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All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

MO-FG-CAMPUS-TeP2-02: First Experiences and Perspectives in Using Direct Multicriteria Optimization (MCO) On Volumetric-Modulated Arc Therapy (VMAT) for Head and Neck Cancer

Purpose: To report the first experiences and perspectives in using direct multicriteria optimization (MCO) on volumetric-modulated arc therapy (VMAT) for head and neck (H&N) cancer. Methods: Ten prior patients with tumors in representative H&N regions were selected to evaluate direct MCO-VMAT in RayStation v5.0 beta. The patients were previously treated by intensity-modulated radiation therapy (IMRT) with MCO on an Elekta linear accelerator with Agility multileaf collimator. To avoid radiating eyes and shoulders, MCO-VMAT required one to three partial-arc groups, with each group consisting of single or dual arcs. All MCO-VMAT plans were approved by a radiation oncologist. The MCO-VMAT and MCO-IMRT plans were compared using V{sub 100}, D{sub 5}, homogeneity index (HI) and conformity index (CI) for planning target volume (PTV), D{sub mean} and D{sub 50} for six parallel organs and D{sub max} for five serial organs. Patient-specific quality assurance (QA) was performed using ArcCHECK for MCO-VMAT and Matrixx for MCO-IMRT with results analyzed using gamma criteria of 3%/3mm. Results: MCO-VMAT provided better V{sub 100} (+0.8%) lower D{sub 5}(− 0.3 Gy), lower HI (−0.27) and comparable CI (+0.05). MCO-VMAT decreased D{sub mean} and D{sub 50} for multiple parallel organs in seven of the ten patients. On average the reduction ranged from 2.1 (larynx) to 7.6 Gy (esophagus). For the nasal cavity and nasopharynx plans significant reduction in D{sub max} was observed for optics (up to 11 Gy) brainstem (6.4 Gy), cord (2.1 Gy) and mandible (6.7 Gy). All MCO-VMAT and -IMRT plans passed clinical QA. MCO-VMAT required slightly longer planning time due to the more complex VMAT optimization. The net beam-on time for the MCO-VMAT plans ranged from 80 to 242 seconds, up to 9 minutes shorter than MCO-IMRT. Conclusion: With similar target coverage, reduced organ dose, comparable planning time, and significantly faster treatment, MCO-VMAT is very likely to become the modality of choice in RayStation v5.0 for H&N cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Advantages and limitations of navigation-based multicriteria optimization (MCO) for localized prostate cancer IMRT planning

Efficacy of inverse planning is becoming increasingly important for advanced radiotherapy techniques. This study’s aims were to validate multicriteria optimization (MCO) in RayStation (v2.4, RaySearch Laboratories, Sweden) against standard intensity-modulated radiation therapy (IMRT) optimization in Oncentra (v4.1, Nucletron BV, the Netherlands) and characterize dose differences due to conversion of navigated MCO plans into deliverable multileaf collimator apertures. Step-and-shoot IMRT plans were created for 10 patients with localized prostate cancer using both standard optimization and MCO. Acceptable standard IMRT plans with minimal average rectal dose were chosen for comparison with deliverable MCO plans. The trade-off was, for the MCO plans, managed through a user interface that permits continuous navigation between fluence-based plans. Navigated MCO plans were made deliverable at incremental steps along a trajectory between maximal target homogeneity and maximal rectal sparing. Dosimetric differences between navigated and deliverable MCO plans were also quantified. MCO plans, chosen as acceptable under navigated and deliverable conditions resulted in similar rectal sparing compared with standard optimization (33.7 ± 1.8 Gy vs 35.5 ± 4.2 Gy, p = 0.117). The dose differences between navigated and deliverable MCO plans increased as higher priority was placed on rectal avoidance. If the best possible deliverable MCO was chosen, a significant reduction in rectal dose was observed in comparison with standard optimization (30.6 ± 1.4 Gy vs 35.5 ± 4.2 Gy, p = 0.047). Improvements were, however, to some extent, at the expense of less conformal dose distributions, which resulted in significantly higher doses to the bladder for 2 of the 3 tolerance levels. In conclusion, similar IMRT plans can be created for patients with prostate cancer using MCO compared with standard optimization. Limitations exist within MCO regarding conversion of navigated plans to deliverable apertures, particularly for plans that emphasize avoidance of critical structures. Minimizing these differences would result in better quality treatments for patients with prostate cancer who were treated with radiotherapy using MCO plans.

