William H. Brune
· Distinguished Professor of MeteorologyVerifiedPennsylvania State University · Department of Meteorology and Atmospheric Science
Active 1971–2025
About
William H. Brune is a Distinguished Professor of Meteorology at Penn State University. His research specialties include atmospheric chemistry and pollution, cloud physics and radiation. Brune studies atmospheric chemistry that removes volatile chemicals lofted into the air by both humans and nature, focusing on hydroxyl (OH), a molecule that acts as the atmosphere’s cleanser. His group has invented instruments to measure atmospheric OH, OH reactivity, aerosol particle formation, and ozone production rates, performing field measurements, laboratory experiments, modeling studies, and uncertainty analysis to improve understanding of atmospheric chemistry and hydroxyl’s role in it. He also studies lightning and weak electrical discharges associated with thunderstorms, using unique instruments to measure weak discharges called corona, and deploying balloon-borne ultraviolet sensors to examine electrical activity in thunderstorms. His work has revealed that lightning and weak discharges produce significant amounts of hydroxyl radicals, integrating disciplines of atmospheric chemistry, electricity, and forest ecology. Brune’s research interests include atmospheric electrical discharges, atmospheric composition from Earth's surface to the stratosphere, aerosol particle formation and aging, and model uncertainty analysis. His contributions have advanced the understanding of atmospheric oxidation processes, lightning chemistry, and the role of electrical discharges in atmospheric chemistry.
Research topics
- Atmospheric sciences
- Meteorology
- Environmental science
- Geology
- Environmental chemistry
- Oceanography
- Computer Science
- Chemistry
- Geography
- Photochemistry
- Physics
- Climatology
- Telecommunications
- Organic chemistry
Selected publications
Communications Earth & Environment · 2025-04-26 · 12 citations
articleOpen accessThe hydroxyl radical controls the removal of many trace gases in the atmosphere and initiates the production of secondary pollutants such as ground-level ozone and secondary organic aerosols. An accurate understanding of the chemistry of this radical is important to understand the self-cleansing capability of the atmosphere and to develop effective control strategies. A previous assessment found that in some regions, measurements of the hydroxyl radical were up to ten times greater than predicted, suggesting an unknown chemical mechanism was responsible. However, recent measurements have revealed interferences associated with some instruments. Here we show that accounting for interferences results in measured hydroxyl radical concentrations that agree with model predictions over a wide range of conditions. This suggests that while there may be gaps in our knowledge of this chemistry in some environments, our understanding of hydroxyl radical chemistry and the self-cleansing capability of the atmosphere is better than previously believed. Measurement interferences may explain some discrepancies between hydroxyl radical measurement and modelling results, as opposed to an unknown chemical mechanism, according to analysis of hydroxyl measurement campaigns and model comparisons.
Spatially separate production of hydrogen oxides and nitric oxide in lightning
Atmospheric chemistry and physics · 2025-05-16 · 1 citations
articleOpen accessSenior authorAbstract. The atmosphere's most important oxidizer, the hydroxyl radical (OH), is generated in abundance by lightning, but the contribution of this electrically generated OH (LOH) to global OH oxidation needs to be better quantified. Part of the uncertainty in this contribution is due to the abundant nitric oxide (NO) also generated in lightning, which rapidly removes the LOH before it can oxidize other pollutants in the atmosphere. However, atmospheric observations and a previous laboratory study show extreme LOH coexists with extreme NO. The only way this electrically generated HOx (LHOx) can possibly survive is if LOH production is spatially separated from the NO production in lightning flashes and laboratory sparks. This hypothesis of spatially separate OH and NO production is further tested here in a series of laboratory experiments, where the OH decays were measured from spark discharges in air which had increasing amounts of NO added to it. The LOH decayed faster as more NO was added to the air, indicating that the LOH was reacting with the added NO and not the spark NO. Thus, LOH from lightning flashes is not immediately consumed by the electrically generated NO but is available to oxidize other pollutants in the atmosphere and contribute to global OH oxidation. Subsequent modeling of the laboratory data also supports the spatially separate production of LOH and NO and further suggests that substantial HONO may also be produced by sparks and lightning in the atmosphere.
JACS Au · 2024-11-22 · 2 citations
articleOpen access1st authorCorrespondingA critical reaction affecting the oxidation chemistry in the middle-to-upper atmosphere occurs between hydroxyl (OH) and hydroperoxyl (HO2). The reaction rate coefficient for OH + HO2 → H2O + O2, here called kOH+HO2, has challenged laboratory kineticists for 50 years. However, several measurements from the past 30 years had approached a rough consensus until the publication of a new study that examined, for the first time, the water vapor dependence of this reaction. According to the study, kOH+HO2 is not the recommended value of 11.0 × 10–11 cm3 molecule–1 s–1, but instead, a water-dependent (∼1 × 10–11 + 2.17 × 10–28[H2O]) cm3 molecule–1 s–1. Our study examines the water dependence of kOH+HO2 using water vapor photolysis of moist air at atmospheric pressure in a flow tube, with direct detection of both OH and HO2. The observed OH decays were due only to the OH reaction with HO2 and, to a lesser extent, the OH loss to the flow tube wall and trace impurities. The resulting kOH+HO2 is (8.54 ± 2.90) × 10–11 cm3 molecule–1 s–1, 68% confidence, independent of water vapor and lower than but consistent with the recommended value.
