Ozone, according to the Oxford Dictionary, is “a colorless unstable toxic gas with a pungent odor and powerful oxidizing properties, formed from oxygen by electrical discharges or ultraviolet light. It differs from normal oxygen (O2) in having three atoms in its molecule (O3).” Depending on the location of ozone in the atmosphere, it can either protect the health of those on Earth or negatively impact it.

The good. The ozone layer occurs in the stratosphere between 9 and 18 miles above the Earth’s surface. This ozone protects the lower troposphere and life on Earth from harmful ultraviolet (UV) radiation. Specifically UVB light which is responsible for numerous negative impacts including cataracts, skin cancer, crop damage and even marine life impact (EPA.gov). Depletion of the upper atmosphere ozone as a result of human activities was first raised as a concern in the 70s and continues today with scientists monitoring ozone depletion areas and holes around the globe.

The bad. The ozone that is the greatest direct concern to human health is that which exists in the troposphere or the layer of the Earth’s atmosphere where we all live and daily activities occur. This layer is formed from natural and human caused activities and is regulated by the Environmental Protection Agency (EPA) and local regulatory agencies like the Colorado Department of Public Health and Environment (CDPHE).

Ozone in the lower atmosphere occurs when sunlight and local oxides of nitrogen (NOx) mix with volatile organic compounds (VOCs). This mixing results in significant impacts on health which increases with concentration levels (measured in parts per billion or ppb). VOCs are generally substances that you can smell and are created by sources such as industries, utilities, and gas powered tools like cars, trucks, buses and even your lawn mower.

High levels of tropospheric ozone can occur at any point throughout the year but most often occur in the summer months when temperatures are higher, winds are less and the sun is high in the sky making conditions ripe for ozone creation. Ozone can very easily be transferred by wind and because of this is a problem in areas far from pollution sources themselves (i.e. the mountains along the Front Range) and is not only an urban problem.

Opportunity for improvement. Ozone is naturally occurring but when mixed with pollution, its concentration can increase dramatically from background levels. The National Ambient Air Quality Standards (NAAQS) were first established in 1971 and are regulated by the United States Environmental Protection Agency (EPA). In 1997 the EPA proposed a drop in ozone attainment standards from 120 ppb to 80 ppb which was implemented much later due to litigation and Congressional action. According to the National Oceanic and Atmospheric Administration (NOAA, 2016), Denver has been out of attainment with the EPA ozone standards since 2007. In December of 2019, the EPA changed non-attainment status from “moderate” to “serious” with a recent recommendation to downgrade the area further to “serious” after continued high ozone summer smog events.

One positive thing regarding ozone is that its concentrations are directly related to pollution and we each have the individual and collective power to reduce pollution levels especially on days that are forecasted for high ozone levels like much of August in the Front Range (in fact, as I write this article, August 19, is an Ozone Action Day Alert with high ozone concentrations or “Unhealthy for Sensitive Groups” in the Denver Metro area). For instance, one example of direct ground ozone action is local Regional Transportation Districts (RTD) Zero Fare for Better Air initiative.

RTD is one of dozens of transportation providers in the state using a new grant program through the Colorado Energy Office as a result of recent Colorado Senate Bill 22-180. Through this Senate Bill, mass transit organizations like RTD are supported to provide free transit for riders with the state government picking up the tab. The goal of August’s free fare campaign is to save riders money while also reducing vehicle emissions during a traditionally high ozone month.

Outside of using mass transit, other things you can do to reduce ozone levels are similar to general pollution reducing efforts but include an element of timing such as limiting your energy use during forecasted high ozone days like reducing your air conditioning use, avoid using gas powered tools such as a lawn mower or chainsaw and using your emissions causing items like filling up at the gas station or mowing your lawn at night when the sun’s rays are no contributing to ozone creation.

For up to date ozone levels along the Front Range and Colorado, check out the CDPHE air quality site https://www.colorado.gov/airquality/ colorado_ summary.aspx or https:// cdphe.colorado.gov/history-of-ozone- in-colorado to learn more about the history of ozone in the Front Range. The EPA AirNow Mobile App is also a great tool for easy access to air quality levels in your area: https://www.airnow. gov/airnow-mobile-app/.

To learn more about reducing air pollutants as well as specific actions on high ozone forecasted days check out the EPA site: https://www3.epa.gov/region1/ airquality/reducepollution.html.