About

Dylan Millet is a Distinguished McKnight University Professor and Co-Director of Graduate Studies in the Department of Soil, Water, and Climate at the University of Minnesota. His research aims to understand the chemical composition of the atmosphere and how it is affected by humans and the biosphere. He employs a combination of field measurements, computer models, and satellite remote sensing to study atmospheric processes at multiple scales. His areas of interest include atmosphere-biosphere interactions, atmospheric chemistry, and climate change. Millet has contributed to advancing knowledge on atmospheric VOCs, their sources and sinks, and their role in climate and air quality. He has received numerous honors, including the 2022 Ascent Award from the American Geophysical Union and the 2021 Distinguished McKnight University Professorship.

Research topics

• Environmental science
• Atmospheric sciences
• Chemistry
• Environmental chemistry
• Geology
• Meteorology
• Photochemistry
• Geography
• Ecology
• Organic chemistry
• Climatology
• Oceanography
• Waste management
• Physics

Selected publications

• Data and code for volatile organic compound retrievals using the Scanning High-resolution Interferometer Sounder

  Open MIND · 2026-01-01

  datasetOpen access

  This archive contains data and code used for developing and testing the Scanning High-resolution Interferometer Sounder (S-HIS) retrievals of volatile organic compounds that are described in the cited manuscript.

  OA PDFDOI

• Contrasting Biogenic Isoprene Emission Responses to La Niña and El Niño Driven by Temperature: Insights from HCHO-Based Global Inversion

  Environmental Science & Technology · 2026-01-19 · 1 citations

  article

  Isoprene strongly influences atmospheric chemistry by consuming hydroxyl radicals, forming secondary organic aerosols, and affecting methane’s lifetime. Accurate monitoring of its emissions is thus essential for understanding biosphere–atmosphere feedbacks, particularly under climate extremes. We develop a regression-based inversion framework to estimate global monthly biogenic isoprene emissions (2019–2024), integrating TROPOspheric Monitoring Instrument (TROPOMI) HCHO columns and LMDZ-INCA atmospheric transport model. Our inversion yields a global annual mean emission of 456 ± 249 TgC yr–1, with a minimum in 2022 (437 TgC, 1.4σ below multiyear mean) and a peak in 2024 (477 TgC, 1.5σ above), closely tracking global annual land surface temperature variations (R = 0.95). Emission anomalies are most pronounced in tropical regions contributing over 80% of global total anomalies during the 2020–2023 La Niña (−30 TgC), 2023–2024 El Niño (+11 TgC), and 2024 Northern Hemisphere extreme warming events (+15 TgC). Attribution analysis confirms surface temperature as the dominant driver of biogenic isoprene anomalies, with increasing sensitivity in Northern high-latitude zones under warming conditions. The updated emissions improve spatial agreement and reduce bias in LMDZ-INCA simulations against independent satellite-based isoprene and ground-based HCHO observations. This work delivers the first HCHO-constrained global isoprene emission data set through 2024, supporting air quality, oxidant budget, and climate feedback studies.

  PublisherDOI

• Comment on egusphere-2025-5532

  2026-01-14

  peer-reviewOpen access

  <strong class="journal-contentHeaderColor">Abstract.</strong> Isoprene is the most significant non-methane hydrocarbon by total emissions and is an important control on the tropospheric oxidative capacity. In the atmosphere, isoprene is oxidized by the hydroxyl (OH) radical on the order of hours depending on local OH concentrations. Using isoprene retrievals from the Cross-track infrared sounder (CrIS), we monitor global isoprene column variability and observe differing isoprene column responses to El Ni&ntilde;o-Southern Oscillation across three tropical regions: Amazonia, the Maritime Continent, and equatorial Africa. We find correlations between isoprene column variability and temperature over Amazonia, which suggests that isoprene emissions drive Amazonian isoprene variability (&ldquo;emissions-controlled&rdquo;). In the Maritime Continent, we find strong correlations between isoprene columns, precipitation and soil moisture, as well as an anti-correlation between isoprene and formaldehyde retrievals. These correlations suggest that isoprene columns may be modulated by non-anthropogenic NO_x emissions, namely soil and biomass burning NO_x (&ldquo;chemistry-controlled&rdquo;), although convection and lightning NO_x may also modulate isoprene column retrievals if the lofted isoprene flux is large enough. In equatorial Africa, both biomass burning and temperature can explain isoprene variability during different periods, representing an intermediate regime with contributions from emissions and chemistry. We suggest that these isoprene regimes are caused by differences in the dynamic temperature and oxidant range between the three regions, and we specifically highlight oil palm plantations in the Maritime Continent as an area of co-located isoprene and soil NO_x fluxes. By leveraging CrIS isoprene retrievals, we can study interactions between VOC and NO_x sources over tropical areas with few <em>in-situ</em> observations.

