Students Design Affordable Black Carbon Hotspot Detectors

Caltech students developed prototypes that can measure black carbon emissions in high pollution neighborhoods.

A group of engineering students from the California Institute of Technology (Caltech) have contributed their design and innovation skills to a project involving modeling and detecting concentrations of black carbon levels in communities. The pollution model aims to map out black carbon hotspots using data from black carbon sensors around city neighborhoods.

The project is spearheaded by senior computer science major Peter Kulits for a chemical engineering course, Challenges in Data Science for Chemical Systems, where he wanted to develop a project combining computer vision and sustainability.  Kulits’ project follows work done in an earlier study by a Caltech alumnus, Robert Griffin, that involved placing pollution trackers and black carbon detectors on Google Street View vehicles in order to collect data about the city’s pollution hotspots.

“My project was to extend their work, to make it possible to identify potential hotspots but without all of the expensive equipment, hopefully just from public data sources,” Kulits said.

Following Griffin’s model, Kulit intended to measure black carbon levels around Pasedena, only to run into problems when they discovered that there was no existing data on black carbon in the city. In order to collect their own data, chemical engineering professor Mike Vicic arranged to purchase a high-end black carbon detector with support from the Caltech Innovation in Education fund. But Kulits’ project also sparked an idea for Vicic’s upcoming fall term Chemical Engineering Laboratory course: to have his students develop smaller, more affordable black carbon sensors.

The $10,000 instrument was used to take black carbon measurements around Pasadena, but was also used as a basis for eight students in Vicic’s course to design and create black carbon detectors that could be built for a fraction of the cost. Black carbon sensors like the one Vicic purchased can typically measure down to the lowest black carbon concentrations (about 0.1 microgram per cubic meter). However, the student detectors only needed to measure black carbon levels that are detrimental to human health, which are at much higher concentrations.

According to Vicic, the student-made detectors feature inexpensive air pumps, emitters, detectors, data-acquisition electronics and other components. Students were given free rein in the design process, which resulted in each device looking and working differently.

“I tell them, ‘Frankensteins are good,'” Vicic says. “Because they’re all proofs of concepts. You’re trying to get through the whole design process quickly to learn what you don’t know you don’t know.”

Prototype designed by Chan Kim. (Image courtesy of Caltech.)

Prototype designed by Chan Kim. (Image courtesy of Caltech.)

Senior student Chan Kim was inspired by N95 masks, and used N95 mask material as the filter sandwiched between two symmetrical chambers magnetically held together, with an LED and photodiode placed on either end. Compared to typical black carbon filters, which are coated in polytetrafluoroethylene (PTFE), N95 masks are both much less costly, and easier to acquire.

Another senior student, Schuyler Dick, took a different approach by drawing air through the device. Black carbon in the air is then deposited onto a filter material. One side of the device has an LED that emits in the infrared spectrum, while the other end is a detector that measures the light coming from the LED. Plexiglass protects both the optical components from the black carbon that collects inside the device. The device measures black carbon concentrations by tracking the decrease in the amount of light passing through the filter as the carbon builds up. 

Prototype designed by Schuyler Dick. (Image courtesy of Caltech.)

Prototype designed by Schuyler Dick. (Image courtesy of Caltech.)

Another student-built prototype used mirrors to bounce light back and forth through a chamber of gas. A sensor detects how much of the light is absorbed to reveal how much black carbon is present. Rather than using expensive optics, senior student Alex Fontani Herreros used pieces of inexpensive glass mirrors within a 3D-printed enclosure.

Prototype designed by Alex Fontani Herreros. (Image courtesy of Caltech.)

Prototype designed by Alex Fontani Herreros. (Image courtesy of Caltech.)

“I have another person who wants to do a system that is a sampler that people would send back to the manufacturer—kind of like a radon detector,” shares Vicic. “He wanted to have a different spot for every day so he could measure how much black carbon was persistent over time or whether the levels changed day to day.”

Black carbon is typically produced by to the incomplete combustion of fossil fuels, wood and other fuels. According to the Climate and Clean Air Coalition, black carbon emissions have a warming impact on climate that is approximately 460 to 1,500 times stronger than carbon dioxide per unit of mass. In 2015 alone, 6.6 million tonnes of black carbon were emitted. Black carbon emissions can also cause serious health conditions including respiratory and cardiovascular diseases, cancer and even birth defects. These effects are more apparent among neighborhoods that are within or near hotspots such as freeways, concrete factories, and areas frequented by large trucks.

According to Vicic, the goal of these student prototypes is to eventually provide affordable detectors to people living in neighborhoods affected by black carbon. This way, people will be able to take black carbon measurements and collect data that can be presented to policymakers.

“You find an area that’s been identified as a potential persistent black carbon hotspot from a model,” added Vicic, “Then you deploy the sensors to residents in that area so you can say, ‘Yes, many of us are being exposed to black carbon.’ It’s not just one sensor in one house.”

Engaging in projects such as this during university enables engineering students to exercise their problem-solving skills in areas relevant to their degree, as well as allowing them to help their community. Projects involving real-world tasks and tools provide students with the opportunity to learn about important topics while also giving them opportunities to work both independently and collaboratively toward a common goal. Every project helps these students to identify their future career path, and helps them follow through on the education that is needed to achieve their desired career, and encourages them to strive academically.

For more information, visit Caltech.