The effect of quarantine policy on pollution emission and the usage of private transportation in urban areas.

Governmental policies, regulations, and responses to the pandemic can benefit from a better understanding of people's resulting behaviours before, during, and after COVID-19. To avoid the inelasticity and subjectivity of survey datasets, several studies have already used some objective variables like air pollutants to estimate the potential impacts of COVID-19 on the urban transportation system. However, the usage of reactant gases and a narrow time scale might weaken the results somehow. Here, both the objective passenger volume of public transport and the concentration of private traffic emitted black carbon (BC) from 2018 to 2023 were collected/calculated to decipher the potential relationship between public and private traffic during the COVID-19 period. Our results indicated that the commuting patterns of citizens show significant (p < 0.01) different patterns before, during, and after the pandemic. To be specific, public transportation showed a significant (p < 0.01) positive correlation with private transportation before the pandemic. This public transportation was significantly (p < 0.01) affected by the outbreaks of COVID-19, showing a significant (p < 0.01) negative correlation with private transportation. Such impacts of the virus and governmental policy would affect the long-term behaviour of individuals and even affect public transportation usage after the pandemic. Our results also indicated that such behaviour was mainly linked to the governmental restriction policy and would soon be neglected after the cancellation of the restriction policy in China.

Adopting electric school buses in the United States: Health and climate benefits.

Electric school buses have been proposed as an alternative to reduce the health and climate impacts of the current U.S. school bus fleet, of which a substantial share are highly polluting old diesel vehicles. However, the climate and health benefits of electric school buses are not well known. As they are substantially more costly than diesel buses, assessing their benefits is needed to inform policy decisions. We assess the health benefits of electric school buses in the United States from reduced adult mortality and childhood asthma onset risks due to exposure to ambient fine particulate matter (PM2.5). We also evaluate climate benefits from reduced greenhouse-gas emissions. We find that replacing the average diesel bus in the U.S. fleet in 2017 with an electric bus yields $84,200 in total benefits. Climate benefits amount to $40,400/bus, whereas health benefits amount to $43,800/bus due to 4.42*10-3 fewer PM2.5-attributable deaths ($40,000 of total) and 7.42*10-3 fewer PM2.5-attributable new childhood asthma cases ($3,700 of total). However, health benefits of electric buses vary substantially by driving location and model year (MY) of the diesel buses they replace. Replacing old, MY 2005 diesel buses in large cities yields $207,200/bus in health benefits and is likely cost-beneficial, although other policies that accelerate fleet turnover in these areas deserve consideration. Electric school buses driven in rural areas achieve small health benefits from reduced exposure to ambient PM2.5. Further research assessing benefits of reduced exposure to in-cabin air pollution among children riding buses would be valuable to inform policy decisions.

Upgrading Passenger Vehicle Emission Standard Helps to Reduce China's Air Pollution Risk from Uncertainty in Electrification.

Upgrading to the CHINA 7 standard is crucial for managing air pollution from passenger vehicles in China. Meanwhile, China aims to achieve carbon neutrality by 2060, which necessitates large-scale replacement of gasoline vehicles with electric vehicles in the future. Consequently, the public might view upgrading gasoline vehicles to the CHINA 7 standard as redundant. However, the emission reduction benefits of upgrading standards in the context of uncertain electrification ambitions have not received adequate attention. Here, we show that upgrading standards will compensate for the absence of emissions reductions due to hindered electrification efforts. In the best scenario, China's CO2 emissions can be reduced to 0.047 Gt and NOx to 8.2 × 103 t in 2050. In nonextreme electrification scenarios with CHINA 7 standard, the emission intensity reduction will remain the main driver for emission reductions, outweighing the electrification contribution. In extreme electrification scenarios, upgrading standards will tackle the increased emissions from plug-in hybrid electric vehicles. Our fleet-level results advocate for early standards upgrades to enhance resilience against air pollution risks arising from uncertainties in electrification. Our evidence from China, with one of the most stringent emission standards, can provide a reference point for the world on the upgrading passenger vehicle emission standard issue.

Cleaning up while Changing Gears: The Role of Battery Design, Fossil Fuel Power Plants, and Vehicle Policy for Reducing Emissions in the Transition to Electric Vehicles.

