Air pollution climatology of particulate matter in Dammam, Saudi Arabia: composition, sources and toxicity

Air pollution in many countries is the largest environmental health stressor on their populations. Investigating key air pollutant sources, their properties and processes of formation in different environments is key to understanding how to implement mitigation strategies appropriately in those countries. The world is rapidly urbanising, leading to larger emissions, burning of fossil fuels and thus increasing air pollution. At present one of the main pollutants of concern in urban centres is particles less than 2.5µm in diameter (PM\(_{2.5}\)). This thesis investigates the air quality in Dammam, Saudi Arabia, including assessment of the air pollution climatology in Dammam using monitoring data from two stations for the period 2016-2019, and primary measurement of particulate matter (PM\(_{2.5}\)) composition, sources and toxicity. PM\(_{2.5}\) was collected on Teflon and quartz filters in the winter and summer from two locations in Dammam. PM\(_{2.5}\) mass concentration and composition were mainly influenced by crustal elements derived primarily from desert and dust storms. Average PM\(_{2.5}\) mass concentrations doubled in the summer compared to the winter and were (on average) three times higher during dust storms than non-dust storm periods. In general, the mean concentrations of most of chemical components of PM were higher in the summer than in the winter. The impact of dust storms on PM\(_{2.5}\) composition was studied. This analysis showed that dust storms increased the concentration of crustal species in PM\(_{2.5}\) by five times, compared to non-dust samples. The mean concentration of organic carbon (OC) was significantly higher during dust storms. The influence of dust storms on most anthropogenic species in PM was limited. Secondary aerosols and OC were the most abundant components of PM\(_{2.5}\) in Dammam, under non-dust periods. PM sources were identified using positive matrix factorisation, based upon detailed chemical composition data. Six factors were estimated to be the sources of PM\(_{2.5}\) . these factors were identified as crustal elements, a nitrate-rich factor, a sulfate-rich factor, sea salt, traffic and biomass burning factors. In addition, the sources of PM\(_{2.5}\) in Dammam excluded the data affected by dust storms data, demonstrating the high contribution of anthropogenic sources, compared with natural sources. The toxicity of PM\(_{2.5}\) in Dammam was measured in vitro using the dithiothreitol (DTT) assay. The results illustrated a negative correlation between crustal elements abundance and DTT activity per unit PM mass (DTTm). DTTm values were lower for dust storm periods than non-dust storms, and DTTm had an inverse correlation with total PM mass. A strong correlation was observed between DTT activity per unit air volume (DTTv) and PM mass concentration. These results provide insight into the toxicity of the constituents of the particles. Thus, linking the predicted health impacts of aerosols to oxidative potential (OP) may be more relevant than considering PM mass concentrations only. In addition, the contribution of sources of PM to DTT values was investigated using PMF. The traffic emission source showed the highest contribution to DTTm, although the traffic factor was the smallest contributor to the PM\(_{2.5}\) 5 mass concentration. Crustal sources, which contributed to 40% of PM\(_{2.5}\) in Dammam, have the lowest contribution (6%) to DTTm. Anthropogenic sources account for 86% of DTTm and 60% of DTTv (and hence the health impacts of PM)