About

Neil Donahue is a professor in the Departments of Chemistry, Chemical Engineering, and Engineering and Public Policy at Carnegie Mellon University. He also serves as the director of the Steinbrenner Institute for Environmental Education and Research. His research focuses on understanding how Earth's atmosphere works and how human activities influence atmospheric processes. Donahue's group specializes in studying the behavior of organic compounds in Earth's atmosphere, particularly the origin and transformations of very small organic particles that impact climate change and human health. His work is critical in understanding how particles scatter light, influence cloud formation, and contribute to health issues such as heart attacks. Donahue is a member of numerous professional societies, a Fellow of the American Geophysical Union, and an editor for several academic journals. He holds a B.S. in Physics from Brown University and a Ph.D. in meteorology from MIT, with previous research experience at Harvard. His contributions extend beyond research, aiming to educate students about climate challenges and applying problem-solving skills to environmental solutions.

Research topics

• Organic chemistry
• Physics
• Meteorology
• Chemistry
• Computer Science
• Inorganic chemistry
• Chemical physics
• Chemical engineering
• Oceanography
• Atmospheric sciences
• Aerospace engineering
• Geography
• Cartography
• Environmental science
• Engineering
• Photochemistry
• Geology

Selected publications

• Comment on egusphere-2025-2412

  2026-01-07

  peer-reviewOpen access1st authorCorresponding

  <strong class="journal-contentHeaderColor">Abstract.</strong> Laboratory experiments addressing complex phenomena such as atmospheric new-particle formation and growth typically involve numerous instruments measuring a range of key coupled variables. In addition to independent calibration, the combined dataset provides not just constraints on the parameters of interest but also on the critical instrument calibrations. Here we find good agreement between production and loss rates of sulfuric acid (H₂SO₄) in an experiment performed at the CERN CLOUD chamber involving oxidation of sulfur dioxide (SO₂) in the presence of ammonia (NH₃) at 58 % relative humidity, driving new-particle formation and growth of particles by H₂SO₄ + NH₃ nucleation initiated by O₃ photolysis via several light sources. This closure requires consistency across numerous parameters, including: the particle number and size distribution; their condensation sink for H₂SO₄; the particle growth rates; the concentration of H₂SO₄; and the nucleation coefficients for both neutral and ion-induced pathways. Our study shows that accurate agreement can be achieved between production and loss of condensable vapors in laboratory chambers under atmospheric conditions, with accuracy ultimately tied to particle number measurement (i.e. a condensation particle counter). This, in turn implies parameters such as the H₂SO₄ concentration and particle size distributions can be determined to a comparable precision.

  PublisherDOI

• Comparison of oxidation products generated from the reaction of α-pinene with hydroxyl radicals, chlorine atoms, and bromine atoms measured using ammonium adduct chemical ionization mass spectrometry

  Environmental Science Atmospheres · 2026-01-01

  articleOpen access

  Comparison of OH-, Cl-, and Br-initiated α-pinene oxidation reveals distinct pathways that form unique gas- and condensed-phase products.

  PublisherOA PDFDOI

• Isoprene chemistry under upper-tropospheric conditions

  Nature Communications · 2025-09-29 · 1 citations

  articleOpen access

  Abstract Isoprene (C 5 H 8 ) is the non-methane hydrocarbon with the highest emissions to the atmosphere. It is mainly produced by vegetation, especially broad-leaved trees, and efficiently transported to the upper troposphere in deep convective clouds, where it is mixed with lightning NO x . Isoprene oxidation products drive rapid formation and growth of new particles in the tropical upper troposphere. However, isoprene oxidation pathways at low temperatures are not well understood. Here, in experiments at the CERN CLOUD chamber at 223 K and 243 K, we find that isoprene oxygenated organic molecules (IP-OOM) all involve two successive $${{{\rm{OH}}}}^{\bullet}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mi>OH</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>∙</mml:mo> </mml:mrow> </mml:msup> </mml:math> oxidations. However, depending on the ambient concentrations of the termination radicals ( $${{{{\rm{HO}}}}_{2}}^{\bullet},\,{{{\rm{NO}}}}^{\bullet}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>HO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo>∙</mml:mo> </mml:mrow> </mml:msup> <mml:mo>,</mml:mo> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mi>NO</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>∙</mml:mo> </mml:mrow> </mml:msup> </mml:math> , and $${{{\rm{NO}}}}_{2}^{\bullet}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>NO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>∙</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> ), vastly-different IP-OOM emerge, comprising compounds with zero, one or two nitrogen atoms. Our findings indicate high IP-OOM production rates for the tropical upper troposphere, mainly resulting in nitrate IP-OOM but with an increasing non-nitrate fraction around midday, in close agreement with aircraft observations.

