Assessing real-world emissions from buses and taxis is vital to comprehend their impact on urban air quality. Such vehicles differ significantly from the majority of the fleet owing to their higher mileage rates. However, few studies have focused on specifically assessing the emissions from this segment of the vehicle fleet. In this context, this study evaluated the real-world emissions of nitrogen oxides (NO_x) from in-use buses and taxis in Dublin, Ireland, using crossroad remote sensing technology. The remote sensing system was deployed at strategic locations throughout the city to capture on-road emissions from passing vehicles. The collected data included vehicle related information such as emission standard, make, and mileage, and pollutants including NO_x. Based on this data, analysis was aimed to understand the impact of Euro emission standard, ambient temperature, mileage, and make of the vehicle on NO_x emissions. The results reveal that the average emissions from taxis reduce by 37% from Euro 5 to Euro 6b, and average emissions from Euro 6 buses are 87% lower compared to Euro 5. The trends in emission factors (EFs) of buses and taxis were similar during summer and winter sampling. Moreover, on comparing the emissions from the top five taxi manufacturers, different trends in the emission factors were observed. Finally, the study found that the effect of vehicle mileage on emissions was unclear for both buses and taxis. In any case, these findings provide valuable insights into the real-world emission performance of the existing fleet of buses and taxis in Dublin and highlight the need for targeted measures to reduce emissions from these vehicles. The results can assist policymakers and urban planners in formulating evidence-based strategies to improve air quality in Dublin and other cities facing similar challenges.

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Emissions from real-world driving are often higher than estimated emission levels based on Euro emissions standards and type-approval tests. Consequently, the air quality in cities has not improved as originally anticipated from fleet renewal and stringent emission regulations for newer vehicles. This paper presents the real-world emission factors (EFs) for in-use cars, taxis, vans, and buses obtained using on-road remote sensing in Dublin city, Ireland. EFs from both petrol and diesel Euro 6 vehicles were significantly improved compared to the EFs of older emission standard vehicles. The analyses indicated that the presence of a few high emitting older vehicles skewed the overall distribution of EFs. Detailed description of variations in EFs for individual pollutants based on changes in emission standards, location, and other driving characteristics were studied and reported, which provide justification for implementing policies targeting fleet renewal.

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Estimating emissions savings from alternative vehicular technologies is essential to streamline urban freight transport policy. We estimate freight emissions in the city of Chennai, India using real-world emission factors obtained from on-board emission measurement systems and trip characteristics collected through an establishment survey. India recently enforced Bharat Stage VI (BS-VI) emission standards and both the central and multiple state governments have introduced battery electric vehicle (BEV) policies. To understand potential benefits, we estimate the emission savings with BS-VI vehicles and BEVs for freight delivery. The BS-VI vehicles reduce tailpipe CO emissions by 20.3%, and HC+NO_x emissions by 74.5%. The GHG emission saving in CO₂ equivalents with BEVs is 50.3%, which increase with a greener energy mix, improved transmission and distribution efficiency, cleaner battery production, and more lifetime vehicle kilometres. BS-VI adoption can deliver significant emission reduction until BEVs and charging infrastructure scale up.

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Introduction: Millions of people in developing countries depend on public transportation for their daily commute to and from work. In particular, buses are the preferred mode of transportation, as they are easily accessible and inexpensive. However, since the bus stops are located on urban arterial roads carrying a high volume of traffic, the passengers waiting for the bus are exposed to a high concentration of particulate matter and noise. Methods: In this study, PM_2.5 (particulate matter with an aerodynamic diameter less than 2.5 μm) concentrations and noise levels were measured at six bus stops in Chennai, India in two phases. The PM_2.5 concentrations were measured using a low-cost portable optical sensor, and the noise levels were measured using an android application installed in a smartphone. Traffic volume and composition data on the road adjacent to the bus stop was also collected. Results: The average of the measured 1-h PM_2.5 concentrations at the bus stops during January and October were 44.2 μg/m³ and 48.5 μg/m³, respectively. On average, the dose of PM_2.5 for all bus stops assuming a waiting time of 15 min was 7.6 μg. The average of the noise levels at the bus stops was 76.8 dBA, and the noise levels exceeded 95 dBA frequently due to the extensive use of horns by the drivers. The results indicate that the passengers waiting at bus stops are exposed to unhealthy magnitudes of air and noise pollution. Conclusion: Considering the effects of exposure to high pollution levels at bus stops, appropriate steps to improve facilities and services (such as providing air conditioning and noise barriers) need to be taken. Also, the location and design of the bus stops should take into consideration the exposure to pollutants for the waiting passengers during the planning phase of development itself.

