Spectral Light Absorption Coefficients Research Articles

Spectral Light Absorption Coefficient of Particles and Colored Dissolved Organic Matter in the Sea of Azov

The research was carried out based on the results of measuring the concentration of chlorophyll-a (TChl-a), spectral coefficient of light absorption by phytoplankton, non-algal particles (NAP) and colored dissolved organic matter (CDOM) in the southern part of the Sea of Azov in different seasons from 2016 to 2020. New data for the Sea of Azov on the variability of the spectral coefficient of light absorption by all optically active components have been obtained. A high (more than an order of magnitude) variability of all studied parameters was shown. The seasonal dynamics of TChl-a shows maxima in winter and summer. A relationship between the phytoplankton absorption and TChl-a has been revealed, which is described by a power function. Significant seasonal differences (two or more times) between the coefficients in the equation for parametrization of light absorption by phytoplankton were revealed. The NAP and CDOM light absorption were parametrized, the ranges of variability of the absorption coefficient and the exponential slope were revealed, and their seasonal dynamics was shown. Annual variability of absorption coefficient of NAP and CDOM was opposite to the annual cycle of TChl-a. The NAP and CDOM absorption coefficients increased after phytoplankton blooms, when TChl-a decreased. The relative contribution of phytoplankton, NAP, and CDOM to the total absorption by particles and dissolved matter at 440 nm varied significantly over the year. The share of phytoplankton was maximum in winter and summer, while in spring and autumn the maximum contribution to absorption was made by CDOM and NAP.

Bio-Optical Characteristics of the Black Sea Coastal Waters near Sevastopol: Assessment of the MODIS and VIIRS Products Accuracy

Purpose. The purpose of the work is to evaluate accuracy of the satellite products for the coastal waters near Sevastopol, generated by the standard algorithms based on the MODIS and VIIRS (installed at the artificial Earth satellites Aqua and Terra, and at Suomi NPP, respectively) data. Methods and Results. In situ sampling was carried out at the station (44°37’26" N and 33°26’05" E) located at a distance of two miles from the Sevastopol Bay. The chlorophyll a concentration was measured by the spectrophotometric method. The spectral light absorption coefficients by optically active components were measured in accordance with the current NASA protocol. The spectroradiometers MODIS and VIIRS Level-2 data with spatial resolution 1 km in nadir around the in situ station (44°37’26"±0°00’32" N and 33°26’05"±0°00’54" E) were used. The satellite products were processed by the SeaDAS 7.5.3 software developed in NASA. The research showed that the standard NASA algorithms being applied to the MODIS and VIIRS data, yielded incorrect values of the optically active components’ content in the Black Sea coastal waters near Sevastopol as compared to the data of in situ measurements in the same region: the satellite-derived “chlorophyll a concentration” was on average 1.6 times lower in spring, and 1.4 times higher in summer; the contribution of phytoplankton to total light absorption at 443 nm was underestimated in 8.7 times; the light absorption by colored detrital matter was overestimated in 2.2 times. Conclusions. The NASA standard algorithms are inapplicable to calculating bio-optical indices in the coastal waters of the Black Sea near Sevastopol since they provide incorrect values of the satellite products (Ca-s, aph-s(443) and aCDM-s(443)). Operative ecological monitoring based on satellite data requires development of a regional algorithm taking into account the seawater optical features in the region and in the coastal zone, in particular.

Bioopticheskiye kharakteristiki pribrezhnykh vod Chernogo morya vblizi Sevastopolya: otsenka tochnosti sputnikovykh produktov, vosstanovlennykh po dannym MODIS i VIIRS

