Periodic Reporting for period 2 - MAARvEL (A Missing Key Property in Atmospheric AeRosol ChEmistry: the Laplace Pressure)
Período documentado: 2021-07-01 hasta 2022-12-31
Despite the major impact of atmospheric particles on climate, air quality and human health, the atmospheric scientific community is currently unable to accurately predict formation rates, concentrations, and the spatial distribution of fine atmospheric aerosols (with aerodynamic diameter ≤ 2.5 μm). Current models typically rely on physical condensation processes to describe the growth and evolution of particles and completely neglect the chemical processes occurring within the condensed phase. Nevertheless, one of the fundamental physical properties of nanoparticles – the Laplace pressure – has never been studied by the atmospheric research community. Using the Young-Laplace equation, the pressure inside the smallest particles is estimated to be up to 1000 times higher than atmospheric pressure. High pressure is anticipated to significantly impact chemical processes in the condensed phase, such as accretion reactions. In order to correctly elucidate the processes directly impacting air quality and climate change, the chemical reactions have to be fully characterized at relevant pressure conditions, i.e. those found in fine particles. Hence, this project aims at characterizing these processes and demonstrating the importance of the Laplace pressure for the growth and evolution of fine atmospheric aerosols. As a result, this project will help to close knowledge gaps associated with the growth and evolution of atmospheric particles. A quantitative understanding of aerosol particlesfrom biogenic and anthropogenic emissions is of greatest importance. However, the precise components and physicochemical processes contributing to it, remain poorly understood. Improving our fundamental knowledge of the chemical and physical processes that govern atmospheric aerosol growth and evolution is critical to better quantification of anthropogenic climate change and impact on air quality.
The main scientific questions of this project are:
1. How does the Laplace pressure impact atmospheric condensed phase chemical reactions?
2. How does the Laplace pressure impact atmospheric condensed phase photochemical reactions?
3. What are the impacts for aerosol growth?
4. How do pressure-driven chemical processes alter aerosol physicochemical properties?
To answer these questions, the research strategy involves characterization of chemical processes occurring in simple bulk solutions and complex nanoparticles in order to demonstrate the role of Laplace pressure in atmospheric chemistry. Kinetics, product distribution, chemical mechanisms as well as physicochemical properties of particles will be determined using highly complementary mass spectrometry and microscope techniques. The proposed work is conceived as a five-year project. As a first step, a wide variety of (photo)chemical reactions will be characterized as the function of the pressure. Bulk solutions will be exposed to increasing pressures, corresponding to different aerosol diameters in the size range 5 - 80 nm. This work effectively serves as a screening process and will provide crucial information on the chemical reactions potentially important for atmospheric nanoparticle chemistry. As the chemical composition of the particle impacts physicochemical properties (i.e. surface tension, viscosity) and thus potentially the internal pressure, This project will need to go beyond simple bulk measurements. To this end, characterization of chemical reactions will be investigated using laboratory-generated particles and photochemical box-model/global models and atmospherically relevant particles. The impact of Laplace pressure-driven chemical processes on aerosol growth and climate-relevant particle properties will be characterized throughout the project. Chemical characterization will be achieved by using highly sensitive mass spectrometry techniques based on the Orbitrap technology. The very high mass resolution of the instrument will allow identification of complex reaction products and support chemical mechanism development. In addition, we are using an extractive electrospray ionization (EESI) inlet coupled to an Orbitrap. This novel analytical technique has never been implemented before on a high-resolution mass spectrometer. In collaboration with colleagues at the Paul Scherrer Institute in Switzerland, we am currently developing this new interface that allows real time characterization atmospheric particle, with extremely high sensitivity (ng m-3) and without any sampling artefacts. The phase and morphology of the particles will be investigated using an environmental transmission electron microscope (E-TEM) having a resolution of 0.19 nm and able to characterize nanometer-sized particles.
The main scientific questions of this project are:
