Dual-coil System Research Articles

Enhancing forming accuracy in aluminum alloy variable-diameter tubes through dual-coil controllable electromagnetic forming

High-accuracy forming of aluminum alloy variable-diameter tubes imposes strict requirements on force field design. Although electromagnetic forming has shown unique advantages in enhancing the formability of aluminum alloy materials, its shortcomings lie in the single and difficult-to-adjust force field, which limits its application in variable-diameter tubes. To address this challenge, a novel dual-coil electromagnetic forming approach with good controllability of force field is proposed. Numerical simulations and experiments are both conducted to showcase the superiority of this approach in forming variable-diameter aluminum alloy tubes. The results demonstrate that the forming accuracy of AA6061-O variable-diameter tubes has significantly improved compared to a traditional single-coil system, in which the maximum die-fitting gap is reduced from approximately 2 mm to less than 0.22 mm. Furthermore, it is identified the force field produced by the single-coil system causes a local cavity gap between the tube and the die, which adversely affects the forming accuracy. In contrast, the improved force field produced by the dual-coil system facilitates bottom-to-top deformation of the tube, thereby avoiding undesirable cavity gaps and achieving high forming accuracy. Importantly, the dual-coil forming system offers significant controllability of the Lorentz force field by adjusting the coil discharge, making it suitable for variable-diameter tubes of different sizes without changing the coil structure. This work represents a substantial advancement in controllable tube forming, offering a new approach to force field design and holding promise for extensive applications in the forming of variable-diameter tubes.

Mathematical modelling of passive displacement dual cooling coil (PDDCC) system in a tropical climate

Unlike the conventional displacement ventilation (DV) systems, the Passive Displacement Dual Cooling Coil (PDDCC) system generates airflow in indoor environments based on natural convection and eliminates the necessity of mechanical ventilation to meet the thermal comfort and indoor air quality requirements. Investigations on such PDDCC systems, though, have been largely limited and its performance capacity and fluid flow behaviour are not fully understood. A mathematical model was, hence, developed in the current study to explore the effects of various boundary conditions on the performance of the PDDCC system. Results obtained from the mathematical model were, first, compared and validated against the measurement readings gathered from an experimental investigation conducted on the PDDCC system in a controlled test environment. The validated mathematical model was then applied to a parametric evaluation where the effects of chilled water supply (CHWS) temperature, flow rate, and return air temperature on the PDDCC system performance were examined. The varying effect of the latent and sensible cooling load was observed at the different boundary conditions applied to the PDDCC model. Slightly more than 32% of rise in total cooling load was predicted by reducing the CHWS temperature which established a much more significant contribution in comparison to the CHWS flow rate which generated approximately 5% rise in the total cooling load. Findings were supported by examining the sensible heat ratio (SHR) and the ratio of Latent cooling load: Sensible cooling load which was then was attributed to the temperature difference between the supply and return air temperature. By ensuring the maximum temperature difference, the total cooling load performance of the PDDCC system can be maximised. The contribution of both the CHWS temperature and flowrate was essential to achieve the maximum cooling load, hence, improving the total cooling performance of the PDDCC as a result.

Defibrillation test in paediatric patients: should be done?

Abstract Funding Acknowledgements Type of funding sources: None. The defibrillation test (DFT) of an implantable cardioverter-defibrillator (ICD) is performed to evaluate ventricular fibrillation detection and termination. In adults, routine defibrillation testing for transvenous ICD is less usually done as some studies found no advantages but some potentially risks associated with. On the other hand, implantation of ICDs in paediatric patients has different characteristics than in adults. The position of the defibrillation coil will change with the body’s growth and could reflect changes in the defibrillation vector. Also, the reasons of implantation of an ICD are different (ventricular arrhythmias frequently associated with adult’s myocardial infarction vs channelopathies, non-ischemic myocardiopathies and congenital heart defects in children and young). There is still lack of information about the utility of the DFT in paediatric patients. Objective To describe the characteristics of paediatric patients who underwent implantation of an ICD , results of DFT and follow-up. Methodology Retrospective cohort study of patients less than 21 years old who underwent implantation of an ICD in the lasts 10 years at a reference paediatric hospital. In DFT, VF was induced by T wave shock, fast burst pacing or continuous direct current. Response of ICD to VF was evaluated. Patients with failure to terminate VF by ICD were defibrillated with external defibrillator. Results 68 patients with 73 ICD implantations (five replacements). Median age was 13 years old. The youngest patient was 2 years old and the oldest 21 years old. 72.6% (53/73) of patients underwent DFT. In 90.6% (48/53) of them, a VF was induced. In two patients (4%, 2/48) the ICD did not terminate the VF. One of these patients had Danon syndrome and the VF did not terminate despite of maximum energy discharged and changes in the vector of defibrillation; the problem was fixed with replacement of the single coil lead by a dual coil system. The other patient had arrhythmogenic cardiomyopathy and the ICD did not detect the VF. During the follow up, there were 20 shocks in 13 patients. 13 shocks were appropriate (and successful). One patient died because of non-arrhythmic illness. Conclusions In paediatric patients, the defibrillation test is useful to ensure both adequate detection of malignant ventricular arrhythmias, as well as their ability to reverse them. Its lack of performance could affect 4% of the implants. Therefore, its performance in paediatric patients is recommended. There could be greater utility in patients with hypertrophic cardiomyopathy.

