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  • Ozone air pollution season is here along with hotter temperatures

    Apr 27, 2020 | Read More News
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    Southern Arizona is now entering the time of the year when levels of an air pollutant called ground-level ozone begin to climb. Fortunately, during most days from April to September the air quality in Pima County is in the good or moderate range. But there are days when the air we breathe can be unhealthy, especially for those who are sensitive to ozone. Inflamed airways, difficulty breathing, coughing and increases in asthma attacks are some of the health effects that can occur by breathing elevated levels of ozone air pollution.

    The U.S. Environmental Protection Agency reviewed health studies in 2015 and determined that the ozone standard needed to be changed to make it even more protective of public health. In 2018, the air in Pima County exceeded the revised U.S. EPA ozone standard on five days. The 2019 ozone season was better than 2018, with only one day exceeding the standard. 

    With many of us home from work or school due to COVID-19, we are driving less and air quality has improved compared to previous years. If, after we return to work and school, we continue to drive less, we could see a milder ozone season this summer, but that also depends on the weather.  

    “Ozone is a very complex air pollutant because it isn’t emitted directly from a source, but is created during a photochemical reaction with two other pollutants when weather conditions are favorable,” said Ursula Nelson, PDEQ Director.  “Ozone needs intense sunlight, still air and the right ratio of volatile organic compounds and nitrogen oxides,” Nelson said. 

    Ground-level ozone, as opposed to the ozone layer that protects us from the solar radiation, tends to be elevated from April through September when our region has more hours of intense sunlight to react with the ozone precursor emissions. In addition, warmer temperatures increase the amount of volatile organic compound (VOC) emissions that evaporate from gasoline, solvents, paints, and even vegetation. VOCs are one of the key ingredients needed for the formation of ozone, along with nitrogen oxides which come primarily from the burning of fossil fuels.
    If ozone levels are high, again, this summer, EPA could designate eastern Pima County as “non-attainment” for the ozone standard which may require restrictions on some businesses that want to expand or move here. 

    “There are many actions we can take as individuals to reduce the emissions that contribute to ozone creation,” said Beth Gorman, Senior Program Manager for PDEQ. “Some of the best ways are to maintain our vehicles, refuel in the evening, share rides, drive and idle our vehicles less, chose one day a week to work from home, and reduce the use of gas powered lawn and garden equipment. If enough people incorporate these changes into their lives, we can help keep our community healthy -- both physically and economically,” Gorman said.

    Hours When Ozone Can Be High

    As depicted here in a graph by Arizona Department of Environmental Quality (ADEQ), ozone is typically highest in the afternoon from around noon until around 6:00 p.m. Real-time ozone air pollution levels are available on the PDEQ website and individuals can sign up with the ADEQ to receive air pollution forecasts in order to plan ahead to reduce exposure and drive less on forecasted high ozone days. 

    Additional information on ground-level ozone is available on the PDEQ website and graphs of historic ozone information are included below. The first graph shows the number of exceedance days if the current ozone standard had been in place going back to 1990 and indicates that, in general, there has been a decline in those unhealthy days. The monitoring site at Saguaro Park East was used because it tends to have the highest ozone readings. 

    Number of Ozone Exceedance Days
    The graph below shows the changing, more protective EPA health standard for ground-level ozone and pollutant concentrations over time.

    Changes in EPA Ozone Standard