AQI Forecast By County
Wednesday, April 26
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Air Quality Map
The map below is a 1-hour snapshot. Click to view all hours recorded since midnight.
Current map

Frequently Asked Questions

1. What are the health effects of air pollution?

Many of us experience some kind of air pollution-related symptoms such as watery eyes, coughing, or wheezing. Even for healthy people, polluted air can cause respiratory irritation or breathing difficulties during exercise or outdoor activities. Your actual risk depends on your current health status, the pollutant type and concentration, and the length of your exposure to the polluted air.

People most susceptible to severe health problems from air pollution are:
  • Individuals with heart disease - such as coronary artery disease or congestive heart failure
  • Individuals with lung disease - such as asthma, emphysema or chronic obstructive pulmonary disease (COPD)
  • Pregnant women
  • Outdoor workers
  • Children under age 14 whose lungs are still developing
  • Elderly residents
  • Athletes who exercise vigorously outdoors
High air pollution levels can cause immediate health problems:
  • Aggravated cardiovascular and respiratory illness
  • Added stress to heart and lungs, which must work harder to supply the body with oxygen
  • Damaged cells in the respiratory system
Long-term exposure to polluted air can have permanent health effects:
  • Accelerated aging of the lungs
  • Loss of lung capacity
  • Decreased lung function
  • Development of diseases such as asthma, bronchitis, emphysema, and possibly cancer
  • Shortened life span
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2. Why do foothill communities like Auburn and Grass Valley show high levels of ozone air pollution even though they're located away from major metropolitan areas?

While the majority of ozone-forming emissions, Volatile Organic Compounds (VOCs) and Oxides of Nitrogen (NOx), are produced in the Sacramento metropolitan area, prevailing winds usually carry these emissions from cars and other sources up into the foothills.

During this transport time, the VOCs and NOx continuously react with the sun's ultraviolet rays to form ground-level ozone. By the time this polluted air reaches the foothills, the majority of the emissions have been converted to ozone causing the foothills to frequently have the highest ozone levels in the region.

When the wind is calm, the emissions and ozone are not transported to the foothills, but remain closer to Sacramento. However, when the wind blows from the north to the south, the highest ozone concentrations actually occur south of Sacramento in areas like Sloughhouse or Jackson.

In addition, foothill communities often have higher levels of ozone air pollution late at night compared to other sites. This occurs because ozone is depleted at night by chemical reactions with fresh NOx emissions from cars and other mobile sources. The foothills have very few fresh NOx emissions, and therefore the ozone isn't "consumed" overnight in this area.

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3. What do Ozone Maps really show?

Ozone maps use real-time air monitoring data to show ozone air pollution levels throughout the region. Most of the time you'll notice ozone forming in the urban area and then moving "out of town" by the afternoon. However, on some occasions it appears that the ozone is being transported from one area to another area when it is actually forming at different rates in the two areas.

For example, in the morning it often appears that moderate levels of ozone are moving from the foothills down into the valley. In reality, ozone levels remain higher in the foothills overnight and through the following morning for reasons discussed in question #2. Therefore, ozone reaches the moderate level sooner. By early afternoon, ozone formation in the urban area is occurring much more rapidly than in the foothills, which allows the ozone levels in Sacramento "catch up" to, and usually exceed, the levels present in the foothills.

In summary, to understand what is really being shown in the ozone movies you must take into account differences in ozone formation rates in different areas as well as transport by varying wind speeds and directions at all times of the day.

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4. What is the main cause of ozone air pollution (smog) in the Sacramento region?

Vehicles and other mobile sources, including trucks, locomotives, buses, motorcycles, agricultural equipment and construction equipment contribute approximately 66 percent of the oxides of nitrogen (NOx) and volatile organic compounds (VOCs) that form ground-level ozone air pollution.

When weather conditions are right, exhaust from the above sources reacts with the sun's ultraviolet rays to form unhealthy levels of ground-level ozone.

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5. Is it safe to do vigorous outdoor exercise on a Spare The Air day?

It is safe to exercise in the morning. Ozone levels climb throughout the day resulting in higher readings in the afternoon and early evening hours. Morning is a good time for biking, walking, jogging or other types of strenuous outdoor activities.

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6. If ozone is invisible, why is there poor visibility on Spare The Air days?

Poor visibility is caused by two factors:

  1. The reddish-brown haze that you often see hanging over the valley is Oxides of Nitrogen, better known as NOx. NOx is converted into ozone air pollution when it "cooks" in the direct ultraviolet rays from the sun. The air districts of the Sacramento region are committed to developing programs to reduce NOx, which will decrease ozone air pollution and improve visibility
  2. Fine particles, consisting mainly of by-products from internal combustion engines like automobiles, contribute to reduced visibility.
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7. Why don't Ozone Maps include Chico? How are the boundaries of the map defined?

The area served by the Ozone Maps primarily includes the federal Sacramento Ozone Nonattainment Area identified by the U.S. Environmental Protection Agency as having a severe ground-level ozone air pollution problem. This area includes all of Sacramento and Yolo counties and portions of El Dorado, Placer, Sutter and Solano counties. Chico is not located within this area, and therefore, is not depicted in the Ozone Maps. However, ozone data from Chico are used to define the northern boundary of the Ozone Maps, so the Maps will be helpful to those living north of the Sacramento region.

In addition, the Map does extend south into northern San Joaquin County to include areas served by Sacramento TV stations, which broadcast Ozone Maps during news and weather reports. To view nationwide maps, please visit

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8. Where are the air monitoring sites located?

Here's a list of the air monitors used to produce Ozone Maps. The monitors located in the Sacramento Ozone Nonattainment Area are marked with an asterisk.

El Dorado
Davis* Goldenland Court* Auburn* Cool* Bethel Island
Vacaville* Del Paso Manor* Colfax* Placerville* Chico
Woodland* Elk Grove* Roseville* Colusa
Folsom* Concord
North Highlands* Grass Valley
Sacramento* Jackson
Sloughhouse* Livermore
San Andreas
San Leandro
White Cloud Mountain
Yuba City
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9. Is there an Air Alert service for the Bay Area?

The Bay Area Air Quality Management District provides email notification of Spare The Air episodes. You can sign up for this service on the Bay Area's Spare The Air website:

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10. Why don't Ozone Maps animate with AOL?

AOL users need to turn "compressed graphics" off. This can be done by:

  • Click "Members" from the top menu bar
  • Select "Preferences"
  • Click "WWW"
  • Click the "Web Graphics" tab
  • Uncheck the box for "Use Compressed Graphics"
  • Reload the Web page to see if the animated GIF loads correctly.
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11. How are Ozone Maps produced?

To produce the Ozone Maps, we do the following:

  • Collect latest hourly data from each of the air monitors listed in question #8
  • Quality control all of the data fro bad or invalid values
  • Contour all of the data based on the location of and value at each site
  • Overlay the colored contours onto a map of the Sacramento region
  • Combine each image into a moving map with frames every 20 minutes, or three frames per hour
  • Send the Ozone Map to the website by 20 minutes past the hour
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