Heterogeneous chemistry of toluene, kerosene and diesel soots

Abstract

Soot samples as potential mimics of atmospheric aerosols have been produced from the combustion of toluene, kerosene and diesel in order to compare the nature of soot produced from a simpler material, toluene, with soots from the fuels kerosene and diesel. Characterisation of the soots using elemental analysis, infrared spectroscopy, solvent extraction, thermal desorption and electron microscopy techniques before and after reaction with ozone allows assessment of the reactivity of soots from these different fuels. Despite the production of toluene and kerosene soots from identical combustion conditions, strong differences in structure and reactivity are observed in terms of their reaction with ozone. However, toluene soot is a much better mimic of diesel soot. It is proposed that the differing reactivities of the soots is related to the nature of the organic carbon and structure of the elemental carbon which vary with soots from the different fuels.

Influence of Combustion Conditions on Hydrophilic Properties and Microstructure of Flame Soot

“…For example, the main characteristic band for the three fuels' flame soot was at 1590 cm −1 , which was assigned to a carbonyl (CO) group bound to an aromatic ring. 13 carbonyl group, assigned to ketone species (1710 cm −1 ), was observed for decane soot. 13,20,21,40,41 As seen in Figure 7, compared to the functional groups on the rich toluene flame soot, no significant changes were observed on the lean toluene flame soot.…”

“…13 carbonyl group, assigned to ketone species (1710 cm −1 ), was observed for decane soot. 13,20,21,40,41 As seen in Figure 7, compared to the functional groups on the rich toluene flame soot, no significant changes were observed on the lean toluene flame soot. For n-hexane and decane soot, the lean flame soot exhibited lower intensities in the peaks of alkynesC−H, aromatic C−H, unsaturated CH 2 , and highly substituted aromatic compounds, while the carbonyl (CO) group bound to an aromatic ring showed a larger intensity than that of the rich flame soot.…”

“…18 Functional groups, including aliphatic or aromatic C−H, carbonyl CO, and ethers C−O, have been confirmed through infrared spectroscopy. 13,20,21 Microstructures including graphitic carbon, disordered carbon, and amorphous carbon have also been detected using Raman spectroscopy. [15][16][17]19,22,23 Recent studies have shown that residence time in the flame and flame temperature can induce modifications in the microstructures and functional groups of soot.…”

Key role of organic carbon in the sunlight-enhanced atmospheric aging of soot by O2

“…Compared with the uptake of gas-phase species by soot, however, the modification of soot during the aging processes remains unclear. A limited number of publications have studied changes of the surface composition and microstructure of soot during reaction with O 3 , NO 2 , and H 2 SO 4 in the dark (2,22,29,30). When soot was exposed to O 3 or NO 2 , oxygen-related species or nitrogencontaining compounds were detected (2,29,30).…”

“…Considering the abundance of O 2 in the troposphere and its higher photoreactivity rate, the photochemical oxidation by O 2 under sunlight irradiation should be a very important aging process for soot. S oot, which originates from incomplete combustion, is a mixture of elemental carbon and organic carbon (OC) compounds (1,2). It has been widely recognized that soot particles in the atmosphere are partly responsible for global climate change.…”