Importance of atmospheric aging in reactivity of mineral dust aerosol: a case study of heterogeneous reaction of gaseous hydrogen peroxide on processed mineral particles

摘要

Atmospheric aging and processing appears to alterphysical and chemical properties of mineral dust aerosol and thus its roleas reactive surface in the troposphere. Yet, previous studies in theatmosphere have mainly focused on the clean surfaces of mineral dustaerosol, and the reactivity of aged mineral aerosol toward atmospheric tracegases is still poorly recognized. This work presents the first laboratoryinvestigation of heterogeneous reactions of gaseous hydrogen peroxide(HO), an important atmospheric oxidant, on the surface ofHNO and SO-processed alumina particles as surrogates of mineraldust aerosol aged by acidic trace gases as a function of relative humidity(RH) and surface coverage of coatings. Pretreatment of the alumina surfaceswith HNO and SO has a strong impact on its reactivity towardHO uptake. On HNO-processed particles, because of the dualrole of the nitrate coating in modifying the reactivity of the particlesurface, namely blocking oxide active sites but altering surfacehygroscopicity, HO uptake seems to decrease in some caseswhereas increase in other cases, largely depending on RH and surfacecoverage of nitrate. On SO-processed particles, the presence ofadsorbed S(IV) species appears to enhance the intrinsic reactivity of thealumina particles due to its affinity for HO, and the uptake ofHO increases by 40–80% in the range of RH from 25% to92% relative to the unprocessed particles. However, when S(IV) iscompletely oxidized to S(VI), the alumina surface is significantlydeactivated and the measured uptake of HO decreased markedly.The mechanisms for heterogeneous reactions of HO with theseprocessed particles are discussed, as well as its potential implications ontropospheric chemistry. The results of our study suggest that the reactivityof mineral dust aerosol toward HO and maybe other atmospherictrace gases will depend on the chemical nature and coverage of the coatingsas well as ambient RH, and thus will vary considerably in different pollutedatmosphere, which should be taken into account in current atmosphericmodels.