Manabu Shiraiwa

Gas uptake and chemical aging of semisolid organic aerosol particles.

Organic substances can adopt an amorphous solid or semisolid state, influencing the rate of heterogeneous reactions and multiphase processes in atmospheric aerosols. Here we demonstrate how molecular diffusion in the condensed phase affects the gas uptake and chemical transformation of semisolid organic particles. Flow tube experiments show that the ozone uptake and oxidative aging of amorphous protein is kinetically limited by bulk diffusion. The reactive gas uptake exhibits a pronounced increase with relative humidity, which can be explained by a decrease of viscosity and increase of diffusivity due to hygroscopic water uptake transforming the amorphous organic matrix from a glassy to a semisolid state (moisture-induced phase transition). The reaction rate depends on the condensed phase diffusion coefficients of both the oxidant and the organic reactant molecules, which can be described by a kinetic multilayer flux model but not by the traditional resistor model approach of multiphase chemistry. The chemical lifetime of reactive compounds in atmospheric particles can increase from seconds to days as the rate of diffusion in semisolid phases can decrease by multiple orders of magnitude in response to low temperature or low relative humidity. The findings demonstrate that the occurrence and properties of amorphous semisolid phases challenge traditional views and require advanced formalisms for the description of organic particle formation and transformation in atmospheric models of aerosol effects on air quality, public health, and climate.

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

Multiphase Chemistry at the Atmosphere–Biosphere Interface Influencing Climate and Public Health in the Anthropocene

This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. Review pubs.acs.org/CR Multiphase Chemistry at the Atmosphere−Biosphere Interface Influencing Climate and Public Health in the Anthropocene Ulrich Po schl* and Manabu Shiraiwa* Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany air contaminants (SHCC) and their multiphase chemical interactions at the atmosphere−biosphere interface, including human lungs and skin, plant leaves, cryptogamic covers, soil, and aquatic surfaces. After an overview of different groups of SHCC, we address the chemical interactions of reactive oxygen species and reactive nitrogen species (ROS, RNS), primary biological and secondary organic aerosols (PBA, SOA), as well as carbonaceous combustion aerosols (CCA) including soot, black/elemental carbon, polycyclic aromatic hydrocarbons, and related compounds (PAH, PAC). ROS and RNS interact strongly with other SHCC and are central to both atmospheric and physiological processes and their coupling through the atmosphere−biosphere interface, for example, in the formation and aging of biogenic and combustion aerosols as well as in CONTENTS inflammatory and allergic immune responses triggered by air pollution. Deposition of atmospheric ROS/RNS and aerosols 1. Introduction and Motivation can damage biological tissues, modify surface microbiomes, and 2. Health- and Climate-Relevant Air Contaminants induce oxidative stress through Fenton-like reactions and 2.1. Reactive Oxygen and Nitrogen Species immune responses. The chemical mechanisms and kinetics are 2.2. Primary Biological Aerosols not yet fully elucidated, but the available evidence suggests that 2.3. Secondary Organic Aerosols multiphase processes are crucial for the assessment, prediction, 2.4. Carbonaceous Combustion Aerosols and handling of air quality, climate, and public health. Caution 2.5. Other Air Contaminants Linking Atmospher- should be taken to avoid that human activities shaping the ic and Physiological Chemistry Anthropocene create a hazardous or pathogenic atmosphere 3. Multiphase Chemical Reactions at Specific Bio- overloaded with allergenic, corrosive, toxic, or infectious logical Interfaces contaminants. 3.1. Lung Lining Fluid Multiphase chemistry deals with chemical reactions, trans- 3.2. Human Skin port processes, and transformations between gaseous, liquid, 3.3. Plant Surfaces and Cryptogamic Covers and solid matter. These processes are essential for Earth system 3.4. Soil and Aquatic Surfaces science and climate research as well as for life and health 4. Conclusions and Outlook sciences on molecular and global levels, bridging a wide range Author Information of spatial and temporal scales from below nanometers to Corresponding Authors thousands of kilometers and from less than nanoseconds to Notes years and millennia as illustrated in Figure 1. Biographies From a chemical perspective, life and the metabolism of most Acknowledgments living organisms can be regarded as multiphase processes References involving gases like oxygen and carbon dioxide; liquids like water, blood, lymph, and plant sap; and solid or semisolid substances like bone, tissue, skin, wood, and cellular 1. INTRODUCTION AND MOTIVATION membranes. Even primitive forms of life and metabolic activity Multiphase chemistry plays a vital role in the Earth system, under anaerobic conditions generally involve multiple liquid climate, and health. Chemical reactions, mass transport, and and solid or semisolid phases structured by cells, organelles, and phase transitions between gases, liquids, and solids are essential membranes. 2 On global scales, the biogeochemical cycling of for the interaction and coevolution of life and climate. chemical compounds and elements, which can be regarded as Knowledge of the mechanisms and kinetics of these processes the metabolism of planet Earth, also involves chemical is also required to address societally relevant questions of global reactions, mass transport, and phase transitions within and environmental change and public health in the Anthropocene, that is, in the present era of globally pervasive and steeply Special Issue: 2015 Chemistry in Climate increasing human influence on planet Earth. 1 In this work, we review the current scientific understanding and recent advances Received: September 1, 2014 in the investigation of short-lived health- and climate-relevant Published: April 9, 2015

