About

Timothy Griffis is a Professor in the Department of Soil, Water, and Climate at the University of Minnesota Twin Cities. He holds a BS from Brock University and a PhD from McMaster University. His research aims to improve the scientific understanding of the biophysical mechanisms that govern the exchange of energy and mass between the Earth's surface and the lower atmosphere. His areas of interest include atmosphere-biosphere interactions, biogeochemistry, and biometeorology. Professor Griffis's work involves developing micrometeorological and optical stable isotope techniques to trace the flow of carbon, nitrogen, and water between land and atmosphere, as well as studying reactive nitrogen cycling at the biosphere-atmosphere interface. His research also encompasses methane and carbon dioxide budgets of tropical and temperate peatlands, biophysical modeling of land-atmosphere trace gas exchange, and the atmospheric transport and fate of herbicides and pesticides. He has contributed to advancing understanding in these fields through extensive research and numerous publications, and he is actively involved in professional societies, editorial roles, and advisory committees related to atmospheric and environmental sciences.

Research topics

• Environmental science
• Geology
• Biology
• Geography
• Ecology
• Botany
• Atmospheric sciences
• Statistics
• Agronomy
• Mathematics

Selected publications

• N ₂ Onet: a global collaborative network facilitating advances in measurement, modeling, and mitigation of agricultural soil nitrous oxide emissions

  Environmental Research Letters · 2026-02-10 · 1 citations

  articleOpen access

  Abstract Nitrogen (N) fertilizer supports global food production, but its use and overuse drive emissions of nitrous oxide (N 2 O), a potent and long-lived greenhouse gas. Understanding the drivers of N 2 O fluxes remains elusive, making it difficult to predict emissions in time and space and to develop and evaluate ways to lower emissions through management. Major scientific uncertainties underlying the understanding of the drivers of N 2 O fluxes identified in a workshop of N 2 O emissions experts include poor process-based understanding of controls on soil N 2 O emissions in the field; insufficient data to reduce uncertainty in N 2 O budgets from the field to regional scales, including N 2 O emission measurements and importantly, field-scale N balances; and high uncertainty in model predictions of soil N 2 O emissions across environmental and management conditions. To reduce these uncertainties, we present the concept of N 2 Onet, a global collaborative initiative to accelerate advances in N 2 O measurement, analyses, and mitigation. N 2 Onet will serve as an observational network of supersites with multi-scale measurements; a database hub for N 2 O flux and ancillary data; and a catalyst for community building, information sharing, and training. By coalescing and coordinating the global community of researchers, N 2 Onet will provide a roadmap for reducing N 2 O emissions from agriculture worldwide.

  PublisherDOI

• Atmospheric Inversion Approach‐Based Constraint on CH ₄ Emissions and Future Projections Under Climate Scenarios for Waste Treatment: A Case Study in Yangtze River Delta Region, China

  Journal of Geophysical Research Atmospheres · 2026-01-22

  article

  Abstract China is the largest methane (CH 4 ) emitter globally, with the Yangtze River Delta (YRD) region recognized as a major emission hotspot. However, due to the scarcity of in situ observations and the complex spatiotemporal variability of these sources, significant uncertainties remain in regional CH 4 emission estimates. To address this, we conducted continuous atmospheric CH 4 concentration measurements from 1 June 2023, to 31 May 2024, at a central YRD site. Using an atmospheric transport model and a Bayesian inversion framework, we quantified monthly and sub‐monthly CH 4 emissions from different source categories, with a focus on waste treatment (including both landfill and wastewater). The results reveal the following key findings: (a) Substantial discrepancies were found between prior and posterior emissions across all categories. At the city scale, posterior annual CH 4 emissions were estimated to be 87.4%, 64.6%, 109.5%, and 91.9% of prior emissions for all categories, waste treatment, rice paddy + wetland, and other sources, respectively, with waste treatment contributing the largest uncertainty. (b) Strong seasonal biases were observed, with waste treatment emissions peaking in August and reaching a minimum in March (a 2.6‐fold variation), while rice paddy emissions were overestimated in May and underestimated in August by a factor of two. (c) CH 4 emissions from waste treatment exhibited high temperature sensitivity, increasing by 29%–31% per 10°C rise. Under future warming scenarios, waste treatment CH 4 emission factors (EFs) will increase by up to 121.3% under SSP5‐8.5 by the end of the century (2091–2100), relative to 2023–2024 levels. In contrast, atmospheric pressure showed negligible influence (3.2% per 1 hPa) on waste treatment CH 4 emissions. (d) More additional observations (i.e., satellite or multiple sites) are strongly suggested to resolve the prior spatial pattern of emissions, especially for fossil fuel‐related sources.

