Short-term exposure to nitrogen dioxide (NO2) is associated with an increased risk for total, cardiovascular, and respiratory mortality, according to a study published in The BMJ. Investigators examined the short-term associations between NO2 and total, cardiovascular, and respiratory mortality in 398 cities from 22 low- to highincome countries/regions. They observed increases of 0.46%, 0.37%, and 0.47% in total, cardiovascular, and respiratory mortality, respectively, with a 10 µg/m3 increase in NO2 concentration on lag 1 day (previous day) on average. After adjustment for copollutants (particulate matter with aerodynamic diameter ≤10 µm or ≤2.5 µm, ozone, sulfur dioxide, and carbon monoxide), these associations remained robust. For all three causes, the pooled concentration-response curves were almost linear, with no discernable thresholds. Across total cities, the proportion of deaths attributable to NO2 concentration above the counterfactual zero level was 1.23%. “The concentration-response curves were linear without discernible thresholds, suggesting a need to revise and tighten the current air quality guidelines of NO2 for greater public health benefit, and to consider a regulation limit for daily mean NO2 concentration,” the authors write.