A chamber study of secondary organic aerosol formation by limonene ozonolysis

Limonene ozonolysis was examined under conditions relevant to indoor environments in terms of temperatures, air exchange rates, and reagent concentrations. Secondary organic aerosols (SOA) produced and particle-bound reactive oxygen species (ROS) were studied under situations when the product of the two reagent concentrations was constant, the specific concentration combinations play an important role in determining the total SOA formed. A combination of concentration ratios of ozone/limonene between 1 and 2 produce the maximum SOA concentration. The two enantiomers, R-(+)-limonene and S-(-)-limonene, were found to have similar SOA yields. The measured ROS concentrations for limonene and ozone concentrations relevant to prevailing indoor concentrations ranged from 5.2 to 14.5 nmol/m(3) equivalent of H2O2. It was found that particle samples aged for 24 h in freezer lost a discernible 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 ROS formed from limonene ozonolysis could be separated into three categories as short-lived, high reactive, and volatile; semi-volatile and relatively stable; non-volatile and low-reactive species based on ROS measurements under various conditions. Such chemical and physical characterization of the ROS in terms of reactivity and volatility provides useful insights into nature of ROS.

A better understanding of the formation mechanism of secondary organic aerosol generated from indoor chemistry allows us to evaluate and predict the exposure under such environments. Measurements of particle-bound ROS shed light on potential adverse health effect associated with exposure to particles.