Experimental investigation of the cooling capacity and thermal performance of the passive displacement dual cooling coil system in tropical climate

This paper focuses on the application of Passive Displacement Dual Cooling Coil (PDDCC) system in an indoor space based on a test lab. Parametric study, first, was carried out using Computational Fluid Dynamics (CFD) simulation to identify the optimum fall duct design for the PDDCC unit. Thermal profiles obtained through the simulations indicated that the fall duct with 300 mm height and 0° taper angle was most suitable as it generated the largest volume of cool air which sufficiently cooled the space. It was then applied to the experiment of the PDDCC units in the test lab to study the system's thermal performance. The total cooling load removed by the two PDDCC units within the indoor space varied from 2.24 kW to 2.93 kW. The latent load removal over the entire experiment duration ranged from 0.7 kW to 1.35 kW where the highest latent heat was removed at the lowest chilled water setpoint temperature of 7.5 °C. Thermal stratification trends displayed that temperature within the room for all chilled water setpoint temperatures (7.5 °C, 8.5 °C, 9.5 °C, and 10.5 °C) corresponded with the increase in heat load within the indoor environment. The humidity level above 1 m ground level was not exceed 56%. The PDDCC system was found to have excellent latent heat removal capability. The PDDCC system was able to produce a thermally comfortable environment for 67% of the experimental permutations. The low humidity level within the test cell allowed to raise the boundary of the acceptable temperature range for achieving human thermal comfort to as high as 26.5 °C.

Cage-Embedded Crown-Type Dual Coil Wireless Power Transfer Based Microwave Brain Stimulation System for Untethered and Moving Mice.

This study proposes a novel brain-stimulated mouse experiment system which is insensitive to the variations in the position and orientation of a mouse. This is achieved by the proposed novel crown-type dual coil system for magnetically coupled resonant wireless power transfer (MCR-WPT). In the detailed system architecture, the transmitter coil consists of a crown-type outer coil and a solenoid-type inner coil. The crown-type coil was constructed by repeating the rising and falling at an angle of 15 ° for each side which creates the H-field diverse direction. The solenoid-type inner coil creates a magnetic field distributed uniformly along the location. Therefore, despite using two coils for the Tx system, the system generates the H-field insensitive to the variations in the position and angle of the receiver system. The receiver is comprised of the receiving coil, rectifier, divider, LED indicator, and the MMIC that generates the microwave signal for stimulating the brain of the mouse. The system resonating at 2.84 MHz was simplified to easy fabrication by constructing 2 transmitter coils and 1 receiver coil. A peak PTE of 19.6% and a PDL of 1.93 W were achieved, and the system also achieved an operation time ratio of 89.55% in vivo experiments. As a result, it is confirmed that experiments could proceed for approximately 7 times longer through the proposed system compared to the conventional dual coil system.

