Light Attenuation Measurements Research Articles

Geometric attenuation function analysis based on V-grooved surfaces.

In this study, we present a simulation addressing the phenomena of shadowing and masking in TE and TM polarized incident plane waves interacting with V-grooved rough surfaces. Blinn's theory on light attenuation posits that such a rough surface is represented by a symmetric, elongated V-shaped groove cavity, considering only the tilt angles of the slopes. Our numerical analysis considers variables such as polarization (TE or TM), wavelength, tilt, and slant of the incident or viewing direction, as well as the material properties of the rough surfaces, to accurately calculate light attenuation on V-grooved rough surfaces. The findings indicate enhanced precision in the measurement of light attenuation on these complex geometries.

Optimization of Mass and Light Transport in Nanoparticle-Based Titania Aerogels.

Aerogels composed of preformed titania nanocrystals exhibit a large surface area, open porosity, and high crystallinity, making these materials appealing for applications in gas-phase photocatalysis. Recent studies on nanoparticle-based titania aerogels have mainly focused on optimizing their composition to improve photocatalytic performance. Little attention has been paid to modification at the microstructural level to control fundamental properties such as gas permeability and light transmittance, although these features are of fundamental importance, especially for photocatalysts of macroscopic size. In this study, we systematically control the porosity and transparency of titania gels and aerogels by adjusting the particle loading and nonsolvent fraction during the gelation step. Mass transport and light transport were assessed by gas permeability and light attenuation measurements, and the results were related to the microstructure determined by gas sorption analysis and scanning electron microscopy. Mass transport through the aerogel network was found to proceed primarily via Knudsen diffusion leading to relatively low permeabilities in the range of 10-5-10-6 m2/s, despite very high porosities of 96-99%. While permeability was found to depend mainly on particle loading, the optical properties are predominantly affected by the amount of nonsolvent during gelation, allowing independent tuning of mass and light transport.

Direct and quantitative assessments of near-infrared light attenuation and spectroscopic detection depth in biological tissues using surface-enhanced Raman scattering

Optical imaging and spectroscopic modalities are of broad interest for in-vivo molecular imaging, fluorescence guided cancer surgery, minimally invasive diagnostic procedures, and wearable devices. However, considerable debate still exists as to how deeply visible and near-infrared (NIR) light could penetrate normal and diseased tissues under clinically relevant conditions. Here we report the use of surface-enhanced Raman scattering (SERS) nanotags embedded in ex-vivo animal tissues for direct and quantitative measurements of light attenuation and spectroscopic detection depth at both the NIR-I and NIR-II spectral windows. SERS nanotags are well suited for this purpose because of their sharp spectral features that can be accurately differentiated from fluorescence and background emission. For the first time, the spectroscopic detection depth is quantitatively defined and measured as the maximal thickness of tissues through which the embedded SERS nanotags are still detected at a signal-to-noise ratio (SNR) of three (99.7% confidence level). Based on data from six types of fresh ex-vivo tissues (brain, kidney, liver, muscle, fat, and skin), we find that the maximum detection depth values range from 1—3 mm in the NIR-I window, to 3—6 mm in the NIR-II window. The depth values are largely determined by two factors – the intrinsic optical properties of the tissue, and the overall SNRs of the system without the tissue (system SNR, a result of nanotag brightness, instrument efficiency, and data acquisition parameters). In particular, there is an approximately linear-logarithmic relationship between the system SNR and maximum detection depth. Thus, the detection of hidden or occult lesions can be improved by three strategies – reducing tissue attenuation, minimizing background noise, and maximizing the system’s performance as judged by SNR.Graphical

Optimization of the Composition of Toluene-Based Liquid Scintillator

Scintillators in general and organic liquid scintillator specifically are widely used as a medium for the detection of charged particles for numerous applications in science, medicine, engineering, and other areas. The composition of the scintillator affects not only its direct performance characteristics, but also the overall cost. Optimization of this composition provides the ability to design particle detectors with an optimized light yield and emission spectra of the detection medium while optimizing the expenses at the same time. This article describes work on toluene-based liquid scintillator component optimization, where PPO is used as a fluor and POPOP as a shifter. The light yield vs. concentration and the changes in the output spectra will be presented. The empirical fit of the output spectrum using the measured contributions of the components is discussed. Further plans include the light attenuation measurements for different compositions.

