Cavity Ring-down Spectroscopy Research Articles

The localised density of H2O2 in the effluent of a cold atmospheric pressure plasma jet determined by continuous-wave cavity ring-down spectroscopy

Although the research on cold atmospheric pressure plasma jets and their applications is steadily growing, several questions remain open regarding fundamental aspects of how reactive species, such as hydrogen peroxide (H2O2), are generated in cold atmospheric pressure plasma jets, and how the composition of reactive species can be tailored for a specific purpose. Accordingly, absolute and spatially resolved distributions of the densities of reactive species in the effluent of cold atmospheric pressure plasma jets are required. In this work, a time efficient way to determine the local distribution of gas phase H2O2 in the effluent of a cold atmospheric-pressure plasma jet using continuous-wave cavity ring-down spectroscopy at a wavelength of 8.12 μm is presented. By a combination of an axial scan and of several radial distributions, the localised density distribution of H2O2 in the effluent of the kINPen-sci plasma jet was obtained. Therefore, the effective absorption length was determined from the evolution of the radial distributions as a function of the distance from the nozzle, which was 1.6 mm close to the nozzle of the plasma jet, and increased to approximately 5 mm at a distance of 10 mm from the nozzle. The maximum density of approximately 2 ⋅ 1014 cm−3 was found in the centre of the effluent close to the nozzle. From the presented localised density distribution, it can be concluded that H2O2 is significantly generated within the plasma zone of the plasma jet. This work presents an important step towards the understanding of formation and consumption mechanisms of biomedically relevant species in the plasma zone and the effluent of a cold atmospheric pressure plasma jet.

Nitrogen fixation in the stag beetle, Ceruchus piceus (Coleoptera: Lucanidae): could insects contribute more to ecosystem nitrogen budgets than previously thought?

Nitrogen (N) is a key nutrient required by all living organisms for growth and development, but is a limiting resource for many organisms. Organisms that feed on material with low N content, such as wood, might be particularly prone to N limitation. In this study, we investigated the degree to which the xylophagous larvae of the stag beetle Ceruchus piceus (Weber) use associations with N-fixing bacteria to acquire N. We paired acetylene reduction assays by cavity ring-down absorption spectroscopy (ARACAS) with 15N2 incubations to characterize rates of N fixation within C. piceus. Not only did we detect significant N fixation activity within C. piceus larvae, but we calculated a rate that was substantially higher than most previous reports for N fixation in insects. While taking these measurements, we discovered that N fixation within C. piceus can decline rapidly in a lab setting. Consequently, our results demonstrate that previous studies, which commonly keep insects in the lab for long periods of time prior to and during measurement, may have systematically under-reported rates of N fixation in insects. This suggests that within-insect N fixation may contribute more to insect nutrition and ecosystem-scale N budgets than previously thought.

Photophysical oxidation of HCHO produces HO2 radicals.

Formaldehyde, HCHO, is the highest-volume carbonyl in the atmosphere. It absorbs sunlight at wavelengths shorter than 330 nm and photolyses to form H and HCO radicals, which then react with O2 to form HO2. Here we show HCHO has an additional HO2 formation pathway. At photolysis energies below the energetic threshold for radical formation we directly detect HO2 at low pressures by cavity ring-down spectroscopy and indirectly detect HO2 at 1 bar by Fourier-transform infrared spectroscopy end-product analysis. Supported by electronic structure theory and master equation simulations, we attribute this HO2 to photophysical oxidation (PPO): photoexcited HCHO relaxes non-radiatively to the ground electronic state where the far-from-equilibrium, vibrationally activated HCHO molecules react with thermal O2. PPO is likely to be a general mechanism in tropospheric chemistry and, unlike photolysis, PPO will increase with increasing O2 pressure.

