Uptake of Pyrene onto Fatty Acid Coated NaCl Aerosol Particles

Abstract

Photoelectric charging experiments monitor the uptake of pyrene onto NaCl aerosol particles coated with either oleic acid or myristic acid. In both cases, thin coatings produce a small net decrease in pyrene uptake. In the larger coverage limit, the uptake of the myristic acid coated particles remains nearly constant whereas the oleic acid coated particles exhibit greater uptake rates than the bare NaCl particles. Fitting the results with a multilayer kinetic model yields uptake rate coefficients as well as parameters that describe the distribution of organic molecules on the aerosol particle surface. The model accounts for the decrease in uptake associated with thin coatings of oleic acid through a concomitant reduction in surface area. The adsorption rate constants for the myristic and oleic acid coated surfaces are 50 and 80 times faster, respectively, than for NaCl. The desorption rates for pyrene on the fatty acid surfaces are faster, as well. For myristic acid coatings, the fast desorption (over 400 times the rate of desorption from NaCl) results in slower net adsorption, whereas for oleic acid (approximately 12 times the desorption rate from NaCl), the net uptake rate increases with coverage. The results also suggest that both myristic acid and oleic acid spread incompletely on the aerosol surfaces under the conditions of these experiments. In the optimized kinetic model, the fatty acids cover approximately 50% of the surface when the nominal coating thickness is approximately 6 nm. The surface is over 90% covered with a nominal coating thickness of 20 nm, which is approximately 10% of particle diameter in these experiments. Very thin oleic acid coatings reduce the surface area of particles consistent with the preferential coverage of highly corrugated or porous regions.

Lifetime of Triplet Photosensitizers in Aerosol Using Time-Resolved Photoelectric Activity

“…The experimental apparatus is similar to that reported previously for laser-based photoemission studies of surface-adsorbed or near-surface species. ,, This experiment extends those studies to include reactive transients formed in the early stages of photochemical reactions. Figure illustrates the experimental setup.…”

“…We have used a laser-based, ambient pressure photoelectric charging scheme in the past to measure the spectroscopy of probe molecules 23−25 on aerosol particle surfaces and to monitor the uptake of polycyclic aromatic hydrocarbons onto model aerosol surfaces. 26 Recently, we used the photoemission yield of iodide to study the anion's affinity for the water−air interface in a supersaturated aerosol. 27 The results demonstrate preferential detection of interfacial species, consistent with an estimated electron attenuation length in water of 1 to 3 nm 28−32 at the energies of this experiment.…”

“…We have used a laser-based, ambient pressure photoelectric charging scheme in the past to measure the spectroscopy of probe molecules − on aerosol particle surfaces and to monitor the uptake of polycyclic aromatic hydrocarbons onto model aerosol surfaces . Recently, we used the photoemission yield of iodide to study the anion’s affinity for the water–air interface in a supersaturated aerosol .…”

Photoemission of Iodide from Aqueous Aerosol Particle Surfaces

“…Figure shows the experimental apparatus, which is similar to that in previous works, especially with regard to the generation and control of the aerosol flows. , We generate atmospheric pressure flows of aqueous aerosol particles using a constant output atomizer (TSI model 3076). The atomizer solution is a mixture of NaCl, KI, and, in some cases, surfactants, and has a total ionic strength of roughly 0.05 mol/L.…”

Core/Shell Microstructure Induced Synergistic Effect for Efficient Water-Droplet Formation and Cloud-Seeding Application

“…Sodium chloride (NaCl) has been used as a typical water-soluble hygroscopic warm-cloud-seeding materials for several decades, − which is more commonly employed than ice-nucleating materials used in a cold cloud, e . g ., dry ice (solid carbon dioxide, CO 2 ), which is associated with high cost and the greenhouse effect, and silver iodide (AgI), which is associated with controversial environmental risk .…”