Kiera Jefferson
Vehicular pollution is a pressing issue, with the road transport sector being a major contributor to emissions of greenhouse gases and air pollution. Motor vehicle exhausts produce greenhouse gases, such as carbon dioxide, nitrous oxide, and methane, which contribute to climate change. Additionally, vehicles emit pollutants such as carbon monoxide (CO), nitrogen dioxide (NO2), particulate matter (PM), and volatile organic compounds (VOCs), which have harmful effects on human health, including respiratory and cardiovascular diseases, and an increased risk of cancer. To address this issue, it is crucial to measure vehicular pollution accurately. There are several methods available to measure vehicle emissions, including laboratory tests, remote sensing, and in-vehicle measurements. These techniques vary in their advantages and limitations, and the choice of method depends on factors such as cost, practicality, and the range of pollutants measured.
| Characteristics | Values |
|---|---|
| Pollutants | Carbon monoxide (CO), nitrogen dioxide (NO2), particulate matter (PM) such as PM 2.5 and ultrafine particles (UFP), volatile organic compounds (VOCs), nitrous oxide, methane, benzene, acrolein, polybrominated diphenyl ethers (PBDEs) |
| Pollutant sources | Vehicle exhaust, off-gassing from materials inside the vehicle, engine, gas tank, and hoses |
| Measurement methods | Portable Emissions Measurement System (PEMS), Remote Emission Sensing (RES), Remote sensing, dynamometer |
| Standards | Euro 5, Euro 6, New European Driving Cycle (NEDC) |
| Testing procedures | Pre-defined speed-time pattern (driving cycle), laboratory testing, real-world driving conditions, remote sensing |
| Results | Pollutant levels inside vehicles were higher than those measured at ambient monitoring stations |
| Health effects | Respiratory and cardiovascular diseases, increased risk of cancer |
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What You'll Learn
Remote sensing
An on-road measurement campaign was conducted in Brisbane, Australia, where three locations were selected to represent different types of adjoining land use and driving behaviour: a freeway on-ramp, a heavily trafficked urban road, and a commercial road in an industrial area. The study aimed to improve the RSD capture rate, high emitter detection, and cold start detection. By supplementing RSD equipment with additional measurement devices, the capture rate of high-emitting vehicles increased by almost 10%.
A dual RS technique has been developed to increase the accuracy of identifying high-emitting vehicles. This technique involves placing two RS systems at a 1-second separation distance under the average driving speed of a given measurement site. Only vehicles that emit pollutants exceeding the cut points at both upstream and downstream RS systems simultaneously are considered high emitters.
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Portable Emissions Measurement System (PEMS)
PEMS is simple and inexpensive to purchase and maintain compared to a chassis dynamometer. Its limitations include relatively heavy and bulky equipment that adds extra weight to the vehicle mass, as well as a limited range of pollutants measured during the test compared to a laboratory test. PEMS instrumentation is also subject to measurement uncertainties and is affected by ambient conditions (e.g. temperature, altitude, vibrations) during real-world driving, making it challenging to ensure repeatability in testing results.
PEMS has been used by governmental agencies like the United States Environmental Protection Agency (USEPA) and various states and private entities to reduce the costs and time involved in making mobile emissions decisions. The European Commission introduced PEMS as a mandatory requirement for light-duty vehicle type approval in 2016. The market for PEMS is expected to grow due to increasing demand from the industry, the importance of accurate and cost-effective testing, and advancements in PEMS technology, making it more compact and easy to install.
The latest PEMS devices can measure eight key emission components simultaneously, including CO, CO2, NO, NO2, NH3, N2O, HCHO, and CH4. They are designed for ease of deployment, consistency in extreme environments, and flexibility to adapt to changing measurement needs.
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Laboratory testing
One common laboratory testing method involves the use of a dynamometer, which simulates driving conditions while collecting and analyzing tailpipe emissions. The vehicle is driven according to a predefined speed-time pattern, and the dynamometer adjusts the level of resistance to mimic the resistance the vehicle would experience on the road. All emissions are collected in sealed bags and subsequently analyzed, with results measured in grams of pollutant per kilometre driven.