The role of long-lived reactive oxygen intermediates in the reaction of ozone with aerosol particles

The heterogeneous reactions of O₃ with aerosol particles are of central importance to air quality. They are studied extensively, but the molecular mechanisms and kinetics remain unresolved. Based on new experimental data and calculations, we show that long-lived reactive oxygen intermediates (ROIs) are formed. The chemical lifetime of these intermediates exceeds 100 seconds, which is much longer than the surface residence time of molecular O₃ (~10⁻⁹ s). The ROIs explain and resolve apparent discrepancies between earlier quantum mechanical calculations and kinetic experiments. They play a key role in the chemical transformation and adverse health effects of toxic and allergenic air-particulate matter, such as soot, polycyclic aromatic hydrocarbons and proteins. ROIs may also be involved in the decomposition of O₃ on mineral dust and in the formation and growth of secondary organic aerosols. Moreover, ROIs may contribute to the coupling of atmospheric and biospheric multiphase processes.

Equilibration timescale of atmospheric secondary organic aerosol partitioning

[1] Secondary organic aerosol (SOA) formed from partitioning of oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs) accounts for a substantial portion of atmospheric particulate matter. In describing SOA formation, it is generally assumed that VOC oxidation products rapidly adopt gas-aerosol equilibrium. Here we estimate the equilibration timescale, τ_(eq), of SOA gas-particle partitioning using a state-of-the-art kinetic flux model. Τ_(eq) is found to be of order seconds to minutes for partitioning of relatively high volatility organic compounds into liquid particles, thereby adhering to equilibrium gas-particle partitioning. However, τ_(eq) increases to hours or days for organic aerosol associated with semi-solid particles, low volatility, large particle size, and low mass loadings. Instantaneous equilibrium partitioning may lead to substantial overestimation of particle mass concentration and underestimation of gas-phase concentration.

Biogenic Potassium Salt Particles as Seeds for Secondary Organic Aerosol in the Amazon

Salty Origins of Fresh Water Cloud droplets above the Amazonian rain forest form mostly around organic aerosols, but the source of the aerosols has been a mystery. Pöhlker et al. (p. 1075) report that particles rich in potassium salts emitted by Amazonian vegetation can act as the seeds for the growth of organic aerosol particles that function as condensation nuclei for water droplets. These specks of biogenic salts provide a surface for the condensation of low- or semi-volatile organic compounds formed by the atmospheric oxidation of isoprene and terpenes, molecules produced in great abundance by many kinds of Amazonian plants. Potassium salt particles account for the previously mysterious initiation sites of aerosol growth above the Amazonian rainforest. The fine particles serving as cloud condensation nuclei in pristine Amazonian rainforest air consist mostly of secondary organic aerosol. Their origin is enigmatic, however, because new particle formation in the atmosphere is not observed. Here, we show that the growth of organic aerosol particles can be initiated by potassium-salt–rich particles emitted by biota in the rainforest. These particles act as seeds for the condensation of low- or semi-volatile organic compounds from the atmospheric gas phase or multiphase oxidation of isoprene and terpenes. Our findings suggest that the primary emission of biogenic salt particles directly influences the number concentration of cloud condensation nuclei and affects the microphysics of cloud formation and precipitation over the rainforest.

Amplification of Light Absorption of Black Carbon by Organic Coating

Photo-absorption by black carbon (BC) aerosol is believed to be enhanced by the internal mixing of BC with volatile compounds. We investigate this effect quantitatively with laboratory experiments. Graphite particles are used as a surrogate for BC, with coatings of oleic acid and glycerol. The photo-absorption of coated graphite with known shell and core diameters are directly measured by a photo-acoustic technique. The size distribution and coating thickness are quantified using a single-particle soot photometer (SP2). The absorption is amplified by ∼30% even with a small coating thickness (shell/core diameter ratio (D p/D c) = 1.2). The amplification reaches as high as 2 at D p/D c = 2. We calculate the amplification of the absorption using a shell/core model of Mie theory. The model generally reproduces the measured amplification well.

