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  • 2020 Ozone Season Finally Over

    Oct 01, 2020 | Read More News
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    Pima County, Ariz. (October 1, 2020) – The last day of September officially marked the end of the ground-level ozone season in Pima County. The 2020 ozone season had numerous exceedances of the EPA health standard along with days of hazy skies burdened with wildfire smoke generated both near and far away. 

    In this region, the highest readings of ozone typically occur from April through September. “Cooler” fall temperatures, the less direct angle of the sun and fewer hours of sunlight make the formation of ground-level ozone less likely beginning in October. Only twice since 1973 have Pima County’s ozone levels been above the current EPA standard after the season ended, according to Arizona Department of Environmental Quality.

    Ground-level ozone, as opposed to the protective ozone layer above us, is formed when vehicle exhaust and other pollutants, including wildfire smoke, react with heat and intense sunlight. Ozone is a complex air pollutant present in the air throughout the United States and has been linked with respiratory illnesses, increased asthma attacks, and even premature death. 

    “The ozone season was a significant challenge this year for the tens of thousands of people in our community whose health is affected when ozone levels begin to climb” said Beth Gorman, Pima County Department of Environmental Quality’s (PDEQ) Senior Program Manager. “Those most at risk include people with lung and heart ailments, the elderly, children, and people who work outside,” Gorman said. 

    Since the beginning of May, PDEQ monitoring sites recorded eight days when ozone levels were high enough to trigger the rating of “Unhealthy for Sensitive Groups”. Seven of the eight exceedance days were due to smoke from local and regional fires. “In addition to tiny particles, wildfire smoke contains volatile organic compounds from vegetative burning and nitrogen oxides from the combustion process itself, which are the main ingredients needed to form ozone” said Gorman. “Fires in the mountains surrounding Tucson, along with smoke transported by wind from fires in other areas, caused the worst ozone season since 2011.” The days with smoke-caused ozone exceedances will be “flagged” to request they not be considered when EPA next reviews the area’s health standard attainment designation.
    Ozone graph 2003-2020
    At times, particulate matter from smoke also permeated the air in Tucson, but not enough to cause an exceedance at our monitoring sites. Individually, smoke particles are so small they cannot be seen by the human eye, but together, they obscure our views and can cause health problems to those exposed to them for an extended period of time. Tiny particles of smoke (around 1 micron or 1/70th of a human hair) can float in the air for days and even weeks. When inhaled, these little bits of air pollution can travel deep into the lungs causing inflammation and can even seep into the bloodstream to be carried to other parts of the body. 

    “To protect our health, EPA sets limits on the number of times a community can exceed a health standard within a certain timeframe. According to the Clean Air Act, EPA is also required to review the national air quality standards periodically to see if health studies show they need to be changed to be more protective,” Gorman said. The recommendation from EPA during its most recent review of the ozone standard is to maintain the current health standard that was implemented in 2015. 

    Historic monitoring data (see graph) depicts changes in the standard over time and shows that, overall, ozone levels have been trending slightly downward in Pima County. 

    Multiple actions can be taken to reduce the emissions that form ozone including driving less, combining errands into one trip, sharing rides, walking, biking, idling less, keeping tires properly inflated, maintaining vehicles, refueling after 6:00 p.m. in the summer, conserving electricity, avoiding the use of gas-powered lawn and garden equipment, and planting low or moderate VOC-emitting trees. 

    “Air quality can be affected by forces we have no control over, such as wildfires, weather, and air pollution transported from other cities,” said Gorman. “What we can control is taking personal action to reduce pollution levels, so if an extraordinary event happens, our air stays healthy to breathe.”

    For information on air quality, health and pollution reduction strategies, visit www.pima.gov\healthyair.