On the cycling of 231Pa and 230Th in benthic nepheloid layers

The naturally-occurring radionuclides protactinium-231 (231Pa) and thorium-230 (230Th) are produced at approximately uniform rates in the ocean and thought to be removed from the water column through a reversible exchange with settling particles. Recent measurements along the U.S. GEOTRACES North Atlantic transect (GA03) revealed two features which are at odds with current understanding about 231Pa and 230Th cycling in the ocean: (i) a sharp decrease in dissolved 231Pa (231Pad) and 230Th (230Thd) activities with depth below 2000–4000 m and (ii) very high particulate 231Pa (231Pap) and 230Th (230Thp) activities near the bottom, at a number of stations between the New England continental shelf and Bermuda. Concomitant measurements of light attenuation from beam transmissometry showed that both features occur in benthic nepheloid layers (BNLs), which suggests that these features may stem, at least partly, from the presence of resuspended sediment in the deep water column.Here we explore the behaviour of 231Pa and 230Th in BNLs by using (i) radionuclide, optical, and hydrographic data from the western segment of GA03 (west of Bermuda) and (ii) a simplified model of particle and radionuclide cycling that includes a lateral particle source. First, the BNLs observed at GA03 stations are characterized from measurements of the beam attenuation coefficient converted to particle concentrations. At all stations, particle concentrations below the clear water minimum were the highest in the bottom mixed layer, whose thickness ranged from 95 to 320 m, and decreased generally with height above the bottom. The thickness of strong BNLs varied from 482 to 1358 m and the vertical integral of particle concentration in excess to that at the clear water minimum varied from 1×104 to 2×106 mg m−2, among different stations. Second, the particle-radionuclide model is fitted to data from stations GT11-04 (New England continental rise) and GT11-08 (Hatteras abyssal plain), where samples for radionuclide analyses were collected in the BNL. The model can reproduce simultaneously the increase of particle concentration with depth, the low 231Pad and 230Thd in the BNLs, and the high 231Pap and 230Thp near the bottom. According to the model, at heights less than about 300 m above the seafloor, the dissolved phase was set primarily by a balance between adsorption and desorption, with vertical turbulent mixing playing a secondary role, whilst the particulate phase behaved largely as a non-reactive constituent supplied laterally and transported vertically by particle settling and turbulent mixing. Sensitivity tests with the model suggest that lateral particle sources near continental slopes and similar reliefs can produce significant biases both in the 230Th normalization method and in the interpretation of sediment 231Pa/230Th records. Our findings yield insights into the influence of sediment resuspension and transport on 231Pa and 230Th in the deep ocean and highlight the need for considering these processes in paleoceanographic applications.

Soil moisture level prediction using optical technique and artificial neural network

This research describes the use of an optical system combined with artificial neural network (ANN) for wireless and nondestructive prediction of soil moisture level. The former system comprising of near infrared (NIR) emitters of wavelengths 1200 nm and 1450 nm, and a photodetector for near real time soil moisture measurement in loams and peats holding different amount of water. There were 63 and 90 sets of data from loams and peats, respectively, used in the development of the dual stage-multiclass ANN model, wherein measurement of light attenuation (from nondestructive system) was correlated with percent soil moisture (from destructive gold standard approach) in pre-measurement stage. The result revealed a relatively good performance in the training of the NN with regression, R, of 0.8817 and 0.8881, and satisfactory error performance of 0.7898 and 1.172, for loams and peats, respectively. The testing of the system on 50 new samples of loam and peat showed a considerably high mean accuracy of 92 % for loams while 82 % was observed for peats. This study attributes the poorer performance of the system used on peats to the detection resolution of percent soil moisture, and structure and properties of the corresponding soil. This work concluded that the developed technology may be feasible for use in the future design and improvement of agricultural soil management.

