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

Abstract

Soot particles are ubiquitous in the atmosphere and have important climatic and health effects. The aging processes of soot during long-range transport result in variability in its morphology, microstructure, and hygroscopic and optical properties, subsequently leading to the modification of soot's climatic and health effects. In the present study the aging process of soot by molecular O 2 under simulated sunlight irradiation is investigated. Organic carbon components on the surface of soot are found to play a key role in soot aging and are transformed into oxygen-containing organic species including quinones, ketones, aldehydes, lactones, and anhydrides. These oxygen-containing species may become adsorption centers of water and thus enhance the cloud condensation nuclei and ice nuclei activities of soot. Under irradiation of 25 mW·cm −2 , the apparent rate constants (k 1,obs ) for loss or formation of species on soot aged by 20% O 2 were larger by factors of 1.5-3.5 than those on soot aged by 100 ppb O 3 . 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.

Formation and emission of large furans and oxygenated hydrocarbons from flames

“…6D. The low fraction of C=O species suggests that our soot samples had not been significantly affected by atmospheric oxygen between flame sampling and XPS measurements (42). The strong XPS signal from oxygen-containing functional groups at large DFFOs suggests that the reduced signal from the mass peaks correlated with oxygen inclusion in the mass spectra recorded at DFFOs of 5.0 mm and 7.5 mm (Fig.…”

Chemical and Toxicological Evolution of Carbon Nanotubes During Atmospherically Relevant Aging Processes

“…64 Flame soot or diesel soot both contain significant organic carbon (OC) including saturated and unsaturated hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and partially oxidized organics. 47,59−61 This OC component is readily oxidized, 56,59 from which quinones have been identified during the oxidation of both soot 57 and PAHs by O 3 . 20,62,63 In contrast to flame or diesel soot, OC was removed from the SWCNTs prior to oxidation in this study (Chemical Evolution During Oxidation: Particle Mass Spectra section), and the most significant products for both atmospheric O 3 and OH oxidation of SWCNT were carboxylic acids or esters, both of which are not redox active.…”

Seasonal variation and light absorption property of carbonaceous aerosol in a typical glacier region of the southeastern Tibetan Plateau

“…When this occurs, these molecules tend to form a new structure by combining with each other or with other molecules (carbonyl C=O and ether C−O) (Daly and Horn, 2009;Cain et al, 2010;Nieto-Gligorovski et al, 2008), which may change the state of OC, EC, or OC / EC ratios. The photochemical oxidation by O 2 under sunlight is an important aging process for EC (Han et al, 2012). Statistical results of EC, OC, and POC concentrations in aerosol from the GHZ site are shown in Table 2.…”

“…The annual mean OC / EC ratio was found to be highest in the monsoon season and lowest in winter. The aging process of EC (or soot) resulting from photochemical oxidation by molecular O 2 and the photooxidation of OC (Han et al, 2012) were likely involved and increased the OC / EC ratio. Photochemical reaction can change their physical and chemical properties from the original molecule of the substance (alkyne C-H (≡C-H) and aromatic C-H (Ar-H)) (Kirchner et al, 2000;Cain et al, 2010).…”