Impurity Analysis of 5.5 N Nitrogen Gas and Its Impact on the Preparation of Class I Type Calibration Gas Mixtures

AbstractKnowledge of impurities in matrix gas is one of the critical requirements for the preparation of class I type calibration gas mixtures (primary reference gas mixtures, PRGMs) as per ISO 6142‐1. PRGMs are prepared gravimetrically using high‐purity component gas and high‐grade nitrogen, here 99.9995 % (5.5 N) as matrix gas. In this study, quantification of gaseous impurities such as moisture (H2O), methane (CH4), and carbon monoxide (CO) in 5.5 N nitrogen is performed using CRDS (cavity ring down spectroscopy). Carbon dioxide (CO2) and total hydrocarbons (THC) are analyzed using gas chromatography flame ionization detector (GC‐FID), while the determination of nitrogen dioxide (NO2) impurity is conducted colorimetrically using a UV‐Vis spectrophotometer. Total impurities in 5.5 N nitrogen are found to be (2945±21.5) ppb. The impact of utilizing this nitrogen is examined through the stability study of ambient range binary component gas mixtures of CH4 and CO in nitrogen and found that 5.5 N nitrogen can be used as matrix gas for preparing PRGMs of CH4 and CO. However, the component gas impurity present in nitrogen potentially affect the accuracy of gravimetrically prepared gas mixture.

Modern methods for identification of atoms, molecules, and aerosols in various objects

The study is aimed at developing highly sensitive methods of laser analytical spectroscopy. The physical mechanisms of forming useful signals (selective ionization signal and cavity ring-down signal) were identified that provided registration of parameters of atomic and aerosol systems in the intensive pulsed laser field. High-sensitive laser methods of laser resonance ionization spectroscopy in vacuum, laser-enhanced ionization spectrometry in flame, and cavity ringdown laser absorption spectroscopy (CRLAS) are used for the determination of ultra-small concentrations of atoms in different phase states of the substance. Samples of aqueous standard solutions and solid metals of s (Li, K, Na, Ca, Cs), p (Al, In), d (Cr, Mn, Fe, Co, Ni, Cu, Ag, Au, Pt, Zn, Hg), f (Yb) elements, aluminum alloys, especially pure solvents, crystals (NH4F, NaF), semi-conductor materials (GaAs, Si) and various aerosols of salts (NaCl, CsCl, NaI, NaF, KCl AgNO3), chemicals, organic dyes, alloys, soils and rocks were studied. The new mechanisms of getting free particles are revealed and new methods increasing the efficiency of atomization, selective ionization and excitation of atoms in systems «flame», «rod – flame», in atomizer «graphite – furnace» are proposed. The particle size distribution of aerosols formed under the impact of high-power laser radiation on the surface of a solid sample has been studied. The dependence of the absolute concentration of aerosol particles on their size has been determined. Aerosol extinction coefficients and extinction efficiency have been measured using intracavity laser spectroscopy. For the first time new parameters of aerosols are revealed by physical and chemical properties of aerosol plumes from solid surfaces and aerosols of salt of metals and organic aerosols. Methods of additives and calibration curve were used to examine the effects of the matrix on the analytical signal of the studied atoms.

A Mid-Infrared Quantum Cascade Laser Ultra-Sensitive Trace Formaldehyde Detection System Based on Improved Dual-Incidence Multipass Gas Cell

Formaldehyde (HCHO) is a tracer of volatile organic compounds (VOCs), and its concentration has gradually decreased with the reduction in VOC emissions in recent years, which puts forward higher requirements for the detection of trace HCHO. Therefore, a quantum cascade laser (QCL) with a central excitation wavelength of 5.68 μm was applied to detect the trace HCHO under an effective absorption optical pathlength of 67 m. An improved, dual-incidence multi-pass cell, with a simple structure and easy adjustment, was designed to further improve the absorption optical pathlength of the gas. The instrument detection sensitivity of 28 pptv (1σ) was achieved within a 40 s response time. The experimental results show that the developed HCHO detection system is almost unaffected by the cross interference of common atmospheric gases and the change of ambient humidity. Additionally, the instrument was successfully deployed in a field campaign, and it delivered results that correlated well with those of a commercial instrument based on continuous wave cavity ring-down spectroscopy (R2 = 0.967), which indicates that the instrument has a good ability to monitor ambient trace HCHO in unattended continuous operation for long periods of time.