Improved estimation of PM2.5 brown carbon contributions to filter light attenuation

Multiwavelength light attenuation measurements have been acquired as part of thermal/optical carbon analysis in the U.S. Chemical Speciation Network (CSN) and the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network beginning in 2016. These are used to estimate PM2.5 brown carbon (BrC) contributions to light absorption at various wavelengths, a useful method for separating biomass burning contributions from other sources. Attenuation of light transmitted through the filter deviates from Beers Law as the mass of light absorbing materials increase. This study estimates the effects of these deviations with empirical adjustment factors applied to samples for CSN from 2016 to 2017 and for IMPROVE from 2016 to 2019. Accounting for the filter loading effect results in an annual average increase of ∼6–7% BrC contribution to light attenuation: from 3.6% to 10.7% for the urban, more heavily loaded CSN samples; and from 23.7% to 29.5% for the non-urban IMPROVE samples. An alternative method is examined for BrC and black carbon (BC) adjustments by calculating the Absorption Ångström Exponent (AAE) for BC (i.e., AAEBC) based on the ratios of 635nm/780nm light attenuation rather than assuming AAEBC of unity. These paired-wavelength calculations result in a median AAEBC of 0.76 for CSN and 0.8 for IMPROVE, with the majority of samples (i.e., 91% of CSN and 70% of IMPROVE) showing AAEBC<1. By assuming negligible contributions from BrC to AAE at longer wavelengths, the amount of light attenuation at shorter wavelengths (e.g., 405nm) where BrC is dominant can be calculated. The paired-wavelength method applied to the filter loading adjusted data has a greater effect on urban (fresh) than on non-urban (aged) aerosols, resulting in a factor of two increase in annual averaged BrC light attenuation (from 10.7% to 21.6%) for CSN and by a factor of 1.11 (from 29.5% to 32.7%) for IMPROVE samples. This result demonstrates the importance of particle loading and AAE correction on quantifying BrC light attenuation from multi-wavelength thermal/optical analysis.

Measurement of smoke generation rate using a full-scale hot smoke test for building smoke exhaust systems

In some countries, test standards have been adopted which measure the effectiveness of smoke exhaust systems in clearing out heat and smoke produced separately. However, because these standards provide no quantitative provisions for dealing with the amount of visual smoke, there is an unclear correlation between the amount of smoke generated and the fire load. This paper applied the homogeneity concept of using a smoke collection box to examine the smoke generation rate of a smoke generator using CO2 as the driving gas. To avoid using the previous visual method of judging the rates, this research used measurement equipment to conduct a scientific analysis. Thus, the results were more objective. The equipment used included a Closed-Circuit Television (CCTV) Camera, a thermocouple, a traditional P-type smoke detector, a digital R-type smoke detector, and light attenuation measurement equipment. Under release pressures of 40, 60 and 80 psi, a 15% smoke density required smoke generation at 6.50, 8.42 and 10.46 m3/s, respectively. Achieving a homogeneous distribution of smoke within the space was accomplished. The data obtained in the test could be used not only to judge the efficiency of a smoke exhaust system but also provide adjustment information for a smoke exhaust system.

Evaluation of black carbon mass concentrations using a miniaturized aethalometer: Intercomparison with a continuous soot monitoring system (COSMOS) and a single-particle soot photometer (SP2)

Ground-based observations of black carbon (BC) aerosols were conducted in spring 2017 in Yokosuka City, south of Tokyo, Japan. Equivalent BC (EBC) mass concentrations were measured using a miniaturized, palm-sized filter-photometer (MicroAeth AE51, EBCAE51) and evaluated against those obtained using a continuous soot monitoring system (COSMOS, EBCCOSMOS) and a single-particle soot photometer (SP2, refractory BC, rBCSP2). We propose methods to account for the following key factors affecting AE51 measurements: (1) the non-linearity of light attenuation (ATN) measurements associated with high-particle loading on the filter (i.e., the loading effect); and (2) the positive artifacts in ATN measurements created by non-refractory materials (nonBC) on the filter. To examine these effects, we employed a custom automated system that switches the two sampling lines for the AE51, one of which was heated to 300 °C to minimize the sampling of nonBC. Alternate operation of the heated and unheated modes (for 15 min) enabled the separation of the described effects. Consistent with previous studies, in the heated mode, sensitivity decreased linearly with increases in ATN (−0.44% per ATN) in comparison with the other aethalometers. When the loading effect was corrected for, the EBCAE51 in the unheated mode still showed some bias relative to EBCCOSMOS and rBCSP2. This bias correlated with—and was successfully corrected for using—the mass ratio of nonBC to BC derived from the SP2. This approach can also be applied to fine-mode aerosol (PM2.5) concentrations measured at environmental monitoring networks, thus eliminating the need for additional SP2 data in the data correction.

