Long-term trends in ambient fine particulate matter from 1980 to 2016 in United Arab Emirates

This paper presents the most comprehensive datasets of ambient fine particulate matter (PM_2.5) for the UAE from 1980 to 2016. The long-term distributions of PM_2.5 showed the annual average PM_2.5 concentrations constantly exceeded the EPA and WHO guidelines. They varied from 77 to 49 μg/m³ with an overall average of 61.25 μg/m³. While the inter-annual variability in PM_2.5 concentrations showed relatively a cyclic pattern, with successive ups and downs, it broadly exhibited an increasing trend, particularly, over the last 14 years. PM_2.5 concentrations displayed a strong seasonal pattern, with greatest values observed during warm summer season, a period of high demand of electricity and dust events. The lowest values found in autumn are attributable to reduced demand of energy. Decreased atmospheric temperatures and high relative humidity coinciding with this period are likely to reduce the secondary formation of PM_2.5. The spatial changes in PM_2.5 concentrations exhibited gradual downward trends to the north and northeast directions. Airborne PM_2.5 is prevalent in the southern and western regions, where the majority of oil and gas fields are located. PM_2.5/PM₁₀ ratio indicated that ambient aerosols are principally associated with anthropogenic sources. Peaks in PM_2.5/CO ratio were frequently observed during June, July, and August, although few were concurrent with March. This indicates that secondary formation plays an important role in PM_2.5 levels measured in these months, especially as the photochemical activities become relatively strong in these periods. The lowest PM_2.5/CO ratios were found during September, October, and November (autumn) suggesting a considerable contribution of primary combustion emissions, especially vehicular emissions, to PM_2.5 concentration. PM_2.5 concentrations are positively correlated with sulfate levels. In addition to sea and dust aerosols, sulfate concentration in the coastal region is also related to fossil fuel burning from power plants, oil and gas fields, and oil industries. The population-weighted average of PM_2.5 in UAE was 63.9 μg/m³, which is more than three times greater than the global population-weighted mean of 20 μg/m³.