Study to examine why some air pollutants rose in Austin as traffic decreased

With fewer cars on the road this spring, many air pollutants decreased, as expected in the Austin-area. At the same time, some air pollutants increased and scientists are working to find out why. 

An analysis of the Texas Commission on Environmental Quality’s data completed by the Capital Area Council of Governments, or CAPCOG, found lower concentrations of nitrogen dioxide and ground-level ozone during the last two weeks of March 2020 than the same two weeks of March 2017, 2018, and 2019.

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According to CAPCOG director of regional planning and services Andrew Hoekzema, nitrogen dioxide and ground-level ozone are “pollutants that are heavily affected by transportation.” 

Hoekzema wrote in the report that the decrease was “consistent with the roughly 50 percent decrease in regional vehicle traffic.”  During the same time period, levels of particulate matter, a pollutant Hoekzema says local experts seldom study, and carbon monoxide increased. 

“It was surprising because of all the pollutants, that’s the one that’s most affected by transportation emissions,” Hoekzema said of carbon monoxide. 

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Hoekzema noted CAPCOG was the “most surprised” but the “least concerned” by its findings on carbon monoxide, explaining “even with an increase the levels (of CO) are very low compared to what would cause health concerns.” 

To determine why carbon monoxide and particulate matter increased in March despite the traffic decline, the City of Austin has contracted with CAPCOG to conduct a study. 

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“It really points to the fact that we need to expand the way that we think about air quality,” said Phoebe Romero, of CAPCOG’s March report. Romero is the environmental program coordinator for the City’s Office of Sustainability. 

Hoekzoma says there are a number reasons the pollutants may have spiked. He says vehicle speed impacts emissions, as does vehicle type. “We saw large decreases in traffic volumes on the road but most of those traffic volumes are from personal vehicles, and those are much smaller and have much fewer emissions per mile than say an 18-wheeler-truck.” 

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Increased delivery services putting more trucks on the road, is one theory that will be explored. Environmental factors also impact pollutants. “Just the weather, wind speed.” said Romero. 

The impact changing work patterns have on power consumption will also be examined. 

“Any opportunity that we have to examine air quality and to further isolate variables that we know typically affect it is an opportunity that we’re going to take,” said Romero. 

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