Light Absorption Measurements Research Articles

Modulation of the vibrational and optical properties in β copper phthalocyanine under compression

Because copper phthalocyanine (CuPc) has significant uses in industrial devices and pigments, it is a subject of great interest in basic scientific research. Studying and adjusting its photoelectric qualities, in particular, has drawn much attention. In this work, in situ high-pressure experiments were used to investigate in detail the vibrational and optical properties of ground-state β-CuPc up to 13 GPa. Both micro-Raman and ultraviolet and visible light (UV–vis) absorption measurements revealed a phase transition occurring around 3 GPa. Notably, the macrocycle breathing vibration was found to have a remarkable characteristic of first weakening and then strengthening in response to this pressure-induced phase transition. The UV–vis absorption data revealed that the bandgaps corresponding to the two absorption edges decrease gradually with increasing pressure, with one edge disappearing entirely above 11 GPa. Furthermore, the blue β-CuPc can be adjusted to dark green at 10 GPa and ultimately entirely black due to the merging of its absorption bands and redshifts at high pressure. This work improves our understanding of CuPc's intrinsic characteristics under harsh settings and manipulates its color effectively.

Absorbance measurement for interdisciplinary educational experiment on cytotoxicity

Abstract We propose a multidisciplinary educational experiment, linking knowledge and skills in physics, biology and information technology through the training and application of the research method by students. From a physics point of view, the experiment consists in light absorption measurement, and in terms of biology, it demonstrates the process of cytotoxicity evaluation by means of the colorimetric method neutral red uptake in vitro test. The test allows to determine the concentration of a test drug at which 50% cytotoxicity (CC50 values) of the cells is observed. After initial exposure to the tested drug, neutral red (NR) is added to the cell culture medium, it is absorbed by the living cells and subsequently released in a desorb buffer. The cell culture medium becomes coloured, and the more intensive colour corresponds to higher cell viability, while more transparent solution corresponds to lower number of living cells. The NR concentration in the solution is estimated by the absorbance value. We measure the absorbance of NR by utilizing a very affordable educational-grade spectrometer and compare its output with that of a professional microplate reader. We show that the educational spectrometer gives a result on the CC50 value that is in agreement with the acceptable values of the official protocol. We include a comment on the results when performing this laboratory exercise in one class of 18 year old students (in their last year of secondary education). The experiment can be also successfully applied in the laboratory practicum of first year university study.

Multiwavelength Photoacoustic Doppler Flowmetry of Living Microalgae Cells.

Photoacoustics can provide a direct measurement of light absorption by microalgae depending on the photosynthesis pigment within them. In this study, we have performed photoacoustic flowmetry on living microalgae cells to measure their flow characteristics, which include flow speed, flow angle, flow direction, and, more importantly, the photoacoustic absorption spectrum, all by observing the photoacoustic Doppler power spectra during their flowing state. A supercontinuum pulsed laser with a high repetition frequency is used as the light source: through intensity modulation at a specified frequency, it can provide wavelength-selectable excitation of a photoacoustic signal centered around this frequency. Our approach can be useful to simultaneously measure the flow characteristics of microalgae and easily discriminate their different species with high accuracy in both static and dynamic states, thus facilitating the study of their cultivation and their role in our ecosystem.

Correcting filter-based aerosol light absorption measurement biases in a coastal urban-industrial region

Correcting filter-based aerosol light absorption measurement biases in a coastal urban-industrial region

Nanofluidic Detection Platform for Simultaneous Light Absorption and Scattering Measurement of Individual Nanoparticles in Flow.

