Exposure to ultrafine particles while walking or bicycling during COVID-19 closures: A repeated measures study in Copenhagen, Denmark

Ultrafine particles (UFP; particulatematter

From late-March to mid-July 2020, UFP was repeatedly measured while walking or bicycling, capturing local COVID-19 closure (`Phase 0') and subsequent phased re-opening (`Phase 1', '2', '2.1' & '3'). A DiSCmini continuouslymeasured particle number concentration (PNC) in thewalker/bicyclist's breathing zone. PNCwhilewalking or bicycling was compared across phased re-openings, and the effect of ambient temperature, wind speed and direction was determined using regression models.

Approximately 40 repeated 20-minute walking and bicycling laps were made over 4 months during societal reopening phases related to the COVID-19 pandemic (late-March to mid-July 2020) in Copenhagen. Highest median PNC exposure of both walking ( 13,170 pt/cm(3), standard deviation (SD): 3560 pt/cm(3)) and bicycling (21,477 pt/cm(3), SD: 8964) was seen during societal closures (Phase 0) and decreased to 5367 pt/cm(3) (SD: 2949) and 8714 pt/cm(3) (SD: 4309) in Phase 3 of re-opening. These reductions in PNC were mainly explained by meteorological conditions, with most of the deviation explained by wind speed (14-22%) and temperature (10-13%). Highest PNC was observed along major roads and intersections.

In conclusion, we observed decreases in UFP exposure while walking and bicycling during societal re-opening phases related to the COVID-19 pandemic, due largely to meteorological factors (e.g., wind speed and temperature) and seasonal variations in UFP levels. (C) 2021 The Authors. Published by Elsevier B.V.