Abstract
Experiments were conducted in a dynamic chamber system to measure the formation of secondary organic aerosol (SOA) and particle-bound reactive oxygen species (ROS) produced from limonene ozonolysis in the presence of NO by varying the ratio of O_3 to NO. A diffusion cell system was used to produce the constant input of limonene in to the chamber, and six sets of experiments were conducted. The concentration of SOA mass and ROS produced were measured at steady-state. ROS, including peroxides, peroxy radicals and ions, was determined using dichlorofluorescin (DCFH) and converted to equivalent H_2O_2 concentration. The particle mass was measured using a tapered element oscillating microbalance (TEOM) and a scanning mobility particle sizer (SMPS) was used to obtain particle volume distributions. The results showed that the SOA mass concentration ranged from 30.3 to 157.3 μg m^(-3), and the ROS concentration ranged from 6.1 to 29.4 nmol m^(-3) of H_2O_2. For the different combinations of NO_x and O_3, the concentration ratio of [O_3]/[NO] around 1 was found to produce highest SOA mass and ROS, which is 157.3 μg m^(-3) and 29.4 nmol m^(-3). The SOA density was estimated by comparing the mass concentrations with the volume concentrations ranged from 1.21 to 1.48 g cm^(-3). The highest SOA density (1.48 g cm^(-3)) occurred with the lowest concentration ratio of [O_3]/[NO]. Compared with other monoterpene and linalool where each has one unsaturated carbon bond in other studies, limonene which has two unsaturated carbon bonds. Thus, it is the most efficient in generating the SOA and ROS concentrations in prior experiments without NO present.
Highlights
Indoor air pollution has attracted public attention for its effect on personal and public health, with substantial focus on emission, transport, formation and removal pathways (Guenther et al, 2000)
The experiments on limonene ozonolysis in the presence of nitric oxide (NO) in a flow chamber system simulate reactions that might be expected to occur in indoor air between infiltrated ozone and limonene off-gassed from household products
Results from this study show that secondary organic aerosol (SOA) in higher quantity will result from events when the initial Nitrogen oxides (NOx)/O3 ratio was around 1
Summary
Indoor air pollution has attracted public attention for its effect on personal and public health, with substantial focus on emission, transport, formation and removal pathways (Guenther et al, 2000). Nojgaard et al (2006) studied the effect of the nitrogen dioxide (NO2) concentration on particle formation of d-limonene ozonolysis, and has found the presence of NO2 resulting in formation of the nitrate radical introduced an additional loss term for ozone. NO2 is produced by oxidation of atmospheric nitrogen during high-temperature fuel combustion In addition to these major NOx sources in indoor environments, ventilation/infiltration from outdoors and surface reactions contribute to indoor NOx concentrations (Weschler and Shields, 1997; Lee et al, 2002). The purpose of limonene ozonolysis with NOx present were investigated to provide new information on SOA yields and the resulting ROS concentrations for different ratios of nitric oxide and ozone similar to the prior study of α-pinene-ozone-NO by Liu and Hopke (2014)
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