Air Quality on local and urban scale

An important part of SMHI's Air Quality research is made up of model development and data analysis of Air Quality on local and urban geographical scales, i.e. when Air Quality is studied in urban areas and in microenvironments relatively close to emission sources. Road traffic and residential wood combustion are two dominant sources.

The concentration of air pollutants in ambient air comes from various sources. A significant contribution to air pollution is long-distance transportation from other parts of Sweden and Europe, but in urban areas the local emission is also meaningful.

An important part of SMHI's Air Quality research therefore consists of model development and data analysis of Air Quality on local and urban geographical scales, which covers horizontal scales from some tens of kilometres down to a few meters, in other words applications within urban areas and inside microenvironments around point sources, in street canyons and close to roads.

Road traffic and residential wood combustion are two dominant sources in the case of local contribution to air pollution.

The climate significance of Air Quality in Sweden

Road wear particles
Road wear particles. Photo: Mats Gustafsson och Göran Blomqvist, VTI.

Sweden's Air Quality is strongly influenced by its geographic location and climate in Northern Europe. In the winter, the temperature is often below zero degrees and rain and snow are common, causing slippery roads and a need for space heating.

For anti-skid treatment, studded tyres and sand are frequently used, creating road wear particles; approximately 80-90% of all PM10 emissions originates from non-exhaust emissions.

Another local source of particles is residential wood combustion, a common primary or supplementary space heating source. Increased use of small-scale biofuel is one alternative being considered given the phasing out of fossil fuels. However, high-emitting old wood stoves can have negative impacts on air quality.

Road traffic - a dominant source of air pollution

One of the largest sources of air pollution is road traffic. Particles, exhaust emissions and emissions from non-exhaust gases, such as tyres, vehicle and road wear, are significant sources.

For the calculation, analysis and assessment of Air Quality near traffic areas, SMHI has developed a model system, SIMAIR, which is a complex yet easy to use tool, accessible via the internet. The model system has been used in national research applications such as studies on the studded tyres environmental impact, assessment of the new EU Air Quality Directive's significance with respect to fine particles (PM2.5), as well as in several national scenario studies.

Air Quality improvements due to reduction of studded tyres use
Calculated 90-percentile daily mean values of PM10 for different scenarios with reduction of studded tyres use. Enlarge Image

Small-scale biofuel combustion - a local environmental problem

Small scale wood combustion is a local environmental problem which often only involves a small number of facilities within a residential area. In order to analyze the Air Quality with respect to emissions from small-scale biofuel combustion, SMHI has developed SIMAIRrwc, which is an internet tool that municipalities in Sweden can use to assess the Air Quality in residential areas with residential wood combustion.

Air Quality improvements due to replacing old wood stoves
From SIMAIRrwc the annual average concentration of PM10 was calculated for a residential area in a medium-sized Swedish town. The figure shows the significant air environment benefits in replacing old wooden stoves with modern environmentally-approved wooden stoves with storage tanks. Enlarge Image

References and further reading

Andersson, S., Bergström, R., Omstedt, G. och Engardt, M., (2008) 'Dagens och framtidens partikelhalter i Sverige. Utredning av exponeringsminskningsmål för PM2.5 enligt nytt luftdirektiv', SMHI Meteorologi, Nr. 133, 35 pp. (In Swedish).

Andersson, S. och Omstedt, G., (2009) 'Validering av SIMAIR mot mätningar av PM10, NO2 och bensen. Utvärdering för svenska tätorter och trafikmiljöer avseende år 2004 och 2005', SMHI Meteorologi, Nr. 137, 125 pp. (In Swedish).

Andersson, S., Omstedt, G. och Robertson, L., (2010) 'Känslighetsanalys, vidareutveckling och validering av SIMAIRs urbana spridningsmodell BUM'. SMHI Meteorologi, Nr. 142, 37 pp. (In Swedish).

Gidhagen, L., Johansson, C., Omstedt, G., Langner, J. and Olivares, G. (2004) 'Model simulations of NOx and ultrafine particles close to a Swedish highway', Environmental Science and Technology 38,.6730-6740.

Gidhagen, L., Johansson, H. and Omstedt, G., (2009) 'SIMAIR - Evaluation tool for meeting the EU directive on air pollution limits'. Atmospheric Environment, 43, 1029-1036, doi:10.1016/j.atmosenv.2008.01.056.

Ketzel, M., Omstedt, G., Johansson, C., During, I., Pohjola, M., Dieterman,O., Gidhagen, L., Wåhlin, P., Lohmeyer, A., Haakana, M. and Berkowicz, R. (2007) 'Estimation and validation of PM2.5/PM10 exhausted and non-exhausted emission factors for practical street pollution modelling', Atmospheric Environment, Vol. 41, pp.9370-9385.

Omstedt, G. (1988) 'An Operational Air Pollution Model', SMHI Report, RMK no. 57, 35 pp. (available from

Omstedt, G., Bringfelt, B. and Johansson, C. (2005) 'A model for vehicle-induced non-tailpipe emissions of particles along Swedish roads', Atmospheric Environment, Vol. 39, pp.6088-6097.

Omstedt, G., Andersson, S. och Bergström, R. (2010) 'Dagens och framtidens luftkvalitet i Sverige. Haltberäkningar av NO2, PM10 och PM2.5 i svenska trafikmiljöer för framtidsscenarier med minskade europeiska emissioner', SMHI Meteorologi, Nr. 140, 56 pp. (In Swedish).

Omstedt, G., Andersson, S., Gidhagen, L. and Robertson, L. (2011) 'Evaluation of new model tools for meeting the targets of the EU Air Quality Directive: A case study on the studded tyre use in Sweden', International Journal of Environment and Pollution, Vol. 47, No. 1/2/3/4, 79-96, DOI: 10.1504/11.47328.