Alyssa Dayan, left, and Tom Hartley Kadhim Shubber/Wired/CC BY-NC 3.0

Before summer 2012, neither 16-year-old Alyssa Dayan nor 17-year-old Tom Hartley, had ever used a Raspberry Pi.

But by March of this year, the duo, who both study at Westminster School in London, had invented a weather and pollution monitoring system called the AirPi. They won first place in a competition "to invent something using a Raspberry Pi to make the world a better place", run by the Raspberry Pi Foundation and PA Consulting Group.


Not only does the AirPi record temperature, humidity, air pressure and light levels, but also monitors for pollutants like carbon monoxide and nitrogen dioxide, both of which are primary pollutants in cities. In February, the pair added a UV sensor to the AirPi platform. The AirPi allows users to send a constant stream of pollution data to the web, which can be seen on the AirPi website, and only costs around £50, which includes the Raspberry Pi itself.

[pullquote source="KeepInline] Pollution in cities continues to be a concern, particularly in the developing world. [link url="http://www.guardian.co.uk/environment/2013/jul/08/northern-china-air-pollution-life-expectancy"]Recent research[/link] on the health impact of pollution in China showed that people in the polluted north of the country died on average 5.5 years earlier than people in the south.

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Closer to home, it is believed that air pollution contributes to the death of 30,000 people per year in the UK. the EU recently announced it was investigating Mayor of London Boris Johnson for allegedly using dust suppressants on roads with pollution sensors to avoid breaching EU rules on pollution levels.

In-depth: The life of Pi: how Britain's biggest hardware hit for a generation came to be "Government data is not very thorough. Either governments don't show you [the data] or they only give you data across a [large area] like a town," says Dayan. "Since pollutants in the air vary with the square of the distance, this is just not accurate enough."


Personal pollution monitoring stations, owned by thousands of citizens across a city, could put data in the hands of the people, giving them the information they need to force change and to sidestep antics like those Boris Johnson is accused of engaging in.

The AirPi weather and pollution monitoring station Courtesy of AirPi

Dayan and Hartley started building the AirPi in October, beginning by prototyping it on a breadboard. Hartley had some experience with the Raspberry Pi before they started, having won one at the Young Rewired State 2012 event in the summer.

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His team's winning project? A program called Smart Move, which used open data sources on the web to "help people find the perfect location for a house, based on factors that were important to them, like crime rate or number of schools nearby," explains Hartley.


[Quote"]Personal pollution monitoring stations, owned by thousands of citizens across a city, could put data in the hands of the people[/pullquote]

By the beginning of 2013, Dayan and Hartley had completed their basic functioning first prototype. "We ordered components and as they arrived one by one we connected them up the Raspberry Pi," says Hartley. "After we got a fully-ish functioning hardware model, we started to develop the website. We wanted a web interface, so that people didn't have to be at their Raspberry Pi [to access their data], they could be anywhere in the world."

They overcame most of the software and hardware challenges by using information readily available online, most notably on Adafruit they say.

But the sensors proved more problematic. The data sheets didn't meet their standards so they recalibrated and tested the sensors themselves in their school's chemistry lab. "We put the sensors into a [vacuum-sealed] glass, so we knew how much air was in there," says Dayan. "We then used syringes to inject tiny amounts of different gases to see how the sensors would respond."

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By comparing the responses with the amount of gas injected, they were able to create their own calibration tables for the sensors.

After winning the competition in March, Dayan and Hartley created a standalone circuit board for the AirPi, which plugs directly into the Raspberry Pi computer. New sensors can be soldered directly on to the AirPi.

We wanted to make our product accessible to as many people as possible Alyssa Dayan

They've had interest from a German computer club, who wanted to buy 10 AirPi kits for educational use, and also organisations in Vietnam and the Phillippines, who wanted to use it for pollution monitoring. The group in the Phillippines wanted 100 kits, they say. They've also presented their invention at events like the London Maker Faire.

However, Dayan and Hartley are aware of the limitations of the current sensors they're using. "They're certainly not as accurate as we would hope, but unfortunately more accurate sensors cost around £60 or more just for one," says Dayan. "We wanted to make our product accessible to as many people as possible."


Problems with the current sensors include varying performance depending on the humidity and the temperature, and different gases skewing the signal slightly.

But they're planning to use data from the AirPi's other sensors to account for these effects. Additionally, by calibrating the response of the cheaper sensors with a more expensive and accurate sensor, they hope to develop an algorithm to correct the difference as much as possible. "If the sensors stayed at the current level, the AirPi will probably be an educational tool," says Dayan. "But if we manage to make them [more accurate], it would have some serious healthcare potential."

In the meantime, Dayan is hoping to study natural sciences at Cambridge University, and Hartley is hoping to attend Imperial College London to study electronic engineering. I imagine they won't have any trouble at all.