Thermal Optical Transmittance Research Articles

Research progress on aero-optical effects of hypersonic optical window with film cooling

AbstractIn recent years, the demand for optical imaging and detection in hypersonic aircraft has been on the rise. The high-temperature and high-pressure compressed flow field near airborne optoelectronic devices creates significant interference with light transmission, known as hypersonic aero-optical effects. This effect has emerged as a key technological challenge, limiting hypersonic optical imaging and detection capabilities. This article focuses on introducing the thermal effects and optical transmission effects of hypersonic aero-optical effects, as along with corresponding suppression techniques. In addition, this article critically reviews and succinctly summarizes the advancements made in hypersonic aero-optical effects testing technology, while also delineating avenues for future research needs in this field. In conclusion, there is an urgent call for further exploration into the study of aero-optical effects under conditions characterized by high Mach, high enthalpy, and high Reynolds number in the future.

Quantifying functional group compositions of household fuel-burning emissions

Abstract. Globally, billions of people burn fuels indoors for cooking and heating, which contributes to millions of chronic illnesses and premature deaths annually. Additionally, residential burning contributes significantly to black carbon emissions, which have the highest global warming impacts after carbon dioxide and methane. In this study, we use Fourier transform infrared spectroscopy (FTIR) to analyze fine-particulate emissions collected on Teflon membrane filters from 15 cookstove types and 5 fuel types. Emissions from three fuel types (charcoal, kerosene, and red oak wood) were found to have enough FTIR spectral response for functional group (FG) analysis. We present distinct spectral profiles for particulate emissions of these three fuel types. We highlight the influential FGs constituting organic carbon (OC) using a multivariate statistical method and show that OC estimates by collocated FTIR and thermal–optical transmittance (TOT) are highly correlated, with a coefficient determination of 82.5 %. As FTIR analysis is fast and non-destructive and provides complementary FG information, the analysis method demonstrated herein can substantially reduce the need for thermal–optical measurements for source emissions.

New PV encapsulants: assessment of change in optical and thermal properties and chemical degradation after UV aging

This work aims to investigate the change in chemical and physical properties of different polymeric materials, potentially usable for photovoltaic modules encapsulation, caused by UV aging. Three classes of polymeric materials have been examined: ethylene-vinyl-acetate (EVA), thermoplastic polyolefins (TPO) and polyolefin elastomers (POE). EVA is currently the most used encapsulant in the photovoltaic field; TPO and POE are new materials, alternative to EVA, which can allow to overcome some of the reliability problems of photovoltaic modules linked to the degradation of EVA properties. Of each of these three material classes, different commercially available encapsulating polymer films, with different chemical formulations, have been examined. Stressful environmental conditions have been simulated in a climatic chamber and the associated changes in optical, thermal and chemical properties of the different encapsulants have been analysed and compared before and after UV aging. The link between the chemical structure, formulation and degradation of the encapsulants with their lifetime under simulated conditions of UV stress has been investigated by the assessment of the changes in thermal stability, optical transmittance, crystallinity, yellowness index and chemical degradation. This study helps to better understand the causes of the module performance reduction due to the degradation of the encapsulant material and is a guide for the selection of encapsulant films with improved characteristics, for the manufacture of more durable PV modules.

A novel measurement system for unattended, in situ characterization of carbonaceous aerosols

Abstract. Carbonaceous aerosol is a relevant constituent of the atmosphere in terms of climate and health impacts. Nevertheless, measuring this component poses many challenges. There is currently no simple and sensitive commercial technique that can reliably capture its totality in an unattended manner, with minimal user intervention, for extended periods of time. To address this issue we have developed the fast thermal carbon totalizator (FATCAT). Our system captures an aerosol sample on a rigid metallic filter and subsequently analyses it by rapidly heating the filter directly, through induction, to a temperature around 800 ∘C. The carbon in the filter is oxidized and quantified as CO2 in order to establish the total carbon (TC) content of the sample. The metallic filter is robust, which solves filter displacement or leakage problems, and does not require a frequent replacement like other measurement techniques. The limit of detection of our system using the 3σ criterion is TC =0.19 µg-C (micrograms of carbon). This translates to an average ambient concentration of TC =0.32 µg-C m−3 and TC =0.16 µg-C m−3 for sampling interval of 1 or 2 h respectively using a sampling flow rate of 10 L min−1. We present a series of measurements using a controlled, well-defined propane flame aerosol as well as wood-burning emissions using two different wood-burning stoves. Furthermore, we complement these measurements by coating the particles with secondary organic matter by means of an oxidation flow reactor. Our device shows a good correlation (correlation coefficient, R2>0.99) with well-established techniques, like mass measurements by means of a tapered element oscillating microbalance and TC measurements by means of thermal–optical transmittance analysis. Furthermore, the homogeneous fast-heating of the filter produces fast thermograms. This is a new feature that, to our knowledge, is exclusive of our system. The fast thermograms contain information regarding the volatility and refractoriness of the sample without imposing an artificial fraction separation like other measurement methods. Different aerosol components, like wood-burning emissions, soot from the propane flame and secondary organic matter, create diverse identifiable patterns.