Characterization and quantification of plasmonic nanoparticles at the single particle level have become increasingly important with the advancements in nanotechnology and their application to various biological analyses including diagnostics, photothermal therapy, and immunoassays. While various nanoparticle detection methodologies have been developed and widely used, simultaneous measurement of light absorption and scattering from individual plasmonic nanoparticles in flow is still challenging. Herein, we describe a novel nanofluidic detection platform that enables simultaneous measurement of absorption and scattering signals from individual nanoparticles within a nanochannel. Our detection platform utilized optical diffraction phenomena by a single nanochannel as both a readout signal for photothermal detection and a reference light for interferometric scattering detection. Through the elucidation of the frequency effect on the detection performance and optimization of experimental conditions, we achieved the classification of gold and silver nanoparticles with a diameter of 20-60 nm at an average accuracy score of 82.6 ± 2.1% by measured data sets of absorption and scattering signals. Furthermore, we demonstrated the concentration determination of plasmonic nanoparticle mixtures using a trained Support vector machine (SVM) classifier. Our simple yet sensitive nanofluidic detection platform will be a valuable tool for the analysis of nanoparticles and their applications to chemical and biological assays.

Síntese e caracterização de filmes de Polipirrol dopados com Tetraquis(4-carboxifenil) porfirina para aplicações fotoelectroquímicas

Photoelectrochemistry is emerging as a promising technology for harvesting and utilizing solar energy in a wide range of applications. However, electrode materials still need to be improved to achieve optimal performance. Conductive polymers emerge as particularly promising organic compounds for this purpose due to their highly versatile properties. In this study, the galvanostatic synthesis of polypyrrole films co-doped with tetrakis(4-carboxyphenyl) porphyrin (PPy/TCPP) on fluorine doped tin oxide (FTO)-coated glass substrates was performed for the first time. In addition, an evaluation of these films as photoelectrodes was performed, focusing on key properties. The incorporation of porphyrin into the polymer matrix was confirmed by UV-Vis and IR characterization. SEM micrographs showed the morphological changes induced by the codopant. Cyclovoltammetry was used to evaluate the conductivity of the film, its electroactivity, electroactive area and HOMO energy level. The chopped chronoamperometry confirmed the photoactivity of the material and its stability for 3000 s. The electrical and optical properties of the polymer were characterized by EIS and light absorption measurements to propose its energy level diagram. The PPy/TCPP coatings were obtained with high homogeneity on FTO, good conductivity, quasi-reversible electrochemical activity to ferrocene probe and stable photoactivity. Electrical characterization indicates high charge flow under illumination. An indirect bandgap of 2.51 eV and a HOMO level value of -4.59 eV were obtained for PPy/TCPP.

Particulate black carbon mass concentrations and the episodic source identification driven by atmospheric blocking effects in Astana, Kazakhstan

Black carbon (BC) is a component of fine particulate matter (PM2.5) that is a key contributor to adverse human health effects and climate forcing. To date, BC mass concentrations and possible sources in Kazakhstan have not been studied. Thus, understanding the temporal variations of BC for a large developing region with a complex climate is useful. In this study, measurements of fine particulate BC mass concentrations in Astana were made from June 2020 to October 2021 by measuring light absorption of PM2.5 on filters. The mean BC concentration was 2.56 ± 1.29 μg m−3 with maximum and minimum monthly mean BC concentrations being 4.56 ± 2.03 μg m−3 and 1.12 ± 0.42 μg m−3 in January 2021 and June 2020, respectively. Temporal analyses of BC, SO2, PM10, NOx, CO, meteorological and atmospheric stability parameters were performed. Aggregated pollutant ‘episodic loadings’ during the heating and non-heating periods were identified. Their relationships with blocking anticyclones and cyclones were investigated by examining the reversal of meridional gradients at 500 hPa geopotential height (GPH) maps and identifying Omega (Ω) and Rex blocking types. Astana has some of the highest BC concentrations of cities worldwide. Seasonal BC source location identification using Conditional Bivariate Probability Function (CBPF) analysis implicated combined heat and power (CHP) plant emissions as the major BC source in Astana. Significant increases in BC concentrations were observed during the cold season due to numerous sources, generally poorer atmospheric dispersion and blocking events. The Concentration Weighted Trajectory (CWT) analysis results showed that the distribution of the 75th percentile of BC during episodic periods actively controlled by blockings exceeding than the entire measurement period, which may reflect cross-border transport and adjacent countries.

