Motorcycle Exhaust Research Articles

The Influence of Fuel Type on MotorcycleVehicle Exhaust Emission Tests

A vehicle engine's performance can be determined through exhaust emission tests. Exhaust emissions contain air pollutants that result from incomplete fuel combustion in the vehicle's combustion chamber. This is usually due to improper oxygen and air mixture conditions. Gasoline (CxHy) burns and reacts with oxygen (O2) to produce carbon dioxide (CO2), water (H2O), as well as non-toxic gases like nitrogen (N2) and water vapor (H2O (g)). However, it also generates toxic gases such as CO, HC, and Nitrogen Oxides (NOx). Motorcycle exhaust emission tests are commonly conducted using a gas analyzer. In this study, a gas analyser was used to measure the amount of CO, CO2, HC, O2, and NOx emitted from motorcycle exhausts. The tests were carried out using the Vario 160 ABS motorcycle with different types of fuel: RON 92 (S), RON 92 (P), RON 90, RON 98, and RON 92 (R). The data was collected at idle, as well as at 1600 rpm, 1800 rpm, and 2000 rpm. Three measurements were taken for each variable, and the average was calculated. The results showed that RON 98 fuel resulted in better combustion compared to RON 90 and RON 92, as indicated by the CO2 content at idle, which was 13.95%. Additionally, when the motorcycle's engine was throttled, RON 98 fuel did not produce any NOx. The study also revealed that RON 92 (S) fuel led to better combustion compared to both of RON 92 (P) and RON 92 (R), as evidenced by the CO content of 0.05%, CO2 content of 13.63%, HC content of 204 ppm, O2 content of 0.03%, and NOx content of 4 ppm at idle.

One-Pot Synthesis of Carbon Nanodots Retrieved from Motorcycle Exhaust: Antibacterial and Antibiofilm Applications

Carbon nanodots (CNDs) are nanoscale carbon-based materials with particle sizes typically less than 10 nm. They are characterized by their unique electronic, optical, and surface properties, as well as their bright and tunable fluorescence across the visible light spectrum. The process involved in synthesizing carbon nanodots is rather energy-consuming, expensive, and complicated. Motorcycle exhausts have been looked at as an environmental pollutant. In this paper, the bright side of motorcycle exhausts has been projected, whereby we have extracted carbon nanodots from motorcycle exhausts, using a simple and straightforward strategy. The nanomaterial was successfully isolated and characterized. The antimicrobial activity of the indigenously prepared nanomaterial was evaluated and coatings were prepared on glass and these nanocarbon coatings were demonstrated for their anti-biofilm activity. The results confirm the innovative and sustainable recovery of antibacterial carbon nanodots from environmental pollutants such as motorcycle exhaust.

Optimization of the cold‐side heat exchanger design to improve the performance of the motorcycle exhaust thermoelectric generator

AbstractThis study optimizes the main parameters of the cold‐side heat exchanger (CHE) longitudinal fin, including fin quantity (Nf), fin thickness (Tf), and fin height (Hf), to enhance the performance of motorcycle exhaust thermoelectric generator units (TGUs) utilizing the computational fluid dynamics approach. The investigation shows that these parameters significantly affect the dissipation area of the CHE heat and the outside air velocity distribution in fin gaps, resulting in the fluctuation of TGU output power. The output power increases with respect to Hf; nevertheless, it first increases as Nf and Tf increase but decreases dramatically when Nf or Tf becomes too large. Besides, Hf significantly affects output power, and its impact is almost independent of Tf and Nf, and vice versa; meanwhile, Tf and Nf have a strong relation. This study proposes two Hf of 40 and 60 mm along with the optimal Tf of 1 mm and Nf of 29, providing significantly high output power, low weight, and compact size for TGU. This work contributes insight into the effect of CHE parameters on the TGU performance, and it is a crucial case study for selecting suitable heat sink parameters for TGU, considering practical requirements and conditions.

