Abstract
Deposition of the gas fraction of Semi-Volatile Organic Compounds (SVOC) may be an important removal pathway and may strongly influence concentrations of organic aerosols due to the gas-particle partitioning of SVOC. All the studies on this process are based on the classic Wesely resistance approach that uses Henry's law constants to calculate a deposition rate scaled on the deposition rate of SO2. However, even highly hydrophobic SVOC could be efficiently removed by the vegetation and soils as shown by numerous studies on Persistent Organic Pollutant (POP) modeling. Moreover, the re-volatilization of deposited SVOC is possible and could influence organic aerosol concentrations.An atmosphere-soil-vegetation module was developed and implemented in the 3D air quality model CHIMERE 2017β to represent the accumulation of compounds in the different compartments of the biosphere and the exchanges between them. The soil compartment was represented with a multi-layer approach (the layers corresponding to different in-soil depths) to simulate the multiphase diffusion of compounds inside the soil. Exchanges of SVOC between the air, soil and vegetation compartments were simulated using bi-directional approaches based on Rg (the gas-phase partitioning in the soil compartment) and Kva the vegetation-air partitioning coefficient. Parameters were estimated based on the physical properties of the compounds and their molecular structure.Simulations performed over Europe show that air-vegetation-soil exchanges may be a more efficient removal pathway than dry deposition of particles for SVOC with a gas-phase fraction above 10%. Considering air-vegetation-soil exchanges in the simulations lead to a decrease of organic aerosol concentrations by 15% and primary SVOC (considered as hydrophobic compounds) may be efficiently removed by those pathways (contrary to what is calculated with the Wesely approach). This decrease of concentrations is mainly due to air-vegetation exchanges. During summer, the use of the Wesely approach may lead to a slight overestimation of deposition fluxes (leading to an underestimation of concentration by 1%).Re-volatilization may limit the amount of deposited SVOC. Depending on assumptions, simulations showed that re-emissions (inversion of exchanges toward the emissions) in summer of SVOC accumulated during winter is theoretically possible and may be a minor source of organic aerosol.
Highlights
While the air-ecosystem nexus is often studied for meteorology and climate applications, food and security, or to better assess the CO2 sequestration power of the biosphere (Lefevre et al, 2007; Boone et al, 2017; Silva and Lambers, 2020), effect of interactions between the at mosphere and biosphere compartments on air pollutants remains an important issue (He et al, 2021)
This study aims at reconciling both approaches by implementing an explicit air-vegetation-soil exchange module in the air quality model CHIMERE and to study the effect of these exchanges on organic aerosol concentrations
A module inspired from Jacobs and van Pul (1996) to treat the ex changes of Semi-Volatile Organic Compounds (SVOC) as well as a few polycyclic aromatic hydrocarbons between the soil or vegetation and atmosphere was implemented in the CHIMERE 2017β (Couvidat et al, 2018) by using some parameters such as the constant octanol-water Kow or the Henry’s law constants, estimated with Sec ondary Organic Aerosol Processor (SOAP) model (Couvidat and Sartelet, 2015)
Summary
While the air-ecosystem nexus is often studied for meteorology and climate applications, food and security, or to better assess the CO2 sequestration power of the biosphere (Lefevre et al, 2007; Boone et al, 2017; Silva and Lambers, 2020), effect of interactions between the at mosphere and biosphere compartments on air pollutants remains an important issue (He et al, 2021). Using the resistance approach of Wesely (1989), several studies suggested that a large part of SVOC are highly soluble in water (effective Henry’s law constant higher than 105 M atm− 1) making the gas-phase fraction of SVOC sensitive to dry and wet deposition (Bessagnet et al, 2010; Knote et al, 2015). Due to the gas-particle partitioning of SVOC, this removal pathway could have a strong impact on Secondary Organic Aerosol (SOA) concentrations. Bessagnet et al (2010) estimated that omitting the dry deposition of gas-phase SVOC could lead to the overestimation of organic aerosols by 50% over Europe. Due to the importance of dry deposition of gas-phase SVOC on organic aerosol concentrations, works on this process are crucial to improve the representation of organic aerosols in air quality models
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.
