Primary pollutants are emitted directly from sources such as vehicles, factories, and power plants. Particulate matter is a primary pollutant that consists of small particles of solid or liquid matter suspended in the air.

Secondary pollutants are formed in the atmosphere from reactions between primary pollutants. Ozone is a secondary pollutant that is formed from reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight.

Greenhouse gases are gases that trap heat in the atmosphere. Carbon dioxide is a greenhouse gas that is released from the burning of fossil fuels.

Air pollution can cause a variety of health problems, including asthma, cancer, and heart disease.

Air pollution can cause a variety of environmental problems, including acid rain, climate change, and loss of biodiversity.

There are a variety of ways to reduce air pollution, including using public transportation, driving less, and conserving energy.

Smog is a type of air pollution that is caused by a combination of ozone, nitrogen dioxide, and particulate matter.

Indoor air pollution can be caused by a variety of sources, including tobacco smoke, cleaning products, and building materials.

There are a variety of ways to reduce indoor air pollution, including opening windows and doors, using an air purifier, and avoiding smoking indoors.

Deposition is the process by which air pollutants are removed from the atmosphere. This can occur through dry deposition, in which pollutants are deposited on surfaces such as plants and buildings, or through wet deposition, in which pollutants are deposited in rain or snow.

Dry deposition can occur through gravitational settling, impaction, and diffusion. Gravitational settling is the process by which particles fall to the ground due to gravity. Impaction is the process by which particles collide with surfaces and stick to them. Diffusion is the process by which particles move from areas of high concentration to areas of low concentration.

Wet deposition can occur through rain, snow, fog, and cloud water. Rain and snow are the most common forms of wet deposition. Fog and cloud water can also deposit pollutants on surfaces.

Advection is the process by which air pollutants are transported from one place to another. This can occur through wind, water currents, or thermal convection.

Advection can be either horizontal or vertical. Horizontal advection is the transport of pollutants from one horizontal location to another. Vertical advection is the transport of pollutants from one vertical location to another.

Air pollutants can be transformed from one form to another through chemical reactions, physical reactions, and biological reactions. Chemical reactions are reactions in which the chemical composition of the pollutants changes. Physical reactions are reactions in which the physical properties of the pollutants change. Biological reactions are reactions in which living organisms transform pollutants.