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The epidemiological studies provide some evidence that long-term NO 2 exposure may decrease lung function and increase the risk of respiratory symptoms.
Although there are fewer epidemiological studies on long-term respiratory effects of NO 2 than those of particulate matternew evidence has been provided in recent years. Both cross-sectional and longitudinal studies indicate an association between NO 2 and lung function. Lung function growth, evaluated in a longitudinal study, was also impaired among these children 22, The NO 2 effect in the cohort study was robust when other pollutants e. PM 10 and O 3 were Nitrogen oxide health in the statistical model, but weakened when acid vapours including NO 2 derived nitric acid were simultaneously considered.
Nitrogen dioxide (no2) pollution
Two cross-sectional studies found Nitrogen oxide health association between NO 2 and cough and phlegm symptoms in adults 94, In most of these studies, NO 2 concentrations at the community level were correlated with PM and ozonemaking it difficult to disentangle an effect of NO 2 per se.
To what extent is mortality being accelerated by long and short-term exposure to NO 2? Methodological limitations constrain identification of harvesting due to NO 2 itself.
The few long-term studies have not shown evidence for association between NO 2 and mortality. Associations have been observed between NO 2 and mortality in daily time-series studiesbut on the basis of present evidence these cannot be attributed to NO 2 itself with reasonable certainty. The of cohort studies investigating associations of long-term exposure to NO 2 in ambient air with mortality is small.
Basic information about no2
Neither the Six Cities Study with data from a cohort of 8 individuals followed over 15 years 82 nor the American Cancer Study with data from individuals followed over 15 years 13 nor the ASHMOG study with 6 non-smoking Adventists in California 9 found an Nitrogen oxide health of mortality risks with outdoor measured NO 2. Cardiopulmonary mortality was associated with background concentration of both pollutants but more consistently with living near a major road These point to the importance of road traffic exhaust, for which NO 2 may be an indicator.
A Czech case-control study Nitrogen oxide health air pollution and infant respiratory mortality showed associations with TSP and NO x The findings are possibly mediated by a higher susceptibility for infections in more polluted air as observed in time-series studies with hospital admissions and mortality data of infants and cannot be attributed to NO x alone. Many recent publications on time-series studies report associations between one hour or hour average concentrations of outdoor NO 2 and mortality modelling ambient NO 2 in single pollutants models.
The European study on short-term exposure to air pollution and mortality and morbidityAPHEA, investigated data from 29 cities and found heterogeneity between the cities. In addition, higher als for PM 10 were detected in cities with higher mean NO 2 levels The reason for this finding is currently unclear.
It could, for example, be due to interactions in atmospheric chemistry or at the pathophysiological level. A Canadian research team published meta analyses on several gaseous pollutants and particles with mortality data from studies published between and summing up 32 different estimates for NO 2 from single pollutant models. They found an overall effect estimate for NO 2 of similar magnitude as for PM 10ozone or carbon monoxide A larger effect size was observed for respiratory mortality. In the multi-pollutant model the effect size for total mortality dropped to one third and became non-ificant, supporting the view that the concentration- response al generated for NO 2 may largely Nitrogen oxide health the consequence of exposure to other pollutants related to NO 2.
The evidence for acute effects of NO 2 comes from controlled human exposure studies to NO 2 alone.
For the effects observed in epidemiological studies, a clear answer to the question cannot be given. Effects estimated for NO 2 exposure in epidemiological studies may reflect other traffic related pollutants, for which NO 2 is a surrogate. Additionally there are complex interrelationships among the concentrations of NO 2PM and O 3 in ambient air.
Controlled human exposure studies have been used to investigate the effects of NO 2 per se and were used as the basis for establishing the Nitrogen oxide health 1-hour guideline value. In epidemiological studies, NO 2 concentrations are often highly correlated with levels of other ambient pollutants either being emitted by the same sources or related through complex atmospheric reactions. NO 2 has been found to be an indicator for often unmeasured traffic related pollutants such as organic and elemental carbon or freshly emitted primary ultrafine particles.
This view is supported by analyses of sources of PM including gaseous pollutants where NO 2 is found to correlate well with traffic In addition, NO 2 might be a marker for the contribution of NO x to the formation of secondary pollutants such as secondary particles and O 3. It is important to note that measurement errors with regard to population average exposure will be Nitrogen oxide health when comparing effects of different pollutants.
In time-series analyses, pollutants with homogenous within-city distributions will be inherently favoured over pollutants with an inhomogeneous distribution. As already stated in response to question 5, a meta analysis of time-series investigations on mortality which included studies published between and was conducted by Stieb et al This analysis included 32 effect estimates for NO 2 from single- pollutant models and 15 from multi-pollutant models.
The multi-pollutant models included particle measures and sometimes in addition O 3 or other gaseous pollutants, further supporting the view that the concentration response al generated for NO 2 is largely, but not necessarily entirely, the consequence Nitrogen oxide health other pollutants emitted by the same source or being derived from NO 2.
In long-term studies, the spatial inhomogeneity of NO 2 levels within a city might weaken the ability to detect effects of NO 2 based on measurements from urban background sites such as in Nitrogen oxide health Harvard Six City Study or the American Cancer Society Study.