Study on the Impact of CDI Limiter and CDI Unlimiter Usage on Motorcycle Fuel Consumption and Exhaust Gas Emissions

Study on the Impact of CDI Limiter and CDI Unlimiter Usage on Motorcycle Fuel Consumption and Exhaust Gas Emissions

Measurement of motorcycle exhaust emissions on urban roads using remote sensing

This study aim to determine motorcycle exhaust emissions and emission factors on urban roads using unintrusive roadside remote sensing equipment, specifically the ETC M752 type version 3.1 from 2020. The research gathered 1012 valid and identified vehicle samples from five locations, comprising four in Jakarta and one in Bandung. The results unveiled median motorcycle emissions: CO2 (13.90%), CO (1.42%), smoke (0%), HC (1499 ppm), and NOx (2447 ppm). These measurements were recorded at an average speed of 21.81 km/h with an average acceleration of 0.05 m/s². Meanwhile the emission factors determined from this study were: 46.50 g/km, 1.95 g/km, 0 g/km, 0.22 g/km, and 0.46 g/km for CO2, CO, soot, HC, and NOx, respectively. An increase in the production year of motorcycles led to a significant reduction in exhaust emissions and emission factors. Across all production year categories, CO and HC emissions remained within acceptable thresholds. CO and HC emission factors already meet Euro 3 standards, while the NOx emission factor still does not meet the standard. Enhancing engine cylinder capacity resulted in a slight uptick in motorcycle exhaust emissions and emission factors. Specifically, the CO and HC emissions on Yamaha motorcycles are lower compared to Honda, while the NOx emissions on Yamaha motorcycles are higher compared to Honda. However, both brands have met Euro 3 standards for CO and HC but not for NOx.

Performance enhancement of the motorcycle exhaust thermoelectric generator - Optimization of the hot-side heat exchanger configuration

The article investigates the influences of three structural parameters of the hot-side heat exchanger (HHE), including the fin quantity, height, and thickness on the mean temperature of its base. The HHE is integrated into the thermoelectric generator unit (TGU), which uses motorcycle exhaust gas as the heat source. These structural parameters have been optimized by using computational fluid dynamics simulation to enhance the heat absorption through the HHE base to maximize the electric power of the TGU. The findings show that these three HHE structural parameters affect both the convection coefficient and the heat transfer area of the HHE. Increasing the fin quantity and height or reducing the fin thickness leads to an increase in the heat transfer surface area of the HHE. On the other hand, the convection coefficient increases by increasing the fin thickness and quantity or decreasing the fin height. The HHE, which has a fin quantity of 21, fin thickness of 1 mm and fin height of 42 mm, produced the maximum TGU electricity power by 8.2 % higher than the original configuration. This study has significant implications for improving the TGU performance and decreasing the size of the HHE configuration, which makes it more compact and lower manufacturing costs.

Thermal uniformity enhancement of the motorcycle exhaust thermoelectric generator—Theory model for predicting heat exchanger fin profile

This paper develops the theoretical model to predict the fin profile of the Hot-side heat exchanger (HHE) to enhance the uniformity of its longitudinal temperature distribution. The developed model can be applied to general cases where heat exchangers have different numbers, heights, pitches, and materials of fins, as well as the thermodynamic and heat transfer parameters of the working fluid. Numerical investigations of two fin profiles' thermal performance are conducted to validate the theoretical model. According to the results, the optimal profile improves the temperature uniformity by 91.3% compared to the original profile. The improvement in the temperature uniformity between thermoelectric modules (TEMs) can be achieved at the cost of reducing the thermoelectric generator unit power. The reductions in heat absorption of the HHE in the current study are not significant, varying from 1.3% to 2.9% at different engine speeds. However, the temperature uniformity can restrict the output power loss due to the significant differences in voltages and amperages produced by TEMs and also can eliminate the deterioration of TEMs’ lifespan.

Development of a CMAQ–PMF-based composite index for prescribing an effective ozone abatement strategy: a case study of sensitivity of surface ozone to precursor volatile organic compound species in southern Taiwan

