Characteristics and Health Risks Associated with Fine Particulate Matter and Its Components in Two Major Cities of Saudi Arabia: A Study of Makkah and Madinah

Urban air pollution, particularly from fine particulate matter (PM₂.₅), is a growing public health concern in many rapidly urbanizing countries and regions, including Saudi Arabia. This thesis investigates the levels, sources, seasonal variations, and health impacts of PM₂.₅ in the cities of Makkah and Madinah. PM₂.₅ monitoring focused on identifying key pollutants—including black carbon (BC), trace elements (TEs), and water-soluble ions (WSIIs)—which were measured using advanced analytical techniques such as Optical Transmissometer (OT-21), Energy Dispersive X-Ray Fluorescence Spectrometry (ED-XRF), and ion exchange chromatography. Source apportionment was carried out through positive matrix factorization (PMF), elemental enrichment factor (EF) calculations, and backward air mass trajectory analysis. The study investigates PM₂.₅ concentrations at five urban sites in Makkah, including Alharam, Ar Rusayfah, Alshoqiyah, Alhajj, and Herra Hospital. Average PM₂.₅ concentrations in these sites ranged from 59.3 μg/m³ to 109 μg/m³, exceeding the World Health Organization’s (WHO) 24-hour guideline of 15 μg/m³ by factors ranging from 4.0 to 7.3. In Madinah, PM₂.₅ concentrations were lower but still exceeded international air quality standards. Average concentrations across five sites, including Al-Awali, Al-Hijra, Uhad, Bab al-Masjid, and Bagidu, ranged from 37.7 μg/m³ to 103.3 μg/m³, with higher concentrations observed in urban and high-traffic areas. Seasonal patterns show that PM₂.₅ concentrations peak in the spring due to increased traffic, construction activities, and meteorological conditions conducive to particulate accumulation, while the winter months exhibit lower concentrations, attributed to improved atmospheric dispersion. The chemical composition analysis revealed that sulfate (SO₄²⁻) was the most abundant ion, followed by ammonium (NH₄⁺) and nitrate (NO₃⁻), which together accounted for approximately 19% of the total PM₂.₅ mass. The study identified multiple sources of PM₂.₅, including combustion of fossil fuels, vehicular emissions, industrial dust, and secondary aerosols, with significant contributions from both local and long-distance transported pollutants. A key objective of the study was to quantify the impact of air pollution exposure on health by examining the association between daily PM₂.₅ concentrations and cardiopulmonary morbidity. The research linked specific PM₂.₅ constituents, including BC and TE like lead (Pb), nickel (Ni), and iron (Fe), to short-term health impacts. In Makkah, BC and Pb were significantly associated with increased hospital admissions for cardiovascular (CVD) and pulmonary diseases. These constituents serve as critical indicators of anthropogenic activity: BC primarily reflects incomplete combustion from heavy traffic and diesel engines, while Pb acts as a tracer for industrial emissions. Furthermore, these associations were particularly pronounced for inpatient admissions, suggesting that individuals with pre-existing conditions are more vulnerable to the acute effects of air pollution. The analysis also revealed that certain populations, such as middle-aged adults and females, showed greater susceptibility to PM₂.₅ exposure, possibly due to biological or behavioral factors. Women, for instance, may experience higher internal doses due to smaller airway diameters or distinct activity patterns .The short-term health risks from BC were comparable to findings from other regions with high pollution levels, such as China and North America, underscoring the need for source-specific mitigation strategies. The results of this study underscore the importance of considering the chemical composition of PM₂.₅ when formulating air quality regulations. The analysis determined that sources of these pollutants in the investigated cities—specifically combustion-derived BC and metal-rich fractions—were associated with a significantly greater likelihood of the adverse health outcomes evaluated. The study finding support targeted emission control strategies, particularly in urban areas and during high-traffic periods such as the pilgrimage seasons. It also calls for stricter rules on vehicle emissions, industrial filtration, and real-time monitoring of air quality. Future research should focus on improving exposure assessment and implementing integrated mitigation strategies to protect public health and promote sustainable urban development.