An improved spectrophotometric method tests the Einstein-Smoluchowski equation: a revisit and update.

Theoretical prediction and experimental measurements of light attenuation in chemically pure and optically transparent solvents have attracted continuous attention, due in part to their curious nature, and in part to the increasing requirements of solvent-related applications. Yet hitherto, a majority of accurate spectrophotometric measurements of transparent solvents upon visible light radiation often end up using long-path-length cells, usually over dozens of cm, rendering the measure costly and complex; meanwhile, the guidance for choosing the Einstein-Smoluchowski equation or its variants as the best formula to predict the light scattering in solvents has remained elusive. Here we demonstrate a simple, versatile and cost-effective spectrophotometric method, enabling a sensitivity of 10-4 dB cm-1 over a 0.5 cm differential path length based on using standard double-beam spectrophotometer. We prove that this method reduces the path length by a factor of 100 while still making its closest approach to the record-low measurement of solvent extinction. We also validate that all the present equations used for predicting the light scattering in the solvent possess similar capacities, suggesting that the criterion for the choice of the appropriate formula simply depends on the equation's practicability. Following the elucidation of the wavelength range where the light scattering dominates the extinction, we further identify differences between scattering coefficients via the theoretical predictions and experimental measures, exposing the need for an improved theory to account for the solvent scattering phenomenon.

In-situ measurement of the scintillation light attenuation in liquid argon in the Gerda experiment

The Gerda experiment searches for the neutrinoless double beta (0νββ) decay in 76Ge in order to probe whether the neutrino is a Majorana particle and to shed light on the neutrino mass ordering. For investigating such a rare decay it is necessary to minimize the background of the experiment. In Phase II of the Gerda experiment the scintillation light of liquid argon (LAr) is used as an additional background veto. In order to estimate the efficiency of such a LAr veto it has to be known how far the scintillation light, which peaks at 128 nm, can travel within the LAr. A dedicated setup was built to measure the attenuation length of the scintillation light in the LAr in-situ within the cryostat of Gerda. The setup is composed of a stainless steel housing with a photomultiplier tube (PMT) at one side and a moveable 90Sr source at the other side to measure the light intensity at different distances between source and PMT. Furthermore, a sophisticated simulation was developed in order to determine the solid angle correction as well as the background for this measurement. The analysis results in an absorption length of 15.8±0.7(stat)−3.2+1.5(syst)cm under the assumption of a scattering length of 70 cm at 128 nm. The obtained value of the absorption length is specific for the LAr in GERDA at the time of the measurement.

Spectroscopy and Light Emitting Diodes Based System in Characterizing External Beam Therapy 3 Films for Solar Ultraviolet Measurement

Gafchromic external beam therapy 3 (EBT3) film has widely been used in medical field applications. Principally, the EBT3 film’s color gradually changes from light green to darker color under incremental exposures by ionizing or even non-ionizing ultraviolet (UV) radiation. Peak absorbance of the EBT3 film can be used to predict absorbed doses by the film. However, until today, related researches still rely on spectrometers for color analysis of EBT3 films. Hence, this paper presents a comparative analysis between results produced by the spectrometer and a much simpler light-emitting diode-photodiode based system in profiling the color changes of EBT3 films after exposure by solar UV radiation. This work has been conducted on a set of 50 EBT3 samples with incremental solar UV exposure (doses). The wavelength in the red region has the best sensitivity in profiling the color changes of EBT3 films for low solar UV exposure measurement. This study foresees the ability of blue wavelength to profile films with a large range of solar UV exposure. The LED (light emitting diode)-based optical system has produced comparable measurement accuracies to the spectrometer and thus, with a potential for replacing the need for a multipurpose spectroscopy system for simple measurement of light attenuation.

