Reactive uptake of NO2 on volcanic particles: A possible source of HONO in the atmosphere

Abstract

The heterogeneous degradation of nitrogen dioxide (NO 2 ) on five samples of natural Icelandic volcanic particles has been investigated. Laboratory experiments were carried out under simulated atmospheric conditions using a coated wall flow tube (CWFT). The CWFT reactor was coupled to a blue light nitrogen oxides analyzer (NO x analyzer), and a long path absorption photometer (LOPAP) to monitor in real time the concentrations of NO 2 , NO and HONO respectively. Under dark and ambient relative humidity conditions, the steady state uptake coefficients of NO 2 varied significantly between the volcanic samples probably due to differences in magma composition and morphological variation related with the density of surface OH groups. The irradiation of the surface with simulated sunlight enhanced the uptake coefficients by a factor of three indicating that photo-induced processes on the surface of the dust occur. Furthermore, the product yields of NO and HONO were determined under both dark and simulated sunlight conditions. The relative humidity was found to influence the distribution of gaseous products, promoting the formation of gaseous HONO. A detailed reaction mechanism is proposed that supports our experimental observations. Regarding the atmospheric implications, our results suggest that the NO 2 degradation on volcanic particles and the corresponding formation of HONO is expected to be significant during volcanic dust storms or after a volcanic eruption.

Photo-enhanced uptake of SO2 on Icelandic volcanic dusts

“…The heterogeneous interaction of SO 2 with the v-dust materials is studied in a horizontal coated-wall flow-tube (CWFT) reactor at atmospheric pressure and room temperature T = 296 K (Figure 1). 24,26,28 The v-dust sample is deposited on the inner surface of a Pyrex tube. Further details about the sample preparation can be found in recent publications.…”

“…Further details about the sample preparation can be found in recent publications. 24,26 The tube is then inserted into the reactor along its main axis, and kept in position by two Viton O-rings sealing the space between the tube and the wall of the reactor. Before each experiment, the sample is left for at least 1 hour under a zero air flow at the RH to be used during the subsequent experiment.…”

“…Physical and chemical properties of the v-dusts have been previously characterized and are reported elsewhere. 24,26 To further characterize the v-dust samples, we determined the surface (topmost 2-10 nm) elemental composition of the v-dusts by X-ray Photoelectron Spectroscopy (XPS) using a Kratos Axis Ultra Instrument. Relative concentrations (in at.%) were determined by highresolution scans at a pass energy of 40 eV for C 1s , O 1s , Si 2p , Al 2p , Fe 2p , Mg 2p , Ca 2p , Na 1s , K 2p , Ti 2p , and Mn 2p using a monochromatic Al X-ray beam centered at 1486.6 eV.…”

“…Photo-induced removal of atmospheric species has been highlighted in previous studies dealing with the degradation of pollutants on the surface of mineral dust proxies, 34,45,46 and on v-dusts, 26 but an accurate description of the heterogeneous physicochemical pathway involved is still lacking. The nature of the photo-induced surface processes can involve Mýrdalssandur v-dust was exposed to 75 ppb of SO 2 at RH = 30% and T = 296 K.…”

Newly identified climatically and environmentally significant high latitude dust sources

“…If the heterogeneous reaction of NO2 on various types of atmospheric particles, e.g., salts, soot, mineral dust and proxies, was addressed in the literature (George et al 2016), the interaction of NO2 with volcanic particles, typical HLD, under atmospheric conditions has only been studied by Romanias et al (2020). They explore the possible formation of short lifetime key atmospheric species, considered as a trigger of numerous atmospheric processes: HONO, a precursor of OH radicals in the atmosphere.…”