Los Angeles Experiences Best Month of Air Quality Since (At Least) 1980

David Ganske
April 2, 2020

Daily life in Los Angeles has changed drastically over the past few weeks due to efforts to contain the spread of COVID-19. In a city where conversations revolve around traffic instead of the weather, Angelenos are taking notice of a new change: air quality.

While the better air quality certainly comes at a huge cost in terms of public health and the economy, hopefully we can learn something about the way the environment reacts and how policymakers (and the public) can improve air quality after the COVID-19 pandemic. At the very least, I hope this article serves as a little bit of good news in the wake of such a terrible public health crisis.

How clear is the air?

Now that a full month of data is available from the U.S. Environmental Protection Agency (EPA), we can see that March 2020 reflected the best month of air quality since at least 1980, the earliest time point from which the EPA Air Quality System reports records.

The EPA uses a measurement called Air Quality Index, or AQI, to understand air quality. A higher AQI value means greater pollution and a higher risk to health for the general public. Monitor locations across the country collect daily measurements of ozone, particle pollution, carbon monoxide, and sulfur dioxide and convert them to separate AQI values. The highest AQI value is then reported as the AQI value for the day.

The chart below shows the average of daily AQI values for each month of March from 2015 to 2020. It’s important to compare the same month as seasonal changes like rainfall, temperature, and wind can drastically impact air quality throughout the year.

The five-year March average AQI daily value from 2015 to 2019 was 66.7, reflecting a “Moderate” AQI category. During March 2020, the average AQI daily value was 46.8 – a 30 percent drop over the previous five-year average!

Here are the data highlights for the Los Angeles-Long Beach-Anaheim, CA geographic area:

  • March 2020 had the longest stretch of “Good” days on the air quality index ever recorded; that’s 21 days, from March 7 through March 27.
  • March 2020 had the lowest average AQI value for any month since 1980, the first year of available U.S. EPA Air Quality System data.

The best way to visualize the change in air quality over time is by creating a multiyear tile plot for a particular region. The graphic below categorizes AQI values for every day from 1980 to the present for the greater Los Angeles area.

From 1980 to 1995, air quality was “very unhealthy” throughout the summer and then steadily improved over subsequent years to where we are today. A big reason for this improvement is California’s Low-Emission Vehicle (LEV) Program standards that addressed automobiles sold from 1994 to 2003. The program was later expanded, and the tile plot shows how much progress California and Los Angeles have made in terms of air quality.

The tile plot also highlights the drastic change that we just experienced this March. The green strip of “Good” air quality is the longest stretch that the region has experienced since 1980.

Figure 3: Multi-Year Tile Plot of Air Quality Index Values

EPA Air Quality System (AQS) - Los Angeles-Long Beach-Anaheim, CA

Why is this happening?

The air quality is so good across Los Angeles right now for several reasons, and it’s not just because of the lack of traffic from the COVID-19 stay at home order. A combination of rain, seasonal changes, reduced traffic, and power generation are also contributing.

Rain: It’s straightforward that rain can clear the air of pollutants and increase visibility. Los Angeles received over an inch of daily precipitation on both March 13 and March 23, contributing to the clean air.

Seasonal Change: March is normally one of the better months of the year from an air quality perspective because temperatures are cooler. Heat and sunlight contribute to pollution by causing some pollutants to undergo chemical reactions, creating smog.

Reduced Traffic: The Road Ecology Center at the University of California-Davis suggests that injury and fatality collisions on California roadways have been reduced by half since Governor Newsom’s shelter-in-place order took effect on March 20.

Reduced Electricity Demand: Closed businesses are already impacting the need for electricity. According to an EPRI Report, New York and California reportedly experienced a 3 to 7 percent reduction in peak demand and energy use in the days following shelter-in-place orders. Moreover, peak power often comes with more emissions as utilities will prioritize hydropower, solar, wind, and nuclear for baseload.

The chart below of daily AQI values during the March shows how values may have started normally (from an air quality perspective) then gradually fell as more people stayed at home and businesses closed.

View to the northwest of the 4th Street Bridge and Downtown LA. You can see the Hollywood sign in the distance. (March 27)


The current air quality in Los Angeles is not sustainable in the short term, nor should it be under the given situation with COVID-19. We all hope that the virus and its impacts will be resolved quickly to reduce (and hopefully reverse) the detrimental effects on health, economy, and beyond. At the same time, policymakers can also use March 2020 and potentially beyond as a case study into how the environment will react to lower emissions.

Wouldn’t it be nice if we could return to normalcy after COVID-19 and have the benefits of clean air?

The good news is that air quality has already drastically improved from 1980 to recent years. This trend can continue through more public transportation, low-emissions or electric vehicles, and renewable power generation in place of fossil fuels.

I hope policymakers and the public take note. In the meantime, better air quality can provide some solace as we deal with the harmful effects of the COVID-19 pandemic.

Looking south from the Hollywood Hills, you could see the Port of Long Beach and SoFi Stadium.

View from Mulholland Drive above the Hollywood Hills toward the San Fernando Valley. (March 27)

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