Bus commuter exposure and the impact of switching from diesel to biodiesel for routes of complex urban geometry

Characterizing sector-oriented roadside exposure to ultrafine particles (PM0.1) via machine learning models: Implications of covariates influences on sectors variability

Ultrafine particles (UFPs; PM0.1) possess intensified health risk due to their smaller size and unique spatial variability. One of major emission sources for UFPs is vehicle exhaust, which varies based on the traffic composition in each type of roadside sector. The current challenge of epidemiological UFPs study is limited characterization ability due to expensive instruments. This study assessed the UFPs particle number concentrations (UFPs PNC) exposure dose for typical healthy adults and children at three different roadside sectors, including industrial roadside (IN), residential roadside (RS), and urban background (UB). Furthermore, this study also developed and utilized machine learning (ML) algorithms that could accurately characterize the UFPs exposure dose and explain the covariates effects on the model outputs, representing the intra-urban variability of UFPs between sectors. It was found that the average inhaled UFPs dose for healthy adults and children during off-peak season (warm period) were 1.71 ± 0.19 × 1010; 1.28 ± 0.22 × 1010; 1.09 ± 0.18 × 1010 #/hour and 1.33 ± 0.15 × 1010; 0.99 ± 0.17 × 1010; 0.86 ± 0.14 × 1010 #/hour at IN, RS, UB. Inhaled UFPs were mainly deposited in tracheobronchial (TB) respiratory fraction for adults (67.7%) and in alveoli (ALV) fraction for children (67.5%). Among three ML algorithms implemented in this study, XGBoost possessed the highest UFPs PNC exposure dose estimation performances with R2 = 0.965; 0.959; 0.929 & RMSE = 0.79 × 108; 0.54 × 108; 0.15 × 105 #/hour at IN, RS, and UB which then followed by multiple linear regression (MLR), and random forest (RF). Furthermore, SHAP analysis from the XGBoost model has successfully pointed out the spatial variability of each roadside sector by quantifying the approximated contributions of covariates to the model's output. Findings in this study highlighted the potential use of ML models as an alternative for preliminary particle exposure source apportionment.

Implications of fuel poverty for indoor black carbon concentrations from space heating

Despite the global transition towards cleaner energy sources observed over the last decade, disparities in access persist worldwide. The dependence on biomass for household heating exacerbates fuel poverty, as economically vulnerable households face challenges in obtaining certified firewood and often resort to using contaminated biomass as a substitute, either partially or completely. We examined black carbon (BC) particle concentrations -a marker for combustion- during wood stove operation through a five-day case study in a typical Chilean household. BC increased rapidly following the ignition of the stove, with the combustion of dry Eucalyptus globulus logs yielding a substantially lower peak (5.29 μg/m3) than when using unclean biomass: 35.75 μg/m3 with demolition wood and painted furniture, and 87.11 μg/m3 with the addition of a blend of particleboard with polystyrene foam. During the latter two events, BC particles remained indoors for about 20 h before the concentrations reverted to pre-spike levels. The slow decay in BC concentrations was further influenced by the infiltration of outdoor air. The mean indoor BC concentrations were comparable to or even exceeded those observed on busy roads in major cities worldwide. These results highlight the risks associated with limited access to clean fuels for indoor heating, alongside inadequate insulation. This study sheds light on the problem of fuel poverty and its adverse effects on health and well-being.

Assessment of PM2.5 Concentration at University Transit Bus Stops Using Low-Cost Aerosol Monitors by Student Commuters

Particulate matter of 2.5 µm and smaller (PM2.5) is known to cause many respiratory health problems, such as asthma and heart disease. A primary source of PM2.5 is emissions from cars, trucks, and buses. Emissions from university transit bus systems could create zones of high PM2.5 concentration at their bus stops. This work recruited seven university students who regularly utilized the transit system to use a low-cost personal aerosol monitor (AirBeam) each time they arrived at a campus bus stop. Each participant measured PM2.5 concentrations every time they were at a transit-served bus stop over four weeks. PM2.5 concentration data from the AirBeam were compared with an ADR-1500 high-cost monitor and EPA PM2.5 reference measurements. This methodology allowed for identifying higher-than-average concentration zones at the transit bus stops compared to average measurements for the county. By increasing access to microenvironmental data, this project can contribute to public health efforts of personal protection and prevention by allowing individuals to measure and understand their exposure to PM2.5 at the bus stop. This work can also aid commuters, especially those with pre-existing conditions who use public transportation, in making more informed health decisions and better protecting themselves against new or worsening respiratory conditions.