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Emissions from motor vehicles lead to significant adverse effect on air quality of cities, with many cities reporting ambient air concentration of pollutants well beyond the permissible standards. In this paper, we determine the effect of changing driving patterns during peak and off-peak periods on emissions from diesel passenger cars. Second-by-second emissions of CO, CO₂, HC, and NO_x were measured during both peak and off-peak periods using portable emission measurement system (PEMS). It is seen that during peak hour, average speed decreases, percentage time spent in acceleration, deceleration, and idling increases, while time spent in cruising mode decreases significantly. Further, EFs are developed for peak and off-peak periods and compared with the Automotive Research Association of India (ARAI) emission standards. The EFs during peak periods are found to be significantly different from off-peak periods. The results of this study would be useful in accurate quantification of emissions.

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Driving cycles are used to understand the driving pattern of vehicles and in estimating their emissions. Although several studies exist on driving cycles worldwide, few studies have focused on developing driving cycles for intra-city buses in heterogeneous traffic conditions. In this study, driving cycles for intra-city buses were developed using real-world GPS data collected during peak and off-peak periods in Chennai city, India. The methodology for the construction of the candidate cycle was based on k-means clustering and one-step Markov modelling. For Markov chain modelling, a transition matrix is constructed which is a probability matrix based on one step succession. To understand the effect of duration of the driving cycle, the candidate cycles were developed for different durations ranging from 400 seconds to 2800 seconds. Further, the average error for each duration of the candidate cycles was determined. The duration which corresponds to the least average error was chosen for developing the final driving cycle. Three driving cycles - corresponding to morning peak hour, off-peak hour, and evening peak hour - were developed. Finally, the developed cycles were compared with the existing local and international cycles. The developed driving cycle was found to be significantly different from the existing cycles for buses.

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Diesel trucks contribute significantly to emissions leading to deterioration in urban air quality. Many recent studies have attempted to quantify real-world emissions from trucks in cities. However, studies on real-world emission from trucks in India are scarce. In this study, we measured real-world emissions of gaseous pollutants (CO, HC, and NO) from twenty trucks of different sizes and emission standards. The trucks were classified into three categories (light-duty diesel trucks (LDDTs), medium-duty diesel trucks (MDDTs), and heavy-duty diesel trucks (HDDTs)) based on their gross vehicle weight (GVW). The tested trucks conformed to Bharat Stage (BS) II, BS III, and BS IV emission standards. A vehicle specific power (VSP) based approach was adopted to model the relationship between vehicle activity and emissions. In addition, real-world emission factors of CO, HC, and NO for all the truck types were determined and compared based on their emission standard. Considerable reductions in emission factors were observed from lower to higher emission control standards for all the pollutants. The CO, HC and NO emission factors from the BS II standard LDDTs were 8.05 g/km, 0.86 g/km, and 8.04 g/km, respectively. The CO emission factor decreased by 29% and 65% respectively, for LDDTs and MDDTs with improved emission standards. The HC emissions (g/km) reduction from BS II to BS III for LDDTs and HDDTs were 49% and 8%, respectively. In the case of MDDTs, HC emission factor reduced by 16% from BS II to BS IV. On comparing with ARAI emission standards, we found that the emission factors of the trucks with GVW less than 3500 kg were higher for all the pollutants. In the case of trucks with GVW greater than 3500 kg, the CO emission factor for BS II and BS III complying trucks were higher than standard values while HC emission factors were lower than the standard values. Further, the emission factors of CO and NO from BS IV standard trucks were higher than the standard values. Moreover, emission factor values from our study were higher than that reported in the literature. Although India aims to adopt BS VI emission standards by 2020, phasing out older vehicles will be the key to mitigate emissions from diesel vehicles.

