Travel and air pollution during COVID-19

Weather Headlines

With the shutdowns of COVID-19, it’s clear that people are traveling less. Vehicle miles fell by more than 60% from early March to mid-April, and demand for flights has been close to zero. But what does this mean for climate change? Last week, we showed that even an unprecedented one-year drop in greenhouse gas emissions won’t halt the rise of long-lasting CO2 in the atmosphere. Short-term air pollutants (which are gone in months, not centuries) are a different story—as seen in recent clean air revelations from India to California. This week, we discuss how ground travel and air pollution are changing locally, and what might happen in the long-term. 

One way to track travel involves our cell phones—which record the maximum daily distance from their initial location. Descartes Labs has aggregated this daily mobility data since March 1st (excluding weekends), and the results are striking. All 50 states saw mobility drop by more than half at some point, relative to a pre-pandemic baseline. In 26 states, the maximum decrease was more than 90%. However, mobility has started to rise again in some places, most noticeably the Southeast and Great Plains.

Transportation accounts for 28% of U.S. greenhouse gas emissions, and it has a major impact on local air quality. Cars, trucks, and shipping emit more than half of the nation’s NOx, a group of smog-forming pollutants led by nitrogen dioxide (NO2). Air pollutants have harmful and unequal health effects, from asthma and breathing problems to increased risk of infection during the pandemic itself. But as travel plummeted, March NO2 levels fell about 30% in the Northeast and 40% in the Southeast, relative to a 2015-2019 baseline. (Stay tuned for other regional before-and-after maps as NASA releases them). 

The cleaner air may not last, as recent mobility trends suggest. Additionally, hotter and sunnier days lead to more air stagnation and ground-level ozone formation, as seen in Los Angeles already. Above all, today’s cleaner skies are a reminder of what lower emissions can do for our health and quality of life. 

METHODOLOGY

Maximum mobility data from March 1st to May 1st was obtained from Descartes Labs. The percent change in mobility for weekdays was analysed relative to a 3-week baseline (February 17th to March 7th) for each state and Washington, DC. The national map illustrates the maximum change in mobility over the study period. Full methodology can be found in Warren and Skillman (2020). The linked NASA images show satellite data of NO2 from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite. 

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