scholarly journals Correction for a measurement artifact of the Multi-Angle Absorption Photometer (MAAP) at high black carbon mass concentration levels

2013 ◽  
Vol 6 (1) ◽  
pp. 81-90 ◽  
Author(s):  
A.-P. Hyvärinen ◽  
V. Vakkari ◽  
L. Laakso ◽  
R. K. Hooda ◽  
V. P. Sharma ◽  
...  
Keyword(s):  
Black Carbon ◽  
Flow Rate ◽  
Accumulation Rate ◽  
Correction Method ◽  
Correction Function ◽  
Carbon Mass ◽  
The Individual ◽  
Measurement Artifact ◽  
Sudden Decrease ◽  
Absorption Photometer

Abstract. The Multi-Angle Absorption Photometer (MAAP) is a widely-used instrument for aerosol black carbon (BC) measurements. In this paper, we show correction methods for an artifact found to affect the instrument accuracy in environments characterized by high black carbon concentrations. The artifact occurs after a filter spot change – as BC mass is accumulated on a fresh filter spot, the attenuation of the light (raw signal) is weaker than anticipated. This causes a sudden decrease, followed by a gradual increase in measured BC concentration. The artifact is present in the data when the BC concentration exceeds ~3 μg m−3 at the typical MAAP flow rate of 16.7 L min−1 or 1 m3 h−1. The artifact is caused by erroneous dark counts in the photodetector measuring the transmitted light, in combination with an instrument internal averaging procedure of the photodetector raw signals. It was found that, in addition to the erroneous temporal response of the data, concentrations higher than 9 μg m−3 (at the flow rate of 16.7 L min−1) are underestimated by the MAAP. The underestimation increases with increasing BC accumulation rate. At a flow rate of 16.7 L min−1 and concentration of about 24 μg m−3 (BC accumulation rate ~0.4 μg min−1), the underestimation is about 30%. There are two ways of overcoming the MAAP artifact. One method is by logging the raw signal of the 165° photomultiplier measuring the reflected light from the filter spot. As this signal is not affected by the artifact, it can be converted to approximately correct absorption and BC values. However, as the typical print formats of the MAAP do not give the reflected signal as an output, a semi-empirical correction method was developed based on laboratory experiments to correct for the results in the post-processing phase. The correction function was applied to three MAAP datasets from Gual Pahari (India), Beijing (China), and Welgegund (South Africa). In Beijing, the results could also be compared against a photoacoustic spectrometer (PAS). The correction improved the quality of all three MAAP datasets substantially, even though the individual instruments operated at different flow rates and in different environments.

scholarly journals Correction for a measurement artifact of the Multi-Angle Absorption Photometer (MAAP) at high black carbon mass concentration levels

2012 ◽  
Vol 5 (5) ◽  
pp. 6553-6576
Author(s):  
A.-P. Hyvärinen ◽  
V. Vakkari ◽  
L. Laakso ◽  
R. K. Hooda ◽  
V. P. Sharma ◽  
...  
Keyword(s):  
Black Carbon ◽  
Flow Rate ◽  
Accumulation Rate ◽  
Correction Method ◽  
Correction Function ◽  
Carbon Mass ◽  
The Individual ◽  
Measurement Artifact ◽  
Sudden Decrease ◽  
Absorption Photometer

Abstract. The Multi-Angle Absorption Photometer (MAAP) is a widely-used instrument for aerosol black carbon observations. In this paper, we show correction methods for an artifact found to affect the instrument accuracy in environments with high black carbon concentrations. The artifact occurs after a filter spot change – as BC mass is accumulated on a fresh filter spot, the attenuation of the light (raw signal) is weaker than anticipated. This causes a sudden decrease, followed by a gradual increase in measured BC concentration. The artifact is present in the data when the BC concentration exceeds ∼3 μg m−3 at the typical MAAP flow rate of 16.7 l min−1 or 1 m3 h−1. The artifact is caused by erroneous dark counts in the photo detector measuring the transmitted light, in combination with an instrument internal averaging procedure of the photo detector raw signals. It was found that in addition to the erroneous temporal response of the data, concentrations higher than 9 μg m−3 (at the flow rate of 16.7 l min−1) are underestimated by the MAAP. The underestimation increases with increasing BC accumulation rate. At a flow rate of 16.7 l min−1 and concentration of about 24 μg m−3 (BC accumulation rate ∼0.4 μg min−1), the underestimation is about 30%. There are two ways of overcoming the MAAP artifact. One method is by logging the raw signal of the 165° photomultiplier measuring the reflected light from the filter spot. As this signal is not affected by the artifact, it can be converted to approximately correct absorption and BC values. However, as the typical print formats of the MAAP do not give the reflected signal as an output, a semi-empirical correction method was developed based on laboratory experiments to correct for the results in the post-processing phase. The correction function was applied to three MAAP datasets from Gual Pahari (India), Beijing (China), and Welgegund (South Africa). In Beijing, the results could also be compared against a Photo-Acoustic Spectrometer (PAS). The correction improved the quality of all three MAAP datasets substantially, even though the individual instruments operated at different flow rates and in different environments.

