The good and bad of LA air quality during the shutdown

COVID-19 hit the pause on LA traffic, reducing some chemicals in the air, but unleashing others


Quiet streets, clear views. The COVID-19 shutdown might be remembered as the moment when people caught a glimpse of car-dependent Los Angeles suddenly without traffic. So, what did this respite from exhaust mean for the air we breathe? 


Yes, in general, the air quality did get better during the more than three months of shutdown. But the story is not pure good news. While some harmful chemicals in the air decreased, others, such as ozone, jumped in to take their place. 



The results surprised even some scientists who have been studying the air in Los Angeles for decades. Ed Avol is a professor at the University of Southern California Keck School of Medicine’s Department of Preventive Medicine. He has spent the past few months observing how the rapid changes in the levels of pollutants altered the balance in the air. 


“It turns out to be quite an interesting time if you’re a chemist because of the intricate dance between some of the pollutants that are involved in the atmosphere,” he said.


First, the good news. Vehicle traffic dropped significantly across the region, as businesses, schools and just about everything else shuttered this spring. That reduced many of the direct emissions that usually flood  the Los Angeles basin.


 “That is tailpipe emissions, emissions that come right out of smokestacks and power plants and so forth,” said Avol, who studies the impact of air pollution on public health. 


That led to a drop in some of the main ingredients that contribute to Los Angeles’s legendary air pollution, such as nitrogen oxides. 


“We know there’s a wide laundry list of health effects associated with those pollutants,” said Avol. 


Lower levels of those chemicals tend to reduce risks for people with preexisting cardiovascular respiratory disease. That could mean fewer visits to the emergency room or reduced reliance on medication. 


There is one other bright spot: Less traffic and better visibility also encouraged people to walk and bike more. That also leads to more positive health outcomes, noted Avol. 


But here’s where the story gets hazy. Los Angeles air pollution is the product of an array of chemicals that react with one another and then bake in the sun, causing additional reactions. If the level of one type of pollutant suddenly drops, it can set off a series of chemical reactions as other elements in the air readjust to the new conditions. And that is essentially what happened over the past few months. 


“You’d think that if the primary pollutants are down, everything would get cleaner,” said Avol. “In fact, what happens in some cases is some things go wild because they’re no longer hampered or held back by any of the other pollutants.”


While there has been less particulate matter and nitrogen oxide, “We’ve seen more in the way of ozone formation, which is a secondary pollutant,” said Avol. “It’s not directly emitted from anything. It is a result of chemistry that takes place in the atmosphere with the ultraviolet radiation from the sun.”


The spike in ozone levels is the not-so-happy part of the story. 


 “Although you can’t see it, so it looks clear, it turns out to have a number of effects, from respiratory irritation, as in taking a breath in hurts your chest, but also long-term effects on cardiovascular disease, even mortality and other respiratory problems,” said Avol. 


That period may be short lived. (Or not.)


Traffic has begun to creep up, increasing the direct emissions that are a mainstay of local pollution. In addition, we’re in the middle of the summer smog season, said Avol, “when air pollution here in Los Angeles gets stagnant for several days at a time and things cook in the air.”