Organic condensation: a vital link connecting aerosol formation to cloud condensation nuclei (CCN) concentrations

Abstract

Abstract. Atmospheric aerosol particles influence global climate as well as impair air quality through their effects on atmospheric visibility and human health. Ultrafine (<100 nm) particles often dominate aerosol numbers, and nucleation of atmospheric vapors is an important source of these particles. To have climatic relevance, however, the freshly nucleated particles need to grow in size. We combine observations from two continental sites (Egbert, Canada and Hyytiälä, Finland) to show that condensation of organic vapors is a crucial factor governing the lifetimes and climatic importance of the smallest atmospheric particles. We model the observed ultrafine aerosol growth with a simplified scheme approximating the condensing species as a mixture of effectively non-volatile and semi-volatile species, demonstrate that state-of-the-art organic gas-particle partitioning models fail to reproduce the observations, and propose a modeling approach that is consistent with the measurements. We find that roughly half of the mass of the condensing mass needs to be distributed proportional to the aerosol surface area (thus implying that the condensation is governed by gas-phase concentration rather than the equilibrium vapour pressure) to explain the observed aerosol growth. We demonstrate the Correspondence to: I. Riipinen (ilona.riipinen@helsinki.fi) large sensitivity of predicted number concentrations of cloud condensation nuclei (CCN) to these interactions between organic vapors and the smallest atmospheric nanoparticleshighlighting the need for representing this process in global climate models.

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation

“…The results of the current work have a number of implications for SOA models. Although the dynamics of an aerosol size distribution reflects the mechanism of growth (22,29), we demonstrate here that it provides a key constraint in interpreting laboratory and ambient SOA formation. Aldehyde injection experiments suggest that peroxyhemiacetal formation by heterogeneous reactions between aldehydes and organic hydroperoxides can have a major impact on SOA formation.…”

“…The measured O:C ratio is subject to ±30% uncertainty (12). distributed proportional to the particle surface area (21,22). The second-order reaction rate coefficient between reactive carbonyl and SVOCs (k BR ), which is estimated to be 12 M −1 ·s −1 (2 × 10 −20 cm 3 ·s −1 ), is found to be the most sensitive parameter in controlling the evolution of the particle size distribution.…”

Organic Constituents on the Surfaces of Aerosol Particles from Southern Finland, Amazonia, and California Studied by Vibrational Sum Frequency Generation

“…(i) Though vitally needed for improving computer modeling efforts aimed at quantitatively predicting SOA particle yields for a given atmospheric gas phase composition, 8 the molecularity of even the first few reactions leading to SOA particle formation is not known and thus needs to be determined;…”

Constraining nucleation, condensation, and chemistry in oxidation flow reactors using size-distribution measurements and aerosol microphysical modelling

“…The lowest-10 volatility vapors condense essentially irreversibly onto particles of all sizes (i.e. "kinetically limited" or irreversible condensation; Riipinen et al, 2011, Zhang et al, 2012. Semi-volatile vapors (with non-trivial partitioning fractions in both the particle and gas phases at equilibrium) have a net condensation to particles that is determined by reversible partitioning (i.e.…”

“…Semi-volatile vapors (with non-trivial partitioning fractions in both the particle and gas phases at equilibrium) have a net condensation to particles that is determined by reversible partitioning (i.e. quasi-equilibrium condensation; Riipinen et al, 2011, Zhang et al, 2012. Kinetically limited condensation is gasphase-diffusion limited and only possible for compounds with effective saturation concentrations (C*; Donahue et al, 2006) 15 < ~10 -3 g m -3 (e.g., low and extremely low volatility organic compounds; LVOCs and ELVOCs); the net SOA uptake to a particle is proportional to the Fuchs-corrected surface area of the particle .…”