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Assessing the impact of vehicular transportation on NOx and PMx concentrations in two metropolitan regions

Michal Landau-Morgenstein and David Broday

Assessing the impact of vehicular transportation on NOx and PMx concentrations in two metropolitan regions: a case study of Gush Dan and Haifa

(Read more)- Nitrogen oxides (NOx) and particulate matter (PM) are prevalent urban air pollutants which have been linked to various adverse health effects. Vehicular transportation is a dominant source of urban NO emissions, which rapidly undergo photochemical oxidation to form NO2, the pollutant of concern for its health effects. Due to its short atmospheric life time, NO is often used as a marker for transportation related pollution when measured near roads. On the other hand, whereas it is known that transportation contributes also to PM concentrations, the extent and size fraction is less understood. Unlike NOx, PM has an atmospheric life time that spans the synoptic scale, and can therefore stem from both local and long range sources. Various studies in Israel have dealt with the contribution of long range transport of PM from South Eastern Europe and the Saharan desert, which contributes to a high background PM level in Israel. Previous studies have estimated that transportation contributes ~33% of the NOx emissions in Israel, 47% in Haifa and 60% in Tel Aviv. Similarly, transportation has been suggested to contribute 20% and 39% of the PM emissions in Haifa and Tel Aviv, respectively.

The main goal of this work was to characterize the contribution of vehicular transportation to NOx and PMx concentrations in two metropolitan regions in Israel: Haifa and Tel Aviv. We studied this question by analyzing air quality monitoring data from all the reporting monitoring stations in the study areas.

It was found that despite the very large emissions from the heavy industry and electricity generation in Haifa, ambient NOx, PM10 and PM2.5 concentrations are significantly higher in Gush Dan, which experiences much higher traffic volumes. Nonetheless, highly resolved temporal patterns revealed a strong traffic signature in the NOx concentrations in Haifa although it experiences lower traffic volumes than Gush Dan. NO2 concentrations at roadside (RS) sites often exceed the national ambient air quality standards, especially at peak rush hours - the very hours people are most exposed to air pollution. Curbside monitoring data revealed that during the rush hour, NOx concentrations can be more than 5 times higher than the corresponding ambient levels. Since most air quality monitors in Israel are placed on buildings' rooftops, far from the normal breathing height, the standard use of monitoring data for exposure estimation is actually underestimating the true population exposure.

Analyses of PM10 and PM2.5 indicate that heavy traffic may contribute up to 21% of the ambient PM concentrations. Weekend decrease in concentrations of both the fine and the coarse fractions indicate that transportation contributes more to PM10 than to PM2.5. Thus, despite the high background PM concentration, local traffic has been identified to contribute significantly to observed urban PM levels. Since vehicle exhaust emissions contribute to the ultrafine particulate fraction whereas monitoring is based on particle mass, this increase actually represents an addition of a very large number of potentially toxic particles.