Critical review of the human data on short-term nitrogen dioxide (NO₂) exposures: Evidence for NO₂no-effect levels

Abstract

Nitrogen dioxide (NO2) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Evidence for health effects of ambient NO2 derives from three types of studies: observational epidemiology, human clinical exposures, and animal toxicology. Our review focuses on the human clinical studies of adverse health effects of short-term NO2 exposures, given the substantial uncertainties and limitations in interpretation of the other lines of evidence. We examined more than 50 experimental studies of humans inhaling NO2, finding notably that the reporting of statistically significant changes in lung function and bronchial sensitivity did not show a consistent trend with increasing NO2 concentrations. Functional changes were generally mild and transient, the reported effects were not uniformly adverse, and they were not usually accompanied by NO2-dependent increases in symptoms. The available human clinical results do not establish a mechanistic pathway leading to adverse health impacts for short-term NO2 exposures at levels typical of maximum 1-h concentrations in the present-day ambient environment (i.e., below 0.2 ppm). Our review of these data indicates that a health-protective, short-term NO2 guideline level for susceptible (and healthy) populations would reflect a policy choice between 0.2 and 0.6 ppm. EXTENDED ABSTRACT: Nitrogen dioxide (NO2) is a ubiquitous atmospheric pollutant due to the widespread prevalence of both natural and anthropogenic sources, and it can be a respiratory irritant when inhaled at elevated concentrations. Natural NO2 sources include volcanic action, forest fires, lightning, and the stratosphere; man-made NO2 emissions derive from fossil fuel combustion and incineration. The current National Ambient Air Quality Standard (NAAQS) for NO2, initially established in 1971, is 0.053 ppm (annual average). Ambient concentrations monitored in urban areas in the United States are approximately 0.015 ppm, as an annual mean, i.e., below the current NAAQS. Short-term (1-h peak) NO2 concentrations outdoors are not likely to exceed 0.2 ppm, and even 1-h periods exceeding 0.1 ppm are infrequent. Inside homes, 1-h NO2 peaks, typically arising from gas cooking, can range between 0.4 and 1.5 ppm. The health effects evidence of relevance to ambient NO2 derives from three lines of investigation: epidemiology studies, human clinical studies, and animal toxicology studies. The NO2 epidemiology remains inconsistent and uncertain due to the potential for exposure misclassification, residual confounding, and co-pollutant effects, whereas animal toxicology findings using high levels of NO2 exposure require extrapolation to humans exposed at low ambient NO2 levels. Given the limitations and uncertainties in the other lines of health effects evidence, our review thus focused on clinical studies where human volunteers (including asthmatics, children, and elderly) inhaled NO2 at levels from 0.1 ...

A rapid assessment of the impact of hazard reduction burning around Sydney, May 2016

“…Since 2005, the literature on human exposure to NO 2 has undergone a number of systematic reviews, as part of the EPA integrated scientific assessment for oxides of nitrogen (EPA, 2008b) and later by Hesterberg et al (2009) and Goodman J et al (2009). The human chamber study evidence was also reviewed by the California Environmental Protection Agency Air Resources Board (CARB, 2007) in their assessment of the California NO 2 standard.…”

Batch fabrication of nanopatterned graphene devices via nanoimprint lithography

“…[26][27][28] For our nanopatterned graphene sensors, we observe a decreased response in the presence of humidity, while for non-patterned graphene, the introduced noise was sufficient to obscure any gas response. We note that even in the humid atmosphere, NO 2 levels below the EU inhalation limits 29 were detected with the nanopatterned devices, which underpins the potential of efficient, large-area nanopatterning methods as a route to better, real-world graphene-based gas sensors.…”

Molecular design of O3 and NO2 sensor devices based on a novel heterostructured N-doped TiO2/ZnO nanocomposite: a van der Waals corrected DFT study

“…NO 2 is a major air pollutant, which has detrimental effects on the air quality with large contribution to the acid rain. NO 2 also causes by photochemical smog, which is harmful and irritant to human body, eyes, throat, nose and lungs [30]. On the other hand, O 3 molecule is a well-known air pollutant, which has detrimental impacts on respiratory tissues and ocular mucosa.…”