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Low-cost sensors can point to solutions for world’s most polluted cities

In the megacity of Dhaka, Bangladesh, the air quality on some days can get downright dangerous. Levels of PM2.5, fine particulate matter linked to heart, lung and cognitive issues, often exceed safe health standards. 

“In Bangladesh, we have a national standard, it’s about 65 micrograms per cubic metre [µg/m3] for 24 hours,” said Riaz Hossain Khan, assistant scientist at BRAC University in Dhaka. But during the dry season, it’s much worse.

“If you measure something during December or January, these months, you’ll find close to 250 or 300.” 

Experts say that’s resulting in kids struggling to breathe on smoggy days, and more middle-aged people developing cough-variant asthma, which can be persistent and chronic. 

40 times the WHO guidelines

While the daily concentrations are bad, the picture for the whole year is no better. Bangladesh topped recent global rankings by IQAir, an air quality technology company, for the highest annual average concentrations of PM2.5, at 79.9 µg/m3. The World Health Organization’s guidelines recommends five µg/m3. 

Of the top 100 cities in the rankings by IQAir, all but one of them are in Asia, with 83 of them in India alone. (Canada, with its record breaking wildfire season, jumped up in the same rankings of the risky pollutant.)

Experts say it highlights a need not just for pollution reduction measures — but for more affordable monitoring and measurement tools to figure out what’s causing the problem in the first place. 

“You can’t make an informed policy decision about air quality without having data,” says Jill Baumgartner, who studies air quality and health at McGill University and has worked in low- to middle-income nations.

“The vast majority of countries  — that are some of the most polluted places — don’t have anything close to what we have in the city of Montreal.” 

Air-quality measuring that’s cheaper and quicker

Typically, ground-based air quality monitoring can use a variety of methods, including: 

  • Gravimetric: Sampling the air and weighing the particulate matter. Considered the “gold standard”, these are collected and analyzed, so are slower as well as more expensive. 

  • Optical: Shining lasers through particles and seeing how light behaves to determine amounts. The benefit here is that it’s cheaper and real-time.  

The more expensive monitoring tends to be used by government regulators, costing “between $20,000 and $30,000 US for each monitoring station,” explains Glory Dolphin Hammes, North American CEO of IQAir. Lower-cost sensors, by comparison, can be around $500. 

The McDougall Creek wildfire burns on the mountainside above houses in West Kelowna, B.C., in August 2023 (Darryl Dyck/The Canadian Press)

Hammes’s company sells air quality monitoring products and manages a platform using regulatory and low-cost sensors around the world. The data gets verified and feeds into real-time online reports as well as those yearly pollution rankings. Cheaper sensors, she says, provide broader coverage and give people actionable information. 

“They are given the power of choice to mask up or to do other means to mitigate the air quality that they’re breathing,” Hammes told CBC News from Los Angeles. 

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Up to gold standards

Progress is also being made on bringing sensors up to a higher standard, according to Olorunfemi Adetona, who researches pollutant exposure and health effects at Ohio State University. 

“The Environmental Protection Agency has tried to calibrate this instrumentation against the more gold standard measurements,” Adetona explained. The EPA has developed methods to integrate the data from the low-cost sensors with that from the more expensive ones.

Vehicles move through the dusty road as air quality decreases during the dry season in Dhaka, Bangladesh, February 19, 2024.
Vehicles move through the dusty road as air quality decreases during dry season in Dhaka, Bangladesh, in February. (Mohammad Ponir Hossain/Reuters)

Adetona cautioned they are not perfect comparisons and wouldn’t be used as official regulatory data, but that they can inform public health.

“The Environmental Protection Agency has tried to calibrate this instrumentation against the more gold standard measurements,” Adetona explained. These calibrations can help serve “as if you were using regulatory monitors.” 

Dhaka’s dilemma 

That’s what Khan and his colleagues are trying to do in Dhaka. Initially, the city only had three government-installed air quality monitors, which he described as too close to each other and at far too high an elevation. 

“The whole Dhaka city is about 306 square [kilometres],” Khan explained. “So there is a large portion of the area that doesn’t have any coverage.” 

He and his team, as part of the Pathways to Equitable Healthy Cities global partnership, installed dozens more. They found the way the land was used influenced air quality: higher concentrations around industries, lower concentrations around more residential areas that had green spaces — and times of the day where intensity differed. Source and time data, Khan says, that’s incredibly valuable to the betterment of policies. 

But Dhaka is complex, reminds Zahidul Quayyum, a colleague of Khan’s and a health economics expert at BRAC University. 

“You cannot clearly distinguish between some of these purely residential areas and [others],” Quayyum told CBC News from Dhaka, explaining that the city’s urban planning is outpaced by its growth. A weave of informal industry, traffic and residential environments make regulating air pollution complicated. 

Smoke rises from the chimneys of brick factories on the outskirts of Dhaka, Bangladesh, March 17, 2024.
Smoke rises from the chimneys of brick factories on the outskirts of Dhaka earlier this month. (Mohammad Ponir Hossain/Reuters)

But change has happened, at least in one of the most publicized sources of air pollution: brick kilns. Many of them operate informally and illegally. 

“They made some changes in the policy, which took the brick kilns out of the city,” Quayyum noted. But politics and business don’t always get along, he says, and when asked whether data is leading to better public health policy, Quayyum is practical.

“Yes, to some extent. But more needs to be done.”

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