Richard M. Kamens - US grants

The purpose of this research is to improve our understanding of the factors that control the gas to aerosol phase distribution of semi-volatile organic compounds. Results from this program will provide modelers with tools to predict vaporization and condensation of semi-volatiles as gas and particle concentrations change with time. Most of the current efforts to predict organic partitioning have been based on equilibrium theory. Although these efforts have substantially advanced our understanding of the partitioning process under ideal conditions, there are strong indications that atmospheric equilibrium between the gas and particle phases may not be established for most compounds of interest over relatively short time scales (minutes to hours). To obtain experimental data to develop and test models of semi-volatile mass transfer between the gas and particle phases, combustion emissions will be aged in a large 190cm3 outdoor Teflon film environmental chamber. Polynuclear aromatic hydrocarbons (PAHs) will be used as example compounds, but the methodology will be applicable to other organic semi-volatile toxics. Net PAH loss rates from particles and the gas phase will be monitored. Rates of PAH mass transfer to the from the particles will be estimated using a new inner particle diffusion model which considers mass transfer in a liquid organic layer surrounding the particle. Three different types of particles will be used. They will be generated from wood, diesel and coal combustion to represent particle types which have different amounts of a "liquid phase" surrounding an inner carbon core. It is expected that the amount and type of organic material that forms this outer layer of the particle will strongly influence inner organic particle diffusion, enthalpies of desorption from the surface, and ultimately rates of particle semi- volatile uptake and loss. By changing the concentration of semi-volatile vapors and/or particles in the chamber, an d thereby perturbing the equilibrium between gas and particle phase organic, these researchers will be able to investigate rates of semi-volatile sorption (condensation) and evolution to and from particles. To radically alter equilibrium conditions, some experiments will be conducted by passing combustion emissions through a large gas stripper/denuder to remove the gas phase semi-volatile component before particles enter the chamber. Semi-volatile deuterated PAH will be added to the gas phase to observe rates of mass transfer to the particles.

This project will investigate the chemical kinetics mechanisms involved in gas phase biogenic reactions. The goal of the project is to develop a predictive model for hydrocarbon aerosol formation as a result of biological gas phase emissions. Currently, biogenic aerosol formation is represented in modeling efforts based on empirically determined parameters. Biogenic aerosols can contribute both to visibility loss on a local scale and to climate forcing effects on a regional scale. The project will involve a number of outdoor chamber experiments to measure terpene gas and particle phase reaction products in the presence of light and nitrogen oxides over a specified temperature range to develop a sequence of kinetic expressions to model aerosol formation.

Project Title: Fate, transport, and toxicity of engineered nanoparticles in the atmosphere
PI: Richard M, Kamens, kamens@unc.edu; Ilona Jaspers (co-PI) ilona_jaspers@med.unc.edu Michael P. Tolocka (co-PI) fizzchem@hotmail.com,
Institution: University of North Carolina at Chapel Hill Chapel Hill, NC, 27599

Submitted to: Interfacial Transport and Thermodynamics Program, # 1414 NSF (EPA# NI-108)
NSF project Officer: Dr. Robert M. Wellek, and Deputy Director, CBET, Division of Engineering, NSF

Project Objective: Determine the atmospheric fate of engineered nanoparticles (ENP) and the effect of aging on the toxicity of this class of materials.

Intellectual merit: The first focus is on the chemical kinetics of ENP atmospheric transformations. ENP will react faster than their micron-sized counterparts found in dusts. The PIs aim to understand how they behave as seed for secondary organic aerosol (SOA) reactions. Because ENP act as photocatalysts, the yield of SOA will be affected. The second focus is to understand the toxicity of this class of materials. They will rapidly screen the ENP for the production of reactive oxygen species (ROS) as measured by a chemical method. Easily reducible species, such as Ni3+ in NixOy will enhance ROS production. The last step is to measure the actual toxicological response of human bronchial epithelial cells. As the materials age, the metal center becomes more oxidized and therefore easily reduced, resulting in increased inflammatory and other biological response to ENP.

For the kinetics experiments, both flow tube and smog chamber studies will be performed. The flow tube studies will be used to determine kinetic parameters of uptake onto their surfaces as a function of relative humidity and particle size. In this way, we can use these parameters for the models that will be developed for their chemical transformations in real atmospheres. To simulate those atmospheres, the smog chamber experiments will be used to determine the fate of ENP as well as their toxicity measured using chemical and in vitro biological methodologies. The chemical method involves the reaction of the suspended particulate matter with dithiothreitol. For the toxicity analysis, they will use differentiated human bronchial epithelial cells or A549 cells grown on membrane support. Cells will be exposed to the fresh or aged ENP. Basolateral supernatants and RNA will be analyzed for the levels of inflammatory cytokines and chemokines and for the levels of intracellular inflammatory mediators as well as markers of oxidative stress.

Broader Impacts: The unique aspect of this research is that the PIs aim to understand the fate of ENP in the atmosphere and their toxicological effect. Accurate measurements of the oxidation and transport of ENP in the atmosphere are essential. The present uncertainties in understanding ENP fate and transport can strongly affect conclusions from studies that may underestimate the potential toxicity of this class of materials, their derivatives, and their influence on atmospheric processes. Detailed kinetic data will benefit modeling efforts by providing a basis to estimate the fate and transport of ENP. Adding these data to existing databases for air-shed models will benefit officials of governmental organizations who use these models to set policies regarding risk assessment and control strategies for generators of ENP. Health effects researchers will benefit from the toxicological data acquired from our experiments as a guide for exposure assessment. In addition, epidemiological studies that aim to locate a causal mechanism for the deleterious effects of ambient particulate matter will benefit from a more precise understanding of what compounds are associated with the aerosol and their toxicity. The proposed research program not only enables the identification of ENP reactions and their kinetics in real time, but also the rapid reaction and data analysis provides greater throughput allowing a greater range of nanoparticle studies.

Supplemental Keywords: air, ambient air, atmosphere, tropospheric, chemical transport, exposure, effects, health effects, human health, dose-response, stressor, chemicals, toxics, particulates, oxidants, intermediates.