Purpose. The purpose of the work is to evaluate accuracy of the satellite products for the coastal waters near Sevastopol, reconstructed by the standard algorithms based on the MODIS and VIIRS (installed at the artificial Earth satellites Aqua and Terra, and at Suomi NPP, respectively) data. Methods and Results. In situ sampling was carried out at the station (44°37'26" N and 33°26'05" E) located at a distance of two miles from the Sevastopol Bay. The chlorophyll a concentration was measured by the spectrophotometric method. The spectral light absorption coefficients by optically active components were measured in accordance with the current NASA protocol. The spectroradiometers MODIS and VIIRS Level 2 data with spatial resolution 1 km in nadir around the in situ station (44°37'26"±0°00'32" N and 33°26'05"±0°00'54" E) were used. The satellite products were processed by the SeaDAS 7.5.3 software developed in NASA. The research showed that the standard NASA algorithms being applied to the MODIS and VIIRS data, yielded incorrect values of the optically active components’ content in the Black Sea coastal waters near Sevastopol as compared to the data of in situ measurements in the same region: the satellite-derived “chlorophyll a concentration” was on average 1.6 times lower in spring, and 1.4 times higher in summer; the contribution of phytoplankton pigments to total light absorption at 443 nm was underestimated in 8.7 times; the light absorption by colored detrital organic matter was overestimated in 2.2 times. Conclusions. The NASA standard algorithms are inapplicable to calculating bio-optical indices in the coastal waters of the Black Sea near Sevastopol since they provide incorrect values of the satellite products (Ca-s, aph-s(443) and aCDM-s(443)). Operative ecological monitoring based on satellite data requires development of a regional algorithm taking into account the seawater optical features in the region and in the coastal zone, in particular.

Dependence of the Photosynthetic Quantum Yield on Phytoplankton Light Absorption: Equations for Assessing Primary Production in the Black Sea

Purpose. Investigations were performed during a scientific cruise to characterize hydrophysical properties, chlorophyll a concentration, photosynthesis-irradiance curves, spectral light absorption coefficients by phytoplankton, and spectral quantum downwelling irradiance. From these results, the dependence of the photosynthetic quantum yield upon environmental factors was studied with the purpose of adapting an algorithm developed for the Baltic Sea so that it can be applied for the Black Sea. Methods and Results. Complex hydrophysical and biological studies were carried out at several depths within the euphotic zone. Spectral bio-optical parameters were measured in accordance with the latest NASA protocols (2018). Experiments to determine the photosynthesis-light relationship were performed under temperature and light conditions similar to those in situ. The quantum yield of photosynthesis was calculated from parameters of photosynthesis-light curves (photosynthesis efficiency, light saturation parameter) and the spectral light absorption coefficients by phytoplankton pigments. It was found out that the main photosynthetic characteristics of phytoplankton, including the maximum photosynthetic quantum yield and the fraction of phytoplankton absorption associated with photoprotective accessory pigments, varied with depth within the euphotic zone, due to phytoplankton acclimation to environment factors during the period of seasonal stratification. The relationship between the photosynthetic quantum yield and the quanta absorbed by photosynthetically active phytoplankton pigments was revealed. The results of this research made it possible to build on the approach developed for other regions and modify the equation for calculating the quantum yield to apply specifically for environmental conditions in the Black Sea. Conclusions. For the first time, comprehensive studies carried out in the Black Sea, including measurements of the photosynthesis-light dependence, spectral light absorption coefficients by phytoplankton and spectral downwelling irradiance as a function of optical depths within the euphotic zone, made it possible to reveal the equation for calculating photosynthetic quantum yield. This new equation can be applied for calculating primary production of the Black Sea using a spectral approach, based both on the results of in situ measurements and remote sensing data.

Zavisimost' kvantovogo vykhoda fotosinteza ot pogloshcheniya sveta fitoplanktonom: polucheniye kolichestvennykh svyazey dlya otsenki pervichnoy produktsii v Chernom more

