Kinetics and Product Formation during the Photooxidation of Butanol on Atmospheric Mineral Dust

Abstract

Mineral dust particles have photochemical properties that can promote heterogeneous reactions on their surfaces and therefore alter atmospheric composition. Even though dust photocatalytic nature has received significant attention recently, most studies have focused on inorganic trace gases. Here, we investigated how light changes the chemical interactions between butanol and Arizona test dust, a proxy for mineral dust, under atmospheric conditions. Butanol uptake kinetics were measured, exploring the effects of UV light irradiation intensity (0-1.4 mW/cm), relative humidity (0-10%), temperature (283-298 K), and butanol initial concentration (20-55 ppb). The composition of the gas phase was monitored by a high-resolution proton-transfer-reaction mass spectrometer (PTR-ToF-MS) operating in HO mode. Water was observed to play a significant role, initially reducing heterogeneous processing of butanol but enhancing reaction rates once it evaporated. Gas phase products were identified, showing that surface reactions of adsorbed butanol led to the emission of a variety of carbonyl containing compounds. Under actinic light these compounds will photolyze and produce hydroxyl radicals, changing dust processing from a sink of VOC into a source of reactive compounds.

Heterogeneous photochemistry of dicarboxylic acids on mineral dust

“…Although the PTR-ToF-MS has a high mass resolution (more than 4000 m/Δm), allowing to differentiate compounds with very close m/z e.g., ethanol ( (Yuan et al, 2017), but it may be altered depending on the actual experimental conditions (for example, humidity) and instrument settings (de Gouw and Warneke, 2007). In an attempt to improve product identification, we measured pure standards for some monocarboxylic acids (butanoic, pentanoic, heptanoic and octanoic) and aldehydes (Ponczek and George, 2018 Control experiments were performed to verify that the OVOCs detected were emitted solely from the photoinduced process and not as a result of i) evaporation from the dicarboxylic acid or; ii) due to the presence of impurities on the dust. For this, acid/dust coated inserts were subject to the same experimental conditions and left overnight in the dark while the concentration of VOC was monitored.…”

“…Experiments were carried out in a horizontal coated wall flow tube reactor, previously described in detail (Jammoul et al, 2008;Ponczek and George, 2018), where the acid-coated dust samples were immobilized on the internal walls of a Pyrex tube insert. The reactor had an outer jacket and was maintained at a constant temperature of K by circulating thermostated water from a chiller bath (Huber CC 130).…”

“…To do so, an aqueous solution of the respective acid was mixed with an ATD suspension in ethanol (absolute, 99% Sigma Aldrich). The final suspension was then transferred to the tube inserts coating their inner walls, similar to the coating process described previously (Ponczek and George, 2018). The tubes were left in an oven at 373 K for 1 h to evaporate the solvents (ethanol and water) except the DCA which boiling points are between 473 and 673 K.…”

“…Mineral dust is the most abundant emitted aerosol accounting for a range between 1000-3000 Tg released into the atmosphere every year (Formenti et al, 2011). Recently, the photo-induced heterogeneous chemistry initiated by near-UV/Vis light-absorbing species (such as TiO 2 , Fe 2 O 3 ) present in mineral aerosol was evinced (Ndour et al, 2009;Ponczek and George, 2018;Romanias et al, 2016;Donaldson, 2012, 2011) and reviewed (Chen et al, 2012;George et al, 2015;Usher et al, 2003). All these studies reveal a new and potentially important pathway of organic compounds processing in the atmosphere.…”

Natural sea-salt emissions moderate the climate forcing of anthropogenic nitrate

“…S2). The European anthropogenic emission inventories are provided by TNO (https://www.tno.nl, last access: 17 January 2020), from the AQMEII project (Air Quality Model Evaluation International Initiative) for PM 2.5 , PM 2.5-10 , NO x , SO 2 , CO, NH 3 and nonmethane volatile organic compounds (Pouliot et al, 2012;Chen et al, 2018b), and from the EUCAARI project (European Integrated project on Aerosol, Cloud, Climate, and Air Quality Interactions) for particulate organic carbon and elemental carbon (Kulmala et al, 2011). The inventories are with a spatial resolution of 1/8 • × 1/16 • longitude-latitude.…”