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Knowledge gap on the health impact of transportation-related emissions in cold climate cities

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About the project

The study's objectives were to understand the magnitude of increased emission rates of vehicles in cold climate cities, explore the impact of increased local air pollution and population exposure to air contaminants, and understand the relevant health impacts. The study was conducted within the concept of urban carrying capacity (UCC) and considered its relevance for Canadian cities. It answered how much scientific evidence supports the reduced UCC related to transportation emission in a cold climate. Identifying the interdisciplinary knowledge gap was one of the critical elements of the study.

UCC includes a wide range of parameters such as air, water, recycling and energy. Many studies looked at the air quality aspect of UCC, and models are available to analyze the impact of technologies and policies on the air quality element of UCC. However, no study has focused on the relationship between UCC and air quality in cold climate regions. Among limited studies on cold climate transportation emissions, a few of them indicated changes of emission factors at -7°C. No analysis was found for impacts of the ambient temperature of below -7°C on vehicle emissions. Overall, the combined relationships among cold temperatures, pollution and related health outcomes are underinvestigated.

Key findings

Many reviewed studies described short-term health outcomes, testing associations between pollution and health outcomes after controlling for temperatures. Only a few studies formally explored the complex modifying effect of cold temperatures on pollution levels and health outcomes. Few papers identified that cold temperatures aggravated the health impact of pollutants like O3, PM2.5, PM10 and CO — for example, their association with increased cardiovascular disease and mortality in the cold seasons.

Specific findings:

  • Vehicular emissions: Several factors cause the effects of cold weather on vehicle emissions. The influential factors are categorized into three groups: (a) vehicle technology, (b) driving and use behaviour and (c) vehicle calibration in connection with target emission regulations. In the vehicle technology, the compromised performance of the vehicle exhaust filtration system due to cold temperature, poor fuel vaporization and mixing, increased engine friction, lube oil degradation, and low conversion efficiency of not sufficiently warm exhaust after-treatment systems of vehicles are influential parameters. Hybrid electric vehicles also suffer from high tailpipe emissions if the powertrain does not often use the engine, causing an even colder exhaust system than that of conventional vehicles. As the regulation does not require vehicle emission testing below -7°C, and even that is not needed in many engines and vehicle classes, the engine and exhaust after-treatment control units may not be strictly calibrated for emission reduction below the legislation threshold of -7°C. These factors can cause up to 10 times more harmful vehicular emissions (HC, CO, NOx, particles) in cold climate, depending on ambient temperature, vehicle technology, cold climate vehicle calibration and trip duration.
  • Human behaviour: Drivers in a cold climate often use more idling time for vehicle warmup and cabin heating, leading to high tailpipe emissions. Vehicle tampering is another factor. Lack of regular emission testing and enforcement has caused exhaust tampering and removal of filtration systems, particularly in cold climate environments when using filters is problematic. These significantly degrade the emission performance of conventional and hybrid electric vehicles in cold temperatures.
  • Health effects: The studied health outcomes in this context included a variety of diseases and symptoms. Some of the health outcomes reported were directly associated with the cold season, implying the seasonality of diseases and increased health vulnerability in the cold season, regardless of pollution. Season modifies the short-term effects of air pollution on morbidity. However, the combined associations between warm/cold seasons, pollutants and health outcomes were seldom identifiable in the literature. Mostly, seasonal relationships were found while removing effects of temperature, suggesting that other co-existing characteristics may impact health besides the temperature. Nevertheless, their impact has not been studied. This represents a clear gap in our understanding of the impact of cold temperatures on pollution and related health outcomes.

Policy implications

The study found many possible policy implications. These include expansion of vehicle emission testing protocols in the emission regulations to lower temperatures suitable for Canadian cities, increased in-use vehicle emission testing in cold regions and enforcement to reduce exhaust tampering. As well, use of remote sensing technologies and portable emission testing of real-world driving emissions in a cold climate could be part of market surveillance of vehicle technologies performance in a cold environment.

Future research needs include:

  1. Measurement and quantification of cold climate impact on vehicle technologies and vehicle emission profile;
  2. Public exposure to vehicle emissions in a cold climate;
  3. Policy recommendation for vehicle emission regulations in Canada under cold climate operation;
  4. Integrated UCC and air pollution modelling for cold climate;
  5. Chemical characterization of vehicle emissions and air pollutants in a cold climate to assess health impacts.

Further information

Read the full report

Contact the researchers

Mahdi Shahbakhti, Associate Professor, Faculty of Engineering, University of Alberta;

Alvaro Osornio-Vargas, Professor, Faculty of Medicine & Dentistry, University of Alberta;

Vahid Hosseini, Associate Professor, School of Sustainable Energy Engineering, Simon Fraser University;

The views expressed in this evidence brief are those of the authors and not those of SSHRC, NSERC, CIHR and the Government of Canada

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