20 Jul 2021

20 Jul 2021

Review status: this preprint is currently under review for the journal ACP.

Contribution of traffic-originated nanoparticle emissions to regional and local aerosol levels

Miska Olin1, David Patoulias2,3, Heino Kuuluvainen1, Jarkko V. Niemi4, Topi Rönkkö1, Spyros N. Pandis2,3, Ilona Riipinen5, and Miikka Dal Maso1 Miska Olin et al.
  • 1Aerosol Physics Laboratory, Tampere University, FI-33014 Tampere, Finland
  • 2Department of Chemical Engineering, University of Patras, GR-26504 Patras, Greece
  • 3Institute of Chemical Engineering Sciences, Foundation for Research and Technology, GR-26504 Patras, Greece
  • 4Helsinki Region Environmental Services Authority (HSY), FI-00066 HSY, Finland
  • 5Department of Environmental Science (ACES) and Bolin Centre for Climate Research, Stockholm University, SE-10691 Stockholm, Sweden

Abstract. Sub-50 nm particles originating from traffic emissions pose risks to human health due to their high lung deposition efficiency and potentially harmful chemical composition. We present a modelling study using an updated EUCAARI number emission inventory, incorporating a more realistic, empirically justified particle size distribution (PSD) for sub-50 nm particles from road traffic. We present experimental PSDs and CO2 concentrations, measured in a highly trafficked street canyon in Helsinki, Finland, as an emission factor particle size distribution (EFPSD), which was then used in updating the EUCAARI inventory. We applied the updated inventory in a simulation using the regional chemical transport model PMCAMx-UF over Europe for May 2008 to test the effect of updated emissions in regional and local scales and in contrast to atmospheric new particle formation (NPF). Updating the inventory increased simulated average total particle number concentrations by only 1 %, although the total particle number emissions were increased to a 3-fold level. The concentrations increased up to 11 % when only 1.3–3 nm-sized particles (nanocluster aerosol, NCA) were considered. These values indicate that the effect of updating overall is insignificant in a regional scale during this photochemically active period, during which the fraction of the total particle number originating through atmospheric NPF processes was 91 %. These simulations give a lower limit for the contribution of traffic to the aerosol levels. Nevertheless, the situation is different when examining the effect of the update spatially or temporally, or when focusing to the chemical composition or the origin of the particles. For example, daily average NCA concentrations increased by a factor of several hundreds or thousands in some locations on certain days. Overall, the most significant effects–reaching several orders of magnitude–from updating the inventory are observed when examining specific particle sizes (especially 7–20 nm), particle components, and specific urban areas. While the model still has a tendency to predict more sub-50 nm particles compared to the observations, the most notable underestimations in the concentrations of sub-10 nm particles are, after updating, overcome and the simulated distributions now agree better with the data observed at locations having high traffic densities. The findings of this study highlight the need to consider emissions, PSDs, and composition of sub-50 nm particles from road traffic in studies focusing on urban air quality. Updating this emission source brings the simulated aerosol levels particularly in urban locations closer to observations, which highlights its importance for calculations of human exposure to nanoparticles.

Miska Olin et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee comment on acp-2021-466', Anonymous Referee #2, 05 Aug 2021
  • RC2: 'Comment on acp-2021-466', Hugo Denier van der Gon, 29 Sep 2021

Miska Olin et al.


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Short summary
An emission factor particle size distribution was determined from the measurements at an urban traffic site. It was used in updating a pre-existing emission inventory and regional modelling was performed after the update. Emission inventories typically underestimate nanoparticle emissions due to challenges in determining them with high certainty. This update reveals that the simulated aerosol levels have previously been underestimated especially for urban areas and for sub-50 nm-sized particles.