We are now more than halfway through the 2020 ozone air pollution season and Pima County Department of Environmental Quality (PDEQ) has recorded two days where levels of this air pollutant exceeded the U.S. Environmental Protection Agency (EPA) health standard.
For comparison purposes, the Phoenix area has had 22 ozone exceedance days so far in 2020. During the entire 2019 ozone season, there was only one ozone exceedance day in Pima County and 39 exceedances in the Phoenix area. A variety of factors determine when ozone levels are unhealthy including sources and amounts of the ingredients (precursors) that form ozone, wind speed and direction, and other meteorological conditions.
Ground-level ozone, as opposed to the ozone layer that protects us from the solar radiation, tends to be elevated from April through September, which is 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) evaporative emissions from gasoline, automobiles, solvents, paints, engines, and even vegetation. VOCs are one of the key ingredients needed for the formation of ozone, along with nitrogen oxides (NOx), which come primarily from combustion sources.
Wildfires also contribute to the formation of ozone. Wildfire smoke contains many compounds including particulate matter, carbon dioxide, carbon monoxide, VOCs and NOx from the burning vegetation. One of this year’s ozone exceedance days occurred on June 11. PDEQ and the U.S. Forest Service staff believe that exceedance was caused by emissions from the Bighorn Fire.
If there are additional ozone exceedances this year, 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.
“We can choose a number of actions to reduce the emissions that contribute to ozone creation and help avoid more exceedance days,” said Beth Gorman, Senior Program Manager for PDEQ. “We can maintain our vehicles by changing the oil, air filters and keeping tires properly inflated; refuel in the evening; share rides with those who have not been exposed to COVID-19; drive and idle our vehicles less; choose at least one day a week to work from home; conserve electricity; and reduce the use of gas-powered lawn and garden equipment. These actions, combined with optimal weather conditions, could keep our community economically and physically healthy by staying in attainment of the EPA health standards,” Gorman said.
Real-time air pollution levels are available from multiple PDEQ monitoring sites and 5-Day Air Quality Forecasts are available from Arizona Department of Environmental Quality.