Analysis of a Flexible Dual-Channel Octagonal Coil System for UHF MRI

Nowadays, MRI is focused on using ultra-high static magnetic fields (> 7 T) to increase the signal-to-noise ratio. The use of high fields, on the other hand, requires novel technical solutions as well as more stringent design criteria for specific absorption rate levels, reducing radiative effect and coil resistance. In this paper, two flexible RF coils for 7 T human magnetic resonance, and 298 MHz ultra-high frequency operations were analyzed and characterized. Imaging of lower human limbs is regarded as a case study. The lumped element theory and subsequent numerical simulations were used to fine-tune the single-coil element and the dual-coil array design, respectively. Here, we demonstrate how the shape, size, configuration, and presence of the sample influence the coil performance. The penetration depth of the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -field and the specific absorption rate values have been determined numerically using two numerical surface phantoms: saline and a multilayer human tissue. A preliminary study in the presence of a saline solution phantom has been carried out to develop and validate the dual-coil system. The frequency response of the dual-coil array was measured to assess its robustness when coupled to twelve human volunteers. We found that our design is robust to variations in the anatomical properties of the human thighs, and hence to coil bending. The presented approach can be useful for the implementation of flexible devices with high sensitivity levels and low specific absorption rate.

Improvement on formability and forming accuracy in electromagnetic forming of deep-cavity sheet metal part using a dual-coil system

A dual-coil electromagnetic forming (EMF) method assisted by radial Lorentz force was proposed herein to achieve the die forming of deep-cavity sheet metal parts. The objective of this study was to certify the extent to which the formability and forming accuracy can be improved by the proposed method. For comparative study, a single-coil EMF system without radial Lorentz force was also utilized. To develop the deformation process, the experiments and simulations of deep-cavity aluminum workpieces under a wide range of voltage combinations were conducted by the single-coil and dual-coil EMF, respectively. The experimental results showed that the dual-coil EMF resulted in the formation of the deep-cavity workpiece with high forming accuracy, maximum die-fitting gap of 0.35 mm, and more uniform thickness distribution. In contrast, the workpiece tended to crack without contacting the die by the single-coil EMF. Based on the simulation results, dynamic deformation behaviors of the deep-cavity workpieces were demonstrated and the underlying mechanisms of the improved formability and forming accuracy were explained. Moreover, the process window of die-fitting gap control indicated that the fittability could be controlled by adjusting the voltage combinations of the dual-coil EMF, and the corresponding optimum voltage of Coil-2 (V2) that contributed to high forming accuracy decreased with the increase of the voltage of Coil-1 (V1). Therefore, the proposed dual-coil EMF exhibits more flexibility and efficiency for producing the deep-cavity sheet metal part with a higher forming accuracy than the single-coil EMF, extending the potential application of the conventional EMF due to the utilization of multiple coils.

Investigation of the electromagnetic attractive forming utilizing a dual-coil system for tube bulging

The electromagnetic force between the tube and the coil is generally dominated by repulsive Lorentz force in the existing electromagnetic tube forming systems. In these cases, the coil has to be placed inside the tube for tube bulging, which makes it difficult to achieve when the inner space of the tube is not large enough to accommodate the coil. To solve this problem, a new electromagnetic tube bulging process with an external dual-coil system was developed in this work. According to both numerical and experimental studies, it has been demonstrated that the AA6061-O aluminum alloy tube with a diameter of 33 mm and a thickness of 1 mm can be attracted toward the coil, and the maximum deformation is more than 4 mm after a single discharge. Meanwhile, the tube deformation can be significantly increased by multiple discharges using the attractive forming process. Furthermore, a series of simulations and experiments were carried out to systematically investigate the attractive forming behavior of the tube under different discharge conditions, showing that the discharge voltages of the two coils and the current waveform controlled by a crowbar circuit have a great impact on the tube forming.

The effect of coil polarity on electromagnetic forming using a multi-coil system

Electromagnetic forming, by combining multiple coils and multiple capacitor banks, is an emerging manufacturing method that can produce flexible spatial-temporal patterns of the Lorentz force to shape metal workpiece. In this process, the polarity of the discharge currents is a key element because it determines the polarity of the magnetic field that is individually induced by each coil, which in turn affects the resulting magnetic field, the Lorentz force, and ultimately the deformation of the workpiece. Aiming to evaluate the potential effects of coil polarity, this paper performed a comparative experimental and numerical study, using a dual-coil system. It is found that the workpiece deformation is sensitive to the coil polarity with respect to both energy efficiency and performance. Furthermore, the analysis of the electromagnetic dynamics shows that the coil polarity would affect the workpiece deformation by altering the electromagnetic interaction between the coils and the workpiece. In this way, both the discharge currents on the coils and the eddy currents on the workpiece would be altered. And consequently, the produced Lorentz forces and thereby the workpiece deformation are affected. The results in this study can be useful for the coil polarity selection that is required in multi-coil forming processes.

