Abstract
Abstract. The gas-particle partitioning and chemical aging of semi-volatile organic aerosol are presented in a newly developed box model scheme, where its effect on the growth, composition, and mixing state of particles is examined. The volatility-basis set (VBS) framework is implemented into the aerosol microphysical scheme MATRIX (Multiconfiguration Aerosol TRacker of mIXing state), which resolves mass and number aerosol concentrations and in multiple mixing-state classes. The new scheme, MATRIX-VBS, has the potential to significantly advance the representation of organic aerosols in Earth system models by improving upon the conventional representation as non-volatile particulate organic matter, often also with an assumed fixed size distribution. We present results from idealized cases representing Beijing, Mexico City, a Finnish forest, and a southeastern US forest, and investigate the evolution of mass concentrations and volatility distributions for organic species across the gas and particle phases, as well as assessing their mixing state among aerosol populations. Emitted semi-volatile primary organic aerosols evaporate almost completely in the intermediate-volatility range, while they remain in the particle phase in the low-volatility range. Their volatility distribution at any point in time depends on the applied emission factors, oxidation by OH radicals, and temperature. We also compare against parallel simulations with the original scheme, which represented only the particulate and non-volatile component of the organic aerosol, examining how differently the condensed-phase organic matter is distributed across the mixing states in the model. The results demonstrate the importance of representing organic aerosol as a semi-volatile aerosol, and explicitly calculating the partitioning of organic species between the gas and particulate phases.
Highlights
Atmospheric aerosols play a key role in the Earth system with great impacts on global air quality, public health, and climate (Boucher et al, 2013; Myhre et al, 2013; Seinfeld and Pandis, 2016)
The temporal evolution of the total organics mass concentrations from the new scheme and the old scheme are presented in Fig. 2 for January and Fig. 3 for July in the four locations under study
3) to the most volatile 106 μg m−3 (“P6” in Figs. 2 and 3). They are distributed between the gas and aerosol phases by gas-particle partitioning, whereas the organics in the original scheme are only represented by one nonvolatile organic aerosol tracer (“organics tracer (OCAR)”)
Summary
Atmospheric aerosols play a key role in the Earth system with great impacts on global air quality, public health, and climate (Boucher et al, 2013; Myhre et al, 2013; Seinfeld and Pandis, 2016). One contribution to the large uncertainty in aerosol radiative forcing is organic aerosol (OA), which is ubiquitous in the atmosphere and contributes to a large portion of submicron particulate mass in various regions around the world (Zhang et al, 2007; Jimenez et al, 2009). Advancements in measurement techniques greatly improved our understanding of the evolution of OA and its lifetime in the atmosphere at the process level (Jimenez et al, 2009). Measurements imply that OA concentrations are potentially underestimated in current models (Tsigaridis et al, 2014). Such a discrepancy hints at large uncertainties in the prediction of aerosol–radiation interactions, their hygroscopicity, aerosol–cloud interactions, and their overall impact on climate (Petters and Kreidenweis, 2007)
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