Precision loss measurements in short lengths of optical fibre by reflectometry without using Rayleigh scattering

To improve accuracy of light attenuation measurements in optical fibres, especially in short ones, tens and hundreds of metres in length, we propose rejecting a conventional reflectometric approach based on Rayleigh scattering intensity measurements. To this end, we propose for the first time the use of boson peaks in Raman scattering, which, on the one hand, produce no interference effects and no related noise in reflectograms, and, on the other, lie within the C-band. Even at a fibre length as short as 50 m, the attenuation measurement error does not exceed 0.002 dB km−1. We demonstrate the possibility of compensating for the temperature variation of boson peak intensity by concurrently obtaining a reflectogram for the anti-Stokes line of the fundamental Raman band.

Analysis of atmospheric attenuation using the Telescope Array central laser data

Located in the western desert of the state of Utah, the Telescope Array (TA) experiment measures the properties of ultra high energy cosmic ray (UHECR) induced extensive air showers. TA employs a hybrid detector comprised of a large surface array of scintillator detectors overlooked by three fluorescence telescopes stations. The TA Low Energy extension (TALE) detector has operated as a monocular Cherenkov/fluorescence detector for nearly five years, and has recently been complemented by a closely spaced surface array to operate in hybrid mode. The TAx4 upgrade is underway and aims to, as the name suggests, quadruple the size of the surface array to improve statistics at the highest energies (post-GZK events). The analysis of the TA fluorescence detectors (FD) data requires knowledge of the degree of the atmospheric attenuation of UV light produced by shower particles. This attenuation depends partially on the amount of aerosols present in the atmosphere at the time of shower observation. Being highly variable, real time measurement of the aerosols light attenuation is accomplished through the use of a central laser facility (CLF) located at the center of the surface array, and in the field of view of the three FDs, as well as, the TALE FD. In this proceeding we will describe the experiment, and the CLF data and analysis, and give results on measured aerosols attenuation, yearly averaged. FD measurements of shower energy and Xmax, involve corrections for atmospheric attenuation due to the presence of aerosols. We discuss the errors introduced into the shower parameters reconstruction due to uncertainty about aerosols attenuation.

Gas-phase composition and secondary organic aerosol formation from standard and particle filter-retrofitted gasoline direct injection vehicles investigated in a batch and flow reactor

Abstract. Gasoline direct injection (GDI) vehicles have recently been identified as a significant source of carbonaceous aerosol, of both primary and secondary origin. Here we investigated primary emissions and secondary organic aerosol (SOA) from four GDI vehicles, two of which were also retrofitted with a prototype gasoline particulate filter (GPF). We studied two driving test cycles under cold- and hot-engine conditions. Emissions were characterized by proton transfer reaction time-of-flight mass spectrometry (gaseous non-methane organic compounds, NMOCs), aerosol mass spectrometry (sub-micron non-refractory particles) and light attenuation measurements (equivalent black carbon (eBC) determination using Aethalometers) together with supporting instrumentation. Atmospheric processing was simulated using the PSI mobile smog chamber (SC) and the potential aerosol mass oxidation flow reactor (OFR). Overall, primary and secondary particulate matter (PM) and NMOC emissions were dominated by the engine cold start, i.e., before thermal activation of the catalytic after-treatment system. Trends in the SOA oxygen to carbon ratio (O : C) for OFR and SC were related to different OH exposures, but divergences in the H : C remained unexplained. SOA yields agreed within experimental variability between the two systems, with a tendency for higher values in the OFR than in the SC (or, vice versa, lower values in the SC). A few aromatic compounds dominated the NMOC emissions, primarily benzene, toluene, xylene isomers/ethylbenzene and C3-benzene. A significant fraction of the SOA was explained by those compounds, based on comparison of effective SOA yield curves with those of toluene, o-xylene and 1,2,4-trimethylbenzene determined in our OFR, as well as others from literature. Remaining discrepancies, which were smaller in the SC and larger in the OFR, were up to a factor of 2 and may have resulted from diverse reasons including unaccounted precursors and matrix effects. GPF retrofitting significantly reduced primary PM through removal of refractory eBC and partially removed the minor POA fraction. At cold-started conditions it did not affect hydrocarbon emission factors, relative chemical composition of NMOCs or SOA formation, and likewise SOA yields and bulk composition remained unaffected. GPF-induced effects at hot-engine conditions deserve attention in further studies.