High-Efficiency Inductively Coupled Plasma Source With Dual Antenna Hybrid Scheme

An innovative, hybrid, inductively coupled, dual-antenna 13.56-MHz radio frequency source of dense low-temperature plasma was developed and experimentally investigated. The electrical and plasma properties of the conventional single-coil inductively coupled plasma source and the upgraded dual-antenna configuration were comparatively studied. As compared to the conventional setup, the dual antenna hybrid scheme maintains the low-temperature plasma with significantly higher electron densities reaching to $1.85\times 10^{12}$ cm−3 at a low electron temperature of 1.7 eV over a large area, and much faster transits to a steady-state plasma. It was also found that the dual-coil system heats electrons more effectively and produces a synergistic effect on the enhancement of power transfer efficiency to the discharge. Significant advantages warrant the efficient employment of this system in many techniques requiring cost effective, convenient, and efficient systems for low electron temperature high-density plasma-based applications.

An Actively Decoupled Dual Transceiver Coil System for Continuous ASL at 7 T.

7 T arterial spin labeling (ASL) faces major challenges including the increased specific absorption rate (SAR) and increased B0 and B1 inhomogeneity. This work describes the design and implementation of a dual-coil system that allows for continuous ASL (CASL) at 7 T. This system consisted of an actively detunable eight-channel transceiver head coil, and a three-channel transceiver labeling coil. Four experiments were performed in 5 healthy subjects: (i) to demonstrate that active detuning during ASL labeling reduces magnetization transfer; (ii) to measure the B1 profile at the labeling plane; (iii) to quantify B0 off-resonance at the labeling plane; and (iv) to collect in vivo CASL data. The magnetization transfer ratio in the head coil was reduced to 0.0 ± 0.2% by active detuning during labeling. The measured B1 profiles in all 5 subjects were sufficient to satisfy the flow-driven adiabatic inversion necessary for CASL, however the actual labeling efficiency was significantly impacted by B0 off-resonance at the labeling plane. The measured CASL percent signal change in gray matter (0.94% ± 0.10%) corresponds with the low labeling efficiency predicted by the B0 off-resonance. This work demonstrates progress in the technical implementation of 7 T CASL, and reinforces the need for improved B0 homogeneity at the labeling plane.

Radial Lorentz force augmented deep drawing for large drawing ratio using a novel dual-coil electromagnetic forming system

In order to overcome the limitations of the existing electromagnetic forming systems for deep drawing, a dual-coil system has been developed for deep drawing of sheet metal with large drawing ratio. In addition to the conventional driving coil that generates the axial Lorentz force on the workpiece, a radial inward force in the flange region is generated by a second coil that is energized by an individual power supply. The axial force pushes the sheet into the die in axial direction, while the radial Lorentz force enhances the material flow of the flange. The effectiveness of the novel system is validated by a series of experiments for deep drawing a cup of AA1060-H24 with drawing ratio of 3.25. It is demonstrated that with the dual-coil system the material flow of the flange can be significantly enhanced, and the maximum forming depth without failure is greatly increased from 8.44mm to 20.28mm. The new electromagnetic forming method is expected to break through the bottleneck of deep drawing and enable major advances in forming metallic parts and components that are difficult to form, by developing driving coils with advanced design.

The effects of dual-coil ignition and axial swirl on spark-assisted controlled autoignition

The work involved an experimental study of a dual-coil ignition system for improved combustion stability and control during four-stroke gasoline controlled autoignition combustion. The ignition system was based upon the ‘redundant-coil’ set-up previously used in motorsport applications, where two conventional induction coils are connected to a common spark plug via an individually assigned diode. Such systems have recently been used for improved tolerance to exhaust gas recirculation in automotive spark ignition engines, but their effects have apparently not been previously reported for spark-assisted controlled autoignition. The basis for the work was therefore to validate such operation at low loads, where spark assist has been most widely suggested as a means of stabilising controlled autoignition combustion. The experiments were undertaken using a thermodynamic single-cylinder research engine equipped with an electrohydraulic, fully variable valvetrain on the inlet and the exhaust. This valvetrain was primarily used to invoke negative valve overlap and later, additionally, to allow study of the asymmetric intake valve operation and the influence of the increased axial swirl ratio within the bulk gas flow. The key observation from the work was that a staged single strike per coil strategy was found to improve the combustion stability significantly when operating at the low-load controlled autoignition boundary, especially when combined with increased axial swirl to promote ignitability between successive strikes. Overall, it was concluded that the system provides a new method for ensuring robust controlled autoignition operation at the lowest loads, with additional ability to help to control the combustion noise.