#828 Non-invasive determination of uric acid in blood during hemodialysis with an optical spent dialysate sensor

Abstract Background and Aims Kt/V urea is conventionally used hemodialysis (HD) adequacy marker, whereas many other uremic toxins with differing removal kinetics affect the mortality of end stage kidney disease (ESKD) patients. Among them, uric acid (UA) has been shown to cause cardiovascular mortality of ESKD patients. Recently, determination of UA concentration in blood with optical sensors during HD has been attempted by Lin et al in 2021 and Żyłka et al in 2023, but the accuracy has been relatively low. Moreover, Żyłka et al measured light absorption of spent dialysate at 573 nm to determine UA concentration, whereas previous research has shown that dialysate and UA have negligible light absorption in that region. The aim of this observational study was to predict concentration of UA with higher accuracy in ESKD patients’ blood during HD with various treatment settings by monitoring spent dialysate noninvasively with an optical sensor. Method Twenty-two ESKD patients on chronic HD were included into the study. Each patient received four 4 h long midweek HD sessions: one standard HD and three haemodiafiltration (HDF) sessions with different settings. Median (interquartile range) settings of the 1 HD session were: effective blood flow (Qb) = 199 (198-199) mL/min, dialysate flow (Qd) = 297 (297-298) mL/min, ultrafiltration rate (UF) = 13 (8-16) mL/min, dialyzer area 1.5 m2 and for the 3 HDF sessions: Qb = 298 (296-356) mL/min, Qd = 788 (489-792) mL/min, substitution fluid flow (Qsubs) = 96 (66-106) mL/min, UF = 11 (8-15) mL/min, dialyzer areas 1.8 m2 and 2.2 m2. Blood samples were collected before the start and at the end of each HD session from the arterial blood line and spent dialysate samples were collected 7, 60, 120, 180 and 240 min after the start from the outlet of the HD machine. Concentration of UA in spent dialysate and serum samples were determined with HPLC. An optical sensor (Optofluid Technologies OÜ, Tallinn, Estonia) was connected to the spent dialysate outlet of the HD machine and ultraviolet (UV) light absorption of spent dialysate was measured online in real time for each HD session. A linear interactions regression model was created using light absorbance at four different UV wavelengths to predict UA concentrations in collected spent dialysate samples. A curve of UA concentration for the whole HD session was determined based on the model and UV absorbance data measured with the optical sensor. Thereafter, UA concentration in spent dialysate at the start and at the end of each session (UAsensor hereinafter) was found from the concentration curve. The data of 88 HD sessions were equally divided into calibration and validation sets. Linear regression model was created using data of calibration set to predict concentration of UA (UApredicted) in blood as follows: UApredicted = a • UAsensor • $\frac{{{\rm{Qd}} + {\rm{\ Qsubs}} + {\rm{UF\ }}}}{{{\rm{Qb}}}}$, where “a” is the slope, UAsensor is the UA concentration in spent dialysate found from the concentration curve of the optical sensor, Qb is effective blood flow and Qd+Qsubs+UF is the total flow of spent dialysate. Subsequently, the accuracy of the model was evaluated on the calibration and validation data using Bland Altman analysis. Results UA concentrations in spent dialysate determined with HPLC and estimated with the optical sensor were strongly correlated (R2 = 0.992) and with comparable accuracy (BIAS±SE) (0.1 ± 3.84) µmol/L. Coefficient of determination 0.951 with the accuracy of 0.00 ± 31.43 µmol/L was achieved for calibration group, and coefficient of determination 0.962 with the accuracy of −7.64 ± 32.06 µmol/L was achieved for validation group between the UA concentration in blood determined with HPLC and corresponding values predicted by the optical sensor, respectively (Fig. 1). Conclusion Concentration of UA in dialysate and blood can be estimated noninvasively and accurately with the optical sensor in real time. This can be used to estimate removal efficiency and levels of UA during HD. In future, removal of other uremic toxins could be additionally monitored leading to a more personalized HD treatment.