Portable Emissions Measurement Systems (PEMS) are another tool used in laboratory testing. PEMS equipment can be installed inside or outside a vehicle and is used to monitor real-time emissions and specific pollutants. While PEMS offers the advantage of being relatively simple and inexpensive, it is limited by the additional weight it adds to the vehicle and the range of pollutants it can measure.
Remote Emission Sensing (RES) is a more recent development in laboratory testing, allowing for the measurement of a large number of vehicles in a short period. RES utilizes a light source and detector to determine vehicle exhaust emissions and can incorporate additional equipment and sensors to gather information about vehicle specifications, speed, acceleration, and ambient conditions.
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Real-world driving emissions (RDE)
RDE tests are carried out in real traffic with varied conditions, including diverse environments such as motorways, country roads, and city environments, as well as higher speeds and abrupt acceleration. This helps to mimic the range of conditions a vehicle might encounter. The specific equipment installed on the vehicle, such as Portable Emission Measuring Systems (PEMS), collects data to verify that legislative caps for pollutants are not exceeded. PEMS equipment contains a variety of instruments for monitoring real-time emissions and specific pollutants. It can be installed inside the vehicle or on a rack outside the vehicle.
The RDE test does not replace laboratory tests such as NEDC and WLTP but complements them. The latest Euro 6 standard brought more stringent requirements in vehicle emission control in Europe, including the RDE test. Currently, the RDE test includes an introductory phase 'Step 1' where manufacturers must adhere to a NOx conformity factor of 2.1. 'Step 2' will reduce this conformity factor to 1.0, with a 0.5 error margin accounting for factors like traffic and weather.
RDE ensures that cars deliver low emissions over on-road conditions. Europe is the first region in the world to introduce such on-road testing, marking a significant advancement in the testing of car emissions.
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Health impact studies
Exposure Studies
Exposure studies focus on assessing the levels of pollutants individuals are exposed to when inside vehicles or near roadways. For instance, the California Air Resources Board (CARB) conducted studies on cars and buses to determine the levels of pollutants inside these vehicles and ways to reduce exposure. Investigators outfitted cars with air monitors and measured pollutant levels during rush hour and non-rush-hour periods in Los Angeles and Sacramento. These studies found that pollutant levels inside vehicles and along roadsides were often significantly higher than those measured at ambient monitoring stations.
Health Risks and Morbidity
Vehicular emissions have been linked to various health risks and increased morbidity and mortality. Pollutants from vehicle exhaust include carbon monoxide (CO), nitrogen oxides (NOx), particulate matter (PM), volatile organic compounds (VOCs), and ultrafine particles (UFP). Exposure to these pollutants can lead to respiratory and cardiovascular diseases, increased risk of cancer, and adverse effects on mental health. Studies have also shown that children living near busy roads or major highways have an elevated risk of developing asthma and reduced lung function.
Near-Highway Pollutants
There is growing evidence of distinct air pollutants downwind from highways, motorways, and freeways, including elevated levels of UFP, black carbon (BC), NOx, and CO. People living or spending substantial time within approximately 200 meters of highways are exposed to higher levels of these pollutants. Health outcome studies of near-highway exposure should consider factors such as the age and state of repair of vehicles, driving conditions, fuel chemistry, and meteorology, as these factors impact emission rates and the kinds of pollutants present.
Congestion and Health Impacts
Traffic congestion significantly increases vehicle emissions and degrades air quality, particularly near large roadways. Epidemiological studies and evaluations have demonstrated the risks of morbidity and mortality for drivers, commuters, and residents living near major roadways due to congestion-related emissions. For example, studies of congestion charging zones in London and Stockholm predicted gains in years-of-life due to reduced traffic-related air pollution. These findings highlight the importance of considering congestion-related impacts in health impact studies.
Urban Areas and Vulnerable Populations
Urban areas with high traffic density, such as Kolkata, India, face severe air quality crises due to vehicular emissions. Studies in these contexts have evaluated the status of air pollution at traffic intersections and vulnerable populations' exposure. The data collected helps assess the impacts of vehicular emissions on air quality and human health, especially in highly polluted megacities. Vulnerable analysis (VA) is a useful tool to set priorities for planning abatement measures and research. Options for reducing air pollution from mobile sources include replacing old vehicles, improving vehicle maintenance, using cleaner fuels, improving traffic management, and expanding mass transit systems.
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