Reactive oxygen species formed in aqueous mixtures of secondary organic aerosols and mineral dust influencing cloud chemistry and public health in the Anthropocene.

Haijie Tong,Andrea M Arangio,Christopher J Kampf,Pascale S J Lakey,Joanna Socorro,Manabu Shiraiwa,Thomas Berkemeier,William H Brune,Ulrich Pöschl

doi:10.1039/c7fd00023e

Abstract

Mineral dust and secondary organic aerosols (SOA) account for a major fraction of atmospheric particulate matter, affecting climate, air quality and public health. How mineral dust interacts with SOA to influence cloud chemistry and public health, however, is not well understood. Here, we investigated the formation of reactive oxygen species (ROS), which are key species of atmospheric and physiological chemistry, in aqueous mixtures of SOA and mineral dust by applying electron paramagnetic resonance (EPR) spectrometry in combination with a spin-trapping technique, liquid chromatography-tandem mass spectrometry (LC-MS/MS), and a kinetic model. We found that substantial amounts of ROS including OH, superoxide as well as carbon- and oxygen-centred organic radicals can be formed in aqueous mixtures of isoprene, α-pinene, naphthalene SOA and various kinds of mineral dust (ripidolite, montmorillonite, kaolinite, palygorskite, and Saharan dust). The molar yields of total radicals were ∼0.02-0.5% at 295 K, which showed higher values at 310 K, upon 254 nm UV exposure, and under low pH (<3) conditions. ROS formation can be explained by the decomposition of organic hydroperoxides, which are a prominent fraction of SOA, through interactions with water and Fenton-like reactions with dissolved transition metal ions. Our findings imply that the chemical reactivity and aging of SOA particles can be enhanced upon interaction with mineral dust in deliquesced particles or cloud/fog droplets. SOA decomposition could be comparably important to the classical Fenton reaction of H2O2 with Fe2+ and that SOA can be the main source of OH radicals in aqueous droplets at low concentrations of H2O2 and Fe2+. In the human respiratory tract, the inhalation and deposition of SOA and mineral dust can also lead to the release of ROS, which may contribute to oxidative stress and play an important role in the adverse health effects of atmospheric aerosols in the Anthropocene.

Highlights

Atmospheric particulate matter suspended in the air can strongly affect climate and public health.[1,2] Their diameters (Dp) vary from nanometers to tens of micrometers, and they are generally categorized into coarse (Dp > 2.5 mm), ne (Dp < 2.5 mm), and ultra ne (Dp < 0.1 mm) particles
During long-range transport, dust can be internally mixed with secondary organic aerosols (SOA) by coagulation and condensation
SOA coatings may contain a substantial fraction of highly oxidized multifunctional organic compounds (HOM) and extremely low volatility compounds (ELVOC)

Summary

Introduction

Atmospheric particulate matter suspended in the air can strongly affect climate and public health.[1,2] Their diameters (Dp) vary from nanometers to tens of micrometers, and they are generally categorized into coarse (Dp > 2.5 mm), ne (Dp < 2.5 mm), and ultra ne (Dp < 0.1 mm) particles. Ambient aerosol particles consisting of inorganic and organic compounds can be emitted both from natural and anthropogenic sources Coarse particles such as mineral dust and sea salts are injected into the troposphere by direct emission.[3] Gaseous volatile organic compounds emitted by vegetation and anthropogenic activities can be oxidised to generate semi-volatile and low volatility products, which can form ultra ne and ne secondary organic aerosols (SOA) by nucleation and gas-to-particle partitioning.[4,5,6]. They can in uence the global radiation budget via scattering and absorption of solar and terrestrial radiation.[8,9] In addition, they can act as cloud condensation or ice nuclei upon interaction with water molecules.[10,11,12,13] During long-range transport, heterogeneous and multiphase chemistry on mineral dust particles may alter their physical and chemical properties and dust may become internally mixed with SOA by coagulation and condensation.[14,15,16,17,18] With respect to health effects, inhalation and deposition of mineral dust into the respiratory tract may cause a broad range of pulmonary, cardio-vascular and occupational lung diseases.[19,20,21,22,23]

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Conclusion