Purpose. Based on the results of the investigations that were performed during the scientific cruise and included the water hydrophysical characteristics, the chlorophyll a concentration, the photosynthesis-light dependences, the spectral light absorption coefficients by phytoplankton, and the spectral quantum downwelling irradiance, the dependence of the photosynthesis quantum yield upon the environmental factors was studied with the purpose of adaptation of the developed for the Baltic Sea approach for assessing the photosynthesis quantum yield, to the Black Sea. Methods and Results. Complex hydrophysical and biological studies were carried out at several depths within the photosynthesis zone. Spectral bio-optical parameters were measured in accordance with the modern NASA protocol (2018). The experiments on studying the photosynthesis-light relationship were performed under the temperature and light conditions close to the in situ ones. The quantum yield of photosynthesis was calculated based on the parameters of photosynthesis-light dependences (photosynthesis efficiency, light saturation parameter) and the spectral light absorption coefficients by phytoplankton pigments. It was found out that the main photosynthetic characteristics of phytoplankton including the photosynthesis maximum quantum yield and the portion of photoprotective accessory pigments in the total light absorption by phytoplankton varied with depth within the euphotic zone due to phytoplankton adaptation to the environment factors during the period of water seasonal stratification. The relationship between the photosynthesis quantum yield and the number of solar energy quanta absorbed by the photosynthetically active phytoplankton pigments was revealed. The results of the performed research allowed for modifying the equation for calculating the quantum yield for the Black Sea environment conditions according to the approach developed for the other water areas. Conclusions. For the first time, comprehensive studies carried out in the Black Sea and including the measurements of the photosynthesis-light dependences, the spectral light absorption coefficients by phytoplankton and spectral downwelling irradiance at particular optical depths within the euphotic zone enabled to reveal the equation for calculating the photosynthesis quantum yield, which could be applied for calculating primary production of the Black Sea using the spectral approach based both on the results of in situ measurements and the remote sensing data.

Vertical Distribution of Bio-Optical Properties of the Azov – Black Sea Basin Waters in April – May, 2019

Purpose. The work is aimed at investigating spatial distribution of the chlorophyll a concentration and the spectral light absorption coefficients by all optically active components in the Azov and Black seas in spring, when the seawater hydrophysical structure changes. Methods and Results. The data collected in the 106th scientific cruise of R/V Professor Vodyanitsky in April 19 – May 10, 2019 were used. The chlorophyll a concentration was measured by the spectrophotometric method. The spectral light absorption coefficients were determined in accordance with the NASA protocol 2018. The optical measurements were performed using the dual-beam spectrophotometer Lambda 35 (PerkinElmer). It was shown that in the surface layer of the Black Sea, the chlorophyll a concentration varied from 0.21 to 1.2 mg/m3. At some stations in the deep-water region, the increased values of this parameter were observed in the lower part of the euphotic zone that was associated with the beginning of seasonal water stratification due to the surface water heating. At these stations, the phytoplankton absorption spectra were more smoothed in the lower part of the euphotic zone than those in the upper layer. In the deep-water region, the non-algal particles contribution to the total particulate light absorption at wavelength 438 nm changed with depth from 40 ± 15 % at the surface to 29 ± 12 % near the bottom of the euphotic zone; whereas in the coastal waters this parameter was almost unchangeable within the water column (54 ± 11 %). No significant change of the colored dissolved organic matter contribution to the total light absorption with depth was revealed (69% on average). In the Sea of Azov, vertical distribution both of the chlorophyll a concentration (6.2 mg/m3 on average) and the spectral light absorption coefficients by all the optically active components was uniform. The non-algal particles contribution to the particulate light absorption was 40 ± 14 %, and the colored dissolved organic matter contribution to the total light absorption constituted 52 ± 6 %. Conclusions. New data on spatial distribution of the chlorophyll a concentration and the spectral light absorption coefficients by the optically active components in the Black and Azov seas were obtained for the spring period when the seawater hydrophysical characteristics changed.

Study of absorption characteristics of phytoplankton, particles and colored dissolved organic matter in Lake Baikal (July 2018 and September 2019)

Results of two scientific cruises carried out in July 2018 and September 2019 were used for an analysis of variability in spectral bio-optical properties of Lake Baikal. Chlorophyll a concentration, spectral light absorption coefficient of phytoplankton, non-algal particles and colored dissolved organic matter varied in ~order of magnitude between stations. Vertical distribution of these bio-optical parameters depended on water column stability in euphotic layer. The chlorophyll a profiles were characterized by maximum near the bottom of euphotic zone. In the layer of deep chlorophyll a maximum the phytoplankton absorption spectra had a specific feature – a local maximum at 550-570 nm. It was associated with relative increasing of phycoerythrin containing species in phytoplankton community. The absorption budget at 440 nm showed that the CDOM was the main optically active component, which provided ~ 50 % contribution to total absorption on averaged over Lake Baikal surface.

