Review of studies on air quality status and its health effects in Iran

Background and Objective: Air pollution is a leading environmental risk factor on health and it is the major cause of death and disease at global level. Air pollution has been shown to have a significant share in the non-communicable diseases (NCDs) burden. After smoking, it is the second cause of deaths due to NCDs, associated with an increased risk of developing acute and chronic diseases and mortality. Materials and Methods:  In this study, a review was initially conducted on the basis of indices conducted in the world, the status of ambient air pollution and its effects on health in Iran and other countries, and then the status of ambient air quality and its effects on health in Tehran metropolitan between 2006 and 2017 were shown, based on the results of the studies conducted by the Environmental Research Institute of Tehran University of Medical Sciences. Results: The results showed that the annual mean of ambient air population-weighted PM2.5 exposure concentration in Iran was about 48 μg/m3, which is relatively lower than its global mean concentration (51 μg/m3). Based on the most recent study (in 2018) about 8.9 (7.5-10.3) million deaths in those aged above 25 years were attributed to exposure to outdoor air PM2.5 in the world. Although there are substantial differences between the results of studies have been done regarding the number of air pollution attributed deaths, numerous studies showed that air pollution is a major cause of death. Results regarding temporal variations of air quality in Tehran that is performed by the Institute for Environmental Research (IER) of Tehran University of Medical Sciences (TUMS), indicated that PM concentration had an increasing trend from 2006 to 2011. The maximum mean concentration of PM2.5 over the past 12 years has occurred in 2011, which was 38 μg/m3. The PM concentration had a decreasing trend from 2012 to 2015, reaching about 30 μg/m3. However, in the years 2016 and 2017, the annual mean PM2.5 concentration in Tehran was increased compared to its corresponding value in 2015. Furthermore, results of this study demonstrated that, in Tehran, not even one day was classified as "good” (AQI=0-50) from 2011 to 2017 based on the air quality index (AQI), but the number of days in which AQI was “moderate” (AQI=51-100) was increased from 2011 to 2015, and the number of days with the AQI of “moderate” reached 80 in 2015, while the rest of the days having an unhealthy air quality. In 2017, AQI was “moderate” in 20 days, “unhealthy for sensitive groups” in 237 days, “unhealthy” in 107 days, and "very unhealthy” in 1 day. The obtained results indicated that about 4878 (3238, 6359( of deaths due to all (natural) causes were attributable to long-term exposure to PM2.5 in Tehran in 2017. Conclusion: Studies showed that air pollution has a considerable share in the number of attributed deaths. Moreover, there were substantial differences between the results of national and international studies in the burden of disease attributed to air pollution. Therefore, there is a crucial need for accessing to reliable data on air pollution as well as baseline mortality and morbidity in order to study the status of air quality and its effects on health over the country.