Impact of the COVID-19 lockdown on roadside traffic-related air pollution in Shanghai, China

The outbreak of COVID-19 has significantly inhibited global economic growth and impacted the environment. Some evidence suggests that lockdown strategies have significantly reduced traffic-related air pollution (TRAP) in regions across the world. However, the impact of COVID-19 on TRAP on roadside is still not clearly understood. In this study, we assessed the influence of the COVID-19 lockdown on the levels of traffic-related air pollutants in Shanghai. The pollution data from two types of monitoring stations—roadside stations and non-roadside stations were compared and evaluated. The results show that NO(2), PM(2.5), PM(10), and SO(2) had reduced by ~30–40% at each station during the COVID-19 pandemic in contrast to 2018–2019. CO showed a moderate decline of 28.8% at roadside stations and 16.4% at non-roadside stations. In contrast, O(3) concentrations increased by 30.2% at roadside stations and 5.7% at non-roadside stations. This result could be resulted from the declined NOx emissions from vehicles, which lowered O(3) titration. Full lockdown measures resulted in the highest reduction of primary pollutants by 34–48% in roadside stations and 18–50% in non-roadside stations. The increase in O(3) levels was also the most significant during full lockdown by 64% in roadside stations and 33% in non-roadside stations due to the largest decrease in NO(2) precursors, which promote O(3) formation. Additionally, Spearman's rank correlation coefficients between NO(2) and other pollutants significantly decreased, while the values between NO(2) and O(3) increased at roadside stations.