Reduction of the Hot Spot Temperature in HTS Coils

A potential future muon collider requires high field solenoids ( 30 T) for the final cooling stage; the Magnet Division at Brookhaven National Laboratory is undertaking the task of demonstrating feasibility using high-temperature superconductors (HTS). The aim is to construct an all-HTS dual-coil system capable of delivering more than 20 T. Recently, a new record for an all-HTS solenoid has been established with a field of 15 T on-axis. In coil tests, it was noticed that during a fast energy extraction, the current in the solenoids decays faster in comparison to the expected exponential decay. This paper describes the effect and shows how it can be simulated using commercial finite element code. The faster current decay helps to lower the integral current density squared with time by about 10% and is therefore beneficial for quench protection.

Transvenous placement of the subcutaneous coil electrode to reduce elevated defibrillation thresholds: an alternative to an azygous or subcutaneous coil

Purpose: Despite waveform optimization, high output devices, dual coil electrodes (DCE) or the addition of a standard (Medtronic Transvene) proximal coil (TVCE) high defibrillation thresholds (DFT) continue to be a problem in patients with implantable cardioverter defibrillator (ICD). Placement of a coil electrode (Medtronic 6996) posterior in the subcutaneous (SQ) tissue (SQCE) reduces DFTs but requires a second procedure in many centers and is not readily applicable to a right-sided implant. Placement of a TVCE in the azygous vein or coronary sinus can be challenging and may be extremely difficult/dangerous to extract. We present an alternative approach to high DFT's by transvenous rather than SQ placement of the SQCE. Methods: Between Sept 2009 and May 2012, eight patients with high DFT's (mean ≥ 35.3 SD ± 2.7) despite a DCE (proximal coil surface area {SA} 860 mm2) or addition of a TVCE (SA 125 mm2) who had a SQCE (SA 500 mm2) placed in the left innominate/SVC (7 left-sided implants) or azygos vein (1 right-sided implant). After connecting the SQCE to the proximal port, the generator was implanted in the subcutaneous space and DFT's repeated. Results: The mean age was 63±16 years (range 30-79) with 3 females and 1 right-sided implant. The initial ICD lead was dual coiled in seven with the addition of a TVCE in one. After removal of the plastic tip, the subcutaneous coil electrode was positioned in the left innominate/SVC (n=7) and the azygos vein (n=1) for the right-sided implant. The mean DFT was reduced from > 35.3 J ± 2.7 to ≤ 20.3 J ± 4.9 (p=0.003) and the high voltage lead impedance reduced from 41.5±16.7 to 31.1±6.8 Ω (p = 0.2) There were no perioperative complications such as lead dislodgements, fractures, infections or sensing problems noted till last follow up. One patient expired from progressive congestive heart failure one year after the implant. None of the patients have had a spontaneous arrhythmic episode and there were no inappropriate therapies recorded since implant till last follow up. Conclusion: Despite a lower SA than the proximal coil of a DCE, transvenous placement of the SQCE in the left innominate/SVC reduces high DFT's below that seen with a dual coil system and does not require a second procedure. For right-sided implants, azygos placement of the subcutaneous coil may be preferred than the conventional transvenous coil for reducing DFT's.

Simulation and Experimental Study on Secondary Voltage of Dual-coil Ignition System

With the intention of improving ignition performance of natural gas engine, a dual-coil ignition system was devised according to energy superposition principle. Using Multisim software and experimental apparatus, the variation of secondary voltage along with discharge time interval was studied by taking simulation and experimental methods. The results show that dual-coil ignition system can enhance the secondary voltage, increase spark duration and accomplish multiple discharge under different discharge time interval compared with single-coil ignition system. So the dual-coil ignition system is conducive to reliable ignition for natural gas engine under different working conditions and it provides a way to optimize the ignition system.

