Abstract
Abstract. It is being suggested that particle-bound or particle-induced reactive oxygen species (ROS), which significantly contribute to the oxidative potential (OP) of aerosol particles, are a promising metric linking aerosol compositions to toxicity and adverse health effects. However, accurate ROS quantification remains challenging due to the reactive and short-lived nature of many ROS components and the lack of appropriate analytical methods for a reliable quantification. Consequently, it remains difficult to gauge their impact on human health, especially to identify how aerosol particle sources and atmospheric processes drive particle-bound ROS formation in a real-world urban environment. In this study, using a novel online particle-bound ROS instrument (OPROSI), we comprehensively characterized and compared the formation of ROS in secondary organic aerosols (SOAs) generated from organic compounds that represent anthropogenic (naphthalene, SOANAP) and biogenic (β-pinene, SOAβPIN) precursors. The SOA mass was condensed onto soot particles (SP) under varied atmospherically relevant conditions (photochemical aging and humidity) to mimic the SOA formation from a mixing of traffic-related carbonaceous primary aerosols and volatile organic compounds (VOCs). We systematically analyzed the ability of the aqueous extracts of the two aerosol types (SOANAP-SP and SOAβPIN-SP) to induce ROS production and OP. We further investigated cytotoxicity and cellular ROS production after exposing human lung epithelial cell cultures (A549) to extracts of the two aerosols. A significant finding of this study is that more than 90 % of all ROS components in both SOA types have a short lifetime, highlighting the need to develop online instruments for a meaningful quantification of ROS. Our results also show that photochemical aging promotes particle-bound ROS production and enhances the OP of the aerosols. Compared to SOAβPIN-SP, SOANAP-SP elicited a higher acellular and cellular ROS production, a higher OP, and a lower cell viability. These consistent results between chemical-based and biological-based analyses indicate that particle-bound ROS quantification could be a feasible metric to predict aerosol particle toxicity and adverse human effects. Moreover, the cellular ROS production caused by SOA exposure not only depends on aerosol type but is also affected by exposure dose, highlighting a need to mimic the process of particle deposition onto lung cells and their interactions as realistically as possible to avoid unknown biases.
Highlights
Ambient particulate air pollution has been identified by the World Health Organization (WHO) as the most severe and urgent public health issue worldwide, mainly affecting people in urban areas (WHO, 2016)
Besides soot particles coated with secondary organic aerosols (SOAs), we investigated the possible effects of aging on pure soot particles, i.e., SP passing through the PAM with no volatile organic compounds (VOCs) added
In the data presented below we defined an organic matter (OM) mass-based reactive oxygen species (ROS) content and particle oxidative potential (OP) to avoid biases due to the mass of soot, which contributes to particle mass but induces little to no ROS production or OP
Summary
Ambient particulate air pollution has been identified by the World Health Organization (WHO) as the most severe and urgent public health issue worldwide, mainly affecting people in urban areas (WHO, 2016). Most ROS analysis techniques mentioned above use offline filter-based methods, where aerosols are analyzed hours (h) or days after collection and likely severely underestimate the true particle-bound, exogenous ROS concentrations because the reactive and short-lived components of ROS such as radicals or some peroxides decay before analysis (Fuller et al, 2014; Krapf et al, 2016; Zhou et al, 2018a; Bates et al, 2019) This makes it difficult to gauge their impact on human health, especially to identify which particle sources contribute to ROS and what atmospheric conditions affect ROS formation in a real-world urban environment.
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