About

Jose-Luis Jimenez is a Distinguished Professor at the University of Colorado Boulder and an Institute Fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES). His research centers on the development and application of advanced instrumentation for real-time, quantitative measurements of the size, chemical composition, and morphology of submicron aerosols. His work is motivated by the importance of atmospheric aerosols in affecting radiation balance (climate forcing), human health, visibility, and acid deposition, with most effects not well understood due to limitations in instrumentation. Jimenez's group also investigates the role of aerosols in the transmission of respiratory diseases such as COVID-19. His extensive contributions to atmospheric chemistry and aerosol science have earned him numerous awards and honors, including being ranked as a top scientist in environmental science, highly cited researcher, and fellow of major scientific societies. He holds a Ph.D. from MIT and has postdoctoral experience at Aerodyne Research, MIT, and Caltech.

Research topics

• Computer Science
• Medicine
• Meteorology
• Physics
• Atmospheric sciences
• Chemistry
• Geology
• Internal medicine
• Environmental science
• Virology
• Political Science
• Telecommunications
• Environmental chemistry
• Engineering
• Oceanography
• Geography
• Biochemical engineering
• Nursing
• Climatology
• Intensive care medicine
• Materials science
• Business
• Mathematics
• Nanotechnology

Selected publications

• Aerosol Scavenging in DC3 and SEAC ⁴ RS Deep Convective Storms

  2026-01-23

  articleOpen access

  Abstract. Convective storms frequently occur over the central US during the late spring and summer impacting upper tropospheric composition, which in turn affects the radiative forcing of the climate system. Two important processes in deep convection are vertical transport and removal of trace gases and aerosols by microphysical scavenging. We calculate scavenging efficiencies of speciated aerosol mass concentrations based primarily on aircraft observations from the Deep Convective Clouds and Chemistry (DC3) and the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) field experiments combined with process-scale modeling. Sulfate and ammonium scavenging efficiencies are generally greater than 75 % for all storms analyzed. Particulate nitrate scavenging efficiencies are moderate (~40 %). In some cases, the particulate nitrate concentrations are larger in the storm outflow region compared to the inflow region. Further analysis shows the role of entrainment of mid-tropospheric particulate nitrate layers and lightning production of nitrogen oxides in affecting the particulate nitrate outflow concentrations. Organic aerosol scavenging efficiencies are greater than 75 % in severe storms, comparable to sulfate and ammonium, but ~50 % for weak and moderate storms. Production of organic acids in cloud water is shown to contribute to organic aerosol mass in the outflow regions for the mid-day storms sampled, which may explain why those storms have lower apparent scavenging efficiencies. These results, which highlight the complex interactions between dynamics, physics, and chemistry in thunderstorms, can be used by chemistry transport models as a way to evaluate convective storm processing of aerosols.

  PublisherOA PDFDOI

• Examining the Effects of Parameterized Changes in Biomass Burning NOx Emissions on Forecasted Air Quality

  2026-03-02

  articleOpen access

  Climate change has led to an increase in the number and size of wildfires in western North America, and their emissions of particulate matter and reactive trace gases threaten to offset otherwise improving air quality. Most air quality models do not dynamically update the chemical composition of biomass burning emissions with each model time step. However, laboratory, field, and satellite remote sensing observations indicate that the chemical composition of wildfire emissions changes with evolving combustion conditions (i.e. flaming vs. smoldering). We have previously shown that the Tropospheric Monitoring Instrument (TROPOMI) can be used to observe day-to-day changes in the chemical composition of wildfire emissions, during the transition from flaming to smoldering combustion. Here, we present the use of the Hourly Wildfire Potential index (HWP) to predict the impact of meteorological changes on wildfire activity, combined with TROPOMI observations of enhanced nitrogen dioxide (NO2) emissions compared with that of carbon monoxide (CO) ( ∆ NO2/ ∆ CO), to parameterize how biomass burning nitrogen oxide (NOx) emissions change with evolving combustion conditions. We implemented this parameterization in the High-Resolution Rapid Refresh model coupled with Chemistry (HRRR-Chem), developed by NOAA Global Systems Laboratory. HRRR-Chem is an experimental and high-resolution (3x3 km2$) atmospheric chemical transport model for the U.S. based on the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). We compared modeled smoke and trace gases with airborne measurements to evaluate our model. Overall, we found that modifying biomass burning NOx emissions based on HWP significantly improved predicted ozone concentrations in smoke plumes.

