Fines for the most severe polluting companies have taken off in recent years, with China, Japan, the EU and the US all imposing penalties ranging from slaps on the wrist to a significant share of profits. But while analyzing data over time can show trends that help identify the world's largest polluters, emission spikes at the city or national level can be trickier. Sensors can detect particles across a larger area, but in cities with several industrial plants, authorities need more effective ways to identify the culprits.

That's where dedicated drones come in. Governments from the US, Poland and China have turned to deploying teams of drones equipped with sensors to monitor for a wide range of different emissions around industrial areas, providing police with real-time data. These drones have proven so useful that their use as pollution watchdogs has been a technological influence, seeing the field move from drones specially designed to this task to modular features and sensors that can be attached to general models.

The Scentroid DR1000 Flying Lab may be the most successful drone designed to specifically fight airborne pollution. Five different sensors track around 35 pollutants, including carbon dioxide, methane, sulfur dioxide and hydrogen sulfide. As acceptable levels of emissions can vary based on weather conditions, the drone also tracks and humidity, temperature and GPS position, allowing authorities to rapidly confirm who is responsible for excessive pollution. Optionally, a thermal imaging camera can be set up with specific configurations for landfills, storage tanks and oil and gas pipelines. This information is immediately relayed to the pilot's laptop in form of a 3D map, helping to quickly identify excessive pollutants and those responsible.

These drones were deployed in 2018 to police in Katowice, Poland. The choice of country is not surprising. Poland is home to 33 of the 50 European cities most affected by smog, according to the World Health Organization. Approximately 80% of Polish energy is generated with coal, and the current government has doubled down on the fossil fuel industry.

Katowice itself has been the second most polluted city in the EU, lying in Poland's coal heartland. It makes sense therefore that the city's police force was an early tester of the Scentroid Flying Lab. Its focus, however, was somewhat different than might have been expected as the drones were used initially to crack down on pollution from residential homes, namely those burning illegal fuels such as “low-quality coal, wood waste and trash."

But where Scentroid has had success, they were not the first. Since 2014, drones have been part of China's massive campaign to rein in pollution, especially over urban areas. That first campaign netted 64 companies in violation of environmental laws; since then, hundreds more have been cited.

Similar drones are being used in China, but are taking efforts one step further. They are not only being used to monitor airborne pollution, but are also taking pictures of buildings, looking for rust, corrosion, and signs of polluting activities that may not be visible from the air.

In more challenging environments, such drones can provide enhanced safety for operators or avoid the risk of sending humans into dangerous areas. Pollutants flaring out of industrial chimneys or drain pipes are often burning hot, radioactive or otherwise contaminated. Landfills or industrial drainage pools can be dangerous for in-person visits for those without protective equipment. These drones sidestep such risks while also working faster than human inspectors by orders of magnitude.

An environmental protection official in China, Chen Baihui, was cited as comparing the work of one drone to that of 60 inspectors. A traditional investigation in Guangdong mandates the use of six inspectors over six days with no guarantee of all the sources of pollution being found.

Despite all these promising results, the use of drones to fight pollution has struggled to become standardized. In 2017, three years after these drones were first launched in China, a study found that “the majority of methods used insofar to keep track of air pollution in major cities rely on fixed monitoring stations…however, the use of such…hardware for pollution is outdated."

Since then, things have sped up considerably. The world's major capitals have brought drones online one by one. Seoul in South Korea has deployed an entire fleet, which are earmarked to go nationwide as part of the Air Map Korea Project. Hong Kong has thought of an innovative approach, harnessing the drones to analyze plumes from the thousands of ships that come through its port and harbor to ensure they burn cleaner maritime fuels.

The latter is another approach where human oversight was falling short. Dr Zhi Ning, from Hong Kong's University of Science and Technology, told the South China Morning Post that previously, police were only “examining ship log books on fuel use, visually assessing smoke opacity, and manually extracting fuel samples for analysis."

The Hong Kong project demonstrates why a major technological advance has enabled the widespread adopting of these drones. The pollution sensors and the drones themselves have become more affordable and adaptable, including the mounting of sensors on general-use drones, not only those specially designed for the task. Even such perennial favorites like as the DJI Phantom 4 drone can be turned into a convenient plastics detector.

With cities from Seoul, Korea to Fairbanks, Alaska now using them, drones are serving as another valuable weapon in the ever-developing arsenal of those fighting against airborne pollution.

Energy and political journalist with experience covering politics, energy, oil and gas, mining, finance, business, Latin America, China, and the Olympics.