When winter descends on Ulaanbaatar, Mongolia, the air turns foul. Here in the world’s coldest capital city, residents light open fires of coal or wood to heat their uninsulated houses. Soot fills the skies, and people don face masks to ward off smog so thick it can hide buildings a few hundred metres away. “White clothing becomes grey after a few hours,” says Munkhmandakh Myagmar, executive director of the Press Institute of Mongolia.

The city is one of the most polluted in the world, according to the World Health Organization (WHO) — and estimates suggest that particulate air pollution causes one-tenth of the city’s deaths. But information about the extent of that pollution is limited and hard to find. The WHO’s online database for pollution has readings from just one year for Ulaanbaatar, showing concentrations of harmful particles called PM10, which have a diameter of 10 micrometres or less, and PM2.5, with a diameter of 2.5 micrometres or less.

Eager to fill the knowledge gap, journalists from the Press Institute are taking matters into their own hands. In collaboration with the Earth Journalism Network — an international group of environmental journalists — Myagmar and her colleagues distributed five devices, each about the size of a child’s lunch box, around the city in July.

Called DustDuinos, the devices measure particulate-matter concentrations and quickly upload the data to a public website. Despite some initial problems with charging and connectivity, preliminary results from a sensor in the city’s centre showed that concentrations of PM10 often surged to at least twice the WHO’s recommended limit.

The DustDuino and other pollution sensors, some of which can be built for as little as US$50, and instructions for which are available online, are part of the next wave in the environmental movement (see ‘Sensors for the people’). Across the globe, journalists, advocacy groups, hackers and others are starting to use low-cost monitoring devices to vastly expand the amount of data that are publicly available on forms of air pollution such as particulate matter and toxic gases. The devices are easy to deploy and can complement data from official networks, which rely on sophisticated but sparsely distributed sensors. The ‘citizen-science’ approach aims to provide high-resolution measurements of air pollution where people actually live. Work is also under way to develop wearable sensors to monitor personal exposure levels.

Built on the principle of openness, such do-it-yourself (DIY) efforts are part of a push to democratize air-quality monitoring so that it no longer remains solely in the domain of governments and academic researchers. But advocates of the approach still have to convince conventional pollution researchers, who worry about the quality and usability of data from cheap sensors operated by relatively untrained people.

Still, everyone agrees that more resources need to go into monitoring air pollution, which kills around 7 million people a year. “It’s the largest, single most important, health risk in the world,” says Joshua Apte, an environmental researcher at the University of Texas at Austin, who sees an emerging role for cheap, plentiful pollution gauges. “The fact that you can buy 50 low-cost sensors for the cost of one regulatory sensor is a tremendously powerful thing.”