| 1. |
- Krecl, Patricia, et al.
(author)
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Characterisation and Source Apportionment of Submicron Particle Number Size Distributions in a Busy Street Canyon
- 2015
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In: Aerosol and Air Quality Research. - : Taiwan Association for Aerosol Research. - 1680-8584 .- 2071-1409. ; 15:1, s. 220-233
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Journal article (peer-reviewed)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), PM10, NOx, 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 MLAC of the day, a higher NOx/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 NOx, 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, NOx and CO can be used to quantify the contribution from diesel and gasoline vehicles.
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| 2. |
- Krecl, Patricia, et al.
(author)
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Trends in black carbon and size-resolved particle number concentrations and vehicle emission factors under real-world conditions
- 2017
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 165, s. 155-168
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Journal article (peer-reviewed)abstract
- Kerbside concentrations of NOx, black carbon (BC), total number of particles (diameter > 4 nm) and number size distribution (28-410 nm) were measured at a busy street canyon in Stockholm in 2006 and 2013. Over this period, there was an important change in the vehicle fleet due to a strong dieselisation process of light-duty vehicles and technological improvement of vehicle engines. This study assesses the impact of these changes on ambient concentrations and particle emission factors (EF). EF were calculated by using a novel approach which combines the NOx tracer method with positive matrix factorisation (PMF) applied to particle number size distributions. NOx concentrations remained rather constant between these two years, whereas a large decrease in particle concentrations was observed, being on average 60% for BC, 50% for total particle number, and 53% for particles in the range 28-100 nm. The PMF analysis yielded three factors that were identified as contributions from gasoline vehicles, diesel fleet, and urban background. This separation allowed the calculation of the average vehicle EF for each particle metric per fuel type. In general, gasoline EF were lower than diesel EF, and EF for 2013 were lower than the ones derived for 2006. The EFBC decreased 77% for both gasoline and diesel fleets, whereas the particle number EF reduction was higher for the gasoline (79%) than for the diesel (37%) fleet. Our EF are consistent with results from other on-road studies, which reinforces that the proposed methodology is suitable for EF determination and to assess the effectiveness of policies implemented to reduce vehicle exhaust emissions. However, our EF are much higher than EF simulated with traffic emission models (HBEFA and COPERT) that are based on dynamometer measurements, except for EFBC for diesel vehicles. This finding suggests that the EF from the two leading models in Europe should be revised for BC (gasoline vehicles) and particle number (all vehicles), since they are used to compile national inventories for the road transportation sector and also to assess their associated health effects. Using the calculated kerbside EF, we estimated that the traffic emissions were lower in 2013 compared to 2006 with a 61% reduction for BC (due to decreases in both gasoline and diesel emissions), and 34-45% for particle number (reduction only in gasoline emissions). Limitations of the application of these EF to other studies are also discussed.
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| 3. |
- Targino, Admir Créso, et al.
(author)
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Surface ozone climatology of South Eastern Brazil and the impact of biomass burning events
- 2019
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In: Journal of Environmental Management. - : Elsevier BV. - 0301-4797 .- 1095-8630. ; 252
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Journal article (peer-reviewed)abstract
- In the austral spring, biomass fires affect a vast area of South America each year. We combined in situ ozone (O-3) data, measured in the states of Sao Paulo and Parana, Brazil, in the period 2014-2017, with aerosol optical depth, co-pollutants (NOx, PM2.5 and PM10) and air backtrajectories to identify sources, transport and geographical patterns in the air pollution data. We applied cluster analysis to hourly O-3 data and split the investigation area of approximately 290,000 km(2) into five groups with similar features in terms of diurnal, weekly, monthly and seasonal O-3 concentrations. All groups presented a peak in September and October, associated with the fire activities and enhanced photochemistry. The highest mean O-3 concentrations were measured inland whilst, besides having lower concentrations, the coastal group was also associated with the smallest diurnal and seasonal variations. The latter was attributed to lower photochemical activity due to frequently occurring overcast weather situation. The mean annual regional contribution of O-3 over the area was 61 mu g/m(3), with large seasonal and intersite variabilities (from 35 to 84 mu g/m(3)). The long-range transport of smoke contributed with between 23 and 41% of the total O-3 during the pollution events. A pollution outbreak in September 2015 caused many-fold increases in O-3, PM2.5 and PM10 across the investigation area, which exceeded the World Health Organisation recommendations. We show that the regional transport of particulates and gas due to biomass burning overlays the local emissions in already highly polluted cities. Such an effect can outweigh local measures to curb anthropogenic air pollution in cities.
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