Attenuation of light in different rock types and implications for rock surface luminescence dating

There is growing interest in rock surface burial and exposure luminescence dating for use in Quaternary science and in archaeology. Such methods have enormous potential both in increasing the range of sedimentary contexts that can be dated, and improving the accuracy and the precision of dating within those contexts. Bleaching of the luminescence signal with depth into the rock surface is likely to vary with lithology. However, previous work on rock surface dating has not systematically studied the differences in light attenuation for rocks of different lithologies, or directly quantified the attenuation of light in different rock surfaces. This study investigates the attenuation of light in different rock types (greywacke, sandstone, two granites and quartzite) using two different approaches: 1) sunlight bleaching experiments, to assess the residual infrared stimulated luminescence signal measured at 50 °C (IRSL50) and the post-IR IRSL signal measured at 225 °C (post-IR IRSL225) at different depths within the rocks after different durations of exposure to daylight; and, 2) direct measurement of light attenuation in rock slices using a spectrometer. Data from the spectrometer shows that for all rocks, attenuation is greater for shorter wavelengths (∼400 nm) than longer ones. A consistent difference in attenuation coefficient is seen when comparing the IRSL50 and the post-IR IRSL225 signals; this is thought to reflect the different sensitivity of these two signals to infrared and visible light. Direct measurement using a spectrometer is much more rapid than undertaking a bleaching experiment, and also provides wavelength-resolved attenuation data. Comparison of the numerical values from the two approaches is complex, but they yield consistent results. For the samples analysed here, the rocks that appear lightest in colour show the least attenuation of light and the luminescence signals are bleached to the greatest depths, and are thus the most suitable for dating using luminescence.

Sampling Strategies to Improve Passive Optical Remote Sensing of River Bathymetry

Passive optical remote sensing of river bathymetry involves establishing a relation between depth and reflectance that can be applied throughout an image to produce a depth map. Building upon the Optimal Band Ratio Analysis (OBRA) framework, we introduce sampling strategies for constructing calibration data sets that lead to strong relationships between an image-derived quantity and depth across a range of depths. Progressively excluding observations that exceed a series of cutoff depths from the calibration process improved the accuracy of depth estimates and allowed the maximum detectable depth (dmax) to be inferred directly from an image. Depth retrieval in two distinct rivers also was enhanced by a stratified version of OBRA that partitions field measurements into a series of depth bins to avoid biases associated with under-representation of shallow areas in typical field data sets. In the shallower, clearer of the two rivers, including the deepest field observations in the calibration data set did not compromise depth retrieval accuracy, suggesting that dmax was not exceeded and the reach could be mapped without gaps. Conversely, in the deeper and more turbid stream, progressive truncation of input depths yielded a plausible estimate of dmax consistent with theoretical calculations based on field measurements of light attenuation by the water column. This result implied that the entire channel, including pools, could not be mapped remotely. However, truncation improved the accuracy of depth estimates in areas shallower than dmax, which comprise the majority of the channel and are of primary interest for many habitat-oriented applications.

Analysis on the Effect of Sensor Views in Image Reconstruction Produced by Optical Tomography System Using Charge-Coupled Device.