Trace Ammonia Equilibrium Pressure of Zirconium Phosphate in Moisture.

Zirconium phosphate-absorbed ammonia gas and the ammonia concentration (pressure) decreased to 2 ppm (ca. 20 Pa). However, it has not been clarified what the equilibrium pressure of zirconium phosphate is during ammonia gas ab/desorption. In this study, the equilibrium pressure of zirconium phosphate during ammonia ab/desorption was measured using cavity ring-down spectroscopy (CRDS). For ammonia-absorbed zirconium phosphate, a two-step equilibrium plateau pressure was observed during the ammonia desorption in gas. The value of the higher equilibrium plateau pressure at the desorption process was about 25 mPa at room temperature. If the standard entropy change (ΔS0) of the desorption process is assumed to be equal to the standard molar entropy of ammonia gas (192.77 J/mol(NH3)/K), the standard enthalpy change (ΔH0) is about -95 kJ/mol(NH3). In addition, we observed hysteresis in zirconium phosphate at different equilibrium pressures during ammonia desorption and absorption. Finally, the CRDS system allows the ammonia equilibrium pressure of a material in the presence of water vapor equilibrium pressure, which cannot be measured by the Sievert-type method.

Primary measurement standards for trace moisture in multiple gases: extension of gas species to He and O2

The National Metrology Institute of Japan developed a multi-gas trace-moisture generator which was designed for generating trace water vapor (trace moisture) in multiple gases. Using this system, we previously developed primary measurement standards for trace moisture in N2 (10 nmol mol−1–5 μmol mol−1) and Ar (10 nmol mol−1–1 μmol mol−1). In this study, we have extended the target gas species; trace-moisture standards in He and O2 in the rage of 10 nmol mol−1 − 1 μmol mol−1 were developed. The relative expanded uncertainty (k = 2) of the trace-moisture standard in He was 0.74 %–5.7 %, and that in O2 was 0.78 %–8.9 %. In addition, we have improved stability of the flow rate of the diluent gas by controlling the temperature around the flow measurement/control systems and re-evaluated the uncertainty of the trace-moisture standards in N2 and Ar. The updated relative expanded uncertainty (k = 2) of the trace-moisture standard in N2 and Ar is 0.41 %–2.6 % and 0.73 %–2.6 %, respectively. The uncertainty budgets of the standards in these four gases are presented. The trace-moisture standard in N2 developed using the multi-gas trace-moisture generator was confirmed to be consistent with the standards realized by other generators, whose international comparability were already ensured. A commercial moisture analyzer (MA) based on the cavity ring-down spectroscopy (CRDS) was connected to the multi-gas trace-moisture generator as a device under test, and its performance was evaluated by comparing the readings with the standard values. The MA showed lower accuracy and stability in the measurement of moisture in He when it was used in the default setting, whereas it performed well in N2. This performance difference is related to the pressure-broadening coefficient of water, which depends on the gas species. We estimated the pressure-broadening coefficients of water by N2, Ar, He and O2 and discuss the gas-type dependence of the performance of CRDS-based MAs.

Real-Time Probing of Melamine-Induced Gold Nanoparticle Aggregation Kinetics via Evanescent-Wave Coupled Cavity Ring-down Spectroscopy.

Insight into the aggregation kinetics of gold nanoparticles (GNPs) is critical for developing a colorimetric assay extensively used in chemical and biomolecular sensing. The aggregation of NPs plays a significant role in many natural and industrial processes, demanding comprehensive perceptions of the aggregation kinetics at a solid-liquid interface. However, the direct observation of the melamine-induced aggregation process of GNPs in the time-domain still remains a challenge. There is little to no information on the fundamental mechanisms of such kinetics using evanescent waves. Total internal reflection (TIR) has been applied to generate the evanescent field (EF), exploring aggregation kinetics near the solid-liquid interface. Here, we utilized a precise optical cavity-based method, an evanescent-wave coupled cavity ring-down spectroscopy (EW-CRDS), that can probe the melamine-induced aggregation kinetics of GNPs. The key feature of the present method is that the evanescent field generated by TIR illumination harnesses the power of CRDS to study 2D fractals via the collision and attachment of the GNPs and their melamine-induced aggregates at the interfacial region in real-time. This kinetic study reveals a critical point for diffusion-limited aggregation and provides insights into the design and optimization of colorimetric sensors that exploit the aggregation of GNPs. Furthermore, the EW-CRDS is a unique analytical approach that helps to deepen our understanding in probing the real-time aggregation process, detecting the presence of aggregator as compared to UV-vis and dynamic light scattering (DLS) spectroscopy.

