Custom-Built Sensors Developed to Track Black Carbon Pollution

Black carbon, often referred to as soot, is known to contribute significantly to global warming and is strongly associated with adverse health consequences.

Black carbon is generated during incomplete combustion of fuels—discharged from marine vessels, large trucks, and trains. For residents staying in urban areas, this air pollutant is a major concern. At present, commercially available sensors are extremely costly, which makes it difficult to track black carbon.

Now, a research team at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), in association with UC Berkeley, has created a new kind of sensor network that is not only more affordable but can also track this particulate matter.

With over 100 custom-built sensors deployed across West Oakland for 100 days, the researchers produced the largest black carbon monitoring network to be installed in a single city. A complete description of the 100×100 air quality network has been published in the journal, Environmental Science and Technology.

Generating a New Technology to Monitor Air Pollution

The new project was mainly introduced to tackle a persistent problem existing in the community—the requirement for more improved tools to track black carbon across both space and time.

Building on a previous study performed at Berkeley Lab, the researchers tackled this issue by constructing the Aerosol Black Carbon Detector, or ABCD for short.

“We generated a technology that didn’t exist to make this invisible problem visible,” stated Thomas Kirchstetter, who heads the Energy Analysis and Environmental Impacts Division at Berkeley Lab, and is an Adjunct Professor of Civil and Environmental Engineering at UC Berkeley.

The ABCD, being small and low-cost, is a compact air quality monitor that can determine black carbon concentration in an air sample.

We had to create a sensor that was as accurate as high-grade, expensive instrumentation, but low enough in cost that we could distribute 100 of them throughout the community.

Thomas Kirchstetter, Scientific Division Director, Energy Analysis and Environmental Impacts Division, Berkeley Lab

Design breakthroughs developed by coauthor Julien Caubel during his PhD research helped the sensors to tolerate variations in humidity and temperature. When the ABCD is left outside for long periods of time, it produces consistent data. For each ABCD, the materials cost less than $500. By contrast, commercially available devices that determine the concentration of black carbon cost several thousands of dollars.

A Well-Distributed Network

The range of sensors was installed across West Oakland, a 15-km² mixed-use industrial/residential neighborhood enclosed by freeways and affected by emissions from the Port of Oakland and other similar industrial activities. In addition, six land-use categories, such as industrial, residential, upwind, truck route, near highway, and port locations, were selected for sensor placement.

It was important to build a well-distributed network across the neighborhood in order to capture pollution patterns.

Chelsea Preble, Study Coauthor and Affiliate, Berkeley Lab

Preble is also a postdoctoral researcher at UC Berkeley.

The researchers, through a partnership with Environmental Defense Fund, the West Oakland Environmental Indicators Project (WOEIP), Port of Oakland, and Bay Area Air Quality Management District, recruited community members who were willing to host the black carbon sensors beyond their businesses and homes.

“Our partnership with WOEIP, in particular working with Ms. Margaret Gordon and Brian Beveridge, was essential to the success of the study,” added Preble.

In order to track all the sensors in real time, including their operating status, and obtain measurements, coauthor Troy Cados created a customized database and website. Then, using 2G, the mobile wireless network, the sensors relayed the concentrations of black carbon to the database every hour.

The study created about 22 million lines of data, providing a better perception of the nature of air pollution on a local scale. The data, currently available for download, is also being utilized by collaborators from the Bay Area Air Quality Management District, UC Berkeley, and other institutions to enhance air pollution modeling tools.

Turning Invisible Pollutants into Data

How did these sensors actually function? The ABCD device pulls air via a white filter, on which black carbon particles were effectively deposited. Within the sensor, optical components periodically determined the amount of light sent via the darkening filter. The concentration of black carbon in the air was based on the amount of the filter that had darkened over time. This method, created many years ago by Berkeley Lab and presently available in the market, acted as a foundation for the innovations in this analysis.

In West Oakland, the team discovered that black carbon differed prominently over time spans as short as one hour and distances as short as 100 m. The most variable and highest levels were linked with truck activity along Maritime Street, usually low in the pre-dawn hours when the Port of Oakland was closed and peaks at the start of business, about eight in the morning.

The team recorded the lowest concentrations of black carbon in the study area on Sundays, when truck activity is usually the lowest, and at upwind locations west of the freeways, close to the bay¸ and the city’s industrial activity.

The majority of the sensors collected data that was enough to determine pollution patterns during the initial 30 days of the study, indicating that analogs—and shorter—analyses may provide useful data to other communities about their air quality.

Partnering with Communities to Advance the Science of Monitoring

This research is an example of how a national laboratory can have a meaningful impact by working with communities. We worked to address a concern that they’ve long had and provided data describing how pollution varies throughout the neighborhood, which can be used to advocate for cleaner air.

Thomas Kirchstetter, Scientific Division Director, Energy Analysis and Environmental Impacts Division, Berkeley Lab

At present, the researchers are working to further develop this novel technology, rendering it more powerful and easier to use so that it can be installed for extended periods of time in other areas.

“We’ve long been involved in the generation of air pollution sensing technologies,” stated Kirchstetter, whose mentor, Tica Novakov, was an inspiration for this work and began the field of black carbon study. “Berkeley Lab has experts in air quality and materials sciences, and can further the science of sensors to continue this path forward,” he added. Ever since the project was completed, Caubel and Cados have established a start-up to create these methods and make them more instantly available.

The study authors include Julian Caubel, Troy Cados, Chelsea Preble, and Thomas Kirchstetter. The study was funded by the Environmental Defense Fund, with in-kind support offered by the Bay Area Air Quality Management District.

In this video, Berkeley Lab researchers show how they created a technology that did not exist to monitor local air pollution across time and space. (Video credit: Marilyn Chung/Berkeley Lab)