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Motor vehicles contribute significantly to the total emissions in a city. Several studies have attempted to quantify emissions from cars, buses, and trucks using laboratory-based or real-world emission tests. However, real-world emissions from motorcycles (or motorized two-wheelers) has not received adequate attention. Unlike developed countries where cars are predominantly used for personal transport, motorcycles are widely used in developing countries. In this study, we quantify emissions of carbon monoxide (CO), hydrocarbons (HC), and nitric oxide (NO) from four typical motorcycles (MC 1, MC 2, MC 3, and MC 4) using real-world emission measurements and develop emission models. We also compare the observed real-world speed-time profiles with the laboratory test cycles and the emission factors developed using real-world emission measurements with the Bharat Stage (BS) emission standards. The real-world emission factors of CO for MC 1, MC 2, MC 3, and MC 4 were 12.3 times, 3.18 times, 9.71 times, and 5.84 times above the respective BS emission standard values. Also, the CO and [HC + NO] emissions from a two-stroke motorcycle (MC 1) were higher than the four-stroke motorcycles. The models presented in this paper can be used to accurately quantify real-world emissions from motorcycles on Indian urban arterials and to formulate policies for air quality improvement.@en

Passenger cars contribute significant emissions in urban areas affecting the air quality of cities. Traditionally, vehicular emission factors (EFs) were developed based on measurements in the laboratory. However, studies indicate that the laboratory measurements are unrepresentative of real-world conditions. In this study, EFs were developed for diesel passenger cars using Portable Emission Measurement Systems (PEMS) on urban arterials with heterogeneous traffic conditions in Chennai, India. Three diesel passenger cars from different manufacturers, of the same age, and complying with Bharat Stage IV (BS IV) emission standards were selected for emission monitoring. The results show that the average carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxides (NOx) emission factors of the passenger cars were 1.28, 0.13, and 0.59 g/km, respectively. In addition, the measured EFs were influenced by the road type with higher emissions on roads with higher speeds and steeper accelerations. Finally, the total annual emissions generated by diesel passenger cars in Chennai city, for the current vehicle activity, were estimated to 7000 tonnes of CO, 750 tonnes of HC, and 2400 tonnes of NOx. Considering the increasing emphasis on electric mobility and public transport, this study provides a timely insight into emissions from diesel passenger cars.@en

Intra-city buses provide essential transportation and mobility services in cities. However, most of the buses in Indian cities run on diesel fuel causing significant emissions and air quality issues. This study aims to quantify the emissions from the buses during peak and off-peak periods using second-by-second activity data collected using global positioning system (GPS) receivers. Four-bus routes plying within the city of Chennai in India was selected and second-by-second speed and acceleration was used to determine the operating mode of the bus. Corresponding emissions were estimated using vehicle specific power (VSP). Results show that the average speed of the bus during peak and off-peak periods were 17.8 kmph and 21.5 kmph, respectively; the corresponding percentages of time idling were 27% and 22%. Further, the percentage increase in total emissions of CO₂, CO, HC and NO_x from the bus during peak periods with respect to off-peak periods was 17%, 16%, 37% and 21%, respectively. This study provides useful insights regarding the operating and emission characteristics of buses that will be valuable to policy makers in improving their service and efficiency.

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Road transport is a significant contributor of pollutant emissions in the cities of developing countries. Driving cycles are required for the estimation of fuel consumption and exhaust emissions from vehicles for emission testing and certification, with many cities having unique cycles for different types of vehicles and roads. However, no driving cycle has been developed for passenger cars and motorcycles in Chennai, India. Thus, the aim of the present study was to develop representative driving cycles for passenger cars and motorcycles which reflect the real-world driving conditions in Chennai, India. On-board diagnostic (OBD) reader and Global Positioning System (GPS) receivers were used to collect second-by-second vehicle speed from a representative set of vehicles for developing the driving cycles. Eleven assessment measures were used in the construction of the driving cycles from the micro-trips. The developed cycles for motorcycles and passenger cars were of 1448 and 1065 s (peak-hour), which were further compared with existing driving cycles. Significant differences were observed between the cycles, thus highlighting the need for city-specific cycles.

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