Experiment on Recording Ozone Absorption Transitions to 3A2 Triplet Electronic State by High-Sensitivity Cavity Ring-Down Spectroscopy in the Range 9350–10 000 cm−1

Experiment on Recording Ozone Absorption Transitions to 3A2 Triplet Electronic State by High-Sensitivity Cavity Ring-Down Spectroscopy in the Range 9350–10 000 cm−1

Impact of breast density on classification of infrared spectroscopy for breath-based breast cancer screening.

e13558 Background: While mammography is currently the standard of care for breast cancer screening, dense breast tissue can significantly degrade results. Alternatively, infrared spectroscopy analysis of breath offers a highly sensitive method for identifying exhaled volatile organic compounds (VOCs), which may circumvent issues with breast density. Methods: Alveolar breath samples were collected onto Tenax TA sorbent tubes using a SohnoXB™ breath sampler. Using four desorb temperatures (75, 150, 225 and 300°C), absorption spectra were measured by infrared cavity ring-down spectroscopy (IR-CRDS), a technique for measuring absorption coefficients due to VOCs in exhaled breath. Missing values in the absorption spectra were backfilled using interpolation, and the spectrum was min-max normalized and quadratic detrended. First and second derivatives of the preprocessed absorption spectra were used as features for a support vector machine machine-learning model. Features were ranked based on minimum redundancy maximum relevance (mRMR). The top 20 ranked features were selected to limit the potential for overfitting and then optimized. Model performance was validated using non-nested leave-one-out cross-validation (LOOCV) and nested LOOCV to provide optimistic and pessimistic results, respectively. Results: Absorption spectra from 111 participants (71 positive, 40 control) were used. Of the positive subjects, 30 had low- and 31 had high-density breast tissue (measures missing for 10). Model performance is outlined. A subgroup analysis compared model performance for subjects with low- and high-density breast tissue for both non-nested and nested LOOCV models. Breast density data was not captured for control subjects thus they were not included in the subgroup analysis. Fisher’s exact test was performed to assess for significant difference between model performance for those with low- vs high-density breast tissue, resulting in a p-value of 1.00. Conclusions: Our results suggest that the classification of alveolar breath using IR-CRDS is a promising technique for the detection of breast cancer that is independent of breast density. Breath analysis may therefore become a new alternative or corroborative to mammography to support clinical decision-making. [Table: see text]

Novel gas exposure system for the controlled exposure of plants to gaseous hydrogen fluoride

Plants can serve as sensitive bioindicators of the presence of contaminant vapors in the atmosphere. This work describes a novel laboratory-based gas exposure system capable of calibrating plants as bioindicators for the detection and delineation of the atmospheric contaminant hydrogen fluoride (HF) as a preparatory step for monitoring release emissions. To evaluate changes in plant phenotype and stress-induced physiological effects attributed to HF alone, the gas exposure chamber must have additional controls to simulate otherwise optimal plant growth conditions including variables such as light intensity, photoperiod, temperature, and irrigation. The exposure system was designed to maintain constant growth conditions during a series of independent experiments that varied between optimal (control) and stressful (HF exposure) conditions. The system was also designed to ensure the safe handling and application of HF. An initial system calibration introduced HF gas into the exposure chamber and monitored HF concentrations by cavity ring-down spectroscopy for a 48-h period. Stable concentrations inside the exposure chamber were observed after approximately 15 h, and losses of HF to the system ranged from 88 to 91%. A model plant species (Festuca arundinacea) was then exposed to HF for 48 h. Visual phenotype stress-induced responses aligned with symptoms reported in the literature for fluoride exposure (tip dieback and discoloration along the dieback transition margin). Fluoride concentrations in exposed tissues compared to control tissues confirmed enhanced fluoride uptake due to HF exposure. The system described herein can be applied to other reactive atmospheric pollutants of interest in support of bioindicator research.

