Uptake of Hg0(g) on TiO2, Al2O3, and Fe2O3 Nanoparticles: Importance in Atmospheric Chemical and Physical Processes

Mineral dust aerosols play an important role in tropospheric chemistry and aerosol-cloud interaction processes. Yet, their interactions with gaseous elemental mercury (Hg-(g)(0)) are not currently well understood. Using a coated-wall flow tube (CWFT) reactor, we measured the uptake of Hg-(g)(0) on some common components of mineral dust aerosols, including TiO2,Al2O3, and Fe2O3, and the effects of irradiation (dark, visible and UV-A) and relative humidity (< 2% to 60%) on the uptake kinetics. Under UV-A irradiation (320-400 nm) in dry air, we measured uptake coefficients (gamma) equal to > 1 x 10(-3) and (3 +/- 1) x 10(-6) on TiO2 and Al2O3, respectively. Under visible light irradiation (380- 700 nm), Hg-(g)(0) uptake was only observed on TiO2, with gamma = (4 +/- 3) x 10(-4). Raising the relative humidity inhibited the uptake on both TiO2 and Al2O3, and the uptake coefficient at 60% RH for TiO2 under UV-A irradiation was lower by ca. 3 orders of magnitude than dry conditions. Furthermore, we observed that water vapor induced the desorption of two distinct fractions from Hg-exposed surfaces via the displacement of weakly, physisorbed Hg and the photocatalyzed reduction of chemisorbed Hg. Based on the uptake coefficients from this report, we estimate that heterogeneous interactions with mineral dust may be significant under conditions with low relative humidity (< 30%) and high dust loading masses. We herein discuss the implication of this study on understanding the life cycle analysis of atmospheric mercury in nature.

Automated summary

Mineral dust aerosols are important for tropospheric chemistry and aerosol-cloud interactions. This study investigated the interactions between gaseous elemental mercury (Hg-(g)(0)) and mineral dust aerosols. The results showed that under UV-A irradiation, TiO2 had a higher uptake coefficient for Hg-(g)(0) than Al2O3, and under visible light irradiation, only TiO2 exhibited uptake. Increasing relative humidity inhibited the uptake on both TiO2 and Al2O3. Moreover, water vapor induced the desorption of mercury from exposed surfaces. This study suggests that heterogeneous interactions with mineral dust may be significant under specific conditions.