Spectral Absorption Coefficient Research Articles

Humic matter: basis for life—a plea for humics care

Humic matter (HM) is the leftover from life and at the same time the source for new life. The resulting complex system with many interactions has become a crucial part for the anthropocene and by this for the survival of mankind. Based on the results of the application of advanced analytical tools, the structures, reactions and interactions of HM are discussed. HM was investigated from different water samples (ground water, bog lake, waste water effluent). Fulvic acids (FA) and humic acids (HA) were isolated from a bog lake and from waste water effluent according to the XAD-method described by the International Humic Substances Society. Parameters like dissolved organic carbon (DOC), spectral absorption coefficient at λ = 254 nm (SAK), AOX (on activated carbon absorbable organically bound halogen) and THM (trihalomethanes) were determined according to ISO standard methods. For additional characterization, size exclusion chromatography coupled with online DOC detection and solid-state NMR were applied. The degradation of HM was studied by heterogeneous photocatalysis with titanium dioxide. Membrane separation, done as ultra- and nanofiltration, was used to characterize different size fractions of HM. The water solubility and hence the omnipresence of HM in aquatic systems opens the door for obtaining well-defined samples for experiments with meaningful results. Information on transport properties and reactivity, derived from the molecular size of HM, was obtained by using membrane filtration at different pore sizes. Photocatalytic degradation of HM was investigated by irradiation of suspensions with TiO2 as catalyst. Small organic acids (e.g. formic acid) were formed before total mineralisation occurred. It can be concluded that the properties of HM are well derivable from their molecular data. The resulting character of HM with respect of the human environment seems to be obviously ambivalent and asks for a sound understanding and proper management to support life in a sustainable way.

Characterization of light absorption by chromophoric dissolved organic matter (CDOM) in the upper layer of the Red Sea

The absorption coefficient of chromophoric dissolved organic matter (CDOM) is a major variable used in developing robust bio‐optical models and understanding biogeochemical processes. Over the last decade, the optical properties of CDOM in the open sea have been intensely studied. However, their variations in clear water are poorly documented, particularly in the Red Sea, owing to the absence of in situ measurements. We performed several cruises in the Red Sea to investigate the spatial distribution of the absorption coefficient of CDOM. The spectral absorption coefficients were determined from 400 nm to 740 nm using a WETLabs ac-s hyper-spectral spectrophotometer. In general, we found a latitudinal gradient in the CDOM absorption coefficient at 443 nm (aCDOM(443)) from south to north that is likely influenced by the exchange of water through the strait of Bab-el-Mandeb and the thermohaline circulation of the Red Sea. However, high aCDOM(443) values were observed in the northern Red Sea due to the existence of a sub-mesoscale feature that may induce an increase in phytoplankton production and lead to CDOM production. The aCDOM(443) covaried with the chlorophyll a concentration ([Chl a],) despite a high scatter. Furthermore, the aCDOM(443) for a given [Chl a] concentration was higher than those predicted by global ocean bio-optical models. This study advances our understanding of CDOM concentration in the Red Sea and may help improve the accuracy of the algorithms used to obtain CDOM absorption from ocean color.

Effects of rainstorm on the spectral absorption properties of chromophoric dissolved organic matter and particles in Lake Qiandao