Abstract. Photochemical ozone pollution is a serious air quality problem under weak synoptic conditions in many areas worldwide. Volatile organic compounds (VOCs) are largely responsible for ozone production in urban areas where nitrogen oxide (NOx) mixing ratios are high while usually not a limiting precursor to ozone (O3). In this study, the Community Multiscale Air Quality model higher-order decoupled direct method (CMAQ-HDDM) at an urban-scale resolution (1.0 km×1.0 km) in conjunction with positive matrix factorization (PMF) was used to identify the dominant sources of highly sensitive VOC species to ozone formation in southern Taiwan, a complex region of coastal urban and industrial parks and inland mountainous areas. First-order, second-order, and cross sensitivities of ozone concentrations to domain-wide (i.e., urban, suburban, and rural) NOx and VOC emissions were determined for the study area. Negative (positive) first-order sensitivities to NOx emissions are dominant over urban (inland) areas, confirming ozone production sensitivity favors the VOC-limited regime (NOx-limited regime) in southern Taiwan. Furthermore, most of the urban areas also exhibited negative second-order sensitivity to NOx emissions, indicating a negative O3 convex response where the linear increase of O3 from decreasing NOx emissions was largely attenuated by the nonlinear effects. Due to the solidly VOC-limited regime and the relative insensitivity of O3 production to increases or decreases of NOx emissions, this study pursued the VOC species that contributed the most to ozone formation. PMF analysis driven by VOCs resolved eight factors including mixed industry (21 %), vehicle emissions (22 %), solvent usage (17 %), biogenic sources (12 %), plastic industry (10 %), aged air mass (7 %), motorcycle exhausts (7 %), and manufacturing industry (5 %). Furthermore, a composite index that quantitatively combined the CMAQ-HDDM sensitivity coefficient and PMF-resolved factor contribution was developed to identify the key VOC species that should be targeted for effective ozone abatement. Our results indicate that VOC control measures should target (1) solvent usage for painting, coating and the printing industry, which emits abundant toluene and xylene; (2) gasoline fuel vehicle emissions of n-butane, isopentane, isobutane, and n-pentane; and (3) ethylene and propylene emissions from the petrochemical industry.

Synthesis of V2O5-MgO/TiO2 mixed oxide nanocomposites for photocatalytic treatment of CO in vehicle exhaust emissions

Photocatalytic nanotechnology is one of the techniques that brings many new breakthroughs since it possesses high potential for the supply of clean energy and the degradation of persistent organic pollutants in the environment. The drawback of photocatalytic materials such as TiO2, ZnO, V2O5 is the activation only under ultraviolet light. To extend the applicability of photocatalytic nanomaterials to a visible light region, recent research has focused on the modification of semiconducting photocatalysts. In this study, V2O5-MgO/TiO2 mixed oxide nanocomposites were synthesised via a sol-gel method by using polyvinyl alcohol as a gelling agent. The basic structural characteristics of nanocomposites were determined by analytical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET, energy dispersive x-ray (EDX), x-ray diffraction (XRD), infrared (IR) and ultraviolet-visible (UV–vis) spectroscopy. The results obtained from EDX and XRD analyses indicate that V2O5 and MgO particles with a size between 14.5 and 21.3 nm were formed and uniformly dispersed in TiO2 phases. Moreover, the effects of oxide weight ratios, illuminating conditions and reaction time on the photocatalytic activity of the nanocomposites were investigated via CO conversion with the input CO concentrations of 8000 ppm. Significantly, the V2O5-MgO/TiO2 nanocomposites were used for treating CO in motorcycle exhaust fumes. The efficiency of the process reached 82% for 10 min, indicating the potential applicability of the V2O5-MgO/TiO2 nanocomposites for the CO treatment of industrial emissions.

Design of Metallic Catalytic Converter using Pareto Optimization to Improve Engine Performance and Exhaust Emissions

In this paper, Metallic Catalytic Converter (MCC) is installed in motorcycle exhausts to produce the minimum CO as well as to produce the optimum engine power. The results from previous research were collected and then used to predict the best MCC design using the Artificial Neural Network Multi-Objective Genetic Algorithm (ANN-MOGA). In addition, the ANN parameter tuning process was also carried out using the Taguchi method to find the initial weighting and bias that is able to provide the best and the most stable performance to predict the best MCC design. The best two sets of design solutions out of 70 sets of Pareto solutions were obtained by ANN-MOGA. Those two MCC designs are the optimum emission design and the optimum multi-objective design. The verification results show that the optimum multi-objective design tends to be superior in terms of CO emissions and engine power. In terms of CO emissions, the optimum multi-objective design gets a larger S/N ratio of -10.98, while the optimum emission design only gets an S/N ratio of -11.21. Meanwhile, in terms of engine power, the optimum multi-objective design gets a larger S/N ratio of 16.13, while the optimum emission design only gets an S/N ratio of 15.86 S/N. It is in line with the ANOVA test results which show that the optimum multi-objective design is proven to be better than the optimum emission design.