Plug-in electric vehicles (PEVs) can reduce air emissions when charged with clean power, but prior work estimated that in 2010, PEVs produced 2 to 3 times the consequential air emission externalities of gasoline vehicles in PJM (the largest US regional transmission operator, serving 65 million people) due largely to increased generation from coal-fired power plants to charge the vehicles. We investigate how this situation has changed since 2010, where we are now, and what the largest levers are for reducing PEV consequential life cycle emission externalities in the near future. We estimate that PEV emission externalities have dropped by 17% to 18% in PJM as natural gas replaced coal, but they will remain comparable to gasoline vehicle externalities in base case trajectories through at least 2035. Increased wind and solar power capacity is critical to achieving deep decarbonization in the long run, but through 2035 we estimate that it will primarily shift which fossil generators operate on the margin at times when PEVs charge and can even increase consequential PEV charging emissions in the near term. We find that the largest levers for reducing PEV emissions over the next decade are (1) shifting away from nickel-based batteries to lithium iron phosphate, (2) reducing emissions from fossil generators, and (3) revising vehicle fleet emission standards. While our numerical estimates are regionally specific, key findings apply to most power systems today, in which renewable generators typically produce as much output as possible, regardless of the load, while dispatchable fossil fuel generators respond to the changes in load.

Health benefits of vehicle electrification through air pollution in Shanghai, China.

Vehicle electrification has been recognized for its potential to reduce emissions of air pollutants and greenhouse gases in China. Several studies have estimated how national-level policies of electric vehicle (EV) adoption might bring very large environmental and public health benefits from improved air quality to China. However, large-scale adoption is very costly, some regions derive more benefits from large-scale EV adoption than others, and the benefits of replacing internal combustion engines in specific cities are less known. Therefore, it is important for policymakers to design incentives based on regional characteristics - especially for megacities like Shanghai - which typically suffer from worse air quality and where a larger population is exposed to emissions from vehicles. Over the past five years, Shanghai has offered substantial personal subsidies for passenger EVs to accelerate its electrification efforts. Still, it remains uncertain whether EV benefits justify the strength of incentives. The purpose of our study is to evaluate the health and climate benefits of replacing light-duty gasoline vehicles (ICEVs) with battery EVs in the city of Shanghai. We assess health impacts due to ICEV emissions of primary fine particulate matter, NOx, and volatile organic compounds, and to powerplant emissions of NOx and SO2 due to EV charging. We incorporate climate benefits from reduced greenhouse gas emissions based on existing research. We find that the benefit of replacing the average ICEV with an EV in Shanghai is US$6400 (2400-14,700), with health impacts of EVs about 20 times lower than the average ICEV. Larger benefits ensue if older ICEVs are replaced, but replacing newer China ICEVs also achieves positive health benefits. As Shanghai plans to stop providing personal subsidies for EV purchases in 2024, our results show that EVs achieve public health and climate benefits and can help inform policymaking strategies in Shanghai and other megacities.

Critical review on the formations and exposure of polycyclic aromatic hydrocarbons (PAHs) in the conventional hydrocarbon-based fuels: Prevention and control strategies.

Polycyclic aromatic hydrocarbons (PAHs) are widely present in the atmosphere and primarily originate from the incomplete burning of fossil fuels and biofuels. Exposure to PAHs leads to harmful effects on human health and the environment. Diesel engines are a major source of PAH production in the transportation sector. Various approaches have been employed to reduce PAH emissions from diesel engines, including the use of biodiesel, green gaseous fuels, exhaust gas recirculation, exhaust after-treatment, and genetically modifying biodiesel with nanoparticles. This review focuses on PAH emissions from different generations of fuels and examines the remedial control actions taken to mitigate PAH formation. The study underscores the necessity for effective regulation of emissions from diesel engines, especially in developing countries where the reliance on fossil fuels is significant. Biodiesel has shown promise in reducing PAHs and carcinogenic pollutants, with higher biodiesel concentrations resulting in lower PAH formation. Replacing diesel with biodiesel and optimizing engine operating conditions are feasible methods to reduce PAH levels in the atmosphere. The use of nanoparticles in fuel blends and higher oxygen content in combustion chambers are also considered potential strategies for pollutant reduction. Additionally, the utilization of hydrogen and ammonia as secondary fuels has been explored as promising alternatives to fossil fuels. The study highlights the importance of further research on the presence of residual PAHs in the atmosphere and the implementation of strategies to curtail vehicular emissions.

