Abstract
Abstract. Atmospheric chambers have been widely used to study secondary organic aerosol (SOA) properties and formation from various precursors under different controlled environmental conditions and to develop parameterization to represent SOA formation in chemical transport models (CTMs). Chamber experiments are however limited in number, performed under conditions that differ from the atmosphere and can be subject to potential artefacts from chamber walls. Here, the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) modelling tool has been used in a box model under various environmental conditions to (i) explore the sensitivity of SOA formation and properties to changes on physical and chemical conditions and (ii) develop a volatility basis set (VBS)-type parameterization. The set of parent hydrocarbons includes n-alkanes and 1-alkenes with 10, 14, 18, 22 and 26 carbon atoms, α-pinene, β-pinene and limonene, benzene, toluene, o-xylene, m-xylene and p-xylene. Simulated SOA yields and their dependences on the precursor structure, organic aerosol load, temperature and NOx levels are consistent with the literature. GECKO-A was used to explore the distribution of molar mass, vaporization enthalpy, OH reaction rate and Henry's law coefficient of the millions of secondary organic compounds formed during the oxidation of the different precursors and under various conditions. From these explicit simulations, a VBS-GECKO parameterization designed to be implemented in 3-D air quality models has been tuned to represent SOA formation from the 18 precursors using GECKO-A as a reference. In evaluating the ability of VBS-GECKO to capture the temporal evolution of SOA mass, the mean relative error is less than 20 % compared to GECKO-A. The optimization procedure has been automated to facilitate the update of the VBS-GECKO on the basis of the future GECKO-A versions, its extension to other precursors and/or its modification to carry additional information.
Highlights
Fine particulate matter impacts visibility (e.g. Han et al, 2012), human health (e.g. Lim et al, 2012; Malley et al, 2017) and climate (e.g. Boucher et al, 2013)
The amount of secondary organic aerosol (SOA) formed from a gaseous precursor depends mainly on its structure and on environmental conditions that influence (i) the concentration and the structure of organic compounds produced during gas-phase oxidation and (ii) their partitioning between the gas and the condensed phase (pre-existing organic aerosol (OA) mass (Coa), temperature, etc.) (e.g. Kroll and Seinfeld, 2008; Ng et al, 2017; Shrivastava et al, 2017)
Reference GECKO-A simulations show generally (1) a fast increase of OA mass concentration during the first 10 h of oxidation, (2) a clear diurnal cycle of OA concentration linked to the temperature variations, with a larger amplitude for the WIN than for the SUM scenarios, (3) higher simulated OA concentrations for the LNOx scenarios with maximum concentration obtained during the summer, (4) a slight increase of OA concentrations with the increase of anthropogenic precursors in the HNOx scenarios and with the increase of biogenic precursors in the LNOx scenarios
Summary
Fine particulate matter impacts visibility (e.g. Han et al, 2012), human health (e.g. Lim et al, 2012; Malley et al, 2017) and climate (e.g. Boucher et al, 2013). A large fraction of fine particles is organic, representing between 20 % and 90 % of the total mass (e.g. Jimenez et al, 2009). This organic fraction can be directly emitted into the atmo-. The amount of SOA formed from a gaseous precursor depends mainly on its structure (carbon chain length, degree of unsaturation, number and type of functional groups, etc.) and on environmental conditions that influence (i) the concentration and the structure of organic compounds produced during gas-phase oxidation (oxidant concentrations and NOx levels, temperature, photolysis, humidity, etc.) and (ii) their partitioning between the gas and the condensed phase (pre-existing OA mass (Coa), temperature, etc.) The amount of SOA formed from a gaseous precursor depends mainly on its structure (carbon chain length, degree of unsaturation, number and type of functional groups, etc.) and on environmental conditions that influence (i) the concentration and the structure of organic compounds produced during gas-phase oxidation (oxidant concentrations and NOx levels, temperature, photolysis, humidity, etc.) and (ii) their partitioning between the gas and the condensed phase (pre-existing OA mass (Coa), temperature, etc.) (e.g. Kroll and Seinfeld, 2008; Ng et al, 2017; Shrivastava et al, 2017)
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