Uptake of NO3 on soot and pyrene surfaces

The reaction of NO3 with methane soot, hexane soot, and solid pyrene was investigated using a flow tube reactor. The uptake of NO3 on fresh soot was fast ( uptake coefficient > 0.1). Based on this result and an assumed density of reactive sites on soot, the time to process or oxidize 90% of a soot surface in the atmosphere would take only approximately five minutes. This suggests that NO3 chemistry can rapidly oxidize soot surfaces under atmospheric conditions. After exposing soot films to NO3 for approximately 180 minutes in the laboratory, the uptake reaches a steady-state value. The steady state uptake coefficients ( assuming a geometric surface area) were 0.0054 +/- 0.0027 and 0.0025 +/- 0.0018 for methane and hexane soot, respectively. These numbers are used to show that heterogeneous reactions between NO3 and soot are not likely a significant sink of gas-phase NO3 under most atmospheric conditions. The uptake of NO3 on fresh pyrene surfaces was also fast ( uptake coefficient > 0.1), and much faster than previously suggested. We argue that under certain atmospheric conditions reactions between NO3 and surface-bound polycyclic aromatic hydrocarbons (PAHs) may be an important loss process of PAHs in the atmosphere.