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

Abstract

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 modeling study using an updated European Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) number emission inventory, incorporating a more realistic, empirically justified particle size distribution (PSD) for sub-50 nm particles from road traffic as compared with the previous version. 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. This was done to test the effect of updated emissions at regional and local scales, particularly in comparison with atmospheric new particle formation (NPF). Updating the inventory increased the 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 at a regional scale during this photochemically active period. During this period, the fraction of the total particle number originating from atmospheric NPF processes was 91 %; thus, 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 closer spatially or temporally or when focusing on the chemical composition or the origin of the particles. For example, the daily average NCA concentrations increased by a factor of several hundred or thousand 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 now overcome. Additionally, the simulated distributions now agree better with the data observed at locations with 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.

Measurement report: Atmospheric new particle formation in a coastal agricultural site explained with binPMF analysis of nitrate CI-APi-TOF spectra

“…Zoomed-in views of these spectra can be found in Figs. S2-S9, and their raw spectra are also available at Olin (2022).…”

“…Atmospheric new particle formation (NPF) and primary emissions are both important sources of the total particle number concentration and cloud condensation nuclei in the global troposphere and in the continental boundary layer (Merikanto et al, 2009;Fountoukis et al, 2012;Posner and Pandis, 2015;Dunne et al, 2016;Kulmala et al, 2016;Gordon et al, 2017;Kerminen et al, 2018;Olin et al, 2022). NPF occurring in different environments has a very diverse behavior and is also not well quantified (Kerminen et al, 2018).…”

“…Data availability. Time series data measured at the Qvidja farm from April to June 2019 together with the raw spectra of the binPMF factors are freely available at https://doi.org/10.5281/zenodo.6394454 (Olin, 2022).…”

Influence of emission size distribution and nucleation on number concentrations over Greater Paris

“…At the local scale, the number of particles was modelled at the local exhaust outlet (Albriet et al, 2010;Xu et al, 2021) and in the plumes of ships (Karl et al, 2020), and at the neighbouring scale (Karl et al, 2016;Kurppa et al, 2020;Ketzel et al, 2021;Kumar et al, 2022) the large influence of nucleation and primary emissions from traffic was stressed. At the regional and global scales, chemistry transport models with model-to-measurement comparisons of number concentrations were performed in the United States (Jung et al, 2010;Zhang et al, 2010a;Kelly et al, 2011) and (more recently) in Europe (Kukkonen et al, 2016;Fountoukis et al, 2012;Patoulias et al, 2018;Fanourgakis et al, 2019;Olin et al, 2022;Patoulias and Pandis, 2022;Frohn et al, 2021). Only a few studies performed simulations over cities (Kukkonen et al, 2016;Frohn et al, 2021) and had poorer statistics than at the regional or global scale (Frohn et al, 2021).…”

“…In the framework of the EUCAARI project, a number emission inventory was built over Europe by size-segregating PM mass emission for the different sectors (Kulmala et al, 2011). Most of the regionalscale studies presented above used this emission inventory (Fountoukis et al, 2012;Patoulias et al, 2018;Patoulias and Pandis, 2022) or an updated version (Olin et al, 2022). Although the number concentrations may be particularly high in cities, number emissions are difficult to estimate.…”