Uptake of Pyrene by NaCl, NaNO3, and MgCl2 Aerosol Particles

Photoelectric charging experiments measure heterogeneous uptake coefficients for pyrene on model marine aerosol particles, including NaCl, NaNO3, and MgCl2. The analysis employs a multilayer kinetic model that contains adsorption and desorption rate constants for the bare aerosol surface and for pyrene-coated surfaces. First coating the aerosol particles with a pyrene layer and following the desorption using both t-DMA and photoelectric charging yields the desorption rate constants. Separate experiments monitor the increase in surface coverage of initially bare aerosol particles after exposure to pyrene vapor in a sliding-injector flow tube. Analyzing these data using the multilayer model constrained by the measured desorption rate constants yields the adsorption rate constants. The calculated initial heterogeneous uptake coefficient, γ0(295 K), is 1.1 × 10–3 for NaCl, 6.6 × 10–4 for NaNO3, and 6.0 × 10–4 for MgCl2. The results suggest that a free energy barrier controls the uptake rate rather than kinematics.