Development of AI-Augmented optimization technique for analysis & prediction of modal mix in road transportation.

Transport sector contribution to global emissions is a known fact, however, the mitigation path to achieve nationally determined goals for carbon reduction is often not specified, A simplified technique based on minimax optimization using Grey relational grade and Random forest narrows down on most contributing input variables from twelve road transport modes. This is a region-specific, scenario-based technique applied to north Punjab, Province of Pakistan that first categorizes modes based on their emission and then integrates with AI modeling using Deep Neural Network to develop sustainable trade-offs for carbon reduction. The output parameter translates the problem into a systematic iterative technique that predicts optimization options with different scenarios to bring out an environment-friendly transport mix. A 25% reduction applied to the five most emission-releasing modes like Diesel Light and Heavy Duty vehicles, Gas Light and heavy-duty vehicles, and Gas-Cars results in 16.54 MT of Carbon dioxide which is 54.35% reduced to the predicted 36.24 MT for the year 2044. Similarly in another scenario replacing 25% Gas and Diesel Light Duty vehicles respectively by adding 50% Petrol Light Duty vehicles leads to 18.94 MT of emissions which brings the emission value in 2044 at par with emission releases of the year 2014. The technique offers a forward path that allows environment-friendly modal mix combinations based on business-as-usual to offer transport mix solutions for carbon reduction. It is a generalized model that is based on a customized transport mix. Future studies can also be applied to intermodal tradeoffs like rail, air, waterways, etc.

Aerosol penetration study for FFP2 half masks regarding protection against diesel particles in underground mines.

Filtering facepieces (FFP), mainly class FFP2 particle half masks (EN 149:2001#x02009;+ A1:2009), are commonly used in European mines to protect workers from respirable dust, especially from particulate matter (PM) with a diameter of 4 µm or less (PM4). The aerosol associated with diesel exhaust (DE) is dominated by submicrometer particles (with a diameter of less than 1 µm) and nanoparticles (size in the range between 10 and 500 nm). In the European Union (EU), the occupational exposure level (OEL) for DE has been defined in terms of elemental carbon (EC) concentration. Based on measurements in underground mines, on average, 60% of EC associated with PM4 was contained in PM with a diameter of 1 µm or less (PM1). Particle number size distribution (PNSD) of PM1 showed that the most numerous were particles in the size range of 20 to 300 nm. Four popular types of certified FFP2 half masks were tested for penetration. Brand new and thermally conditioned masks of each type were included in the study. NaCl aerosol in the particle size range of 7 to 270 nm was used for tests. Filtration efficiencies of 98.5% (median) or higher were achieved. Aerosol penetration was a function of particle size. Maximum penetration was observed between 20 and 60 nm, depending on the type of mask. During filtration, aerosol characteristics changed. Nanoparticles ranging in size from 7 to about 60 nm were removed to a very limited extent. The change was more noticeable for brand-new masks compared to the thermally conditioned ones. Usually, aerosol penetration through thermally conditioned masks was lower and more consistent. It was confirmed that the half masks of the FFP2 class are capable of filtering submicrometer aerosol in particle size range 7 to 270 nm with an efficiency exceeding 96% and can contribute to achieving compliance with the OEL for DE in the mining sector.

Mitigation strategies for controlling urban particulate pollution from traffic congestion: Road expansion and road public transport.

The mismatch between urban transportation demands and local transportation supplies in municipal regions may cause serious traffic congestion and high vehicle exhaust emissions (VEEs). Although it has been found that road expansion and the provision of road public transport can mitigate traffic congestion and VEEs, the effectiveness of these public strategies in alleviating traffic congestion-related VEEs has been empirically compared in few studies. With the use of a panel dataset for 260 prefecture-level cities in China from 2013 to 2018, we fill this gap via empirically examining the effects of several popular strategies that promote the efficiency of urban road transportation, including road expansion and road public transport provision, on urban air pollution of fine particulate matter (PM2.5). Then we further investigate metrics measured by passenger and freight volumes based on local urban road coverage that can suitably reflect the mismatch degree between local transportation demands and supplies. The empirical results indicated a positive and statistically significant correlation between urban PM2.5 levels and road expansion but not between PM2.5 levels and road public transport, suggesting that road expansion may unintentionally increase the transportation volume and thus local PM2.5 levels. Importantly, we found that the passenger and freight volumes per unit road length are negatively and significantly correlated with the local particulate pollution concentration across different model specifications, while the passenger and freight volumes of road transportation do not directly affect local PM2.5 levels. We also employed a series of robustness tests to overcome the concerns associated with measurement errors, omitted variable biases, model misspecifications and endogeneity, and consistent results were obtained. These results indicated that when facing limited public budgets, the passenger and freight volumes per unit road length should be considered to measure the effectiveness of road infrastructure investments in alleviating local particulate pollution caused by traffic congestion.

