摘要:

Atmospheric aging appears to alter physical and chemical properties of mineral dust aerosol and thus its role as reactive surface in the troposphere. Yet, previous studies in the atmosphere have mainly focused on the pristine surfaces of mineral dust aerosol, and the reactivity of aged mineral dust toward atmospheric trace gases is poorly recognized. This work presents the first laboratory investigation of heterogeneous reactions of gaseous hydrogen peroxide (H₂O₂), an important atmospheric oxidant, on the surfaces of HNO₃ and SO₂-processed calcium carbonate particles as surrogates of atmospheric mineral dust aged by acidic trace gases. It is found that the processing of the calcium carbonate particles with HNO₃ and SO₂ has a strong impact on their reactivity toward H₂O₂. On HNO₃-processed particles, the presence of nitrate acts to either decrease or increase H₂O₂ uptake, greatly depending on RH and surface coverage of nitrate. On SO₂-processed particles, the presence of surface sulfite appears to enhance the intrinsic reactivity of the mineral particles due to its affinity for H₂O₂, and the uptake of H₂O₂ increases significantly relative to the pristine particles, in particular at high RH. The mechanisms for heterogeneous reactions of H₂O₂ with these processed particles are discussed, as well as their potential implications on tropospheric chemistry. The results of our study suggest that the reactivity of mineral dust aerosol toward H₂O₂ and maybe other trace gases is markedly dependent on the chemical composition and coverage of the coatings as well as ambient RH, and thus will vary considerably in different polluted air masses.