Elucidation of rotational-interaction coupling and collision-induced effects in rovibrational transitions of β-N2O isotopologue at 7.8 µm mid-infrared region by cavity ring-down spectroscopy

High-sensitive cavity ring-down spectroscopy (CRDS) coupled with a cw-quantum cascade laser operating at 7.8 μm mid-infrared (MIR) region has been employed to investigate the rovibrational interaction coupling for various MIR rotational transitions of the P-and R-branches in the ν1 fundamental vibrational band (1000 ← 0000) of the β-site-specific isotopologue of nitrous oxide (β-N2O) i.e., 15N14N16O. The coupled rotational interaction was experimentally quantified from the high-resolution CRDS data and a data-driven approach was taken for the approximation of the Herman-Wallis series. Moreover, J-dependent pressure-broadened absorptions and their collision lifetimes in response to foreign-perturbing gas molecules were investigated to understand the collision-induced rotational quantum effect in β-N2O molecule. This study reveals an experimental elucidation of the fundamental infrared physics underlying rovibrational interaction and its coupling to the vibrational and rotational degrees of freedom for a non-centrosymmetric linear polyatomic molecule possessing a permanent dipole moment. Moreover, the experimentally probed interference-free spectral lines of β-N2O molecule attributing different spectroscopic signatures in the MIR region may drive new applications in environmental monitoring, biological and biomedical diagnostics in the future.

Investigating the effect of nanolime treatment on the drying kinetics of Clipsham limestone

Climate change poses an ever-increasing risk to our stone built heritage. Among conservation actions, the use of consolidant products is considered a possible response to this challenge, and the adoption of nanolimes has been widely studied showing promising results. However, while the effectiveness and method of application has been assessed, few studies have probed the changes in drying kinetics following treatment. In fact, a drastic alteration of the water transport might lead to further anomalies. This study investigates the influence of nanolimes dispersed in ethanol on the drying kinetics of Clipsham limestone using cavity ring-down spectroscopy. The degree of treatment was assessed by gravimetry, Raman spectroscopy, optical microscopy, colorimetry, optical profilometry and thin section analysis. Results showed an increase in the dry mass, observable colour changes and decrease in surface roughness. Small but reproducible increases were observed in the evaporation flux for phase I behaviour following treatment, however, no changes were observed in the total mass of water released or the phase II diffusivity. Determination of the activation energy associated with phase II drying was unchanged following treatment . These results indicate that following treatment there has been little-to-no change in the internal surfaces and structure of the stone to affect vapour transport.

Calculated and Empirical Values of Vibronic Transition Dipole Moments of Reactive Chemical Intermediates for Determination of Concentrations.

Absorption spectroscopy has long been known as a technique for making molecular concentration measurements and has received enhanced visibility in recent years with the advent of new techniques, like cavity ring-down spectroscopy, that have increased its sensitivity. To apply the method, it is necessary to have a known molecular absorption cross section for the species of interest, which typically is obtained by measurements of a standard sample of known concentration. However, this method fails if the species is highly reactive, and indirect means for attaining the cross section must be employed. The HO2 and alkyl peroxy radicals are examples of reactive species for which absorption cross sections have been reported. This work explores and describes for these peroxy radicals the details of an alternative approach for obtaining these cross sections using quantum chemistry methods for the calculation of the transition dipole moment upon whose square the cross section depends. Likewise, details are given for obtaining the transition moment from the experimentally measured cross sections of individual rovibronic lines in the near-IR Ã-X̃ electronic spectrum of HO2 and the peaks of the rotational contours in the corresponding electronic transitions for the alkyl (methyl, ethyl, and acetyl) peroxy radicals. In the case of the alkyl peroxy radicals, good agreement for the transition moments, ≈20%, is found between the two methods. However, rather surprisingly, the agreement is significantly poorer, ≈40%, for the HO2 radical. Possible reasons for this disagreement are discussed.