Measurement of light absorption by chromophoric dissolved organic matter using a type-II liquid capillary waveguide: assessment of an achievable accuracy

Light absorption by chromophoric dissolved organic matter (CDOM) in the ocean is often measured using liquid waveguide capillary cells coupled to spectral array detectors. This type of optical setup is affected by several sources of uncertainties related to the waveguide and the detector. Uncertainties from the waveguide arise from errors in the effective path length and the effects of water salinity, while errors related to the detector are due to the non-linearity in the response, internal stray light, and wavelength accuracy. Here, uncertainties in the measurements of the spectral absorption coefficient of CDOM due to the optical setup itself were investigated in detail. The related systematic errors were very often significant (2–15%) and larger than expected from simple measurement uncertainty (±1%). However, they can be corrected by characterizing the detector’s response for non-linearity and stray light, regularly performing calibrations for the detector’s wavelength response, and routinely measuring the waveguide’s effective path length. Including such corrections and timely calibrations reduces the uncertainties related to the spectrophotometric measurements to about ±2%. Uncertainties related to the necessary handling of samples are not included here.

Selective detection of azelnidipine in pharmaceuticals via carbon dot mediated spectrofluorimetric method: A green approach.

A spectrofluorimetric method using fluorescent carbon dots (CDs) was developed for the selective detection of azelnidipine (AZEL) pharmaceutical in the presence of other drugs. In this study, N-doped CDs (N-CDs) were synthesized through a single-step hydrothermal process, using citric acid and urea as precursor materials. The prepared N-CDs showed a highly intense blue fluorescence emission at 447 nm, with a photoluminescence quantum yield of ~21.15% and a fluorescence lifetime of 0.47 ns. The N-CDs showed selective fluorescence quenching in the presence of all three antihypertensive drugs, which was used as a successful detection platform for the analysis of AZEL. The photophysical properties, UV-vis light absorbance, fluorescence emission, and lifetime measurements support the interaction between N-CDs and AZEL, leading to fluorescence quenching of N-CDs as a result of ground-state complex formation followed by a static fluorescence quenching phenomenon. The detection platform showed linearity in the range 10-200 μg/ml (R2 = 0.9837). The developed method was effectively utilized for the quantitative analysis of AZEL in commercially available pharmaceutical tablets, yielding results that closely align with those obtained from the standard method (UV spectroscopy). With a score of 0.76 on the 'Analytical GREEnness (AGREE)' scale, the developed analytical method, incorporating 12 distinct green analytical chemistry components, stands out as an important technique for estimating AZEL.

Evaluating coarse PM composition and sources based on bulk and molecular speciation of PM2.5 and PM10 in Nanjing, East China

To understand the differences in the composition and sources of PM2.5 and PM10 caused by coarse particles, integrated PM2.5 and PM10 samples were synchronously collected in Nanjing, East China, in summer 2020 and winter 2020/2021. Bulk and molecular speciation and light absorption measurements of aerosol extracts were performed, followed by positive matrix factorization (PMF) based on the PM2.5 and PM10 data sets, respectively. The difference in average concentrations of total bulk species between PM2.5 and PM10 was mainly caused by the distribution of considerable NO3–, SO42–, Ca2+, and organic carbon (OC) in coarse particles. Coarse PM influenced by abrasion products from tire wear and leaves contributed about half of the low-volatility n-alkanes in summer. The contribution of coarse PM to biomass burning tracers and water-soluble OC increased in winter when biomass combustion was excessively active. More than 70% of sugar polyols were attributable to coarse PM in summer, and biomass burning could be an important source in winter. The light-absorbing organic chromophores were almost entirely associated with PM2.5, but water-soluble organic carbon (WSOC) exhibited stronger light absorption in PM10 extracts than in PM2.5 extracts possibly due to the influence of coarse PM on pH. PMF analysis indicated that biomass burning, aqueous-phase reactions, and processed dust were the main contributors of organic matter and its light absorption in winter. Biogenic primary and secondary sources made discernable contributions only in summer. The differences between PM2.5 and PM10 were likely attributed to mixing of crustal dust, combustion particles, and surface reactions.

