Mobile Sensors Attached to Vehicles can Directly Measure Greenhouse Gas Emissions in Cities

Although cities have a vital role in minimizing the emission of greenhouse gases to tackle climate change, the direct measurement of the emissions has always been difficult.

Researchers from the UBC have now developed an innovative technique to measure the emission of carbon dioxide, considered to be the most significant greenhouse gas emitted, directly at street level. The outcomes of the research have been recently reported in a paper published in the journal Atmospheric Measurement Techniques.

The technique for developing the mobile sensors and the inferences obtained from attaching these sensors to car-share vehicles in the city of Vancouver have been described here by Joseph Lee, the lead author of the paper as well as a recent UBC graduate, and Andreas Christen, senior author of the paper and a professor in geography and the atmospheric science program.

The Operation Mechanism of the Mobile Sensors

The team headed by Lee created tiny, lightweight sensors that can be easily attached to vehicles while they move in the city. The researchers got in touch with car2go regarding the use of five of their vehicles to analyze the sensors as it was important to demonstrate the fact that the sensors are highly compact enough to be attached to smaller vehicles such as Smart cars. In reality, the lighter weight of the sensors allowed them to be carried by even cyclists on their bikes.

Christen stated that the main function of the sensors is measuring the emitted carbon dioxide and the street level location at a given point of time. Then, the data is compared with simultaneous measurements acquired from sensors positioned on a tower over the city, thus enabling the calculation of origin of the emissions.

For instance, on average, if the carbon dioxide concentration is far higher at the street level than the tower level, then it can be said that the mobile sensors are positioned in a part of the city at which the emissions are high. On the contrary, if the concentration at the street level is lower than the tower level, the sensors are positioned in a part where carbon dioxide is readily absorbed by trees, for instance, close to the surface.

Outcomes of Using the Sensors to Map Carbon Dioxide Emissions in Vancouver

Lee stated that the vehicles with the sensors were driven in Vancouver for a time period of 3.5 hours on two afternoons. As expected, the highest emissions were recorded in downtown Vancouver and on certain arterial roads. However, there were also many areas in which carbon dioxide had been absorbed, such as in Stanley Park and in certain lushly vegetated localities.

In these places, the vegetation and trees were expected to absorb carbon dioxide at a higher rate than the rate at which it was locally emitted by humans. In general, the measured data confirmed the anticipation of the research team.

Significance of the New Technique and the Importance of Measuring Greenhouse Gas Emission at Street Level

Lee stated that the technique was innovative in that it combined multiple mobile sensors with tower data and, as a result, minutely measured the emissions across large parts of the city. Although many researchers have earlier tried to perform street-level mapping of carbon dioxide levels by means of mobile sensors, they were unsuccessful in transforming their levels to emissions.

Christen added that accurate data regarding the amount and area of greenhouse gas emissions in cities is highly significant for designing emission reduction plans. At present, governments normally model and report the emission of carbon dioxide by using fuel statistics at rough scales. However, from the perspective of policy and planning, it is mandatory to obtain fine-grained and detailed information on emissions from particular streets, blocks, or localities and on the way in which emissions get altered over time.

For instance, if cities plan to minimize the emissions by introducing more hybrid or electric vehicles to their transit systems, it would be highly significant for them to be in a position to monitor and map the effectiveness of the emission reduction plan at the local level. The innovative mobile mapping technology developed by the researchers can aid in the detailed monitoring of the emissions over time.

The Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the BC Knowledge Development Fund funded the study. The vehicles for the research were provided by car2go, and the moovel lab in Germany funded the trips.