Specifying the light-absorbing properties of aerosol particles in fresh snow samples, collected at the Environmental Research Station Schneefernerhaus (UFS), Zugspitze

Abstract. Atmospheric aerosol particles like mineral dust, volcanic ash and combustion particles can reduce Earth's snow and ice albedo considerably even by very small amounts of deposited particle mass. In this study, a new laboratory method is applied to measure the spectral light absorption coefficient of airborne particles that are released from fresh snow samples by an efficient nebulizing system. Three-wavelength photoacoustic absorption spectroscopy is combined with refractory black carbon (BC) mass analysis to determine the snow mass-specific and BC mass-specific absorption cross sections. Fullerene soot in water suspensions are used for the characterization of the method and for the determination of the mass-specific absorption cross section of this BC reference material. The analysis of 31 snow samples collected after fresh snowfall events at a high-altitude Alpine research station reveals a significant discrepancy between the measured snow mass-specific absorption cross section and the cross section that is expected from the BC mass data, indicating that non-BC light-absorbing particles are present in the snow. Mineral dust and brown carbon (BrC) are identified as possible candidates for the non-BC particle mass based on the wavelength dependence of the measured absorption. For one sample this result is confirmed by environmental scanning electron microscopy and by single-particle fluorescence measurements, which both indicate a high fraction of biogenic and organic particle mass in the sample.

Pre-monsoon air quality over Lumbini, a world heritage site along the Himalayan foothills

Abstract. Lumbini, in southern Nepal, is a UNESCO world heritage site of universal value as the birthplace of Buddha. Poor air quality in Lumbini and surrounding regions is a great concern for public health as well as for preservation, protection and promotion of Buddhist heritage and culture. We present here results from measurements of ambient concentrations of key air pollutants (PM, BC, CO, O3) in Lumbini, first of its kind for Lumbini, conducted during an intensive measurement period of 3 months (April–June 2013) in the pre-monsoon season. The measurements were carried out as a part of the international air pollution measurement campaign; SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley – Atmospheric Brown Clouds). The main objective of this work is to understand and document the level of air pollution, diurnal characteristics and influence of open burning on air quality in Lumbini. The hourly average concentrations during the entire measurement campaign ranged as follows: BC was 0.3–30.0 µg m−3, PM1 was 3.6–197.6 µg m−3, PM2. 5 was 6.1–272.2 µg m−3, PM10 was 10.5–604.0 µg m−3, O3 was 1.0–118.1 ppbv and CO was 125.0–1430.0 ppbv. These levels are comparable to other very heavily polluted sites in South Asia. Higher fraction of coarse-mode PM was found as compared to other nearby sites in the Indo-Gangetic Plain region. The ΔBC ∕ ΔCO ratio obtained in Lumbini indicated considerable contributions of emissions from both residential and transportation sectors. The 24 h average PM2. 5 and PM10 concentrations exceeded the WHO guideline very frequently (94 and 85 % of the sampled period, respectively), which implies significant health risks for the residents and visitors in the region. These air pollutants exhibited clear diurnal cycles with high values in the morning and evening. During the study period, the worst air pollution episodes were mainly due to agro-residue burning and regional forest fires combined with meteorological conditions conducive of pollution transport to Lumbini. Fossil fuel combustion also contributed significantly, accounting for more than half of the ambient BC concentration according to aerosol spectral light absorption coefficients obtained in Lumbini. WRF-STEM, a regional chemical transport model, was used to simulate the meteorology and the concentrations of pollutants to understand the pollutant transport pathways. The model estimated values were ∼ 1. 5 to 5 times lower than the observed concentrations for CO and PM10, respectively. Model-simulated regionally tagged CO tracers showed that the majority of CO came from the upwind region of Ganges Valley. Model performance needs significant improvement in simulating aerosols in the region. Given the high air pollution level, there is a clear and urgent need for setting up a network of long-term air quality monitoring stations in the greater Lumbini region.

Correction of pathlength amplification in the filter-pad technique for measurements of particulate absorption coefficient in the visible spectral region.