Comprehensive investigation of a building integrated crossed compound parabolic concentrator photovoltaic window system: Thermal, optical and electrical performance

Integrating PV solar cells with concentrators into window systems can not only generate electricity for a building, but also has the potential to enhance the thermal resistance of the building's windows without a significant sacrifice of light transmittance for passive daylight. A novel system, known as the crossed compound parabolic concentrator photovoltaic window, has been recently studied for its electrical properties. However, its thermal and optical performance, particularly in terms of the overall heat transfer coefficient (U-value) and total optical transmittance when integrated into a building, remains unexamined. These factors are crucial for predicting the system's impact on a building's energy efficiency and indoor comfort. Therefore, this paper aims to investigate the U-value of this window system under various temperature scenarios and the optical transmittance of the window at different incident angles. The thermal conductance was assessed through numerical simulations using a computational fluid dynamics model, which was validated by experimental measurements conducted in a large climate chamber. The optical transmittance was investigated using a validated 3D ray-tracing model. The total optical transmittance and electricity generation were calculated for typical sunny days in winter and summer under London's climate conditions. Additionally, alternative designs were developed to explore the impact of pitch between adjacent optics on the thermal conductance and optical transmittance of the window. The results showed that the window with a configuration of Dx = Dy = 5 mm (where Dx and Dy represent the horizontal and vertical pitches, respectively, between two adjacent solar optics) achieved the lowest U-value (2.566 W/m2·K). This U-value is slightly lower than that of the original window design, which has a U-value of 2.575 W/m2·K. The original window configuration with Dx = Dy = 1.77 mm produces the highest power output. Specifically, it generates 499.25 Wh/m2 on a typical sunny day in winter and 162.73 Wh/m2 on a typical sunny day in summer. However, it exhibits the lowest transmittance (14.6 % on a typical sunny day in winter and 25.2 % on a typical sunny day in summer, respectively), indicating that it is more suitable for buildings with a higher window-to-wall ratio to ensure an adequate amount of natural light. For buildings with a lower window-to-wall ratio, the CCPC-PV window should be designed with a larger horizontal pitch, such as 15 mm and 30 mm, to meet indoor illuminance requirements while also providing enhanced thermal performance and additional power output.

Preparation and Optical Properties of Nd:Bi2Ti2O7 Laser Crystal with Disordered Structure and Attractive Multiwavelength Emission Characteristics.

Laser crystals with multiwavelength emission characteristics are potential light sources for terahertz radiation. Herein, the pure and Nd-doped Bi2Ti2O7 (BTO) laser crystals with sizes up to 16 × 13 × 5 mm3 were successfully grown using the flux method in the KF-B2O3-CaBi4Ti4O15 growth system. The crystal structure, ideal morphology, chemical, mechanical, and thermal properties, optical transmission and Raman spectra, refractive index, absorption, and fluorescence spectra, as well as fluorescence lifetimes, were systematically studied. Besides, the spectral parameters of Nd3+ ions in the BTO crystal were systematically calculated based on the Judd-Ofelt theory. The Nd:BTO crystal has a wide transmittance range (0.44-7.30 μm), a small coefficient of thermal expansion (5.80 × 10-6 K-1), and a large absorption full width at half-maximum (fwhm) (31.2 nm) at around ∼804 nm, making it more potential for use in high-power laser systems. Moreover, fluorescence spectra show four emission peaks at 1054, 1062, 1104, and 1112 nm. The strong multiwavelength emission property makes Nd:BTO a promising laser crystal, serving as a potential light source for terahertz radiation.