  PublisherDOI

• Supplementary material to "Aerosol Scavenging in DC3 and SEAC ⁴ RS Deep Convective Storms"

  2026-01-23

  articleOpen access

  DC3 caseThe 18 May 2012 case, sampled near Ogallala, Nebraska in the vicinity of a cold front, had a SWEAT Index of 283 categorizing it as a moderate, single cell storm.The storm was quite strong with respect to the 20 dBZ cloud top heights of 14 km MSL, reports of hail of one inch diameter (Herndon, 2012a), and periods of high lightning flash rates.The storm had relatively higher anthropogenic and agriculture signatures and lower biogenic signatures based on VOC measurements.The environment had a dry aerosol extinction of 31 Mm -1 , which is slightly higher than typical rural conditions (Barth et al., 2015).The BL f(OA) was 36%, underscoring the weaker influence of biogenic VOCs. May 2012 DC3 caseThe 29 May 2012 storm, sampled north of Oklahoma City, Oklahoma as a line of supercell storms, had a SWEAT Index of 422 producing large hail (up to 3 inch diameter) and a weak tornado.With its high convective available potential energy and 0-6 km wind shear, 20 dBZ cloud top heights exceeded 17 km MSL altitude.Vertical velocities exceeded 50 m s -1 (DiGangi et al., 2016).The central Oklahoma region has characteristics of both anthropogenic and biogenic VOCs with nearby oil and gas fields in central Oklahoma and north Texas, urban influences (Oklahoma City), and vegetation in eastern Oklahoma.The BL f(OA) was 53% and the dry aerosol extinction was 36 Mm -1 , slightly higher than typical rural conditions.This case is the same as that studied by Yang et al. (2015).

  PublisherDOI

• Isomer-resolved online analysis of organic aerosols using ion mobility mass spectrometry

  2026-04-10

  articleOpen access

  Abstract. Secondary organic aerosol (SOA) makes up much of the particulate matter in the troposphere and impacts global climate and human health, though uncertainties regarding the sources and properties of SOA limit our understanding of these effects. New analytical techniques are required to better characterize the molecular composition of SOA, including methods that can identify isomeric compounds that may have different contributions to SOA properties such as hygroscopicity or volatility. We present a method for isomer-resolved analysis of SOA using a commercially available chemical ionization ion-mobility time-of-flight mass spectrometer (CI-IMS-TOF) and a Vaporization Inlet for Aerosols (VIA). The compatibility of the VIA and the CI-IMS-TOF was assessed through the analysis of 10 carboxylic acid standards across a large temperature range (30 - 170 °C). Ion drift times were found to be stable to within 0.075% of their initial values after drift time calibration. The VIA-CI-IMS-TOF was also used to collect real-time ion mobility and mass spectra of SOA constituents during an α-pinene ozonolysis chamber experiment. Several reaction products were identified in the SOA using synthetic standards, including structural isomers of C8H12O4 and C9H14O4. Temporal evolution of reaction products was used to assess formation timescales and determine the generation of oxidation for individual isomers. Both iodide and bromide reagent ions were used in the VIA-CI-IMS-TOF to achieve a more comprehensive analysis of SOA. This study demonstrates the performance of the VIA-CI-IMS-TOF for online, isomer-resolved analysis of organic aerosol and its potential for improving the current understanding of SOA composition.

  PublisherOA PDFDOI

• Secondary Organic Aerosol Yields from NO ₃ Oxidation of Phenolic, Aromatic, and Heterocyclic VOCs: Implications for Biomass Burning Plumes

  ACS ES&T Air · 2025-10-04

  articleSenior authorCorresponding

  Biomass burning secondary organic aerosol (BBSOA) has become an important research area in atmospheric science, particularly due to the ongoing global increase in wildfire activity. BBSOA can form from the reactions of emitted volatile organic compounds (VOCs) and gas-phase evaporated primary organic aerosols (POA) with atmospheric oxidants such as O3, OH, and NO3. While some studies have examined SOA formation from OH during daytime BB events, fewer have considered the potentially significant role of NO3. In this chamber study, vapor wall loss (VWL)-corrected SOA yields from the NO3 oxidation of five known BBVOCs: catechol, phenol, styrene, furfural, and methyl furfural are reported. SOA from NO3 reactions of phenol, furfural, and methyl furfural have not been previously reported, to our knowledge. VWL corrections increased the measured SOA yield by 30–41% across an OA range of ∼5 to ∼500 μg m–3, which represents aerosol concentrations from dilute to concentrated biomass burning plumes. Catechol had the highest yield at OA = 100 μg m–3 (1.5), followed by furfural (0.17) and styrene (0.17), with phenol (0.08) and methyl furfural (0.10) having the lowest yields. A wildfire case study is also presented to illustrate the importance of both evaporation and chemistry in understanding BB aerosol composition, though their relative importance is highly dependent on oxidant concentrations, temperature, and dilution rates. Finally, an extractive electrospray soft ionization mass spectrometer (EESI) was used to obtain data on potential molecular species in each experiment, and the nitrocatechol mass yield for the reaction of catechol with NO3 is determined to be 0.90 ± 0.35.

