Role of the Aerosol Substrate in the Heterogeneous Ozonation Reactions of Surface-Bound PAHs

Abstract

To probe how the aerosol substrate influences heterogeneous polycyclic aromatic hydrocarbon (PAH) oxidation, we investigated the reaction of surface-bound anthracene with gas-phase ozone on phenylsiloxane oil and azelaic acid aerosols under dry conditions in an aerosol flow tube with offline analysis of anthracene. The reaction exhibited pseudo-first-order kinetics for anthracene loss, and the pseudo-first-order rate coefficients displayed a Langmuir-Hinshelwood dependence on the gas-phase ozone concentration on both aerosol substrates. The following parameters were found: for the reaction on phenylsiloxane oil aerosols, K(O3) = (1.0 +/- 0.4) x 10(-13) cm(3) and k(I)(max) = (0.010 +/- 0.003) s(-1); for the reaction on azelaic acid aerosols, K(O3) = (2.2 +/- 0.9) x 10(-15) cm(3) and k(I)(max) = (0.057 +/- 0.009) s(-1), where K(O3) is a parameter that describes the partitioning of ozone to the surface and k(I)(max) is the maximum pseudo-first-order rate coefficient at high ozone concentrations. The K(O3) value for the reaction of surface-bound anthracene and ozone on azelaic acid aerosols is similar to the K(O3) value that we obtained in our previous study for the reaction of surface-bound benzo[a]pyrene and ozone on the same substrate. This finding supports our earlier hypothesis that the substrate influences the partitioning of ozone to the surface irrespective of the organic species (i.e., PAH) adsorbed to it. Preliminary ab initio calculations were performed to investigate whether there is a relationship between the relative binding energies of the ozone-substrate complex and the K(O3) values for the different substrates studied. A comparison between kinetic results obtained on aerosol substrates and thin films is presented.

Heterogeneous ozonation of suspended malathion and chlorpyrifos particles

“…About 0.2 g azelaic acid used to generate nucleus is put in a small boat-shaped ceramic container positioned at the center of the first quartz tube. Azelaic acid is chosen as the nucleus because it has little reactivity with ozone (Kwamena et al, 2007). The temperature of the first quartz tube is set at 413 K. Fig.…”

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

“…They also revealed that some of the reaction products included surfacebound ketone, lactone, and anhydride groups. Other research teams extended this work to specific surface-bound compounds (including polycyclic aromatics, 43,[53][54][55][56][57][58] biogenic volatile organics, 59 biomass burning products, 60 and fungicides 61 ) and functionalities at well-characterized aerosol surfaces. [62][63][64][65][66] Within the body of literature on O 3 reactions with aerosols, investigations of the ozonolysis of oleic acid aerosols are of particular interest because these particulates appear in relative high abundance in certain regions of the atmosphere.…”

Homogeneous and heterogeneous reactions of phenanthrene with ozone

“…Two tandem 3 cm (outer diameter) Â 40 cm (length) quartz tubes heated with heating tapes were used as an aerosol generator. Azelaic acid was chosen as the model nucleus because it was almost inert to ozone (Kwamena et al, 2007). A small ceramic container containing w0.4 g azelaic acid was positioned at the center of the first tube.…”