Development and Characterization of a Thermal Denuder for Aerosol Volatility Measurements

Aerosol particles have important impacts on visibility, acid deposition, climate, and human health, although large uncertainties remain in quantifying their chemical composition and atmospheric transformations. However, of the organic aerosol mass, only a small fraction has been compositionally resolved, and little work has been done on the volatility and partitioning of organic compounds between the gas and particle phases. Thermodenuders provide information on the volatility of chemical species in ambient particulate matter by passing the particles through a heated region and measuring changes in chemical composition or size. Unfortunately, currently available thermodenuders suffer from short residence times, uneven heating, and inflexible operating conditions, and they have not been sufficiently well-characterized to allow for the quantitative determination of vapor pressures. This project will develop and test an improved thermodenuder system that can interface to essentially any aerosol instrumentation or suite of instruments (e.g., aerosol mass spectrometers or scanning mobility particle sizers). Phase I will involve (1) detailed physical modeling of the thermodenuder design to optimize performance and flexibility, (2) construction of the improved thermodenuder, (3) characterization and evaluation with laboratory and ambient aerosol particles, and (4) development of a model for the volatility spectrum of ambient organic particulate matter. Commercial Applications and other Benefits as described by the awardee: The additional volatility information provided by the thermodenuder should strengthen primary organic aerosol emission inventories, provide further insight into secondary aerosol formation mechanisms, and improve the ability of atmospheric chemistry models to predict ambient aerosol loadings. The instrument should be ideally suited for the characterization and control of aerosol emissions from a variety of industrial and energy production processes, including aircraft combustors, gas turbines, fluidized bed combustors, diesel combustors, and conventional furnaces.