14 Feb 2023
 | 14 Feb 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

An aldehyde as a rapid source of secondary aerosol precursors: Theoretical and experimental study of hexanal autoxidation

Shawon Barua, Siddharth Iyer, Avinash Kumar, Prasenjit Seal, and Matti Rissanen

Abstract. Aldehydes are common constituents of natural and polluted atmospheres, and their gas-phase oxidation has recently been reported to yield highly oxygenated organic molecules (HOM) that are key players in the formation of atmospheric aerosol. However, insights into the molecular level mechanism of this oxidation reaction have been scarce. While OH initiated oxidation of small aldehydes, with two to five carbon atoms, under high NOx conditions generally leads to fragmentation products, longer chain aldehydes involving an initial non-aldehydic hydrogen abstraction can be a path to molecular functionalization and growth. In this work, we conduct a joint theoretical-experimental analysis of the autoxidation chain reaction of a common aldehyde, hexanal. We computationally study the initial steps of OH oxidation at the RHF-RCCSD(T)-F12a/VDZ-F12//ωB97X-D/aug-cc-pVTZ level, and show that both aldehydic (on C1) and non-aldehydic (on C4) H-abstraction channels contribute to HOM via autoxidation. The oxidation products predominantly form through the H-abstraction from C1 and C4, followed by fast unimolecular 1,6 H-shifts with rate coefficients 1.7 × 10−1 s−1 and 8.6 × 10−1 s−1, respectively. Experimental flow reactor measurements at variable reaction times show that hexanal oxidation products including HOM monomers up to C6H11O7 and accretion products C12H22O9−10 form within 3 seconds reaction time. Kinetic modeling simulation including atmospherically relevant precursor concentrations agrees with the experimental results and the expected timescales. Finally, we estimate the hexanal HOM yields up to seven O atoms with mechanistic details through both C1 and C4 channels.

Shawon Barua et al.

Status: open (until 10 Apr 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-128', Robin Shannon, 10 Mar 2023 reply

Shawon Barua et al.


Total article views: 306 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
206 93 7 306 33 3 5
  • HTML: 206
  • PDF: 93
  • XML: 7
  • Total: 306
  • Supplement: 33
  • BibTeX: 3
  • EndNote: 5
Views and downloads (calculated since 14 Feb 2023)
Cumulative views and downloads (calculated since 14 Feb 2023)

Viewed (geographical distribution)

Total article views: 296 (including HTML, PDF, and XML) Thereof 296 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 22 Mar 2023
Short summary
This work illustrates how a common volatile hydrocarbon, hexanal, has the potential to undergo atmospheric autoxidation leading to prompt formation of ambient aerosol, deteriorating the air quality of urban atmospheres. We used a combined state-of-the-art quantum chemical modelling and flow reactor experiments under atmospheric conditions to resolve the autoxidation mechanism of hexanal initiated by a common oxidant.