Abstract
Abstract. Reactions between hydrocarbons and ozone or hydroxyl radicals lead to the formation of oxidized species, including reactive oxygen species (ROS), and secondary organic aerosol (SOA) in the troposphere. ROS can be carried deep into the lungs by small aerodynamic particles where they can cause oxidative stress and cell damage. While environmental studies have focused on ROS in the gas phase and rainwater, it is also important to determine concentrations of ROS on respirable particles. Samples of PM2.5 collected over 3 h at midday on 40 days during November 2011 and September 2012 show that the particulate ROS concentration in Austin, Texas, ranged from a minimum value of 0.02 nmoles H2O2 m−3 air in December to 3.81 nmoles H2O2 m−3 air in September. Results from correlation tests and linear regression analysis on particulate ROS concentrations and environmental conditions (which included ozone and PM2.5 concentrations, temperature, relative humidity, precipitation and solar radiation) indicate that ambient particulate ROS is significantly influenced by the ambient ozone concentration, temperature and incident solar radiation. Particulate ROS concentrations measured in this study were in the range reported by other studies in the US, Taiwan and Singapore. This study is one of the first to assess seasonal variations in particulate ROS concentrations and helps explain the influence of environmental conditions on particulate ROS concentrations.
Highlights
Peroxides are generated in ambient air from alkene ozonolysis and photochemical reactions with volatile organic compounds (VOCs) and NOx (Seinfeld and Pandis, 2006)
The mean (± SD) concentration of reactive oxygen species (ROS) on PM2.5 samples collected over 3 h around midday in Austin, Texas, on 40 days between November 2011 and September 2012 was 1.25 ± 1.1 nmoles m−3
We measured the concentration of ROS associated with PM2.5 in an urban, semi-arid environment over the course of a year
Summary
Peroxides are generated in ambient air from alkene ozonolysis and photochemical reactions with volatile organic compounds (VOCs) and NOx (Seinfeld and Pandis, 2006). Photochemical models suggest that peroxides can be present in both polluted and clean air (Kleinman, 1986; Heikes et al, 1996), which is confirmed by measurements (Walker et al, 2006; Snow et al, 2007). Its concentration in rainwater and snow has been measured since the late nineteenth century (Schöne, 1874), and studies have found strong seasonal and diurnal variations in the concentrations of H2O2 and other reactive oxygen species (ROS) in rainwater, water vapor, and air in gas phase (Singh et al, 1986; Gunz and Hoffman, 1990, and references within; Ayers et al, 1992; Dollard and Davies, 1992; Lee et al, 2000; Yamada et al, 2002; Liu et al, 2003; Zhang et al, 2012). Data on peroxide and ROS concentrations in the aerosol phase are limited
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