  PublisherDOI

• Productivity dynamics of agroecosystems under prevailing and alternative management practices across the United States

  Agricultural and Forest Meteorology · 2026-05-17

  articleOpen access

  • Alternative practices enhance productivity and extend carbon uptake. • Carbon uptake period drives productivity consistently across sites. • Precipitation extends carbon uptake mainly under alternative management. Industrialized agriculture has dramatically increased crop yields over the last century, but this has led to soil erosion and reductions in soil organic matter, raising concerns about the long-term sustainability of agroecosystems under weather variability. The first step towards restoring soil organic matter in agroecosystems is achieving sustained net ecosystem carbon uptake, as reflected in positive net ecosystem productivity (NEP). Thus, we evaluated how prevailing and potentially more sustainable, alternative management practices influenced NEP across a range of agroecosystems in the United States. Specifically, we analyzed eddy covariance data from eleven Long-Term Agroecosystem Research cropland locations to compare gross primary productivity (GPP) and NEP dynamics in the two systems. At seven locations spanning diverse environments, mean annual NEP was higher under the alternative management. Five of these sites with cover crops exhibited longer carbon uptake period (CUP) than their prevailing management counterparts. Importantly, a longer CUP was associated with increases in both annual sum of GPP and NEP and their peak values. Increased precipitation at the alternative sites enhanced CUP length, which contributed to higher overall productivity while prevailing systems showed no sensitivity to precipitation. The relationship between annual NEP and CUP showed steeper slopes at drier sites, indicating potential benefits for NEP gains associated with extended CUP. Our findings demonstrate that sustainable management practices can strengthen carbon uptake capacity, highlighting their importance for maintaining agroecosystem productivity.

  PublisherDOI

• AmeriFlux FLUXNET-1F US-MBP Marcell Bog Lake Peatland

  DOE Lawrence Berkeley National Laboratory (LBNL) Repository · 2026-04-04

  datasetOpen access

  This is the AmeriFlux Management Project (AMP) created FLUXNET-1F version of the carbon flux data for the site US-MBP Marcell Bog Lake Peatland. This is the FLUXNET version of the carbon flux data for the site US-MBP Marcell Bog Lake Peatland produced by applying the standard ONEFlux (1F) software. Site Description - The study site is a fen within the Marcell Experimental Forest, which has been monitored for fluxes and environmental variables at various points in time. In 2007 an EC tower was established to monitor CO2/H2O fluxes within the peatland. Methane observations were added in 2009 and have been ongoing since. This site has also been referred to as Bog Lake Fen in the past.

  PublisherDOI

• Soil and tree stem greenhouse gas fluxes from nutrient-rich and nutrient-poor tropical peatland forests

  2026-03-14

  articleOpen access

  Tropical peatland forests are significant sources and sinks of greenhouse gases (GHG), yet the relative contributions of soil and tree stem fluxes have remained poorly quantified, particularly CH4 and N2O fluxes across gradients of nutrient availability. We conducted simultaneous measurements of CO2, CH4 and N2O fluxes from both soil and tree stems using soil and stem chamber in two contrasting tropical peat swamp forests: a nutrient-rich in Quistococha, Peru and a nutrient-poor in Maludam, Sarawak, Malaysia. Our results showed higher soil CO2, CH4 and N2O fluxes from Quistococha nutrient-rich forest. Tree stem respiration was consistently higher in the nutrient-poor forest across all dominant species in both forests. Tree stem CH4 fluxes exhibited distinct patterns, with significantly higher emissions from the nutrient-rich forest, while displaying species-specific behaviour among dominant tree species. Mauritia flexuosa palm stems in Quistococha showed high emission of CH4 from stems with potential CH4 sinks from specific species from both forests. N2O emissions were also species-specific and higher from the nutrient-rich forest, with negligible fluxes observed from the species in the nutrient-poor forest. From stem fluxes to tree fluxes upscaling, we found that the majority of total ecosystem GHG flux originated from soil with minimal contribution from the dominant tree species. In conclusion, these findings highlighted tree stems from tropical peatland can act as sources and sinks and that nutrient availability influence on the magnitude of greenhouse gas emissions.