Concurrent measurements of atmospheric ammonia concentrations in the megacities of Beijing and Shanghai by using cavity ring-down spectroscopy

Ammonia (NH3) is a vital precursor of secondary aerosols, which play an important role in urban air pollution. The passive observation of NH3 in the urban atmosphere showed higher concentrations than conventionally believed; however, the NH3 dynamics remain limited due to the paucity of active measurements with fast response instruments. In this study, intensive online measurements of ambient NH3 were conducted using cavity ring-down spectroscopy in late spring and early summer 2020 at the megacities of Beijing and Shanghai in northern and southern China. The results show that the average NH3 concentration in Beijing (23.1 ± 10.3 ppb) was nearly double that in Shanghai (12.0 ± 5.0 ppb). This spatial difference was confirmed by satellite column observations and bottom-up emission patterns. In addition, there was a significant increase in NH3 concentrations during the morning in our study. This special diurnal profile was a universal feature, with an occurrence frequency exceeding 50% in both cities. These frequent morning increases were mainly caused by motor vehicle emissions, with an additional contribution from the residual layer breakup for one-quarter of the days in the morning increase. On these days, the NH3 concentration increased by approximately 20% due to the downward mixing of the residual layer rupture. The unique data observed here could be used to validate the chemistry and transport models at a higher time resolution and improve the understanding of the current status of NH3 pollution in the urban atmosphere.

Material Circularity: A Novel Method for Biobased Carbon Quantification of Leather, Artificial Leather, and Trendy Alternatives

In the past, climate change led the United Nations to define the Sustainable Development Goals Statement “blueprint to achieve a better and more sustainable future” and the European Commission to promote the “bioeconomy” concept and to launch the Green Deal Policy. Accordingly, the COP26 conference proposed a drastic reduction of fossil-based fuels and materials, in favor of biobased materials which should ensure intrinsic carbon neutrality. Contextually, many startups and established materials suppliers proposed new, trendy materials claiming sustainability advantages but, in many cases, without robust scientific backing. The need for transparency in terms of circularity led us to exploit a fast, reliable and easily deployable analytical method for assessing the biogenic carbon fraction in a variety of industrial materials. Our research team identified a radiocarbon analysis based on Saturated-absorption CAvity Ring-down (SCAR) spectroscopy as a quick and effective method for such a scope. Here we demonstrate its use for the determination of biogenic/fossil carbon proportions of polymeric and coated materials such as leather, coated textiles and trendy alternatives used in the fashion industry, with the scope of defining their intrinsic renewable content. The reliability of the SCAR method is validated through a comparison with the results obtained by the benchmark technique.

Experimental determination of Rayleigh scattering cross-sections at 408 nm

Cavity ring-down spectroscopy (CRDS) has been applied to retrieve accurate Rayleigh scattering cross-sections, {upsigma }_{mathrm{Rayl}.} for a set of atmospheric gases at ~ 408 nm. Step pressure changes and pressure ramps were used in three different but similar optical cavities to measure light extinction by N2, O2, Ar, CO, CO2, N2O, CH4 and synthetic air (SA). The experimentally determined {upsigma }_{mathrm{Rayl}.} were compared with {upsigma }_{mathrm{Rayl}.} values calculated for these atmospheric gases using knowledge of extrapolated literature values of the refractive index (n) and King correction factors measured in different spectral regions.The difference between measured and calculated {upsigma }_{mathrm{Rayl}.} using the most recently published dispersion relationship for N2O and CH4 is ~ 0.6%. This confirms the improved accuracy of the new dispersion relationship. The calculated and measured {upsigma }_{mathrm{Rayl}.} agreed on average within 0.6%, 2.4%, 1.2%, 2.2%, and 1.5% for the gases CO2, N2 O2, SA, and Ar at ~ 408 nm. However, for CO, the difference is 4.1%, i.e. more than twice the error. This implies that improved knowledge of the dispersion relationship for CO, and thus the refractive index and King correction factors, would be of value to calculate {upsigma }_{mathrm{Rayl}.} in the blue spectral region.