Comparison of Isoprene Chemical Mechanisms with Chamber and Field Observations
ACS Earth and Space Chemistry · 2024-10-10 · 1 citations
articleOpen access1st authorCorrespondingThe importance of global isoprene emissions has stimulated studies of oxidation mechanisms that follow the initial reaction of isoprene with atmospheric hydroxyl (OH). A key question involves the speed and pathways by which isoprene products isomerize. Some reactions in these mechanisms generate new hydroxyl, perhaps enough to recycle most hydroxyl. This research examines five different isoprene oxidation mechanisms using observations from a 2013 field study in an Alabama forest and a 2014 companion study in the Caltech Environmental Chamber. Model mechanisms and observations were compared for OH, hydroperoxyl (HO2), and the isoprene oxidation products: isoprene hydroxyhydroperoxide (ISOPOOH), isoprene epoxydiol (IEPOX), hydroxyacetone, formaldehyde, methacrolein, and methyl vinyl ketone. Observed hydroxyl is generally simulated within uncertainties for both the chamber and the field studies, indicating that hydroxyl recycling is well captured by current model mechanisms, although two mechanisms are slightly better than the other three. When the observed and modeled uncertainties are considered, no currently accepted mechanism is clearly superior to the others for simulating isoprene products. For atmospheric conditions typical of forests–abundant isoprene and low nitric oxide–these model mechanisms produce concentrations of isoprene products that can be substantially different from observations and from each other. This result suggests both the common and different parts of the chemical mechanisms need to be reexamined, particularly by observing the later-generation products directly.
ChemRxiv · 2024-11-03 · 1 citations
preprintOpen accessFreshly emitted air pollutants may not represent real-world exposure conditions in human studies, especially for communities exposed to aged air pollutants. This study presents the design and characterization of a new oxidative flow reactor (OFR), named the Fast-oxidation Box (FoxBox, volume of 1019 L). Our aim is to simulate atmospheric aging of diesel exhaust (DE) with this system for cellular (in vitro) and controlled human studies, a unique capability globally. We measured: (a) residence time distribution (RTD) for DE-derived CO2, SO2, and particles, (b) DE particle transmission efficiency, (c) low-volatility organic compounds (LVOC) losses, and (d) particle size distribution, secondary organic aerosol (SOA) formation, and aerosol mass spectra of DE during photochemical oxidation (from OH exposure of (1.9 to 9.5)×1011 molec cm-3 s). Our results demonstrate turbulent flow-like conditions in FoxBox with narrower RTD for particles than gases. The particle transmission efficiency was nearly 100% for mobility diameters between 15 and 615 nm. LVOC losses to FoxBox walls were minimal. The changes in particle size distributions (e.g., formation of ultrafine particles) and chemical composition (e.g., SOA formation, increased O:C, etc.) during photochemical oxidation in FoxBox were like those observed in the atmosphere and other OFRs. Our preliminary study on cell viability found that photochemical oxidation significantly reduced cell viability, supporting observations that communities distant from air pollution sources are affected and vulnerable. The controlled human exposures with more realistic aerosol characteristics, such as those produced by FoxBox, may provide critical insight in this regard that has been lacking to date.
Spatially separate production of hydrogen oxides and nitric oxide in lightning
2024-11-26 · 2 citations
preprintOpen accessSenior authorCorrespondingAbstract. The atmosphere’s most important oxidizer, the hydroxyl radical (OH), is generated in abundance by lightning, but the contribution of this electrically generated OH (LOH) to global OH oxidation remains highly uncertain. Part of this uncertainty is due to the abundant nitric oxide (NO) also generated in lightning, which could rapidly remove the LOH before it can oxidize other pollutants in the atmosphere. However, evidence from a previous laboratory study indicated LOH is not immediately consumed by NO, possibly because LOH’s production is spatially separated from the NO production in lightning flashes. This hypothesis of spatially separate OH and NO production is further tested here in a series of laboratory experiments, where the OH decays were measured from spark discharges in air which had increasing amounts of NO added to it. The LOH decayed faster as more NO was added to the air, indicating that the LOH was reacting with the added NO, and not the spark NO. Thus, LOH from lightning flashes is not immediately consumed by the electrically generated NO but is available to oxidize other pollutants in the atmosphere and contribute to global OH oxidation. Subsequent modelling of the laboratory data also supports the spatially separate production of LOH and NO, and further suggests that substantial HONO is also produced by sparks and lightning in the atmosphere.