61 RADIATION PROTECTION AND DOSIMETRY↗
NASA NTRS1989

Theoretical studies of the transition metal-carbonyl systems MCO and M(CO)2, M = Ti, Sc, and V

Large Gaussian basis sets and an electron correlation treatment are used in ab initio calculations on the transition metal-carbonyl systems MCO and N(CO)2 for M = Ti, Sc, and V. The results show that high-spin ground states are favored for the monocarbonyl molecules, and that for the dicarbonyl molecules there is a competition between high, intermediate, and low spin states which are very close in energy. Dissociation energies of 0.62 eV for Ti-CO and 1.02 for Ti(CO)2 are found, relative to the ground state Ti atomic asymptote and CO 1Sigma(+). The binding energy per carbonyl for the three metal atoms is shown to be significantly lower for the dicarbonyl than for the the monocarbonyl molecules.

Barnes, Leslie A.↗
DOE OSTI2020

Characterization of the Alkali Metal Oxalates (MC2O4-) and their formation by CO2 reduction via the Alkali Metal Carbonites (MCO2-)

The reduction of carbon dioxide to oxalate has been studied by experimental Collisionally Induced Dissociation (CID) and vibrational characterization of the alkali metal oxalates, supplemented by theoretical electronic structure calculations. The critical step in the reductive process is the coordination of the heterocumulene CO2 to an alkali metal anion, forming a metal carbonite MCO2 ablt to subsequently add a second CO2 molecule. While the energetic demand for these reactions is generally low, we find that the degree of activation of CO2 in terms of charge transfer and transition state energies is the highest for lithium and systematically decreases down the group (M - Li - Cs).

Jestila, Joakim S.↗
DOE OSTI2014

Multicriteria optimization informed VMAT planning

We developed a patient-specific volumetric-modulated arc therapy (VMAT) optimization procedure using dose-volume histogram (DVH) information from multicriteria optimization (MCO) of intensity-modulated radiotherapy (IMRT) plans. The study included 10 patients with prostate cancer undergoing standard fractionation treatment, 10 patients with prostate cancer undergoing hypofractionation treatment, and 5 patients with head/neck cancer. MCO-IMRT plans using 20 and 7 treatment fields were generated for each patient on the RayStation treatment planning system (clinical version 2.5, RaySearch Laboratories, Stockholm, Sweden). The resulting DVH of the 20-field MCO-IMRT plan for each patient was used as the reference DVH, and the extracted point values of the resulting DVH of the MCO-IMRT plan were used as objectives and constraints for VMAT optimization. Weights of objectives or constraints of VMAT optimization or both were further tuned to generate the best match with the reference DVH of the MCO-IMRT plan. The final optimal VMAT plan quality was evaluated by comparison with MCO-IMRT plans based on homogeneity index, conformity number of planning target volume, and organ at risk sparing. The influence of gantry spacing, arc number, and delivery time on VMAT plan quality for different tumor sites was also evaluated. The resulting VMAT plan quality essentially matched the 20-field MCO-IMRT plan but with a shorter delivery time and less monitor units. VMAT plan quality of head/neck cancer cases improved using dual arcs whereas prostate cases did not. VMAT plan quality was improved by fine gantry spacing of 2 for the head/neck cancer cases and the hypofractionation-treated prostate cancer cases but not for the standard fractionation–treated prostate cancer cases. MCO-informed VMAT optimization is a useful and valuable way to generate patient-specific optimal VMAT plans, though modification of the weights of objectives or constraints extracted from resulting DVH of MCO-IMRT or both is necessary.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

SU-F-T-401: Three-Dimensional Conformal Planning Using Low-Segment Multi-Criteria Optimization for Hippocampal Avoidance Whole Brain Radiotherapy