Service Based Practical Technology Drinking Water Heater with Heat Smoke Recovery of Multipurpose Diesel Motorcycle Exhaust for Wooden Fisherman Boat Power

The gas power cycle of a four-stroke combustion engine is obtained from a mixture of diesel injection+compressed hot air as the working fluid, which in this case is taken from a versatile type of diesel engine from all kinds of fishing communities on the north coast of Java Island, it can be said that in general the use of multipurpose diesel engines used as a propulsion engine for fishing boats. A common sight for Pantura fishermen is hot smoke exhaust from the exhaust of a multipurpose diesel motor driving a wooden fishing boat released into the air. Eventually, it becomes a source of air pollution around the ship, especially nitrogen oxides, which are toxic to human respiration; hot smoke waste resulting from the combustion process released through the piston engine exhaust system still contains valuable energy potential in the form of hot gas released by the exhaust which if attempted to heat the hot gas energy before being discharged into the ambient air, the heat energy can be recovered by installing additional heat exchangers as a benefit of heat sources for heat exchange heaters or heaters the result is cold drinking water turns into hot drinking water. Heat balance is the calculation of the heat released in the combustion of fuel+air in the combustion chamber and its utilization in the transfer of cold fluids to hot fluids, which is the heat energy content of explosion in compression combustion engines based on fossil fuels. All heat products of combustion cannot be converted 100% into practical motor work or power; energy transfer is lost from the combustion motor, such as 25%, to cooling water 32%, in the exhaust gas 34%, pumping losses, 3%, losses -friction loss between parts due to lousy machining inaccuracy 6% and radiation to the air environment. A drinking water heater with hot smoke recovery from a versatile diesel motor exhaust driving a wooden fishing boat works by recovering or recovering heat energy from the exhaust gas in the exhaust directly from the combustion process cycle in a piston-type combustion engine. The hot flue gas flow is forced into direct contact with the wall of the heat exchanger tube before exiting the exhaust. As long as the piston combustion motor is running, the hot stream from the exhaust gas flows into the shell & tube heat exchanger shell. This experiment aims to get clean hot water 70OC with a linked cold water mass = 0.0064 kg/s at 28OC. Another effect of this experiment is to control exhaust emissions into the atmosphere from internal combustion engines.

PEMBANGKIT ENERGI PADA KNALPOT MOTOR 4 LANGKAH MENGGUNAKAN TERMOELEKTRIK GENERATOR

Resources to produce energy is one of the increasing needs of society. So that there is an imbalance of load growth with the addition of power plants which will cause an energy deficit or an electrical energy crisis. There have been many studies on alternative energy power plants, one of which is the use of waste heat by using a thermoelectric generator. In this study, a thermoelectric power plant was tested by utilizing motorcycle exhaust heat for charging AAA batteries. When testing the output search, it was found that the highest current in a parallel circuit with 4 thermoelectrics is 104.4 mA and the highest voltage in a series circuit with 4 thermoelectrics is 0.83 V. Then, a AAA battery charging test is carried out using a 4 thermoelectric series circuit. From the results of the battery charging test, it was found that the battery voltage increased over the charging time period from the original 0.08 V to 1.05 V at the end of the charging time period. the current flowing in the circuit during the first 10 minutes is 48.2 mA, at the 20th minute it is 65.5 mA, at the 30th minute it reaches 91.2.Keywords: thermoelectric, energy generation, battery charging

Development of psychoacoustics index for motorcycle exhaust noise by multiple regression method

Exhaust sound is an essential characteristic of a motorcycle when it comes to the interest of young motorcycle riders. It has become such an essential characteristic that riders, after looking into the performance, style, and ergonomics, look into the exhaust sound produced by the muffler. It has thus become critical for motorcycle manufacturers to tune their mufflers in such a way that they are appealing to the customers while adhering to sound emission regulations. As per the current trend of Indian motorcycle rider’s scenario, more attention is given to sound attributes like beat feeling, sportiness, and pleasantness. This research paper aims to develop a psychoacoustic model that can rate the exhaust sound of motorcycles targeting the Indian customer’s preferences and interests with regard to the engine exhaust sound. Presently, a study has been carried out on beat feeling, sportiness, and pleasantness, a perceivable attribute of sound in the family of motorcycles. Motorcycle buyers often perceive the exhaust sound of motorcycles in idling conditions at some distance away from the muffler, which formed the basis while recording exhaust sounds. Initially, exhaust sounds were recorded, which led to the calculation of psychometrics as objective variables. The calculated objective variables were given as input to the multiple regression model. A jury panel consisting of experienced NVH professionals and riders evaluated these sounds on a 7-point evaluation scale. These subjective ratings were given as the target variable to the multiple regression model. The obtained model was later validated with subjective data of motorcycles, including those at the prototype stage. Thus, a model has been established to aid exhaust designers in comparing their motorcycle at different prototype stages with the competitor’s vehicle, allowing them to make an early decision with respect to the muffler design modifications, thereby reducing the time-consuming and expensive jury tests.