Optical tomography (OPT) is a method to capture a cross-sectional image based on the data obtained by sensors, distributed around the periphery of the analyzed system. This system is based on the measurement of the final light attenuation or absorption of radiation after crossing the measured objects. The number of sensor views will affect the results of image reconstruction, where the high number of sensor views per projection will give a high image quality. This research presents an application of charge-coupled device linear sensor and laser diode in an OPT system. Experiments in detecting solid and transparent objects in crystal clear water were conducted. Two numbers of sensors views, 160 and 320 views are evaluated in this research in reconstructing the images. The image reconstruction algorithms used were filtered images of linear back projection algorithms. Analysis on comparing the simulation and experiments image results shows that, with 320 image views giving less area error than 160 views. This suggests that high image view resulted in the high resolution of image reconstruction.

Variation within and between cyanobacterial species and strains affects competition: Implications for phytoplankton modelling

Cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii are two harmful species which co-occur and successively dominate in freshwaters globally. Within-species strain variability affects cyanobacterial population responses to environmental conditions, and it is unclear which species/strain would dominate under different environmental conditions. This study applied a Monte Carlo approach to a phytoplankton dynamic growth model to identify how growth variability of multiple strains of these two species affects their competition.Pairwise competition between four M. aeruginosa and eight C. raciborskii strains was simulated using a deterministic model, parameterized with laboratory measurements of growth and light attenuation for all strains, and run at two temperatures and light intensities. 17 000 runs were simulated for each pair using a statistical distribution with Monte Carlo approach.The model results showed that cyanobacterial competition was highly variable, depending on strains present, light and temperature conditions. There was no absolute ‘winner’ under all conditions as there were always strains predicted to coexist with the dominant strains, which were M. aeruginosa strains at 20°C and C. raciborskii strains at 28°C. The uncertainty in prediction of species competition outcomes was due to the substantial variability of growth responses within and between strains. Overall, this study demonstrates that within-species strain variability has a potentially large effect on cyanobacterial population dynamics, and therefore this variability may substantially reduce confidence in predicting outcomes of phytoplankton competition in deterministic models, that are based on only one set of parameters for each species or strain.

An evaluation of mass absorption cross-section for optical carbon analysis on Teflon filter media

ABSTRACTBlack carbon (BC) or elemental carbon (EC) is a by-product of incomplete fuel combustion, and contributes adversely to human health, visibility, and climate impacts. Previous studies have examined nondestructive techniques for particle light attenuation measurements on Teflon® filters to estimate BC. The incorporation of an inline Magee Scientific OT21 transmissometer into the MTL AH-225 robotic weighing system provides the opportunity to perform optical transmission measurements on Teflon filters at the same time as the gravimetric mass measurement. In this study, we characterize the performance of the inline OT21, and apply it to determine the mass absorption cross-section (MAC) of PM2.5 BC across the United States. We analyzed 5393 archived Teflon® filters from the Chemical Speciation Network (CSN) collected during 2010–2011 and determined MAC by comparing light attenuation on Teflon® filters to corresponding thermal EC on quartz-fiber filters. Results demonstrated the importance of the initial transmission (I0) value used in light attenuation calculations. While light transmission varied greatly within filter lots, the average I0 of filter blanks during the sampling period provided an estimate for archived filters. For newly collected samples, it is recommended that filter-specific I0 measurements be made (i.e., same filter before sample collection). The estimated MAC ranged from 6.9 to 9.4 m2/g and varied by region and season across the United States, indicating that using a default value may lead to under- or overestimated BC concentrations. An analysis of the chemical composition of these samples indicated good correlation with EC for samples with higher EC content as a fraction of total PM2.5 mass, while the presence of light-scattering species such as crustal elements impacted the correlation affecting the MAC estimate. Overall, the method is demonstrated to be a quick, cost-effective approach to estimate BC from archived and newly sampled Teflon® filters by combining both gravimetric and BC measurements.Implications: Robotic optical analysis is a valid, cost-effective means to obtain a vast amount of BC data from archived and current routine filters. A tailored mass absorption cross-section by region and season is necessary for a more representative estimate of BC. Initial light transmission measurements play an important role due to the variability in blank filter transmission. Combining gravimetric mass and BC analysis on a single Teflon® filter reduces costs for monitoring agencies and maximizes data collection.