Articles | Volume 11, issue 12
Atmos. Chem. Phys., 11, 5897–5915, 2011

Special issue: European Integrated Project on Aerosol-Cloud-Climate and Air...

Atmos. Chem. Phys., 11, 5897–5915, 2011

Research article 22 Jun 2011

Research article | 22 Jun 2011

Aerosol ageing in an urban plume – implication for climate

P. Roldin1, E. Swietlicki1, A. Massling1,*, A. Kristensson1, J. Löndahl1, A. Eriksson1,2, J. Pagels2, and S. Gustafsson3 P. Roldin et al.
  • 1Division of Nuclear Physics, Lund University, 221 00, Lund, Sweden
  • 2Division of Ergonomics and Aerosol Technology, Lund University, Sweden
  • 3Environmental Department, City of Malmö, Sweden
  • *now at: National Environmental Research Institute, Dept. of Atmospheric Environment, Aarhus University, Denmark

Abstract. The climate effects downwind of an urban area resulting from gaseous and particulate emissions within the city are as yet inadequately quantified. The aim of this work was to estimate these effects for Malmö city in southern Sweden (population 280 000). The chemical and physical particle properties were simulated with a model for Aerosol Dynamics, gas phase CHEMistry and radiative transfer calculations (ADCHEM) following the trajectory movement from upwind of Malmö, through the urban background environment and finally tens and hundreds of kilometers downwind of Malmö. The model results were evaluated using measurements of the particle number size distribution and chemical composition. The total particle number concentration 50 km (~ 3 h) downwind, in the center of the Malmö plume, is about 3700 cm−3 of which the Malmö contribution is roughly 30%. Condensation of nitric acid, ammonium and to a smaller extent oxidized organic compounds formed from the emissions in Malmö increases the secondary aerosol formation with a maximum of 0.7–0.8 μg m−3 6 to 18 h downwind of Malmö. The secondary mass contribution dominates over the primary soot contribution from Malmö already 3 to 4 h downwind of the emission sources and contributes to an enhanced total surface direct or indirect aerosol shortwave radiative forcing in the center of the urban plume ranging from −0.3 to −3.3 W m−2 depending on the distance from Malmö, and the specific cloud properties.

Final-revised paper