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Seasonal and diurnal cycles of 0.25–2.5 μm aerosol fluxes over urban Stockholm, Sweden
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
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2011 (English)In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, no 5, 935-951 p.Article in journal (Refereed) Published
Abstract [en]

Size resolved aerosol and gas fluxes were measured in Stockholm from 1 April 2008 to 15 April 2009 over both urban and green sectors. CO2 and H2O fluxes peaked in daytime for all seasons. CO2 concentrations peaked in winter. Due to vegetation influence the CO2 fluxes had different diurnal cycles and magnitude in the two sectors. In the urban sector, CO2 fluxes indicated a net source. The sector dominated by residential areas and green spaces had its highest aerosol fluxes in winter. In spring, super micrometer concentrations for both sectors were significantly higher, as were the urban sector rush hour fluxes. The submicrometer aerosol fluxes had a similar diurnal pattern with daytime maxima for all seasons. This suggests that only the super micrometer aerosol emissions are dependent on season. During spring there was a clear difference in super micrometer fluxes between wet and dry streets. Our direct flux measurements have improved the understanding of the processes behind these aerosol emissions. They support the hypothesis that the spring peak in aerosol emissions are due to road dust, produced during the winter, but not released in large quantities until the roads dry up during spring, and explain why Stockholm has problems meeting the EU directive for aerosol mass (PM10).

Place, publisher, year, edition, pages
2011. Vol. 63, no 5, 935-951 p.
National Category
Natural Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-61682DOI: 10.1111/j.1600-0889.2011.00551.xISI: 000296030800010OAI: oai:DiVA.org:su-61682DiVA: diva2:437030
Available from: 2011-08-26 Created: 2011-08-26 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Traffic Emissions of Aerosols
Open this publication in new window or tab >>Traffic Emissions of Aerosols
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Non-exhaust traffic emissions are unregulated, yet the mass emission of non-exhaust particles may be larger than exhaust emissions. In addition, their emission factors (EF) are more uncertain than exhaust emissions. This thesis presents aerosol flux measurements in Stockholm using the eddy covariance method. Prior to this work, no direct flux measurements using micrometeorological techniques had been performed to study non-exhaust emissions. The challenges of measuring non-exhaust emissions include low particle number concentrations and the complex meteorological influences due to the dependence on road suspension processes. A novel approach applied here is the use of simultaneous flux measurements of CO2 and particles enabling improved parameterizations and understanding of source processes. It was shown that the EF for particles in the size range 0.25 to 2.5µm diameter are only 0.1% of the total particle number EF, indicating that ultrafine particles dominate the number fluxes. Sub- and super-micron particle emissions have been quantified, characterized, and parameterized. Dependence on wind speed, road surface condition and CO2 correlation indicates that the super-micron particles are primarily emitted through wind and vehicle induced turbulence. On the other hand, good correlation between sub-micron particles and CO2 flux indicates that these particles are primary emissions from traffic. The sub-micron particles (0.25 to 0.6 µm Dp) consisted of 60% semi-volatile components and 40% of non-volatile material. For the super-micron particle emissions, clear seasonal characteristics were found with the highest average values during spring. Heavy duty vehicles were found to emit 30 times more than light duty vehicles per km. This indicates that trucks and buses are more efficient at suspending super-micron particles than light duty vehicles. These results are consistent with the hypothesis that the particles originate from abrasion of road surfaces by studded tires.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm University, 2011. 96 p.
Keyword
Primary Aerosol Emissions, Carbon Dioxide Emissions, Traffic Aerosol, Urban Aerosol, Traffic Activity, Emission Factors, Eddy Covariance, Aerosol Flux
National Category
Meteorology and Atmospheric Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-61673 (URN)978-91-7447-337-7 (ISBN)
Public defence
2011-09-28, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 3: In press. Paper 4: Submitted.Available from: 2011-09-06 Created: 2011-08-25 Last updated: 2011-09-07Bibliographically approved

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Vogt, MatthiasAhlm, LarsJohansson, Christer
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