Long-term trends of black carbon and particle number concentrations and their vehicle emission factors in Stockholm

Black carbon (BC) and particle number (PN) concentrations are usually high in cities due to traffic emissions. European mitigation policies, including Euro emission standards, have been implemented to curb these emissions. We analyzed BC and PN (particle diameter Dp > 4 nm) concentrations in Stockholm spanning the years 2013-2019 (BC) and 2009-2019 (PN) measured at street canyon and rooftop sites to assess the effectiveness of the implemented policies. Combining these data with inverse dispersion modeling, we estimated BC and PN emission factors (EFBC and EFPN) for the mixed fleet, reflecting real-world driving conditions. The pollutants showed decreasing trends at both sites, but PN concentrations remained high at the canyon site considering the World Health Organization (WHO) recommendations. BC concentrations declined more rapidly than PN concentrations, showing a -9.4% and -4.9% annual decrease at the canyon and -7.2% and -0.5% at the rooftop site in the years 2013-2019. The EFBC and EFPN trends showed that the mitigation strategies for reducing particulate emissions for on-road vehicles were successful over the study period. However, the introduction of biofuels in the vehicle fleet -ethanol and later rapeseed methyl ester (RME)- increased the concentrations of particles with Dp < 10 nm before the adoption of particulate filters in the exhausts. Stricter Euro emission regulations, especially with diesel particulate filters (DPF) in Euro 5, 6, and VI vehicles, led to 66% decrease in EFBC and 55% in EFPN. Real-world EFBC surpassed HBEFA (Handbook Emission Factors for Road Transport) database values by 2.4-4.8 times; however, direct comparisons between real-world and HBEFA EFPN are difficult due to differences in lower cut-off sizes and measurement techniques. Our results underscore the necessity for revising the HBEFA database, updating laboratory testing methods and portable emission measuring systems (PEMS) measurements to account for liquid condensate contributions to PN measurements.

Relative contributions of ambient air and internal sources to multiple air pollutants in public transportation modes

Commuters are often exposed to relatively high air pollutant concentrations in public transport microenvironments (TMEs) because of their proximity to emission sources. Previous studies have mainly focused on assessing the concentrations of air pollutants in TMEs, but few studies have distinguished between the contributions of ambient air and internal sources to the exposure of commuters to air pollutants. The main objective of this study was to quantify the contributions of ambient air and internal sources to the measured particulate matter and gaseous pollutant concentrations in selected TMEs in Hong Kong, a high-rise, high-density city in Asia. A sampling campaign was conducted to measure air pollutant concentrations in TMEs in Hong Kong in July and November 2018 using portable air quality monitors. We measured the concentrations of each pollutant in different TMEs and quantified the infiltration of particulate matter into these TMEs. The double-decker bus had the lowest particulate matter concentrations (mean PM1, PM2.5, and PM10 concentrations of 5.1, 9.5, and 13 μg/m3, respectively), but higher concentrations of CO (0.9 ppm), NO (422 ppb), and NO2 (100 ppb). For all the TMEs, about half of the PM2.5 were PM1 particles. The Mass Transit Railway (MTR) subway system had a PM2.5/PM10 ratio of about 0.90, whereas the PM2.5/PM10 ratio was about 0.60-0.70 for the other TMEs. The MTR had infiltration factor estimates <0.4 for particulate matter, lower than those of the double-decker bus and minibus. The MTR had the highest contribution from internal sources (mean PM1, PM2.5, and PM10 concentrations of 4.6, 13.4, and 15.8 μg/m3, respectively). This study will help citizens to plan commuting routes to reduce their exposure to air pollution and help policy-makers to prioritize effective exposure reduction strategies.

