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Air quality monitors mounted on public transit see pollution other sensors miss

Every time I go outside, I check the air quality.

I use the United States Environmental Protection Agency’s (EPA) AirNow App, which grabs data from a nearby monitor located in downtown Los Angeles, about four miles from where I live. It’s a habit I picked up upon learning that poor air quality contributes to 100,000-200,000 deaths in the U.S. every year. City pollution is also a huge contributor to climate change, contributing over 75% of global carbon dioxide (CO2) emissions.

In order to reduce the impact cities have on our health and climate, the EPA and National Oceanic and Atmospheric Administration (NOAA) currently oversee monitoring stations across the US that measure both air pollutants and greenhouse gases. However, each instrument can cost over $20,000, and this limits the number each city can afford. As a result, approximately 120 million Americans currently live in a county without a single EPA small particle pollution monitor and, despite our warming planet, NOAA regularly monitors CO2 in only 17 states.

The growing need to fill in these monitoring gaps had led to a rise in the development of low-cost air quality sensors. Companies like Purple Air sell equipment that costs around $200 and they rely on community science to dramatically expand the urban air quality network for a fraction of the cost. That said, since this equipment is not as accurate or reliable as traditional monitoring stations, their data is seldom used when creating new environmental regulations. Plus, $200 is still out of reach for many low-income communities; even with these cheaper options, there’s still a lack of monitoring equipment in neighborhoods that are disproportionately burdened by air pollution.

But a new study published in Environmental Science & Technology has demonstrated that a new, lower-cost monitoring method exists that might revolutionize how cities sample air pollution.

“By putting an instrument on a mobile platform, you’re able to get a lot more coverage”
It all started in 2014 when Logan Mitchell, then a postdoctoral scholar at the University of Utah, began sampling Salt Lake Valley air out of the window of a Transit Express (TRAX) light rail train. “We put the instruments in the driver’s cab right under [their seat],” Mitchell, now a research assistant professor, remembers fondly. Since then, they’ve upgraded their method, but the principle is still the same.

Sitting on the roofs of three TRAX trains are research-grade instruments (similar to what the EPA monitors use), which measure a suite of pollutants including nitrogen dioxide, ozone, fine particulate matter, methane, and CO2. The trains run along the corresponding Red, Green, and Blue Lines that transverse Utah’s Salt Lake Valley metropolitan area, which includes Salt Lake City and its suburbs. Mitchell explains: “By putting an instrument on a mobile platform, you’re able to get a lot more coverage. It’s equivalent to installing a whole network [of traditional air quality monitors] and…it’s a lot more cost effective.” That’s because, even though a single TRAX monitor has a price tag of $40,000 each, it’s able to capture the same data as 30 stationary instruments, which altogether would end up costing over $1 million to install.

Read more: Air quality monitors mounted on public transit see pollution other sensors miss


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