1. How does the Laplace pressure impact atmospheric condensed phase chemical reactions?
2. How does the Laplace pressure impact atmospheric condensed phase photochemical reactions?
3. What are the impacts for aerosol growth?
4. How do pressure-driven chemical processes alter aerosol physicochemical properties?
To answer these questions, the research strategy involves characterization of chemical processes occurring in simple bulk solutions and complex nanoparticles in order to demonstrate the role of Laplace pressure in atmospheric chemistry. Kinetics, product distribution, chemical mechanisms as well as physicochemical properties of particles will be determined using highly complementary mass spectrometry and microscope techniques. The proposed work is conceived as a five-year project. As a first step, a wide variety of (photo)chemical reactions will be characterized as the function of the pressure. Bulk solutions will be exposed to increasing pressures, corresponding to different aerosol diameters in the size range 5 - 80 nm. This work effectively serves as a screening process and will provide crucial information on the chemical reactions potentially important for atmospheric nanoparticle chemistry. As the chemical composition of the particle impacts physicochemical properties (i.e. surface tension, viscosity) and thus potentially the internal pressure, This project will need to go beyond simple bulk measurements. To this end, characterization of chemical reactions will be investigated using laboratory-generated particles and photochemical box-model/global models and atmospherically relevant particles. The impact of Laplace pressure-driven chemical processes on aerosol growth and climate-relevant particle properties will be characterized throughout the project. Chemical characterization will be achieved by using highly sensitive mass spectrometry techniques based on the Orbitrap technology. The very high mass resolution of the instrument will allow identification of complex reaction products and support chemical mechanism development. In addition, we are using an extractive electrospray ionization (EESI) inlet coupled to an Orbitrap. This novel analytical technique has never been implemented before on a high-resolution mass spectrometer. In collaboration with colleagues at the Paul Scherrer Institute in Switzerland, we am currently developing this new interface that allows real time characterization atmospheric particle, with extremely high sensitivity (ng m-3) and without any sampling artefacts. The phase and morphology of the particles will be investigated using an environmental transmission electron microscope (E-TEM) having a resolution of 0.19 nm and able to characterize nanometer-sized particles.
To determine whether atmospherically relevant reactions are slowed down or accelerated by the pressure, systematic characterization of chemical reactions relevant for aerosol chemistry must be performed. Hence we tested a wide screening of the extensive variety of reactions possibly occurring within nanometre-sized aerosols. In order to do so, we combined solutions of two atmospherically relevant reactants, and expose the mixture to increasing pressures corresponding to different aerosol diameters (between 5 and 80 nm). This was sufficient for mapping out the wide range of reactions potentially influenced by the Laplace pressure. For these experiments we followed the same protocol that was successfully used in our preliminary studies on the reaction of glyoxal and ammonium sulphate in solution. In addition we developed a new experimental device to directly monitor the evolution of reactants in real time. This high pressure reactor vessel allows in-situ UV/Vis characterization of the absorbance of the chemical compounds at various pressures (i.e. 1 to 1000 bar) at room temperature. Briefly, it is constituted of two parts: the unit used to pressurize the liquid, and the second unit to monitor the chemical reactions under pressure. Using these complementary approaches, we have explored a wide variety of chemical reactions including aldol reactions, radical propagation, Baeyer-Villiger reactions, iomidazole formation, esterification, decompoosition, diels alder reactions, and photochemical processes (i.e. photosensitized reactions). Hence we were able to characterize the product formation, kinetics and mechanisms as the function of the pressure for atmospheric relevant conditions.
Meanwhile analytical developments were made to be able to chemically characterize aerosol particles below 100 nm in diameter. The extractive electrospray (EESI) operates by introducing the analyte directly into the solvent spray, thus eliminating the need for collection on a filter. Electrospray (ESI) based ionization is commonly used in mass spectrometry. It is an ambient pressure, soft ionization technique avoiding thermal decomposition of the analyte and produces minimal fragmentation. Although this technique has been previously used in atmospheric chemistry and in other fields of chemistry, the geometry of the inlet has been recently greatly optimized providing an unrivalled sensitivity (i.e. ng m-3). Despite the low detection limit and the high time resolution (∼1 Hz) of the EESI, it was coupled only to TOF mass analyzer that is suitable for atmospheric research. However the mass resolving power remained limited for an accurate identification of the compounds forming aerosol particles. As a result we developed a new generation of EESI source to be coupled with an Orbitrap mass spectrometer. The combination of the soft ionization capability of the EESI and the ultrahigh mass resolution of Orbitrap allowed for real time, near-molecular characterization of organic aerosol. Detection limits as low as a ten of ng m-3 with linearity up to hundreds of μg m-3 at 0.2 Hz time resolution were observed for single and mixed component calibrations. The EESI-Orbitrap system performance was further evaluated with laboratory generated SOA and filter extracts of ambient particulate matter. The performance and stability of the EESI-Orbitrap are now sufficient enough to characterize the chemical composition of newly formed aerosol as a function of the size and aerosol growth.
To resolve how aerosols grow, we must achieve a complete understanding of the chemical composition of both the gas and the particle phases. Indeed, we have to characterize the gas-to-particle conversion in order to distinguish whether the products are formed in gas or particle phases. To do so, we performed an intensive, 10 weeks, laboratory campaign at the Paul Scherrer Institute (Switzerland) where we deployed a wide variety of mass spectrometers including 2 Orbitrap and 3 time-of-flight mass analysers to characterize and quantify the gaseous and particulate phases. Firstly monoterpenes and naphthalene were used as model compounds for the generation of organic aerosol, then more complex mixture were generated by mixing precursors. Experiments were performed using an atmospheric simulation chamber operated in steady-state conditions; meaning that a constant flow of reactants and oxidants will continuously be added to the chamber. Oxidation of these VOCs by ozone and/or OH radicals will lead to the formation of a wide variety of (highly) oxygenated volatile compounds allowing the generation of particles under various experimental conditions (T and RH). Aerosol particles were size- and time resolved characterized in order to provide an unique description of the dynamic of the processes leading to the formation of aerosol particles.