Reduced commuter exposure to PM2.5 and PAHs in response to improved emission standards in bus rapid transit systems in Mexico

We evaluated impacts of progressive technological updates to bus rapid transit (BRT) systems on in-cabin concentrations of particulate matter with an aerodynamic diameter ≤2.5 μm (PM2.5), and the various polyaromatic hydrocarbons (PAHs) to which commuters were exposed. PM2.5 samples were collected and real-time concentrations measured from October 2017 to March 2020 inside cabins of BRT buses equipped with Euro IV, V and VI diesel emission standards in the Mexico City Metropolitan Area (MCMA). For effective comparison, similar samplings and measurements were carried out on trains in the MCMA underground (MCU) system. Peak in-cabin PM2.5 concentrations decreased significantly (p < 0.05) by 35% from Euro IV to Euro V buses, and by 80% from Euro IV to Euro VI buses. PM2.5 concentrations inside Euro VI buses were significantly lower (p < 0.05) than in Euro IV and Euro V buses and in underground trains. The in-cabin excess (ICE) of PM2.5 relative to ambient concentrations was significantly (p < 0.05) higher for Euro IV than for Euro V buses during morning the traffic peak, and consistently higher than for Euro VI buses. Indeed, ICEs calculated for Euro VI buses were always lower than those for electricity-powered underground trains. The frequency of hotspots decreased from Euro IV to Euro VI buses due to the combined effect of low emissions and closed, air-conditioned cabins. Concentrations of total PAHs including carcinogenic species also decreased from Euro IV to Euro V buses and were below limits of detection aboard Euro VI buses. This work shows that in real-life conditions, advanced diesel technologies and cabin design significantly reduce commuters' exposure to PM2.5 and to toxic PAH compounds.

Enhanced diesel emissions at low ambient temperature: hazardous materials in fine particles

The emission of fine particles (PM_2.5) from diesel trucks is enhanced by low ambient temperatures, which is a fact that has attracted considerable attention. Carbonaceous matter and polycyclic aromatic hydrocarbons (PAHs) are the dominant hazardous materials in PM_2.5. These materials induce severe adverse effects on air quality and human health and contribute to climate change. The emissions from heavy- and light-duty diesel trucks were tested at an ambient temperature of - 20 to - 13 ℃ and 18-24 ℃. This is the first study to quantify the enhanced carbonaceous matter and PAH emissions from diesel trucks at very low ambient temperatures based on an on-road emission test system. Features affecting diesel emissions, including driving speed, vehicle type, and engine certification level, were considered. The emissions of organic carbon, elemental carbon, and PAHs significantly increased from - 20 to - 13 ℃. The empirical results revealed that intensive abatement of diesel emissions at low ambient temperatures could benefit human health and have a positive influence on climate change. Considering the widespread applications worldwide, an investigation into diesel emissions of carbonaceous matter and PAHs in fine particles at low ambient temperatures is urgently required.

Commuter's personal exposure to air pollutants after the implementation of a cable car for public transport: Results of the natural experiment TrUST

Commuters in urban settlements are frequently exposed to high concentrations of air pollutants due to their proximity to mobile sources, making exposure to traffic-related air pollutants an important public health issue. Recent trends in urban transport towards zero- and low-tailpipe emission alternatives will likely result in decreased exposure to air pollutants. The TrUST (Urban transformations and health) study offers a unique opportunity to understand the impacts of a new cable car (TransMiCable) in underserved communities within Bogotá, Colombia. The aims of this study are to assess the personal exposure to fine particulate matter (PM_2.5), equivalent Black Carbon (eBC), and Carbon Monoxide (CO) in transport micro-environments and to estimate the inhaled dose per trip during mandatory multimodal trips before and after the implementation of the TransMiCable. We collected personal exposure data for Bus-Rapid-Transit (BRT) feeder buses, regular buses, informal transport, pedestrians, and TransMiCable. TransMiCable showed lower exposure concentration compared to BRT feeder and regular buses (PM_2.5: 23.6 vs. 87.0 μg m^-3 (P ≤ 0.001) and eBC: 5.2 vs. 28.2 μg m^-3 (P ≤ 0.001), respectively). The mean concentration of PM_2.5 and eBC inside the TransMiCable cabins were 62 % and 82 % lower than the mean concentrations in buses. Furthermore, using a Monte Carlo simulation model, we found that including the TransMiCable as a feeder is related to a 54.4 μg/trip reduction in PM_2.5 inhaled dose and 35.8 μg/trip in eBC per trip. Those changes represent a 27 % and 34 % reduction in an inhaled dose per trip, respectively. Our results show that PM_2.5, eBC, and CO inhaled dose for TransMiCable users is reduced due to lower exposure concentration inside its cabins and shorter travel time. The implementation of a cable car in Bogotá is likely to reduce air pollution exposure in transport micro-environments used by vulnerable populations living in semi-informal settlements.