为了研究暴雨事件对千岛湖有色可溶性有机物（CDOM）和颗粒物吸收光谱的影响，利用2016年暴雨前（3月1-6日）和暴雨后（4月6-11日）采集的水样，对暴雨前、后千岛湖水体CDOM、浮游藻类和非藻类颗粒物的吸收光谱特征进行分析，探讨暴雨事件对其造成的影响.结果表明：千岛湖作为典型的深水型内陆湖泊，其CDOM、浮游藻类颗粒物和非藻类颗粒物的吸收强度较太湖等浅水型湖泊弱.暴雨前，CDOM光谱吸收系数a_CDOM（λ）值在0~0.6 m^-1范围内变化，其光谱拟合系数S_CDOM的均值为0.0158±0.00145 nm^-1.暴雨前浮游藻类光谱吸收在总颗粒物中占主导，a_ph（λ）在0~0.35 m^-1范围内变化，非藻类颗粒物光谱吸收系数a_NAP（λ）在0~0.15 m^-1范围内变化，其光谱拟合系数S_NAP均值为5.62±0.57 μm^-1；暴雨后CDOM光谱吸收系数a_CDOM（λ）值在0~1.6 m^-1范围内变化，其光谱拟合系数S_CDOM的均值为0.0157±0.00101 nm^-1.暴雨后浮游藻类光谱吸收系数a_ph（λ）在0~2.5 m^-1范围内变化，非藻类颗粒物光谱吸收在部分区域已占据主导地位，a_NAP（λ）在0~0.8 m^-1范围内变化，其光谱拟合系数S_NAP均值为5.72±0.68 μm^-1.由CDOM吸收特征值相对分子质量M值得出，暴雨前、后千岛湖不同区域CDOM组成都以富里酸为主，且暴雨前M值分布较均匀，暴雨后M值呈现从新安江向缓冲区、东南区递增的趋势，这说明西北区随暴雨输入的腐殖酸增加了CDOM的相对分子质量.暴雨对S_NAP值影响较大的区域为西北区、西南区、东北区，对西南区影响最小.本研究为使用光学手段深入探讨暴雨事件对千岛湖水环境的影响提供重要依据.;To study the influence of heavy rainfall on absorption characteristics of chromophoric dissolved organic matter (CDOM) and particles in Lake Qiandao, the samples were collected on March 1-6, 2016 (before the rainstorm) and April 6-11, 2016 (after the rainstorm). The spectral absorption of CDOM, phytoplankton and non-algal particles (NAP) in the lake were analyzed and the influence of rainstorm was discussed. The results showed that Lake Qiandao, as a typical deep inland lake, its spectral absorption coefficients of CDOM, phytoplankton and NAP is small, compared with shallow lakes like Lake Taihu. The CDOM spectral absorption coefficients varied in the range of 0-0.6 m^-1, the mean value of the spectral fitting coefficient of CDOM(S_CDOM) was 0.0158±0.00145 nm^-1 before the rainstorm. The spectral absorption of phytoplankton before the rainstorm dominated the absorption of total particles, varied in the range of 0-0.35 m^-1. The spectral absorption coefficients of NAP varied in the range of 0-0.15 m^-1, and the mean value of spectral fitting coefficient of NAP(S_NAP) was 5.62±0.57 μm^-1 before the rainstorm; The CDOM spectral absorption coefficients varied in the range of 0-1.6 m^-1 S_CDOM was 0.0157±0.00101 nm^-1 after the rainstorm. The spectral absorption of phytoplankton varied in the range of 0-2.5 m^-1. NAP absorption dominated the absorption of particles in some regions after the rainstorm, a_NAP(λ)varied in the range of 0-0.8 m^-1 and S_NAP was 5.72±0.68 μm^-1. The M value showed that CDOM composition of the different regions of the lake is mainly fulvic acid both before and after the rainstorm, the spatial distribution of M value is relative even before the rainstorm. However, the M value showed an increasing trend from the Xin'anjiang to the buffer area and southeastern area after the rainstorm, which indicates that humic acids increased the relative molecular mass of CDOM in the northwestern area. Rainstorm had the greatest impact on the northwestern, southwestern and northeastern areas regarding the value of S_NAP, with the smallest impact on the southwestern area. This study provides an important basis for the use of optical means to further explore the impact of heavy rainfall on aquatic environment of Lake Qiandao.

