An aerosol is a suspension of fine solid particles or liquid droplets in
air or another gas. Aerosols can be natural or anthropogenic. The term
aerosol commonly refers to the particulate/air mixture, as opposed to the
particulate matter alone. Examples of natural aerosols are fog or mist, dust,
forest exudates, and geyser steam. Examples of anthropogenic aerosols include
particulate air pollutants, mist from the discharge at hydroelectric dams,
irrigation mist, perfume from atomizers, smoke, dust, steam from a kettle,
sprayed pesticides, and medical treatments for respiratory illnesses. When a
person inhales the contents of a vape pen or e-cigarette, they are inhaling an
anthropogenic aerosol.