Fuel Consumption and Traffic Emissions Evaluation of Mixed Traffic Flow with Connected Automated Vehicles at Multiple Traffic Scenarios

To analyze the impact of different proportions of connected automated vehicles (CAVs) on fuel consumption and traffic emissions, this paper studies fuel consumption and traffic emissions of mixed traffic flow with CAVs at different traffic scenarios. Firstly, the car-following modes and proportional relationship of vehicles in the mixed traffic flow are analyzed. On this basis, different car-following models are applied to capture the corresponding car-following modes. Then, Virginia Tech microscopic (VT-micro) model is adopted to calculate the instantaneous fuel consumption and traffic emissions. Finally, based on three typical traffic scenarios, a basic segment with bottleneck zone, ramp of the freeway, and signalized intersection, a simulation platform is built based on Python and SUMO to obtain vehicle trajectory data, and the fuel consumption and traffic emissions in different scenarios are obtained. The results show that (1) In different traffic scenarios, the application of CAVs can reduce fuel consumption and traffic emissions. The higher the penetration rate, the more significant the reduction in fuel consumption and traffic emissions. (2) In the three typical traffic scenarios, the advantages of CAVs are more evident in the signalized intersection. When the penetration rate of CAVs is 100%, the fuel consumption and traffic emissions reduction ratio is as high as 32%. It is noteworthy that the application of CAVs in urban transportation will significantly reduce fuel consumption and traffic emissions.

Source Apportionment and Source-specific Health Risk of Heavy Metals in Urban Road Dust of Jinan City, East China

For a better regional and source-risk-based control of heavy metals in urban environments, this study provides a source-specific health risk assessment by combining the models of United States Environmental Protection Agency health risk assessment and positive matrix factorization (PMF). The calculated data were optimized by the geochemical speciation of target 10 potentially toxic heavy metals. The results demonstrated that the mean concentrations of most heavy metals in urban dust of Jinan City exceeded their corresponding background values, especially that of cadmium (Cd) and zinc (Zn) exhibiting a mean of 12.9 and 7.84 times those of their backgrounds. Cd, Zn, copper, lead and manganese in road dust existed mainly in extractable forms, exhibiting higher bio-availability. The PMF receptor model determined four sources of heavy metals in urban road dust, namely industrial discharges (41.1%), natural and coal combustion sources (27.8%), traffic emissions (22.8%), and building material and manufacturing sources (8.3%). All the studied heavy metals presented low or negligible non-carcinogenic risk (non-CR) for adults and children, while the lifetime carcinogenic risk (CR) of Cd was in an acceptable level. Regarding source-specific health risks, the highest non-CR was derived from industrial discharges, while CR from traffic emissions, which were mainly associated with the higher content and bio-availability of Pb and Cd in the dust. Moreover, the risk contributions of industrial discharges and traffic emissions were 35.9% and 60.6% for non-CR and CR, respectively, presenting a significant difference with the apportioned source characteristics, thus deep-revealing the potentially source-based risks of heavy metal in urban environment.

Black carbon modeling in urban areas: investigating the influence of resuspension and non-exhaust emissions in streets using the Street-in-Grid model for inert particles (SinG-inert)