Functional data analysis applied to the multi-spectral correlated–k distribution model

The Ck (Correlated-k) approach is among the most used method for the approximate modelling of the radiative properties of gases both in uniform and non-uniform media. One of its main defects is that the treatment of non-uniform gas paths is founded on the assumption of correlation - in fact co-monotonicity - of gas absorption coefficients in distinct states which is not rigorously verified for actual spectra. This correlation assumption fails as soon as large temperature gradients are encountered along the radiative path lengths. In order to circumvent this problem, a method based on functional data analysis (FDA) - referred to as the MSCk model in this work - was proposed in Refs. [1,2]. The principle of the method is to group together wavenumbers with respect to the spectral scaling functions - defined as the ratio between spectral absorption coefficients in distinct states - so that the correlation/co-monotonicity assumption can be considered as exact over the corresponding intervals of wavenumbers. Very few details were provided up to now about the application of FDA within the frame of the MSCk model. Indeed, most of our previous works were dedicated to the derivation of the methods itself. Accordingly, in the present paper, we mostly focus our attention on the mathematical definition of clusters of scaling function, quantities which are used to build spectral intervals over which gas spectra in distinct states are assumed to be scaled. The comparison of different clustering methods together with the criterion to select an appropriate number of clusters are described and discussed and the application of this approach for several test cases, including 3D geometries, are presented.

Improved Spectral Absorption Coefficient Grouping Strategies in Radiation Heat Transfer Calculations for H2O–CO2-Soot Mixtures

In the present work, strategies for the grouping of the spectral absorption coefficients used in multiscale (MS) multigroup (MG) full-spectrum k-distribution models were improved by considering the effects of variations in both temperature and species molar ratio on the correlated-k characteristics of the spectra of H2O–CO2-soot mixtures. The improvements in the accuracy of predictions of radiation heat transfer characteristics resulting from these new grouping strategies were evaluated using a series of semi-one-dimensional (1D) cases with significant temperature, participating species molar ratio, and pressure inhomogeneities. Finally, evaluations of grouping strategies were presented on calculation of the full-spectrum thermal images of an actual aeroengine combustor.

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.

Online analysis: Deeper insights into water quality dynamics in spring water

We have studied the dynamics of water quality in three karst springs taking advantage of new technological developments that enable high-resolution measurements of bacterial load (total cell concentration: TCC) as well as online measurements of abiotic parameters. We developed a novel data analysis approach, using self-organizing maps and non-linear projection methods, to approximate the TCC dynamics using the multivariate data sets of abiotic parameter time-series, thus providing a method that could be implemented in an online water quality management system for water suppliers. The (TCC) data, obtained over several months, provided a good basis to study the microbiological dynamics in detail. Alongside the TCC measurements, online abiotic parameter time-series, including spring discharge, turbidity, spectral absorption coefficient at 254nm (SAC254) and electrical conductivity, were obtained. High-density sampling over an extended period of time, i.e. every 45min for 3months, allowed a detailed analysis of the dynamics in karst spring water quality. Substantial increases in both the TCC and the abiotic parameters followed precipitation events in the catchment area. Differences between the parameter fluctuations were only apparent when analyzed at a high temporal scale. Spring discharge was always the first to react to precipitation events in the catchment area. Lag times between the onset of precipitation and a change in discharge varied between 0.2 and 6.7h, depending on the spring and event. TCC mostly reacted second or approximately concurrent with turbidity and SAC254, whereby the fastest observed reaction in the TCC time series occurred after 2.3h. The methodological approach described here enables a better understanding of bacterial dynamics in karst springs, which can be used to estimate risks and management options to avoid contamination of the drinking water.

