Global estimates of ambient NO 2 concentrations and long-term health effects during 2000-2019.

High concentrations of ambient NO ₂ causes serious air pollution and could also pose great threats to human health. However, the long-term trends (20-year) and potential health effects of ambient NO ₂ exposure globally still shows high uncertainties. In this work, the field measurements, satellite dataset, GEOS-Chem output, and multiple geographical covariates were incorporated into the multi-stage model to investigate the global evolutions of ambient NO ₂ during 2000-2019. The results indicated that the cross-validation (CV) R ² values of ambient NO ₂ based on multi-stage model displayed satisfied performance (R ²  = 0.78), which was superior to the individual model. Besides, the out-of-bag R ² was 0.75, which suggested the multi-stage model showed the better transferability. At the spatial scale, the NO ₂ concentrations followed the order of China (16.9 ± 9.0 μg/m ³ ) > India (15.5 ± 5.6 μg/m ³ ) > United States (10.7 ± 5.6 μg/m ³ ) > Europe (7.7 ± 4.5 μg/m ³ ), which was in consistent with the anthropogenic NO _x emission. At the temporal scale, the ambient NO ₂ levels in China experienced persistent increases (0.29 μg/m ³ /year) during 2000-2013, whereas they showed slight decreases (-0.23 μg/m ³ /year) during 2013-2019. The ambient NO ₂ levels in the United States experienced continuous decreases during 2000-2019 (-0.20 μg/m ³ /year), while both of India and Europe remained relatively stable. Long-term NO ₂ exposure inevitably increased premature mortalities. The global premature all-cause mortalities associated with the excessive NO ₂ exposure increased from 288,169 (95% CI: 43,650, 527,971) to 461,301 (95% CI: 69,973, 843,996) in the past 20 years. This study would provide sufficient policy support for future ambient NO ₂ mitigation.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Rui Li reports financial support was provided by East China Normal University. Employment reports a relationship with East China Normal University that includes: employment. Rui Li has patent pending to Yes. We declare all of the authors do not have interest conflicts. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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