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.
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.”
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.
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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. |
| 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. |
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.
| Pollutants | Description | Averaging Period | State Standard | Federal Standard |
| CO | Carbon Monoxide | 1 Hr | 20 ppm | 35 ppm |
| CO | Carbon Monoxide | 8 Hr | 9 ppm | 9 ppm |
| O3 | Ozone | 1 Hr | 0.09 ppm | N/A |
| O3 | Ozone | 8 Hr | 0.07 ppm | 0.075 ppm |
| NO2 | Nitrogen Dioxide | 1 Hr | 0.18 ppm | N/A |
| SO2 | Sulphur Dioxide | 1 Hr | 0.25 ppm | N/A |
| SO2 | Sulphur Dioxide | 24 Hr | 0.04 ppm | 0.14 ppm |
| PM10 | Particulate Matter 10 | 1 Hr | N/A | N/A |
| PM10 | Particulate Matter 10 | 24 Hr | 50 µg/m3 | 150 µg/m3 |
| PM2.5 | Fine Particulate Matter | 1 Hr | N/A | N/A |
| PM2.5 | Fine Particulate Matter | 24 Hr | N/A | 35 µg/m3 |