PM2.5 Composition, Sources, and Health Risks in Madinah, Saudi Arabia: A Pre-Vision 2030 Baseline

Madinah, Saudi Arabia, is a hot-desert pilgrimage city receiving millions of religious visitors annually, yet its fine particulate matter (PM2.5) has not been chemically characterized. The city whose population is periodically influx by millions of religious visitors, generating concentrated increases in vehicular activity while simultaneously exposing a large transient population to ambient air pollution. Despite this, its fine particulate matter (PM2.5) has not been chemically characterized. Twenty-four-hour PM2.5 samples were collected at five urban sites between December 2014 and February 2016 and analyzed for black carbon, water-soluble inorganic ions, and trace elements; sources were resolved by enrichment factors and positive matrix factorization (PMF), and screening-level inhalation risks estimated for eight PM2.5-bound metals. Site means ranged from 37.7 ± 20.5 µg m−3 at Uhad to 103 ± 50.7 µg m−3 at Al-Awali, exceeding the World Health Organization 24-h guideline of 15 µg m−3 at all sites in every season. Observed site–cycle means ranged from 37.7 ± 20.5 µg m−3 at Uhad to 103 ± 50.7 µg m−3 at Al-Awali, with concentrations exceeding the World Health Organization 24-h guideline of 15 µg m−3 across the monitored site–cycle datasets. Reconstructed mass was dominated by organic matter (53–80.5%) and crustal material (15–53%). Sulfate was the dominant water-soluble ion, but secondary inorganic aerosols contributed only 1–22% of mass, resembling rapidly urbanizing arid cities rather than Asian or European megacities. PMF resolved five sources: crustal dust, industrial mixed dust, oil combustion, vehicular emissions, and secondary aerosols. Hazard quotients remained below unity and cumulative carcinogenic risks below 10−6, principally from chromium and nickel. Because these measurements precede the Vision 2030 urban-transformation program, they establish a chemically resolved reference state for evaluating future air-quality change in Madinah.