A5045017762- Atmospheric chemistry and aerosols
- Atmospheric Ozone and Climate
- Atmospheric and Environmental Gas Dynamics
- Air Quality and Health Impacts
- Air Quality Monitoring and Forecasting
- Plant responses to elevated CO2
- Atmospheric aerosols and clouds
- Advanced Chemical Sensor Technologies
- Vehicle emissions and performance
- Plant biochemistry and biosynthesis
- Plant Water Relations and Carbon Dynamics
- Odor and Emission Control Technologies
- Catalytic Processes in Materials Science
- Innovative Microfluidic and Catalytic Techniques Innovation
- Hydrocarbon exploration and reservoir analysis
- Forest Insect Ecology and Management
- Catalysis and Oxidation Reactions
- Isotope Analysis in Ecology
- Environmental and biological studies
- Process Optimization and Integration
- Geography and Environmental Studies
- Spacecraft and Cryogenic Technologies
- Phytochemistry Medicinal Plant Applications
- Zeolite Catalysis and Synthesis
- Analytical Chemistry and Chromatography
Colby College
2018-2023
Harvard University
2014-2021
Harvard University Press
2015-2019
Planetary Science Institute
2001-2016
Amherst College
2004-2016
UPMC Altoona
2009
Pennsylvania State University
2009
California Institute of Technology
2002-2006
University of California, Irvine
1997-1999
A new method for the detection of gas-phase hydroperoxides is described. The clustering chemistry CF3O- exploited to produce speciated measurements several with high sensitivity and fast time response. Correspondence airborne observations made this technique established HPLC illustrated. appears be a highly versatile reagent ion both weak strong acids in atmosphere.
Abstract. A suite of offline and real-time gas- particle-phase measurements was deployed at Look Rock, Tennessee (TN), during the 2013 Southern Oxidant Aerosol Study (SOAS) to examine effects anthropogenic emissions on isoprene-derived secondary organic aerosol (SOA) formation. High- low-time-resolution PM2.5 samples were collected for analysis known tracer compounds in SOA by gas chromatography/electron ionization-mass spectrometry (GC/EI-MS) ultra performance liquid chromatography/diode...
Abstract. Substantial amounts of secondary organic aerosol (SOA) can be formed from isoprene epoxydiols (IEPOX), which are oxidation products mainly under low-NO conditions. Total IEPOX-SOA, may include SOA other parallel pathways, was quantified by applying positive matrix factorization (PMF) to mass spectrometer (AMS) measurements. The IEPOX-SOA fractions (OA) in multiple field studies across several continents summarized here and show consistent patterns with the concentration gas-phase...
Abstract The Observations and Modeling of the Green Ocean Amazon 2014–2015 (GoAmazon2014/5) experiment took place around urban region Manaus in central Amazonia across 2 years. pollution plume was used to study susceptibility gases, aerosols, clouds, rainfall human activities a tropical environment. Many aspects air quality, weather, terrestrial ecosystems, climate work differently tropics than more thoroughly studied temperate regions Earth. GoAmazon2014/5, cooperative project Brazil,...
Large particles containing nitric acid (HNO3) were observed in the 1999/2000 Arctic winter stratosphere. These situ observations made over a large altitude range (16 to 21 kilometers) and horizontal extent (1800 on several airborne sampling flights during period of weeks. With diameters 10 20 micrometers, these sedimenting have significant potential denitrify lower A microphysical model trihydrate is able simulate growth sedimentation sizes stratosphere, but nucleation process not yet known....
Abstract. The yield of particle mass in secondary organic aerosol (SOA) formed by dark ozonolysis was measured for 0.3–22.8 ppbv reacted α-pinene. Most experiments were conducted using a continuous-flow chamber, allowing nearly constant SOA concentration and chemical composition several days. For comparison, some also batch mode. Reaction conditions 25°C, 40% RH, dry (NH4)SO4 seed particles, excess 1-butanol. loading independently an spectrometer scanning mobility sizer, the two measurements...
