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.

Modern atmosphere NPF and growth

Analysis of NPF at SGP

We use mass spectrometer measurements along with supporting data at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in rural Oklahoma to study the vertical distribution of new particle formation (NPF) within the boundary layer. The reduced nitrogen compounds emitted from agricultural activities in the area contribute to nucleation at the surface, while temperature gradients through the boundary layer can drive NPF aloft. Using the same datasets, we also investigate the state of the atmosphere during NPF events that originate at the surface at SGP versus events that nucleate aloft/elsewhere and are then transported to the site to explore what conditions lead to either local or transported NPF events.

Current students on project: Bri Dobson, Maxwell Lee

Funded by DOE 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.

Modeling of CDN Enhancement from NPF

When particles grow large enough during an NPF event, they can act as cloud condensation nuclei, which is important for the formation of low clouds in the atmosphere. Low clouds, which cover up to 20% of the Earth at any given time, play a crucial role in the climate system by reflecting solar radiation back into space. Increased aerosol emissions due to anthropogenic activity can enhance cloud droplet number (CDN) via the Twomey effect, leading to cloud brightening. NPF over agricultural regions is particularly understudied in this regard. Using a 0-dimensional parcel model and real aerosol size distribution data from SGP, we can examine the potential enhancement of CDN from NPF by simulating updrafts characteristic of low clouds in this region.

Current students on project: Maxim Muter

Laboratory simulations of haze formation in Early Earth and exoplanet analog atmospheres

Planetary hazes, such as the one that surrounds Saturn’s moon Titan and the one that was likely present in Early Earth’s atmosphere, are common in our solar system and likely in exoplanetary atmospheres. Planetary haze can affect the radiative balance of the atmosphere and may act as a source of prebiotic molecules. However, the mechanisms driving organic haze formation in diverse atmospheric compositions are unknown. We use our CIMS to investigate the gas-phase chemistry leading to organic aerosol formation in Early Earth analog atmospheres. We are also using the CIMS and an Aerosol Mass Spectrometer (AMS) to study sulfur photochemistry relevant to Early Earth, Venus, and exoplanetary hazes.

Current students on project: Hanalei Lewine, Jeff Price, Natalie Couch

Funded by: NASA Habitable Worlds (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.

Previous research projects

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.

Recent Publications

Lewine, H. R.; Meepage, J. N.; Welker, J. K.; Stanier, C. O.; Stone, E. A.; Browne, E. C.: Secondary Organic Aerosol Formation from Early-Generation Oxidation Products of Decamethylcyclopentasiloxane Depends on Seed Aerosol Composition, Env. Sci. Atmos., doi:10.1039/D5EA00063G, 2025.

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.

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.

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.

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.

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