A5052025683- Atmospheric chemistry and aerosols
- Atmospheric Ozone and Climate
- Air Quality and Health Impacts
- Atmospheric and Environmental Gas Dynamics
- Air Quality Monitoring and Forecasting
- Spectroscopy and Laser Applications
- Atmospheric aerosols and clouds
- Chemical Thermodynamics and Molecular Structure
- Advanced Chemical Physics Studies
- Catalytic Processes in Materials Science
- Mass Spectrometry Techniques and Applications
- Advanced Chemical Sensor Technologies
- Vehicle emissions and performance
- Analytical Chemistry and Chromatography
- Methane Hydrates and Related Phenomena
- Analytical chemistry methods development
- Indoor Air Quality and Microbial Exposure
- Water Quality Monitoring and Analysis
- Fire effects on ecosystems
- Toxic Organic Pollutants Impact
- Free Radicals and Antioxidants
- Phase Equilibria and Thermodynamics
- Wind and Air Flow Studies
- Catalysis and Oxidation Reactions
- Plant responses to elevated CO2
Jet Propulsion Laboratory
2017-2025
University of Manchester
2014-2024
California Institute of Technology
2018-2024
National Aeronautics and Space Administration
2023
Institute of Atmospheric Physics
2022
Chinese Academy of Sciences
2022
Max Planck Institute for Chemistry
2022
Guangzhou Institute of Geochemistry
2022
King Abdulaziz University
2022
National Centre for Atmospheric Science
2012-2021
Ozonolysis is a major tropospheric removal mechanism for unsaturated hydrocarbons and proceeds via "Criegee intermediates"--carbonyl oxides--that play key role in oxidation models. However, until recently no gas-phase Criegee intermediate had been observed, indirect determinations of their reaction kinetics gave derived rate coefficients spanning orders magnitude. Here, we report direct photoionization mass spectrometric detection formaldehyde oxide (CH(2)OO) as product the CH(2)I with O(2)....
Although carbonyl oxides, "Criegee intermediates," have long been implicated in tropospheric oxidation, there few direct measurements of their kinetics, and only for the simplest compound class, CH2OO. Here, we report production reaction kinetics next larger Criegee intermediate, CH3CHOO. Moreover, independently probed two distinct CH3CHOO conformers, syn- anti-, both which react readily with SO2 NO2. We demonstrate that anti-CH3CHOO is substantially more reactive toward water than...
Abstract. Eleven instruments for the measurement of ambient concentrations atmospheric ammonia gas (NH3), based on eight different methods were inter-compared above an intensively managed agricultural field in late summer 2008 Southern Scotland. To test over a wide range concentrations, was fertilised with urea midway through experiment, leading to increase average concentration from 10 100 ppbv. The deployed included three wet-chemistry systems, one offline analysis (annular rotating batch...
The chemistry of carbonyl oxides, known as Criegee intermediates, is central to many aspects tropospheric chemistry. For decades it has been that these reactive species, whose electronic structure contains zwitterionic and biradical character, are formed in the ozonolysis alkenes. However only recently direct measurements their reaction kinetics have become possible. In this perspective we describe most recent progress understanding reactivity historically elusive molecules, explore...
Rate coefficients are directly determined for the reactions of Criegee intermediates (CI) CH2 OO and CH3 CHOO with two simplest carboxylic acids, formic acid (HCOOH) acetic (CH3 COOH), employing complementary techniques: multiplexed photoionization mass spectrometry cavity-enhanced broadband ultraviolet absorption spectroscopy. The measured rate in excess 1×10(-10) cm(3) s(-1) , several orders magnitude larger than those suggested from many previous alkene ozonolysis experiments assumed...
Criegee intermediates (CIs), carbonyl oxides formed in ozonolysis of alkenes, play key roles the troposphere. The decomposition CIs can be a significant source OH to tropospheric oxidation cycle especially during nighttime and winter months. A variety model-measurement studies have estimated surface-level stabilized intermediate (sCI) concentrations on order 1 × 104 cm-3 105 cm-3, which makes non-negligible contribution oxidising capacity terrestrial boundary layer. reactions sCI with water...
Abstract Aircraft and satellite observations indicate the presence of ppt (ppt ≡ pmol/mol) levels BrO in free troposphere with important implications for tropospheric budgets ozone, OH, mercury. We can reproduce these GEOS‐Chem global chemistry model by including a broader consideration multiphase halogen (Br‐Cl) than has been done past. Important reactions regenerating from its nonradical reservoirs include HOBr + Br − /Cl both aerosols clouds, oxidation ClNO 3 ozone. Most is troposphere,...
Abstract. Recent studies have recognised highly oxygenated organic molecules (HOMs) in the atmosphere as important formation of secondary aerosol (SOA). A large number focused on HOM from oxidation biogenically emitted monoterpenes. However, anthropogenic vapours has so far received much less attention. Previous identified importance aromatic volatile compounds (VOCs) for SOA formation. In this study, we investigated several compounds, benzene (C6H6), toluene (C7H8), and naphthalene (C10H8),...
Abstract. We present an updated mechanism for tropospheric halogen (Cl + Br I) chemistry in the GEOS-Chem global atmospheric chemical transport model and apply it to investigate radical cycling implications oxidants. Improved representation of HOBr heterogeneous its pH dependence our simulation leads less efficient recycling mobilization bromine radicals enables include mechanistic sea salt aerosol debromination without generating excessive BrO. The resulting mean BrO mixing ratio is 0.19...
