| The formation of secondary organic aerosol (SOA) produced from ozonolysis of three biogenic hydrocarbons was examined using a dynamic chamber system that allowed the simulation of ventilated indoor environments. Experiments were conducted at room temperature (21--24°C), RH&sim6--7% and air exchange rate of 0.67 h-1. An effort was made to keep the product of two reagents concentrations constant. The results suggest that under the conditions when the product of the two reagent concentrations was constant, the ratio of terpene to ozone concentration plays an important role in determining the total SOA formed. The concentrations of particle-bound reactive species (ROS), including peroxides, peroxy radicals and ions that could penetrate into the lungs and deliver oxidative stress to the tissue causing damages were quantitatively determined from filters collected. ROS was determined using dichlorofluorescin (DCFH) such that resulting fluorescent intensities were converted to equivalent H2O2 concentrations.A combination of concentrations in ozone limited region produced the maximum SOA concentrations for linalool ozonolysis. The measured ROS concentrations for linalool and ozone concentrations relevant to prevailing indoor concentrations ranged from 0.71 to 2.53 nmol/m3 equivalents of H2O 2. It was found that particle samples aged for 24 hours at room temperature lost a significant fraction of the ROS compared to fresh samples. The residual ROS concentrations ranged from 15% to 69%. Compared with other terpene species like alpha-pinene that have one endocyclic unsaturated carbon bond, linalool was less efficient in potential SOA formation yields.A combination of concentration ratios of ozone/limonene between 1 and 2 produced the maximum SOA concentrations. The two enantiomers, R-(+)-limonene and S-(-)-limonene, were found to have similar SOA yields. SOA densities were estimated ranging from 1.17 to 1.26 g/cm3. The measured ROS concentrations for limonene and ozone concentrations relevant to prevailing indoor concentrations ranged from 5.2 to 14.5 nmol/m3 equivalents of H2O2. It was found that particle samples aged for 24 hours in freezer lost a noticeable fraction of the ROS compared to fresh samples. The residual ROS concentrations were around 83%--97% of the values obtained from the analysis of samples immediately after collection. The SOA formed from limonene ozonolysis could be separated into three categories as short-lived and volatile, semi-volatile and non-volatile species based on ROS measurements under various conditions. Such physical characterization of the ROS in terms of reactivity and volatility provides some insights into nature of ROS.A combination of concentrations in ozone limited region produced the maximum SOA concentrations for alpha-pinene ozonolysis. Measured ROS concentrations at alpha-pinene and ozone concentrations relevant to prevailing indoor concentrations ranged from 1.1 to 7.2 nmol/m3 of H2O2. Particle density was determined by combining scanning mobility particle sizer (SMPS) measurements with mass collected on filters to obtain particle volume and mass concentrations, respectively. Partitioning theory suggests that with increased SOA mass loading, even more volatile species partition into the particle phase relative to low SOA mass loadings. Other recent studies have found changes in the composition of the SOA depending on the precursor VOC concentrations. This behavior was reflected in these experiments in terms of a change of density. Measured densities ranged from 1.07 to 1.69 g/cm 3. |
