09 Aug 2021

09 Aug 2021

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

Simulation of the effects of low volatility organic compounds on aerosol number concentrations in Europe

David Patoulias1,2 and Spyros N. Pandis1,2 David Patoulias and Spyros N. Pandis
  • 1Department of Chemical Engineering, University of Patras, Patras, Greece
  • 2Institute of Chemical Engineering Sciences, Foundation for Research and Technology – Hellas (FORTH/ICE-HT), Patras, Greece

Abstract. PMCAMx-UF, a three-dimensional chemical transport model focusing on the simulation of the ultrafine particle size distribution and composition has been extended with the addition of reactions of chemical aging of semi-volatile anthropogenic organic vapors, the emissions and chemical aging by intermediate volatile organic compounds (IVOCs) and the production of extremely low volatility organic compounds (ELVOCs) by monoterpenes. The model is applied in Europe to quantify the effect of these processes on particle number concentrations. The model predictions are evaluated against both ground measurements collected during the PEGASOS 2012 summer campaign across many stations in Europe and airborne observations by a Zeppelin measuring above Po-Valley, Italy. PMCAMx-UF reproduces the ground level daily average concentrations of particles larger than 100 nm (N100) with normalized mean error (NME) of 45 % and normalized mean bias (NMB) close to 10 %. For the same simulation, PMCAMx-UF tends to overestimate the concentration of particles larger than 10 nm (N10) with a daily NMB of 23 % and a daily NME of 63 %. The model was able to reproduce more than 75 % of the N10 and N100 airborne observations (Zeppelin) within a factor of 2.

The ELVOC production by monoterpenes is predicted to lead to surprisingly small changes of the average number concentrations over Europe. The total number concentration decreased due to the ELVOC formation by 0.2 %, the N10 decreases by 1.1 %, while N50 increased by 3 % and N100 by 4 % due to this new SOA source. This small change is due to the nonlinearity of the system with increases predicted in some areas and decreases in others, but also the cancelation of the effects of the various processes like accelerated growth and accelerated coagulation. Locally, the effects can be significant. For example, an increase in N100 by 20–50 % is predicted over Scandinavia and significant increases (10–20 %) over some parts of central Europe. The ELVOCs contributed on average around 0.5 μg m−3 and accounted for 10–15 % of the PM2.5 OA. The addition of IVOC emissions and their aging reactions led to surprising reduction of the total number of particles (Ntot) and N10 by 10–15 and 5–10 %, respectively, and to an increase of the concentration of N100 by 5–10 %. These were due to the accelerated coagulation and reduced nucleation rates.

David Patoulias and Spyros N. Pandis

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-2021-655', Anonymous Referee #1, 30 Aug 2021
  • RC2: 'Comment on acp-2021-655', Anonymous Referee #2, 03 Sep 2021

David Patoulias and Spyros N. Pandis

David Patoulias and Spyros N. Pandis


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Short summary
Our simulations indicate that the recently identified production and subsequent condensation effect of extremely low volatility organic compounds has a smaller than expected effect on the total concentration of atmospheric particles. On the other hand, the oxidation of intermediate volatility organic compounds leads to decreases of the ultrafine particle concentrations. These results improve our understanding of the links between secondary organic aerosol formation and ultrafine particles.