Which process is a source of outdoor air pollution? Check all that apply.

burning gasoline at a refinery

releasing fumes at a chemical plant

emitting particles from a dump truck

releasing radon gas from a generator

emitting carbon monoxide from a heater

The correct answers are:

- burning gasoline at a refinery

- releasing fumes at a chemical plant

- emitting particles from a dump truck

- releasing radon gas from a generator

- emitting carbon monoxide from a heater

The outdoor air pollution can be caused by both natural processes and human activities. The human activities though seem to have surpassed the natural processes and the air pollution they cause. The biggest outdoor air polluters are the industry, the combustion of fossil fuels by the vehicles, and the solid fuel burning. There's also natural polluters, like the windblown dust, the biogenic processes of the vegetation, bush-fires, volcanic activities, though all fall in the shadow of the human caused polluters in the past century.