Regulating light-duty vehicle emissions: an overview of US, EU, China and Brazil programs and its effect on air quality

Improving spatial disaggregation of vehicular emission inventories

Precise estimates of vehicular emissions at fine spatial scales are essential for effective emission reduction strategies. Achieving high-resolution vehicular emission inventories necessitates detailed data on traffic flow, driving patterns, and vehicle speeds for each road network segment. However, in developing countries, the lack of comprehensive traffic data, limited infrastructure, and insufficient monitoring systems constrains the development of high-resolution inventories. This gap poses significant challenges for accurately quantify emissions in regions that often experience rapid urbanisation and traffic growth. Here, we propose a novel method to enhance the spatial disaggregation of large-scale vehicular emission inventories. By analysing road-level emissions data from 63 Brazilian municipalities, we developed a model that predicts weighting factors to disaggregate vehicular emissions into a gridded format, based on the proportion of primary road lengths. Our findings indicate that the predicted weighting factors significantly improve the spatial disaggregation of vehicular emissions compared to the traditional road density method by reasonably increasing the emissions in high vehicular activity areas. This approach not only provides more accurate representations of vehicular emissions for urban planning in Brazil but also offers a solution that can be adapted to enhance top-down vehicular emissions inventories globally. Our study offers a valuable tool that can be tailored to various regions, enabling more precise urban planning and policy-making for air quality management worldwide.

Emission performance evaluation of urban passenger car fleet through field investigation data in a megacity

Continued improvements in living standards and the economic well-being in the megacities have led to a huge surge in vehicular density. The worst environmental outcome of the same has been persistent unsafe urban air quality, thanks to vehicular emission. Further, the existing inspection and maintenance programs, conceived to check such emission remain largely ineffective, particularly in developing countries. This is due to the absence of a thorough assessment of the vehicle's compliance with the in-use emission norms generated through reliable field investigation data. To address this gap, the present comprehensive study collected real-time tailpipe emission data from 2040 cars in Delhi, India. Exhaust emission parameters, namely, CO (carbon monoxide), HC (hydrocarbon), and SE (smoke emission), were recorded from both petrol and diesel-driven cars of private ownership, in collaboration with the emission compliance test centers. The performance of cars was assessed in terms of their compliance with the in-use BS (Bharat Stage) emission norms. The one-of-its-kind study reported the petrol cars to be highly compliant toward the BS IV norm while faring even better toward BS II for both CO and HC emissions (80-90%). The conformance to the HC norm was found to be typically better than that for CO (85-90% versus 75-80%). For the diesel-driven cars, BS III compliance levels were reported relatively better compared to BS IV (90% in the case of the former against 80% in the latter's case). Further, the study puts forward a clear indication that the in-use emission norm and maintenance status of cars have a direct and negative relationship with tailpipe emission parameters. Cars of both overseas and domestic origin have almost equal degrees of compliance with the emission norms (over 80% in any case). The study recommends the incorporation of these two critical vehicular variables, i.e., maintenance status and in-use emission standard in the emission certification policy.

Direct measurement of brake and tire wear particles based on real-world driving conditions

With implementing vehicle emission control policies, tailpipe particulate emissions have been gradually controlled, and the relative contribution of non-tailpipe particulate emissions, such as brake and tire wear, has further increased. A unified and scientific method for sampling non-tailpipe particulate matter (PM) emissions is essential to improve the accuracy of the emission characteristics and factors. This study proposes a novel sampling method based on real-world driving conditions to obtain information on emissions and extract characteristic conditions for tire and brake pad wear. We extracted 200 representative braking segments for simulation experiments based on road type, initial and final velocities, temperature, and deceleration rate. Two standard test cycles to simulate the tire wear conditions of the front and rear wheels were constructed based on velocity, lateral, and vertical forces. Under the real-world driving condition test cycle, the emission factors of PM2.5 and PM10 for brake wear particles of passenger vehicles were 2.66 mg/km and 11.65 mg/km, respectively. In contrast, the emission factors of PM2.5 and PM10 for tire wear particles were 0.21 mg/km and 1.27 mg/km, respectively. Moreover, this study provides insights and basic data for localizing and improving the emission model, which can enhance its applicability and accuracy.

The impacts from cold start and road grade on real-world emissions and fuel consumption of gasoline, diesel and hybrid-electric light-duty passenger vehicles

Progressively stringent regulations regarding vehicle emissions and fuel economy have spurred technology diversification in light-duty passenger vehicles (LDPVs). To assess the real-world emissions and fuel economy performances of hybrid electric vehicles (HEVs) compared to conventional internal combustion engine (ICE) vehicles, on-road measurements of ten gasoline, four diesel and six full hybrid LDPVs were performed using portable emissions measurement systems (PEMS) in Macao, China. The hot-running emission results indicate that the high emission risks of gasoline vehicles are associated with high mileage and old model years. Diesel vehicles are found to be the highest pollutant emitters in this study due to the intentional removal of aftertreatment systems. Under hot-running conditions, HEVs, as expected, could achieve carbon-reduction benefits of approximately 30 % (i.e., lower CO₂ emissions and fuel consumption) compared to their conventional gasoline counterparts, while no measurable reduction in pollutant emissions was observed except in NO_X (~70 % reduction). In contrast, the cold-start extra emissions (CSEEs) of CO₂ reached 120-364 g/start for these HEVs, even exceeding the maximum values of conventional gasoline vehicles. However, the higher CO₂ CSEEs of HEVs can be far offset by their hot-running emission reduction benefits. For tailpipe pollutants, the CSEEs of the HEVs were reduced by 21 %-68 % on average in comparison to those of conventional gasoline vehicles. Furthermore, strong correlations (R² values of 0.69-0.89) between the road grades and relative emissions were observed. These results can provide necessary information regarding the improvement of future LDPV emission models and inventories.