  PublisherOA PDFDOI

• Global impact of anthropogenic NH ₃ emissions on upper tropospheric aerosol formation

  Proceedings of the National Academy of Sciences · 2025-10-27

  articleOpen access

  Anthropogenic ammonia (NH 3 ) emissions have significantly increased in recent decades due to enhanced agricultural activities, contributing to global air pollution. While the effects of NH 3 on surface air quality are well documented, its influence on particle dynamics in the upper troposphere-lower stratosphere (UTLS) and related aerosol impacts remain unquantified. NH 3 reaches the UTLS through convective transport and can enhance new particle formation (NPF). This modeling study evaluates the global impact of anthropogenic NH 3 on UTLS particle formation and quantifies its effects on aerosol loading and cloud condensation nuclei (CCN) abundance. We use the EMAC Earth system model, incorporating multicomponent NPF parameterizations from the CERN CLOUD experiment. Our simulations reveal that convective transport increases NH 3 -driven NPF in the UTLS by one to three orders of magnitude compared to a baseline scenario without anthropogenic NH 3 , causing a doubling of aerosol numbers over high-emission regions. These aerosol changes induce a 2.5-fold increase in upper tropospheric CCN concentrations. Anthropogenic NH 3 emissions increase the relative contribution of water-soluble inorganic ions to the UTLS aerosol optical depth (AOD) by 20% and increase total column AOD by up to 80%. In simulations without anthropogenic NH 3 , UTLS aerosol composition is dominated by sulfate and organic species, with a marked reduction in ammonium nitrate and aerosol water content. This results in a decline of aerosol mass concentration by up to 50%. These findings underscore the profound global influence of anthropogenic NH 3 emissions on UTLS particle formation, AOD, and CCN production, with important implications for cloud formation and climate.

  PublisherOA PDFDOI

• Isoprene Aerosol Growth in the Upper Troposphere: Application of the Diagonal Volatility Basis Set to CLOUD Chamber Measurements

  ACS ES&T Air · 2025-09-15

  articleOpen accessSenior authorCorresponding

  Isoprene oxygenated organic molecules (IP-OOM) can nucleate new particles in the upper troposphere. These particles may grow into cloud condensation nuclei and influence the clouds and climate. However, little is known about the individual species driving growth and whether they undergo condensed-phase reactions. We conducted isoprene oxidation experiments at 223 and 243 K in the CLOUD chamber at CERN. Gas-phase concentrations were measured with chemical ionization mass spectrometers (NO3–-CIMS, Br–-MION2-CIMS, and NH4+-CIMS). Growth rates from 8 to 20 nm were measured by a Neutral Cluster and Air Ion Spectrometer. Particle-phase composition was measured by a filter sampling chemical ionization mass spectrometer. We use the diagonal volatility basis set (dVBS) analysis framework to compare gas- and particle-phase measurements and assess species and processes influencing growth. We find that kinetically limited condensation of a few species dominates particle composition and growth. Particle-phase processes, including oligomerization and organonitrate hydrolysis, do not influence the early growth. dVBS growth rate predictions can explain 90% of the measured growth, dominated by kinetic condensation of low-volatility species. Our findings indicate that initial growth of IP-OOM particles under cold, low-acid conditions may be controlled and modeled by the kinetically limited condensation of low-volatility compounds.

  PublisherDOI

• Incomplete mass closure in atmospheric nanoparticle growth

  npj Climate and Atmospheric Science · 2025-02-26 · 8 citations

  articleOpen access

  Abstract Nucleation and subsequent growth of new aerosol particles in the atmosphere is a major source of cloud condensation nuclei and persistent large uncertainty in climate models. Newly formed particles need to grow rapidly to avoid scavenging by pre-existing aerosols and become relevant for the climate and air quality. In the continental atmosphere, condensation of oxygenated organic molecules is often the dominant mechanism for rapid growth. However, the huge variety of different organics present in the continental boundary layer makes it challenging to predict nanoparticle growth rates from gas-phase measurements. Moreover, recent studies have shown that growth rates of nanoparticles derived from particle size distribution measurements show surprisingly little dependency on potentially condensable vapors observed in the gas phase. Here, we show that the observed nanoparticle growth rates in the sub-10 nm size range can be predicted in the boreal forest only for springtime conditions, even with state-of-the-art mass spectrometers and particle sizing instruments. We find that, especially under warmer conditions, observed growth is slower than predicted from gas-phase condensation. We show that only a combination of simple particle-phase reaction schemes, phase separation due to non-ideal solution behavior, or particle-phase diffusion limitations can explain the observed lower growth rates. Our analysis provides first insights as to why atmospheric nanoparticle growth rates above 10 nm h −1 are rarely observed. Ultimately, a reduction of experimental uncertainties and improved sub-10 nm particle hygroscopicity and chemical composition measurements are needed to further investigate the occurrence of such a growth rate-limiting process.

