Characterisation and Source Apportionment of Submicron Particle Number Size Distributions in a Busy Street Canyon

Abstract

Street canyons are well-known hot spots due to the harmful exposure to high concentrations of atmospheric pollutants emitted mainly by motor vehicles. We report on measurements of air pollutants conducted in a street canyon in Stockholm (Sweden) in spring 2006. Particle number size distributions (PNSD) were measured in the 25-606 nm range, along with total particle number, light-absorbing carbon mass concentration (M LAC ), PM 10 , NO x , CO, traffic rate (TR), vehicle speed and meteorological variables. We used PNSD as input to the positive matrix factorisation (PMF) analysis to identify and apportion the pollutant sources. All pollutants showed distinct diurnal patterns, with highest concentrations in weekday mornings (08:00-09:00). TR was always higher on weekdays, except for the early hours (00:00-06:00). The raise in the weekend early-hour TR was accompanied by the largest M LAC of the day, a higher NO x /CO ratio compared to weekdays and a modal shift of PNSD towards larger diameters (47-56 nm), indicates a change in the vehicle fleet share to being dominated by diesel-run taxis. The largest contribution to the submicron particles was observed for winds blowing along the canyon, transporting particles emitted by vehicles accelerating from the traffic lights at the intersection, uphill towards the measurement site, and from the nearby streets. Three PMF factors were identified: local emissions from a mixed fleet dominated by gasoline engines, local traffic emissions highly impacted by diesel vehicles, and urban background aerosol. On average, gasoline-fuelled vehicles largely contributed to NO x , and particle number concentrations (54-65%), whereas M LAC sources were dominated by diesel emissions, especially at weekends in the early hours (73%). The urban background contribution was rather low (4-13%) and with little dependence on the weekday. This work demonstrated how particle size distribution measurements, together with M LAC , NO x and CO can be used to quantify the contribution from diesel and gasoline vehicles.

Local and Regional Contributions to Black Carbon Aerosols in a Mid-Sized City in Southern Brazil

“…Diesel-powered vehicles, which are usually a smaller fraction of the fleet, make a proportionally large contribution to total number concentrations (Kittelson et al, 2006). For example, Krecl et al (2015) showed that 73% of BC particles in Stockholm come from diesel emissions, especially in the early hours at weekends.…”

Experimental Comparison of Two Portable and Real-Time Size Distribution Analyzers for Nano/Submicron Aerosol Measurements

“…More recently, the smaller-sized PM categories of PM 1.0 and ultrafine particulates in the < 100 nm range (UFP) have been attracting growing research attention (Young et al, 2013;Jayaratne et al, 2015;Krecl et al, 2015;Lin et al, 2015). The PM size is critical to its toxicity by inhalation.…”

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“…Os particulados PTS e PI, com o CO e o NO 2 , apresentam picos pela manhã, entre 07h00 e 10h00, e no período das 17h00 às 22h00, horário de maior fluxo de veículos. Esses picos corroboram o observado por Gioda et al (2016), em estudo realizado no Rio de Janeiro, onde também foram verificados picos de poluentes nos horários de grande tráfego de veí-culos; também Krecl et al (2015), em estudo realizado em Estocolmo, identificaram picos de aumento de concentração de poluentes coincidindo com o aumento do número de veículos no trânsito. É possível verificar que a concentração de SO 2 sofre um acúmulo nas primeiras horas do dia até as 17h00 e posteriormente sofre redução até as 24h00, provavelmente devido à interação entre a radiação e o calor acumulado no final do dia.…”

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