Short-term associations between daily mortality and ambient particulate matter, nitrogen dioxide, and the air quality index in a Middle Eastern megacity

There is limited evidence for short-term association between mortality and ambient air pollution in the Middle East and no study has evaluated exposure windows of about a month prior to death. We investigated all-cause non-accidental daily mortality and its association with fine particulate matter (PM; 2.5; ), nitrogen dioxide (NO; 2; ), and the Air Quality Index (AQI) from March 2011 through March 2014 in the megacity of Tehran, Iran. Generalized additive quasi-Poisson models were used within a distributed lag linear modeling framework to estimate the cumulative effects of PM; 2.5; , NO; 2; , and the AQI up to a lag of 45 days. We further conducted multi-pollutant models and also stratified the analyses by sex, age group, and season. The relative risk (95% confidence interval (CI)) for all seasons, both sexes and all ages at lag 0 for PM; 2.5; , NO; 2; , and AQI were 1.004 (1.001, 1.007), 1.003 (0.999, 1.007), and 1.004 (1.001, 1.007), respectively, per inter-quartile range (IQR) increment (18.8 μg/m; 3; for PM; 2.5; , 12.6 ppb for NO; 2; , and 31.5 for AQI). In multi-pollutant models, the PM; 2.5; associations were almost independent from NO; 2; . However, the RRs for NO; 2; were slightly attenuated after adjustment for PM; 2.5; but they were still largely independent from PM; 2.5; . The cumulative relative risks (95% CI) per IQR increment reached maximum during the cooler months, including: 1.13 (1.06, 1.20) for PM; 2.5; at lag 0-31 (for females, all ages); 1.17 (1.10, 1.25) for NO; 2; at lag 0-45 (for males, all ages); and 1.13 (1.07, 1.20) for the AQI at lag 0-30 (for females, all ages). Generally, the RRs were slightly larger for NO; 2; than PM; 2.5; and AQI. We found somewhat larger RRs in females, age group >65 years of age, and in cooler months. In summary, positive associations were found in most models. This is the first study to report short-term associations between all-cause non-accidental mortality and ambient PM; 2.5; and NO; 2; in Iran.