17 Jan 2022
17 Jan 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

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

Karine Sartelet1, Youngseob Kim1, Florian Couvidat2, Maik Merkel3, Tuukka Petäjä4, Jean Sciare5, and Alfred Wiedensohler3 Karine Sartelet et al.
  • 1CEREA, École des Ponts ParisTech, EdF R&D, IPSL, 77455 Marne la Vallée, France
  • 2INERIS, 60550 Verneuil en Halatte, France
  • 3Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 4Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, 00014, Finland
  • 5Laboratoire des Sciences du Climat et de l’Environnement, Gif-sur-Yvette, France

Abstract. With the growing evidence that high particle number concentrations may impact health, modelling their emissions and understanding formation processes is necessary, especially in cities where many people are exposed. As emission inventories of particle numbers and size distribution over cities are usually not available, a methodology is defined to estimate them from PM2.5 emissions, ratios PM1/PM2.5 and PM0.1/PM2.5 by activity sector. In this methodology, a fitting parameter is used to redistribute the number concentrations in the lowest emission diameter range. This parameter is chosen by comparing measured and simulated number concentrations during non-nucleation days. The emission size distribution is then finely discretised by conserving both mass and number in each of the size ranges where emissions are specified. The methodology is applied over Greater Paris during the MEGAPOLI campaign (July 2009). Three-dimensional simulations are performed using the chemistry-transport model Polair3D/Polyphemus coupled to the aerosol module SSH-aerosol to represent the evolution of particles by condensation/evaporation, coagulation and nucleation, with a sectional approach for the size distribution. The model is first compared to measurements during non-nucleation days, and the influence over the month of July 2009 of three different nucleation parameterisations is assessed: a binary (sulfuric acid, water), ternary (sulfuric acid, ammonia, water) and heteromolecular (extremely-low volatile organic compounds (ELVOC) from monoterpenes and sulfuric acid). The modelled number concentrations compare very well to measurements with an average normalised mean error of 42 % for the daily number concentrations of particles larger than 10 nm, and 37 % for the number concentrations of particles larger than 100 nm. The influence of the binary nucleation is low, and the ternary nucleation scheme leads to better simulated number concentrations (in terms of bias and error) at only one site out of three, but it systematically reduces the model to measurement correlation, suggesting that ternary nucleation may not be the dominant process in new particle formation. However, the relative bias and error, as well as the correlation at suburban sites, are systematically improved using the heteromolecular nucleation scheme involving sulfuric acid and ELVOC from monoterpenes. This suggests that heteromolecular nucleation may be important in cities, especially at suburban sites in summer, and that a better characterisation of the emissions of ELVOC precursors from traffic is needed.

Karine Sartelet et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-22', Anonymous Referee #1, 06 Feb 2022
  • RC2: 'Comment on acp-2022-22', Anonymous Referee #2, 04 Apr 2022

Karine Sartelet et al.

Karine Sartelet et al.


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Short summary
A methodology is defined to estimate number emissions from an inventory providing mass emissions. Number concentrations are simulated over Greater Paris using different nucleation parameterizations (binary, ternary involving sulfuric acid and ammonia, heteromolecular involving sulfuric acid and extremely-low volatil organics ELVOC). The model to measurement comparisons show that ternary nucleation may not be a dominant process for new-particle formation in cities, but stress the role of ELVOC.