

The solid fraction includes soot and ash; the liquid fraction consists of tar droplets; common gaseous components include carbon dioxide, carbon monoxide, nitrogen oxides, sulfur dioxide, and a variety of volatile organic compounds, including formaldehyde and polycyclic aromatic hydrocarbons.

Sources include wildfires, residential wood burning, vehicle exhaust, industrial processes, and tobacco combustion.

Smoke characteristics depend on the fuel and conditions; it varies in color, density, and how long it persists in the air. Particulate matter in smoke is often described by size, such as PM2.5 and PM10.

Health and environmental effects include respiratory irritation, exacerbation of asthma and COPD, and broader cardiovascular risks from prolonged exposure. Smoke also reduces visibility and alters climate through scattering and absorption of radiation, with effects varying by composition.

Air quality indices and standards monitor PM2.5 and PM10 to manage exposure and inform public health advisories.