At ground level, ozone (O3) is formed by a series of reactions, under the influence of sunlight, involving volatile organic compounds (VOC) combining with a group of air pollutants known as nitrogen oxides (NOx). VOC and NOx are called ozone precursors. Volatile organic compounds are emitted by automobiles and various commercial and industrial sources. Nitrogen oxides are by-products of burning fuel in automobiles and heavy industries. Ozone, a colorless gas, is the main ingredient of smog. Ozone concentrations can vary from time of year and from year to year. Changing weather patterns (especially the number of hot, sunny days), periods of air stagnation, wind patterns and other factors contribute to ozone formation.

Ozone injures vegetation, damages materials (rubber and fabrics) and affects the respiratory system. Repeated exposure to ozone pollution may cause permanent damage to the lungs. Short-term exposure to ozone can cause chest pains, nausea, throat irritation, congestion, shortness of breath, pain when inhaling deeply, wheezing and coughing. It can worsen bronchitis, heart disease, emphysema, and asthma, and reduce lung capacity.

The ozone season for the Roanoke Valley generally runs from May through September.  Current ozone levels and daily Air Quality Index (AQI) forecasts can be found on the Virginia DEQ website: http://www.deq.virginia.gov/.

The table below shows the AQI for ozone:


Ozone in the Roanoke Valley: 

Meeting the Ozone Health Standard: To determine if an area is in compliance with the ozone 8 – hour health standard, EPA takes the fourth highest reading for three consecutive years then averages them.  Based on the new 2008 ozone standard, to be in compliance (attainment), the 3-year average must be 75 ppb or lower.  If the average is 76 ppb or higher, then the area is out of compliance (non-attainment).  Under the old 1997 ozone standard, in April 2004, EPA designated the Roanoke area as nonattainment for the 8-hour ozone standard based on the 3-year average from 2001 – 2003.  However, Roanoke entered into an Ozone Early Action Plan (EAP), which deferred implementation of the 8-hour standard if the ozone standards were met by Dec. 31, 2007. Since Roanoke met the EPA requirements for the EAP, Roanoke was able to defer the stigma and requirements of being designated as nonattainment.

Decreasing Ozone Levels: Ground-level ozone has decreased in recent years.  Some explanations include less Vehicles Miles Traveled, less NOx emissions from regional coal-fired power plants (pollutions controls, units shutdown, units converted to other fuel sources), stricter EPA regulations (vehicle emissions, point sources), an increase in the use of cleaner vehicles, and local strategies.  Occasionally, weather also influences ozone levels.

Below are charts that represent the Roanoke Valley’s ozone data from 1997 to 2013, provided by the VA DEQ.