Thermal-optical Analysis Methods Research Articles

Thermal-optical characteristics analysis of an aerial camera optical system.

Ambient temperature is one of the important factors affecting the imaging quality of the optical system. Therefore, it is necessary to analyze the thermal-optical characteristics of the optical system when studying the imaging quality of the optical system. Taking the self-made aerial camera optical system as an example, this paper reports the use of the finite element software ANSYS to analyze the thermal stress of the aerial camera optical system, the use of the homogeneous coordinate transformation method to remove the rigid body displacement caused by the mirror surface, and the performance of a Zernike polynomial simulation on the processed surface data. Together, the Zernike coefficients obtained after the fitting are substituted into the ZEMAX optical software to express the surface shape obtained after deformation to analyze the changes in optical imaging quality under thermal environmental conditions. The results of the experiment show that when the working environmental temperature is 50°C, the (MTF) decreases from 0.371 to 0.315 and, when the working environmental temperature is -40∘C, the MTF decreases from 0.371 to 0.285. The comparison results of the experiment and simulation show that the environmental temperature is heating up or, under the condition of cooling, the imaging quality of the aerial camera will be reduced. The thermal-optical analysis method can be used to simulate the actual use conditions of the aerial camera optical system and predict the imaging quality change trend of the optical system. The method of thermo-optical analysis has important guiding significance for the design of an optical-mechanical system.

The influence of temperature calibration on the OC–EC results from a dual-optics thermal carbon analyzer

Abstract. Thermal–optical analysis (TOA) is a widely used technique that fractionates carbonaceous aerosol particles into organic and elemental carbon (OC and EC), or carbonate. Thermal sub-fractions of evolved OC and EC are also used for source identification and apportionment; thus, oven temperature accuracy during TOA analysis is essential. Evidence now indicates that the "actual" sample (filter) temperature and the temperature measured by the built-in oven thermocouple (or set-point temperature) can differ by as much as 50 °C. This difference can affect the OC–EC split point selection and consequently the OC and EC fraction and sub-fraction concentrations being reported, depending on the sample composition and in-use TOA method and instrument. The present study systematically investigates the influence of an oven temperature calibration procedure for TOA. A dual-optical carbon analyzer that simultaneously measures transmission and reflectance (TOT and TOR) is used, functioning under the conditions of both the National Institute of Occupational Safety and Health Method 5040 (NIOSH) and Interagency Monitoring of Protected Visual Environment (IMPROVE) protocols. The application of the oven calibration procedure to our dual-optics instrument significantly changed NIOSH 5040 carbon fractions (OC and EC) and the IMPROVE OC fraction. In addition, the well-known OC–EC split difference between NIOSH and IMPROVE methods is even further perturbed following the instrument calibration. Further study is needed to determine if the widespread application of this oven temperature calibration procedure will indeed improve accuracy and our ability to compare among carbonaceous aerosol studies that use TOA.

Evaluation of the carbon content of aerosols from the burning of biomass in the Brazilian Amazon using thermal, optical and thermal-optical analysis methods

Abstract. Aerosol samples were collected at a pasture site in the Amazon Basin as part of the project LBA-SMOCC-2002 (Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate). Sampling was conducted during the late dry season, when the aerosol composition was dominated by biomass burning emissions, especially in the submicron fraction. A 13-stage Dekati low-pressure impactor (DLPI) was used to collect particles with nominal aerodynamic diameters (Dp) ranging from 0.03 to 0.10 μm. Gravimetric analyses of the DLPI substrates and filters were performed to obtain aerosol mass concentrations. The concentrations of total, apparent elemental, and organic carbon (TC, ECa, and OC) were determined using thermal and thermal-optical analysis (TOA) methods. A light transmission method (LTM) was used to determine the concentration of equivalent black carbon (BCe) or the absorbing fraction at 880 nm for the size-resolved samples. During the dry period, due to the pervasive presence of fires in the region upwind of the sampling site, concentrations of fine aerosols (Dp<2.5 μm: average 59.8 μg m−3) were higher than coarse aerosols (Dp> 2.5 μm: 4.1 μg m−3). Carbonaceous matter, estimated as the sum of the particulate organic matter (i.e., OC × 1.8) plus BCe, comprised more than 90% to the total aerosol mass. Concentrations of ECa (estimated by thermal analysis with a correction for charring) and BCe (estimated by LTM) averaged 5.2 ± 1.3 and 3.1 ± 0.8 μg m−3, respectively. The determination of EC was improved by extracting water-soluble organic material from the samples, which reduced the average light absorption Ångström exponent of particles in the size range of 0.1 to 1.0 μm from >2.0 to approximately 1.2. The size-resolved BCe measured by the LTM showed a clear maximum between 0.4 and 0.6 μm in diameter. The concentrations of OC and BCe varied diurnally during the dry period, and this variation is related to diurnal changes in boundary layer thickness and in fire frequency.

