Long-term exposure to low-level NO2 and mortality in the southeastern US Öffentlichkeit
Qian, Yaoyao (Spring 2021)
Abstract
Background
Mounting evidence has shown that the long-term exposure to fine particulate matter and ozone can increase mortality. However, the health effects associated with long-term exposure to nitrogen dioxide (NO2) are less clear, in particular the evidence is scarce for NO2 at low levels below the current National Ambient Air Quality Standards (NAAQS).
Methods
We constructed a population-based full cohort comprised of all Medicare beneficiaries (aged ≥65, N=13,590,387) in the Southeastern US from 2000-2016, and then further defined the below-guideline cohort that only included those who were always exposed to low-level NO2, with annual means below the current NAAQS (i.e., ≤53 ppb). We applied previously estimated spatially- and temporally-resolved NO2 concentrations and assigned annual means to study subjects based on ZIP code of residence. Cox proportional hazards models were used to examine the association between long-term exposure to low-level NO2 and all-cause mortality, adjusting for potential confounders.
Results
About 99.95% of the Medicare beneficiaries in the southeastern US were always exposed to low-level NO2 over the study period. We observed a statistically significant association between long-term exposure to low-level NO2 and all-cause mortality, with a hazard ratio (HR) of 1.040 (95% CI: 1.031, 1.050) in single-pollutant models and a HR of 1.042 (95% CI: 1.033, 1.052) in multi-pollutant models (adjusting for PM2.5 and ozone), per 10 ppb increase in annual NO2concentrations. The penalized spline indicates a linear dose-response relationship across the entire NO2 exposure range. Subjects who are white, female, and residing in urban areas are more vulnerable to long-term NO2 exposure.
Conclusion
Using a large cohort, we provide epidemiological evidence that long-term exposure to NO2, even below the NAAQS guideline, was significantly linearly associated with a higher risk of mortality, independent of PM2.5 and ozone. Improving air quality by reducing NO2 emissions may yield substantial health benefits.
Table of Contents
Table of Contents
1. Introduction
2. Materials and Methods
2.1 Study Population
2.2 Exposure
2.3 Covariates
2.4 Statistical analysis
3. Results
4. Discussion
5. References
6.Tables
6.1 Table 1. Descriptive statistics for the study population.
6.2 Table 2. Spatial and Temporal Variability of Annual NO2 levels (ppb) in years 2000-2016
6.3 Table 3. Estimated Hazard Ratio of Mortality (95% CI) associated with an Increase of 10 ppb in NO2 Concentration.
7. Figures
7.1 Figure 1. The spatial distribution of NO2 concentrations (2000-2016) in the Southeastern US
7.2 Figure 2. The dose-response relationship between long-term exposure to NO2 and all-cause mortality.
7.3 Figure 3. The hazard ratios of mortality associated with a 10 ppb increase in NO2 concentrations for study subgroups.
8. Supplementary Tables
8.1 Table S1. Estimated Hazard Ratio of Mortality (95% CI) associated with an Increase of 10 ppb in NO2 Concentration at different levels of confounding adjustment
8.2 Table S2. Estimated Hazard Ratio of Mortality (95% CI) associated with an Increase of 10 ppb in NO2 Concentration by state
9. Supplementary Figures
9.1 Figure S1. The map of major roads in the Southeastern US
9.2 Figure S2. The temporal trend of NO2 concentrations (2000-2016) in the Southeastern US
About this Master's Thesis
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