  PublisherDOI

• Comment on egusphere-2025-5532

  2026-01-26

  peer-reviewOpen access

  <strong class="journal-contentHeaderColor">Abstract.</strong> Isoprene is the most significant non-methane hydrocarbon by total emissions and is an important control on the tropospheric oxidative capacity. In the atmosphere, isoprene is oxidized by the hydroxyl (OH) radical on the order of hours depending on local OH concentrations. Using isoprene retrievals from the Cross-track infrared sounder (CrIS), we monitor global isoprene column variability and observe differing isoprene column responses to El Ni&ntilde;o-Southern Oscillation across three tropical regions: Amazonia, the Maritime Continent, and equatorial Africa. We find correlations between isoprene column variability and temperature over Amazonia, which suggests that isoprene emissions drive Amazonian isoprene variability (&ldquo;emissions-controlled&rdquo;). In the Maritime Continent, we find strong correlations between isoprene columns, precipitation and soil moisture, as well as an anti-correlation between isoprene and formaldehyde retrievals. These correlations suggest that isoprene columns may be modulated by non-anthropogenic NO_x emissions, namely soil and biomass burning NO_x (&ldquo;chemistry-controlled&rdquo;), although convection and lightning NO_x may also modulate isoprene column retrievals if the lofted isoprene flux is large enough. In equatorial Africa, both biomass burning and temperature can explain isoprene variability during different periods, representing an intermediate regime with contributions from emissions and chemistry. We suggest that these isoprene regimes are caused by differences in the dynamic temperature and oxidant range between the three regions, and we specifically highlight oil palm plantations in the Maritime Continent as an area of co-located isoprene and soil NO_x fluxes. By leveraging CrIS isoprene retrievals, we can study interactions between VOC and NO_x sources over tropical areas with few <em>in-situ</em> observations.

  PublisherDOI

• Supplementary material to "Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity"

  2025-11-03

  articleOpen access

  Note S1.Calculation of glyoxal yields using DSMACC Our DSMACC simulations were set to the meteorological and chemical environments of a surface location in Southern China (Zou et al., 2023).The meteorological and chemical variables were fixed based on measurements from a field campaign in Hong Kong SAR, China (Xiong et al., 2025) : atmospheric surface pressure 1007 hPa; surface temperature 293 K; 5 10 3 ppm of H 2 O (relative humidity of 22%), 0.7 ppm of CO, 40 ppb of O 3 .5 To constrain the production and concentration of OH in the model, two proxy compounds (named OHPRE and OHDECAY)were added in the mechanisms as a producer and consumer of OH.Under a typical NO X concentration (1 ppb), we constrained a baseline OHPRE and OHDECAY to get a daily mean OH production rate of 1.3 10 6 molecules cm -3 s -1 with daily mean OH concentration of 1.6 10 6 molecules cm -3 .We conducted sensitivity simulations with NO concentrations ranging from 0.1 ppb to 5 ppb, assuming an ambient NO 2 to NO concentrations ratio of 4. At each NO X sensitivity experiment, we preturb 10 OHPRE and OHDECAY by scale factors from 0.01 to 100, in order to cover real conditions of NO X and OH concentrations in the atmosphere.

  PublisherDOI

• Revisiting the global budget of atmospheric glyoxal: updates on terrestrial and marine precursor emissions, chemistry, and impacts on atmospheric oxidation capacity

  Atmospheric chemistry and physics · 2025-11-03

  articleOpen access

  Abstract. Atmospheric glyoxal (CHOCHO) plays critical yet incompletely understood roles in tropospheric chemistry. Current models substantially underestimate glyoxal abundance over both land and ocean, indicating knowledge gaps in our understanding of its sources and sinks. Here, we present an improved global simulation of atmospheric glyoxal using the GEOS-Chem model, advanced by recent theoretical, experimental, and observational insights on precursor emissions, chemical pathways, and heterogeneous losses. By applying top-down-constrained biogenic isoprene emissions, enhancing biomass burning emissions, and revising glyoxal yields from isoprene, monoterpenes, and glycolaldehyde oxidation, we estimated a global atmospheric glyoxal source of 40 Tg yr−1 and a global burden of 15 Gg, substantially reducing low bias of simulated glyoxal abundance against in situ and TROPOMI satellite observations over land. The improved representation of glyoxal and its precursors increases simulated global mean surface ozone by 4.5 ppb (17 %) and SOA formation by 17.9 Tg yr−1 (13 %), indicating stronger atmospheric oxidation capacity. Further inclusion of a hypothetical secondary marine glyoxal production to match TROPOMI glyoxal observations over the global oceans increased the global source of atmospheric glyoxal to 106 Tg yr−1 and its global burden to 39 Gg, substantially improving agreement with in situ (NMB from −92 % to 12 %) over the ocean. This enhanced marine glyoxal source increased surface HO2 concentrations and OH reactivity over tropical oceans by 6.5 % and 1.9 %. However, this hypothetical marine glyoxal source cannot be accounted for by known marine NMVOC emissions; its existence remains highly uncertain and warrants further investigation. Our work helps reconcile major model-measurement discrepancies for atmospheric glyoxal, enhances its utility as a volatile organic compound (VOC) proxy, and underscores the need to further investigate glyoxal sources and chemistry.