Examining the variability of rock glacier meltwater in space and time in high-elevation environments of Utah, United States

Rock glaciers are common geomorphic features in alpine landscapes and comprise a potentially significant but poorly quantified water resource. This project focused on three complementary questions germane to rock glacier hydrology: 1) Does the composition of rock glacier meltwater vary from year to year? 2) How dependent is the composition of rock glacier meltwater on lithology? And 3) How does the presence of rock glaciers in a catchment change stream water chemistry? To address these questions, we deployed automated samplers to collect water from late June through mid-October 2022 in two rock-glacierized mountain ranges in Utah, United States characterized by different lithologies. In the Uinta Mountains of northern Utah, where bedrock is predominantly quartzite, water was collected at springs discharging from two rock glaciers previously shown to release water in late summer sourced from internal ice. In the La Sal Mountains of southeastern Utah, where trachyte bedrock is widespread, water was collected at a rock glacier spring, along the main stream in a watershed containing multiple rock glaciers, and from a stream in a watershed where rock glaciers are absent. Precipitation was also collected, and data loggers for water temperature and electric conductivity were deployed. Water samples were analyzed for stable isotopes with cavity ring-down spectroscopy and hydrochemistry with ICP-MS. Our data show that water discharging from rock glaciers in the Uinta Mountains exhibits a shift from a snowmelt source to an internal ice source over the course of the melt season that is consistent from year to year. We also found that the chemistry of rock glacier water in the two study areas is notably different in ways that can be linked back to their contrasting bedrock types. Finally, in the La Sal Mountains, the properties of water along the main stream in a rock-glacierized basin resemble the properties of water discharging from rock glaciers, and strongly contrast with the water in a catchment lacking rock glaciers. Collectively these results underscore the role of rock glaciers as an agent influencing the hydrochemistry of water in high-elevation stream systems.

Impactor collection efficiencies can modify the uncertainty of multiply charged particles in optical extinction measurements

The complex distribution of particle charge states resulting from neutralization processes by radioactive or soft X-ray charge neutralizers is a well-documented problem in aerosol science. Here, we demonstrate that non-idealities in the collection efficiency of an impactor allows for the transmission of an unexpected population of multiply charged particles by a differential mobility analyzer that can bias optical measurements. The extinction cross sections (Cext) of ammonium sulfate particles were quantified using cavity ring-down spectroscopy and particle counting. Particles were selected by electrical mobility (i.e., a metric of particle size) using a differential mobility analyzer (DMA) or electrical mobility and mass selected by a tandem DMA and aerosol particle mass analyzer (APM), respectively, to elucidate multiple charging artifacts. Measured Cext exhibited statistically significant differences at particle sizes near the impactor cut point implying that these multiply charged particles should not be present and could not be confirmed by parallel size distribution measurements. Additionally, comparison of Cext with Mie theory demonstrates that misclassification of the multiply charged particles can give rise to numerically accurate results. To understand these observations, the collection efficiency (CE) of four impactors from similar electrostatic classifiers was investigated. From these measurements, it was determined that the nominal and actual diameters of the impactors differed by −0.5% (457 μm vs. (455 ± 1) μm, respectively (uncertainty is 1σ standard deviation)) but the average Stk50 (the Stokes number at the cut-point, D50) values differed by ≈ 23% (0.23 vs. 0.18 ± 0.01, respectively). The measured CE as a function of √Stk (a metric of particle aerodynamic size) exhibits a long tail toward higher √Stk values, allowing for transmission of the larger and multiply charged particles observed in the optical measurements. These measurements highlight the utility of using orthogonal, spectroscopic methods to quantify the presence of multiply charged particles.