Atmos. Chem. Phys. Discuss., 10, 21521-21545, 2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The relationship between 0.25–2.5 μm aerosol and CO2 emissions over a city
M. Vogt1, E. D. Nilsson1, L. Ahlm1, E. M. Mårtensson1, and C. Johansson1,2
1Department of Applied Environmental Science (ITM), Stockholm University, 10691 Stockholm, Sweden
2City of Stockholm Environment and Health Administration, Box 8136, 10420 Stockholm, Sweden

Abstract. Unlike exhaust emissions, non-exhaust traffic emissions are completely unregulated and there are large uncertainties in the non-exhaust emission factors required to estimate the emissions of these aerosols. This study provides the first published results of direct measurements of size resolved emission factors for particles in the size range 0.25–2.5 μm using a new approach deriving aerosol emission factors from the CO2 emission fluxes. Because the aerosol and CO2 emissions have a common source and because the CO2 emission per fuel or traffic amount are much less uncertain than the aerosol emissions, this approach has obvious advantages. Therefore aerosol fluxes were measured during one year using the eddy covariance method at the top of a 118 m high communication tower over Stockholm, Sweden. Maximum CO2 and particle fluxes coincides with the wind direction with densest traffic within the footprint area. Negative fluxes (uptake of CO2 and deposition of particles) coincides with an urban forest area. The fluxes of CO2 were used to obtain emission factors for particles by assuming that the CO2 fluxes could converted to amounts of fuel burnt. The estimated emission factors for the fleet mix in the measurement area are, in number 1.4×1011 [particle veh−1 km−1]. Assuming spherical particles of density 1600 kg/m3 this corresponds to 27.5 mg veh−1 km−1. Wind speed influence the emission factor indicating that wind induced turbulence may be important.

Citation: Vogt, M., Nilsson, E. D., Ahlm, L., Mårtensson, E. M., and Johansson, C.: The relationship between 0.25–2.5 μm aerosol and CO2 emissions over a city, Atmos. Chem. Phys. Discuss., 10, 21521-21545, doi:10.5194/acpd-10-21521-2010, 2010.
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