Accretion Product Formation from Self‐ and Cross‐Reactions of RO₂ Radicals in the Atmosphere

Abstract

Hydrocarbons are emitted into the Earth's atmosphere in very large quantities by human and biogenic activities. Their atmospheric oxidation processes almost exclusively yield RO radicals as reactive intermediates whose atmospheric fate is not yet fully unraveled. Herein, we show that gas-phase reactions of two RO radicals produce accretion products composed of the carbon backbone of both reactants. The rates for accretion product formation are very high for RO radicals bearing functional groups, competing with those of the corresponding reactions with NO and HO . This pathway, which has not yet been considered in the modelling of atmospheric processes, can be important, or even dominant, for the fate of RO radicals in all areas of the atmosphere. Moreover, the vapor pressure of the formed accretion products can be remarkably low, characterizing them as an effective source for the secondary organic aerosol.

Impact of anthropogenic and biogenic sources on the seasonal variation in the molecular composition of urban organic aerosols: a field and laboratory study using ultra-high-resolution mass spectrometry

“…These compounds are consistent with products from lignin pyrolysis ( Fig. S4, Bertrand et al, 2017Bertrand et al, , 2018 and contributed significantly to the CHO signal recorded for primary wood-burning emissions but less for aged emissions (57 %,49 %,44 % of CHO aromatic;5 %,3 %,3 % of condensed aromatic;and 38 %,48 %,53 % of non-aromatic for fresh, 10 h, and 30 h atmospherically aged emissions, respectively). The ambient wood-burning pollution showed a similar distribution of the CHO signal as aged laboratory wood-burning emissions (Magadino -46 % aromatic, 6 % condensed aromatic, 48 % non-aromatic; San Vittore -44 % aromatic, 4 % condensed aromatic, 52 % non-aromatic), and the detailed chemical composition was similar to the fresh laboratory woodburning emissions (Fig.…”

Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction

“…Although these channels have generally been reported to be minor for small peroxy radicals (e.g. Lightfoot et al, 1992;Orlando and Tyndall, 2012), recent studies suggest that they may be more significant for larger peroxy radicals containing oxygenated substituents, and they have been reported to play a role in the formation of lowvolatility products in a number of studies (Ziemann, 2002;Ng et al, 2008;Ehn et al, 2014;Jokinen et al, 2014;Mentel et al, 2015;Rissanen et al, 2015;Berndt et al, 2015Berndt et al, , 2018aZhang et al, 2015;McFiggans et al, 2019). These reactions may therefore play a potentially important role in particle formation and growth in the atmosphere.…”

Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance

“…Substituted RO2s have higher self-/cross-reaction rate constants (Orlando and Tyndall, 152 2012). RO2+RO2 of highly substituted primary RO2 can be as high as ~10 -11 cm 3 molecule -1 s -1 (Orlando 153 and Tyndall, 2012 reported to self-/cross-react at ~10 -10 cm 3 molecule -1 s -1 (Berndt et al, 2018). In the present work, we 155 make a simplification to adapt to the generic RO2 treatment by assuming a single self-/cross-reaction 156 rate constant for generic RO2 in each case.…”