Optimization model for bus priority control considering carbon emissions.

To study the impact of bus priority control (BPC) on traffic carbon emissions under the strategies of speed guidance, green extension (GE), and red truncation (RT), with consideration of the main influencing factors such as delay, stopping times, and speed, a combination optimization method was used to develop a bi-level optimization model for BPC. The optimal carbon-emission reductions of buses and social vehicles with different fuel types in the upstream section of the intersection and the intersection control area was the upper-level objective, and the optimal total passenger-delay reduction was the lower-level objective. The Gauss - Seidel iterative algorithm was used to solve the model. Finally, the model was applied to the analysis of calculation cases. The results indicated that after BPC was adopted under the guidance acceleration strategy, the reductions in the carbon emissions and total delay of passenger were optimal when the guidance speed was 38 km/h, i.e. 12.67% and 21.05%, respectively. Under the guidance acceleration and GE strategy, the reductions in the carbon emissions and total delay of passenger were optimal when the guidance speed was 39 km/h and the GE was 6 s, i.e. 27.49% and 38.62%, respectively. Under the guidance deceleration and RT strategy, the reductions in the carbon emissions and total delay of passenger were optimal when the guidance speed was 29 km/h and the RT was 6 s, i.e. 22.18% and 33.52%, respectively. The model reduced the carbon emissions and total delay of passenger in the upstream section of the intersection and the intersection control area to achieve the optimal overall traffic benefit for the intersection.

Two bus signal priority control strategies ­ green extension and red truncation ­ were studied.Carbon emission and delay calculation methods under the bus priority control were developed.Considering carbon-emission reductions of buses and social vehicles with different fuel types under different working conditions.Three control methods were studied: guidance acceleration, guidance acceleration and green extension, and guidance deceleration and red truncation.

Urban policy interventions to reduce traffic-related emissions and air pollution: A systematic evidence map.

BACKGROUND: Urban areas are hot spots for human exposure to air pollution, which originates in large part from traffic. As the urban population continues to grow, a greater number of people risk exposure to traffic-related air pollution (TRAP) and its adverse, costly health effects. In many cities, there is a need and scope for air quality improvements through targeted policy interventions, which continue to grow including rapidly changing technologies. OBJECTIVE: This systematic evidence map (SEM) examines and characterizes peer-reviewed evidence on urban-level policy interventions aimed at reducing traffic emissions and/or TRAP from on-road mobile sources, thus potentially reducing human exposures and adverse health effects and producing various co-benefits. METHODS: This SEM follows a previously peer-reviewed and published protocol with minor deviations, explicitly outlined here. Articles indexed in Public Affairs Index, TRID, Medline and Embase were searched, limited to English, published between January 1, 2000, and June 1, 2020. Covidence was used to screen articles based on previously developed eligibility criteria. Data for included articles was extracted and manually documented into an Excel database. Data visualizations were created in Tableau. RESULTS: We identified 7528 unique articles from database searches and included 376 unique articles in the final SEM. There were 58 unique policy interventions, and a total of 1,139 unique policy scenarios, comprising these interventions and different combinations thereof. The policy interventions fell under 6 overarching policy categories: 1) pricing, 2) land use, 3) infrastructure, 4) behavioral, 5) technology, and 6) management, standards, and services, with the latter being the most studied. For geographic location, 463 policy scenarios were studied in Europe, followed by 355 in Asia, 206 in North America, 57 in South America, 10 in Africa, and 7 in Australia. Alternative fuel technology was the most frequently studied intervention (271 times), followed by vehicle emission regulation (134 times). The least frequently studied interventions were vehicle ownership taxes, and studded tire regulations, studied once each. A mere 3 % of studies addressed all elements of the full-chain-traffic emissions, TRAP, exposures, and health. The evidence recorded for each unique policy scenario is hosted in an open-access, query-able Excel database, and a complementary interactive visualization tool. We showcase how users can find more about the effectiveness of the 1,139 included policy scenarios in reducing, increasing, having mixed or no effect on traffic emissions and/or TRAP. CONCLUSION: This is the first peer-reviewed SEM to compile international evidence on urban-level policy interventions to reduce traffic emissions and/or TRAP in the context of human exposure and health effects. We also documented reported enablers, barriers, and co-benefits. The open-access Excel database and interactive visualization tool can be valuable resources for practitioners, policymakers, and researchers. Future updates to this work are recommended. PROTOCOL REGISTRATION: Sanchez, K.A., Foster, M., Nieuwenhuijsen, M.J., May, A.D., Ramani, T., Zietsman, J. and Khreis, H., 2020. Urban policy interventions to reduce traffic emissions and traffic-related air pollution: Protocol for a systematic evidence map. Environment international, 142, p.105826.