Research on the Effect of the Addition of Trembesi Leaf Extract on Motorcycle Exhaust Emissions

One of the reasons for the air pollution that occurs at this time is the emission of the motorcycle exhaust. According to some sources, the trembesi leaves can absorb the level of exhaust emissions. By making extracts from trembesi leaves and added to the exhaust part of the motorcycle. Because the exhaust part is the last place of discharge of combustion waste from the combustion process that occurs on motorcycles and the result is that when the motorcycle has not been added trembesi leaf extract can produce a level of emission of Nitrogen Oxide (Nox) exhaust gases of 0.21 ppm. While the results are different when already added trembesi leaf extract can produce a level of emission of Nitrogen Oxide (NOx) exhaust gases of 0.16 ppm So it can be concluded that trembesi leaf extract can absorb or reduce the level of emission of Nitrogen Oxides (NOx), and meet the requirements of nitrogen oxide (NOx) exhaust emission levels applied in Indonesia, which is 0.17 for speeds below 1300 rpm.

Study on the effects of guide fins structures on the flow and thermal uniformity of the motorcycle exhaust thermoelectric generator

PurposeThe purpose of this paper is to investigate the effect of different guide fins structures (i.e. single-layer and double-layer guide fins) on the exhaust flow and thermal uniformity of the motorcycle exhaust thermoelectric generator.Design/methodology/approachOne single-layer guide fins structure and three double-layer guide fins structures are numerically investigated in terms of exhaust flow uniformity with different exhaust properties. Then, the double-layer guide fins structure achieving the highest flow uniformity is fabricated and experimentally investigated on a motorcycle at different engine speeds together with the single-layer guide fins structure to evaluate the thermal uniformity.FindingsThe double-layer guide fins structure obtains a better flow uniformity and thermal uniformity compared to the single-layer structure. Among surveyed structures, the double-layer structure with three closed V-shape guide fins achieves the highest flow uniformity. This structure also improves the thermal uniformity from 3.0 to 90.1% in comparison with the single-layer structure in experiments.Originality/valueIn this paper, the double-layer guide fins structures are derived from the improvement of the single-layer guide fins structure. The fluid flow uniformity index is applied as a measure for assessing the exhaust flow uniformity. The enhancement of thermal uniformity of the double-layer guide fins structure is expected to increase the longevity and performance of the motorcycle exhaust thermoelectric generator.

Thermal uniformity enhancement of the motorcycle exhaust thermoelectric generator—Part 2: Muffler outlet optimization

AbstractFollowing the development of the muffler with the optimal guide fins (MOGF) in the companion paper (Part 1), this study optimizes the muffler outlet in terms of structure and geometry to further improve the thermal uniformity of the hot‐side heat exchanger (HHE). Two outlet structures and two outlet geometry parameters (i.e., outlet angle φ and outlet position y) are proposed. The exhaust flow uniformity of HHE serves as an assessment criterion in numerous computational fluid dynamics simulations to determine the optimal outlet structure and optimal values of φ and y. The outlet of the MOGF is then modified based on the simulation results to create the muffler with the optimal guide fins and outlet (MOGFO). Various experiments on the MOGFO are conducted to verify the simulation results and evaluate the improvement of the HHE's thermal uniformity. The simulation results prove that the optimal outlet improves the exhaust flow uniformity by 1.78% on average compared with the original outlet. In experiments, the combination of optimal muffler's outlet and optimal muffler's guide fins on the MOGFO raises the thermal uniformity of HHE by an average of 22.71% and 50% compared with the MOGF and the muffler model with nonoptimal guide fins and outlet in Part 1, respectively. The remarkable outcomes of this paper, together with Part 1, are expected to enhance the efficiency and lifespan of the thermoelectric generator unit.

Thermal uniformity enhancement of the motorcycle exhaust thermoelectric generator—Part 1: Guide fins optimization

AbstractIn this study, the hot‐side heat exchanger (HHE) thermal uniformity in the thermoelectric generator unit (TGU) is enhanced by optimizing the muffler's guide fins. Three parameters of the guide fins (i.e., fin gap δ, fin angle θ, and fin position x) are proposed. Various muffler models with different guide fins’ geometry are numerically investigated to achieve the optimal set of δ, θ, and x parameters by assessing the exhaust flow uniformity of the HHE. The optimal muffler model is then simulated to compare with the nonoptimal muffler model. The HHE's thermal uniformity of these two models is experimentally investigated under various testing conditions. The results show that the parameters of δ and θ significantly affect the exhaust flow uniformity of the HHE, whereas the variable of x only has a minor influence. Thanks to the optimal values of δ, θ, and x, the exhaust flow uniformity increases 11.23% on average compared to the nonoptimal model. Consequently, the thermal uniformity is improved, and the maximum temperature difference on the HHE of the optimal model is 35% lower on average than that of the nonoptimal model. The improvement in thermal uniformity resulting from this study is expected to increase the performance and lifespan of the TGU.

