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Pollution from vehicles down in Clark County, but outdoor burning rises

The cloud of COVID-19 comes with a thin silver lining: air pollution usually caused by commuting vehicles is down in major metropolitan areas, due to more people staying home.

But in Clark County, the full picture is a little more complicated.

Our region hasn’t seen pollution drop as significantly. In fact, according to various metrics monitored by the Southwest Washington Clean Air Agency, there hasn’t been much change at all — although emissions from cars are down, other kinds of pollutants, like those that come from wood burning, are up.

“While automobiles are still a concern, the majority of our air pollution comes from backyard burning, wood stoves and fireplaces,” said Uri Papish, the organization’s executive director. “During the governor’s stay-at-home order we have more people at home, which can lead to an increase in backyard burning.”

The number of backyard fires reported to the SWCAA between April and June is up 40 percent compared with the same time period last year, Papish added.

“This increase is either from an increase in burning, or because we have more people at home complaining about their neighbors burning,” Papish said.

To sum it up, the impact of COVID-19 on the region’s air quality is, so far, a wash. According to SWCAA’s particulate pollution monitor in Vancouver, particulate levels in the air between April and June of this year are similar to the levels in 2019 and 2018.

“We may be seeing an increase in outdoor burning being offset by a decrease in automobile emissions, construction, and a reduction in some industrial activities,” Papish said.

A particulate pollution monitor from the Washington State Department of Ecology, located along Northeast 84th Avenue in Vancouver, reported similar results. The monitor “does not show a significant change in concentrations in March to May 2020 compared to March to May 2016-2019,” said Beth Friedman, a natural resource scientist with the department’s air quality program.

Traffic down

As The Columbian reported last week, the number of commuters on the road plummeted during the early weeks of the COVID-19 pandemic. While traffic has since partially rebounded, it’s not at pre-coronavirus levels.

Bridge crossings are one useful measurement; before the stay-at-home order was put in place, the Interstate 5 Bridge saw between 125,000 and 149,000 weekday commuters, and the Interstate 205 bridge saw 149,000 to 175,000. But by the end of March, those figures had nearly halved, with around 80,000 daily crossings on I-5 and 89,000 on I-205.

In more densely populated metropolitan areas, most pollution comes from automobiles. Those places are seeing a marked improvement in air quality right now.

The Washington State Department of Ecology reports that emissions of carbon monoxide (CO), oxides of nitrogen (NOx), and black carbon (BC) are all down substantially in the Seattle/Tacoma region. According to Friedman, the department tracks air quality during daylight hours along the area’s major roadways.

Compared with the last five years, Friedman said, the data indicates “that decreased traffic due to the shutdown has positively impacted air quality.”

“Specifically, CO concentrations were on average 19 percent lower in 2020, NOx concentrations were on average 33 percent lower in 2020, and BC concentrations were on average 34 percent lower in 2020,” Friedman said.

She added that Vancouver has also likely benefited from a decrease in the number of cars on the road, even as other factors weigh against that benefit.

“There is no doubt that certain pollutants from automobiles have been down based on reduced traffic and fewer vehicle miles traveled,” Papish said.

“The question is whether it has been enough to affect overall air pollution levels in our area. It’s not as obvious here as it is in some major metropolitan areas where the primary source of air pollution is automobiles.”

Limits to the data

We still don’t know the full extent of the stay-at-home order’s impact on air quality, Friedman and Papish emphasized.

Both reported that weather patterns have a substantial effect on how pollution moves and settles. Without a full study of this year’s meteorological conditions compared with years prior, any conclusions they can draw from day-to-day air quality monitoring are limited.

“It’s hard to compare pollution levels from year to year and know what’s causing a change without also analyzing weather conditions,” Papish said. “SWCAA has not done an analysis on that.”

And closures related to COVID-19 slowed down more than just individual commuter vehicles. Other sources of pollution, like manufacturing, may also have strayed from their usual operations. The big-picture impact of those changes are still — literally and metaphorically — up in the air.

“We won’t know how much industrial activity has been scaled back until we get year-end emission reports from those businesses,” Papish said.



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