Toward Cleaner Transport Alternatives: Reduction in Exposure to Air Pollutants in a Mass Public Transport

Commuters are often exposed to higher concentrations of air pollutants due to its proximity to mobile sources. Despite recent trends in urban transport toward zero- and low-tailpipe emission alternatives, the assessments of the impact of these transformations on commuter exposure are limited by the low frequency of such studies. In this work, we use a unique data set of personal exposure concentration measurements collected over the span of 5 years to analyze changes due to the introduction of a new fleet for Bogotá's Bus Rapid Transit System. In that system, over a thousand Euro-II and -III diesel-powered buses were replaced with Euro-VI compressed natural gas and filter-equipped Euro-V diesel buses. We measured personal exposure concentrations of equivalent black carbon (eBC), fine particulate (PM_2.5), and ultra fine particles (UFP) during and after the retirement of old buses and the introduction of new ones. Observations collected prior to the fleet renewal were used as baseline and later compared to data collected over two follow-up campaigns in 2019 and 2020. Significant reductions in the concentration of PM_2.5 and eBC were observed during the 2019 campaign, with a 48% decrease for mean in-bus eBC (89.9 to 46.4 μg m^-3) and PM_2.5 (180.7 to 95.4 μg m^-3) concentrations. Further reductions were observed during the 2020 follow-up, when the fleet renovation was completed, with mean in-bus eBC decreasing to 17.7 μg m^-3 and PM_2.5 to 42.3 μg m^-3. These observations imply nearly a 5-fold reduction in eBC exposure and a 4-fold decrease in PM_2.5. There was a much smaller reduction of in-bus UFP concentration between 2019 and 2020, indicating a persistent presence of high particle number concentrations in the near-road environment despite the fleet renovation process. In-bus UFP concentrations ranged between 65 000 and 104 500 cm^-3 during the follow-up campaigns. The results in this work illustrate the immediate benefits of reducing personal exposure through the adoption of vehicles with more stringent emission standards.

Analysis of cold-start NO2 and NOx emissions, and the NO2/NOx ratio in a diesel engine powered with different diesel-biodiesel blends

In the transportation sector, the share of biofuels such as biodiesel is increasing and it is known that such fuels significantly affect NOx emissions. In addition to NOx emission from diesel engines, which is a significant challenge to vehicle manufacturers in the most recent emissions regulation (Euro 6.2), this study investigates NO₂ which is a toxic emission that is currently unregulated but is a focus to be regulated in the next regulation (Euro 7). This manuscript studies how the increasing share of biofuels affects the NO₂, NOx, and NO₂/NOx ratio during cold-start (in which the after-treatment systems are not well-effective and mostly happens in urban areas). Using a turbocharged cummins diesel engine (with common-rail system) fueled with diesel and biofuel derived from coconut (10 and 20% blending ratio), this study divides the engine warm-up period into 7 stages and investigates official cold- and hot-operation periods in addition to some intermediate stages that are not defined as cold in the regulation and also cannot be considered as hot-operation. Engine coolant, lubricating oil and exhaust temperatures, injection timing, cylinder pressure, and rate of heat release data were used to explain the observed trends. Results showed that cold-operation NOx, NO₂, and NO₂/NOx ratio were 31-60%, 1.14-2.42 times, and 3-8% higher than the hot-operation, respectively. In most stages, NO₂ and the NO₂/NOx ratio with diesel had the lowest value and they increased with an increase of biofuel in the blend. An injection strategy change significantly shifted the in-cylinder pressure and heat release diagrams, aligned with the sudden NOx drop during the engine warm-up. The adverse effect of cold-operation on NOx emissions increased with increasing biofuel share.

