Revealing the chemical composition and sources of carbonaceous aerosols in PM2.5: Insights from the Omicron-22 lockdown in Shanghai

The COVID-19 pandemic, particularly the Omicron-22 lockdown in Shanghai, provided a unique opportunity to examine the influence of lockdown and decreasing human activities on the urban atmosphere environment. Here, we explored the chemical compositions and sources of carbonaceous aerosols during the pre-lockdown, lockdown, and post-lockdown periods in 2022, Shanghai. The mean concentrations of organic carbon (OC) and element carbon (EC) were 4.40 ± 1.58 and 1.05 ± 0.41 μg/m³ pre-lockdown, 1.60 ± 0.99 and 0.30 ± 0.13 μg/m³ during lockdown, and 2.66 ± 2.01 and 0.47 ± 0.19 μg/m³ post-lockdown, respectively. Normal alkanes (n-alkanes) and polycyclic aromatic hydrocarbons (PAHs) concentrations were 27.5 ± 9.77 and 1.81 ± 1.34 ng/m³ pre-lockdown, 10.6 ± 5.84 and 1.50 ± 0.67 ng/m³ during lockdown, and 7.27 ± 3.86 and 1.44 ± 0.23 ng/m³ post lockdown, respectively, with a further decline noted post-lockdown. A notable decrease in carbonaceous aerosols was observed during the lockdown. Carbonaceous aerosols showed a marked decrease during the lockdown, with OC and EC increasing by 60% post-lockdown, while n-alkanes and PAHs continued to decline. Although the composition of OC, EC, and PAHs remained stable, n-alkanes, particularly C₂₉-C₃₄, significantly increased due to plant wax emissions. Source apportionment indicated that coal combustion and industrial emissions were the primary contributors across all periods, with reduced transport emissions having limited impact on OC, EC, and PAH sources. This study highlights the air quality improvements from reduced anthropogenic activities, offering insights for future pollution mitigation policies.