Purpose: Hippocampus avoidance whole brain radiotherapy (HA-WBRT) has been shown to reduce the risk of neurocognitive dysfunction. This type of treatment has the potential of insurance company payment denial due to increased cost of intensity modulated radiotherapy (IMRT), while the accepted modality for WBRT is three-dimensional conformal radiotherapy (3DCRT). The purpose of this study is to assess HA-WBRT treatment plans using 3DCRT and multi-criteria optimization (MCO) that meets the RTOG 0933 criteria. Methods: Ten patients with brain metastases at least 0.5cm away from the hippocampal avoidance region as defined in RTOG 0933 were selected in this study. HA-WBRT treatment plans with MCO 3DCRT technique (MCO-3D) was generated with beam arrangements and dose constraints following the RTOG 0933 guidelines. MCO-3D plans were compared with plans using MCO IMRT techniques (MCO-IMRT) with same beam arrangements and dose constraints. Evaluation parameters included D98% D2% and dose homogeneity index of PTV, and Dmax and D100% of the hippocampi. The OAR doses were also evaluated. Results: For MCO-IMRT plans, PTV D2% and hippocampi Dmax and D100% met RTOG 0933 objectives in all ten patients (PTV D2%<37.5Gy; Hippocampi Dmax<16Gy and D100%<9Gy). One patient met the RTOG 0933 PTV D98% objective (PTV D98%>25Gy) and 9/10 patients met acceptable variation (PTV D98%<25Gy). For MCO-3D plans, PTV D2% met RTOG 0933 objective for all patients; 1/10 patient for PTV D98% and 6/10 patients for Hippocampi Dmax and 7/10 patients for hippocampi D100% met RTOG 0933 objective. All the other patients met the RTOG 0933 acceptable variation requirement. (PTV D98%<25Gy; Hippocampi Dmax<17Gy and D100%<10Gy). Conclusion: All dosimetric parameters of MCO-3D plans met the criteria of at least acceptable variation per RTOG 0933. This may be helpful in cases where there is denial of patient’s medical insurance coverage due to the use of IMRT for HA-WBRT.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-G-BRC-02: A Novel Multi-Criteria Optimization Approach to Generate Deliverable Intensity-Modulated Radiation Therapy (IMRT) Treatment Plans

Purpose: To present a novel multi-criteria optimization (MCO) solution approach that generates treatment plans with deliverable apertures using column generation. Methods: We demonstrate our method with 10 locally advanced head-and-neck cancer cases retrospectively. In our MCO formulation, we defined an objective function for each structure in the treatment volume. This resulted in 9 objective functions, including 3 distinct objectives for primary target volume, high-risk and low-risk target volumes, 5 objectives for each of the organs-at-risk (OARs) (two parotid glands, spinal cord, brain stem and oral cavity), and one for the non-target non-OAR normal tissue. Conditional value-at-risk (CVaR) constraints were utilized to ensure at least certain fraction of the target volumes receiving the prescription doses. To directly generate deliverable plans, column generation algorithm was embedded within our MCO approach for aperture shape generation. Final dose distributions for all plans were generated using a Monte Carlo kernel-superposition dose calculation. We compared the MCO plans with the clinical plans, which were created by clinicians. Results: At least 95% target coverage was achieved by both MCO plans and clinical plans. However, the average conformity indices of clinical plans and the MCO plans were 1.95 and 1.35, respectively (31% reduction, p<0.01). Compared to the conventional clinical plan, the proposed MCO method achieved average reductions in left parotid mean dose of 5% (p=0.06), right parotid mean dose of 18% (p<0.01), oral cavity mean dose of 21% (p=0.03), spinal cord maximum dose of 20% (p<0.01), brain stem maximum dose of 61% (p<0.01), and normal tissue maximum dose of 5% (p<0.01), respectively. Conclusion: We demonstrated that the proposed MCO method was able to obtain deliverable IMRT treatment plans while achieving significant improvements in dosimetric plan quality.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

X-ray-induced catalytic active-site reduction of a multicopper oxidase: structural insights into the proton-relay mechanism and O 2 -reduction states

