Contrast in air pollution components between major streets and background locations: Particulate matter mass, black carbon, elemental composition, nitrogen oxide and ultrafine particle number

Policies to reduce outdoor air pollution concentrations are often assessed on the basis of the regulated pollutants. Whether these are the most appropriate components to assess the potential health benefits is questionable, as other health-relevant pollutants may be more strongly related to traffic.The aim of this study is to compare the contrast in concentration between major roads and (sub)urban background for a large range of pollutants and to analyze the magnitude of the measured difference in the street – background for major streets with different street configurations.Measurements of PM10, PM2.5, particle number concentrations (PNC), black carbon (BC), elemental composition of PM10 and PM2.5 and NOx were conducted simultaneously in eight major streets and nine (sub)urban background locations in the Netherlands. Measurements were done six times for a week during a six month period in 2008.High contrasts between busy streets and background locations in the same city were found for chromium, copper and iron (factor 2–3). These elements were especially present in the coarse fraction of PM. In addition, high contrasts were found for BC and NOx (factor 1.8), typically indicators of direct combustion emissions. The contrast for PNC was similar to BC. NO2 contrast was lower (factor 1.5). The largest contrast was found for two street canyons and two streets with buildings at one side of the street only.The contrast between busy streets and urban background in NO2 was less than the contrast found for BC, PNC and elements indicative of non-exhaust emissions, adding evidence that NO2 is not representing (current) traffic well. The study supports a substantial role for non-exhaust emissions including brake- and tyre wear and road dust in addition to direct combustion emissions. Significant underestimation of disease burden may occur when relying too much on the regulated components.

Research highlights
► High contrasts were found for chromium, copper and iron (factor 2–3).
► High contrasts were found for BC and NOx (factor 1.8).
► NO2 contrast was lower (factor 1.5), and is not representing (current) traffic well.
► Non-exhaust emissions are important in addition to exhaust emissions in urban areas.