Characterisation of vehicle emissions in a road tunnel in Lisbon

In urban areas, road traffic is one of the main sources of air pollutants, mainly as particulate matter (PM). Knowledge about fingerprints of vehicle emissions under real-world driving conditions is scarce for Europe, especially in Portugal. The aim of this study was to characterise and quantify vehicle emissions through road tunnel measurements. The sampling campaign was carried out during one week inside a road tunnel and simultaneously in an urban background site in Lisbon. PM2.5 and PM2.5–10 filters were analysed by PIXE for elemental composition and by a thermal-optical transmittance technique for the determination of organic carbon (OC) and elemental carbon (EC). PM2.5 and PM10 concentrations were, at least, 20 and 10 times higher than those found in the background, respectively. Inside the tunnel, particle organic matter (POM), EC and other anthropogenic compounds accounted for more than 90.0% of the PM2.5 mass. Fe, Ca, Si, S and Cu represented 88.7% of the PM2.5-bound elements, while Fe, Cl, Ca, Si, Cu, Zn, Na, S, Ba mostly contributed to the PM2.5–10 elemental mass fraction (93.8%). Total carbon represented about 58.5% of PM2.5 and 26.5% of PM2.5–10. EC presented a high tunnel/background ratio (T/B = 35.4 for PM2.5 and 48.8 for PM2.5–10). Cu, Fe, Cr, Ba, Mn, Zn and Rb, which are key tracers of tyre and brake wear, showed a T/B > 70 and very good correlations between them. The emission factors (EF) of PM2.5 and PM10 were estimated to be 139 ± 20.7 and 172 ± 23.9 mg veh−1 km−1. The average EF of OC and EC in PM2.5 were 30.9 ± 6.48 and 44.6 ± 7.33 mg veh−1 km−1. This real-world study contributes to define road traffic emission profiles in urban areas, provide data to update European emission inventories, and evaluate the impact of traffic-generated PM on human health and the environment.

Development of drone-based filter sampling system for carbonaceous aerosol analysis using thermal–optical transmittance method

Development of drone-based filter sampling system for carbonaceous aerosol analysis using thermal–optical transmittance method

Restoration of a Textile Artefact: A Comparison of Cleaning Procedures Applied to a Historical Tapestry from the Quirinale Palace (Rome)

The cleaning of textile artefacts and in particular historical tapestries is generally carried out using standard methods. Different cleaning procedures, including a new method based on a hydro-aspiration mechanism, recently developed by restorers with the aim of improving the efficiency of the cleaning system, were applied to a historical tapestry belonging to the lower edge of one of the tapestries of the “Ulysses Stories” series exhibited at the Quirinale Palace (Rome). The tapestry was made of wool and silk and has precious decorations made of metal yarns, which are particularly fragile. The new cleaning system was compared with the traditional methods commonly used by restorers for tapestry cleaning. For this purpose, the quantity and chemical composition of the particles removed and collected on quartz fibre filters by applying the different cleaning systems, were estimated by means of analytical techniques, such as IC (Ion Chromatography) for the quantification of the ionic species collected into the rinsing water, the TOT (Thermal Optical Transmittance) method for the quantification of the carbonaceous particles and SEM-EDX (Scanning Electron Microscopy coupled to Energy Dispersive X-ray Spectroscopy) for yarn morphological characterization and elemental analysis of the deposited particles. The objective of this study is to identify the correct cleaning method to apply to the polymaterial tapestry and, in particular, to the gilded silver and gold metallic yarns, whose conservation state requires the preservation of the “self-protection” patina necessary for the future exhibition inside the Quirinale Palace. The new hydro-aspiration method was found to be more efficient in removing dirt and preserving the structure of the metallic threads being in this way less invasive in detaching the fragile surface patina and at the same time more effective in removing dirt.

