Reactions on Atmospheric Dust Particles: Surface Photochemistry and Size-Dependent Nanoscale Redox Chemistry

Abstract

Mineral dust aerosol is indisputably an important component of the Earth's atmosphere and provides a reactive surface for heterogeneous chemistry to occur. These reactions can alter concentrations of key trace atmospheric gases as well as change the physicochemical properties of the dust particles. The focus of this Perspective article is on several new mechanisms and reaction pathways identified in laboratory studies on components of mineral dust and on nanodust, a potentially new source of metal-containing dust from engineered nanomaterials. These reactions include surface photochemical mechanisms for renoxification and sulfur dioxide oxidation and size-dependent redox chemistry of metalcontaining dusts in low-pH environments including naturally occurring iron oxides and engineered metal nanoparticles. These newly identified reactions have the potential to play an important role in atmospheric chemistry.

Sulfur isotope fractionation during heterogeneous oxidation of SO<sub>2</sub> on mineral dust

“…Uptake and decomposition of ozone, which increases the basicity and oxidising capacity of the surface, is highest when irradiated and at around ∼35 % RH (Hanisch and Crowley, 2003;Nicolas et al, 2009). Many components of dust, particularly iron and titanium oxides, are photosensitive and show increased uptake and oxidation due to the formation of election-hole pairs Rubasinghege et al, 2010). The photoreactivity of Ti is supported by the lower fractionation factor for Mineral assemblage 4 when exposed to O 3 or light as discussed in Sect.…”

“…Freshly-emitted Sahara dust is very hydrophobic (Kaaden et al, 2009), whereas sulfate-coated mineral dust has increased CCN activity and may even act as "giant CCN" (Levin et al, 1996), while sulfate coatings reduce the ice nuclei activity of mineral dust (Cziczo et al, 2009;Pruppacher and Klett, 1997). Mineral dust is a particularly important source of iron in nutrient-limited open ocean waters, and chemical aging can reduce the pH of dust, increasing the solubility and bioavailability of iron (Jickells et al, 2005;Gasso et al, 2010;Rubasinghege et al, 2010;. Heterogeneous oxidation of SO 2 on dust can lead to reductions of >50 % in SO 2 concentration, and may account for 50-70 % of sulfate production in dust source regions (Dentener et al, 1996;Xiao et al, 1997;Zhu et al, 2010).…”

First long-term and near real-time measurement of trace elements in China's urban atmosphere: temporal variability, source apportionment and precipitation effect

“…In urban atmospheres, ambient trace elements typically represent a small fraction of PM 2.5 on a mass basis, while elemental species like Cd, As, Co, Cr, Ni, Pb and Se are considered as human carcinogens even in trace amounts (Iyengar and Woittiez, 1988;Wang et al, 2006;Olujimi et al, 2015). It has been shown that Cu, Cr, Fe and V have several oxidation states that can participate in many atmospheric redox reactions (Litter, 1999;Brandt and van Eldik, 1995;Seigneur and Constantinou, 1995;Rubasinghege et al, 2010a), which can catalyze the generation of reactive oxygenated species (ROSs) that have been associated with direct molecular damage and with the induction of biochemical synthesis pathways (Charrier and Anastasio, 2012;Strak et al, 2012;Rubasinghege et al, 2010b;Saffari et al, 2014;Verma et al, 2010;Jomova and Valko, 2011). Additionally, lighter elements such as Si, Al and Ca are the most abundant crustal elements next to oxygen, which can typically constitute up to 50 % of the elemental species in remote continental aerosols (Usher et al, 2003;Ridley et al, 2016).…”

Thermal and photochemical reactions of NO2 on chromium(iii) oxide surfaces at atmospheric pressure

“…They also studied the photochemistry of nitrate ions formed on Al 2 O 3 by exposure to gaseous nitric acid followed by evacuation. 33,34,96,97 At the shortest irradiation times studied, NO 2 was the major gas-phase product at 20-80% RH, whereas NO dominated at RH o1%. This is similar to our observations of the interaction of NO 2 Since a significant amount of water vapor is present in the atmosphere, the heterogeneous reactions would be similar to our results under humid conditions.…”