Spectrophotometric measurement of particulate matter retained on filters is the most common and practical method for routine determination of the spectral light absorption coefficient of aquatic particles, ap(λ), at high spectral resolution over a broad spectral range. The use of differing geometrical measurement configurations and large variations in the reported correction for pathlength amplification induced by the particle/filter matrix have hindered adoption of an established measurement protocol. We describe results of dedicated laboratory experiments with a diversity of particulate sample types to examine variation in the pathlength amplification factor for three filter measurement geometries; the filter in the transmittance configuration (T), the filter in the transmittance-reflectance configuration (T-R), and the filter placed inside an integrating sphere (IS). Relationships between optical density measured on suspensions (ODs) and filters (ODf) within the visible portion of the spectrum were evaluated for the formulation of pathlength amplification correction, with power functions providing the best functional representation of the relationship for all three geometries. Whereas the largest uncertainties occur in the T method, the IS method provided the least sample-to-sample variability and the smallest uncertainties in the relationship between ODs and ODf. For six different samples measured with 1nm resolution within the light wavelength range from 400 to 700nm, a median error of 7.1% is observed for predicted values of ODs using the IS method. The relationships established for the three filter-pad methods are applicable to historical and ongoing measurements; for future work, the use of the IS method is recommended whenever feasible.

Spectral optical properties of long-range transport Asian dust and pollution aerosols over Northeast Asia in 2007 and 2008

Abstract. As a part of the IGAC (International Global Atmospheric Chemistry) Mega-cities program, aerosol physical and optical properties were continuously measured from March 2007 to March 2008 at an urban site (37.57° N, 126.94° E) in Seoul, Korea. Spectral optical properties of long-range transported Asian dust and pollution aerosols have been investigated based on the year long measurement data. Optically measured black carbon/thermally measured elemental carbon (BC/EC) ratio showed clear monthly variation with high values in summer and low values in winter mainly due to the enhancement of light attenuation by the internal mixing of EC. Novel approach has been suggested to retrieve the spectral light absorption coefficient (babs) from Aethalometer raw data by using BC/EC ratio. Mass absorption efficiency, σabs (=babs/EC) at 550 nm was determined to be 9.0±1.3, 8.9±1.5, 9.5±2.0, and 10.3±1.7 m2 g−1 in spring, summer, fall, and winter, respectively with an annual mean of 9.4±1.8 m2 g−1. Threshold values to classify severe haze events were suggested in this study. Increasing trend of aerosol single scattering albedo (SSA) with wavelength was observed during Asian dust events while little spectral dependence of SSA was observed during long-range transport pollution (LTP) events. Satellite aerosol optical thickness (AOT) and Hysplit air mass backward trajectory analyses as well as chemical analysis were performed to characterize the dependence of spectral optical properties on aerosol type. Results from this study can provide useful information for studies on regional air quality and aerosol's effects on climate change.

Determination of the particulate absorption of microalgae using a point‐source integrating‐cavity absorption meter: verification with a photometric technique, improvements for pigment bleaching, and correction for chlorophyll fluorescence

The determination of the spectral light absorption coefficient of planktonic algae in seawater is crucial for many applications, including optical remote sensing. Common techniques are adversely affected by light‐scattering effects, or by low particle concentrations in situ. Measurements with a point‐source integrating‐cavity absorption meter (PSICAM) can overcome both difficulties. In our study, we assessed the performance of a PSICAM for measuring the absorption coefficients of microalgae by a comparison with state‐of‐the‐art techniques. The PSICAM was evaluated by comparative measurements of diluted algal cultures with a photometric setup, where the sample cuvette is placed in the center of an integrating sphere (CIS). The accuracy of both the CIS and the PSICAM technique was calibrated against a commercial spectrophotometer by measurements of dense algal cultures. The remaining sources of error for the PSICAM technique were the bleaching procedure and chlorophyll fluorescence. We propose an improved bleaching technique and introduce a correction procedure for the fluorescence effects. Applying both, the overall differences between PSICAM and CIS measurements were less than ± 1%. We further demonstrate that the accuracy of the PSICAM is at least as good as that of a commercial spectrophotometer, but its precision should be two to three orders of magnitude higher. Due to its high sensitivity and accuracy, and to the fact that sources of error can be identified and accounted for, the PSICAM has a great potential to significantly improve the determination of absorption spectra of particulate matter in natural seawater.

A method of calculating selfconsistent potentials for a mixture of chemical elements

Quantum mechanical models of a substance and, in particular, a modified Hartree-Fock-Slater model are used to determine the thermal conductivity and spectral light absorption coefficients. The case when the substance is a mixture of chemical elements is considered.