The Role of Physician Advocacy in Supporting Policy Change That Reduces Leaded Aviation Gasoline Emissions.

BACKGROUND: Leaded aviation gasoline (AvGas) accounts for 70%, or 935,082 pounds, of total lead emissions in the United States and has been repeatedly linked to elevated blood lead levels (BLLs) in those living in the vicinity of airports using AvGas. The well-established link between lead exposure and adverse health outcomes provided a platform ripe for environmental health advocates and pediatric health experts to assist a local environmental health organization in addressing lead waste from a local airport, Montgomery-Gibbs Executive Airport (MYF). METHOD: We detail the steps we took, as a physician clean-air advocacy group. We provide a qualitative analysis of our efforts in addressing leaded air pollution through targeted and creative environmental health advocacy through three main avenues: government, public awareness, and academia. OBJECTIVES: Our actions were taken to ensure the City of San Diego installed an unleaded fuel tank at MYF to reduce leaded aviation gasoline usage and subsequently lead air pollution in the surrounding area. DISCUSSION: Ultimately, the identified objective of an unleaded fuel tank was added to the San Diego City budget and scheduled for construction. We hope our actions can serve as a framework to provide concrete steps for clinicians and other advocates to enact change in their communities.

Evaluating traffic emission control policies based on large-scale and real-time data: A case study in central China.

The traffic control policies, including "Odd and Even" (OAE) and "One Day Per Week" (ODPW), were adopted in Zhengzhou, China. In this study, we use the bottom-up policy evaluation framework to capture the temporal-spatial characteristics of traffic conditions and vehicle emissions under various traffic restriction scenarios. Moreover, we use the street-scale simulation model to evaluate the effectiveness of improving air quality. Results showed that the improvements in traffic conditions led to the emission decrease by about 28.3 % for carbon monoxide (CO), 16.2 % for nitrogen oxide (NOx), 21.3 % for particulate matter (PM2.5), and 23.2 % for total hydrocarbon (THC) under OAE. During ODPW, total vehicle emissions decreased by 14.1 % for CO, 10.2 % for NOx, 13.7 % for PM2.5, and 12.4 % for THC. However, the spatial analysis indicates traffic restrictions could not significantly reduce those emissions caused by high traffic volume; besides, buses, middle-duty trucks, and heavy-duty trucks have partly offset the reduction benefit from restrictions. The air quality simulation results reveal no significant concentration decrease of CO and nitrogen dioxide (NO2) in most areas. With the update of vehicles, stricter management of high-emission vehicles, and limited coverage for implementation of policies, the traffic control policies were not as effective as before. The limitations of the restriction policies are gradually prominent, and upgrade policies are urgently needed to continuously improve urban air quality in the future.

Advances in emission control of diesel vehicles in China.

Diesel vehicles have caused serious environmental problems in China. Hence, the Chinese government has launched serious actions against air pollution and imposed more stringent regulations on diesel vehicle emissions in the latest China VI standard. To fulfill this stringent legislation, two major technical routes, including the exhaust gas recirculation (EGR) and high-efficiency selective catalytic reduction (SCR) routes, have been developed for diesel engines. Moreover, complicated aftertreatment technologies have also been developed, including use of a diesel oxidation catalyst (DOC) for controlling carbon monoxide (CO) and hydrocarbon (HC) emissions, diesel particulate filter (DPF) for particle mass (PM) emission control, SCR for the control of NOx emission, and an ammonia slip catalyst (ASC) for the control of unreacted NH3. Due to the stringent requirements of the China VI standard, the aftertreatment system needs to be more deeply integrated with the engine system. In the future, aftertreatment technologies will need further upgrades to fulfill the requirements of the near-zero emission target for diesel vehicles.

