Tackling the mortality from long-term exposure to outdoor air pollution in megacities: Lessons from the Greater Cairo case study.

Objective: The poor outdoor air quality in megacities of the developing world and its impact on health is a matter of concern for both the local populations and the decision-makers. The objective of this work is to quantify the mortality attributable to long-term exposure to PM2.5, NO, and O in Greater Cairo (Egypt).

Methods: We analyze the temporal and spatial variability of the three pollutants concentrations measured at 18 stations of the area. Then, we apply the method recommended by the WHO to estimate the excess mortality. In this assessment, three different shapes (log-linear, linear, and log-log) of the concentration-response functions (CRF) are used.

Results: With PM2.5 concentrations varying from 50 to more than 100µg/m in the different sectors of the megacity, the spatial variability of this pollutant is found to be one important cause of uncertainty on the excess mortality associated with it. Also important is the choice of the CRF. With the average (75µg/m) PM2.5 concentration and the most favorable log-log shape of the CRF, 11% (CI, 9-14%) of the non-accidental mortality in the population older than 30 years can still be attributed to PM2.5, which corresponds to 12520 (CI, 10240-15930) yearly premature deaths. Should the Egyptian legal 70µg/m PM10 limit (corresponding to approximately 37.5µg/m for PM2.5) be met, this number would be reduced to 7970, meaning that 4550 premature deaths could be avoided each year. Except around some industrial or traffic hot spots, NO concentration is found to be below the 40µg/m air quality guideline of the WHO. However, the average concentration (34µg/m) of this gas exceeds the stricter 10µg/m recommendation of the HRAPIE project and it is thus estimated that from 7850 to 10470 yearly deaths can be attributed to NO. Finally, with the ozone concentration measured at one station only, it is found that, depending on the choice of the CRF, between 2.4% and 8.8% of the mortality due to respiratory diseases can be attributed to this gas.

Conclusion: In Greater Cairo, PM2.5 and NO constitute major health risks. The best estimate is that in the population older than 30 years, 11% and 8% of the non-accidental mortality can be attributed to these two pollutants, respectively.