AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM11
Formation of Nitro-PAH on Flyash Particle Surfaces: The Significance of Particle Substrate on PAH Nitration

Thursday, November 5, 1998, 11:40 am, Room 309

Session: Oxide Surface Chemistry
Presenter: G.S. Strossman, Charles Evans & Associates
Authors: G.S. Strossman, Charles Evans & Associates
T.F. Fister, Charles Evans & Associates
R.W. Odom, Charles Evans & Associates
R.W. Linton, University of North Carolina, Chapel Hill
Correspondent: Click to Email
Polycyclic aromatic hydrocarbons (PAH) are present in the atmosphere in both the gas phase and condensed onto particle surfaces. Coal flyash particles are an important source of condensed PAH since both are byproducts of coal combustion. Many PAHs are hazardous in their own right due to their carcinogenic or mutagenic nature; however another factor to be considered is the transformation of PAH into potentially more harmful analogues during their exposure to the atmosphere. One example is the formation of nitro-PAH after exposure of the parent PAH to atmospheric NO@sub 2@. A full understanding of these reactions requires determining how the near surface composition of flyash particles can affect the rate of nitration of adsorbed PAH. The PAH studied in this work was benzo[a]pyrene (BaP). BaP was chosen for its reactivity and because its size (5 rings) makes it likely to exist in the atmosphere primarily in the condensed phase. Submonolayer coverages of BaP on four different flyashes were exposed to NO@sub 2@ in both dry air and with different levels of relative humidity. The samples were analyzed by TOF-SIMS, a technique that can both obtain surface elemental information and detect low levels of organic molecular species on single particles in the 3-10 @micron@ range. The results show a distinct relationship between the particle compositions and the formation of nitro-BaP, both macroscopically and among individual particles within a single flyash sample. Furthermore, for two Class C (calcium-rich) flyashes, the role played by the substrate is distinctly different between dry air and humid air exposures, while for a class F flyash (high Al, Si and Fe, low Ca) no such difference is observed.