Abstract. The photo-oxidation chemistry of isoprene (ISOP; C5H8) was studied in a continuous-flow chamber under conditions such that the reactions isoprene-derived peroxyl radicals (RO2) were dominated by hydroperoxyl (HO2) pathway. A proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) with switchable H3O+ and NO+ reagent ions used for product analysis. products methyl vinyl ketone (MVK; C4H6O) methacrolein (MACR; differentiated using ions. MVK MACR yields via HO2 pathway...
Significance For isolated regions of the planet, organic peroxy radicals produced as intermediates atmospheric photochemistry have been expected to follow HO 2 rather than NO pathways. Observational evidence, however, has lacking. An accurate understanding relative roles two pathways is needed for quantitative predictions concentrations particulate matter, oxidation capacity, and consequent environmental climate impacts. The results herein, based on measurements, find that ratio reaction...
Abstract. Biogenic volatile organic compounds (BVOCs) from the Amazon forest region represent largest source of carbon emissions to atmosphere globally. These BVOC dominantly consist and intermediate-volatility terpenoid that undergo chemical transformations in form oxygenated condensable gases secondary aerosol (SOA). We collected quartz filter samples with 12 h time resolution performed hourly situ measurements a semi-volatile thermal desorption gas chromatograph (SV-TAG) at rural site...
Abstract. We describe the implementation of a biochemical model isoprene emission that depends on electron requirement for synthesis into Farquhar–Ball–Berry leaf photosynthesis and stomatal conductance is embedded within global chemistry-climate simulation framework. The production calculated as function transport-limited photosynthesis, intercellular atmospheric carbon dioxide concentration, canopy temperature. vegetation biophysics module computes photosynthetic uptake coupled with...
Abstract. A sampler for volatile organic compounds (VOCs) was developed deployment on a multicopter unmanned aerial vehicle (UAV). The designed to collect gas- and aerosol-phase VOCs up four commercially available VOC-adsorbent cartridges subsequent offline analysis by thermal-desorption gas chromatography. had mass of 0.90 kg dimensions 19 cm ×20 ×5 cm. Power consumption < 10 kJ in typical 30 min flight, representing 3 % the total UAV battery capacity. Autonomous operation data...
The emissions, deposition, and chemistry of volatile organic compounds (VOCs) are thought to be influenced by underlying landscape heterogeneity at intermediate horizontal scales several hundred meters across different forest subtypes within a tropical forest. Quantitative observations scientific understanding these scales, however, remain lacking, in large part due historical absence canopy access suitable observational approaches. Herein, VOC concentrations the near-canopy atmosphere was...
The chemical pathways for the production of secondary organic aerosols (SOA) are influenced by concentration nitrogen oxides (NOx), including organonitrates (ON). Herein, a series experiments conducted in an environmental chamber investigated and partitioning total from α-pinene photo-oxidation <1 to 24 ppb NOx. Gas-phase particle-phase (gON pON, respectively) were measured laser-induced fluorescence (LIF). composition particle phase mass simultaneously characterized online aerosol...
Abstract. The cloud condensation nuclei (CCN) properties of ammonium sulfate particles mixed with organic material condensed during the hydroxyl-radical-initiated photooxidation isoprene (C5H8) were investigated in continuous-flow Harvard Environmental Chamber. CCN activation curves measured for particle mass concentrations 0.5 to 10.0 μg m−3, NOx from under 0.4 ppbv up 38 ppbv, mobility diameters 70 150 nm, and thermodenuder temperatures 25 100 °C. At °C, observed accurately described by a...
