Gas-phase broadband spectroscopy using active sources: progress, status, and applications

Broadband spectroscopy is an invaluable tool for measuring multiple gas-phase species simultaneously. In this work we review basic techniques, implementations, and current applications for broadband spectroscopy. We discuss components of broadband spectroscopy including light sources, absorption cells, and detection methods and then discuss specific combinations of these components in commonly used techniques. We finish this review by discussing potential future advances in techniques and applications of broadband spectroscopy

Can COSMOTherm Predict a Salting in Effect?

We have used COSMO-RS, a method combining quantum chemistry with statistical thermodynamics, to compute Setschenow constants (K-S) for a large array of organic solutes and salts. These comprise both atmospherically relevant solute-salt combinations, as well as systems for which experimental data are available. In agreement with previous studies on single salts, the Setschenow constants predicted by COSMO-RS (as implemented in the COSMOTherm program) are generally too large compared to experiments. COSMOTherm overpredicts salting out (positive K-S), and/or underpredicts salting in (negative K-S). For ammonium and sodium salts, K-S values are larger for oxalates and sulfates, and smaller for chlorides and bromides. For chloride and bromide salts, K-S values usually increase with decreasing size of the cation, along the series Pr4N+ <Et4N+ <Me4N+Peer reviewe

Gas-phase broadband spectroscopy using active sources: progress, status, and applications

Broadband spectroscopy is an invaluable tool for measuring multiple gas-phase species simultaneously. In this work we review basic techniques, implementations, and current applications for broadband spectroscopy. We discuss components of broadband spectroscopy including light sources, absorption cells, and detection methods and then discuss specific combinations of these components in commonly used techniques. We finish this review by discussing potential future advances in techniques and applications of broadband spectroscopy

Open-path dual-comb spectroscopy of methane and VOC emissions from an unconventional oil well development in Northern Colorado

We present results from a field study monitoring methane and volatile organic compound emissions near an unconventional oil well development in Northern Colorado from September 2019 to May 2020 using a mid-infrared dual-comb spectrometer. This instrument allowed quantification of methane, ethane, and propane in a single measurement with high time resolution and integrated path sampling. Using ethane and propane as tracer gases for methane from oil and gas activity, we observed emissions during the drilling, hydraulic fracturing, millout, and flowback phases of well development. Large emissions were seen in drilling and millout phases and emissions decreased to background levels during the flowback phase. Ethane/methane and propane/methane ratios varied widely throughout the observations

Bostonia: The Boston University Alumni Magazine. Volume 16

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Secondary Organic Aerosol Formation from alpha-dicarbonyls in Aerosol Water: Salt Interactions and Multi-Phase Chemistry

This thesis advances our understanding of secondary organic aerosol (SOA) formation from small, water soluble molecules like glyoxal and methyl glyoxal that partition to the aerosol aqueous phase according to Henry\u27s law. Their partitioning behavior can be altered by the presence of inorganic salts, which are abundant in aerosols. If the molecules become more soluble this is called \u22salting in\u22 and the reverse is \u22salting out\u22. We present the first measurements of salting constants of glyoxal and methyl glyoxal in the aerosol-relevant salts ammonium sulfate, ammonium nitrate, sodium chloride, and sodium nitrate, as well as additional salts for theory-measurement comparison purposes: tetramethylammonium bromide, tetrabutylammonium bromide, and sodium oxalate. We find that glyoxal \u22salts in\u22 to all salts tested, while methyl glyoxal \u22salts out\u22. Explanations for their salting behavior are presented using quantum-mechanical calculations to quantify molecule-ion attractions and proposed literature mechanisms to predict repulsive forces (solution volume decrease upon salt addition, dielectric decrement). We calculate a ΔG of interaction (the enthalpy for replacing a water molecule in the hydration shell of an ion with an organic molecule) for isoprene epoxydiol (IEPOX) and its ring-opening product methyl tetrol with sulfate, and given the structural similarities of IEPOX and methyl tetrol with methyl glyoxal, we find that the values are similar to the value for methyl glyoxal. Therefore we predict that trans-Β-IEPOX and its methyl tetrol likely salt out with a salting constant similar to methyl glyoxal. Partitioning also influences reactivity. In a series of simulation chamber experiments we have studied the effect of NH3 on the rate of gly-SOA formation and find that in the presence of added NH3 we observe a significant enhancement in total SOA mass formed from glyoxal, especially in the formation of nitrogen-containing products (imidazoles) and the overall aerosol N/C. We present the results of simulation chamber experiments that focus on the chemical composition of gly-SOA. We are able to identify a number of imidazoles resulting from the reaction of glyoxal + NH4+ . We also use time-resolved data to propose a mechanism for their formation. By comparing imidazole formation under a variety of different chamber conditions we are able to determine under what conditions they will contribute most strongly to brown carbon formation. We have further used a box model to simulate SOA formation in Mexico City during the MCMA-2003 campaign using an explicit aqueous-phase mechanism for glyoxal processing (gly-SOA). This gly-SOA was compared to SOA from semi/intermediate volatility gases (S/I VOC) using a near explicit gas-phase oxidation mechanism, and two different volatility basis sets to characterize their partitioning. We also have applied our measured salting constants to predict SOA formation over the continental United States using the Community Multi-scale Air Quality Model (CMAQ). Significant SOA forms from the further reactions of these precursors in the aerosol, but the effect of salt is most important. The small Henry\u27s law constant for methyl glyoxal combined with the fact that it salts out means that even though methyl glyoxal is far more abundant in the gas phase than glyoxal, methyl glyoxal forms significantly less SOA than glyoxal. Our results suggest that salts also play an important role in modulating the SOA formation from isoprene

Potential of Aerosol Liquid Water to Facilitate Organic Aerosol Formation: Assessing Knowledge Gaps about Precursors and Partitioning.