Should black carbon concentration from aethalometer measurements onboard of UAVs be additionally corrected? - What is the impact of rapid relative humidity changes on our measurements?

2021 ◽  
Author(s):  
Grzegorz Florczyk ◽  
Krzysztof Markowicz
Keyword(s):  
Relative Humidity ◽  
Black Carbon ◽  
Mass Concentration ◽  
Strong Dependence ◽  
Correction Method ◽  
Atmospheric Measurements ◽  
Atmospheric Sciences ◽  
Humidity Chamber ◽  
Carbon Mass ◽  
The Impact

<p>Relative humidity and rates of its change are relevant parameters in atmospheric sciences. Observations of output data of AE-51 aethalometer operating in ACS1000 humidity chamber reveal strong dependence of attenuation on rapid relative humidity changes. Data collected in winter 2020/21 suggests a probability of similar effect occurring during UAV measurements as thermodynamic parameters could change fast during such runs. Two AE-51 devices were connected in the WET and DRY ACS1000 humidity chamber's channels. During periodic relative humidity oscillations, incident negative peaks of equivalent black carbon mass concentration coincide with high negative derivatives of relative humidity. In most extreme cases values of -1000 ng/m3 equivalent black carbon mass concentration were recorded in parallel with relative humidity derivative of -1.5 %/min. These correlations seem to play an important role in atmospheric measurements as vertical profiles of aerosol parameters such as attenuation are collected using UAV runs during which relative humidity varies significantly. Our goal is to propose a correction method to minimise these anomalies.</p>

scholarly journals EFFECT OF TUBE PITCH ON HEAR TRANSFER IN SPRINKLED TUBE BUNDLE

2015 ◽  
Vol 55 (5) ◽  
pp. 329 ◽  
Author(s):  
Petr Kracík ◽  
Jiří Pospíšil
Keyword(s):  
Flow Rate ◽  
Tube Bundle ◽  
Thin Liquid Film ◽  
Thermal Conditions ◽  
Tube Length ◽  
Falling Film ◽  
Constant Flow Rate ◽  
Physical Conditions ◽  
The Individual ◽  
Tube Pitch

Water flowing on a sprinkled tube bundle forms three basic modes: the Droplet mode (the liquid drips from one tube to another), the Jet mode (with an increasing flow rate, the droplets merge into a column) and the Membrane (Sheet) mode (with a further increase in the flow rate of the falling film liquid, the columns merge and create sheets between the tubes. With a sufficient flow rate, the sheets merge at this stage, and the tube bundle is completely covered by a thin liquid film). There are several factors influencing both the individual modes and the heat transfer. Beside the above-mentioned falling film liquid flow rate, these are for instance the tube diameters, the tube pitches in the tube bundle, or the physical conditions of the falling film liquid. This paper presents a summary of data measured at atmospheric pressure, with a tube bundle consisting of copper tubes of 12 millimetres in diameter, and with a studied tube length of one meter. The tubes are situated horizontally one above another at a pitch of 15 to 30 mm, and there is a distribution tube placed above them with water flowing through apertures of 1.0mm in diameter at a 9.2mm span. Two thermal conditions have been tested with all pitches: 15 °C to 40 °C and 15 °C to 45 °C. The temperature of the falling film liquid, which was heated during the flow through the exchanger, was 15 °C at the distribution tube input. The temperature of the heating liquid at the exchanger input, which had a constant flow rate of approx. 7.2. litres per minute, was 40 °C, or alternatively 45 °C.

scholarly journals Comparison of different models to calculate the viscosity of biogas and biomethane in order to accurately measure flow rates for conformity assessment

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Karine Arrhenius ◽  
Oliver Büker
Keyword(s):  
Binary Mixtures ◽  
Flow Rate ◽  
Correction Method ◽  
Gas Mixtures ◽  
Conformity Assessment ◽  
Flow Rates ◽  
Unknown Composition

AbstractThe study presents an optimised method to correct flow rates measured with a LFE flowmeter pre-set on methane while used for gas mixtures of unknown composition at the time of the measurement. The method requires the correction of the flow rate using a factor based on the viscosity of the gas mixtures once the composition is accurately known. The method has several different possible applications inclusive for the sampling of biogas and biomethane onto sorbent tubes for conformity assessment for the determination of siloxanes, terpenes and VOC in general. Five models for the calculation of the viscosity of the gas mixtures were compared and the models were used for ten binary mixtures and four multi-component mixtures. The results of the evaluation of the different models showed that the correction method using the viscosity of the mixtures calculated with the model of Reichenberg and Carr showed the smallest biases for binary mixtures. For multi-component mixtures, the best results were obtained when using the models of Lucas and Carr.

