Evaporation-Induced Transformations in Volatile Chemical Product-Derived Secondary Organic Aerosols: Browning Effects and Alterations in Oxidative Reactivity
LIYUAN ZHOU, Zhancong Liang, Yiming Qin, Chak K. Chan, King Abdullah University of Science and Technology
Abstract Number: 46
Working Group: Aerosol Chemistry
Abstract
Volatile chemical products (VCPs) are increasingly recognized as a significant source of volatile organic compound (VOC) emissions in urban atmospheres, potentially serving as key anthropogenic precursors for secondary organic aerosol (SOA) formation. This study investigates the formation of VCP-derived SOA and its physicochemical property changes. Specifically, we examine the effect of aerosol evaporation on the molecular composition, mass absorption coefficient, and reactive oxygen species (ROS) generation in SOA produced through ozonolysis of a representative room deodorant air freshener. Upon aerosol evaporation through a diffusion dryer, the solutes become highly concentrated, accelerating reactions between them. Consequently, VCP SOA exhibited a marked 42% reduction in peroxide content along with a noticeable browning, indicating significant physicochemical transformations. These transformations predominantly occurred at moderate relative humidity (RH) levels around 40% during the reduction from 80%, rather than at lower RHs (12-20%), suggesting the crucial role of aerosol liquid water in facilitating these chemical reactions. Molecular characterization revealed that evaporating VCP SOA produces several highly conjugated nitrogen-containing products, possibly through interactions between carbonyl compounds, either pre-existing in VCP SOA or transformed from peroxides during evaporation, and reduced nitrogen species in the aerosol phase. These compounds likely serve as chromophores responsible for the observed brownish coloration of the sample. In addition, we used heterogeneous oxidation of sulfur dioxide (SO2) as a probe of the reactivity of VCP SOA, which showed enhanced photochemical sulfate production upon drying, hinting at underlying enhanced photosensitization chemistry. Direct measurements of reactive species, including singlet oxygen (1O2), superoxide (O2•-), and hydroxyl radicals (•OH) showed higher abundances in dried VCP SOA samples than in undried samples when exposed to light. Our study underscores the crucial impact of drying on transforming the physicochemical properties of VCP-derived SOA, affecting the global atmospheric radiative balance and modifying its chemical dynamics in the atmosphere.