Pengaruh Pola Pelapisan Isolator di Bagian Header Terhadap Temperatur Knalpot Sepeda Motor

The heat of vehicle engine emission is still can be used in order to efficiency effort and thermal polution preventive activity. This research is aimed to get the effect of the insulator coating pattern on the header on the motorcycle exhaust temperature. The reserach is done for Honda Scoopy motorcycle with engine rotation vary as 1000, 1500 and 2000 rpm. Isolator insulation vary for insulation pattern as 0, 1 and 2 cm in distance. The temperatures of exhaust are measured in 4 points measurement with K type thermocouple. The result shows that insulator coating pattern affects the temperature of the exhaust gas heat dissipation exhaust pipe (header) motorcycle exhaust.
 Keywords: header, exhaust, isolator insulation, heat

PROTOTYPE ALAT UJI KEBISINGAN DAN EMISI GAS PADA KNALPOT KENDARAAN BERMOTOR MENGGUNAKAN ARDUINO UNO

Transportation from every era has always been a special concern for the government in Indonesia. This is inseparable from the increasing number of motorcycle users, so that the increase in the number of vehicles clearly has a negative impact on health, especially from smoke pollution which contains carbon monoxide (CO) compounds produced or from the noise. This study aims to determine the level of noise and gas emissions in vehicle exhaust. The tool used to measure gas emissions is MQ-2 while noise is measured by a sound sensor which is then processed on the Arduino and then displayed on the LCD. This type of research is exploratory observation and data analysis is described descriptively. The results of the study are a tool that is able to detect gas emissions and noise in the motorcycle exhaust with a sound sensor response of 2-3 seconds while the Mq2 sensor with a response time of 5-6 seconds takes longer.

Comprehensive volatile organic compound measurements and their implications for ground-level ozone formation in the two main urban areas of Vietnam

Volatile organic compounds (VOCs) and oxygenated VOCs (OVOCs) were measured in Ho Chi Minh City (HCMC) and Hanoi, the two largest and most populous cities in Vietnam. The purpose of this study is to better understand the VOC atmospheric composition and their role in ground-level ozone formation. Online measurements of a wide range of VOCs and other pollutants were conducted using numerous instruments during different seasons (dry and rainy) in HCMC and Hanoi (spring). Our results show that the mean mixing ratio of total measured VOCs in Hanoi was 80.8 ± 40.7 ppb (mean ± standard deviation), and was similar to that observed during the rainy season (75.2 ± 44.8 ppb) in HCMC. During the dry season campaign in HCMC, which was coincident with the Hanoi campaign, total VOC was around 50% lower (40.7 ± 19.5 ppb), largely a result of increased planetary boundary layer (PBL) height and the direction of the prevailing wind. VOC profiles in both cities were dominated by alkanes (31–35%) and OVOCs (27–33%) and the proportion of alkenes (13–17%) and aromatics (12–19%) were comparable. Similarities in diurnal variation for most VOC species (except for isoprene) are seen in both cities with two clear peaks during the morning (7:00–8:00 a.m.) and evening (18:00 p.m.) rush hours, as observed for vehicular-combustion tracers (acetylene and CO). Comparisons of the ambient ratios of paired VOCs, namely i/n-pentane, and toluene/benzene, with those reported in motorcycle exhaust, roadside and gasoline samples indicate that motorcycle-related emission is likely a major contributor to VOC pollution. According to the propylene-equivalent concentration (PE conc.) and maximum incremental reactivity (MIR) methods, alkenes and aromatics were determined to be the main contributors to reactivity and ozone potential formation. Furthermore, the initial mixing ratio of VOC species was estimated based on the photochemical age method. The consumed VOCs (initial VOCs minus measured VOCs) has a similar variation trend to ground-level ozone, and a good correlation is observed in HCMC. In contrast, this result was not seen in Hanoi despite relatively high levels of PE conc. and MIR.