The 2017 Ozone Season

What is an "Ozone Season"?


An ozone season is a period of time in which ground-level ozone, which is the most common type of air pollution we have in the Alamo Region, typically reaches its highest concentrations in the air we breathe. In this region, the ozone season stretches from March through November. Ground-level ozone reaches its highest concentrations during these months because ozone forms when nitrogen oxides mix with volatile organic compounds in intense sunlight, and sunlight is strongest from April through November. It is during this time that we are most likely to have exceedances of the National Ambient Air Quality Standard for ground-level ozone. Due to additional atmospheric conditions at certain times during these months, April through May and August through September tend to have the highest concentrations of ground level ozone.

Air Quality Exceedances and Ozone Action Day Alerts


According to the new National Ambient Air Quality Standard (NAAQS) set by the U.S. Environmental Protection Agency (EPA) in 2015, ozone levels are considered to be unhealthful when they rise above 70 parts per billion (ppb). The standard is based readings taken at regulatory monitors during eight-hour blocks of time. EPA uses the average of the annual fourth highest eight-hour daily maximum concentrations from three years of air quality monitoring data to determine whether the ozone standard has been violated.

High concentrations of ozone can cause shortness of breath, coughing, wheezing, headaches, nausea, eye and throat irritation, and lung damage. People who suffer from lung diseases like bronchitis, pneumonia, emphysema, asthma, and colds have even more trouble breathing when the air is polluted. These effects can be worse in anyone who spends significant periods of time exercising or working outdoors.

When it is anticipated by scientists at the Texas Commission on Environmental Quality (TCEQ) that an exceedance of the 70 ppb standard threshold during an 8-hour period will occur the next day, the TCEQ issues an Ozone Action Day, so that health precautions and preventative measures may be taken.Health precautions may include limiting outdoor activity, while preventative measures may include driving less or avoiding traffic congestion, since the formation of ozone in this region is linked in great part to vehicle exhaust.

2017 Exceedances and Alerts


As of August 9, 2017, there have been only two Ozone Action Day forecasts during the 2017 Ozone Season for the Alamo Region, but there have been four days when there have been threshold exceedances (that is, ozone was high enough to be considered unhealthy), as indicated in the following table:
Date Alert Level
Highest 8-hour reading at Regulatory Site
05/06/17 Orange 68 - San Antonio Northwest (orange level was not reached)
05/07/17 No Alert Issued 74 - San Antonio Northwest and 72 - Camp Buillis
06/08/17 No Alert Issued 89 - Camp Bullis and 80 - San Antonio Northwest
08/01/17 No Alert Issued 75 - San Antonio Northwest and 72 - Camp Bullis
08/04/17 No Alert Issued 73 - San Antonio Northwest and 72 - Camp Bullis
08/09/17 Orange 60 - San Antonio Northwest (orange level was not reached)
For more information, review 2017 Ozone Season Resources.