Heterogeneous reaction of NO2 with feldspar, three clay minerals and Arizona Test Dust.

Heterogeneous reaction of NO2 with mineral dust aerosol may play important roles in troposphere chemistry, and has been investigated by a number of laboratory studies. However, the influence of mineralogy on this reaction has not been well understood, and its impact on aerosol hygroscopicity is not yet clear. This work investigated heterogeneous reactions of NO2 (∼10 ppmv) with K-feldspar, illite, kaolinite, montmorillonite and Arizona Test Dust (ATD) at room temperature as a function of relative humidity (<1% to 80%) and reaction time (up to 24 hr). Heterogeneous reactivity towards NO2 was low for illite, kaolinite, montmorillonite and ATD, and uptake coefficients of NO2, γ(NO2), were determined to be around or smaller than 1×10-8; K-feldspar exhibited higher reactivity towards NO2, and CaCO3 is most reactive among the nine mineral dust samples considered in this and previous work. After heterogeneous reaction with NO2 for 24 hr, increase in hygroscopicity was nearly insignificant for illite, kaolinite and montmorillonite, and small but significant for K-feldspar; in addition, large increase in hygroscopicity was observed for ATD, although the increase in hygroscopicity was still smaller than CaCO3.