During X-ray data collection from a multicopper oxidase (MCO) crystal, electrons and protons are mainly released into the system by the radiolysis of water molecules, leading to the X-ray-induced reduction of O 2 to 2H 2 O at the trinuclear copper cluster (TNC) of the enzyme. In this work, 12 crystallographic structures of Thermus thermophilus HB27 multicopper oxidase ( Tth -MCO) in holo, apo and Hg-bound forms and with different X-ray absorbed doses have been determined. In holo Tth -MCO structures with four Cu atoms, the proton-donor residue Glu451 involved in O 2 reduction was found in a double conformation: Glu451a (~7 Å from the TNC) and Glu451b (~4.5 Å from the TNC). A positive peak of electron density above 3.5σ in an F o - F c map for Glu451a O ε2 indicates the presence of a carboxyl functional group at the side chain, while its significant absence in Glu451b strongly suggests a carboxylate functional group. In contrast, for apo Tth -MCO and in Hg-bound structures neither the positive peak nor double conformations were observed. Together, these observations provide the first structural evidence for a proton-relay mechanism in the MCO family and also support previous studies indicating that Asp106 does not provide protons for this mechanism. In addition, eight composite structures ( Tth -MCO-C1–8) with different X-ray-absorbed doses allowed the observation of different O 2 -reduction states, and a total depletion of T2Cu at doses higher than 0.2 MGy showed the high susceptibility of this Cu atom to radiation damage, highlighting the importance of taking radiation effects into account in biochemical interpretations of an MCO structure.

copper depletion↗
DOE OSTI2019

Machine-Learning Analysis of Moisture Carryover in Boiling Water Reactors

Moisture carryover (MCO) is modeled in the General Electric Type-4 boiling water reactor (BWR) using machine-learning methods and data from operating plants. Understanding MCO and the conditions that give rise to an elevated value is important since excessive MCO can damage critical turbine components, can result in elevated dose levels to on-site personnel, and can interfere with late-cycle power management. The analysis of MCO takes into account simplifying reactor symmetries and important geometric dependencies. The plant data are taken from several reactors and were collected over multiple years and multiple fuel cycles. A brief description of the origin of MCO in U.S. BWR plants is given. A machine-learning model is constructed from the data using applicable algorithms and data-reduction techniques. Matching model complexity with available data is one of the more challenging machine-learning tasks. Too many features and too little data will lead to overfitting. The data for each fuel cycle included over 6876 original features, 9 for each fuel bundle. Two approaches are used to reduce the data set into a manageable number of features. The first was an engineering analysis that resulted in the selection of steam quality Q and steam liquid phase velocity V L as the main features driving MCO. Using a Q and a V L for each fuel bundle gives 1528 Q and a V L feature describing the reactor behavior. An analysis of different functional forms of these two variables led to the actual inputs to the neural network model. The second approach involved the use of statistical techniques such as Pearson’s correlation and k-means analysis. The identified groupings of bundles behaved similarly. Treating each grouping as a single feature further reduced the input variable set to a manageable number. Here, a model selection criterion is proposed, and results are presented along with a discussion of related issues.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

MO-G-304-04: Generating Well-Dispersed Representations of the Pareto Front for Multi-Criteria Optimization in Radiation Treatment Planning

Purpose: To present a novel multi-criteria optimization (MCO) solution approach that generates well-dispersed representation of the Pareto front for radiation treatment planning. Methods: Different algorithms have been proposed and implemented in commercial planning software to generate MCO plans for external-beam radiation therapy. These algorithms consider convex optimization problems. We propose a grid-based algorithm to generate well-dispersed treatment plans over Pareto front. Our method is able to handle nonconvexity in the problem to deal with dose-volume objectives/constraints, biological objectives, such as equivalent uniform dose (EUD), tumor control probability (TCP), normal tissue complication probability (NTCP), etc. In addition, our algorithm is able to provide single MCO plan when clinicians are targeting narrow bounds of objectives for patients. In this situation, usually none of the generated plans were within the bounds and a solution is difficult to identify via manual navigation. We use the subproblem formulation utilized in the grid-based algorithm to obtain a plan within the specified bounds. The subproblem aims to generate a solution that maps into the rectangle defined by the bounds. If such a solution does not exist, it generates the solution closest to the rectangle. We tested our method with 10 locally advanced head and neck cancer cases. Results: 8 objectives were used including 3 different objectives for primary target volume, high-risk and low-risk target volumes, and 5 objectives for each of the organs-at-risk (OARs) (two parotids, spinal cord, brain stem and oral cavity). Given tight bounds, uniform dose was achieved for all targets while as much as 26% improvement was achieved in OAR sparing comparing to clinical plans without MCO and previously proposed MCO method. Conclusion: Our method is able to obtain well-dispersed treatment plans to attain better approximation for convex and nonconvex Pareto fronts. Single treatment plan can be achieved when given bounds on the objectives.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2013

