Modelling the contribution of biogenic VOCs to new particle formation Modelling the contribution of biogenic VOCs to new particle formation in the Jülich plant atmosphere chamber Modelling the contribution of biogenic VOCs to new particle formation

Abstract

We used the MALTE-BOX model including near-explicit air chemistry and detailed aerosol dynamics to study the mechanisms of observed new particle formation events in the Jülich Plant Atmosphere Chamber. The modelled and measured H 2 SO 4 (sul-furic acid) concentrations agreed within a factor of two. The modelled total monoter-5 pene concentration was in line with PTR-MS observations, and we provided the distributions of individual isomers of terpenes, when no measurements were available. The aerosol dynamic results supported the hypothesis that H 2 SO 4 is one of the critical compounds in the nucleation process. However, compared to kinetic H 2 SO 4 nu-cleation, nucleation involving OH oxidation products of monoterpenes showed a bet-10 ter agreement with the measurements, with R 2 up to 0.97 between modelled and measured total particle number concentrations. The nucleation coefficient for kinetic H 2 SO 4 nucleation was 2.1 × 10 −11 cm 3 s −1 , while the organic nucleation coefficient was 9.0 × 10 −14 cm 3 s −1. We classified the VOC oxidation products into two subgroups including extremely low-volatility organic compounds (ELVOCs) and semi-volatile organic 15 compounds (SVOCs). These ELVOCs and SVOCs contributed approximately equally to the particle volume production, whereas only ELVOCs made the smallest particles to grow in size. The model simulations revealed that the chamber walls constitute a major net sink of SVOCs on the first experiment day. However, the net wall SVOC uptake was gradually reduced because of SVOC desorption during the following days. Thus, in or-20 der to capture the observed temporal evolution of the particle number size distribution, the model needs to consider reversible gas-wall partitioning.