Selected Aspects of Sustainable Mobility Reveals Implementable Approaches and Conceivable Actions

The transportation sector plays a prominent role in driving the economy of any given nation. However, with the recent tensions arising in and around the transportation sector, sustainable mobility concepts have evolved. However, it is quite unclear whether sustainable mobility is feasible and exhibits economic returns, environmental benefits, and societal advantages. Hence, taking into account the environmental, economic, and social impact, and technical possibilities, this study intends to analyse sustainable mobility in relation to economic returns, environmental benefits and societal advantages using bibliometric analysis. For this study, we considered two decades of research, from 2001 to 2021. An in-depth search was performed on articles generated in the last two decades to assess the state of the literature on sustainable mobility. The most reverent, frequently referenced papers and influential journals in the field of sustainable mobility were identified. The acquired findings highlight the most prominent publications, journals, and authors who have made significant contributions to sustainable mobility studies, as well as the sub-areas or themes linked to sustainable mobility. Overall, the analysis discovered current paradigms, significant research topics, and a relationship between the domains of sustainable mobility studies. Meanwhile, this study also demonstrates advancements in the primary themes and sub-areas during the previous 20 years and alterations in future research fields. In addition, this study identified the promotion of rapid-reliable-safe-convenient (RRSC) transportation services, reduction in urban car traffic, and support to low transportation demand as the critical steps that require immediate attention in order to build a sustainable mobility future. We also observed that hydrogen would be a promising fuel and potential technology for the future mobility sector in the post-COVID era.

Effects of the implementation of a mass rapid transit system on mortality rates attributed to cardiorespiratory complications in Taipei

Although Taipei City has encountered a fall in ambient air pollutant levels since 1996, the year its mass rapid transit (MRT) system commenced operation, no apparent study investigated changes in risks of death attributed to respiratory, cardiovascular, and cerebrovascular diseases in Taipei during this 23-year period. In order to examine the relationship between MRT and occurrence of respiratory and cardiovascular illnesses attributed to air contaminants, exposure over the 23 year duration was subdivided into the following periods: reference period 1 (1992-1995); period 2 (1996-2004), a time when there was a total track length of 67 km; period 3 (2005-2015), when the total track length was lengthened to 131.1 km; and period 4 (2016-2020), when it was further extended to 146.2 km. Taichung City, no MRT system, was used as an external reference population. The effect of Taipei's MRT system on rates of cause-specific death rates was analyzed using robust generalized Poisson regression models. After adjusting for age-standardized rates (ASRs), a decrease in relative risks (RRs) was found for non-trauma death and respiratory disease from periods 2 to 4. Even though the RRs were greater than 1.0 for cardiovascular and cerebrovascular diseases for periods 2 to 4, a downward trend was still noted in these RRs in Taipei. These findings suggest a relationship exists between air pollutant exposure and mortality. In addition, data demonstrated that implementation of the MRT in Taipei exerted beneficial health effects as evidenced by lower mortality rates.

Energy Saving and CO2 Reduction Potential from Partial Bus Routes Reduction Model in Bangkok Urban Fringe

Bus networks in many capital cities are long distances and partially overlapping with each other. As a result, waiting time is high and energy consumption efficiency is poor. Bus operators in many countries tried to reform their bus routes to reduce waiting time and fuel costs by reducing overlapping bus routes. However, most of the reformed bus routes were complicated, which caused discomfort to passengers to use the bus service. To overcome this problem, this study proposed a new bus reformed model called the Partial Bus Routes Reduction in Urban Fringe Model (PBRU) which was a simple and passenger-friendly route operation. It resulted in 14% of total inbound and 16% of total outbound passengers receiving the benefit of waiting time reduction. Most passengers wait twice at the resident bus-stop and transfer point. As a result, the overall waiting time increased by 0.72–3.75 min. The reduction of fuel consumption was consistent with increasing load factors and dependent on the time period. The bus reform operations during the off-peak hours had more benefits in terms of waiting time reduction, energy-saving potential, and CO2 reduction than during the rush hours.