South Coast AQMD Issues Ozone Advisory Due to Heat Wave

Valid Monday May 31, 2021 through Friday June 04, 2021

This advisory is in effect through Friday. South Coast AQMD will issue an update if additional information becomes available.

High temperatures are expected to persist over the next several days throughout the South Coast Air Basin and the Coachella Valley, increasing the likelihood of poor air quality in many areas.

Levels of ground-level ozone (smog) – the predominant summertime pollutant – are likely to reach the Unhealthy or higher Air Quality Index (AQI) levels in the Santa Clarita Valley, the San Gabriel Mountains, the San Gabriel Valley, the Inland Empire and the San Bernardino Mountains.

The National Weather Service (NWS) is predicting high temperatures over southern California that will last through this week. This is due to an upper air high pressure ridge located over northern California and a low pressure system over Baja California. Temperatures will be highest in deserts and inland areas and are predicted to last through Friday, when cooling will begin into the weekend and next week.  Elevated temperatures, which enhance ozone formation rates, coupled with predicted light winds may cause unusually high and persistent levels of ozone pollution.

When air quality is Unhealthy and reaches an air quality index (AQI) range of 151 to 200, everyone may begin to experience some adverse health effects, and residents with higher sensitivity to air pollution may experience more serious effects.  When air quality is Very Unhealthy with an AQI range of 201 to 300, everyone in the region may experience more serious health effects.

Ozone air pollution can cause respiratory health problems, including trouble breathing, asthma attacks, and lung damage.  Research also indicates that ozone exposure can increase the risk of premature death.  Children, older adults, and people with asthma or COPD may be more sensitive to the health effects of ozone.

Areas of direct impacts and poor air quality may include portions of:

Los Angeles County:  West San Gabriel Valley (Area 8), East San Gabriel Valley (Area 9), Pomona-Walnut Valley (Area 10), Santa Clarita Valley (Area 13), San Gabriel Mountains (Area 15)

Orange County:  Northern Orange County (Area 16)

Riverside County:  Corona-Norco (Area 22), Metropolitan Riverside County (Area 23), Perris Valley (Area 24), Lake Elsinore (Area 25), Temecula Valley (Area 26), Anza Valley (Area 27), Hemet-San Jacinto Valley (Area 28), San Gorgonio Pass (Area 29), Coachella Valley (Area 30), East Riverside County (Area 31)

San Bernardino County:  Northwest San Bernardino Valley (Area 32), Southwest San Bernardino Valley (Area 33), Central San Bernardino Valley (Area 34), East San Bernardino Valley (Area 35), West San Bernardino Mountains (Area 36), Central San Bernardino Mountains (Area 37), East San Bernardino Mountains (Area 38)

South Coast AQMD Advisory updates can be found at the following link:

To subscribe to air quality alerts, advisories and forecasts by email, go to

To view current air quality conditions by region in an interactive map, see

For real-time air quality information, maps, notifications and health alerts in your area, download our award-winning South Coast AQMD app at:

Hourly air quality forecasts are available at Check the hourly air quality forecast and the “Cleanest Time of Day” to help plan outdoor activities when the air quality is better.

For a map of South Coast AQMD Forecast Areas, see

What To Do When Air Pollution Reaches Unhealthful Levels:

Unhealthy for Sensitive Groups:  Air Quality Index (AQI) is 101 – 150.  Although the general public is not likely to be affected at this AQI range, people with heart or lung disease, older adults and children are at a greater risk from exposure to air pollution.  People with heart or lung disease, older adults, and children should reduce prolonged or heavy exertion.

Unhealthy:  AQI is 151 – 200.  Everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects.  People with heart or lung disease, older adults, and children should avoid prolonged or heavy exertion.  Everyone else should reduce prolonged or heavy exertion.

Very Unhealthy:  AQI is 201 – 300.  Everyone may experience more serious health effects.  People with heart or lung disease, older adults, and children should avoid all physical activity outdoors.  Everyone else should avoid prolonged or heavy exertion.

South Coast AQMD is the air pollution control agency for major portions of Los Angeles, Orange, San Bernardino, and Riverside counties, including the Coachella Valley. For news, air quality alerts, event updates and more, please visit us at, download our award-winning app, or follow us on Facebook, Twitter and Instagram.

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