What is Ozone?
Ozone (O3) is a colorless, odorless gas comprised of three oxygen atoms, making it a reactive oxgyen species (ROS). Depending on where it is located in the atmosphere, ozone can have both beneficial and deleterious effects on your health (see figure 1).
Tropospheric Ozone (Ground-level Ozone)
Where does ground level ozone come from?
Ground level ozone is the primary component of smog and is generated from chemical reactions between UV rays (sunlight), heat, oxides of nitrogen (NOx) and volatile organic compounds (VOCs). These NOx and VOCs are emitted into the atmosphere through exhaust from the incomplete burning of fuel in automobiles, trucks, aircrafts, ships and industrial facilities, as well as several natural sources (EPA, 1999).
Ozone levels tend to increase during the day an peak in the early evening. Levels also tend to be higher in summer months. This is because reactions that cause ground level ozone require sunlight's UV rays and the heat of the day to have time to work on theprimary pollutants, NOx and VOC. During the night fewer primary pollutants are made (less driving, industry) and air currents dilute the ozone formed during that day. This is why you may have been told it is better to exercise outside in the morning or why the air may just not 'breathe well' if you are out in an urban area around 5pm in July vs December.
Why We Care
With more than 100 million people in the United States living in areas that
fail the clean air quality standards set by the U.S. Environmental Protection
Agency (EPA), ozone exposure remains an important topic of interest (Chuang et al., 2009; Federal Registrar,
2008). Studies have shown links between oxidative stress and health
complications such as asthma, chronic obstructive pulmonary disease (COPD),
idiopathic pulmonary fibrosis and acute respiratory distress syndrome (ARDS)
(Biswas &Rahman, 2009; EPA, 1999; Chuang et
al., 2009). Even at low levels, chronic exposure to ozone has been
shown to cause strutural injury to the lung and chronic inflammation (Van Bree et al., 2001). To learn more about
these diseases, check out our Lungs Page.
Understanding the air around us
As part of the Clean Air Act, the EPA is required to set National Ambient Air Quality Standards to monitor concentrations of certain air pollutants that are considered to harmful to the environment or health of the general public (EPA, 2010). To learn more about learn more about about these standards, check out the EPA’s webpage.
As an indicator of a location’s daily air quality and based on these standards, the EPA determines an Air Quality Index (AQI). The AQI is calculated for five major air pollutants that are regulated under the Clean Air Act: Ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide (AIRnow, 2010). Of these five pollutants, ground-level ozone and airborne particles pose the greatest threat to the general public’s health in the United States (AIRnow, 2010).
The AQI is the color coded scale that you may see reported in the news. It is set to a scale of 0 to 500 and is divided by relative health impact into the six color categories.
contents from: http://www.airnow.gov/index.cfm?action=aqibasics.aqi
To find out what the air quality in your area is and how it ranks compared to other cities, check out the American Lung Association's 2010 State of the Air results.