The Chemistry of Carbonaceous Soot Aerosols and Nitric Acid
Jennifer E. Leisch1,2, R.S. Disselkamp2, M.A. Carpenter2, J.P. Cowin2
The study reported here examines the reaction between carbonaceous aerosols and nitric acid with both high and low nitric acid exposure. Two different experimental configurations were used. The first set of experiments utilized an aerosol chamber to react soot with HNO3. Fourier-transform infrared spectroscopy (FTIR) was used to monitor the reaction between the soot and HNO3. Slides were placed inside the chamber to collect unreacted and reacted soot samples for later analysis using scanning electron microscopy (SEM). The second experiment exposed glass slides coated with hexane soot to the vapors of HNO3 (70% by wt.), dry HNO3 (1:1 HNO3:H2SO4), and water alone. These slides were then analyzed for morphological changes using SEM. The samples analyzed are compared here to unreacted hexane soot.
It was found that upon introduction of FW2 Degussa soot into the aerosol chamber, a stepwise decrease in nitric acid concentration is seen, with a consequent rise in NO2 products. The decrease in HNO3 is due to chemistry occurring at the surface of the soot. Hexane soot particles from the second experimental configuration exposed to 70% HNO3 underwent an obvious morphological change. The porous, distinct features typical of unreacted soot lost distinction and structure upon exposure to HNO3. The specimens exposed to the dry HNO3 and H2O do not appear to have a large morphological change, implying that water may facilitate the reaction between soot and HNO3.
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