Nitrogen-Dioxide Remains a Valid Air Quality Indicator

Abstract

In epidemiological studies, both spatial and temporal variations in nitrogen dioxide (NO2) are a robust predictor of health risks. Compared to particulate matter, the experimental evidence for harmful effects at typical ambient concentrations is less extensive and not as clear for NO2. In the wake of the “Diesel emission scandal—Dieselgate”, the scientific basis of current limit values for ambient NO2 concentrations was attacked by industry lobbyists. It was argued that associations between NO2 levels and medical endpoints were not causal, as NO2 in older studies served as a proxy for aggressive particulate matter from incineration processes. With the introduction of particle filters in diesel cars, NO2 would have lost its meaning as a health indicator. Austria has a high percentage of diesel-powered cars (56%). If, indeed, associations between NO2 concentrations and health risks in previous studies were only due to older engines without a particle filter, we should expect a reduction in effect estimates over time as an increasing number of diesel cars on the roads were outfitted with particle filters. In previous time series studies from Vienna over shorter time intervals, we have demonstrated distributed lag effects over days up to two weeks and previous day effects of NO2 on total mortality. In a simplified model, we now assess the effect estimates for moving 5-year periods from the beginning of NO2 monitoring in Vienna (1987) until the year 2018 of same and previous day NO2 on total daily mortality. Contrary to industry claims of a spurious, no longer valid indicator function of NO2, effect estimates remained fairly stable, indicating an increase in total mortality of previous day NO2 by 0.52% (95% CI: 0.35–0.7%) per 10 µg/m3 change in NO2 concentration.

COVID-19 and air pollution in Vienna—a time series approach

“…in volunteers exposed in an exposure chamber [1]. This is particularly true for nitrogen dioxide [2] for which we have also demonstrated short-term effects in previous time series studies in Vienna [3,4]. One explanation of significant effects of the irritant gas in epidemiological studies in the absence of effects in experimental settings would be through an indirect pathway: nitrogen dioxide at typical environmental concentrations would not damage cells of the respiratory epithelium directly but would still increase their susceptibility to other factors including allergens [5] or infectious agents.…”

“…Based on these findings, we expected an effect of air pollution on COVID-19-related mortality. We have demonstrated significant effects of air pollution on mortality before [3,4] and effect estimates were usually larger the more specific the cause of death. But the more specific the cause of death, the rarer would be the events.…”

Air Pollution Is Associated with COVID-19 Incidence and Mortality in Vienna, Austria

“…The city of Vienna maintains a dense air quality monitoring network that has been used to examine health impacts of air pollution before [ 18 ]. The density of pollution-monitoring stations allows for an analysis of air pollution effects on COVID-19 infections and deaths on the basis of rather small urban areas.…”

Impact of COVID-19 containment and closure policies on tropospheric nitrogen dioxide: A global perspective

“…Among these pollutants, NO 2 is notable as increased levels have been seen to affect the distribution of ozone ( Villena et al, 2012 ) and give rise to secondary inorganic aerosol pollutants ( Behera and Sharma, 2011 , Gkatzelis et al, 2021 ). Furthermore, NO 2 and its associated secondary pollutants ( Sokan-Adeaga et al, 2019 ) are respiratory irritants, thus metrics centered around NO 2 have frequently been used as robust indicators of health risks ( Moshammer et al, 2020 ). In fact, many studies have found that air pollutants could increase COVID-19 cases ( Zhu et al, 2020 ) and mortality ( Wu et al, 2020 ).…”