Interface design of transparent thermoelectric epitaxial ZnO/SnO2 multilayer film for simultaneous realization of low thermal conductivity and high optical transmittance

A transparent thermoelectric material requires not only high thermoelectric performance but also high optical transmittance. However, in transparent nanostructured thermoelectric materials, the nanostructure interface brings the trade-off relationship between thermal conductivity and optical transmittance. We propose an approach for the simultaneous control of thermal conductivity and optical transmittance in the epitaxial nanostructured films, where carriers can be smoothly transported. This is realized by the interface design based on the three strategies: (1) a large atomic mass difference at the heterointerface for low thermal conductivity; (2) heterointerface with almost the same refractive index and flat surface for high optical transmittance; and (3) epitaxial heterointerface for smooth carrier transport. We formed epitaxial ZnO/SnO2 multilayer films based on this design guideline. The multilayer films exhibit lower thermal conductivity and higher optical transmittance than an ever reported transparent nanostructured thermoelectric material. These results highlight that this design is promising to realize high-performance transparent nanostructured thermoelectric materials.

Effect of WO3 on physical and magneto-optical properties of TeO2–La2O3–WO3 glasses for magneto-optics application

The ternary TeO2–La2O3–WO3 glasses with a formula of (100 − y − x)TeO2–yLa2O3–xWO3 (y = 5 and 10 mol%; x = 10 to 25 mol%) were made by the melting and casting method for high Verdet constant diamagnetic magneto-optical (MO) materials in the application of MO devices operating at 1550 nm. The compositional effects of WO3 and La2O3 contents on key glass properties of thermal stability, Knoop hardness, optical transmission, and Verdet constant, were systematically studied for both series of glasses. High transparency level (T: >70 %) in the region from 0.4 to 5.2 μm and a high refractive index (n: 2.05 at 1550 nm) were obtained in the studied glasses. The tellurite glasses with 5 mol% of La2O3 exhibited higher thermal stability and refractive indices than those with 10 mol% La2O3. The 85TeO2–5La2O3–10WO3 glass exhibited a large Verdet constant value of 3.95 rad/(T·m) at 1550 nm among the studied glasses. These results show that the presented TeO2–La2O3–WO3 glasses have considerable potential as diamagnetic MO materials for MO device applications operating at 1550 nm.

Numerical investigation of the influence of process parameters and tool path on the temperature in the laser glass deposition (LGD) process

Additive manufacturing has gained interest in the industry due to its flexibility in design and the possibility to integrate functionalities. Thereby, glass has a high potential to be developed also in this field due to its thermal stability, chemical resistance, and optical transmission. Laser glass deposition is a method for fabricating glass components on a glass substrate. The energy input and the resulting temperature are crucial factors in this process, which can influence the material properties and the resulting geometry. Also, depending on the temperature in the substrate, difficulties such as high residual stresses or thermal shock can occur. The temperature on the glass substrate and in the melt zone can be changed either directly by the laser power or laser spot size, or indirectly by other process variables such as travel speed or path planning strategy. In this study, the energy input and the resulting temperature in the melt zone are numerically investigated under selected process parameters. Based on this, a regression function was created so that the generated temperature can be calculated by corresponding laser power, laser spot diameter, and axis velocity. Moreover, different tool path strategies for the production of horizontally multilayered surfaces were thermally investigated. The results showed a more uniform temperature profile with zigzag movement than the spiral tool path. The influence of the turning point angle in path planning on the temperature change was also investigated. It was observed that the 90° corner in contrast to the smaller angle has no significant influence on the temperature change.

Source identification and ambient trace element concentrations of PM10 using receptor modeling in an urban area of Chhattisgarh, India

This study investigated seasonal variation in PM10 aerosols and associated trace metal concentrations in an urban city Raipur, India. PM10 aerosols were monitored at Raipur for the year 2015 to 2019. Eighteen trace elements (Al, Ba, Ca, Cr, As, Mn, Sb, Se, Sr, Cu, Fe, Ga, Mg, Ni, Ti, V, Pb, Zn) and (EC and OC) were analyzed using atomic absorption spectroscopy and thermal optical transmittance technique. A receptor-based positive matrix factorization (PMF) model was used to identify the possible sources with qualitative analysis of crustal enrichment factor, back-trajectory analysis using concentration weighted trajectory (CWT) to predict potential locations of distant sources, and correlation between different species. The average PM10 aerosol mass concentration during the study period was found to be 184.91 ± 114 µg/m³. Seasonally, the average winter–time PM10 concentration (193.49 ± 129.18 µg/m³) was found higher as compared to summer time (176.32 ± 65.80 µg/m³) during the study period. Five sources were identified including the iron and steel industry (30%), biomass and waste combustion (28.7%), vehicular emissions (21%), heavy oil combustion (17.4%), and crustal dust (2.9%). The study provides information on major sources affecting air quality.

