Further interpretation of the acute effect of nitrogen dioxide observed in Canadian time-series studies

Abstract

In this paper, the pooled NO 2 association with nonaccidental mortality is examined across 10 cities in Canada in single-and two-pollutant time-series models. The results reaffirm that NO 2 has the strongest association with mortality, particularly in the warm season. Although attributing such effects to NO 2 cannot be ruled out, it is plausible that NO 2 is acting as an indicator for some other exposure affecting the population. This could include PM 2.5 , as has been suggested from some personal exposure data, but it could also be indicating a more specific type of PM 2.5 , such as traffic-related particles, given that in cities the main source of NO 2 is motor vehicle exhaust. NO 2 could also be acting as a surrogate for other pollutant(s) originating from motor vehicles or high-temperature combustion, such as volatile organic compounds (VOCs) or polycyclic aromatic hydrocarbons. Another possibility is other oxidized nitrogen species (''NO z '') or photochemically produced pollutants that can co-vary with NO 2 , especially during urban stagnation events. Data to test these different possibilities across several Canadian cities are examined. The focus is on correlations in time or space between NO 2 and other pollutants that are more strongly linked to vehicle emissions. The results support the hypothesis that NO 2 is a better indicator than PM 2.5 of a range of other toxic pollutants. This includes VOCs, aldehydes, NO z and particle-bound organics in motor vehicle exhaust. Thus, overall, the strong effect of NO 2 in Canadian cities could be a result of it being the best indicator, among the pollutants monitored, of fresh combustion (likely motor vehicles) as well as photochemically processed urban air.

Effects of diurnal variations in temperature on non-accidental mortality among the elderly population of Montreal, Québec, 1984–2007

“…This three-day lag was based on previous analyses which showed that the effects of air pollution did not persist past lag 2 days and the response functions were consistent with linearity (Brook et al 2007;Goldberg 2003;Goldberg 2006;Goldberg et al 2011). …”

Panel discussion review: session two — interpretation of observed associations between multiple ambient air pollutants and health effects in epidemiologic analyses

“…The investigators noted that in Canadian cities, the major source of nitric oxide (NO) (80-90%) was exhaust from motor vehicles or other forms of transportation, suggesting that ambient concentrations of NO 2 might be serving as a surrogate of primary traffic-related pollutants. An updated analysis of the multicity Canadian study further examining the association of NO 2 and mortality is presented by Brook et al (2007) in this special issue. The findings suggest that NO 2 may be a better indicator of motor vehicle fine particles than PM 2.5 , thereby offering one explanation as to why some epidemiologic studies have found a stronger association between mortality and NO 2 than with PM 2.5 .…”

Ground‐level nitrogen dioxide concentrations inferred from the satellite‐borne Ozone Monitoring Instrument

“…Strong associations exist between NO 2 and nonaccidental mortality in daily time series studies [Steib et al, 2003;Burnett et al, 2004;Samoli et al, 2006]. NO 2 concentrations are also highly correlated with other pollutants either emitted by the same sources or formed through complex reactions in the atmosphere [e.g., Brook et al, 2007]. Complete spatial coverage of ground-level NO 2 measurements are needed for exposure assessment.…”