Abstract
Abstract. When hydrocarbons (HCs) are atmospherically oxidized, they form particulate oxidizers, including quinones, organic hydroperoxides, and peroxyacyl nitrates (PANs). These particulate oxidizers can modify cellular materials (e.g., proteins and enzymes) and adversely modulate cell functions. In this study, the contribution of particulate oxidizers in secondary organic aerosols (SOAs) to the oxidative potential was investigated. SOAs were generated from the photooxidation of toluene, 1,3,5-trimethylbenzene, isoprene, and α-pinene under varied NOx levels. Oxidative potential was determined from the typical mass-normalized consumption rate (reaction time t = 30 min) of dithiothreitol (DTTt), a surrogate for biological reducing agents. Under high-NOx conditions, the DTTt of toluene SOA was 2–5 times higher than that of the other types of SOA. Isoprene DTTt significantly decreased with increasing NOx (up to 69 % reduction by changing the HC ∕ NOx ratio from 30 to 5). The DTTt of 1,3,5-trimethylbenzene and α-pinene SOA was insensitive to NOx under the experimental conditions of this study. The significance of quinones to the oxidative potential of SOA was tested through the enhancement of DTT consumption in the presence of 2,4-dimethylimidazole, a co-catalyst for the redox cycling of quinones; however, no significant effect of 2,4-dimethylimidazole on modulation of DTT consumption was observed for all SOA, suggesting that a negligible amount of quinones was present in the SOA of this study. For toluene and isoprene, mass-normalized DTT consumption (DTTm) was determined over an extended period of reaction time (t = 2 h) to quantify their maximum capacity to consume DTT. The total quantities of PANs and organic hydroperoxides in toluene SOA and isoprene SOA were also measured using the Griess assay and the 4-nitrophenylboronic acid assay, respectively. Under the NOx conditions (HC ∕ NOx ratio: 5–36 ppbC ppb−1) applied in this study, the amount of organic hydroperoxides was substantial, while PANs were found to be insignificant for both SOAs. Isoprene DTTm was almost exclusively attributable to organic hydroperoxides, while toluene DTTm was partially attributable to organic hydroperoxides. The DTT assay results of the model compound study suggested that electron-deficient alkenes, which are abundant in toluene SOA, could also modulate DTTm.
Highlights
Epidemiological studies have linked human exposure to fine particulate matter (PM2.5, aerodynamic diameter < 2.5 μm) to increased morbidity and mortality from respiratory and cardiovascular diseases
Our secondary organic aerosols (SOAs) yields for isoprene SOA were lower than those reported in other studies (Carlton et al, 2009; Xu et al, 2014) because the temperatures in our outdoor experiments were higher than those sourced from indoor chambers
For SOA consisting of non-catalytic redox compounds, DTTm is more appropriate than DTTt for assessing oxidative potential because of the nonlinear relationship between DTT consumption and reaction time (Fig. 3)
Summary
Epidemiological studies have linked human exposure to fine particulate matter (PM2.5, aerodynamic diameter < 2.5 μm) to increased morbidity and mortality from respiratory and cardiovascular diseases (e.g., asthma, myocardial infarction, stroke; Brook et al, 2010; Chen et al, 2013; Davidson et al, 2005; Jansen et al, 2005; Katsouyanni et al, 1997; van Eeden et al, 2005). ROS can induce oxidative stress in pulmonary systems, followed by a cascade of inflammation responses and the apoptosis of lung cells (Danielsen et al, 2011; Li et al, 2003, 2008). Particulate organic compounds such as quinones and polyaromatic hydrocarbons can react with cellular reducing agents (e.g., NADPH) and form ROS (i.e., H2O2 and O−2 ; Kumagai et al, 2012). Quinone compounds, commonly found in primary combustion particulates (Danielsen et al, 2011; Jakober et al, 2007), are known to be important contributors to the DTT response of combustion particles
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
