Black carbon temporal trends and associated health and economic impacts in Tehran

Atmospheric black carbon (BC) particles resulting from the incomplete combustion of both fossil and non-fossil sources recently gained significant attention globally due to their potential health impacts. This study aimed to investigate the temporal trends of ambient BC in urban traffic (Sharif station) and background (Setad-e-Bohran station) air pollutants monitoring sites in Tehran, and to estimate its health and economic burdens from March 2017 to March 2018. The mean BC concentration in the traffic and urban background sites in cold seasons was 6.4 μg/m3 and 3.4 μg/m3. During the warm season, these figures were 4.4 μg/m3 and 2.3 μg/m3, respectively. Our observations indicated that ambient BC concentration was lower during weekends, more likely due to decreased traffic levels compared to weekdays. Our results showed that the concentration of BC and the BC/PM2.5 ratio were higher during nighttime in Tehran, likely due to high atmospheric stability and increased transit of heavy-duty diesel vehicles. We found strong correlation coefficients between BC, CO (BC–CO, r = 0.83, p < 0.01), NO2 (BC– NO2, r = 0.64, p < 0.01), PM2.5 (BC- PM2.5, r = 0.89, p < 0.01) and other components of PM2.5 (BC- other components of PM2.5, r = 0.81, p < 0.01). We estimated that long-term exposure to ambient air BC resulted to 424 (95% Confidence Interval (CI): 400–510) deaths in adults ≥25 y/r from all-natural causes. Mortality due to BC exposure for ischemic heart disease, stroke, chronic obstructive pulmonary disease and lung cancer were 82, 28, 25, and 16, respectively. Exposure to BC caused an economic loss of 161.6 [95% CI: 105.5–213.8] million US$ due to all-cause mortality. Almost 11% of mortality and economic loss of PM2.5 in Tehran is due to BC, which can be avoided by adopting and implementing appropriate and sustainable air quality abatements.