Abstract
Abstract. Atmospheric chromophoric organic matter (COM) plays a fundamental role in photochemistry and aerosol aging. However, the effects of photodegradation on chemical components and photochemical reactivity of COM remain unresolved. Here, we report the potential effects of photodegradation on carbon contents, optical properties, fluorophore components and photochemical reactivity in aerosol. After 7 d of photodegradation, fluorescent intensity and the absorption coefficient of COM decrease by 71.4 % and 32.0 %, respectively. Photodegradation makes a difference to the chemical component of chromophore and the degree of aerosol aging. Low-oxidation humic-like substance (HULIS) is converted into high-oxidation HULIS due to photooxidation. Photodegradation also changes the photochemical reactivity. The generation of triplet-state COM (3COM*) decreases slightly in ambient particulate matter (ambient PM) but increases in primary organic aerosol (POA) following photodegradation. The results highlight that the opposite effect of photodegradation on photochemical reactivity in POA and ambient PM. However, the generation of singlet-oxygen (1O2) decreases obviously in POA and ambient PM, which could be attributed to photodegradation of precursors of 1O2. The combination of optical property, chemical component and reactive oxygen species has an important impact on the air quality. The new insights on COM photodegradation in aerosol reinforce the importance of studying dissolved organic matter (DOM) related with the photochemistry and aerosol aging.
Highlights
Atmospheric chromophoric organic matter (COM) is an important component of biomass combustion emissions and secondary organic aerosol (SOA) (Andreae and Gelencser, 2006; Budisulistiorini et al, 2017; Graber and Rudich, 2006; Zappoli et al, 1999)
The results suggest that WSOC is more photodegraded than MSOC in primary organic aerosol (POA)
In WSOC of POA, the proportion of OC1 (OC1 and OC2-4 are the different stages in the process of thermal– optical analysis) decreases significantly and OC1 was the major loss of OC
Summary
Atmospheric chromophoric organic matter (COM) is an important component of biomass combustion emissions and secondary organic aerosol (SOA) (Andreae and Gelencser, 2006; Budisulistiorini et al, 2017; Graber and Rudich, 2006; Zappoli et al, 1999). Photodegradation plays an important role in the components and properties of COM and thereby changes photochemical activity. Aromatic ketones (Canonica et al, 2006; Marciniak et al, 1993), benzophenone (Encinas et al, 1985) and phenanthrene (Wawzonek and Laitinen, 1942) have been identified as the precursors of 3COM∗ Chemical probes, such as 2,4,6-trimethylphenol (TMP) and sorbic acid (SA), are applicable to evaluate the yield of 3COM∗ (Zhou et al, 2019; Moor et al, 2019; Chen et al, 2021). Considering the potential effect of ROS on aerosol aging and air quality, it is necessary to clarify the path and mechanism of COM-generating ROS. In order to illustrate the characteristic and mechanism of COM photodegradation and the effect of COM photodegradation on aerosol aging, we simulate the process of COM photodegradation and COM-generating ROS in the laboratory. The objectives of the study are (1) to clarify the change of carbon content during the COM photodegradation process, (2) to explore the effect of photodegradation on fluorophores and optical properties, and (3) to investigate the effect of COM photodegradation on photochemical reactivity (photochemical reactivity is evaluated by 3COM∗ and 1O2)
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