Stay-at-home Policies and Air Quality: PM2.5-bound PAHs Trends and Population Health during COVID-19 at a Suburban Area in Giza, Egypt

Abstract During the COVID-19 pandemic, partial lockdown measures in Egypt created a natural experiment to assess their impact on toxic polycyclic aromatic hydrocarbons (PAHs) bound to fine particulate matter (PM 2.5 ) in semi-arid regions. While global air quality changes during lockdowns are documented, data on PAH characterization and associated health risks in understudied subtropical North African urban areas remain scarce. This study addresses this gap by examining changes in PAH profiles, sources, and population risks in suburban Giza. Daily PM 2.5 samples collected in 2020 across pre-lockdown, partial lockdown (weekdays/weekends), and post-lockdown periods were analyzed for 16 priority PAHs using GC-FID. Sources were apportioned via molecular diagnostic ratios, and health risks were evaluated using U.S. EPA models for incremental lifetime cancer risk (ILCR). Results showed that PM 2.5 and ΣPAHs concentrations decreased significantly during lockdown (by 44% and 61%, respectively), yet remained dominated by 4–6 ring PAHs from persistent pyrogenic sources, mainly traffic. Benzo[a]pyrene (BaP) consistently exceeded WHO standards. Critically, incremental lifetime cancer risk (ILCR) values for dermal contact and ingestion remained above the U.S. EPA’s 10⁻⁴ risk threshold across all periods, indicating a sustained elevated cancer risk for residents. These findings underscore that short-term emission reductions are insufficient; sustainable, stringent policies targeting traffic and combustion sources are urgently needed to mitigate long-term public health risks in Cairo and similar arid urban environments. GRAPHICAL ABSTRACT