Seasonal trends in the composition and ROS activity of fine particulate matter in Baghdad, Iraq

Baghdad suffers from severe atmospheric particulate matter (PM) pollution and has limited infrastructure to monitor and control PM-pollution. To help better understand the nature of particulate matter in Baghdad, daily PM2.5 samples were collected every 6th day from September, 2012 to September, 2013. The samples were analyzed for chemical composition and cellular oxidative stress activity using a macrophage-based assay. The annual average PM2.5 concentration was 50 ± 19 μg m−3, and was comprised of approximately 28% crustal materials, 26% organic carbon (OC), 17% sulfate, 12% elemental carbon (EC), and 8.0% ammonium ion. No clear seasonal trend was observed for the total PM2.5 mass and PM2.5 OC, but EC exhibited higher concentrations in the warmer months, likely due to the extensive use of electric generators operated by diesel and gasoline for cooling. April showed the lowest levels of both EC and OC compared with other months due to both sand and rainstorm events which led to increased deposition and dispersion of local emissions. Concentrations of nitrate ion were low in all seasons due to the high temperatures and low humidity, but slightly higher levels were observed in the cooler months of winter. The oxidative stress (reactive oxygen species (ROS)) activity (59 ± 35 μg Zymosan equivalents m−3) of the PM was relatively lower than in other studied areas. Association between the water soluble PM constituents and the oxidative activity was investigated using a multi-linear regression model which showed no strong relationships between ROS activity and the water soluble components of PM2.5, but a moderate correlation of water soluble organic carbon from biomass burning (WSOC-BB) was observed (R2 = 0.52). Biomass burning PM has been shown to be an important contributor to ROS activity in other published studies, but additional work is needed to better understand the sources leading to the ROS activity in Baghdad.