A cold laboratory hyperspectral imaging system to map grain size and ice layer distributions in firn cores

Abstract. The Greenland and Antarctic ice sheets are covered in a layer of porous firn. Knowledge of firn structure improves our understanding of ice sheet mass balance, supra- and englacial hydrology, and ice core paleoclimate records. While macroscale firn properties, such as firn density, are relatively easy to measure in the field or lab, more intensive measurements of microstructural properties are necessary to reduce uncertainty in remote sensing observations of mass balance, model meltwater infiltration, and constrain ice age – gas age differences in ice cores. Additionally, as the duration and extent of surface melting increases, refreezing meltwater will greatly alter firn structure. Field observations of firn grain size and ice layer stratigraphy are required to test and validate physical models that simulate the ice-sheet-wide evolution of the firn layer. However, visually measuring grain size and ice layer distributions is tedious, is time-consuming, and can be subjective depending on the method. Here we demonstrate a method to systematically map firn core grain size and ice layer stratigraphy using a near-infrared hyperspectral imager (NIR-HSI; 900–1700 nm). We scanned 14 firn cores spanning ∼ 1000 km across western Greenland’s percolation zone with the NIR-HSI mounted on a linear translation stage in a cold laboratory. We leverage the relationship between effective grain size, a measure of NIR light absorption by firn grains, and NIR reflectance to produce high-resolution (0.4 mm) maps of effective grain size and ice layer stratigraphy. We show the NIR-HSI reproduces visually identified ice layer stratigraphy and infiltration ice content across all cores. Effective grain sizes change synchronously with traditionally measured grain radii with depth, although effective grains in each core are 1.5× larger on average, which is largely related to the differences in measurement techniques. To demonstrate the utility of the firn stratigraphic maps produced by the NIR-HSI, we track the 2012 melt event across the transect and assess its impact on deep firn structure by quantifying changes to infiltration ice content and grain size. These results indicate that NIR-HSI firn core analysis is a robust technique that can document deep and long-lasting changes to the firn column from meltwater percolation while quickly and accurately providing detailed firn stratigraphy datasets necessary for firn research applications.

Site‐selective fluorescence and spectroscopic properties of Yb‐doped lanthanum titanate glasses

AbstractYtterbium‐doped lanthanum titanate glasses were prepared by levitation melting for the detailed characterization of the spectroscopic properties in the rare‐earth titanate glass host. Low‐temperature fluorescence spectroscopy reveals distinct site‐selectivity in both static and lifetime fluorescence measurements suggesting an absence of clustering as well as significant variation of local ytterbium environments. Typical site‐selectivity behavior of a shrinking Stark manifold with lower excitation energy is observed. At 77 K, both the mean emission frequency and the fluorescence lifetime initially increase as the excitation energy decreases from about 11100 to 10750 and then slightly decrease at lower excitation energy. Temperature‐dependent lifetime measurements between 77 and 420 K show a decreasing lifetime with increasing temperature and are well described by a two‐level thermal activation model. The temperature‐dependent fluorescence spectroscopy coupled with a room temperature white light absorption measurement allow the determination of the Stark energy levels of in lanthanum titanate glass as well as the calculation of the laser cross‐sections.

Toward More Accurate Modeling of Canopy Radiative Transfer and Leaf Electron Transport in Land Surface Modeling

AbstractModeling leaf photosynthesis is essential for quantifying the carbon, water, and energy fluxes of the terrestrial biosphere. However, due to the lack of simultaneous measurements of leaf light absorption and gas exchange, canopy radiative transfer (RT) and photosynthesis modeling often rely on simplified assumptions about light absorption and electron transport. These assumptions ignore variations in leaf biophysical traits and environmental conditions. In this study, we utilized a next‐generation land surface model (LSM)—CliMA Land, which incorporates hyperspectral canopy RT and provides a more accurate representation of trait variations. We evaluated the potential bias in electron transport estimates introduced by the broadband RT schemes used in traditional LSMs. Additionally, we explored the impact of different leaf electron transport parameterization schemes on global‐scale photosynthesis and fluorescence modeling. We showed that (a) traditional LSMs that disregard the impacts of leaf temperature and leaf traits on electron transport tend to overestimate electron transport rates. (b) Photosynthesis and fluorescence within a grid can exhibit biases exceeding 20%, with these biases demonstrating contrasting seasonality. (c) Global estimates of integrated photosynthesis and fluorescence differ by 8.1% and 8.8%, respectively. These results underscore the importance of adopting more sophisticated and accurate modeling schemes, such as hyperspectral canopy RT, in future LSMs and Earth system modeling to enhance the reliability of modeling outcomes.