Abstract. Fluxes of biogenic volatile organic compounds, including isoprene, monoterpenes, and oxygenated VOCs measured above a mixed forest canopy in central Massachusetts during the 2005 2007 growing seasons are reported. Mixing ratios were using proton transfer reaction mass spectrometry (PTR-MS) fluxes computed by disjunct eddy covariance technique. Isoprene was far predominant BVOC emitted at this site, with summer mid-day average 5.3 4.4 mg m−2 hr−1 2007, respectively. In comparison,...
The oxidation of isoprene is a globally significant source secondary organic material (SOM) atmospheric particles. relative importance different parallel pathways, however, remains inadequately understood and quantified. SOM production from photooxidation was studied under hydroperoxyl-dominant conditions for <5% humidity at 20 °C in the presence highly acidic to completely neutralized sulfate Isoprene separated by using two continuously mixed flow reactors connected series operated steady...
Abstract. An understanding of how anthropogenic emissions affect the concentrations and composition airborne particulate matter (PM) is fundamental to quantifying influence human activities on climate air quality. The central Amazon Basin, especially around city Manaus, Brazil, has experienced rapid changes in past decades due ongoing urbanization. Herein, concentration submicron PM pollution downwind Manaus metropolitan region are reported as part GoAmazon2014/5 experiment. A...
Observational evidence of isoprene oxidation shows that nitrogen oxides amplify the OH concentrations over Amazon forest.
Volatile organic compounds (VOCs) are important pollutants that affect air quality and atmosphere–ecosystem interactions. Atmospheric sampling onboard a multicopter unmanned aerial vehicle (UAV), serving as an economical flexible measurement technique, collects valuable VOC data sets at intermediate spatial scales of hundreds meters. In this study, we deployed UAV-based sampler in South China conducted samplings two locations over the canopy subtropical forest. The collected samples were...
Abstract. The influence of second-generation products on the particle mass yield β-caryophyllene ozonolysis was systematically tested and quantified. approach to vary relative concentrations first- by adjusting concentration ozone while observing changes in yield. For all wall-loss corrected organic Morg this study (0.5 < 230 μg m−3), data show that particle-phase material composed for most part products. 0.5< 10 m−3, a range which overlaps with atmospheric concentrations, 20% not...
Abstract. Methanol is the second most abundant volatile organic compound in troposphere and plays a significant role atmospheric chemistry. While there consensus about dominant of living plants as major source reaction with OH sink methanol, global methanol budgets diverge considerably terms source/sink estimates, reflecting uncertainties approaches used to model empirical data separately constrain these terms. Here we compiled micrometeorological flux from eight different study sites...
Abstract. Methyl ethyl ketone (MEK) is an important compound in atmospheric chemistry. While attention has been paid mostly to anthropogenic sources of MEK, recently it shown that biogenic are globally as ones. However, the origin MEK yet be completely elucidated. We present full mechanism by which within-plant transformation methyl vinyl (MVK) and, a minor extent, 2-butanol and 3-buten-2-ol, source MEK. Such observed red oak for both exogenous MVK, taken up from atmosphere, endogenous MVK...
The uptake of gas-phase dicarboxylic acids to organic particulate matter (PM) was investigated probe the role PM physical state in exchange processes between semivolatile molecules and PM. A homologous series molecules, specifically isotopically labeled 13C-dicarboxylic acids, used conjunction with aerosol mass spectrometry obtain a quantitative characterization for different relative humidities (RHs). produced by dark ozonolysis unlabeled α-pinene. 13C-labeled oxalic, malonic,...
The production of secondary organic material (SOM) by the reactive uptake isoprene photooxidation products was investigated using partially to wholly neutralized sulfuric acid particles.
Abstract We present OH observations made in Amazonas, Brazil during the Green Ocean Amazon campaign (GoAmazon2014/5) from February to March of 2014. The average diurnal variation peaked with a midday (10:00–15:00) 1.0 × 10 6 (±0.6 ) molecules cm −3 . This was substantially lower than previously reported other tropical forest photochemical environments (2–5 while simulated reactivity lower. observational data set used constrain box model examine how well current reaction mechanisms can...