Understanding global secondary organic aerosol amount and size-resolved condensational behavior

Abstract

Abstract.Recent research has shown that secondary organic aerosols (SOA) are major contributors to ultrafine particle growth to climatically relevant sizes, increasing global cloud condensation nuclei (CCN) concentrations within the continental boundary layer (BL). However, there are three recent developments regarding the condensation of SOA that lead to uncertainties in the contribution of SOA to particle growth and CCN concentrations: (1) while many global models contain only biogenic sources of SOA (with annual production rates generally 10-30 Tg yr −1 ), recent studies have shown that an additional source of SOA around 100 Tg yr −1 correlated with anthropogenic carbon monoxide (CO) emissions may be required to match measurements. (2) Many models treat SOA solely as semi-volatile, which leads to condensation of SOA proportional to the aerosol mass distribution; however, recent closure studies with field measurements show nucleation mode growth can be captured only if it is assumed that a significant fraction of SOA condenses proportional to the Fuchs-corrected aerosol surface area. This suggests a very low volatility of the condensing vapors. (3) Other recent studies of particle growth show that SOA condensation deviates from Fuchs-corrected surface-area condensation at sizes smaller than 10 nm and that size-dependent growth rate parameterizations (GRP) are needed to match measurements. We explore the significance of these three findings using GEOS-Chem-TOMAS global aerosol microphysics model and observations of aerosol size distributions around the globe. The change in the concentration of particles of size D p > 40 nm (N40) within the BL assuming surface-area condensation compared to mass-distribution net condensation yielded a global increase of 11 % but exceeded 100 % in biogenically active regions. The percent change in N40 within the BL with the inclusion of the additional 100 Tg SOA yr −1 compared to the base simulation solely with biogenic SOA emissions (19 Tg yr −1 ) both using surface area condensation yielded a global increase of 13.7 %, but exceeded 50 % in regions with large CO emissions. The inclusion of two different GRPs in the additional-SOA case both yielded a global increase in N40 of < 1 %, however exceeded 5 % in some locations in the most extreme case. All of the model simulations were compared to measured data obtained from diverse locations around the globe and the results confirmed a decrease in the model-measurement bias and improved slope for comparing modeled to measured CCN Published by Copernicus Publications on behalf of the European Geosciences Union. S. D. D'Andrea et al.: Understanding global secondary organic aerosol amountnumber concentration when non-volatile SOA was assumed and the extra SOA was included.

Ambient Particulate Matter Size Distributions Drive Regional and Global Variability in Particle Deposition in the Respiratory Tract

“…Simulations using GEOS-Chem-TOMAS have been evaluated against observations of long-term, size-resolved number concentrations (Croft et al, 2016;D'Andrea et al, 2013;Kodros & Pierce, 2017;Westervelt et al, 2013) and aerosol optical depth (Kodros et al, 2016). While GEOS-Chem-TOMAS has shown skill at reproducing variability in size-resolved aerosol concentrations, we acknowledge that measurements of aerosol size distributions (and thus model evaluations) are limited.…”

“…In addition to local emissions, observations show variability in particle size distributions and chemical composition due to transport of PM (e.g., Dunlea et al, 2009;Xu et al, 2017). Finally, observations and modeling studies show that microphysical processes such as new-particle formation events (e.g., Hodshire et al, 2016;Merikanto et al, 2009;Westervelt et al, 2014), condensation to and evaporation of particles (e.g., Bian et al, 2017;Bougiatioti et al, 2014;D'Andrea et al, 2013), in-cloud aqueous oxidation (e.g., Hoppel & Frick, 1990), coagulation (e.g., Sakamoto et al, 2016;Westphal & Toon, 1991), wet deposition (e.g., Croft et al, 2012;Dentener et al, 2006), and dry deposition (e.g., Sehmel, 1980;Zhang et al, 2001) substantially influence particle number and mass distributions (Croft et al, 2016;Kodros & Pierce, 2017).…”

A global lightning parameterization based on statistical relationships among environmental factors, aerosols, and convective clouds in the TRMM climatology

“…The aerosol data component in this research is derived using a global chemical-transport model, GEOS-Chem (www.geos-chem.org) with the online TwO-Moment Aerosol Sectional microphysics module (TOMAS) [Adams and Seinfeld, 2002;Pierce and Adams, 2009;D'Andrea et al, 2013;Pierce et al, 2013]. Pierce et al [2013, and references therein] and van der Werf et al [2010] provide supporting details about the nucleation, growth, and new-particle formation schemes, as well as the global GFED3 emissions inventories used for the current GEOS-Chem simulations.…”

Atmospheric new particle formation at the research station Melpitz, Germany: connection with gaseous precursors and meteorological parameters

“…The model then distributes this material onto the existing sectional size distribution according to either the mass in each section (thermodynamic limit) or the Fuchs-corrected surface area (kinetic limit). The work of D' Andrea et al (2013) includes even a variant in which the growth of particles by SOA condensation is highly size dependent in the nucleation-mode size range based on experimental evaluations . The rough estimate of a SOA yield and the inclusion of two alternative condensation mechanisms reflect the considerable uncertainties in current knowledge with regard to the condensational growth process.…”