Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications

Abstract

Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O 3 and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget.autoxidation | ELVOC | monoterpenes | isoprene | new particle formation F ormation and subsequent growth of new aerosol particles is a major source of cloud condensation nuclei (CCN) in the global troposphere (1, 2), and a big contributor to the large reported uncertainty in the radiative forcing by aerosol−cloud interactions (3-7). Multiple field studies have shown that CCN production is tightly connected with the oxidation of biogenic volatile organic compounds (BVOC) emitted by terrestrial ecosystems (8-11). To explain these observations, large-scale model simulations demonstrate a need for a BVOC oxidation mechanism in the atmosphere that produces very low volatility organic vapors with molar formation yields of at least a few percent per reacted precursor compound (12)(13)(14).The existence and formation mechanisms of essentially nonvolatile organic vapors in the atmosphere have puzzled scientists for some time (14-16). Such extremely low volatile organic compounds (ELVOC) (17) were recently detected, both in laboratory studies and in the ambient atmosphere (18), yet typical atmospheric oxidation chemistry schemes do not explain ELVOC produced on a time scale of minutes or hours. Furthermore, current state-of-the-art models using available chemistry schemes have systematically failed to reproduce the observed concentrations and volatility of organic aerosol components (17, 19). A plausible exp...

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