Metadata about: Abstract We investigated changes in traffic-related air pollutant concentrations in an urban area during the COVID-19 pandemic. The study area was in a mixed commercial-residential neighborhood in Somerville (MA, USA), where traffic is the dominant source of air pollution. Measurements were conducted between March 27 and May 14, 2020, coinciding with a dramatic reduction in traffic (71% drop in car and 46% drop in truck traffic) due to business shutdowns and a statewide stay-at-home advisory. Indicators of fresh vehicular emissions (ultrafine particle number concentration [PNC] and black carbon [BC]) were measured with a mobile monitoring platform on an interstate highway and major and minor roadways. Depending on road class, median PNC and BC contributions from traffic were 60–68% and 22–46% lower, respectively, during the lockdown compared to pre-pandemic conditions. A higher BC:PNC concentration ratio was observed during the lockdown period perhaps indicative of the higher fraction of diesel vehicles in the fleet during the lockdown. Overall, the scale of reductions in ultrafine particle and BC concentrations was commensurate with the reductions in traffic. This natural experiment allowed us to quantify the direct impacts of reductions in traffic emissions on neighborhood-scale air quality, which are not captured by the regional regulatory-monitoring network. Results underscore the importance of measurements of appropriate proxies for traffic emissions at relevant spatial scales. Our results are also useful for exposure analysts, and city, and regional planners evaluating traffic-related air pollution impact mitigation strategies.

About: Abstract We investigated changes in traffic-related air pollutant concentrations in an urban area during the COVID-19 pandemic. The study area was in a mixed commercial-residential neighborhood in Somerville (MA, USA), where traffic is the dominant source of air pollution. Measurements were conducted between March 27 and May 14, 2020, coinciding with a dramatic reduction in traffic (71% drop in car and 46% drop in truck traffic) due to business shutdowns and a statewide stay-at-home advisory. Indicators of fresh vehicular emissions (ultrafine particle number concentration [PNC] and black carbon [BC]) were measured with a mobile monitoring platform on an interstate highway and major and minor roadways. Depending on road class, median PNC and BC contributions from traffic were 60–68% and 22–46% lower, respectively, during the lockdown compared to pre-pandemic conditions. A higher BC:PNC concentration ratio was observed during the lockdown period perhaps indicative of the higher fraction of diesel vehicles in the fleet during the lockdown. Overall, the scale of reductions in ultrafine particle and BC concentrations was commensurate with the reductions in traffic. This natural experiment allowed us to quantify the direct impacts of reductions in traffic emissions on neighborhood-scale air quality, which are not captured by the regional regulatory-monitoring network. Results underscore the importance of measurements of appropriate proxies for traffic emissions at relevant spatial scales. Our results are also useful for exposure analysts, and city, and regional planners evaluating traffic-related air pollution impact mitigation strategies.

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