Laboratory studies of ozone uptake on processed mineral dust

After atmospheric aging and processing, mineral dust particles are often coated with nitrates, sulfates, and organics. In this study, laboratory experiments were done to simulate possible changes in the reactivity of mineral dust particles after being processed or aged in the atmosphere. Initial uptake coefficients of ozone on processed and unprocessed dust were measured with a Knudsen cell reactor and the relative reactivities are compared. In particular, the reactive uptake of ozone with mineral oxide particles that had been pretreated by exposure to nitric acid, sulfur dioxide, and organics are compared to particles that had not been pretreated. In some cases, it was found that the reactivity of ozone with pretreated particles was significantly reduced whereas in other cases the reactivity was enhanced. For example, the reactive uptake of ozone decreased by approximately 70% for alpha-Al2O3 particles coated with a layer of nitrate from reaction with nitric acid compared to particles that did not have a nitrate coating, whereas pretreatment of alpha-Al2O3 with sulfur dioxide showed a 33% enhancement toward ozone reactivity. For organic coatings, it was determined that SiO2 particles functionalized with a C-8-alkene displayed enhanced reactivity toward ozone by 40% relative to untreated SiO2, while SiO2 particles functionalized with a C-8-alkane exhibited decreased reactivity by approximately 40% relative to untreated SiO2 particles. The reaction mechanism of ozone uptake with these particles is discussed, as well as the impact on the chemistry of ozone on coated mineral dust aerosol in the troposphere. (C) 2003 Elsevier Ltd. All rights reserved.