Ozone season in full swing

Ozone season is in full swing, and local air quality experts are tracking differences in ozone and other pollution levels due to social distancing measures and telework practices in place because of the COVID-19 pandemic.

Ozone season runs from April until September when temperatures rise, and our region has more hours of sunlight. Those additional hours of sunlight and warmer temperatures lead to increased ground-level ozone production.

The monthly average concentration of nitrogen oxides (NOx) in the region dropped, however, in March 2020 compared to March 2019. NOx is a precursor chemical that combines photochemically with volatile organic compounds (VOCs) to form ozone. Vehicles contribute around half of the NOx in the region.

Maximum concentrations of ozone, a lung-irritating chemical at ground level, dropped slightly as well in March 2020 compared to March 2019. The 2019 ozone season was even better than 2018 and 2017, with only one day exceeding the U.S. Environmental Protection Agency ozone standard compared to five days during each of the previous two years.

“Both of these recent drops are likely influenced by reductions in vehicle miles traveled in the region and the corresponding reduction in tailpipe emissions, although it’s important to note that meteorology highly influences ozone formation as well based upon wind speed, cloud cover, precipitation and temperature,” said Pima Association of Governments’ Air Quality Planning Coordinator Dustin Fitzpatrick.

It’s too early to tell if there are any long-term positive air quality impacts. However, some of the lessons learned from the stay-at-home period could continue.

“Moving forward, we’ll continue to evaluate the regional air quality trends in the coming months,” Fitzpatrick added.