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. We evaluate monoterpene-derived peroxy radical (MT-RO2) unimolecularautoxidation and self- and cross-reactions with other RO2 species in theGEOS-Chem global chemical transport model. The formation of associated highlyoxygenated organic molecules (HOMs) and accretion products are tracked incompetition with other bimolecular reactions. Autoxidation is the dominantfate up to 6–8 km for first-generation MT-RO2, which can undergounimolecular H shifts. Reaction with NO can be a more common fate forH-shift rate constants &lt; 0.1 s−1 or at altitudes higher than 8 km due to the imposed Arrhenius temperature dependence of unimolecularH shifts. For MT-derived HOM-RO2, generated by multistep autoxidationof first-generation MT-RO2, reaction with other RO2 species is predictedto be the major fate throughout most of the boreal and tropical forestregions, whereas reaction with NO dominates in the temperate and subtropicalforests of the Northern Hemisphere. The newly added reactions result inan approximate 4 % global average decrease in HO2 and RO2,mainly due to faster self-/cross-reactions of MT-RO2, but the impactupon HO2, OH, and NOx abundances is only important in the planetary boundary layer (PBL) over portions of tropical forests. Predicted HOMconcentrations in MT-rich regions and seasons can exceed total organicaerosol predicted by the standard version of the GEOS-Chem model depending on theparameters used. Comparisons to observations reveal that large uncertaintiesremain for key reaction parameters and processes, especially with respect to thephotochemical lifetime and volatility of HOMs as well as the rates and branching ofassociated RO2 accretion products. Further observations and laboratorystudies related to MT-RO2-derived HOMs and gas-phase RO2 accretionproduct formation kinetics – especially their atmospheric fate, such asgas–particle partitioning, multiphase chemistry, and net secondary organic aerosol formation – areneeded.

atmospheric chemistry and physics

Global simulations of monoterpene-derived peroxy radical fates and the distributions of highly oxygenated organic molecules (HOMs) and accretion products