10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Atmospheric Nanocluster Aerosol Emitted from Road Traffic
HEINO KUULUVAINEN, Topi Rönkkö, Panu Karjalainen, Jorma Keskinen, Risto Hillamo, Jarkko Niemi, Liisa Pirjola, Hilkka Timonen, Sanna Saarikoski, Erkka Saukko, Anssi Järvinen, Henna Silvennoinen, Antti Rostedt, Miska Olin, Jaakko Yli-Ojanperä, Pekka Nousiainen, Anu Kousa, Miikka Dal Maso, Tampere University of Technology, Tampere, Finland
Abstract Number: 1183 Working Group: Combustion-Generated Aerosols: the Desirable and Undesirable
Abstract Traffic is a significant source of atmospheric aerosol particles. Because of their small size and complicated chemical and physical characteristics, atmospheric particles emitted from traffic pose a significant risk to human health and contribute to anthropogenic forcing of climate. Previous research has established that vehicles emit primary aerosol particles and contribute to secondary aerosol particle formation by emitting aerosol precursors. Our recent studies have extended the characterization of traffic emission to cover the smallest particles of traffic environments, referred as nanocluster aerosol (NCA), i.e. the particles in a size range of 1.3–3.0 nm. In the publication by Rönkkö et al. (2017), we reported the significant presence of traffic-originated NCA particles in the vicinity of traffic, determined the emission factors for the NCA, and evaluated its global importance. Our findings demonstrate that, in urban air, extremely small particles form a significant fraction of the total particle number and are a direct result of road traffic emissions. Thus, our findings also imply that an atmospheric nucleation process is not necessary for the formation of a large number of particles in urban areas.
Concentrations and fractions of NCA were measured in three experiments covering a wide range of urban environments. Stationary measurements were carried out at a roadside environment next to a major road in a semiurban area and in an urban street canyon in Helsinki, Finland. In addition, a mobile laboratory was used for a long-distance on-road study through Western Europe. These measurements were supported by experiments in an engine laboratory where the particle emissions of a modern heavy-duty diesel engine were measured at three different engine load conditions. In the engine laboratory experiments, the exhaust was sampled using a partial flow sampling and dilution system previously proved to mimic the real-world exhaust nanoparticle formation. In all the experiments, the NCA concentrations were measured by using a particle size magnifier (PSM, Airmodus Ltd) together with condensation particle counters (CPC). Also carbon dioxide (CO2) concentrations were measured parallel with the NCA concentrations in order to determine emission factors for the NCA.
In the semiurban roadside environment, the NCA represented a fraction of 20–54% of the total particle concentration in ambient air. The observed NCA concentrations and fractions were depended on the diurnal pattern of traffic and on the wind direction. The emission factors of NCA for traffic were 2.4·1015 (kg·fuel)-1 in the roadside environment, 2.6·1015 (kg·fuel)-1 in the street canyon, and 2.9·1015 (kg·fuel)-1 in the on-road study. However, the emissions were not associated with all vehicles and all driving conditions. In the engine laboratory experiments, the emission factors of exhaust NCA varied from a relatively low value of 1.6·1012 (kg·fuel)-1 to a high value of 4.3·1015 (kg·fuel)-1 depending on the engine load. The high fractions of NCA observed in urban areas indicate that these small particles may have a significant effect on human health and global climate. The determined emission factors showed that the NCA is directly emitted from road traffic and, by using these emission factors, its contribution can be estimated on a global scale.
Acknowledgements This research was funded by Tekes, Academy of Finland (Grants 283455, 259016, and 293437), Cleen Ltd (MMEA project), Dinex Ecocat Oy, Neste Corporation, AGCO Power, and Ab Nanol Technologies Oy. The authors thank Anders Svens and Harri Portin (HSY) for their technical support during roadside measurements.
References Rönkkö, T. et al. 2017. Traffic is a major source of atmospheric nanocluster aerosol. Proceedings of the National Academy of Sciences of the United States of America, 114 (29), 7549-7554.