Simple methods for identification of radiative properties of highly-porous ceria ceramics in the range of semi-transparency

PurposeThe aim of this paper is to present advanced experimental–numerical methods for identification of spectral absorption and scattering properties of highly porous ceria ceramics in the range of semi-transparency at room and elevated temperatures.Design/methodology/approachAt room temperature, a period of quasi-steady oscillations of the sample surface temperature generated in response to recurrent laser heating at fixed values of the maximum and minimum temperature of the irradiated surface is measured along with the normal-hemispherical reflectance. Radiative properties are then identified using a combined heat transfer model. At elevated temperatures, an analytical solution proposed in an earlier study for zirconia ceramics is used to retrieve spectral absorption coefficient of ceria ceramics from the measured normal emittance.Findings and Originality/valueThis method can be used to obtain small absorption coefficient of ceria ceramics at room temperature. The required measurements of both the normal-hemispherical reflectance and the period of quasi-steady oscillations of the irradiated surface temperature of the ceramics sample between fixed values of the maximum and minimum temperatures can be readily conducted using thermal laboratory equipment. Another method has been suggested for identification of the spectral absorption coefficient of ceria ceramics at elevated temperatures. This method is based on a relation between the measured normal emittance of an isothermal sample and the absorption coefficient.

Higher values of spectral response, absorption coefficient and external quantum efficiency of solar cell in the form of pyramids

This paper presents a study on spectral response, absorption coefficient and external quantum efficiency of solar cell in the form of pyramid [1, 2]. We investigate to what extent and under what conditions we want to take advantage of ray incidence Seven times [3, 4]. It is found that these analyses can be used to determine the optimal surface texture which provides the best light trapping for solar cells in terms of the total internal reflection occurring in the high-index medium at incidence angles larger than the nominal critical angle [3–9]. One of the main contributions of this paper is the analysis and quantification of the influence of the opening between the heads of the two closest pyramids in textured surface for solar cells and its application on the photovoltaic parameters. In this model we show that the material can have seven successive incident ray absorptions instead of five currently, where we changed the direction of the reflected ray, by identifying and install the angle between the two neighbouring pyramids, the incidence angle, the opening between the heads of the two closest pyramids and their height. Thus, with an angle between the two neighbouring pyramid fixed at 12° and for angle of incidence fixed at 84°. For these values of the angle between the two neighbouring pyramids and incidence angle, the opening between the heads of the two closest pyramids fixed at 2.10 μm for a pyramid height of 10 μm. This leads to the largest possible increase in optical efficiency, such as spectral response, Absorption Coefficient and External Quantum Efficiency. The results are in good agreement with the available literature.

Light absorption by ordered planar structure of crystalline silicon particles: Simulation as applied to enhancement of the solar cell performance

Light absorption by a single spherical crystalline silicon (c-Si) particle and by monolayers of submicron c-Si particles arranged in triangular lattice is examined within the wavelength range from 0.28 to 1.12 μm. Data for spectral and integrated (over the terrestrial solar spectral irradiance “Global tilt” ASTM G173-03) absorption coefficients of monolayer demonstrating the possibility to enhance light absorption by a particulate active layer of crystalline silicon are presented. They are calculated in the quasicrystalline approximation of the theory of multiple scattering of waves. It is shown that in the narrow wavelength intervals (up to 10 nm) the spectral absorption coefficient of monolayer can be more than 100 times larger than the one of the plane-parallel plate of equal volume of material. Some results on the transmittance and reflectance of partially ordered monolayer are presented as well. The potentialities of light absorption enhancement in a single monolayer and three-monolayer system are considered.

Deposition of CZTSe thin films and illumination effects on the device properties of Ag/n-Si/p-CZTSe/In heterostructure

Abstract Characterization of Cu 2 ZnSnSe 4 (CZTSe) thin films deposited by thermal evaporation sequentially from the pure elemental sources and in-situ post annealing was carried out at 400 C under Se evaporation atmosphere. Another annealing process was applied in nitrogen atmosphere at 450 °C to get polycrystalline monophase CZTSe film structure. XRD analysis together with Raman spectroscopy was used to determine the structural properties. Spectral optical absorption coefficient evaluated from transmission data showed the band gap value of 1.49 eV for annealed film. Electrical measurements indicated that CZTSe thin films have p-type semiconductor behavior with the carrier density and mobility values of 10 −19 cm −3 and 0.70 cm 2 /(V.s). Illumination effects on the device properties of Ag/n-Si/p-CZTSe/In heterostructure were investigated by analyzing current-voltage(I-V) and frequency dependent capacitance-voltage(C-V) data. Under the illumination, Ag/n-Si/p-CZTSe/In heterostructure showed photodiode behavior having V oc value of 100 mV and I sc value of 27.5 μA. With the illumination, series resistances (R s ), diode ideality factor (n) and barrier height (Φ b ) decreased and shunt resistance (R sh ) increased. Capacitance value at lower frequency decreased due to the illumination effect.