  PublisherOA PDFDOI

• A mechanistic understanding of the varying yields of highly oxygenated organic molecules

  Nature Communications · 2025-12-09 · 1 citations

  articleOpen access

  Highly oxygenated organic molecules (HOM) play a crucial role in the formation and growth of atmospheric particles, thereby influencing air quality and climate. A comprehensive understanding of HOM formation, particularly an accurate quantification of their yields, is essential to constrain the climate and health impacts of aerosols. Previous studies often reported constant HOM yields as averages, overlooking nuanced changes. Here we revisit several experimental datasets and demonstrate that HOM yields from single volatile organic compounds (VOCs) can vary by more than a factor of 3, depending on numerous parameters affecting peroxy radicals (RO2) autoxidation. Additionally, we propose a concept of RO2 oxidation fraction, which provides a unified explanation for variations in the HOM yields. Our findings indicate that applying the laboratory-derived HOM yields to the interpretation of ambient data may lead to substantial biases, especially when VOC and oxidant concentrations in the laboratory were higher than those in the real atmosphere. HOM formation from a same VOC can vary by over a factor of three depending on chemical conditions. A RO₂ oxidation fraction concept explains this variability and cautions against directly applying lab yields to the atmosphere.

  PublisherOA PDFDOI

• A diagonal volatility basis set to assess the condensation of organic vapors onto particles

  Environmental Science Atmospheres · 2025-01-01 · 3 citations

  articleOpen accessSenior author

  run at 243 K are consistent with volatility driven condensation forming the large majority of particle mass, with no compounds clearly within the infeasible region.

  PublisherOA PDFDOI

• Anthropogenic organic aerosol in Europe produced mainly through second-generation oxidation

  Nature Geoscience · 2025-03-01 · 13 citations

  articleOpen access

  Exposure to anthropogenic atmospheric aerosol is a major health issue, causing several million deaths per year worldwide. The oxidation of aromatic hydrocarbons from traffic and wood combustion is an important anthropogenic source of low-volatility species in secondary organic aerosol, especially in heavily polluted environments. It is not yet established whether the formation of anthropogenic secondary organic aerosol involves mainly rapid autoxidation, slower sequential oxidation steps or a combination of the two. Here we reproduced a typical urban haze in the 'Cosmics Leaving Outdoor Droplets' chamber at the European Organization for Nuclear Research and observed the dynamics of aromatic oxidation products during secondary organic aerosol growth on a molecular level to determine mechanisms underlying their production and removal. We demonstrate that sequential oxidation is required for substantial secondary organic aerosol formation. Second-generation oxidation decreases the products' saturation vapour pressure by several orders of magnitude and increases the aromatic secondary organic aerosol yields from a few percent to a few tens of percent at typical atmospheric concentrations. Through regional modelling, we show that more than 70% of the exposure to anthropogenic organic aerosol in Europe arises from second-generation oxidation.

  PublisherOA PDFDOI

• <i>Environmental Science: Atmospheres</i> five years on

  Environmental Science Atmospheres · 2025-01-01

  articleOpen access1st authorCorresponding

  Editor-in-Chief Neil Donahue reflects on the fourth year of Environmental Science: Atmospheres and looks ahead at the plans for year 5.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Cosmics Leaving OUtdoor Droplets (CLOUD) Consortium Membership

  NSF · $262k · 2018–2022

• Interactions between Organic Oxidation and Acid-base Chemistry during Particle Formation and Growth

  NSF · $853k · 2022–2025

• Collaborative Research: United States University CLOUD (Cosmics Leaving OUtdoor Droplets) Consortium Membership

  NSF · $348k · 2022–2026

• Mixing Thermodynamics in Atmospherically Relevant Organic Aerosol Systems

  NSF · $456k · 2010–2014

• Constraining the Role of Gas-Phase Organic Oxidation in New-Particle Formation

  NSF · $470k · 2015–2018

Frequent coauthors

• Markku Kulmala

  University of Helsinki

  265 shared

• Douglas R. Worsnop

  University of Helsinki

  241 shared

• J. Kirkby

  Goethe University Frankfurt

  209 shared

• Jonathan Duplissy

  Helsinki Institute of Physics

  187 shared

• Katrianne Lehtipalo

  University of Helsinki

  176 shared

• Armin Hansel

  Universität Innsbruck

  146 shared

• Tuukka Petäjä

  143 shared

• Urs Baltensperger

  Paul Scherrer Institute

  133 shared

Labs

• Center for Atmospheric Particle Studies (CAPS)PI

  Directory of faculty, graduate students, and alumni from the Center for Atmospheric Particle Studies (CAPS) at Carnegie Mellon University (CMU).

Education

• B.A.

  Brown University

  1984

• Ph.D., Meteorology and Atmospheric Chemistry

  Massachusetts Institute of Technology

  1991

Awards & honors

• Fellow of the American Geophysical Union
• ranked #20 in the aerosol specialty on ScholarGPS
• Scott Institute Seed Grants