NO2 levels inside vehicle cabins with pollen and activated carbon filters: A real world targeted intervention to estimate NO2 exposure reduction potential.

Traffic related nitrogen dioxide (NO2) poses a serious environmental and health risk factor in the urban environment. Drivers and vehicle occupants in general may have acute exposure to NO2 levels. In order to identify key controllable measures to reduce vehicle occupant's exposure, this study measures NO2 exposure inside ten different vehicles under real world driving conditions and applies a targeted intervention by replacing previously used filters with new standard pollen and new activated carbon cabin filters. The study also evaluates the efficiency of the latter as a function of duration of use. The mean in-vehicle NO2 exposure across the tested vehicles, driving the same route under comparable traffic and ambient air quality conditions, was 50.8 ± 32.7 µg/m3 for the new standard pollen filter tests and 9.2 ± 8.6 µg/m3 for the new activated carbon filter tests. When implementing the new activated carbon filters, overall we observed significant (p < 0.05) reductions by 87 % on average (range 80 - 94.2 %) in the in-vehicle NO2 levels compared to the on-road concentrations. We further found that the activated carbon filter NO2 removal efficiency drops by 6.8 ± 0.6 % per month; showing a faster decay in removal efficiency after the first 6 months of use. These results offer novel insights into how the general population can control and reduce their exposure to traffic related NO2. The use and regular replacement of activated carbon cabin air filters represents a relatively inexpensive method to significantly reduce in-vehicle NO2 exposure.

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With the development of high-density and high-rise buildings on both sides of the street, widespread attention has been paid to the applicability of the traditional greening model of 'the more trees, the better atmospheric environment' in dealing with air pollution in urban street canyons. Clarifying the characteristics of street canyons greening and its planting design pattern on the reduction of emission pollutants by vehicles is an important prerequisite for the improvement of air quality in the street canyons. Based on literature review, we compared the applicability and limitations of the three methods, including field observation, wind tunnel test, and numerical simulation. We further analyzed the effects of roadside trees and hedges on the dispersion and deposition of air pollutants, and put forward a framework of adaptive greening design for air quality improvement. Finally, we proposed that future studies should address the creation of graphic languages for roadside greening design, the development of technical guidelines for evaluating the exposure of air pollution, and the optimization of parameterization schemes for the physical processes of greening effect in computational fluid dynamics models. Overall, our review could provide ideas and reference for the subsequent research.

Computational fluid dynamics-based optimal installation strategy of air purification system to minimize NOX exposure inside a public bus stop.

At public bus stops, NOX pollutants discharged by regularly stopping buses quickly accumulate, exposing waiting passengers to high levels of air pollutants, which creates a threat to public health. The environmental protection agency (EPA) presents air quality standards for NOX, a significant pollutant that causes lung diseases such as asthma when exposed to the human body. To handle this problem, air purification systems are installed inside bus stops in many public places. However, it is challenging to maintain a low concentration of NOX inside public bus stops due to the persistent inflow of bus exhaust gas. Therefore, it is crucial to design an optimal location for an air purification system to meet air environment standards for respiratory areas. This study proposed a computational fluid dynamics (CFD)-based optimal installation strategy for an air purification system to minimize NOX exposure inside a public bus stop. The CFD model was developed to numerically analyze NO2 exposure with the actual design value for a public bus stop in Ulsan, South Korea. The local NO2 concentration was evaluated in the human breathing zone. The case study was performed according to the locations of the inlet and outlet of the air purification system. A transient CFD simulation was performed to analyze the effect of the air purification system on pollutants generated from the stationary bus by time flow in various cases. NO2 concentration and exposure reduction effectiveness (ERE) were analyzed and compared for each case in the breathing zone. In the optimal case, the ERE of NO2 was confirmed to be 35.9 %, and the NO2 concentration according to the air quality standards of EPA could be maintained at 0.1 ppm or less. The theoretical framework proposed in this study can be generalized to design air purification systems for general external facilities.