Measuring the uncertainty assessment of an experimental device used to determine the thermo-optico-physical properties of translucent construction materials

Studying the thermo-optical properties of construction materials (i.e. thermal conductivity, optical reflectance, optical transmittance, and optical absorbance) is essential for improving human comfort within a building. Typically, these properties are measured independently using specific equipment. The emergence of new innovative construction structures, such as translucent materials, makes the experimental characterization of these properties more challenging to observe. Recently, a new device, called MulticoefMeter (McM), which rapidly and simultaneously measures all these properties, has been created. The study described in this article covers the calculation technique for estimating measurement uncertainties linked to morphology, the parts, and the physical formula of the experimental apparatus. The measurement uncertainty estimates are obtained from knowledge of the color of the system’s walls, placement, and form of the McM components, placement of the measurement sensors, and the application of measurement collection equipment. Therefore, a thorough calculation analysis was performed on the sub-systems. Calculations are divided into two categories: those based on mathematical tools and information given by the makers and those based on experimental observations obtained during reliability testing. These uncertainties originate from statistical tools, geometric tolerance of the system, comparison with standards, and the error propagation laws of the physical models’ link with the device. All these uncertainties were summed up and given a global value, no more than 5%, conforming to the ASTM standard (E1225). Finally, a general method to quantify the measurement uncertainty value of any experimental device was proposed.

Contribution of coal combustion to black carbon: Coupling tracers with the aethalometer model

Black carbon (BC) aerosol characteristics have been analysed from January 2016 to March 2017 in an urban background area (León, Spain), located in a coal-mining region, where this fuel is commonly used. The monthly and seasonal variations of BC and source contributions were examined. The mean equivalent BC concentration (eBC) during cold and warm months were 1.0 ± 0.5 and 0.6 ± 0.2 μg m−3, respectively. eBC can be further divided into eBCff (eBC from liquid fossil fuel) and eBCbb+cc (eBC from biomass burning plus coal combustion), with mean annual values of 0.6 ± 0.3 and 0.3 ± 0.3 μg m−3 (cold months) and 0.4 ± 0.2 μg m−3 and 0.1 ± 0.1 μg m−3 (warm months), respectively. The eBC obtained from the aethalometer and the elemental carbon (EC) quantified through a Thermal Optical Transmittance method presented a significant strong positive correlation in both warm (r = 0.82) and cold (r = 0.88) periods. A mass absorption cross-section (MAC) of 4.46 ± 0.16 between two techniques has been obtained. In the cold period, a multilinear regression model to decouple eBCbb from eBCcc was established (r2 = 0.85) based on two tracers: arsenic for coal combustion and potassium for biomass burning. The model application enabled us to distinguish the contributions to eBCbb+cc (as a function of the variance explained by the tracers) in the cold period: 74% from biomass burning and 26% from coal combustion. The highest eBCcc concentration was estimated for December 2016 and January 2017 (0.18 μg m−3). This result was supported by the Absorption Ångström Exponent (AAE), which showed the maximum value in January 2017 (1.43 ± 0.37) due to the high biomass burning and coal combustion contributions.

Influence of Meteorological Conditions and Fire Hotspots on PM0.1 in Northern Thailand during Strong Haze Episodes and Carbonaceous Aerosol Characterization

