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Traffic-related nanocluster particles have longer lifetime than expected

Traffic-related nanocluster particles have longer lifetime than expected

The lifetime of smallest, nanocluster aerosol (NCA) particles is longer than expected. This study indicates that NCA may play a significant role in urban environments since part of NCA particles remain in the particle population and grow by condensation.

Finnish Meteorological Institute participated in a study led by Tampere University where the dispersion of nanocluster particles (NCA, particle diameter 1.3-4nm) from a major road was characterized. Recent studies have shown that a significant fraction of traffic-related particles are only few nanometers in diameter. Based on this study, NCA may play a significant role in urban environments, since, rather than being scavenged by larger particles, NCA particles remain in the particle population and grow by condensation.

The roadside measurements showed that NCA concentration fell more rapidly than the total particle concentration, especially during the morning. However, a significant amount of NCA particles remained as the aerosol population evolved. Modelling studies showed that, while dilution is the main process acting on the total particle concentration, deposition also had a significant impact. Condensation and possibly enhanced deposition of NCA were the main plausible processes explaining why dispersion is faster for NCA than for total particle concentration, while the effect of coagulation on all size ranges was small.

The NCA concentrations were measured near a major highway in the Helsinki region of Finland, varying the distance from the highway. Additionally, modelling studies were performed to gain further information on how different transformation processes affect NCA dispersion.

Research was done in tight co-operation between Tampere University, Finnish Meteorological institute, and Metropolia University of Applied Sciences. The research and results presented are funded by Business Finland (MMEA and Cityzer -projects), HSY, Pegasor Oy and the Maj and Tor Nessling Foundation.

Further information:

Senior researcher Hilkka Timonen, Finnish Meteorological Institute, tel. +358 50 380 2864, hilkka.timonen@fmi.fi

Kangasniemi, O., H. Kuuluvainen, J. Heikkilä, L. Pirjola, J. V. Niemi, H. Timonen, S. Saarikoski, T. Rönkkö, and M. Dal Maso (2019), Dispersion of a Traffic Related Nanocluster Aerosol Near a Major Road, Atmosphere, 10(6), 309, doi:10.3390/atmos10060309. https://www.mdpi.com/2073-4433/10/6/309


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