However, NO 2 has been shown to be an appropriate indicator for assessing long-term exposure to traffic related air pollution. An example of a long-term study using this inhomogeneity is a recent European cohort study on mortality Therefore, the interpretation of the short-term as well as long-term epidemiological studies is that these are not primarily Nitrogen oxide health to NO 2 per se but to other unmeasured traffic related pollutants or to secondary pollutantswhich have complex interrelationships with NO 2.
Potential pollutants for which NO 2 might be an indicator include black smoke, organic and elemental carbon and ultrafine particles see also section on PM. There have been few controlled human exposure studies on interactions with other chemical pollutants, although several studies show that NO 2 exposure enhances responses to inhaled pollens.
Some epidemiological studies have explored statistical interactions of NO 2 with other pollutants, including particlesbut the findings are not readily interpretable. The of new studies using human controlled exposures to assess the effect of multiple pollutants including NO 2 is limited. The combination of NO 2 and O 3 was addressed by showing a reduction in cardiac Nitrogen oxide health which was largest for NO 2 in combination with O 3.
Human controlled exposure studies have suggested that single and multiple controlled exposures to concentrations of NO 2 in excess of those normally achieved in ambient air can sensitize the airways of adult asthmatic subjects to the Nitrogen oxide health effect of an inhaled allergen to which they are specifically sensitized, The late response defined as 3 to 10 hours after administration of sub-acute allergen concentrations seemed to be more affected than the immediate response.
Short term exposure to air pollutants including NO 2 in a road tunnel has also been shown to enhance the asthmatic response to allergen The mechanistic basis for these interactions has not been elucidated.
Nitrogen dioxide has serious impact on health | umweltbundesamt
Epidemiological time-series analyses addressing possible synergisms between NO 2 and other pollutants have focused on the role of NO 2 as an effect modifier of the association between PM and health outcomes. A possible interpretation of the APHEA2 could be that NO 2 might serve as an indicator for the presence of more toxic particles such as traffic related particles. Generally, the statistical analyses assessing effect modification carry with them the inherent limitation that in complex mixtures the pollutants themselves are indicators and that Nitrogen oxide health error further reduces the ability to disentangle their contributions as discussed in the rationale on question 6.
With the level of evidence available it is not yet possible to state with a sufficient degree of confidence whether NO 2 is able to synergize with PM or to state that NO 2 is a valid indicator for more toxic PM present under these conditions. What are the critical characteristics? In general, individuals with asthma are expected to be more responsive to short-term exposure to inhaled agents, when compared to individuals without asthma. Controlled human exposure studies of short-term responses of persons with and without asthma to NO 2 have not been carried out.
There is limited evidence from epidemiological studies Nitrogen oxide health individuals with asthma show steeper concentration-response relationships.
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Small-scale human exposure studies have not shown consistent effects of NO 2 exposure on airways reactivity in persons with asthma, even at exposure Nitrogen oxide health higher than typical ambient concentrations.
As for other pollutants, children can reasonably be considered to be at increased risk. There is limited evidence for influence of the other listed factors on the effects of NO 2. In healthy adults changes in lung function in experiments with controlled human exposure to NO 2 occur only at concentrations in excess of those normally encountered in ambient air. However, asthmatic subjects are characterized by having airways that are hyper-responsive to a wide variety of inhalation stimuli and, as a consequence, might be expected to exhibit a greater airways response to NO 2 than in normal subjects.
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Small scale human exposure studies in adult asthmatics with mild to moderate disease have failed to demonstrate consistent effects of NO 2 on either baseline airway calibre or on direct e. It is noteworthy that there are no studies that have included Nitrogen oxide health normal and asthmatic subjects in the same study, nor patients with severe disease.
Some cross sectional studies in adults and children have shown associations between ambient NO 2 concentrations and impaired lung function 93,but it is not possible to determine whether this is due to NO 2 itself or to the secondary pollutants that are derived from it. Several new longitudinal cohort studies have also shown associations between outdoor NO 2 concentrations and impaired growth in lung function 22, 23, 24, but this effect is mostly weakened when the pollutant models take of the effects of other outdoor pollutants such Nitrogen oxide health ozoneparticles or acid aerosols and indoor exposures.
In the study of Horak et al. Cross sectional studies using symptoms, lung function and hospital admissions have provided some evidence for an increased association between NO 2 exposure and asthma but the effects are not consistent 79, 94,,, As with the cross section and cohort studiesNO 2 effects on asthma appear to be more prominent in children,, than in adults 94,as observed for the aggravating effects of other air pollutants on asthma As might be predicted, there are also greater associations between outdoor NO 2 exposure and respiratory outcome measures in children who spend more time outdoors 22, Some epidemiological studies have reported Nitrogen oxide health effects of NO 2 on asthma or lung function changes but these are inconsistent.
There is also limited evidence that lower educational attainment is a risk factor for NO 2 with risk estimates that are independent of smoking, diet or alcohol, but less than observed for particulate matter and could be explained by increased exposure to air pollutants 12, 13, The evidence is not adequate to establish a threshold for either short or long-term exposure. While a of epidemiological studies have described concentration-response relationships between ambient NO 2 and a range of health outcomes, there is no evidence Nitrogen oxide health a threshold for NO 2.
As noted in the introduction, threshold points in dose-response relationships are not readily established, based on either experimental or observational data. In general, current exposures in Europe are below this range.