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 O3 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.

Keywords: ELVOC; autoxidation; isoprene; monoterpenes; new particle formation.

Fig. 1.

Effect of low oxygen level and OH scavenger (propane, C₃H₈, or hydrogen, H₂) on ELVOC production during oxidation of (A) limonene and (B) myrcene. During low-oxygen experiments, ELVOC formation is significantly suppressed as O₂ addition to the intermediate reaction products becomes slower. During limonene oxidation, only a few ELVOC species are affected by OH scavenging, illustrating that ozonolysis is the main pathway for ELVOC formation in our experiment. In the case of myrcene, a clear decrease in total ELVOC was observed upon OH scavenging, demonstrating the role of OH oxidation in the ELVOC formation pathway. C₁₀H₁₆O₇ and C₁₀H₁₄O₇ are identified as dimers from small ozonolysis-produced RO₂ radicals.

Fig. 2.

Total ELVOC concentrations as a function of reacted terpene (O₃ and OH radical reaction). The experimental molar yields are calculated from the slopes. Uncertainty of all of the measurements is −50/+100%. Reaction conditions are given in SI Appendix.

Fig. 3.

Annual average CN, CCN(1.0%), and CCN(0.2%) concentrations in control experiment (CTRL, top row), and the relative effects of SOA, ELVOC, and isoprene. Note the different color scales in each panel. Four regions for detailed analysis are indicated in the first panel.