Black carbon (BC) is a primary and inert pollutant often used as a traffic tracer. Even though its concentrations are generally low at the regional scale, BC presents very high concentrations in streets (at the local scale), potentially with important effects on human health and the environment. Modeling studies of BC concentrations usually underestimate BC concentrations due to uncertainties in both emissions and modeling. Both exhaust and non-exhaust traffic emissions present uncertainties, but the uncertainties with respect to non-exhaust emissions, such as tire, brake, and road wear as well as particle resuspension, are particularly high. In terms of modeling, street models do not always consider the two-way interactions between the local and regional scales. Using a two-way modeling approach, a street with high BC concentrations may influence urban background concentrations above the street, which can subsequently enhance the BC concentrations in the same street. This study uses the multiscale Street-in-Grid model (SinG) to simulate BC concentrations in a suburban street network in Paris, taking the two-way coupling between local and regional scales into account. The BC concentrations in streets proved to have an important influence on urban background concentrations. The two-way dynamic coupling leads to an increase in BC concentrations in large streets with high traffic emissions (with a maximal increase of about 48 %) as well as a decrease in narrow streets with low traffic emissions and low BC concentrations (with a maximal decrease of about 50 %). A new approach to estimate particle resuspension in streets is implemented, strictly respecting the mass balance on the street surface. The resuspension rate is calculated from the available deposited mass on the street surface, which is estimated based on particle deposition and wash-off parameterizations adapted to street-canyon geometries. The simulations show that particle resuspension presents a low contribution to BC concentrations, as the deposited mass is not significant enough to justify high resuspension rates. Non-exhaust emissions, such as brake, tire, and road wear, may largely contribute to BC emissions, with a contribution that is equivalent to exhaust emissions. Here, a sensitivity analysis of BC concentrations is performed by comparing simulations with different emission factors of tire, brake, and road wear. The different emission factors considered are estimated based on the literature. We found a satisfying model–measurement comparison using high tire wear emission factors, which may indicate that the tire emission factors usually used in Europe are probably underestimated. These results have important policy implications: public policies replacing internal combustion engines with electric vehicles may not eliminate BC air pollution but only reduce it by half.

Reconstructing urban CO₂ emissions utilising the radiocarbon composition of tree rings from the Wellington Region, New Zealand

<p>This study demonstrates the utility of tree ring radiocarbon analysis to quantify a temporal record of recently-added fossil fuel-derived carbon dioxide (CO₂ff) in the urban atmosphere, to retrospectively measure emissions and potentially validate local emissions inventories. Currently, there is no internationally recognised method to test emissions inventories against direct atmospheric estimations of CO₂ff. With the increasing interest in emissions control legislation, independent and objective research to validate emissions reported by governments and industries is needed. As CO₂ff emissions are completely depleted in radiocarbon (¹⁴C), an observed decrease in the ¹⁴C content of the atmosphere is mostly due to additions of CO₂ff. As trees incorporate CO₂ from the local atmosphere into annual growth rings, it was hypothesised that an urban located tree would reflect emission rates of its local surroundings. Measurements of the ¹⁴C content of cellulose were made from the annual tree rings of a Kauri tree (Agathis australis), located in the downtown area of the Wellington suburb of Lower Hutt (KNG52). This record was compared with tree rings from two Kauri at a nearby coastal site (NIK19 and NIK23) and the long-term clean air ¹⁴CO₂ record from Baring Head. The clean air Kauri trees, NIK19 and NIK23, demonstrated excellent agreement with the Baring Head atmospheric record, indicating that the trees were accurately sampling the atmosphere. The KNG52 tree, demonstrated good agreement with the clean air record in the early part of the record (with some variability), however, exhibited significantly lower Δ¹⁴CO₂ values from the 1980s onward. Calculation of the influence of the terrestrial biosphere on the ¹⁴CO₂ record showed very little impact, determining that the variability seen was due to local additions of CO₂ff. Historic CO₂ff emissions were calculated using the Δ¹⁴CO₂ measurements from the KNG52 ¹⁴CO₂ record for the period 1972 – 2012. Biosphere correction calculations showed that the biosphere was the dominant influence on the record in the early part of the record (1972 – 1980), with fossil fuel emissions dominating the record from 1980s onward. The observations were compared qualitatively with meteorological data and urban development in the area to assess variability in CO₂ff. A minor trend towards lower wind speeds associated with higher levels of CO₂ff was identified, indicating that local meteorology may be responsible for 10% change seen in the record. The influence of local development demonstrated some possible relation but a correlation was not significant. The KNG52 CO₂ff record was compared with national-level reported liquid (road traffic) emissions from the Carbon Dioxide Information Analysis Centre (CDIAC). The observed KNG52 CO₂ff in the tree ring record appeared to increase in tandem with road traffic emissions.</p>