Radiative transfer analysis of the effect of ink dot area on color phase in inkjet printing

This study discusses a mechanism of inkjet printing and investigates the effect of ink contrast on the color phase of the printed object. Inkjet printing is a popular printing method for home use, but its color repeatability is occasionally broken. To verify this problem, we calculated the radiative transfer equation on the surface of an object printed by an inkjet printer, and the color was quantitatively estimated. The ink dot area and spectral reflectance of the printed samples were measured. Furthermore, the spectral reflectance of the objects printed with different dot areas were theoretically calculated. By comparing the measured and calculated reflectance, we estimated the scattering coefficient of the paper and absorption coefficient of the ink. We quantitatively calculated the color with the HSV color system. The hue changed with dot area rate. It is considered that this is caused by the broad range of the spectral absorption coefficients of inks. We believe that this study will aid the development of ink without color change and improve the color repeatability of inkjet printers.

Optical characterization of carbon quantum dots in colloidal suspensions

The remarkable feature of carbon quantum dots is the strong broadband photoluminescence of their colloidal solutions, which is observed on a variety of simple synthetic routes. This article describes the production of carbon nanodots (C-dots) with an average size of 3 nm in poly(ethylene glycol) by laser ablation and the evaluation of the spectral molar absorption coefficient, e(λ), of these particles. In parallel we investigate optical properties as photoluminescence, lifetime and by a thermally managed Eclipse Z-scan we describe the thermo-optical properties of this colloidal suspension.

Monitoring the seasonal dynamics of physicochemical parameters from Atoyac River basin (Puebla), Central Mexico: multivariate approach

Spatiotemporal variations of ten physicochemical parameters in the water quality of Atoyac River basin, Central Mexico, were obtained from 22 sampling sites (66 samples in total) located all along the basin for three different seasons (dry, rainy and winter). Multivariate statistical techniques such as correlation matrix, factor analysis (FA) and cluster analysis (CA) were used as a tool to understand the process. Physicochemical parameters such as temperature (T), pH, conductivity (λ), dissolved oxygen (DO), spectral absorption coefficient (SAC), oxidation–reduction potential (ORP), turbidity, 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and total suspended solids (TSS) were analyzed. Extremely high values of pH (10.24), conductivity (1870 µS/cm) and reduced redox potential (−370.1 mV) were observed in the dry season, whereas elevated TSS of 2996 mg/L was detected during the rainy season. The results elucidated high influence from the adjoining industrial, agricultural and urban zones, making the river unsuitable for life. FA generated varifactors, which accounted for cumulative % of 75.04 (dry), 76.22 (rainy) and 79.96 (winter) clearly grouping the external factors responsible for these significant values indicating the source of contamination. Cluster analysis facilitated the ease of classifying the sampling sites based on the similarities of physicochemical parameters. This study carried out in different seasons using multivariate statistical techniques would definitely prove to be an efficient tool for the restoration and establishing the real-time monitoring stations along this important river basin of Mexico.

Diffusion Approximation to Radiation Heat Transfer in Semitransparent Medium

Conduction-radiation heat transfer problem is usually formulated with a highly nonlinear integrodifferential equation. In this paper we describe a simple technique for modeling radiation heat transfer in a semi-transparent medium with arbitrary varying spectral absorption coefficient and purpose a computational model (described by a coupled system of elliptic-parabolic PDEs) based on flux limited diffusion theory. Numerical simulations of a glass cooling problem in one dimension show that the proposed method is comparable to a higher order discrete ordinate (S8) method.