  PublisherDOI

• Spatial-temporal variations of atmospheric NH ₃ concentration and its dry deposition across China based on one decade of satellite and ground-based observations

  2025-07-10

  preprintOpen access

  Abstract. Ammonia (NH3), a key alkaline gas in the atmosphere, significantly influences ecosystem nitrogen cycling and the formation of fine particulate matter (PM2.5). However, limited ground-based monitoring hinders understanding of NH3’s spatial and temporal dynamics and its dry deposition across China, which is ranked as one of global largest NH3 emission hotspots. This study integrated 2013–2023 satellite-derived NH3 column concentrations from the Cross-track Infrared Sounder (CrIS) with ground in-situ observations. We used the GEOS-Chem transport model and a random forest algorithm to simulate NH3 dry deposition fluxes and explore the driving forces behind observed trends. Our results show that NH3 concentrations were the highest in the North China Plain (>10 ppb), with notable annual and seasonal increases. NH3 concentration in 2023 were 14–31 % higher than in 2013. CrIS retrievals aligned well with in-situ data, though were generally about twice as high. Dry deposition fluxes exhibited a clear east-west gradient, with maxima in the North China Plain and Sichuan Basin. Increases in NH3 concentrations and deposition were most pronounced in urban, cropland, and forest regions, with urban areas experiencing the fastest growth and grasslands the highest total deposition. The national mean NH3 concentration and dry deposition flux were 4.98 ppb and 0.51 g m⁻2 yr⁻1, respectively. Anthropogenic emissions explained 77 % of the variability in NH3 concentration trend, while meteorological factors accounted for the remainder. 70 %–80 % of deposition trend was governed by atmospheric NH3 concentration changes. This study highlights growing ammonia pollution and informs nitrogen management strategies in China.

  PublisherOA PDFDOI

• Observed CO2 concentration reveals steep decrease of anthropogenic emissions in winters of 2021 and 2022 in Hangzhou and Yangtze River Delta region, China

  The Science of The Total Environment · 2025-03-24 · 2 citations

  article
  PublisherDOI

• Decadal changes in atmospheric ammonia and dry deposition across China inferred from space-ground measurements and model simulations

  Atmospheric chemistry and physics · 2025-12-08

  articleOpen accessCorresponding

  Abstract. Ammonia (NH3), a key alkaline gas in the atmosphere, significantly influences ecosystem nitrogen cycling and the formation of fine particulate matter (PM2.5). However, limited ground-based monitoring hinders understanding of NH3's spatial and temporal dynamics and its dry deposition across China, which is ranked as one of the largest global NH3 emission hotspots. This study integrated 2013–2023 satellite-derived NH3 column concentrations from the Cross-track Infrared Sounder (CrIS) with adjustments from approximately five years ground in-situ ground observations to derive spatial-temporal variation in ground-level NH3 concentrations across China. We also used the GEOS-Chem transport model and a random forest algorithm by using emission inventories and reanalysis meteorological fields to simulate NH3 dry deposition velocity and fluxes, and explore the mechanisms driving observed trends. The CrIS observations results show that column-averaged (averages from ground to ∼ 1 km) NH3 concentrations were the highest in the North China Plain (> 10 ppb), with notable annual and seasonal increasing trends. NH3 concentrations in 2023 were 13.8 %–30.6 % higher than in 2013. CrIS retrievals aligned well with in-situ data, though were generally about twice as high. After applying the regression equation between ground in-situ observations and CrIS column-averaged NH3 concentrations, we derive the spatial-temporal ground-level (1–1.5 m) NH3 concentrations and dry deposition fluxes from 2013 to 2023. The NH3 dry deposition fluxes exhibited a clear east-west gradient, with maxima in the North China Plain, and another hotpot region is also observed in the Sichuan Basin, southwestern China. Increases in ground-level NH3 concentrations and deposition were most pronounced in urban, cropland, and forest regions, with urban areas experiencing the fastest growth and grasslands the highest total deposition. The national mean ground-level NH3 concentration and dry deposition flux were 4.98 ppb and 0.51 g NH3 m−2 yr−1, respectively. Anthropogenic emissions explained 77.4 % of the variability in ground-level NH3 concentration trend, and meteorological factors accounted for the remainder. Besides, 72.6 %–81.2 % of the NH3 dry deposition trend was governed by NH3 concentration changes. This study identifies the underlying cause of increasing ammonia pollution, which can be used to better inform nitrogen management strategies in China.

