Pollutants in the air, otherwise known as particle matter (PM) can wreck havoc on people.  PM is made up of a mix of solid, liquid, and gas particles that get trapped in the air.  Some of these particles are large enough to see with the naked eye, but most are microscopic.  When in large quantities they can give the air a hazy appearance.  Short term exposure to PM can lead to allergy like symptoms such as sore throats, difficulty in breathing, itchy eyes, runny noses, and sometimes nausea.  Long term exposure to PM rich air can cause cancers and leads to the deaths of millions world wide each year.  Throughout the world cities, where PM tends to be worse, are enacting actions to lessen PM numbers.  However, finding accurate ways of testing for PM can be very difficult.

Air sampling stations set up devices to check air quality on a regular basis.  Though these stations have given us a lot of useable data, they also have some problems.  The first is that they use mostly heavy, stationary monitoring devices, and as air moves it is important to be able to test it at different locations.  The other problem is that these monitoring systems are extremely expensive.  They can cost anywhere from $50,000 to $100,000 each and require specialized operators.  Some companies have taken to testing the air with balloons or helicopters too.  While balloons are cost efficient they can only test air on a vertical axis.  A helicopter can be overly expensive too, but it’s blades also disturb the air to much to get quality samples.  This is why many researchers are turning to drone technologies to test the air for PM levels. 

Professor of Electrical and Eomputer engineering and Bioengineering at the University of California, Los Angeles, Aydogan Ozcan has created a new device that can be used with drones to test air quality.  Called C-Air, it is a small airborne microscope that sucks in air samples.  The device weighs less than 1.5lbs, and scans 13 liters of air per minute giving Ozcan and his team a 93% accuracy reading of PM levels.  Yichen Wu, a doctoral student working on the project said, “Our technique will make air pollution detectors much more portable and affordable, while at the same time being highly accurate and could have far reaching public health benefits.”  C-Air can be mounted on a tether, atop of a building, or as Ozcan said, “any medium-sized drone—for instance, the DJI Phantom—should satisfy our application.”  Currently Ozcan and his team have the C-Air attached to a DJI Flame Wheel, a rugged 4-6 rotor drone geared towards hobbyist droners.  

To test the C-Air Ozcan sent the drone up over one of California’s EPA approved air quality monitoring stations for several hours.  The nozzle on the C-Air drew in air that was automatically passed over a sticky coverslip.  Red, green and blue LED lights shine over the coverslip allowing a color complementary metal-oxide semiconductor image sensor to take pictures of particles stuck to the coverslip.  The images are then uploaded to a cloud system and can be customized to scan for a wide range of particles in the air.  The measurements taken by the C-Air drone device closely matched those taken by the EPA’s stationary device.

Though Ozcan’s C-Air device is a first of it’s kind, he and his team are not the first to be using drones to test air pollutants.  One of the main problems that those using drones to test PM is that the primary space that needs to be tested is in restricted airspace such as that around an airport, congested highways, and city environments.  Getting permission from the FAA to fly a drone in these areas can be very difficult.  Which is why one researcher in Alaska is showing a lot of promise with drone air quality testing.  Because of Alaska’s remoteness, finding areas to test drones is easy.

Catherine Cahill is a professor of Atmospheric Chemistry at the University of Alaska Fairbanks.  She also is the director of the Alaska Center for UAS Integration and runs the Pan-Pacific UAS Test Range Complex (one of the FAA’s 7 official UAS test sites).  For the last 30 years Professor Cahill has been analyzing PM in the Alaskan environment.  Recently she and her team have begun to use several different drones to gather air samples to test.  She said, “Unmanned aircraft offer incredible possibilities for monitoring pollution.  We can follow plumes, and fly out into the Arctic, and develop maps to improve models of pollution distribution.”  One of the unique environmental issues in Alaska is the temperature inversions where a layer of warm air settles over a layer of cold air.  In most of the world this would be opposite as the the air gets colder as it rises.  These inversions can trap PM low to the ground as it is doing in Fairbanks, Alaska’s second largest city.

In Fairbanks one of the issues leading to an increase in PM levels is when people are burning wood and other materials.  Cahill went on to say, “We’ve had trouble monitoring and modeling the inversions in the past, so one thing we hope to do in the winter is to use unmanned aircraft, most likely the Ptarmigan, to take vertical profiles of the atmosphere at low altitudes during the worst periods, when people are burning wood and a lot of smoke is getting trapped.”   The Ptarmigan is just one of the drone models Cahill uses.  This drone is a single operator hexarotor drone and is 31.5 inches long.  It  is ideal for operating in cold environments and can carry a payload just over 3lbs for about 20 minutes at a time.   The next drone they are using are is 75 inch long, two operator, single rotor drone called the Responder.   The Responder can carry a payload of 6.6lbs for 35 minutes and can support fully autonomous operations.  And finally, Cahill and her team also use the long range, fixed wing drone the Scan Eagle.  The Scan Eagle has a 10ft wingspan, can carry a payload over 7lbs, and remain airborne for up to 18 hours.

All of the drones that Professor Cahill is using in Alaska can be fitted with a number of different sensors and cameras for gathering data.  It stands to reason that she could easily use Professor Ozcan’s C-Air device, as long as it can hold up to the extreme weather conditions of Alaska.  Weather always has to be taken into account for Cahill.  “In the cold, plastic can get brittle, so you can shatter rotors—we go to carbon fiber instead,” Cahill said. “Icing is also a huge challenge for us, and we actually work with folks to put drones in an icing wind tunnel, doing experiments with de-icing coatings and active de-icing systems that get rid of ice in flight.” 

While many cities have adopted clean air policies and measures, testing the air quality is a must.  These tests need to be run continuously to pinpoint exactly why and from where PM concentrations are coming from.  With the use of devices like the C-Air and drones these testing practices can easily become second nature.  They are easy to use, can be operated without specialized training, are cost effective, and most importantly they give an accurate picture of the pollution levels.  For Cahill, this is a reality, while for Ozcan working in city environments, the logistics are still being worked out by the FAA.  As Professor Cahill said, the goal with drones that can test air pollutants is to get permission from the FAA “to fly over cities safely, so that they can be used to their fullest potential.  That way we can get the information about the air that we need to protect people.”

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