Fabrication of Reference Filter for Measurements of EC (Elemental Carbon) and OC (Organic Carbon) in Aerosol Particles

Reference filters with uniformly deposited, known masses of elemental carbon (EC) and organic carbon (OC) were produced by a spray-drying method and a carbon aerosol sampling system. Submicrometer carbon particles were produced by nebulizing a carbon black hydrosol and a potassium hydrogen phthalate (KHP; C 6 H 4 (COOK)(COOH)) solution. Total carbon (TC) concentrations measured at three different locations on the filter showed that the carbon particles were uniformly distributed on the filter. Reference filters were analyzed using thermal optical analysis methods (TOA) IMPROVE and NIOSH 5040-NIIH, and the measured concentrations of TC, EC, and OC were compared to the gravimetrically measured concentrations. TC measurements by both TOA methods used were in excellent agreement with gravimetrically measured TC. It was found that the IMPROVE method produced approximately 3.5 times as much pyrolytically generated elemental carbon (PEC) as did the NIOSH 5040-NIIH method. However, no PEC was detectable on refere...

Controlled generation of black carbon particles from a diffusion flame and applications in evaluating black carbon measurement methods

Measurements of black carbon (BC) concentration have long been uncertain. Neither a BC standard or a technique that provides a reliable measurement of BC exist, which precludes the evaluation and optimization of BC measurement methods. In this manuscript, we describe the generation of BC particles (mass absorption efficiency ∼8.5 m 2 g −1 and single scattering albedo ∼0.2 at 530 nm) using an inverted diffusion flame. This flame is remarkably stable and can be used to generate a wide range of nearly constant concentrations of BC particles for many (e.g., 10+) hours. The particles contain essentially no organic carbon (OC), so the quantification of BC mass using any of the thermal or thermal–optical analysis (TOA) methods is straightforward instead of highly uncertain. In this case, the TOA measurement of BC can be used to evaluate the accuracy of other BC measurement methods. In this paper, we demonstrate the application of the diffusion flame in evaluating BC measurements made with filter-based light transmission methods, and in particular the aethalometer. We show that the amount of light attenuated by a BC-laden filter increases in less than constant proportion to the BC mass loading, and thus the effective BC attenuation coefficient decreases with increased BC mass loading. When sampling BC at constant concentration, the aethalometer erroneously reports decreasing concentrations of BC as its filter becomes increasingly loaded because it treats the attenuation coefficient as a constant. A simple method to correct erroneous aethalometer data when sampling aerosols with low single scattering albedo is presented. Another application of the diffusion flame considered in this paper is the development of BC standards for TOA. We envision the preparation of filter samples with known amounts of BC mixed with other aerosol constituents, which may help in understanding the uncertainty in and optimizing TOA measurements, and may be of use in future TOA method comparison studies. Toward this end, we demonstrate that the diffusion flame can be used to replicate filter samples with known amounts of BC. Additionally, we show that the combustion temperature of BC during TOA depends on sample composition, which suggests that the temperature-defined carbon fractions of some thermal and TOA methods may be of limited value.

Study of overlapping transitions in polymers by combined differential scanning calorimetry and thermal optical analysis methods

In some polymers, thermal transitions and molecular relaxation processes may be situated closely together on the temperature scale or may actually overlap. In such cases, observations by differential scanning calorimetry. (DSC) may lead to ambiguous results or to erroneous conclusions. In many instances, the ambiguity can be removed by making additional measurements at the same scanning rate on polymer samples of similar past history by thermal optical analysis (TOA). The combined use of these two types of measurements, DSC and TOA, is here applied to a study of transitions and structural changes in several types of cellulose acetate. From the results obtained, it is possible to resolve and identify various overlapping thermal processes such as the glass transition of the polymer chains, subsequent crystallization, melting of ordered phases and thermal degradation.