COVID-19 Social Distancing and Air Pollution in New York City
By Ahmed Mustafa and Timon McPhearson
Millions of people are staying at home as many cities worldwide have taken measures to slow the outbreak of the novel coronavirus (COVID-19). New York City (NYC) has been the hardest hit by COVID-19 spreading and it is now labeled as both the current ‘epicenter’ and the ‘vanguard’ of the pandemic (Angel et al., 2020) in the US and worldwide. As a result, on March 7, 2020, Governor Cuomo declared a state of emergency in New York, on March 13, 2020, NYC banned large gatherings, and on March 16, 2020, NYC closed the majority of businesses, restaurants, and schools. The orders to stay at home and practice social distancing have now lasted for several weeks and will possibly be extending from weeks to months. Multiple news reports and articles shared observations showing a decrease in concentrations of Nitrogen Dioxide (NO2) in the atmosphere as an apparent result of stay-at-home and limited human activity. For example, the Daily Mail (Morrison, 2020), Euro News (Katanich, 2020), National Geographic Society (Gardiner, 2020), NYC Department of Health (NYC Government, 2020), and many others published reports on the apparent drastic decline in air pollution in global megacities such as NYC during this period of shelter in place and other COVID-19 social distancing measures. However, though anecdotal observations are compelling, it is unclear whether social distancing and other policies and changes in human behavior associated with the current pandemic are causing declines in air pollution. In fact, there are multiple factors that have an interdependent impact on how, and where, different levels of pollution are found which makes it difficult to demonstrate an explicit relationship between cleaner air and the stay-at-home orders.
We collected and processed the Nitrogen Dioxide (NO2) levels, emitted by road traffic and other fossil fuel combustion processes, and weather data for NYC weekly for two months between February 1, 2020 and May 1, 2020. We collected the Copernicus Sentinel-5P satellite data which provides one of the most accurate satellite measurements of NO2. Weekly weather data were collected from Phase 2 of the North American Land Data Assimilation System (NLDAS-2).
What Does the Data Show?
Figure 1 shows the monthly average NO2 in 2019 and the first months of 2020. The figure reveals that NO2 concentrations tend to be lower in the spring and summer than in the fall and winter. This is in line with other studies that have detected similar seasonal patterns in Cabauw (The Netherlands) and Calcutta (India) (Demuzere et al., 2009; Mondal et al., 2000). During cold seasons, atmospheric stability, as a result of frequent inversion layer that happens when the upper air layer is warmer than a lower one, leads to the accumulation of pollutants (Tiwari et al., 2015). Although it is normal to see lower NO2 levels in March and April than January and February, there is a notable drop in 2020 compared to 2019. This can be “partly” correlated with the COVID-19 lockdown in NYC which began in mid-March due to COVID-19 stay-at-home orders. The annual drop in concentrations of air pollutants including NOx (Figure 2) in the USA, that is largely driven by federal and state implementation of air quality regulations (Sullivan et al., 2018), can easily confuse the relation between potentially cleaner air and the COVID-19 lockdown in NYC.
More importantly, variations in weather conditions are substantial determinants in NO2 and other air pollutants concentrations (Borge et al., 2019). For example, high wind speed causes the dispersal and dilution of pollutants. Wind can also blow NO2 from areas that have higher NO2 concentrations, e.g., industrial areas, to residential areas causing increased NO2 levels. Precipitation washes out the air and can relatively reduce pollutants in the air whereas air temperatures play an important role in the chemical reactions of pollutants in the air.
Here, we plot the average weekly wind speed, temperature, and precipitation in NYC between February 1 and May 1, 2020, to illustrate examples of the complexity of interactions between NO2 and weather conditions (Figure 3). We find an inverse relationship with wind speed with the concentration of NO2 during this time period likely explained by higher wind speed affecting the dispersal of the NO2 concentration. Precipitation and temperature data also reveal inverse relationships with NO2, especially during windy weather conditions. Figure 3 highlights two peaks of NO2 concentration during the weeks started on February 22 (before the lockdown) and April 4 (during the lockdown). Although the peak of April 4 is lower than February 22, the weather conditions were not the same. While the wind speed and precipitation rates were roughly similar during the two weeks, the temperature was significantly higher in the week of April 4. Higher temperatures help accelerate the oxidization of NO2 in the air and, therefore, lower the NO2 concentration (Khoder, 2002).
Stay-at-home and social distancing during the COVID-19 pandemic appear to have resulted in a decrease in air pollution over some of the world’s most crowded places. However, it remains unclear to what extent these policies and changes in human behavior have contributed to observations of decreased air pollution. Preliminary analyses in New York City support a conclusion that many factors affect the level of air pollution and it remains unclear to what extent observed reductions in air pollution are due to the dramatic changes in behaviors during enforced stay-at-home policies. Improving our understanding of how fundamental transformations of human behavior during the pandemic effects the environment will require more detailed analysis to provide insights and clarifying how stay-at-home policies or similar efforts to reduce the spread of the coronavirus will impact environmental quality such as air pollution in cities.
Read more at https://arxiv.org/pdf/2005.10303
References
Angel, S., Blei, A., Lamson-Hall, P., & Tamayo, M. (2020). The Coronavirus and the Cities: Explaining Variations in the Onset of Infection and in the Number of Reported Cases and Deaths in U.S. Metropolitan Areas [Working paper]. https://marroninstitute.nyu.edu/uploads/content/The_Coronavirus_and_the_Cities%2C_27_March_data%2C_final_draft_31_March_2020_VersApril3.pdf
Borge, R., Requia, W. J., Yagüe, C., Jhun, I., & Koutrakis, P. (2019). Impact of weather changes on air quality and related mortality in Spain over a 25 year period [1993–2017]. Environment International, 133, 105272. https://doi.org/10.1016/j.envint.2019.105272
Demuzere, M., Trigo, R. M., Vila-Guerau de Arellano, J., & Lipzig, N. P. M. van. (2009). The impact of weather and atmospheric circulation on O3 and PM10 levels at a rural mid-latitude site. Atmospheric Chemistry and Physics, 9(8), 2695–2714. https://doi.org/10.5194/acp-9-2695-2009
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Sullivan, T. J., Driscoll, C. T., Beier, C. M., Burtraw, D., Fernandez, I. J., Galloway, J. N., Gay, D. A., Goodale, C. L., Likens, G. E., Lovett, G. M., & Watmough, S. A. (2018). Air pollution success stories in the United States: The value of long-term observations. Environmental Science & Policy, 84, 69–73. https://doi.org/10.1016/j.envsci.2018.02.016
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Ahmed Mustafa is a Research Fellow at the Urban Systems Lab, The New School.
Timon McPhearson is Director at the Urban Systems Lab, and Associate Professor of Urban Ecology at The New School. @timonmcphearson