  PublisherDOI

• 1 The United States and the Second Spanish Republic (1931–1936). An Overview from a Monetary Policy Perspective

  Boydell and Brewer eBooks · 2025-12-11

  book-chapter1st authorCorresponding

  1 The United States and the Second Spanish Republic (1931–1936). An Overview from a Monetary Policy Perspective was published in Foes to Friends. Spain, the United States and the United Kingdom from the Civil War to the Cold War on page 6.

  PublisherDOI

• Deconvolution of Partitioning Delays from Time-Resolved Trace Gas Measurements

  ACS ES&T Air · 2025-09-10

  articleCorresponding

  Time-resolved measurements of low-volatility gas-phase compounds are limited by partitioning of the analyte to instrument surfaces, resulting in what are known as partitioning delays. These delays slow instrument responses and affect the accuracy of subsequent analyses. In this work, we introduce a deconvolution algorithm that corrects measurements affected by partitioning delays. We evaluate the performance of this algorithm using synthetic data and also demonstrate its utility in correcting partitioning delays in airborne nitric acid measurements. We compare the effectiveness of deconvolution to the current best practice for partitioning delays: frequent subtraction of instrument background. Frequent background measurements are outperformed by the deconvolution algorithm when sample concentrations are changing faster than the instrument response time. The deconvolution algorithm can be applied to time series that include frequent measurement of instrument backgrounds, enabling reanalysis of past data. Furthermore, the algorithm does not rely on any coincident data; it is effective without any external information about the true time series of an analyte. When applied to nitric acid measurements from a wildfire smoke plume, deconvolution increases the calculated normalized excess mixing ratio (ΔHNO3/ΔCO) by 72%. We conclude that the deconvolution algorithm is applicable to ground, airborne, and eddy covariance measurements of “sticky” compounds.

  PublisherDOI

• Particulate Matter Concentrations Derived from Airborne High Spectral Resolution Lidar Measurements Using Machine Learning Regression

  2025-10-09

  articleOpen access

  Abstract. We use measurements of near-surface aerosol backscatter, extinction, and depolarization acquired by four NASA Langley Research Center airborne High Spectral Resolution Lidars (HSRLs) in machine learning (ML) regression algorithms to derive concentrations of particulate matter (PM) with aerodynamic diameters less than 2.5 mm (PM2.5), 10 mm (PM10), and the PM2.5/PM10 ratio. The ML regression models are trained using airborne HSRL measurements acquired over major metropolitan regions in the United States and Asia that are coincident with hourly surface PM2.5 and PM10 measurements from the EPA air quality system and similar networks in other countries. We examine several regression methods and find that exponential Gaussian Process regression (GPR) algorithms consistently give the best performance in terms of the lowest root-mean-square (RMS) errors and the highest correlations. When evaluated using surface measurements withheld from the training sets, ML models that use the HSRL near-surface measurements of aerosol backscatter and aerosol intensive properties such as depolarization, backscatter color ratio, and lidar ratio typically give the best performance with RMS differences in PM2.5 retrievals around 5 mg m-3 and correlation coefficients above 0.8, respectively. Corresponding RMS differences and correlation coefficients for PM10 retrievals are 11 mg m-3 and 0.7 and corresponding RMS differences and correlation coefficients for PM2.5/PM10 are 0.17 and 0.75. This retrieval performance is achieved using airborne HSRL measurements alone and so does not depend on external knowledge of or assumptions regarding aerosol type, aerosol mass extinction efficiency, aerosol hygroscopic growth, the ratio of PM2.5 to PM10, particle density, or relative humidity. PM2.5 values in the training set range from about 5 to 80 mg m-3; PM10 values range from about 10 to 100 mg m-3. Accurate retrievals of PM outside these ranges would require commensurate training data. We present examples of PM retrievals in the United States as well as Asia when HSRL measurements were acquired when the aircraft flew systematic "raster-scan" patterns for several hours over major urban areas. We show that these PM2.5 retrievals are in good agreement with PM2.5 derived from coincident airborne in situ measurements near the surface as well as aloft. We describe also how the distribution of PM2.5 varies with aerosol type and altitude over these regions. We use the HSRL measurements of aerosol extinction and retrievals of surface PM2.5 along with HSRL retrievals of aerosol type to derive estimates of the fine mode aerosol mass extinction efficiency (MEEf) for major aerosol types identified by an updated HSRL aerosol classification method. MEEf ranges from about 2.6 ± 0.5 m2 g-1 for maritime aerosol to 5.0 ± 0.7 m2 g-1 for smoke. These estimates of MEEf are also in good agreement with values derived from airborne in situ measurements. We also discuss how this methodology may be applied to measurements from the Atmospheric Lidar (ATLID) on the EarthCARE satellite.

