Carbon monoxide

Nitrogen dioxide

Ozone

Particulate matter

Primary pollutants are emitted directly from sources, while secondary pollutants are formed in the atmosphere.

Primary pollutants are more harmful to human health than secondary pollutants.

Secondary pollutants are more harmful to the environment than primary pollutants.

Primary pollutants are more difficult to control than secondary pollutants.

A set of standards for outdoor air quality established by the U.S. Environmental Protection Agency (EPA).

A set of standards for indoor air quality established by the World Health Organization (WHO).

A set of standards for air quality established by the European Union (EU).

A set of standards for air quality established by the United Nations Environment Programme (UNEP).

Carbon monoxide, nitrogen dioxide, ozone, particulate matter, lead, and sulfur dioxide

Carbon monoxide, nitrogen dioxide, ozone, particulate matter, lead, and mercury

Carbon monoxide, nitrogen dioxide, ozone, particulate matter, lead, and arsenic

Carbon monoxide, nitrogen dioxide, ozone, particulate matter, lead, and chromium

A measure of how clean or polluted the air is.

A measure of how much air pollution is in the air.

A measure of how harmful air pollution is to human health.

A measure of how much air pollution is emitted from sources.

Good, moderate, unhealthy for sensitive groups, unhealthy, very unhealthy, and hazardous

Good, moderate, unhealthy, very unhealthy, and hazardous

Good, moderate, unhealthy, and very unhealthy

Good, moderate, and unhealthy

An air quality forecast predicts future air quality conditions, while an air quality alert warns of current or imminent unhealthy air quality conditions.

An air quality forecast is issued by the National Weather Service, while an air quality alert is issued by the Environmental Protection Agency.

An air quality forecast is based on computer models, while an air quality alert is based on real-time air quality measurements.

An air quality forecast is issued for a specific location, while an air quality alert is issued for a region.

Respiratory problems, cardiovascular problems, and cancer

Skin problems, eye problems, and headaches

Birth defects and developmental problems

All of the above

Vehicles, power plants, and industrial facilities

Forest fires and agricultural burning

Natural sources such as volcanoes and dust storms

All of the above

Drive less and walk or bike more

Use public transportation or carpool

Reduce energy consumption

Support renewable energy sources

All of the above

A federal law in the United States that regulates air pollution

A federal law in the United Kingdom that regulates air pollution

A federal law in the European Union that regulates air pollution

A federal law in the United Nations that regulates air pollution

To protect public health and the environment from air pollution

To reduce air pollution emissions

To improve air quality

All of the above

The National Ambient Air Quality Standards (NAAQS)

The New Source Review (NSR) program

The Prevention of Significant Deterioration (PSD) program

The Title V operating permit program

All of the above

Air pollution emissions have decreased

Air quality has improved

Public health has improved

All of the above

Population growth

Economic growth

Climate change

All of the above