Meanwhile analytical developments were made to be able to chemically characterize aerosol particles below 100 nm in diameter. The extractive electrospray (EESI) operates by introducing the analyte directly into the solvent spray, thus eliminating the need for collection on a filter. Electrospray (ESI) based ionization is commonly used in mass spectrometry. It is an ambient pressure, soft ionization technique avoiding thermal decomposition of the analyte and produces minimal fragmentation. Although this technique has been previously used in atmospheric chemistry and in other fields of chemistry, the geometry of the inlet has been recently greatly optimized providing an unrivalled sensitivity (i.e. ng m-3). Despite the low detection limit and the high time resolution (∼1 Hz) of the EESI, it was coupled only to TOF mass analyzer that is suitable for atmospheric research. However the mass resolving power remained limited for an accurate identification of the compounds forming aerosol particles. As a result we developed a new generation of EESI source to be coupled with an Orbitrap mass spectrometer. The combination of the soft ionization capability of the EESI and the ultrahigh mass resolution of Orbitrap allowed for real time, near-molecular characterization of organic aerosol. Detection limits as low as a ten of ng m-3 with linearity up to hundreds of μg m-3 at 0.2 Hz time resolution were observed for single and mixed component calibrations. The EESI-Orbitrap system performance was further evaluated with laboratory generated SOA and filter extracts of ambient particulate matter. The performance and stability of the EESI-Orbitrap are now sufficient enough to characterize the chemical composition of newly formed aerosol as a function of the size and aerosol growth.
To resolve how aerosols grow, we must achieve a complete understanding of the chemical composition of both the gas and the particle phases. Indeed, we have to characterize the gas-to-particle conversion in order to distinguish whether the products are formed in gas or particle phases. To do so, we performed an intensive, 10 weeks, laboratory campaign at the Paul Scherrer Institute (Switzerland) where we deployed a wide variety of mass spectrometers including 2 Orbitrap and 3 time-of-flight mass analysers to characterize and quantify the gaseous and particulate phases. Firstly monoterpenes and naphthalene were used as model compounds for the generation of organic aerosol, then more complex mixture were generated by mixing precursors. Experiments were performed using an atmospheric simulation chamber operated in steady-state conditions; meaning that a constant flow of reactants and oxidants will continuously be added to the chamber. Oxidation of these VOCs by ozone and/or OH radicals will lead to the formation of a wide variety of (highly) oxygenated volatile compounds allowing the generation of particles under various experimental conditions (T and RH). Aerosol particles were size- and time resolved characterized in order to provide an unique description of the dynamic of the processes leading to the formation of aerosol particles.
Products, kinetics and chemical mechanisms will be determined in nearly-monodisperse aerosols as a function of particle size (i.e. pressure). Consequently, we will be able to (i) evaluate if the kinetics obtained in the initial part of the project can be extrapolated to particle phase chemistry; (ii) determine if the product distribution is similar with the ones obtained using the high pressure reactor vessel; (iii) describe changes in chemical mechanism as a function of the size; (iv) evaluate the global implication of chemical reactions driven by the Laplace pressure in atmospheric chemistry.
By systematically characterizing gas and particle phase species, formed from the oxidation of a various precursors, we will be able to (i) characterize how the particle phase composition changes as a function of the size; (ii) determine to what extent chemical reactions contribute to aerosol growth; and (iii) determine which subset of OVOC are involved in particle phase processes. The attempted results are critical for an accurate model implementation of aerosol formation. Resolving the role of heterogeneous reactions will determine to what extent particle processes, and thus the Laplace pressure, have to be accounted for in atmospheric models. The comprehensive experimental data related to aerosol growth will bring about a monumental leap forward in our ability to model these processes.
By systematically characterizing gas and particle phase species, formed from the oxidation of a various precursors, we will be able to (i) characterize how the particle phase composition changes as a function of the size; (ii) determine to what extent chemical reactions contribute to aerosol growth; and (iii) determine which subset of OVOC are involved in particle phase processes. The attempted results are critical for an accurate model implementation of aerosol formation. Resolving the role of heterogeneous reactions will determine to what extent particle processes, and thus the Laplace pressure, have to be accounted for in atmospheric models. The comprehensive experimental data related to aerosol growth will bring about a monumental leap forward in our ability to model these processes.