Effect of sub-urban scale lockdown on air pollution in Beijing

After recovering from epidemic COVID-19 by April, China suffered a setback in June with an outbreak in Xinfadi market in the Fengtai District in southwest Beijing. Decreased emissions of air pollutants has characterised cities under lockdown, which has led to observations of reduced pollutant levels particularly in cities such as Wuhan, where restrictions were strongly imposed earlier in 2020. Daxing the closest monitoring site, unsurprisingly shows the largest change before and during the local lockdown in terms of NO₂ concentrations: 31.9 ± 8.8 μg m⁻³ just before and 21.2 ± 7.38 μg m⁻³ locked-down. Traffic flows and NO₂ fell on Beijing's Third Ring Road, while rush hour CO peaks disappeared from some inner roads. The broad daytime peak in SO₂ concentrations seems to remain, but the concentrations appear lower. The partial lockdown had a clear influence on human behaviour (expressed as mobile phone activity), visits to important sites, passengers and freight on roads and fuel production. These changes were broadly consistently with the reduced pollutant concentrations and their diurnal cycles. While the lockdown was restricted to a small part of Beijing in June 2020, the more general social response meant changes in pollutant concentrations were more broadly found across the core of Beijing.