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The Air Quality Index
 | Overview of the Air Quality Index |
The Air Quality Index (AQI) is a nationally uniform index, established by the Federal Environmental Protection Agency (EPA), used to provide the public with information on air pollutants. The AQI may be used to provide information on pollutant concentrations for ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The AQI is "normalized" across pollutants so that an index value of 100 represents the level of health protection associated with the federal health-based Ambient Air Quality Standard for each pollutant. The AQI was developed through extensive coordination with public information, health, and air quality experts, as well as input from the general public. Numerical values, descriptors, and colors are used to indicate the AQI.
Problem pollutants in the Yuba-Sutter Region are Ozone and Particulate Matter (PM10); their concentrations and Index values are reviewed daily. The Ozone AQI is determined by calculating the highest consecutive 8-hour average period for the day. The PM10 AQI is determined by calculating the 24-hour average from midnight to midnight. The pollutant generating the highest Index value is used to indicate the AQI.
The AQI is presented as a "projected" value for the current day and is generated using local and regional air pollution monitoring data, pollution trends, weather predictions, AQI predictions for the Sacramento region obtained from www.sparetheair.com , and lessons learned from Smog City at www.smogcity.com . Local air pollution data is collected from the air monitoring stations in Yuba City and Pleasant Grove. [ Information about state air monitoring stations can be reviewed here ]
Ozone, the triatomic form of oxygen (O
3), is a gaseous atmospheric constituent. Ground level, or tropospheric, ozone is the prime ingredient of smog, the pollution that blankets many urban areas during the summer. It is created both naturally and by photochemical reactions involving gases resulting from human activities (photochemical smog). Ozone forms primarily from the chemical reaction of volatile organic compounds (e.g. industrial processes, fuel combustion) and nitrogen oxides (e.g. fuel combustion) in the presence of elevated temperatures and ultraviolet light from the sun.Ozone in the upper atmosphere, the stratosphere, blocks out harmful ultraviolet radiation from the sun, but nearer the ground it traps infrared radiation reflected back up from Earth and contributes to heating the air near the planet’s surface, the so-called "Greenhouse Effect." So, more ozone can mean rising temperatures near ground-level, contributing to global warming.
Although near-ground ozone has some beneficial effects, providing excited oxygen atoms needed to produce the free hydroxyl (OH) radicals that help to bind other chemicals like sulfur and cleanse them from the atmosphere, excess ozone proves harmful to the health of humans and plants.
In high concentrations,
tropospheric ozone can be harmful to a wide range of living organisms.
When inhaled, even at low levels, ozone can cause respiratory problems and aggravated
asthma in children, the elderly, those with respiratory disease, and even otherwise
healthy adults who are working or exercising outside on a smoggy day. Children are most at
risk from exposure to ozone because they are often active outside in summertime smog.
Long-term exposures to ozone may lead to premature aging of the lungs and chronic
respiratory illnesses. Ozone also harms the environment by damaging crops, harming
sensitive waterways, and reducing visibility. For example, too much ozone can
retard tree growth or even kill trees. And if too many trees die, there will be
more carbon dioxide (CO2) in
the air, further trapping heat and raising the temperature of the planet. For
additional information on ozone visit the ARB's web site at
http://www.arb.ca.gov/research/aaqs/caaqs/ozone-1/ozone-1.htm or go
here and Search for key words.
Stratospheric Ozone
In the stratosphere, ozone is created by the interaction between solar ultraviolet radiation and molecular oxygen (O2). Stratospheric ozone plays a decisive role in the stratospheric radiative balance (absorption of UV radiation). Depletion of stratospheric ozone, due to chemical reactions that may be enhanced by climate change, results in an increased ground-level flux of ultraviolet (UV-B) radiation, which may be responsible for increased incidents of skin cancer and crop damage.
Particulate matter (PM) can be a mixture of solid particles and liquid
droplets that include smoke, soot, dust, salt, acids and metals. It can also form when
chemical reactions occur in the atmosphere due to man-made emissions, such as automobile
exhaust and industrial operations. Particulate matter may be produced by mother nature
(e.g. pollen, ocean salt spray, soil erosion) and by human activity (e.g. rock crushing,
cement production, agricultural operations, fuel combustion products, wood burning, motor
vehicles). Major sources of PM include:
-Motor vehicle exhaust
-Woodburning stoves and fireplaces
-Dust from construction, roads, landfills and agriculture
-Wildfires and brush/waste burning
-Industrial sources
-Windblown dust from open lands.
Programs designed to reduce PM include emission reduction measures from woodstoves and fireplaces; cleaner-burning fuels; emission control devices for motor vehicles and industrial facilities; dust control for roads, construction and landfills; and, measures to mitigate windblown dust with the use of landscaping methods. California EPA and Federal EPA regulate "respirable" particles at the 10 micron level (PM10) and "fine" particles at the 2.5 micron level (PM2.5). Respirable and fine particles travel deep into the lungs and have been linked to premature deaths, chronic bronchitis and aggravated asthma. Early episodes of extreme pollution by fine particles -- the most famous of which occurred in Donora, Pennsylvania and London in the 1930's, 40's, and 50's and killed thousands of people -- highlighted the importance of addressing this form of air pollution. We now understand that even at low concentrations fine particles which are inhaled and become imbedded deeply into the lungs are linked to premature death, chronic bronchitis and aggravated asthma. Children with asthma, the elderly and people with cardiovascular or respiratory disease are especially at risk from fine particle pollution. Particulate matter also reduces visibility in our national parks and wilderness areas. For more details and current regulatory action visit the ARB's web site at http://www.arb.ca.gov/pm/pm.htm.
What are Ambient Air Quality Standards?
An ambient air quality standard sets legal limits on the level of an air pollutant in the outdoor (ambient) air necessary to protect public health. The federal Clean Air Act requires that the U.S. Environmental Protection Agency (U.S. EPA) establish National Ambient Air Quality Standards and reassess, at least every five years, whether adopted standards are adequate to protect public health based on current scientific evidence. U.S. EPA is required to rely on the advice of an independent scientific panel, the Clean Air Scientific Advisory Committee. California has established ambient air quality standards equal to or stricter than the federal standards. In addition, California has standards for pollutants not addressed in the federal standards (View state and federal Standards). [Return to top of page]