Impact of the 2020 COVID-19 lockdown on the concentration of non-methane volatile organic compounds in a UK urban atmosphere

The changes in air quality brought about by the COVID-19 lockdowns can provide valuable insight into how longer-term reductions in emissions might affect atmospheric composition. In urban Leicester UK, the 2020 COVID “lockdown” brought about several notable changes in atmospheric composition, including a considerable decrease (20–60%) in concentrations of non-methane volatile organic compounds (NMVOCs). Given their varied emission sources and lifetimes, NMVOC data can give valuable insights into how behavioural change impact atmospheric composition. The total concentration of 48 NMVOCs at roadside (RS) sites decreased from a pre-lockdown (sampled 16th-24th March 2020) concentration of 181.3 ± 41.4 μg/m³ to 82.0 ± 12.8 μg/m³ during lockdown (LD, sampled 18th-21st May 2020), before rebounding to a concentration of 236.3 ± 23.9 μg/m³ post lockdown (post-LD, sampled 14th-17th Sept 2020). A similar pattern was observed at urban background (UB) sites with concentrations reducing during lockdown to 96.8 ± 39.5 μg/m³ from a pre-lockdown (pre-LD) concentration of 123.2 ± 24.6 μg/m³ and then increasing to 168.6 ± 29.1 μg/m³ post-LD. Generally, despite the decrease in NMVOC concentrations during the LD, an increase in O₃ level was observed. This was attributed to decreased emissions of NO_x and the subsequent repartioning of O_x. This research assessed the quantitative effect of changes in vehicular and related anthropogenic emissions on air quality, providing valuable insights for the formulation of future air pollution controls.