Research
Understanding the mechanisms through which aerosol particles form and grow is critical for constraining a planet’s energy budget, however, our knowledge of the key processes governing particle formation and growth in diverse environments remains weak. In the coming decades, our knowledge of particle formation and growth will continue to be challenged as changing climate and anthropogenic emissions alter the chemical regimes of modern-day atmospheric chemistry on Earth and measurements from, for instance, the James Webb Space Telescope and NASA’s Dragonfly mission offer increasingly chemically resolved insights into planetary atmospheres much different from our own. My group's research focuses on improving our understanding of aerosol formation and growth using a combination of field measurements, laboratory experiments, modeling, and instrument/method development.
New Particle Formation (NPF) and Growth
Atmospheric new particle formation (NPF) followed by growth of the particles to ~50-100 nm plays a critical role in our ability to understand how aerosols affect cloud lifecycle, properties, and processes and more generally the earth’s radiative balance. Our understanding of NPF and growth however remains incomplete in part because ambient measurements of these processes in diverse ecosystems remain sparse and because these processes are governed by a complex interplay of chemistry and the physical state of the atmosphere. Since 2016, we have been investigating NPF and growth at the Department of Energy Atmospheric Radiation Measurement Southern Great Plains (SGP) research station. Despite accounting for approximately half of habitable land use, the atmospheric chemistry of agricultural regions is understudied. To investigate NPF and growth, we deploy state-of-the-art mass spectrometers to measure the chemical composition of the atmosphere. We supplement these intensive operating periods with analysis of the long-term measurements at this site. Currently we are investigating the role of vertical and horizontal transport in NPF and improving the understanding of the atmospheric chemistry of key NPF precursors such as amines.
Current students on project: Bri Dobson, Daniel Katz
Funded by DOE DE-SC0020175 & DE-SC0023533 in collaboration with Aerodyne and Brookhaven National Lab
Recent Publications
Katz, D. J.; Abdelhamid, A.; Stark, H. J.; Canagaratna, M. R.; Worsnop, D. R.; Browne, E. C.: Chemical Identification of new particle formation and growth precursors through positive matrix factorization of ambient ion measurements, Atmos. Chem. Phys., 23, 5567–5585, doi:10.5194/acp-23-5567-2023, 2023.
Laboratory simulations of haze formation in Titan- and exoplanetary-like atmospheres
Planetary hazes, such as the one that surrounds Saturn’s moon Titan, are common in our solar system and may potentially be important in exoplanetary atmospheres. Planetary haze can affect the radiative balance of the atmosphere and may act as a source of prebiotic molecules. We use our APi-MS and CIMS to investigate the role ambient ions and neutral organic nitrogen gases play in the formation of haze particles. We have recently begun to investigate the role sulfur compounds play in early Earth and exoplanetary haze by using an Aerosol Mass Spectrometer (AMS) to study how trace levels of hydrogen sulfide affects the physical properties and composition of organic haze.
Current students on project: Nate Reed
Funded by: NASA Habitable Worlds (80NSSC20K0232 & 80NSSC23K1526 )
Recent Publications
Reed, N. W.; Jansen, K. T.; Schiffman, Z. R.; Tolbert, M. A.; Browne, E. C.: The Influence of Hydrogen Sulfide on the Optical Properties of Planetary Organic Hazes: Implications for Exoplanet Climate Modeling, Astrophys. J. Lett., 954, L44, doi:10.3847/2041-8213/acf1a2, 2023.
Reed, N. W.; Wing, B. A.; Tolbert, M. A.; Browne, E. C.: Trace H2S Promotes Organic Aerosol Production and Organosulfur Compound Formation in Archean Analog Haze Photochemistry Experiments, Geophys. Res. Lett., 49, e2021GL097032, doi:10.1029/2021GL097032, 2022.
Multi-generational products of atmospheric siloxane oxidation
Several million tons of organosilicon compounds, most notably volatile methyl siloxanes (VMS), are manufactured annually for use in a variety of applications including personal care products and adhesives. Despite estimates that over 90 percent of VMS environmental loading is present in the atmosphere, the multigenerational chemistry of VMS remains poorly constrained. We use an environmental simulation chamber to investigate the atmospheric oxidation of siloxanes. We are specifically interested in the oxidation kinetics, oxidation mechanism, and aerosol formation potential. These studies improve our understanding of the environmental fate of these contaminants of emerging concern.
Current student on project: Hanalei Lewine
Funded by NSF GEO-2029017 previously by CHE-1808606
Recent Publications
Alton, M. W.; Browne, E. C.: Atmospheric degradation of cyclic volatile methyl siloxanes: Radical chemistry and oxidation products, ACS Environmental Au, doi:10.1021/acsenvironau.1c00043, 2, 3, 263-274, 2022.
Alton, M. W.; Browne, E. C.: Atmospheric Chemistry of Volatile Methyl Siloxanes: Kinetics and Products of Oxidation by OH Radicals and Cl Atoms, Environ. Sci. Tech., 54(10), 5992-5999, doi: 10.1021/acs.est.0c01368, 2020. Video describing the work
Reduced nitrogen uptake into SOA
Due to decreasing levels of nitrogen oxides, reduced nitrogen (rN), particularly ammonia, is becoming increasingly important. Laboratory experiments have hinted that ammonia may affect the formation and composition of secondary organic aerosol (SOA), however, little is known about the fate of nitrogen once it enters into the particle-phase. One area of interest is whether rN forms salts or molecular compounds upon uptake into aerosol. Our work with the University of Eastern Finland utilizes many instrumental techniques that probes both the gas phase and aerosol phase.
Current students on project: N/A
Instrument & Method Development
Because we are interested in novel atmospheric constituents, an overarching theme of our work has been on instrument and method development. We develop new reagent ions for chemical ionization mass spectrometry and we design new methods for measuring the chemical compositions of aerosol. We also design new data visualization techniques for mass spectral data and work on algorithm development for processing long-term atmospheric measurements.
Current students on project: Daniel Katz
Funded by ASMS Research Award 2019, CIRES Innovative Research Project
Recent Publications
Alton, M. W.; Stark, H. J.; Canagaratna, M. R.; Browne, E. C.: Generalized Kendrick analysis for improved visualization of atmospheric mass spectral data, Atmos. Meas. Tech., 16, 3273–3282, doi:10.5194/amt-16-3273-2023, 2023.
Berry, J. L.; Day, D. A.; Elseberg, T.; Palm, B. B.; Hu, W.; Abdelhamid, A.; Schroder, J. C.; Karst, U.; Jimenez, J. L.; Browne, E. C.: Laser Ablation-Aerosol Mass Spectrometry-Chemical Ionization Mass Spectrometry for Ambient Surface Imaging, Anal. Chem., 90(6), 4046–4053, doi:10.1021/acs.analchem.7b05255, 2018.