Temperature dependence of the gas-particle partitioning of selected VOCs.

The gas-particle partitioning coefficients for volatile organic compounds (VOCs) are difficult to acquire because discriminating the small mass fraction of the VOCs in the aerosol particle relative to that in the gas phase is challenging. In this paper, we report the temperature dependence of the gas-particle partitioning coefficient (Kp) for n-butanol (n-BuOH) and trichloroethylene (TCE). Using the bench-scale system that we developed, we measured the Kp of surrogate VOCs, n-BuOH, and TCE onto inorganic (ammonium sulfate, Am Sulf) and organic (succinic acid, SA) aerosol particles at a fixed relative humidity (RH) of 35%. At this RH level and temperature range of 278.15-308.15 K, the ln Kp for TCE and n-BuOH partitioning on SA aerosol particles were -27.0 ± 0.70 to -27.9 ± 0.01 and -13.9 ± 0.03 to -17.4 ± 0.17. In contrast, the ln Kp for TCE and n-BuOH partitioning on Am Sulf aerosol particles ranged from -26.4 ± 0.70 to -27.4 ± 0.71 and -14.1 ± 0.03 to -17.1 ± 0.17, respectively. Results showed that TCE fitted well with the classic van't Hoff relationship. The enthalpy of desorption (ΔHdes) for TCE was constant over the temperature range of 278.15 K to 308.15 K, behaving similarly to 1,2-dichlorobenzene. At a similar temperature range, n-BuOH partitioning into both aerosol particles exhibited nonlinear temperature dependence. The minimum ratio of ΔHdes (Am Sulf:SA) for n-BuOH partitioning on each aerosol type was at ∼278.15 K. The magnitude of the entropy ΔSdes for all VOCs was <1 kJ mol-1.

A method to measure the partitioning coefficient of volatile organic compounds in nanoparticles.

The partitioning behavior of volatile organic compounds (VOCs) into nanoparticles is less studied compared to those of semivolatile organic compounds (SVOCs) because of the lower concentration of the VOCs that is expected to partition into particles. One challenge in measuring the accurate partition coefficient of VOCs is quantifying their low mass fraction that sorbed on nanoparticles and differentiating them from the high VOC concentrations present in the gas-phase. Systematically characterizing the partitioning coefficient at a specific environmental condition is also difficult when sampling in the field. During field sampling, thermal and non-thermal issues such as sampling artifacts and non-equilibrium conditions because of a dynamic environment often result in considerable variability in the measured partition coefficients. In this study, we developed a bench-scale system that can achieve precise control of the experimental condition (e.g., relative humidity, temperature, and particle composition) and allow us to measure the low concentration of 1,2-dichlorobenzene in the particles. A similar set up can be used to study the low mass fraction of other VOCs partitioning in nanoparticles. The detailed but uncomplicated system setup may assist other researchers that investigate the global fate and transport and health effects of VOCs.•A bench-scale system was built in the laboratory to study the gas-to-particle partitioning•Experimental conditions can be controlled and easily varied•The system enables the systematic study of a single environmental factor on the partitioning process.

Partitioning of volatile organic compounds to aerosols: A review.

Although volatile organic compounds (VOCs) exist mainly in the gas-phase rather than in aerosols, the concentrations of VOCs measured from aerosols are comparable to those of semi-volatile organic compounds, which preferentially partition into aerosols. VOCs that partition into aerosols may raise health effects that are generally not exerted by aerosols or by VOCs alone. So far, only scant reports on VOC/aerosol partitioning are available in the extant literature. In this review, we discuss findings presented in recent studies on the partition mechanism, factors affecting the partition process, existing knowledge gaps, and recommendations to help address these gaps for future research. Also, we have surveyed the different models that can be applied to predict partition coefficients and the inherent advantage and shortcoming of the assumptions in these models. A better understanding of the partition mechanism and partition coefficient of VOCs into aerosols can improve prediction of the global fate and transport of VOCs in the environment and enhance assessment of the health effects from exposure to VOCs.

Environmentally Persistent Free Radicals: Insights on a New Class of Pollutants.

Environmentally persistent free radicals, EPFRs, exist in significant concentration in atmospheric particulate matter (PM). EPFRs are primarily emitted from combustion and thermal processing of organic materials, in which the organic combustion byproducts interact with transition metal-containing particles to form a free radical-particle pollutant. While the existence of persistent free radicals in combustion has been known for over half-a-century, only recently that their presence in environmental matrices and health effects have started significant research, but still in its infancy. Most of the experimental studies conducted to understand the origin and nature of EPFRs have focused primarily on nanoparticles that are supported on a larger micrometer-sized particle that mimics incidental nanoparticles formed during combustion. Less is known on the extent by which EPFRs may form on engineered nanomaterials (ENMs) during combustion or thermal treatment. In this critical and timely review, we summarize important findings on EPFRs and discuss their potential to form on pristine ENMs as a new research direction. ENMs may form EPFRs that may differ in type and concentration compared to nanoparticles that are supported on larger particles. The lack of basic data and fundamental knowledge about the interaction of combustion byproducts with ENMs under high-temperature and oxidative conditions present an unknown environmental and health burden. Studying the extent of ENMs on catalyzing EPFRs is important to address the hazards of atmospheric PM fully from these emerging environmental contaminants.