Master Console, SMC

The Master Console oversees the function of Computer Systems in Firing room 1 (FR1). Master Console Operators, MCOs' for short, are our customer. I was integrated into the System Monitoring and Control (SMC) software team that is under the guidance of David Slaiman, who is the product group lead. I have been brought up to speed with System Monitoring and Control. The initial time spent reading SMC software design description and understanding how it works. The current Firing Room 1 Console Display is a floor layout giving the MCO two essential pieces of information which are Health and Status. When an issue arises, the MCO has to look on the display to find which console is affected and then the MCO must use the Reference designator from the display to manually search for the Portal Workstation (PWS) installed in the console using the hardware map; which is a long process to lookup a PWS if an issue is present. My project is to make the FR1 Console Display easier for the MCO's to pinpoint PWS's without having to lookup additional resources in the process. My project also includes updating Firing Room 1 Console Display to include the F1R Non-Redundant Set. The display does not have good use of space and functionality. PWS numbers were not present in the previous design and are the critical component in efficient understanding and administration of the consoles. Part of the process includes getting feedback from the customer, instead of just emailing them with a question, we made a proposal with changes so they could respond and give us their input; which proved to be an effective method for engaging them. In order to do this I had to use the Display Editor (DE) tool developed by NASA, Paint.Net and Visio. The process I have been using has been Visio to alter the floor layout of Firing Room and take advantage of the white areas, and then I take the altered floor plan into Paint.Net. Once in Paint.Net I put the new floor plan as a background to the standard console display. Paint.Net also serves as a tool to create the new service state bars for the new background; finally I used the DE to assemble everything and setup the right CUI's for each PWS.

MCO↗
NASA NTRS2013

SMC Message Browser Projects

I work directly with the System Monitoring and Control (SMC) software engineers who develop, test and release custom and commercial software in support of the Kennedy Space Center Spaceport Command and Control System. (SCCS). SMC uses Commercial Off-The-Shelf (COTS) Enterprise Management Systems (EMS) software which provides a centralized subsystem for configuring, monitoring, and controlling SCCS hardware and software used in the Control Rooms. There are multiple projects being worked on using the COTS EMS software. I am currently working with the HP Operations Manager for UNIX (OMU) software which allows Master Console Operators (MCO) to access, view and interpret messages regarding the status of the SCCS hardware and software. The OMU message browser gets cluttered with messages which can make it difficult for the MCO to manage. My main project involves determining ways to reduce the number of messages being displayed in the OMU message browser. I plan to accomplish this task in two different ways: (1) by correlating multiple messages into one single message being displayed and (2) to create policies that will determine the significance of each message and whether or not it needs to be displayed to the MCO. The core idea is to lessen the number of messages being sent to the OMU message browser so the MCO can more effectively use it.

OMU↗
DOE OSTI2019

Synthesis of MgCo 2 O 4 -coated Li 4 Ti 5 O 12 composite anodes using co-precipitation method for lithium-ion batteries

In the present work, we report synthesis of MgCo 2 O 4 (MCO)/Li 4 Ti 5 O 12 (LTO) composites for Li-ion battery anodes by a co-precipitation method. The objective here is to replace expensive Co with Mg and also to exploit advantages of both MCO and LTO. Three samples of MCO/LTO particles with different MCO proportion have various average particle sizes of 38.1, 56.9, and 58.5 nm, confirmed by scanning electron microscopy. Electrochemical studies show that a MCO/LTO anode offers a discharge capacity of ca. 300 mAh g -1 , which is two times higher than that achieved by pristine LTO. The MCO/LTO anode also retains 75% of its initial capacity, even if the discharge rate is increased to 5 C. Cyclic stability test reveals that the composite anode still maintains nearly 85.5% of its initial capacity after 150 cycles. Electrochemical impedance spectroscopy indicates that the equivalent series resistance of MCO/LTO electrodes is significantly lower than that of LTO, i.e., from 35.5 to 9.9 Ω. The enhanced performance of the composite electrodes can be attributed to its improved conductivity as well as to the surface modification of LTO particles by MCO nanoparticle deposition which leads to increased number of active sites on the former.

