Air Quality

As the air pollution control agency for all of Orange County and major portions of Los Angeles, Riverside and San Bernardino Counties, the South Coast Air Quality Management District collects data on current air quality, provides forecasts and analyzes trends in levels of pollutants. In addition, South Coast AQMD staff models and provides data for specific projects.

What is air pollution?

Air pollution is a complex mixture of gases and small particles suspended in the air. The different health effects of air pollution are dependent on how much of the pollutant is in the air, how long a person is exposed, as well as the person’s health conditions, age, and genetic background. Children, elderly people, and people with certain health conditions, such as diabetes, heart or lung disease, are more sensitive to the health effects of air pollution.

In California, “smog” is primarily driven by two pollutants: particulate matter (PM) and ozone. This table provides information on these two pollutants:

Particulate Matter (PM)


Type of pollutant

Small particles




Where does it come from?

  • Combustion sources: cars, trucks, trains, ships, aircraft, certain types of facilities, meat cooking, residential wood burning, wildfires

  • Natural sources: dust storms

  • Much of the PM2.5 in the inland regions is formed from several pollutants mixing or reacting in the air.

  • Ozone is formed when several gaseous pollutants react in the presence of sunlight.

  • Most of these gases are emitted from mobile sources.

Is it visible?

Yes, but only at very high levels


What are the main health effects?

Cardiovascular and respiratory



What are the most affected areas?

  • Areas near major roadways, ports, railyards, and other combustion sources.

  • Inland areas and valleys.

Inland areas and valleys


While air quality has improved tremendously in our region over the past few decades, the South Coast and Salton Sea air basins continue to have days where pollutants can reach unhealthy levels. The time of the day or year, and weather conditions can significantly affect the pollutant levels at a particular day and time. The South Coast Air Quality Management District provides information on how to check the current air quality, predictions for future air quality, and what actions you can take, depending on the conditions.

How can I check the Air Quality in my area?

The Air Quality Index (AQI) was developed to help translate data collected from air pollutant monitoring stations into a scale. The AQI is a number that ranges from 0 to 500 that indicates how clean or polluted the air is, and what associated health effects might be of concern to diverse individuals within a population. The AQI focuses on health affects individuals may experience within a few hours or days after breathing polluted air. The higher the AQI value, the greater the level of air pollution and the greater the health concern.

The AQI is divided into six categories and each category is assigned a color to help visualize the information on the Current AQI map. Type your address in the box in upper left-hand corner of the Current AQI map ( and match the color to the legend.


 Good (0 to 50). Air quality is considered satisfactory, and air pollution poses little or no risk.


 Moderate (51 to 100). Air quality is acceptable; however, unusually sensitive people should consider limiting prolonged outdoor exertion. 


 Unhealthy for Sensitive Groups (101 to 150). The following groups should limit prolonged or heavy outdoor exertion: People with heart disease, pregnant women, children and older adults, people with lung disease, such as asthma


 Unhealthy (151 to 200). Everyone may begin to experience some adverse health effects (e.g. difficulty breathing and throat irritation), and members of the sensitive groups may experience more serious effects. The following groups should avoid prolonged time outdoors: People with heart disease, pregnant women, children and older adults, people with lung disease, such as asthma.


 Very Unhealthy (201 to 300). This would generate a health alert suggesting that everyone may experience more serious health effects. The following groups should avoid all outdoor physical activity: People with heart disease, pregnant women, children and older adults, people with lung disease, such as asthma. Everyone else should avoid prolonged or heavy outdoor activity. 


 "Hazardous" (greater than 300). This would trigger health warnings of emergency conditions. The entire population is more likely to be affected. Everyone should avoid all physical activity outdoors.


For more information about the AQI, its calculation and pollutants measured visit the Environmental Protection Agency (EPA)’s Air Quality Index (AQI) basics Link to external website. website.  

Air Quality Guidance for Schools (PDF)

Related information: 

Sign-up for Air Alerts
(Customizable email alerts)

Please visit Link to external website. for current hydrogen sulfide (H2S) monitored values in the Salton Sea area or to sign-up for H2S alerts. 

Newsletter Sign Up
Periodic newsletter updates via Email on a variety of air quality-related topics

South Coast Air Quality Management District

21865 Copley Dr, Diamond Bar, CA 91765



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