Abstract. Measurements of OH, HO2, complex RO2 (alkene- and aromatic-related RO2) total radicals taken during the integrated Study AIR Pollution PROcesses in Beijing (AIRPRO) campaign central summer 2017, alongside observations OH reactivity, are presented. The concentrations were elevated, with reaching up to 2.8×107moleculecm-3, HO2 peaking at 1×109moleculecm-3 concentration 5.5×109moleculecm-3. reactivity (k(OH)) peaked 89 s−1 night, a minimum afternoon ≈22s-1 on average. An experimental...
Carbonyl oxide species play a key role in tropospheric oxidation of organic molecules and low-temperature combustion processes. In the late 1940s, Criegee first postulated participation carbonyl oxides, now often called "Criegee intermediates," ozonolysis alkenes. However, despite decades effort, no gas phase intermediate has before been observed. As result, knowledge reactions heretofore inferred by indirect means, with derived rate coefficients spanning orders magnitude. We have directly...
Criegee biradicals, i.e., carbonyl oxides, are critical intermediates in ozonolysis and have been implicated autoignition chemistry other hydrocarbon oxidation systems, but until recently the direct measurement of their gas-phase kinetics has not feasible. Indirect determinations intermediate often rely on introduction a scavenger molecule into an system analysis effects yields products associated with reactions. Carbonyl species, particular hexafluoroacetone (CF(3)COCF(3)), used as...
Laboratory studies of atmospheric chemistry characterize the nature atmospherically relevant processes down to molecular level, providing fundamental information used assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor quality, and stratospheric ozone depletion. have a central role in addressing incomplete knowledge chemistry. This article highlights evolving science needs for this community emphasizes our is far...
Food-cooking organic aerosols (COA) are one of the primary sources submicron particulate matter in urban environments. However, there still many questions surrounding source apportionment related to instrumentation as well semivolatile partitioning because COA evolve rapidly ambient air, making more complex. Online measurements emissions from cooking different types food were performed a laboratory characterize particles and gases. Aerosol mass spectrometer (AMS) showed that relative...
This paper describes the development of a new sampling and measurement method to infer methane flux using proxy measurements CO2 concentration wind data recorded by Unmanned Aerial Systems (UAS). The described trialed here is appropriate spatial scale landfill sites analogous greenhouse gas emission hotspots, making it an important for low-cost rapid case study quantification fluxes from currently uncertain (but highly important) sources. We present these UAS-based derive instantaneous test...
A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary (SOA). Isoprene (IP) and monoterpenes (MT) most important precursors SOA originating forests. The climate impacts OA currently estimated through parameterizations water uptake drastically simplify complexity OA. We combine laboratory experiments, thermodynamic modeling, field observations, modeling (1) explain molecular mechanisms behind RH-dependent...
Abstract. The Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) programme is an international collaborative project focusing on understanding the sources, processes health effects of air pollution Beijing megacity. APHH-Beijing brings together leading China UK research groups, state-of-the-art infrastructure quality models to work four themes: (1) sources emissions pollutants; (2) atmospheric affecting urban pollution; (3) exposure impacts; (4) interventions...
Abstract Air quality and heat are strong health drivers, their accurate assessment forecast important in densely populated urban areas. However, the sources processes leading to high concentrations of main pollutants, such as ozone, nitrogen dioxide, fine coarse particulate matter, complex areas not fully understood, limiting our ability air accurately. This paper introduces Clean for London (ClearfLo; www.clearflo.ac.uk) project’s interdisciplinary approach investigate poor elevated...
Carbonyl oxides ("Criegee intermediates"), formed in the ozonolysis of alkenes, are key species tropospheric oxidation organic molecules and their decomposition provides a non-photolytic source OH atmosphere (Johnson Marston, Chem. Soc. Rev., 2008, 37, 699, Harrison et al., Sci. Total Environ., 2006, 360, 5, Gäb Nature, 1985, 316, 535, ). Recently it was shown that small Criegee intermediates, C.I.'s, react far more rapidly with SO2 than typically represented models, (Welz, Science, 2012,...
Organic aerosol particles are known to often absorb/desorb water continuously with change in gas phase relative humidity (RH) without crystallization. Indeed, the prevalence of metastable ultraviscous liquid or amorphous phases is well-established solutes far exceeding bulk solubility limits. Particles expected become increasingly viscous drying, a consequence plasticizing effect water. We report here measurements variation particle viscosity RH (equal condensed activity) for range organic...
Trace atmospheric concentrations of carboxylic acids have a potent effect upon the environment, where they modulate aqueous chemistry and perturb Earth's radiative balance. Halogenated are produced by tropospheric oxidation halocarbons considered persistent pollutants because their weak sinks. However, recent studies reported rapid reactions between selected Criegee intermediates, which may provide an efficient gas-phase removal process. Accordingly, absolute rate coefficients two CH2OO...
Criegee intermediates are important species formed during the ozonolysis of alkenes. Reaction stabilized with various like SO2 and NO2 may contribute significantly to tropospheric chemistry. In laboratory, self-reaction can be an loss pathway for thus needs characterized obtain accurate bimolecular reaction rate coefficients. Cavity ring-down spectroscopy was used perform kinetic measurements reactions CH2OO at 293 K under low pressure (7 30 Torr) conditions. For + (8), a coefficient k8 =...