  PublisherOA PDFDOI

• Supplementary material to "Global biogenic isoprene emissions 2013–2020 inferred from satellite isoprene observations"

  2025-08-18

  articleOpen access
  PublisherDOI

• Supplementary material to "Inferring drivers of tropical isoprene: competing effects of emissions and chemistry"

  2025-12-02

  articleOpen access
  PublisherDOI

• Global decadal measurements of methanol, ethene, ethyne, and HCN from the Cross-track Infrared Sounder

  Atmospheric measurement techniques · 2025-02-07 · 8 citations

  articleOpen accessCorresponding

  Abstract. Volatile organic compounds (VOCs) play an important role in modulating the atmosphere's oxidizing capacity and affect tropospheric ozone, carbon monoxide, formaldehyde, and organic aerosol formation. Space-based observations can provide powerful global information to advance our knowledge of these processes and their changes over time. We present here the development of new retrievals for four key VOCs (methanol, ethene, ethyne, and HCN) based on thermal infrared radiance observations from the satellite-borne Cross-track Infrared Sounder (CrIS). We update the Retrieval of Organics from CrIS Radiances (ROCR) algorithm developed previously for isoprene to explicitly account for the spectral signal dependence on the VOC vertical profile shape, and we apply this updated retrieval (ROCRv2) to derive column abundances for the targeted species across the full Suomi NPP CrIS record (2012–2023). The CrIS data are well correlated with ground-based Network for the Detection of Atmospheric Composition Change (NDACC) retrievals for methanol (r = 0.77–0.84); HCN and ethyne exhibit lower correlations (r = 0.36–0.44 and 0.56–0.65, respectively) with an apparent 40 % CrIS–NDACC disparity for ethyne. The results reveal robust global distributions of the target VOCs from known biogenic, biomass burning, and industrial source regions, and they demonstrate the impact of anomalous events such as the 2015–2016 El Niño. They also highlight the importance of accurate vertical profile constraints when evaluating and interpreting thermal infrared data records. Initial comparisons of the CrIS observations to predicted VOC distributions from the GEOS-Chem chemical transport model point to large uncertainties in our current understanding of the atmospheric ethene budget as well as to underestimated HCN, ethyne, and methanol sources.

  PublisherDOI

• NASA Earth Science Division provides key data

  Science · 2025-07-10 · 2 citations

  letter1st authorCorresponding
  PublisherDOI

Recent grants

• MRI: Acquisition of a High Resolution Proton-Transfer-Reaction Time-Of-Flight Mass Spectrometer (PTR-TOF-MS) for Research in Land And Atmospheric Science

  NSF · $643k · 2014–2018

• CAREER: Budget and Impacts of Atmospheric Organic Acids from Ground and Space-based Observations

  NSF · $727k · 2012–2018

• Collaborative Research: Forest-Atmosphere Volatile Organic Compound (VOC) Exchange for a Coniferous Ecosystem - Closing the Flux Budget

  NSF · $564k · 2019–2023

• Top-Down Constraints on North American Biogenic Volatile Organic Compounds (VOC) Emissions From Tall Tower Measurements and Lagrangian Particle Dispersion Modeling

  NSF · $462k · 2009–2013

Frequent coauthors

• A. H. Goldstein

  106 shared

• Kelley C. Wells

  University of Minnesota

  86 shared

• J. A. de Gouw

  Cooperative Institute for Research in Environmental Sciences

  67 shared

• C. Warneke

  NOAA Chemical Sciences Laboratory

  59 shared

• Timothy J. Griffis

  University of Minnesota

  56 shared

• Hariprasad D. Alwe

  Wageningen University & Research

  50 shared

• Julian Marshall

  Seattle University

  50 shared

• D. R. Blake

  University of California, Irvine

  48 shared

Labs

• Atmospheric ChemistryPI

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Awards & honors

• Ascent Award, American Geophysical Union (2022)
• Distinguished McKnight University Professor (2021)
• NSF CAREER Award (2012)
• Fellow, Institute on the Environment (2011)
• McKnight Land-Grant Professorship (2010)