Effective emissions reduction of high-mileage fleets through a catalytic converter and oxygen sensor replacement program.

High-mileage vehicles such as taxis make disproportionately large contributions to urban air pollution due to their accelerated engine deterioration rates and high operation intensities despite their small proportions of the total fleet. Controlling emissions from these high-mileage fleets is thus important for improving urban air quality. This study evaluates the effectiveness of a pilot repair program in reducing emissions from taxis in Hong Kong which account for about 2 % of the total licensed vehicles. The emission factors of a large sample of 684 in-service taxis (including 121 for an emission survey program and 563 for a pilot repair program) were measured on transient chassis dynamometers. The results showed that 63 % of the sampled taxis failed the driving cycle test before the pilot repair program. Most of failed taxis were NO related and 91 % of failed taxis exceeded the emission limits of at least two regulated pollutants simultaneously. After the pilot repair program by replacing catalytic converters and oxygen sensors, the failure rate was significantly reduced to only 7 %. In addition, the fleet average NO, HC and CO emission factors were reduced by 85 %, 82 % and 56 %, respectively. In addition, on-road remote sensing measurements confirmed the real-world emission reductions from the taxis that participated in the pilot repair program. These findings led to the implementation of a large-scale replacement program for all taxis in Hong Kong during 2013-2014, which was estimated to have reduced the total HC, CO and NO emissions by about 420, 2570 and 1000 t per year, respectively (equivalent to 5-8 % emission reductions from the whole road transport sector). Therefore, reducing emissions from the small high-mileage fleets is a highly cost-effective measure to improve urban air quality.

A prospective study to evaluate CO2 emission mitigation strategies for highway transportation.

Ranking as one of the largest mobility modes for passengers and freight, highway transportation globally accounts for huge amounts of fossil-based energy consumption and greenhouse gas emissions. Correspondingly, on-road transportation causes detrimental effects on air quality, climate change, and global warming, particularly over the short term. In order to prevent a further escalation of this detrimental environmental issue, long-term efficacious policies aimed at reducing the transportation-driven CO2 emission should be urgently enacted and implemented on a global scale. Thus, this paper presents an exploratory study with the main objective of investigating the impact of four adopted mitigation scenarios that suggest switching to Euro 6 vehicle emission standards, increasing the average urban traffic speed limits, encouraging public transport, and increasing the proportion of hybrid electric vehicles. This study then compared and contrasted each strategy and its subgroups with a reference scenario projected for the year 2025. The evidence from this research showed that transition to Euro 6 compliant vehicles significantly decarbonizes the transportation sector, yet more vehicle electrification is required to achieve the Paris Climate Agreement targets. The results also indicate that by 2025, a 10% shift from passenger cars to public transport will decrease CO2 emissions by 3%, whilst increasing the urban traffic speed by 10 km/h will yield a 1.38% CO2 gas emission saving.

Study on Emission Characteristics and Emission Reduction Effect for Construction Machinery under Actual Operating Conditions Using a Portable Emission Measurement System (Pems).

With the acceleration of urban construction, the pollutant emission of non-road mobile machinery such as construction machinery is becoming more and more prominent. In this paper, a portable emissions measurement system (PEMS) tested the emissions of eight different types of construction machinery under actual operating conditions and was used for idling, walking, and working under the different emission reduction techniques. The results showed that the pollutant emission of construction machinery is affected by the pollutant contribution of working conditions. According to different emission reduction techniques, the diesel oxidation catalyst (DOC) can reduce carbon monoxide (CO) by 41.6-94.8% and hydrocarbon (HC) by 92.7-95.1%, catalytic diesel particulate filter (CDPF) can reduce particulate matter (PM) by 87.1-99.5%, and selective catalytic reduction (SCR) using urea as a reducing agent can reduce nitrogen oxides (NOx) by 60.3% to 80.5%. Copper-based SCR is better than vanadium-based SCR in NOx reduction. In addition, the study found that when the enhanced 3DOC + CDPF emission reduction technique is used on forklifts, DOC has a "low-temperature saturation effect", which will reduce the emission reduction effect of CO and THC. The use of Burner + DOC + CDPF emission reduction techniques and fuel injection heating process will increase CO's emission factors by 3.2-3.5 and 4.4-6.7 times compared with the actual operating conditions.