2024-11-26
preprintOpen accessSenior authorJournal of Geophysical Research Atmospheres · 2024-07-17 · 11 citations
articleOpen accessAbstract Tropospheric ozone (O 3 ) is an important greenhouse gas that is also hazardous to human health. The formation of O 3 is sensitive to the levels of its precursors NO x (≡NO + NO 2 ) and peroxy radicals, for example, generated by the oxidation of volatile organic compounds (VOCs). A better understanding of this sensitivity will show how changes in the levels of these trace gases could affect O 3 levels today and in the future, and thus air quality and climate. In this study, we investigate O 3 sensitivity in the tropical troposphere based on in situ observations of NO, HO 2 and O 3 from four research aircraft campaigns between 2015 and 2023. These are OMO (Oxidation Mechanism Observations), ATom (Atmospheric Tomography Mission), CAFE Africa (Chemistry of the Atmosphere Field Experiment in Africa) and CAFE Brazil, in combination with simulations using the EMAC atmospheric chemistry—climate model. We use the metric α (CH 3 O 2 ) together with NO to investigate the O 3 formation sensitivity. We show that O 3 formation is generally NO x ‐sensitive in the lower and middle tropical troposphere and is in a transition regime in the upper troposphere. By distinguishing observations impacted by lightning or not we show that NO from lightning is the most important driver of O 3 sensitivity in the tropics. NO x ‐sensitive chemistry predominates in regions without lightning impact, with α (CH 3 O 2 ) ranging between 0.56 and 0.82 and observed average O 3 levels between 35 and 55 ppbv. Areas affected by lightning exhibit strongly VOC‐sensitive O 3 chemistry with α (CH 3 O 2 ) of about 1 and average O 3 levels between 55 and 80 ppbv.
Ultraviolet radiation as a proxy measurement for electrically generated hydroxyl radicals
2024-03-08
preprintOpen accessSenior authorCorrespondingReaction with hydroxyl radical (OH) initiates the removal of many pollutants from the atmosphere that impact human health and climate, but can also lead to the formation of different pollutants. Extreme amounts of OH are directly produced by lightning and other, weaker electrical discharges in the atmosphere, although estimates of the global impact of this source of OH are highly uncertain due to the limited field data. However, obtaining more field data is difficult, as measuring electrically generated OH with traditional OH-detecting instruments risks exposing both the instrument and the user to dangerous electrical currents. A possible alternative approach is to use the ultraviolet (UV) radiation generated by the electrical discharges as a proxy measurement for OH generation. Using a laboratory setup, the relationship between OH and UV radiation in different types of electrical discharges is investigated and quantified as a first step toward designing an instrument that can be safely deployed around electrical discharges in the field, leading to more certain estimates of the global impact of electrically generated OH.
Re-assessment of hydroxyl radical chemistry using new observation data and model comparisons
2024-03-08
preprintOpen accessSenior authorCorrespondingAtmospheric formation of ozone and secondary organic aerosols as well as the removal of greenhouse gases such as methane and hydrofluorocarbons depend on the fast radical cycling of the hydroxyl radical (OH). Previous measurements of these radicals in forest environments have shown serious discrepancies with model predictions, bringing into question our understanding of OH radical chemistry, especially in regions characterized by low NOx (NOx = NO + NO2) and high biogenic volatile organic compound (BVOC) concentrations. However, previous studies have discovered that some OH radical measurement techniques may be sensitive to interferences, such as from the ozonolysis of BVOCs. This has the potential to cause artificially high observations of OH especially in forested areas. In this work, we present an analysis of previous measurements of OH radical concentrations from rural, suburban, and urban areas while accounting for the measured interferences and covering a wide range of NOx concentrations. This re-assessment provides insight regarding our current understanding of OH radical recycling under low NOx and high BVOC conditions.
Recent grants
Measurement and Interpretation of OH, HO2, and OH Reactivity during BEARPEX 09
NSF · $457k · 2009–2012
NSF · $536k · 2018–2022
NSF · $197k · 2019–2023
Feasibility Study for the Atmospheric Measurement of Potential Aerosol Mass (PAM)
NSF · $176k · 2005–2007
NSF · $197k · 2009–2013
Frequent coauthors
- 133 shared
R. C. Cohen
University of California, Berkeley
- 125 shared
Xinrong Ren
- 121 shared
J. L. Jiménez
- 117 shared
J. A. de Gouw
Cooperative Institute for Research in Environmental Sciences
- 105 shared
P. O. Wennberg
California Institute of Technology
- 96 shared
Alan Fried
Institute of Arctic and Alpine Research
- 96 shared
Jeff Peischl
National Oceanic and Atmospheric Administration
- 92 shared
D. R. Blake
University of California, Irvine
Labs
William H. BrunePI
Awards & honors
- Penn State Department of Meteorology and Atmospheric Science…
- Penn State University-Level Alumni Awards
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