Periodic Reporting for period 4 - MAARvEL (A Missing Key Property in Atmospheric AeRosol ChEmistry: the Laplace Pressure)
Período documentado: 2024-07-01 hasta 2025-07-31
Despite their strong influence on climate, air quality, and human health, predicting the formation rates, concentrations, and spatial distributions of fine aerosols (≤ 2.5 μm) remains challenging. Current models largely describe particle growth through physical condensation and neglect chemical reactions within the condensed phase. A fundamental but unexplored property of nanoparticles is Laplace pressure: according to the Young–Laplace equation, internal pressures in the smallest particles can reach up to 1,000 times atmospheric pressure, conditions expected to substantially alter condensed-phase chemistry such as accretion and photochemistry. Understanding aerosol formation and evolution therefore requires characterizing chemical reactions under pressure conditions relevant to fine particles.
This project aims to identify and quantify condensed-phase chemical processes in atmospheric particles and to demonstrate the role of Laplace pressure in aerosol growth and evolution. Although aerosols from biogenic and anthropogenic sources are central to atmospheric chemistry, their detailed composition and governing physicochemical processes remain poorly constrained. Improving this understanding is essential for more accurate assessments of anthropogenic impacts on climate and air quality.
Scientific Questions
How does Laplace pressure influence condensed-phase chemical and photochemical reactions in atmospheric particles?
What are the implications of pressure-driven chemistry for aerosol growth and physicochemical properties?
Research Strategy
Chemical processes will be investigated in bulk solutions and nanoparticles using complementary mass spectrometry and microscopy techniques over five years. Initial screening will examine a wide range of (photo)chemical reactions as a function of pressure in bulk solutions corresponding to particle diameters of 5–80 nm, identifying reactions most relevant to nanoparticle chemistry. Because chemical composition affects surface tension, viscosity, and internal pressure, key reactions will also be studied in laboratory-generated particles, photochemical box models, global models, and atmospherically relevant aerosols. The impact of Laplace pressure–driven chemistry on aerosol growth and climate-relevant properties will be quantified throughout the project.
Analytical Approach
High-resolution Orbitrap mass spectrometry will be used to identify reaction products and develop chemical mechanisms. A novel extractive electrospray ionization (EESI) inlet enables real-time, highly sensitive (ng m⁻³) analysis of aerosol particles without sampling artifacts. Particle phase state and morphology will be characterized using environmental transmission electron microscopy (E-TEM) with 0.19 nm resolution. Together, these approaches will elucidate how Laplace pressure–driven chemistry controls aerosol composition, growth, and properties, advancing understanding of processes that govern air quality and climate-relevant aerosols.
This project aims to identify and quantify condensed-phase chemical processes in atmospheric particles and to demonstrate the role of Laplace pressure in aerosol growth and evolution. Although aerosols from biogenic and anthropogenic sources are central to atmospheric chemistry, their detailed composition and governing physicochemical processes remain poorly constrained. Improving this understanding is essential for more accurate assessments of anthropogenic impacts on climate and air quality.
Scientific Questions
How does Laplace pressure influence condensed-phase chemical and photochemical reactions in atmospheric particles?
What are the implications of pressure-driven chemistry for aerosol growth and physicochemical properties?
Research Strategy
Chemical processes will be investigated in bulk solutions and nanoparticles using complementary mass spectrometry and microscopy techniques over five years. Initial screening will examine a wide range of (photo)chemical reactions as a function of pressure in bulk solutions corresponding to particle diameters of 5–80 nm, identifying reactions most relevant to nanoparticle chemistry. Because chemical composition affects surface tension, viscosity, and internal pressure, key reactions will also be studied in laboratory-generated particles, photochemical box models, global models, and atmospherically relevant aerosols. The impact of Laplace pressure–driven chemistry on aerosol growth and climate-relevant properties will be quantified throughout the project.
Analytical Approach
High-resolution Orbitrap mass spectrometry will be used to identify reaction products and develop chemical mechanisms. A novel extractive electrospray ionization (EESI) inlet enables real-time, highly sensitive (ng m⁻³) analysis of aerosol particles without sampling artifacts. Particle phase state and morphology will be characterized using environmental transmission electron microscopy (E-TEM) with 0.19 nm resolution. Together, these approaches will elucidate how Laplace pressure–driven chemistry controls aerosol composition, growth, and properties, advancing understanding of processes that govern air quality and climate-relevant aerosols.
To assess whether atmospherically relevant chemical reactions are accelerated or inhibited by pressure, we performed a systematic screening of aerosol-phase chemistry. Solutions containing pairs of relevant reactants were exposed to pressures corresponding to aerosol diameters of 5–80 nm, enabling efficient identification of reactions influenced by Laplace pressure. All experiments followed protocols established in our preliminary glyoxal–ammonium sulfate studies.
In parallel, we developed a high-pressure reactor that enables real-time monitoring of reactant evolution via in situ UV–Vis absorbance at pressures from 1 to 1,000 bar and room temperature. The system combines a pressurization unit with an optical module for reaction monitoring under pressure. Using this approach, we investigated a broad range of atmospherically relevant reactions, including aldol and Baeyer–Villiger reactions, radical propagation, imidazole formation, esterification, decomposition, Diels–Alder reactions, and (photo)sensitized photochemistry. For each system, pressure-dependent kinetics, product distributions, and reaction mechanisms were characterized under atmospherically relevant conditions.
