engleski

Carbon as a main traffic pollutant in centre of Zagreb, Croatia

Narrow city streets engulfed by tall buildings are favourable to a general effect of a “canyon” in which pollution accumulates strongly on a relatively small area because of weak or inexistent ventilation. The aim of this study was to determine and compare levels of elemental carbon (EC) and organic carbon (OC) mass concentrations in PM10 particles between seasons and different years collected during at one such street canyon location in the centre of Zagreb in 2011, 2012 and 2013. Daily samples of airborne particles were collected on pre- fired quartz fibre filters. PM10 mass concentrations were determined gravimetrically. Samples were analysed for OC and EC with thermal/optical transmittance method (TOT) with a NIOSH-like protocol. Preliminary measurements showed seasonal and yearly variations of mass concentrations for carbon species in PM10. The higher concentrations were observed during the cold periods of the year (winter and autumn), while lower concentrations were recorded during summer and spring. The OC/EC ratio exhibited the same behaviour. Average yearly mass concentrations of PM10 and OC/EC ratios decreased during the years: 2011>2012>2013 indicating a negative trend, opposite to EC and OC content in PM10 which increased 2011<2012<2013. This increase of carbon content in PM originated from traffic and traffic jams due to the increased number of traffic lights and vehicles standing with engines running. This could also explain the reducing particle concentration because vehicles stood more than they moved and raised less dust from the road itself. Daily EC and OC maximums were recorded in the cold period of 2012. Therefore, a lower temperature during wintertime favours the condensation of organic compounds onto pre- existing particles and higher OC mass concentrations and OC content in PM10. Likewise, in the colder months higher EC concentrations originate from increased traffic and vehicle fuel combustion.

air quality ; EC ; OC ; traffic-related pollutant ; street canyon effect

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