Probing Temperature-Induced Plasmonic Nonlinearity: Unveiling Opto-Thermal Effects on Light Absorption and Near-Field Enhancement.

Precise measurement and control of local heating in plasmonic nanostructures are vital for diverse nanophotonic devices. Despite significant efforts, challenges in understanding temperature-induced plasmonic nonlinearity persist, particularly in light absorption and near-field enhancement due to the absence of suitable measurement techniques. This study presents an approach allowing simultaneous measurements of light absorption and near-field enhancement through angle-resolved near-field scanning optical microscopy with iterative opto-thermal analysis. We revealed gold thin films exhibit sublinear nonlinearity in near-field enhancement due to nonlinear opto-thermal effects, while light absorption shows both sublinear and superlinear behaviors at varying thicknesses. These observations align with predictions from a simple harmonic oscillation model, in which changes in damping parameters affect light absorption and field enhancement differently. The sensitivity of our method was experimentally examined by measuring the opto-thermal responses of three-dimensional nanostructure arrays. Our findings have direct implications for advancing plasmonic applications, including photocatalysis, photovoltaics, photothermal effects, and surface-enhanced Raman spectroscopy.

Insight into the Role of NH3/NH4+ and NOx/NO3- in the Formation of Nitrogen-Containing Brown Carbon in Chinese Megacities.

Particulate brown carbon (BrC) plays a crucial role in the global radiative balance due to its ability to absorb light. However, the effect of molecular formation on the light absorption properties of BrC remains poorly understood. In this study, atmospheric BrC samples collected from six Chinese megacities in winter and summer were characterized through ultrahigh-performance liquid chromatography coupled with Orbitrap mass spectrometry (UHPLC-Orbitrap MS) and light absorption measurements. The average values of BrC light absorption coefficient at a wavelength of 365 nm (babs365) in winter were approximately 4.0 times higher than those in summer. Nitrogen-containing organic molecules (CHNO) were identified as critical components of light-absorbing substances in both seasons, underscoring the importance of N-addition in BrC. These nitrogen-containing BrC chromophores were more closely related to nitro-containing compounds originating from biomass burning and nitrogen oxides (NOx)/nitrate (NO3-) reactions in winter. In summer, they were related to reduced N-containing compounds formed in ammonia (NH3)/ammonium (NH4+) reactions. The NH3/NH4+-mediated reactions contributed more to secondary BrC in summer than winter, particularly in southern cities. Compared with winter, the higher O/Cw, lower molecule conjugation indicator (double bond equivalent, DBE), and reduced BrC babs365 in summer suggest a possible bleaching mechanism during the oxidation process. These findings strengthen the connection between molecular composition and the light-absorbing properties of BrC, providing insights into the formation mechanisms of BrC chromophores across northern and southern Chinese cities in different seasons.

Increase in precipitation scavenging contributes to long-term reductions of light-absorbing aerosol in the Arctic

