Carbon monoxide (CO) is a colorless, odorless gas that is formed when carbon in fuel is not burned completely. Sources include motor vehicle exhaust, industrial processes such as metals processing and chemical manufacturing, residential wood burning, and natural sources such as forest fires.

Nitrogen oxides (NOx) is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. Many of the nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide (NO2) along with particles in the air can often be seen as a reddish-brown layer over many urban areas.

Ozone (O3) is a gas created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents as well as natural sources emit NOx and VOCs that help form ozone. Ground-level ozone is the primary constituent of smog.

Sulfur dioxide (SO2) belongs to the family of sulfur oxide gases (SOx). SOx gases are formed when fuel containing sulfur, such as coal and oil, is burned, and when gasoline is extracted from oil, or metals are extracted from ore. SO2 dissolves in water vapor to form acid, and interacts with other gases and particles in the air to form sulfates and other products that can be harmful to people and their environment.

Particulate Matter 10 (PM10) or "inhalable coarse particles," or “particle pollution” are smaller than 10 micrometers in diameter. Typically found near roadways and dusty industries. PM10 is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. Once inhaled, these particles can affect the heart and lungs and cause serious health effects.

Particulate Matter 2.5 (PM2.5) or "fine particles," are 2.5 micrometers in diameter and smaller. Often found in smoke and haze, these particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.

Mapping of current air quality data

Air quality forecasts for the South Coast Air Quality Management District are prepared for nearly 40 source/receptor areas, or forecast areas. These forecast areas are displayed on the current air quality map. Most of these areas have one or more air monitoring stations that measure air pollutants and meteorological data. The real-time measurement of five criteria pollutants factor into the current Air Quality Index (AQI) reading. This monitoring equipment is distributed among the permanent air monitoring stations, as follows:

• 30 stations measure ozone;
• 26 stations measure carbon monoxide (CO);
• 25 stations measure nitrogen dioxide (NO2);
• 11 stations measure real-time PM10;
• 9 stations measure real-time PM2.5.

The sites selected for the equipment are chosen based on how well the location represents local air quality, local emission sources and transport issues, the relative severity of the problem from the predominant pollutant in the area, and financial factors, such as the cost of equipment, maintenance and support staff. For areas where a particular criteria pollutant is not monitored, the closest station or a combination of surrounding stations are mapped to that area. These substitute stations are known as proxy stations. The use of proxies allows the closest available monitoring data to be applied to forecast areas that otherwise do not have monitoring equipment for a specific criteria pollutant.

Explanation of standards

Introduction

The Air Quality Index (AQI) is an index for reporting daily air quality. It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. 

The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. Environmental Protection Agency (EPA) calculates the AQI for five major air pollutants regulated by the Clean Air Act: 

1. Ground-level Ozone (O3) 
2. Particle Pollution, also known as particulate matter (PM10 and PM2.5) 
3. Carbon Monoxide (CO) 
4. Sulfur Dioxide (SO2) and 
5. Nitrogen Dioxide (NO2). 

For each of these pollutants, EPA has established national air quality standards to protect public health. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.

Note: As an area with severe challenges to meeting federal Clean Air Act standards by their mandated deadlines, the state of California has established standards that are more stringent than federal standards for certain pollutants, including Ozone (O3) and Nitrogen Dioxide (NO2). Both state and federal standards are shown in the data tables that accompany the air quality map.

How does AQI work?

Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. 

For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality. 

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. 

AQI values below 100 are generally thought of as satisfactory. When AQI values reach above 100, air quality is considered to be unhealthy for certain sensitive groups of people. The higher the AQI values climb above 100, increasingly more people may become susceptible to the effects of the unhealthy air.”

Understanding the AQI range

The purpose of the AQI is to help you understand what local air quality means to your health. To make it easier to understand, the AQI is divided into six categories. Each category corresponds to a different level of health concern. There are six levels of health concern.

Good :  The AQI value for your community is between 0 and 50. Air quality is considered satisfactory, and air pollution poses little or no risk.

Moderate:  The AQI for your community is between 51 and 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people. For example, people who are unusually sensitive to ozone may experience respiratory symptoms.

Unhealthy for Sensitive Groups: When AQI values are between 101 and 150, members of sensitive groups may experience health effects. This means they are likely to be affected at lower levels than the general public. For example, people with lung disease are at greater risk from exposure to ozone, while people with either lung disease or heart disease are at greater risk from exposure to particle pollution. The general public is not likely to be affected when the AQI is in this range.

Unhealthy:  Everyone may begin to experience health effects when AQI values are between 151 and 200. Members of sensitive groups may experience more serious health effects.

Very Unhealthy:  Values between 201 and 300 trigger a health alert, meaning everyone may experience serious health effects.

Hazardous:  Values over 300 trigger health warnings of emergency conditions. The entire population is more likely to be affected.

Understanding the AQI color code

EPA has assigned a specific color to each AQI category to make it easier for people to understand quickly whether air pollution is reaching unhealthy levels in their communities.

Air Quality Map Help

Data is shown on the map for the areas within the South Coast Air Quality Management District only-- all of Orange County, and major portions of Los Angeles, Riverside and San Bernardino counties in Southern California. For air quality information on areas outside of this district, but still in California visit the California Air Pollution Control Officer's Association Web site or the California Air Resources Board Web site. For areas outside of California, visit the  U.S Environmental Protection Agency Web site. 

Double-click on an area in the map to zoom in, or use your mouse scroll-wheel to zoom in or out on the map.

Enter a full address, partial address or place name in the text box next to the "Search" button (ESRI World Geocoder), and then click "Search" to go to that location.

When searching follow these rules:

A full address: To ensure the best possible match, include as much of the address as you can. Use commas to separate lines in the address.

A partial address: To ensure the best possible match, include as much of the address as possible. To search for an intersection, use & between the street names.

A place or neighborhood name: To ensure the best possible match, include as much of the name as you can.

Click on an area to see a popup that displays the area number and name, the AQI category and value, identifies the pollutant associated with the AQI value, the date and time of the reading, and provides a link to more detailed measurement data.

Best viewed with Internet Explorer 7 or greater. 

When viewed with Internet Explorer (IE) versions earlier than version 7, the pop-up window with details about the current air quality for the selected SRA displays for only a short time. You can freeze the pop-up window to allow you to view the detailed information and to click on the link to the hourly data by moving your cursor continuously in the pop-up window.