Jun 17 2016
In Delhi, India’s capital, the blue sky is partially becoming a very rare sight especially during winter, when a thick white haze suffocates the city. David Hagan, an MIT PhD candidate studying atmospheric chemistry and a Fellow in the MIT Tata Center for Technology and Design, states that the quality of air in the is quantifiably considered to be the worst at a global level.
David Hagan, a Tata Fellow and PhD candidate in civil and environmental engineering, is designing and building low-cost sensors that could be deployed in dense networks to monitor air pollution. Here, Hagan makes some last-minute tweaks to his prototype in a hotel room in New Delhi, India. Photo: Shriya Parekh
“Beijing has bad episodes, but Delhi is worse because of the meteorology,” says Hagan. “It’s hot, it’s humid, and in the winter an inversion layer settles in. Delhi is a perfect reactor of anthropogenic and biogenic particulates.”
In the meantime, the lack of particular data has annoyed the governments and scientists hoping to comprehend to intricate environments of megacities in China and India, where the quality of air is inextricably connected to energy systems. Emissions in megacities like Delhi can be detected from varied source such as open burning of biomass for cooking and warmth, fossil fuel-driven power plants, and automobiles, each developing a variety of particles.
Hagan along with his advisor, Associate Professor Jesse Kroll of the Department of Civil and Environmental Engineering, treated this complexity as a motivation to develop an air quality sensor that is inexpensive and compact. They hope to use this sensor in dense networks all over cities like Delhi, in order to log precise and real-time data on the chemistry of the air.
Air quality monitoring is often discussed as an either-or situation. One can have expensive, regulatory-grade monitors or else distributed, low-cost sensors. But in reality it’s a continuum, with a tradeoff between cost, size, and power on one hand, and accuracy, precision, and sensitivity on the other. We’re somewhere in the middle of the continuum, with enough accuracy and precision to provide quantitative measurements.
Kroll
“If we can generate a better data set,” Hagan adds, “it could lead to a sustainable public good.”
Epidemiologists are concerned about the production of PM2., which is a particulate matter less than 2.5 microns across. These fine particulates are extensively caused by fuel combustion, and when inhaled they lead to terrible health effects, including heart attack, lung disease and asthma. A recent study by the Chittaranjan National Cancer Institute established the fact that half of the population of Delhi’s schoolchildren have suffered permanent lung damage.
In Manhattan the highest level of PM2.5 you’ll see is about 12 micrograms per cubic meter. Delhi can be anywhere from 150 to 1,000 micrograms per cubic meter, so the levels are dozens of times higher. However, there is no safe level of PM2.5. We all have a long way to go to make it better.
Hagan
Hagan and Kroll already possess a number of prototypes on the ground in India, reporting data every 30 seconds to a remote server. Two units are located at Place in south Delhi, and four units are located near Place in south Delhi, co-located with a regulatory-grade sensor for calibration. Two units are placed in Pune, near Mumbai, and one is mobile, where Hagan can be seen to frequently travel with it on rickshaws all over Delhi.
Delhi has almost 20 regulatory-grade sensors and the cost for each sensor ranges between 50,000 and $100,000. The sensor developed by Kroll and Hagan costs “on the order of $1,000” per unit, says Hagan, and provides comparable performance, measuring six kinds of gases (CO, SO2, NO2, NO, O3 and volatile organic compounds) and 16 size groups, or “bins,” of particles, varying from coarse to fine. These sensors can be deployed in bulk volumes because of their low cost, and this develops an opportunity to map pollutant distribution at higher levels of detail.
A number of do-it-yourself and inexpensive devices already exist in the market, but the sensitivity of Hagan’s design, together with its potential to measure particles as tiny as 380 nanometers across, sets it apart.
Most low-cost sensors only measure one size bin of particulate — coarse. I’m very interested in both the atmospheric chemistry and the user experience, which is why my sensor is different. There hasn’t been a low-cost sensor made with a good mix of quality components and a well-engineered interface.
Hagan
We’re interested in measurements with reasonably good spatial coverage, but that are also directly comparable to those from regulatory-grade monitors and that provide insight into the chemical changes that pollutants undergo in the atmosphere.
Kroll
As part of this learning process, Hagan and Kroll have also studied how the sensors will react to different environmental circumstances.
Hagan and Kroll together with other MIT researchers have subjected varied generations of sensors to the seasonal changes of the Boston area, where two small grids are up and functioning, one in Dorchester and the other in the MIT campus. These varied generations of sensors have also been subjected to highly variable conditions around the Hawaiian volcano Kilauea.
With an improved prototype, both Hagan and Kroll are currently starting to understand how the dirty air and intense heat of Delhi will affect the performance of the sensor. One of the sensors placed in Nehru Place became majorly clogged with black grime, and this prevented the sir from passing through, thus resulting in recording low pollutant numbers.
Hagan states that transparency plays a significant role for the project’ success. He further says, “It’s important to be honest about what the sensor is measuring and what its limitations are.” He adds, “The next generation will be much better,” referring to a robust filtration system to avoid clogging and a smaller and more energy-efficient design.
Hardware is only one part of the equation. Hagan went on to write the algorithms that infer the raw data of the sensor. He imagines a wide range of possible applications for the data in both private and public sectors. Academic and government researchers could use it to detect emission sources and develop mitigation strategies. Office buildings and factories will be able to incorporate the sensors into their HVAC systems for monitoring the quality of indoor air. Entrepreneurs might be able to purchase access and then utilize the data in commercial products, like smartphone apps and in-home monitoring systems that enable people to see real-time information on the air that they breathe.
It is not possible to come up with immediate solutions for millions of those living in Delhi under the influence of air pollution every single day.
This research was supported by the MIT Tata Center for Technology and Design.
The report features in the Spring 2016 issue of Energy Futures, the magazine of the MIT Energy Initiative.