An Adaptive Response Surface Method Using Bayesian Metric and Model Bias Correction Function

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Lei Shi ◽  
Ren-Jye Yang ◽  
Ping Zhu
Keyword(s):  
Response Surface ◽  
Bias Correction ◽  
Adaptive Response ◽  
Large Scale ◽  
Correction Method ◽  
Data Uncertainty ◽  
Correction Function ◽  
Surface Model ◽  
Model Bias ◽  
Adaptive Response Surface Method

The Bayesian metric was used to select the best available response surface in the literature. One of the major drawbacks of this method is the lack of a rigorous method to quantify data uncertainty, which is required as an input. In addition, the accuracy of any response surface is inherently unpredictable. This paper employs the Gaussian process based model bias correction method to quantify the data uncertainty and subsequently improve the accuracy of a response surface model. An adaptive response surface updating algorithm is then proposed for a large-scale problem to select the best response surface. The proposed methodology is demonstrated by a mathematical example and then applied to a vehicle design problem.

scholarly journals Ultra-Widefield Fluorescein Angiography Image Brightness Compensation Based on Geometrical Features

Sensors ◽  
2021 ◽  
Vol 22 (1) ◽  
pp. 12
Author(s):  
Wojciech Więcławek ◽  
Marta Danch-Wierzchowska ◽  
Marcin Rudzki ◽  
Bogumiła Sędziak-Marcinek ◽  
Slawomir Jan Teper
Keyword(s):  
Image Quality ◽  
Fluorescein Angiography ◽  
Imaging Modality ◽  
Correction Method ◽  
Correction Function ◽  
Image Brightness ◽  
Geometrical Features ◽  
Noticeable Improvement ◽  
Manual Processing ◽  
Image Quality Measures

Ultra-widefield fluorescein angiography (UWFA) is an emerging imaging modality used to characterise pathologies in the retinal vasculature, such as microaneurysms (MAs) and vascular leakages. Despite its potential value for diagnosis and disease screening, objective quantitative assessment of retinal pathologies by UWFA is currently limited because laborious manual processing is required. In this report, we describe a geometrical method for uneven brightness compensation inherent to UWFA imaging technique. The correction function is based on the geometrical eyeball shape, therefore it is fully automated and depends only on pixel distance from the center of the imaged retina. The method’s performance was assessed on a database containing 256 UWFA images with the use of several image quality measures that show the correction method improves image quality. The method is also compared to the commonly used CLAHE approach and was also employed in a pilot study for vascular segmentation, giving a noticeable improvement in segmentation results. Therefore, the method can be used as an image preprocessing step in retinal UWFA image analysis.

scholarly journals Spatial Characterization of Black Carbon Mass Concentration in the Atmosphere of a Southeast Asian Megacity: An Air Quality Case Study for Metro Manila, Philippines

2018 ◽  
Vol 18 (9) ◽  
pp. 2301-2317 ◽  
Author(s):  
Honey Dawn Alas ◽  
Thomas Müller ◽  
Wolfram Birmili ◽  
Simonas Kecorius ◽  
Maria Obiminda Cambaliza ◽  
...  
Keyword(s):  
Air Quality ◽  
Black Carbon ◽  
Mass Concentration ◽  
Southeast Asian ◽  
Spatial Characterization ◽  
Metro Manila ◽  
Carbon Mass

scholarly journals Long-term observations of tropospheric particle number size distributions and equivalent black carbon mass concentrations in the German Ultrafine Aerosol Network (GUAN)

2016 ◽  
Vol 8 (2) ◽  
pp. 355-382 ◽  
Author(s):  
Wolfram Birmili ◽  
Kay Weinhold ◽  
Fabian Rasch ◽  
André Sonntag ◽  
Jia Sun ◽  
...  
Keyword(s):  
Black Carbon ◽  
Particle Number ◽  
Measurement Data ◽  
Urban Traffic ◽  
Data Evaluation ◽  
Size Distributions ◽  
Evaluation Procedures ◽  
Carbon Mass ◽  
Ultrafine Aerosol ◽  
Mass Concentrations

Abstract. The German Ultrafine Aerosol Network (GUAN) is a cooperative atmospheric observation network, which aims at improving the scientific understanding of aerosol-related effects in the troposphere. The network addresses research questions dedicated to both climate- and health-related effects. GUAN's core activity has been the continuous collection of tropospheric particle number size distributions and black carbon mass concentrations at 17 observation sites in Germany. These sites cover various environmental settings including urban traffic, urban background, rural background, and Alpine mountains. In association with partner projects, GUAN has implemented a high degree of harmonisation of instrumentation, operating procedures, and data evaluation procedures. The quality of the measurement data is assured by laboratory intercomparisons as well as on-site comparisons with reference instruments. This paper describes the measurement sites, instrumentation, quality assurance, and data evaluation procedures in the network as well as the EBAS repository, where the data sets can be obtained (doi:10.5072/guan).

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