Spectral Apparatus with a Cryogenic, High-Throughput, Multipass Gas Cell for Studies of Absorption of Radiation by Gaseous Media

Spectral systems with an MKhK-6 cryogenic, high-throughput, multipass gas cell for studying the absorption spectra of gaseous media with high spectral resolution in the 0.1–6 μm range at pressures of 100 to 5·106 Pa and temperatures of 180–300 K are discussed. Their use in measurements of spectral absorption coefficients, temperature dependences of the spectral transmission function, and parameters of spectral absorption lines is examined.

Radiation Heat Transfer in the Molten Salt FLiNaK

The molten fluoride salt eutectic LiF-NaF-KF (FLiNaK) has been proposed as a coolant for use in Generation IV reactors designed to operate at temperatures at which radiation heat transfer (RHT) may be significant. Little research has been performed into the absorption coefficient of FLiNaK as it pertains to thermal RHT. An estimate of the spectral absorption coefficient for FLiNaK has been generated using informed assumptions and existing data for the constituent salts. The effect of heat transfer, as it pertains to flowing salt in circular cross-section pipes with heated walls, has been investigated for laminar flow using a mathematical model. The combined energy equation, in various geometries, was solved for laminar flow, with the radiative heat flux calculated using the differential approximation. The percentage of energy transferred by radiation to the salt was found to be primarily a function of pipe diameter, wall temperature, and the salt absorption coefficient. A map of temperatures and pipe diameters has been generated, which indicates where RHT is significant. A correlation has been proposed, based on the mathematical model, to account for increase in Nusselt number due to radiation. Additional discussion is included on the effects of wall emissivity and high Reynolds flows.

Improved MSMGFSK Models Apply to Gas Radiation Heat Transfer Calculation of Exhaust System of TBCC

The multiscale multigroup full-spectrum k-distribution (MSMGFSK) model was improved to adapt to radiation heat transfer calculations of combustion gas flow field with large temperature and pressure gradient. The improvements in calculation accuracy resulting from new sorting strategy of the spectral absorption coefficients were validated using a series of semi-1D problem in which strong temperature, pressure, and mole fraction inhomogeneities were present. A simpler method to attain compatibility between the MSMGFSK model and the gray-wall radiation emission has been established and validated. Finally, estimates are given for the calculation of wall radiation heat transfer characteristics and thermal emission imaging of the exhaust system of the parallel turbine-based combined cycle (TBCC) engine, using finite volume method (FVM) and ray trace method (RT), respectively.

Measurement System for Study of Absorption Spectra of Gaseous Media at High Pressures

A system for measuring the absorption spectra of gaseous media at pressures of 0.01–150 atm in the 0.3–25 μm range is considered. Its suitability for studying pressure-induced absorption owing to intermolecular collisions and for measuring spectral absorption coefficients, integrated band intensities, and spectrum line profiles is discussed.

Application of SAC254 measurement for the assessment of micropollutant removal in the adsorptive treatment stage of a municipal wastewater treatment plant

In 2010, the Mannheim wastewater treatment plant was expanded with an adsorptive treatment stage to remove organic micropollutants (OMPs). Differences in the removal efficiencies of the OMPs investigated were determined over four years of operation by applying different powdered activated carbon (PAC) products and a constant volume-proportional dosing of 10 mg PAC/L. Possible influences on the removal efficiency are discussed here on the basis of the data obtained, exemplified for the analgesic diclofenac. The analyses show that the removal efficiency is influenced significantly by the spectral absorption coefficient (SAC) of the biologically treated wastewater at a wavelength of 254 nm (SAC254). Therefore, in order to ensure the constant treatment performance desired, the dosage of PAC should be adjusted to the measured SAC254 values. Moreover, as the SAC254 reduction correlates with the removal efficiency of OMPs, the additional determination of its reduction allows indirect control of the actual removal performance achieved. The SAC254 reduction can also be used for targeted control of the PAC dosage.