  PublisherOA PDFDOI

• Network of networks: Time series clustering of AmeriFlux sites

  Agricultural and Forest Meteorology · 2025-06-24 · 2 citations

  articleOpen access

  • Air temperature and net radiation followed a latitude gradient in clustering. • Clustering of fluxes was related to mean annual temperature and precipitation. • Site uniqueness was quantified, and proximal sites pairs were more similar. • Unique sites were in urban, open water, mountains, Hawaii, and Latin America. Environmental observation networks, such as AmeriFlux, are foundational for monitoring ecosystem response to climate change, management practices, and natural disturbances; however, their effectiveness depends on their representativeness for the regions or continents. We proposed an empirical, time series approach to quantify the similarity of ecosystem fluxes across AmeriFlux sites. We extracted the diel and seasonal characteristics (i.e., amplitudes, phases) from carbon dioxide, water vapor, energy, and momentum fluxes, which reflect the effects of climate, plant phenology, and ecophysiology on the observations, and explored the potential aggregations of AmeriFlux sites through hierarchical clustering. While net radiation and temperature showed latitudinal clustering as expected, flux variables revealed a more uneven clustering with many small (number of sites < 5), unique groups and a few large (> 100) to intermediate (15–70) groups, highlighting the significant ecological regulations of ecosystem fluxes. Many identified unique groups were from under-sampled ecoregions and biome types of the International Geosphere-Biosphere Programme (IGBP), with distinct flux dynamics compared to the rest of the network. At the finer spatial scale, local topography, disturbance, management, edaphic, and hydrological regimes further enlarge the difference in flux dynamics within the groups. Nonetheless, our clustering approach is a data-driven method to interpret the AmeriFlux network, informing future cross-site syntheses, upscaling, and model-data benchmarking research. Finally, we highlighted the unique and underrepresented sites in the AmeriFlux network, which were found mainly in Hawaii and Latin America, mountains, and at under-sampled IGBP types (e.g., urban, open water), motivating the incorporation of new/unregistered sites from these groups.

  PublisherDOI

• Supplementary material to "Spatial-temporal variations of atmospheric NH ₃ concentration and its dry deposition across China based on one decade of satellite and ground-based observations"

  2025-07-10

  preprintOpen access
  PublisherDOI

Recent grants

• Collaborative Research: Experimental and Modeling Study of Ecosystem-Atmosphere Oxygen Isotopic Fluxes and Discrimination Mechanisms

  NSF · $125k · 2005–2009

• CAREER: Measurement and Modeling of Land-Atmosphere Isotopic Carbon Dioxide (CO2) Exchange in the Upper Midwest, United States

  NSF · $601k · 2006–2012

• Closing the Regional Ammonia and Nitrous Oxide Budgets of an Intensive Agricultural Region

  NSF · $499k · 2016–2021

• Collaborative Research: Isotopic Fingerprinting of Nitrous Oxide Emissions from the United States Corn Belt

  NSF · $400k · 2021–2026

Frequent coauthors

• John M. Baker

  United States Department of Agriculture

  147 shared

• Ankur R. Desai

  University of Wisconsin–Madison

  140 shared

• Dennis Baldocchi

  University of California, Berkeley

  131 shared

• N. A. Brunsell

  University of Kansas

  129 shared

• Martha C. Anderson

  125 shared

• Glynn Hulley

  Jet Propulsion Laboratory

  123 shared

• Simon J. Hook

  123 shared

• Gregory Halverson

  Jet Propulsion Laboratory

  123 shared

Education

• PhD, Earth and Environmental Science

  McMaster University

  2000

Awards & honors

• Fellow of the American Meteorological Society, 2025
• The 2012 Editors’ Citation for Excellence in Refereeing for…
• National Science Foundation, Career Award, 2006
• CFANS Distinguished Teaching Award, 2006