Characterization of size–fractionated PM10 and associated heavy metals at two semi–arid holy sites during Hajj in Saudi Arabia

The size–fractionation of inhalable particles and their heavy metal content during the Hajj season have yet to be explored. The principal objective of this study is to evaluate the concentration of heavy metals associated with six different PM10 fractions to which pilgrims are exposed during Hajj. Two holy sites (Mina and Arafat) characterized by the simultaneous obligatory stay of all pilgrims and concomitant intense vehicular emissions were selected for sampling. Characterization of inhalable PM, their fractional size distribution and concentration of heavy metals were investigated. The sum of total fractions (coarse+fine) as PM10 was recorded at an average of 181.3 μg/m3 at Mina and 289.6 μg/m3 at Arafat during peak days of the Hajj period, corresponding to Arabic (8–12 Dhu Al–Hijjah). The average concentration (μg/m3) of coarse (3.0 to 10.0 μm) and fine fractions (3.0 to ≤0.49 μm), and their relative percentages were recorded [Mina: 62.2, 34.2% (fine), 119.1, 65.8% (coarse); Arafat: 114.5, 35.9% (fine), 175.1, and 64.1% (coarse)]. The metal concentrations associated with these fractions, their enrichment factor, and possible adverse effects on pilgrims were assessed. Cd and Se were highly enriched, followed by Cr, Pb, Cu, Ni and Co, indicating vehicular emissions as the likely anthropogenic source. Air Quality indices were calculated based on PM10 and PM2.5 particulate concentrations in ambient air during the Hajj period, and the days were categorized in relation to health impacts. This work provides crucial information and alerts about the possible impact of PM on ambient air quality, and data suggests pilgrims, particularly susceptible groups, should adopt suitable precautionary preventive measures during the Hajj period.