ABSTRACT Northern Thailand has long been severely affected by haze from biomass burning containing fine and ultrafine aerosols in the dry period. The carbonaceous PM0.1 comprising elemental carbon (EC) and organic carbon (OC) collected during the haze and non-haze periods in Chiang Mai, Thailand was investigated. The PM0.1 levels during the haze periods were about 3 times higher than the non-haze periods, a significant increase. PM0.1 concentration was strongly correlated with atmospheric relative humidity and the number of forest fire hotspots. Carbonaceous aerosol characteristics in PM0.1 were analyzed with the thermal/optical transmittance (TOT) method following the IMPROVE protocol. The concentrations of OC and EC, distribution of OC and EC and OC/EC ratios in PM0.1 were evaluated. Average OC and EC mass concentrations in PM0.1 were 6.8 ± 2.7 and 1.4 ± 0.5 µg m–3 during the haze periods, significantly higher than those during the non-haze periods; 1.9 ± 0.9 and 0.5 ± 0.2 µg m–3. The OC/EC ratio increased linearly with the number of hotspots. This indicated significant contribution from biomass burning to the PM0.1. This was strongly supported by the 48-hr backward trajectory simulation, that indicated both domestic and transboundary aerosol transports. Because both organic and elemental carbon are the light-absorbing carbonaceous aerosols, the increase during the haze periods contributed to regional air quality and climate. This study enhances the understanding of PM0.1 behavior in Chiang Mai, Thailand, during the haze periods in upper southeast Asia.

Near infrared hyperspectral imaging as a tool for quantifying atmospheric carbonaceous aerosol

The quantitative determination of atmospheric organic carbon (OC), elemental carbon (EC) and total carbon (TC) is of utmost relevance due to its influence on global warming, visibility degradation, and human health. Thermal-optical transmission (TOT) is the most common analytical method used to analyze them. Nevertheless, it is destructive, time-consuming, and only a small portion of the sample is analyzed. Here, near infrared spectroscopy coupled with a hyperspectral detector (HSI-NIR), together with multivariate data analysis, comes as a reliable alternative.This work aims at establishing a methodology for the quantitation of the carbonaceous content in atmospheric particulate matter (PM) fusing HSI-NIR and multivariate data analysis, and being validated with TOT analysis. Principal Component Analysis and Multivariate Curve Resolution analysis, used as qualitative tools, confirmed concentration trends in the PM samples, and contributions from the chemical composition of both the filter material and aerosol samples. The Partial Least Squares (PLS) regression models developed were optimized using interval Partial Least Squares (iPLS) selection and showed a high correlation between the HSI-NIR spectra and TOT measurements: R2Cal = 0.99, 0.94 and 0.99 for the OC, EC and TC contents, respectively. Finally, the spatial distribution of the carbonaceous content in the filter samples was assessed using a homogeneity percentage (%H). This showed values higher than 50% for all cases, which indicated that no distributional inhomogeneities were observed in the filters and corroborated the efficient operation of the sampling system. This study demonstrated the feasibility of using HSI-NIR for the quantitative assessment of carbonaceous particulate matter in air pollution monitoring.

Exposure assessment of elemental carbon, polycyclic aromatic hydrocarbons and crystalline silica at the underground excavation sites for top-down construction buildings.

Enclosed underground excavation worksite has an environment with poor ventilation and exposure to hazardous substances from diesel engine exhaust and construction materials. The objective of this study was to evaluate the exposure level of elemental carbon (EC), organic carbon (OC), total carbon (TC), polycyclic aromatic hydrocarbons (PAHs), dust and crystalline silica (CS) during underground excavation work for top down construction buildings. Active local air sampling for EC, OC, and TC (n = 105), PAHs (n = 50), dust (n = 34) and CS (n = 34) was conducted from inside and outside the excavator at underground excavation workshop in four different construction sites. EC, OC, TC and CS were sampled with each respirable and total particulates. EC, OC, and TC were collected on quartz-filter and analyzed using the thermal optical transmittance method. PAHs was collected on polytetrafluorethylene filter with XAD-2 and analyzed using liquid chromatography with fluorescence detector. CS and particulates were collected on poly vinyl chloride filter and analyzed using fourier-transform infrared spectroscopy. The geometric mean of respirable EC, OC, TC, total PAHs, respirable dust and respirable CS were 8.69 μg/m3, 34.32 μg/m3, 44.96 μg/m3, 6.818 μg/m3 0.13 mg/m3 and 0.02 mg/m3 from inside the excavator and 33.20 μg/m3, 46.53 μg/m3, 78.21 μg/m3, 3.934 μg/m3, 0.9 mg/m3 and 0.08 mg/m3 from outside the excavator (underground excavation workshop), respectively. The EC and RCS concentration from outside the excavator is significantly higher than that of inside the excavator (p<0.01). The worksite with rock ground, higher vehicle density, blasting and enclosed environments had higher exposure to EC than other sites (p<0.05). There was no significant difference of EC concentration between total and respirable particulates. In top down construction sites, EC concentrations during underground excavation work exceeded recommended exposure limits as 20 μg/m3, accounted for about 50% of the total sample, and the level of concentration of RCS exceeded 1.5 times of occupational exposure limit, 0.05 mg/m3. Efforts are needed to minimize exposure to diesel engine exhaust and silica in underground excavation sites. Management of diesel engine vehicle, supply of fresh air and ventilation and introducing water facilities to create wet environment in underground worksites are strongly suggested.

