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Reactive oxygen species in fresh and aging SHS particles

Institution: Lawrence Berkeley National Laboratory
Investigator(s): Mohamad Sleiman, Ph.D
Award Cycle: 2009 (Cycle 18) Grant #: 18FT-0105 Award: $132,137
Subject Area: General Biomedical Science
Award Type: Postdoctoral Fellowship Awards

Initial Award Abstract
Secondhand smoke (SHS) is a major source of human exposure to particulate matter in indoor environments, and accounts for a small but measurable fraction of the urban fine organic aerosol material. Particles present in SHS are in the fine to ultrafine particle size range (0.02 μm – 2 μm), are inhaled deep into the lungs and cause an array of adverse health effects such as coronary heart disease, lung cancer, chronic obstructive pulmonary disease (COPD), etc. At present, one of the biggest gaps in our knowledge relates to whether these effects are mediated by the particles or their chemical constituents, and to which specific compounds are most responsible for the observed health effects. There is increasing evidence that reactive oxygen species (ROS) are a key factor in the mechanisms conducing to adverse health effects. Very little is known about the formation of ROS is SHS particles and about their temporal evolution as SHS ages. However, this is of potentially great importance in fully understanding the adverse health effects of SHS exposure, especially because SHS particles may undergo dynamic complex transformations that could significantly transform their chemical composition, physical and toxicological properties (e.g. size, density, hygroscopicity, ROS concentrations).

The aim of this project is to investigate how chemical aging of SHS, in particular oxidation processes by sunlight and ozone, influences human exposure to reactive oxygen species (ROS), which lead to pulmonary and systemic oxidative stress. The objective of this application is to identify mechanisms involved in the generation of ROS on SHS particles during the time between emission of SHS and its inhalation. This knowledge will contribute to provide more accurate exposure assessments and to improve our understanding of the potential health effects of SHS particle-bound oxidative species. Our hypothesis is that the toxicity of SHS particles may increase during aging, via production of highly oxidized compounds and ROS, even while physical processes such as ventilation cause reduction of concentrations of SHS particles.

To accomplish the goal of this project, we will develop and validate new experimental approaches using on-line analytical instruments such as aerosol mass spectrometer and automated monitoring of ROS with fluorescent probes. Aging experiments will be carried out using two reactor setups: an aerosol flow tube reactor and a continuous stirred tank reactor. This will allow us to investigate during both short and long periods of time (minutes to hours) the influence of ozone and sunlight on SHS particles under controlled conditions (temperature, light, humidity and concentration of coexisting gas-phase species), simulating realistic scenarios corresponding to typical indoor or outdoor environments. The experimental work will be realized at the Lawrence Berkeley National Laboratory (Indoor Environment Department, in collaboration with the Advanced Light Source Division). At the completion of this study, we expect to obtain original qualitative data on the chemical composition of SHS particles, as well as quantitative measurements of ROS concentration changes during aging of SHS. The results of this study will contribute to improve our understanding of human exposure to SHS particles and related health effects.