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Clean air, year round.

The lockdowns and restrictions that resulted from the Covid-19 public health emergency pandemic have come to an end. Though experts are still very wary of the disease, their advice is now more focused on avoiding the symptoms of “long covid” than stopping the spread of the virus. During the pandemic from 2020 to 2022, Americans stayed home and went out a lot less. Greenhouse gasses from transportation makeup around a quarter of emissions in the US, so it stands to reason that air pollution was probably improved by the pandemic, right? Or are we jumping to conclusions?

The EPA makes historical air quality data going back decades available for anyone to peruse, so we took a look at pollution from 2018 through 2022 to see what kinds of improvements have been made. We are huge fans (pun intended) of the nine cities where Molekule air purifiers are most active, which are Austin, Chicago, Dallas, Houston, Los Angeles, New York City, San Diego, San Francisco, and Seattle.

These are also among the largest cities in the US and where more than 20% of the population lives. So we went back into the last 5 years of EPA records to see if pollution really changed all that much as a result of the lockdowns and more working at home. Like every aspect of air quality, there wasn’t a simple answer, but it was clear that post-pandemic pollution looks a lot like pre-pandemic pollution.

Chart showing AQI from 2018 to 2022 and annual averages in San Diego, San Francisco, Los Angeles, and Seattle

The West Coast from 2018 to 2022

Air quality varies considerably up and down the west coast of America. Los Angeles’s severe smog problems of the 1980s spurred a lot of EPA regulation that helped, but the geography is still susceptible to temperature inversions that hold bad air in around the city. Seattle, by contrast, is known for being close to powerful storms that bring a lot of rain but ideally exchanges stagnant air with fresh. However, since about 2017, wildfires have plagued the west coast at the end of each year. Here’s what the AQI looked like for the past five years.

Aerial view of cityscape with an orange smoggy sky

Even though people were driving less, the wildfire season has had a very negative impact on air quality in the west. In most west coast cities, 2020 was a bad year for air quality due to wildfire, despite travel decreasing. In Los Angeles and in San Diego air quality didn’t really change at all as a result of the pandemic. Both San Francisco and Seattle, however, had better air quality on average in 2021 and 2022 as the public health emergency ended.

Sunset photograph of Seattle's Public Market Center sign

It is not quite clear why the cities are so different. The Seattle department of transportation estimates that traffic dropped as much as 40% from 2019 to 2020, and in San Francisco by 15%. During that same time, LA traffic dropped by only 5%, which could account for the difference if it were not true that San Diego traffic dropped by the same amount as San Francisco. Like LA, San Diego’s poor air quality likely comes from periodic inversion layers that trap pollution. The nitrogen dioxide that primarily results from car exhaust in LA is thought to account for as much as a 60% increase in Covid deaths for every 9 ppb, which is only about 10 AQI points.


One study found that as wildfire smoke makes air quality worse, deaths from Covid rise at about half of the rate as wildfire air pollution. This means that when air quality is twice as bad due to wildfire smoke, 3 people die from Covid instead of 2.

Chart showing AQI averages from 2018 to 2022 for Chicago, Austin, Houston, Dallas, and NYC

Central and East Coast 2018 to 2022

Elsewhere in America wildfires had less of an impact, and we can see more of the impact of less driving.

Aerial view of a smoggy cityscape

In the major urban areas New York and Chicago, there was a bit of an improvement in air quality during 2019 and 2020, but by 2021 had caught up to where it would have been without the pandemic. In Texas air quality did not change much as a result of the pandemic, either. The weather in Texas tends to be hot and the state government is not fond of regulating emissions. This results in problems with ozone, particle pollution, and the smog that results from the two.

Aerial view of a smoggy cityscape

One exhaustive study on deaths in Cook County, Illinois (where Chicago is), found a particularly strong association with Covid mortality and the ozone that results from industry in and around Chicago. Each 4 ppb increase in ozone came along with a 29% increase in Covid deaths. According to the AQI, “good” air quality is anything under 54 ppb of ozone, so even at lower-than-recommended levels it can kill people. The authors of the study did note that comorbidities likely played a large role, or that ozone makes other chronic heart and lung diseases more likely to kill, not just Covid.

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