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Vehicle Emissions Have Dropped (Duh), But The Effect On SoCal's Air Is Complicated

The intersections of the 5, 10, 60, and 101 freeways near downtown Los Angeles during what is usually rush hour. (Chava Sanchez/LAist)
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You don't need us to tell you that Los Angeles' skies are cleaner and clearer right now as the COVID-19 pandemic has the majority of us staying in our homes and off the roads.

The current air quality is helping us see more of the horizon at the moment, but the science is still out on what exactly its impacts will be -- even in the short term.

Still, the current crisis does offer researchers an opportunity to measure the L.A. Basin in a reduced-emissions setting.

In a basic sense, yes: less driving equals cleaner air. But, as a couple of those researchers told me recently, the chemistry playing out in our local airspace is more complex than that.

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We know transportation-related emissions -- our private cars, along with heavy trucks, planes, trains, etc. -- are behind about 80% of our region's air pollution.

Philip Fine, deputy executive officer for the South Coast Air Quality Management District, told us recently there had been fewer of those heavy trucks on the road as traffic at our local ports declined, and that slowdown began when China locked down much of its manufacturing to curb the spread of COVID-19. Much of that reduced heavy truck traffic happened in late February and early March.

"Some of that has been resolved and as long as demand for goods remains in the U.S., that may not drop as much as, say, the light-duty traffic, where people are under orders to stay home," Fine said.

But researchers can't yet say with scientific certainty by how much -- or what the effects of that drop in emissions will be.

One complicating factor I wrote about last week: March typically is already one of our better months for air quality, given the weather patterns that roll through (as in late-winter rain storms).

"Hopefully we'll get some more clarity in the next week or two, when we can look at some data under some more stagnant weather conditions," Fine told me in late March.


The San Gabriel Mountains are seen from the Interstate 10 in East Los Angeles, Monday, March 30, 2020. (Damian Dovarganes/AP)

One person looking at that more recent data is Cesunica Ivey, assistant professor of chemical and environmental engineering at UC Riverside. She studies air pollution and its effects on humans, particularly within the Inland Empire.

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"Pollution levels are not wildly different, on average, for the month of March in the South Coast Air Basin," Ivey told me. "We see the biggest drop in traffic-related activity in the last week of March, where people really started taking the shutdown very seriously."

Ivey looked at regional data collected by the California Air Resources Board's ground-based measuring network in the days since California Gov. Gavin Newsom issued a stay-at-home order. She focused on hourly levels of nitrogen dioxide, or NO2 for short.

Most NO2 comes from our fuel-burning cars and trucks, but is also generated by power plants and factories. Ivey said that, based on data from the last week of March, NO2 levels dropped up to 50% in some cases during the evening commute.

But there's also ozone -- better known as smog -- a new chemical that forms when NO2 and other car emissions get baked by the sun. Ozone levels are typically higher in the Inland Empire in the afternoon and evening because much of L.A.'s daily air pollutants get carried into the region's air.

OK, science time: vehicle emissions both cause smog and turn around and eat up some of that smog later in the day. The end result is that ozone levels typically decrease in the evening.

But, Ivey explained, because our typical routine for emitting NO2 -- particularly the evening commute -- has fundamentally changed, the smog that forms over our inland areas is lingering in the air longer, meaning those areas are seeing noticeably higher ozone levels in the hours between 6 p.m. and midnight.

Ivey stressed that while ozone levels were higher than usual in SoCal's inland region at the end of March, they're still "within the expected range for this time of year."

"It's just [that], from an atmospheric chemistry standpoint, we do see some very interesting behavior during the week that is typically not the case when we have regular traffic," she said.


Two pairs of hikers maintain social distance as they mingle at Vista View Point in Griffith Park in Los Angeles on Friday, March 20, 2020. (Chris Pizzello/AP)

At a time where we could all use some good news, it might be tempting to see that difference (literally -- you can go outside and see it) and think it's at least one positive sign to the health crisis that's completely upended our lives. But the experts who study air pollution and its relation to transportation say there is no such upside.

One expert I talked to said environmental advocates and regulatory agencies he's talking to "don't see any silver lining here."

"The silver lining is if we were able to actually transition to electric vehicles, or transition more to public transit and give people the spatial access to live their lives fully -- and without polluting the air and impacting the climate," J.R. DeShazo, director of the UCLA Luskin Center for Innovation and a professor of public policy, told me.

DeShazo says we can't compartmentalize "only the benefits" and ignore "the huge human costs and employment costs." Even if air quality is improved and that alleviates health impacts of pollution short-term, that benefit is outmatched by the unprecedented global health crisis we're facing.

"We're seeing how important travel is to producing employment opportunities and educational opportunities and access to health care," he said. "I think we have to be very cautious in how we interpret this impact."



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