The new generation of tools could revolutionize air quality measures for city residents and governments alike.

Air pollution is a global problem, especially in rapidly modernizing nations. But before countries can tackle it they have to be able to measure it, and that seemingly simple task has turned out to be surprisingly difficult. Satellite and fixed, ground-based sensors have limitations that prevent them from providing accurate, up-to-the-minute readings of pollution in the neighborhoods and slums that get it worst.

But a new generation of small, portable, cheap air sensors could revolutionize pollution measurements for citizen scientists and governments alike. Compact sensors like the AirBeam or San Francisco-based Aclima’s triangular sensor nodes have been deployed to measure the air of U.S. metros in real-time. By connecting the sensors to the Internet, tools such as these have made it possible to compile massive datasets of air quality in cities.

The result could be a dramatic improvement in measuring pollution and a wealth of information to guide the process of making city air safer for the people who breathe it.

Limited understanding

Even the wealthiest cities have very little fine-grained understanding of air pollution patterns. That’s because the traditional modes of measuring air quality are not optimized for tracking daily or personal exposure. For standardized data on air quality around the world, scientists turn to satellites. Up in the sky, orbiting satellites can ping the Earth’s surface and measure particulate matter, using the same sensor for measurements around the globe.

Of course, not every country can access a satellite, and these data have their own weaknesses: cloud cover and bright reflections from ice and snow can mess with their readings. Satellite data are great for generating baseline air quality measurements, but not so great for gauging real-time fluctuations in local pollution.

Fixed ground-based sensors, on the other hand, measure the air “where people live and breathe,” says Angel Hsu, director of the environmental performance measurement program at Yale University. These can be quite expensive, though, and they can’t accurately represent a whole city because airflow, pollution, and micro-climates differ from neighborhood to neighborhood.

For instance, several years ago, the U.S. embassy in Beijing caused a stir by tweeting air quality readings taken from its rooftop sensor that conflicted with the official Beijing government measurements. Those numbers differed in part because they were measuring different air, Hsu says.

The New York State Department of Environmental Conservation uses 17 stationary sensors to measure ambient air quality from elevated positions throughout New York City to measure whether baseline air quality is in compliance with the Clean Air Act. That’s vital to the city’s health, but it leaves an opening for more specific data, says Michael Heimbinder, executive director of HabitatMap, a nonprofit that maps crowdsourced environmental data to reveal the health and hazards of urban communities.

“They’re looking to measure the background level, they’re not looking to measure personal exposures. That’s just a different mandate,” Heimbinder says. “For us, we’re really looking at personal exposures, what is it like for the person who’s walking to work, at work, at school? What kind of air are they breathing in on a day to day basis?”

This air sensor at the U.S. embassy compound in Beijing measured fine particulate matter in that part of town. (REUTERS/U.S. Embassy Press Office)

Air sensors go mobile

Building on the availability of off-the-shelf sensor and miniaturized GPS technology, Heimbinder oversaw the creation of a portable air quality sensor called the AirBeam.

The lightweight AirBeam fits in the palm of your hand and costs $250, but performs comparably to the standard $5,000 air quality instruments. It measures temperature and humidity, but also PM 2.5, the fine particulate matter that gets into lungs and causes hospitalization and premature death from heart and respiratory disease. The Airbeam can also transmit measurements via a smartphone to crowdsourced datasets that map out the recorded air readings.

The next step for HabitatMap is to find funding to distribute the sensors to low-income communities of color that are particularly vulnerable to air pollution. Heimbinder hopes that crowdsourcing local data on the air quality where people live will be useful in guiding policy responses.

For instance, if local monitors pick up excessive pollutants coming into a park from a particular intersection, a community could use that data to plant a buffer of greenery in between, says Carlos Restrepo, a research scientist and adjunct professor at New York University’s Wagner Graduate School of Public Service who has worked with the AirBeam team. Or if particular buildings show up as pollution sources, the remote sensors will provide evidence to push for cleaner equipment there.

On the individual level, people carrying sensors can make more informed decisions about how they move through the city. When George Thurston, professor of environmental medicine and population health at NYU School of Medicine, tried to measure the day-to-to pollution exposure of asthmatic schoolchildren in the South Bronx in the early 2000s, the most portable method was sticking $5,000 sensors in rolling backpacks. Now, with instantaneous geolocated air sensing, Thurston envisions trip-planning apps like Google Maps or Waze offering different navigation options based on the pollution exposure of different routes.

“Air pollution information could enter into the algorithm and change the way people travel—what we call ‘prudent avoidance’ in the field, where you wisely avoid the problem,” Thurston says.

People are already mapping out their neighborhood air pollution in other North American cities, including Toronto and Pittsburgh. But these sensors serve a more basic role in developing countries, says Hsu, who also teaches environmental studies at Yale-NUS College in Singapore. Just like cell phones leapfrogged landline telecommunications in much of the world, cheap and portable sensors can fill in for countries that lack the money or human resources to establish baseline data through the traditional route.

“If you’re a rapidly urbanizing, developing, and changing country like China or India or most of South Asia, then those fixed-base monitors are a very costly way to monitor air,” Hsu says. “You may not be targeting the places that are changing most quickly and could also have the greatest exposure to increasing and worsening air pollution.”

Rethinking cities

The benefits of portable sensors don’t stop when you go indoors, because air pollution doesn’t either. To better understand how cities operate, you have to gather real-time data from the streets and from inside buildings. Aclima has begun that process by setting up a total of 6,000 sensors in 500 nodes throughout 21 Google buildings around the world. This created what Aclima cofounder and CEO Davida Herzl calls the single largest dataset of real-time indoor environmental sensor data.

While photographing Denver streets last summer, the Google Street View cars gathered air quality data with Aclima sensors. (Aclima)

Further capitalizing on the partnership with Google, Aclima installed sensors on three of Google’s Street View cars that crisscrossed Denver last summer. While the cars photographed the neighborhoods they also captured air quality data, which Aclima calibrated with heavy-duty EPA sensors to check for accuracy. The validation tests succeeded, so two months ago Aclima launched a similar program with Street View cars in the Bay Area. Merging the data from indoors and outdoors starts to paint a previously unknown picture of how urban design influences quality of life.

“We can start to make decisions about how we’re designing our cities with data we haven’t had before,” Herzl says.

Data collection will continue through the end of the year, but initial results point to the scope of its value. For instance, Herzl says, when a 2013 BART strike led to more people driving to work, Aclima’s indoor sensors picked up higher concentrations of fine particulate matter seeping into the workplaces. Conversely, on one Bike to Work Day, the sensors found decreases in the pollution from vehicles entering the indoor environments.

This level of granularity allows cities to map out exactly how their transportation affects other aspects of life. “It’s not just about energy any more,” says Herzl, “It’s about our well-being, our ability to do great work and not go home with a headache to our family.”

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