Oxidative Potential of PM2.5 in Dammam, Saudi Arabia, and the effect of dust storms.

The ability of particulate matter (PM) to generate reactive oxygen species and induce oxidative stress in human body is known as oxidative potential (OP). OP is considered an important indicator of the toxicity of PM, which is associated with adverse health impacts. Linking the predicted health impacts of aerosols to OP may be more relevant than considering PM mass only. In this study, we determined the OP of PM_2.5 (PM with aerodynamic diameter less than 2.5 µm) in Dammam, Saudi Arabia, in order to understand the relationship of OP to PM mass and composition in the present and absent of dust storm.
PM_2.5 was collected from two locations in Dammam city in the winter and summer of 2018. The first location was the city centre as an urban area while the second one was in the campus of Imam Abdulrahman Bin Faisal University as an urban background area. OP was quantified using dithiothreitol (DTT) assay. The mean PM_2.5 mass in the summer (120.5 µg/m³) was nearly  twice that in the winter (62.6 µg/m³). The average OP activity per air volume (DDTv) in the winter was 1.14 nmol min^-1 m^-3 while in the summer it was 1.77 nmol min^-1 m^-3. Conversely, the mean OP activity per PM mass (DDTm) in the winter was 24.56 pmol min^-1 µg^-3 while it was lower in the summer at 17.3 pmol min^-1 µg^-3. Results showed an inverse correlation between PM mass and DDTm, while there was a positive correlation between PM mass and DDTv. Even though the average mass of PM_2.5 in the summer was almost twice that in the winter, the average DDTm was lower in the summer compared to winter. This is due to the much lower oxidative potential in dust storm particles, which contribute significantly to the summertime PM_2.5. Our results suggest that OP is driven by PM composition rather than mass.