Abstract
Abstract. The oxidation of biogenic volatile organic compounds (BVOCs) gives a range of products, from semi-volatile to extremely low-volatility compounds. To treat the interaction of these secondary organic vapours with the particle phase, global aerosol microphysics models generally use either a thermodynamic partitioning approach (assuming instant equilibrium between semi-volatile oxidation products and the particle phase) or a kinetic approach (accounting for the size dependence of condensation). We show that model treatment of the partitioning of biogenic organic vapours into the particle phase, and consequent distribution of material across the size distribution, controls the magnitude of the first aerosol indirect effect (AIE) due to biogenic secondary organic aerosol (SOA). With a kinetic partitioning approach, SOA is distributed according to the existing condensation sink, enhancing the growth of the smallest particles, i.e. those in the nucleation mode. This process tends to increase cloud droplet number concentrations in the presence of biogenic SOA. By contrast, an approach that distributes SOA according to pre-existing organic mass restricts the growth of the smallest particles, limiting the number that are able to form cloud droplets. With an organically mediated new particle formation mechanism, applying a mass-based rather than a kinetic approach to partitioning reduces our calculated global mean AIE due to biogenic SOA by 24 %. Our results suggest that the mechanisms driving organic partitioning need to be fully understood in order to accurately describe the climatic effects of SOA.
Highlights
Biogenic volatile organic compounds (BVOCs), such as monoterpenes and isoprene, are emitted into the atmosphere by vegetation (Guenther et al, 1995, 2006) and are rapidly oxidised
A global annual mean negative first aerosol indirect effect (AIE) is maintained under the mass-based approach because the contribution of organic oxidation products to new particle formation is sufficient to outweigh the impact of suppressed growth on cloud droplet number concentrations (CDNC) (Fig. 2d)
We tested two assumptions about the way secondary organic material is added to existing particles – a kinetic approach where material condenses according to the surface area of existing particles and a mass-based approach where the material condenses according to the organic mass present in existing particles
Summary
Biogenic volatile organic compounds (BVOCs), such as monoterpenes and isoprene, are emitted into the atmosphere by vegetation (Guenther et al, 1995, 2006) and are rapidly oxidised. The oxidation of BVOCs yields products with lower volatility, which may partition to the particle phase forming secondary organic aerosol (SOA). Organic compounds contribute a large fraction of submicron aerosol mass (Murphy et al, 2006; Zhang et al, 2007; Jimenez et al, 2009) with important impacts on air quality and climate (Fiore et al, 2012; Scott et al, 2014). The availability of CCN controls cloud droplet number concentrations (CDNC) and subsequently cloud albedo; the manner in which organics are distributed has potential implications for the first aerosol indirect effect (AIE) of biogenic SOA
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