25 ENERGY STORAGE↗
DOE OSTI2014

Smooth cubic commensurate oxides on gallium nitride

Smooth, commensurate alloys of 〈111〉-oriented Mg{sub 0.52}Ca{sub 0.48}O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1999

Report on the loss of the Mars Climate Orbiter Mission : JPL special review board

The Mars Climate Orbiter (MCO) was launched on December 11, 1998. The MCO was to arrive at Mars and begin orbit insertion on September 23, 1999. The Mars Orbit Insertion (MOI) burn, a 16-minute maneuver to slow the spacecraft and enable capture into an orbit around Mars, began on schedule. Five minutes into the maneuver, and approximately 49 seconds before the anticipated time for loss of communication, the MCO was occulted by Mars. Thereafter, no contact with the spacecraft could be established. On September 24, 1999, an internal JPL team (the MCO Peer Review Team) was appointed to help investigate the reason for the loss of spacecraft signal. The Peer Review Team's findings are presented in this report.

Mars Climate Orbiter↗
DOE OSTI2023

Dynamic oxidation of (Mn,Co) 3 O 4 -Coated interconnects for solid oxide electrolysis cells

Solid oxide electrolysis cell stacks are expected to experience dynamic conditions when using renewable electricity derived from wind or solar power. To address this scenario, (Mn,Co) 3 O 4 (MCO)-coated Crofer 22 APU interconnect coupons are subjected to thermal cycling, and intermittent current density, with gas compositions relevant to high-temperature electrolysis (elevated steam:hydrogen ratio and oxygen content). Defects are also intentionally introduced in the MCO coating, to assess whether the difference in oxidation properties of the adjacent coated and uncoated (defective) surfaces causes sufficient stress to damage the protective oxide scale. Specimens with defects are subjected to oxidation for 1000 h at 800 °C, or thermal cycling. Before thermal cycling, some specimens are pre-oxidized to create a thick oxide scale to mimic the scale thickness expected after ~30 kh operation. In all cases, the coating and oxide scale remain well adhered with no cracking observed. Area-specific resistance (ASR) is monitored in both single-atmosphere and dual-atmosphere conditions, and the ASR is stable and is not impacted by dynamic cycling of the current density. Finally, this work provides confidence that the MCO coated interconnect will function as needed in dynamic operation conditions, even with coating defects.

08 HYDROGEN↗
DOE OSTI2022

The concentration of BTEX in selected urban areas of Malaysia during the COVID-19 pandemic lockdown

Volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene and xylene (BTEX) are air pollutants that harm human health. This study aims to identify BTEX concentrations before the lockdown known as the Movement Control Order was imposed (BMCO), during the implementation of the Movement Control Order (MCO), and then during the Conditional Movement Control Order (CMCO). These orders were introduced during the COVID-19 pandemic in Malaysia. The study utilised data measured by the continuous monitoring of BTEX using online gas chromatography instruments located at three urban area stations. Here, the results showed that the BTEX concentrations reduced by between –38% and –46% during the MCO compared to the BMCO period. The reduction of human mobility during the MCO and CMCO influenced the lower BTEX concentrations recorded at a station within the Kuala Lumpur area. The results of the BTEX diagnostic ratios and principal component analysis showed that the major source of BTEX, especially during the BMCO and CMCO periods, was motor vehicle emissions. Further investigation, using correlation analysis and polar plots, showed that the BTEX concentrations were also influenced by meteorological variables such as wind speed, air temperature and relative humidity.

54 ENVIRONMENTAL SCIENCES↗