Special Coils Development at the National High Magnetic Field Laboratory in Toulouse

The Laboratoire National des Champs Magnetiques Intenses (LNCMI) develops different types of coils suited to specific experiments. We present some recent developments on magnet design. Several coils are dedicated to experiments in large scale facilities in France and Switzerland. A 30 T split-pair coil for X-rays diffraction and one 40 T coil for plasma physics at the LULI, two 30 T coils with axial access (one with an conical bore) for X-ray diffraction and absorption experiments. A 40 T wide angle conical access solenoid with a high duty-cycle for neutron scattering at the ILL is being constructed. For use at the installation in Toulouse we have developed, apart from our standard 60 and 70 T coils, several special coils: a coil with a long optical path with 30 T transverse magnetic field and a 90 T long pulse dual coil system.

Magnet Development Program at the WHMFC

In 2008, the Wuhan National High Magnetic Field Center (WHMFC) was set up at the Huazhong University of Science and Technology, Wuhan, China. The objective of the pulsed magnet program is to produce pulsed magnetic fields in the range of 50 to 80 T. The following pulsed magnets were initially conceived: 1) 50-80 T monolithic magnets energized by one or a few modules of the 1 MJ capacitor bank, 2) a 50 T/100 ms flattop long pulse magnet energized by the 100 MJ/100 MVA pulse generator, 3) a 60 T/200 ms long pulse magnet energized by the 12 MJ capacitor bank, and 4) an 80 T dual coil system energized by two capacitor bank modules. In addition, a 16 T PPMS and a 7 T SQUID-VSM systems were acquired. Currently, work on a 40 T long pulse magnet energized by lead acid battery units and the acquisition of a 400 MHz NMR spectrometer are in progress.

Development of Pulsed Magnets at WHMFC

At the Wuhan High Magnetic Field Center (WHMFC), software packages for pulsed magnet design have been developed. Magnets of bore sizes from 12 to 34 mm with peak field in the range of 50 to 80 T have been designed using these software packages. The monolithic coil magnets are energized by a capacitor bank. One dual coil system for peak field of 80 T is energized by two separate capacitor banks and another system for 50 T, 100 ms flat top field by the 100 MVA/100 MJ pulse generator. All magnets were internally reinforced with Zylon fiber composite and externally with carbon fiber. Five prototype pulsed magnets have been manufactured and tested. Four of these were made with soft copper wire. The fifth was made with high conductivity, high strength wire containing Nb micro-filaments in a Cu matrix. Testing of the magnets designed for 50, 60 and 75 T with bore size of 34,18 and 12 mm is in progress.

The determination of ambient formaldehyde using a dual coil system and an assessment of dominant factors that influence its abundance in Korea

An enhanced dual coil 2,4-dinitrophenylhydrazine (DNPH) derivatization method (dual coil/DNPH) allowed the quantitative determination of formaldehyde (HCHO) in ambient air. In this method, traceable HCHO was collected using a coil sampler connected in series and lacking a long sampling tube. It was then analyzed using liquid chromatography followed by UV detection of the DNPH derivatives. The method is based on the reaction of formaldehyde with DNPH to produce 2,4-dinitrophenylhydrazone. The detection limits (3sigma) were 0.10-0.40 ppbv with a precision ranging from 0.84 to 4.09% RSD. The results of dual coil/DNPH and conventional DNPH cartridge methods were generally well correlated: HCHO (dual coil/DNPH)=0.97 (+/-0.13) vs. HCHO (DNPH Cartridge)+0.33 (+/-0.33), r=0.82. The dual coil/DNPH method was used to measure gaseous HCHO in the atmosphere of Metropolitan Seoul during the summer 2000 and 2001, and in Gwangju during the fall of 2001 and 2002. The daytime mean concentration of HCHO was 4.52 (+/-5.69) and 3.21 (+/-1.27) ppbv in Metropolitan Seoul for 10-12 August 2000 and 29-31 May 2001, respectively, and 1.73 (+/-0.98), 3.04 (+/-2.25), 2.70 (+/-1.70), and 2.01 (+/-2.28) ppbv in Gwangju City during 22-27 September 2001, 17-24 October 2001, 9-13 October 2002, and 28 October to 2 November 2002, respectively. The HCHO in Seoul from 10-12 August 2000 was mainly the result of photochemical processes, while direct emissions from vehicles and long-range transport of air from China contributed during 29-31 May 2001. During 22-27 September 2001, 17-24 October 2001, and 9-13 October 2002 in Gwangju, the HCHO came primarily from photochemical processes, although some air affected by biomass burning admixed in the late afternoon. The increase in the HCHO concentration on 20 October 2001 and from 28 October to 2 November 2002 was attributed mainly to direct emissions from biomass burning in farmland near the measurement site.