Abstract. We investigated long-term changes using a harmonised 22-year data set of aerosol light absorption measurements, in conjunction with air mass history and aerosol source analysis. The measurements were performed at Zeppelin Observatory, Svalbard, from 2002 to 2023. We report a statistically significant decreasing long-term trend for the light absorption coefficient. However, the last 8 years of 2016–2023 showed a slight increase in the magnitude of the light absorption coefficient for the Arctic haze season. In addition, we observed an increasing trend in the single-scattering albedo from 2002 to 2023. Five distinct source regions, representing different transport pathways, were identified. The trends involving air masses from the five regions showed decreasing absorption coefficients, except for the air masses from Eurasia. We show that the changes in the occurrences of each transport pathway cannot explain the reductions in the absorption coefficient observed at the Zeppelin station. An increase in contributions of air masses from more marine regions, with lower absorption coefficients, is compensated for by an influence from high-emission regions. The proportion of air masses en route to Zeppelin, which have been influenced by active fires, has undergone a noticeable increase starting in 2015. However, this increase has not impacted the long-term trends in the concentration of light-absorbing aerosol. Along with aerosol optical properties, we also show an increasing trend in accumulated surface precipitation experienced by air masses en route to the Zeppelin Observatory. We argue that the increase in precipitation, as experienced by air masses arriving at the station, can explain a quarter of the long-term reduction in the light absorption coefficient. We emphasise that meteorological conditions en route to the Zeppelin Observatory are critical for understanding the observed trends.

The investigation of diesel soot emission using instrument combination of multi-wavelength photoacoustic spectroscopy and scanning mobility particle sizer

The parallel measurements of wavelength dependent optical absorption, particle number size distribution have made by a multi wavelength photoacoustic spectrometer (4λ-PAS) and scanning mobility particle sizer (SMPS) respectively at different modes of a diesel engine using two different types of fuel. The thermal evolution of the emission was also investigated using posterior temperature treatment of emission. The bimodal size distribution of emitted particles at a set reference temperature has been observed regardless of the applied fuel at idle. However, the emitted particulate assembly had lognormal size distribution falls into the accumulation mode at all other defined engine modes and both fuel types. The total number- and volume concentration (TNC and TVC) showed retrograde tendency with the increasing torque and rpm independently of the applied fuel types. The TNC values decreased up to 50% for both fuels with engine operation changes from idle engine mode(em#1) to low engine mode(em#2). With further increase in torque and rpm of engine, the change in TNC is negligible. On the other hand, the TVC remains more or less the same for idle to low engine mode transition and increased more than 60% for high mode (em#3) transition. The Optical Absorption Coefficient (OAC) values measured at the operational wavelengths of the 4λ-PAS instrument decreased at all wavelengths with increasing rpm and torque. The wavelength dependency quantified by Aerosol Ängström Exponent (AAE) was applied here for qualitative analysis of the carbonaceous emission and showed decreased values towards the higher engine speed and torque output of the engine. The proposed technique can be used as real-time, precise and accurate measurement of light absorption by DPM aerosols, which opens up novel possibilities for the volatility and thermal evolution investigation of diesel emissions.

Long-term dynamics of spectral water transparency in the surface layer of Lake Teletskoye in summer

The article presents the long-term experimental data on spectral water transparency in the surface layer of Lake Teletskoye (21 sampling stations) obtained in summer of 2017‒2022. During the study period, values of the light attenuation index calculated at the natural logarithmic base at four wavelengths (430, 450, 550 and 670 nm) ranged within 0.2‒4.0 m‒1. The index of light absorption by yellow substance varied from 0.1 to 3.2 m‒1. Relative transparency measured with the use of a white Secchi disk made up 0.8‒11.7 m at its average of 6.3 m. Over a 6-year study period, the content of chlorophyll-a in the surface layer was 0.1‒4.1 mg/m3 that corresponded to the oligotrophic type of lakes. The concentration of yellow substance in the lake, optically determined through measuring light absorption by yellow substance at a wavelength of λ=450 nm, ranged from 0.9 to 15.0 g/m3. Calculations of the spectral contribution of the main optically active components of lake water to light attenuation in the surface layer of Lake Teletskoye in various sampling sites indicated that yellow substance and suspension had the greatest optical effect on the total attenuation. It is shown that the optic structure of the study reservoir (dynamics of major primary hydro-optical properties) depends on spatial-temporal variability of concentrations of different optically active components influenced by the in-water processes closely related with those occurred in the lake catchment.

Concurrent measurements of phytoplankton productivity and light absorption from a global carbon hotspot: Variability, features, and causes

Concurrent measurements of phytoplankton productivity and light absorption from a global carbon hotspot: Variability, features, and causes