Isoprene epoxydiol (IEPOX), glyoxal, and methylglyoxal are ubiquitous water-soluble organic gases (WSOGs) that partition to aerosol liquid water (ALW) and clouds to form aqueous secondary organic aerosol (aqSOA). Recent laboratory-derived Setschenow (or salting) coefficients suggest glyoxal's potential to form aqSOA is enhanced by high aerosol salt molality, or "salting-in". In the southeastern U.S., aqSOA is responsible for a significant fraction of ambient organic aerosol, and correlates with sulfate mass. However, the mechanistic explanation for this correlation remains elusive, and an assessment of the importance of different WSOGs to aqSOA is currently missing. We employ EPA's CMAQ model to the continental U.S. during the Southern Oxidant and Aerosol Study (SOAS) to compare the potential of glyoxal, methylglyoxal, and IEPOX to partition to ALW, as the initial step toward aqSOA formation. Among these three studied compounds, IEPOX is a dominant contributor, ∼72% on average in the continental U.S., to potential aqSOA mass due to Henry's Law constants and molecular weights. Glyoxal contributes significantly, and application of the Setschenow coefficient leads to a greater than 3-fold model domain average increase in glyoxal's aqSOA mass potential. Methylglyoxal is predicted to be a minor contributor. Acid or ammonium - catalyzed ring-opening IEPOX chemistry as well as sulfate-driven ALW and the associated molality may explain positive correlations between SOA and sulfate during SOAS and illustrate ways in which anthropogenic sulfate could regulate biogenic aqSOA formation, ways not presently included in atmospheric models but relevant to development of effective control strategies

Potential of Aerosol Liquid Water to Facilitate Organic Aerosol Formation: Assessing Knowledge Gaps about Precursors and Partitioning

Isoprene epoxydiol (IEPOX), glyoxal, and methylglyoxal are ubiquitous water-soluble organic gases (WSOGs) that partition to aerosol liquid water (ALW) and clouds to form aqueous secondary organic aerosol (aqSOA). Recent laboratory-derived Setschenow (or salting) coefficients suggest glyoxal’s potential to form aqSOA is enhanced by high aerosol salt molality, or “salting-in”. In the southeastern U.S., aqSOA is responsible for a significant fraction of ambient organic aerosol, and correlates with sulfate mass. However, the mechanistic explanation for this correlation remains elusive, and an assessment of the importance of different WSOGs to aqSOA is currently missing. We employ EPA’s CMAQ model to the continental U.S. during the Southern Oxidant and Aerosol Study (SOAS) to compare the potential of glyoxal, methylglyoxal, and IEPOX to partition to ALW, as the initial step toward aqSOA formation. Among these three studied compounds, IEPOX is a dominant contributor, ∼72% on average in the continental U.S., to potential aqSOA mass due to Henry’s Law constants and molecular weights. Glyoxal contributes significantly, and application of the Setschenow coefficient leads to a greater than 3-fold model domain average increase in glyoxal’s aqSOA mass potential. Methylglyoxal is predicted to be a minor contributor. Acid or ammonium - catalyzed ring-opening IEPOX chemistry as well as sulfate-driven ALW and the associated molality may explain positive correlations between SOA and sulfate during SOAS and illustrate ways in which anthropogenic sulfate could regulate biogenic aqSOA formation, ways not presently included in atmospheric models but relevant to development of effective control strategies

Secondary organic aerosol formation from semi- and intermediate-volatility organic compounds and glyoxal: Relevance of O/C as a tracer for aqueous multiphase chemistry

International audienceThe role of aqueous multiphase chemistry in the formation of secondary organic aerosol (SOA) remains difficult to quantify. We investigate it here by testing the rapid formation of moderate oxygen-to-carbon (O/C) SOA during a case study in Mexico City. A novel laboratory-based glyoxal-SOA mechanism is applied to the field data, and explains why less gas-phase glyoxal mass is observed than predicted. Furthermore, we compare an explicit gas-phase chemical mechanism for SOA formation from semi- and intermediate-volatility organic compounds (S/IVOCs) with empirical parameterizations of S/IVOC aging. The mechanism representing our current understanding of chemical kinetics of S/IVOC oxidation combined with traditional SOA sources and mixing of background SOA underestimates the observed O/C by a factor of two at noon. Inclusion of glyoxal-SOA with O/C of 1.5 brings O/C predictions within measurement uncertainty, suggesting that field observations can be reconciled on reasonable time scales using laboratory-based empirical relationships for aqueous chemistry