  PublisherOA PDFDOI

• Impact of CrIS-Derived NH ₃ Emission Updates on Simulated Nitrate and Ammonium Aerosols over East Asia

  Environmental Science & Technology · 2025-12-25

  articleOpen access

  Fine particulate matter (PM1 diameter <1 μm) strongly affects air quality and health, with sulfate, nitrate, and ammonium (SNA) as major components across East Asia. Because NH3 is a key precursor of SNA formation, accurate NH3 emission data are essential for reliable SNA simulations. This study improves NH3 emission inventories in East Asia by integrating the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) and the Cross-Track Infrared Sounder (CrIS), with extensive evaluation against ground-based and aircraft observations from the Korea-United States Air Quality (KORUS-AQ) campaign. Iterative linear inversion of NH3 emissions using WRF-Chem markedly enhances simulations of nitrate and ammonium, in agreement with both the aircraft and surface measurements. The absolute biases of nitrate and ammonium were reduced from 89.7 and 50.1% to 13.6 and 0.6%, respectively, compared to the aircraft observations over Seoul. However, uncertainties in nocturnal NH3 emissions remain potential sources of nighttime biases in nitrate and ammonium. Overall, the results indicate that nitrate aerosol in most of East Asia is sensitive to NH3 emission changes. To advance our understanding of SNA formation and support effective aerosol mitigation policies, improved characterization of the diurnal cycle of NH3 emissions through ground-based monitoring and high-resolution geostationary satellite observations is urgently needed.

  PublisherDOI

• The Impact of UVC Light on Indoor Air Chemistry: A Modeling Study

  Environmental Science & Technology · 2025-07-30 · 2 citations

  articleOpen access

  Germicidal ultraviolet light (GUV) is gaining attention for air disinfection, particularly following the COVID-19 pandemic. GUV air cleaning devices use 222 or 254 nm light to remove airborne and surface pathogens from indoor environments, although their impact on indoor chemistry has received limited attention. This modeling study investigates the impact of GUV light on indoor air pollutant concentrations. In a simulated, occupied classroom using a 222 nm lamp with an average room irradiance of 1 μW cm–2, the predicted ozone production rate was 0.33 mg h–1 for an air change rate of 0.5 h–1, leading to surface interactions with occupants and inanimate surfaces that formed secondary products including nonanal, decanal, and 4-oxopentanal. By contrast, ozone concentration increased by 0.19 mg h–1 at 0.5 h–1 in the presence of a 254 nm lamp with an average room irradiance of 15 μW cm–2, primarily due to infiltration. The long-term health benefits of GUV light disinfection need to be quantitatively compared to the health harms due to GUV-induced pollution to allow a more complete assessment of the benefits of this technology.

  PublisherDOI

Recent grants

• The Chemistry of Oxidation Flow Reactors (OFR) and the Sources of Semivolatile and Intermediate Volatility Secondary Organic Aerosol (SOA) Precursors in Recent NSF Field Studies

  NSF · $642k · 2018–2022

• Collaborative Research: Characterization of Sources and Processes of Organic Fine Particulate Matter in Mexico City

  NSF · $150k · 2005–2009

• Collaborative Research: Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER)

  NSF · $535k · 2014–2017

• Collaborative Research: The Effects of Anthropogenic-Biogenic Interactions on Secondary Organic Aerosol Formation

  NSF · $560k · 2013–2016

• Real-Time Size and Composition Aerosol Measurements on the NSF C-130 Aircraft and Integrated Data Analysis

  NSF · $200k · 2005–2008

Frequent coauthors

• Pedro Campuzano‐Jost

  1157 shared

• D. A. Day

  Cooperative Institute for Research in Environmental Sciences

  862 shared

• J. A. de Gouw

  Cooperative Institute for Research in Environmental Sciences

  500 shared

• Benjamin A. Nault

  Johns Hopkins University

  492 shared

• Brett B. Palm

  University of Washington

  432 shared

• Weiwei Hu

  Guangzhou Institute of Geochemistry

  394 shared

• Douglas R. Worsnop

  University of Helsinki

  386 shared

• P. F. DeCarlo

  Johns Hopkins University

  324 shared

Education

• Ph.D.

  Massachusetts Institute of Technology

  1999

• Other

  Aerodyne Research / M.I.T.

  2000

• Other

  California Institute of Technology

  2002

Awards & honors

• College Scholar Award, University of Colorado (2014)
• AGU Ascent Award (2012)
• Kenneth T. Whitby Award of the American Association for Aero…
• Rosenstiel Award of the RSMAS School, University of Miami (2…
• National Science Foundation Young Investigator "CAREER" Awar…