A short-term rise in nitrogen dioxide air pollution could be tied to a bump in local mortality rates the next day, researchers showed in a large international study.
Across 398 cities (located mostly in the U.S., Europe, and Asia), each 10 μg/m3 increase in ground-level NO2 concentration was associated with increases in mortality the next day that persisted after adjustment for other air pollutants:
- Total mortality up 0.46%
- Cardiovascular mortality up 0.37%
- Respiratory mortality up 0.47%
Concentration-response curves, based on data from 1973 to 2018, were almost linear with no minimum threshold for harm, reported Haidong Kan, MD, PhD, of Fudan University in Shanghai, and colleagues in an epidemiological study published online in The BMJ.
“This result suggests that NO2 is associated with considerable health risks even at levels below health based standards and guidelines, including the current WHO air quality guidelines,” the group wrote.
Cities participating in the study had a median average annual nitrogen dioxide concentration of 26.9 μg/m3. The WHO sets a target of 40 μg/m3 in annual mean concentration of NO2 in air quality guidelines.
Ambient nitrogen dioxide primarily comes from vehicle and power plant emissions. The U.S. Environmental Protection Agency concluded in 2016 that there is a causal relationship between short-term exposure to NO2 and respiratory effects; evidence was deemed insufficient to blame exposure for total mortality and cardiovascular effects, however.
“Our findings from this multi-location analysis add to the supporting evidence for causal associations between short term exposure to NO2 and non-respiratory endpoints,” Kan and colleagues wrote.
“Although reduction of NO2 to zero is infeasible, our analysis provides insight into the public health benefits of substantial reductions in NO2, suggesting considerable health benefits from stricter control of NO2 emissions and tightening of the regulatory limits of NO2 in future revisions of WHO air quality guidelines,” they noted.
For their epidemiological study, the investigators drew upon the Multi-City Multi-Country Collaborative Research Network. Mortality data, obtained from local authorities within each country, captured 62.8 million total deaths from 1973 to 2018.
That most data were obtained from select developed areas precluded global generalization of the findings, Kan’s team cautioned.
Furthermore, their database was subject to potential exposure misclassification and coding errors.
Study authors reported support from the National Natural Science Foundation of China, China Medical Board Collaborating Program, Medical Research Council in the U.K., Natural Environment Research Council in the U.K., European Union’s Horizon 2020 Project Exhaustion, Spanish Ministry of Science and Innovation, German Federal Ministry of Education and Research, the Environmental Restoration and Conservation Agency in Japan, the Czech Science Foundation, the Shanghai Municipal Science and Technology Commission, the Australian National Health and Medical Research Council, and the Academy of Finland.
Kan had no conflicts of interests listed.