In parallel, we developed analytical capabilities to chemically characterize aerosol particles smaller than 100 nm using extractive electrospray ionization (EESI). EESI introduces analytes directly into a solvent spray, eliminating filter collection and minimizing fragmentation and thermal decomposition. Recent inlet optimization has significantly improved sensitivity (ng m⁻³) and time resolution (~1 Hz). To overcome limitations of prior EESI–TOF implementations, we developed a next-generation EESI source coupled to an Orbitrap mass spectrometer, enabling real-time, near-molecular-level aerosol characterization with detection limits of tens of ng m⁻³, linearity up to hundreds of μg m⁻³, and a time resolution of 0.2 Hz. System performance was validated using laboratory-generated secondary organic aerosol and ambient particle extracts, demonstrating robustness for resolving the composition of newly formed aerosols as a function of particle size and growth.
Finally, understanding aerosol growth requires simultaneous characterization of gas- and particle-phase composition to distinguish formation pathways. To this end, we conducted a 10-week laboratory campaign at the Paul Scherrer Institute, deploying multiple mass spectrometers (two Orbitraps and three time-of-flight instruments) to measure gaseous and particulate species in parallel. Monoterpenes and naphthalene were used as initial model precursors, followed by increasingly complex mixtures. Experiments were performed in a steady-state atmospheric simulation chamber with continuous reactant and oxidant input. Oxidation by ozone and/or OH radicals produced a wide range of oxygenated volatile compounds, driving particle formation under controlled temperature and humidity. Aerosol size and composition were resolved in time, providing a dynamic description of the processes governing aerosol formation and growth.
In parallel, we developed a high-pressure reactor that enables real-time monitoring of reactant evolution via in situ UV–Vis absorbance at pressures from 1 to 1,000 bar and room temperature. The system combines a pressurization unit with an optical module for reaction monitoring under pressure. Using this approach, we investigated a broad range of atmospherically relevant reactions, including aldol and Baeyer–Villiger reactions, radical propagation, imidazole formation, esterification, decomposition, Diels–Alder reactions, and (photo)sensitized photochemistry. For each system, pressure-dependent kinetics, product distributions, and reaction mechanisms were characterized under atmospherically relevant conditions.
In parallel, we developed analytical capabilities to chemically characterize aerosol particles smaller than 100 nm using extractive electrospray ionization (EESI). EESI introduces analytes directly into a solvent spray, eliminating filter collection and minimizing fragmentation and thermal decomposition. Recent inlet optimization has significantly improved sensitivity (ng m⁻³) and time resolution (~1 Hz). To overcome limitations of prior EESI–TOF implementations, we developed a next-generation EESI source coupled to an Orbitrap mass spectrometer, enabling real-time, near-molecular-level aerosol characterization with detection limits of tens of ng m⁻³, linearity up to hundreds of μg m⁻³, and a time resolution of 0.2 Hz. System performance was validated using laboratory-generated secondary organic aerosol and ambient particle extracts, demonstrating robustness for resolving the composition of newly formed aerosols as a function of particle size and growth.
Finally, understanding aerosol growth requires simultaneous characterization of gas- and particle-phase composition to distinguish formation pathways. To this end, we conducted a 10-week laboratory campaign at the Paul Scherrer Institute, deploying multiple mass spectrometers (two Orbitraps and three time-of-flight instruments) to measure gaseous and particulate species in parallel. Monoterpenes and naphthalene were used as initial model precursors, followed by increasingly complex mixtures. Experiments were performed in a steady-state atmospheric simulation chamber with continuous reactant and oxidant input. Oxidation by ozone and/or OH radicals produced a wide range of oxygenated volatile compounds, driving particle formation under controlled temperature and humidity. Aerosol size and composition were resolved in time, providing a dynamic description of the processes governing aerosol formation and growth.
Products, kinetics, and reaction mechanisms will be determined in nearly monodisperse aerosols as a function of particle size (i.e. pressure). This approach will allow us to (i) evaluate whether kinetics derived in the initial project phase apply to particle-phase chemistry; (ii) assess consistency between product distributions observed in aerosols and those measured in high-pressure reactors; (iii) identify size-dependent changes in chemical mechanisms; and (iv) quantify the broader implications of Laplace pressure–driven chemistry for atmospheric processes.
By systematically characterizing gas- and particle-phase species formed during precursor oxidation, we will (i) quantify how particle composition evolves with size; (ii) determine the contribution of chemical reactions to aerosol growth; and (iii) identify subsets of oxygenated volatile organic compounds (OVOCs) involved in particle-phase processes. These results are essential for improving representations of aerosol formation in atmospheric models. Clarifying the role of heterogeneous chemistry will establish when particle-phase processes—and thus Laplace pressure—must be explicitly included. The comprehensive dataset generated will substantially advance our ability to model aerosol growth and evolution.
By systematically characterizing gas- and particle-phase species formed during precursor oxidation, we will (i) quantify how particle composition evolves with size; (ii) determine the contribution of chemical reactions to aerosol growth; and (iii) identify subsets of oxygenated volatile organic compounds (OVOCs) involved in particle-phase processes. These results are essential for improving representations of aerosol formation in atmospheric models. Clarifying the role of heterogeneous chemistry will establish when particle-phase processes—and thus Laplace pressure—must be explicitly included. The comprehensive dataset generated will substantially advance our ability to model aerosol growth and evolution.