Vertical Variation of Carbonaceous Aerosols with in the PM2.5 Fraction in Bangkok, Thailand

ABSTRACT Asian megacities are undergoing rapid population and infrastructure growth, which is resulting in significant air quality problems linked to atmospheric fine particles (PM2.5). This study focuses on characterizing carbonaceous aerosols in an urban area of Bangkok, Thailand. The Microclimate and Air Pollutants Monitoring tower is located on the edge of Kasetsart University campus and was used to perform vertical measurements. Mass concentration data were collected using area dust monitors (ADR1500) at different levels above the ground (30 m, 75 m, and 110 m) during two time periods, daytime (08:00–19:00) and nighttime (20:00–07:00), throughout the monsoon season in 2015. All relevant micrometeorological parameters were simultaneously monitored. Backward air mass trajectories were calculated using HYSPLIT to assess the possible external pollution contributions. The thermal optical transmittance (TOT) method following the NIOSH 870 protocol was used to determine amounts of elemental carbon (EC) and organic carbon (OC) in samples. A data analysis showed average PM2.5 values at observation heights of 30 m, 75 m, and 110 m of 6.21 ± 2.45, 8.12 ± 3.65, and 9.03 ± 3.93 µg m–3, respectively; corresponding OC concentrations of 4.13 ± 2.65, 4.01 ± 4.07, and 4.11 ± 3.58 µg m–3, respectively, and EC concentrations of 1.02 ± 0.84, 1.07 ± 0.95, and 0.50 ± 0.70 µg m–3, respectively. The results show distinct gradients of increasing concentrations of PM2.5 with increasing elevation in contract with the OC and EC concentrations which decrease with height.

Exploring Differences and Correlation Between Thermal-optical Transmittance Elemental Carbon (EC) and Reflectometer Black Carbon (BC) from an Urban and a Rural Site in the Philippines

The Philippines has among the highest black carbon (BC) and elemental carbon (EC) concentrations in atmospheric particulate matter in Asia. Despite numerous studies, there is no single, generally accepted measure or method of analysis for this group of atmospheric particulates. Given the high concentrations of BC and EC in the country, the Philippines offers an interesting case to study BC and EC. To gain a better understanding of the similarities and differences of these quantities, BC and EC in an urban (Valenzuela City) and a rural site (Angat, Bulacan) were compared from September 2011 to August 2012. BC was measured using reflectometry, while EC was measured using the thermal-optical (TO) transmittance analysis. Mean concentrations of EC and BC were 5.54 ± 2.1 μg/cm3 and 6.54 ± 2.5 μg/cm3 in Valenzuela City and 1.82 ± 0.7 μg/cm3 and 1.28 ± 0.7 μg/cm3 in Angat, Bulacan. Cluster analysis showed that in both urban and rural sites, EC1 had the highest correlation to BC among the three EC fractions. Additionally, EC2 and EC3 were poorly correlated with BC but were highly correlated with each other. Similarly, conditional probability function (CPF) analysis revealed that BC and EC1 originated from nearly the same directions, while EC2 and EC3 do not. These results suggest that BC and EC1 are more related to each other than EC2 and EC3, providing insights into the similarities and differences between BC and EC. To maximize the comparability of BC and EC, optimal values of ε – used in reflectometry – were determined for the urban and rural sites. Valenzuela and Angat had optimal ε values of 6.31 m2g–1 and 1.89x 10–9m2g–1, respectively. The optimal ε value in Valenzuela is close to the generally used ε value, 7.0 m2g–1, while the optimal ε value in Angat is arguably too small and needs further assessment.