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation

Organic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs). Typical experimental measurements of SOA formation include total SOA mass and atomic oxygen-to-carbon ratio. These measurements, alone, are generally insufficient to reveal the extent to which condensed-phase reactions occur in conjunction with the multigeneration gas-phase photooxidation. Combining laboratory chamber experiments and kinetic gas-particle modeling for the dodecane SOA system, here we show that the presence of particle-phase chemistry is reflected in the evolution of the SOA size distribution as well as its mass concentration. Particle-phase reactions are predicted to occur mainly at the particle surface, and the reaction products contribute more than half of the SOA mass. Chamber photooxidation with a midexperiment aldehyde injection confirms that heterogeneous reaction of aldehydes with organic hydroperoxides forming peroxyhemiacetals can lead to a large increase in SOA mass. Although experiments need to be conducted with other SOA precursor hydrocarbons, current results demonstrate coupling between particle-phase chemistry and size distribution dynamics in the formation of SOAs, thereby opening up an avenue for analysis of the SOA formation process.

Kinetic limitations in gas-particle reactions arising from slow diffusion in secondary organic aerosol

The potential for aerosol physical properties, such as phase, morphology and viscosity/ diffusivity, to affect particle reactivity remains highly uncertain. We report here a study of the effect of bulk diffusivity of polycyclic aromatic hydrocarbons (PAHs) in secondary organic aerosol (SOA) on the kinetics of the heterogeneous reaction of particle-borne benzo[a]pyrene (BaP) with ozone. The experiments were performed by coating BaP-ammonium sulfate particles with multilayers of SOA formed from ozonolysis of alpha-pinene, and by subsequently investigating the kinetics of BaP loss via reaction with excess ozone using an aerosol flow tube coupled to an Aerodyne Aerosol Mass Spectrometer (AMS). All reactions exhibit pseudo-first order kinetics and are empirically well described by a Langmuir-Hinshelwood (L-H) mechanism. The results show that under dry conditions (RH < 5%) diffusion through the SOA coating can lead to significant mass transfer constraints on the kinetics, with behavior between that previously observed by our group for solid and liquid organic coats. The reactivity of BaP was enhanced at -50% relative humidity (RH) suggesting that water uptake lowers the viscosity of the SOA, hence lifting the mass transfer constraint to some degree. The kinetics for -70% RH were similar to results obtained without SOA coats, indicating that the SOA had sufficiently low viscosity and was sufficiently liquid-like that reactants could rapidly diffuse through the coat. A kinetic multi-layer model for aerosol surface and bulk chemistry was applied to simulate the kinetics, yielding estimates for the diffusion coefficients (in cm2 s(-1)) for BaP in alpha-pinene SOA of 2 x 10(-14), 8 x 10(-14) and > 1 x 10(-12) for dry (RH < 5%), 50% RH and 70% RH conditions, respectively. These results clearly indicate that slow diffusion of reactants through SOA coats under specific conditions can provide shielding from gas-phase oxidants, enabling the long-range atmospheric transport of toxic trace species, such as PAHs and persistent organic pollutants.

Hazardous components and health effects of atmospheric aerosol particles: reactive oxygen species, soot, polycyclic aromatic compounds and allergenic proteins

Abstract This review outlines recent advances in the investigation of the chemical properties, molecular interactions and health effects of hazardous compounds in atmospheric aerosols, in particular reactive oxygen species (ROS), soot, polycyclic aromatic compounds (PACs) and allergenic proteins. Epidemiological studies show correlations between air particulate matter and adverse health effects of air pollution including allergy, asthma, cardiovascular and respiratory diseases, but the causative relations and mechanisms of interaction on the molecular level are still unclear. ROS generated by photochemical and heterogeneous reactions in the atmosphere seem to play a key role in aerosol health effects and provide a direct link between atmospheric and physiological multiphase processes. Soot and PACs can trigger formation of ROS in vivo, leading to inflammation and cellular damage. PACs as well as allergenic proteins are efficiently oxygenated and nitrated upon exposure to ozone and nitrogen dioxide, which leads to an enhancement of their toxicity and allergenicity.