Reconstructing urban CO₂ emissions utilising the radiocarbon composition of tree rings from the Wellington Region, New Zealand

<p>This study demonstrates the utility of tree ring radiocarbon analysis to quantify a temporal record of recently-added fossil fuel-derived carbon dioxide (CO₂ff) in the urban atmosphere, to retrospectively measure emissions and potentially validate local emissions inventories. Currently, there is no internationally recognised method to test emissions inventories against direct atmospheric estimations of CO₂ff. With the increasing interest in emissions control legislation, independent and objective research to validate emissions reported by governments and industries is needed. As CO₂ff emissions are completely depleted in radiocarbon (¹⁴C), an observed decrease in the ¹⁴C content of the atmosphere is mostly due to additions of CO₂ff. As trees incorporate CO₂ from the local atmosphere into annual growth rings, it was hypothesised that an urban located tree would reflect emission rates of its local surroundings. Measurements of the ¹⁴C content of cellulose were made from the annual tree rings of a Kauri tree (Agathis australis), located in the downtown area of the Wellington suburb of Lower Hutt (KNG52). This record was compared with tree rings from two Kauri at a nearby coastal site (NIK19 and NIK23) and the long-term clean air ¹⁴CO₂ record from Baring Head. The clean air Kauri trees, NIK19 and NIK23, demonstrated excellent agreement with the Baring Head atmospheric record, indicating that the trees were accurately sampling the atmosphere. The KNG52 tree, demonstrated good agreement with the clean air record in the early part of the record (with some variability), however, exhibited significantly lower Δ¹⁴CO₂ values from the 1980s onward. Calculation of the influence of the terrestrial biosphere on the ¹⁴CO₂ record showed very little impact, determining that the variability seen was due to local additions of CO₂ff. Historic CO₂ff emissions were calculated using the Δ¹⁴CO₂ measurements from the KNG52 ¹⁴CO₂ record for the period 1972 – 2012. Biosphere correction calculations showed that the biosphere was the dominant influence on the record in the early part of the record (1972 – 1980), with fossil fuel emissions dominating the record from 1980s onward. The observations were compared qualitatively with meteorological data and urban development in the area to assess variability in CO₂ff. A minor trend towards lower wind speeds associated with higher levels of CO₂ff was identified, indicating that local meteorology may be responsible for 10% change seen in the record. The influence of local development demonstrated some possible relation but a correlation was not significant. The KNG52 CO₂ff record was compared with national-level reported liquid (road traffic) emissions from the Carbon Dioxide Information Analysis Centre (CDIAC). The observed KNG52 CO₂ff in the tree ring record appeared to increase in tandem with road traffic emissions.</p>

Optimisation of a Numerical Model to Simulate the Dispersion and Chemical Transformations Within the Oxides of Nitrogen/Ozone System as Traffic Pollution Enters an Urban Greenspace

Urban greenspace has many health benefits, including cleaner air than the surrounding streets. In this study, a detailed exercise has been conducted to measure concentrations of NO/NO2/NOx and O3 within an urban greenspace, the University of Birmingham campus, using continuous analysers, as well as transects of NO2 measured with diffusion tubes. Concentrations have been simulated using the ADMS-Roads model which has been optimised initially using NOx concentrations for traffic emissions on surrounding roads, background concentrations, and meteorological data considering four candidate sites. Optimisation for prediction of NO2 shows the critical importance of the NO2:NOx ratio in traffic emissions, for which a derivation from atmospheric measurements is consistent with a value derived from optimisation of the model fit to roadside data. After optimisation, the model gives an excellent fit to continuous data measured at roadside. Comparison of model predictions with transects of NO2 across the greenspace also show generally good model performance. The incorporation of dry deposition processes for the nitrogen oxides into the model leads to a reduction of less than 1% in predicted concentrations, leading to the conclusion that the cleaner air within urban greenspace is primarily the result of dispersion rather than deposition processes.