Login 
It’s late morning on a grey and dreary day at the cusp of winter. The air is heavy, the grass sodden from last night’s rain, crows wheel in the clouds. A mysterious craft waits patiently in the mud, resting on spindly legs, with multiple sensors and lights blinking green and red. At a signal from the pilot-in-command, the craft springs graciously into the air to hover effortlessly above the ground, its eight rotor blades spinning dizzyingly fast, giving rise to a low, whirring drone.
Sadly, this isn’t the opening scene to a new Star Wars film. It’s the scene as a group of atmospheric scientists stand unglamorously in a cold, muddy field trying to understand the greenhouse gas and air quality implications of fracking (or, more technically, hydraulic fracturing).
Fracking. It’s one of those words that seems to instil a sense of dread; one of those words that is politically charged enough to be avoided, except perhaps after a few pints down the pub. The industry is controversial, not least in the UK, where the government announced a pause on hydraulic fracturing whilst they investigate the associated risks, after seismic activity near the popular seaside resort of Blackpool.
Fracking licences were previously granted throughout England, with Cuadrilla paving the way forward in Lancashire.
However, it’s not just the potential for earthquake damage that makes fracking so controversial. The impact of the industry on the atmosphere is of huge public, and regulatory, concern. Fracking is, after all, a process for extracting fossil fuels, and in a world where the effects of climate change are beginning to take shape, it’s no wonder people are worried.
“the atmosphere is dynamic. Single point measurements, or snapshots of the atmosphere, are not always representative of what’s really happening”
Hydraulic fracturing
Hydraulic fracturing is an innovative process for extracting oil or natural gas from rock formations which more conventional extraction methods are unable to access. High pressure ‘fracking fluid’ (essentially water, sand and additives) are forced into rocks to create cracks, from which oil and gas can flow to the surface. Since fracking commenced at scale in the USA from 2010, the USA has developed from a net importer to a net exporter of natural gas, proving just how lucrative this energy source can be. Proponents of fracking highlight these economic benefits and the advantages of replacing coal with natural gas, which is proposed to be less damaging to the environment, though this, in itself, is contended. Those who oppose fracking argue that any benefits are eclipsed by environmental impacts, such as the stimulation of earthquakes, ground water contamination and air pollution. As such, fracking is restricted in many countries, and banned outright in others.
To fully understand the impact that any new industry has on its environment, we need to know what the environment looked like before the industry was in place. For scientists, we call the state of the environment before the new industry starts operating, the “baseline”. Measuring the baseline involves monitoring a range of environmental parameters to form a picture of the pre-existing conditions. As the environment changes on daily, monthly and seasonal scales, it is often necessary to measure the baseline conditions for long periods of time, sometimes years. For a simple analogy, the baseline process is akin to taking a photograph of a field before building a new housing development. You can then compare the before-photo with the end result to assess the changes to the surrounding environment. The Environmental Baseline project, led by the British Geological Survey, did just this, measuring many components of the local atmosphere, biosphere and geosphere (which includes geological activity and ground water), over two years prior to hydraulic fracturing operations in Lancashire.
There’s another important reason for measuring a baseline: it can allow for the characterisation of other pre-existing local and regional sources
of, for example, atmospheric pollution. It can often be difficult to identify and suitably characterise impacts of different pollution sources, particularly if they emit the same chemicals. Take fracking for example, which can result in the emission of methane gas. There could be many other local sources of methane, ranging from gas leaks and landfill sites to agriculture (including cows), which together muddy the water when trying to determine the impact of a single industry. Measuring a baseline can help understand the local and regional picture.
There are, of course, difficulties to long term monitoring. Many of the high precision instruments required for such monitoring are expensive. They also require regular maintenance to ensure accuracy, through systematic calibration and data validation. This can be time consuming. Scientists know only too well how fickle instruments can be, and keeping them running over several years, through heat waves and freak storms, is no easy task. Single, fixed-site monitoring stations also have limitations. What they measure is totally dependent on the wind direction. If you’re trying to measure emissions from a fracking site to the east of your station, but the wind is only blowing from the north, well… you won’t be sampling what you want to see.
Greenhouse gases
Atmospheric greenhouse gas concentrations in the atmosphere have been rapidly rising since the onset of the industrial revolution in Britain in the 1700s. Concentrations of the two major greenhouse gases (carbon dioxide (CO2) and methane (CH4)) are continuing to increase due, in part, to technological and societal advances, and the rapid development of newly emerging economies, but also to various natural feedback cycles that are outside of our control.
“the atmosphere is dynamic. Single point measurements, or snapshots of the atmosphere, are not always representative of what’s really happening”
Quantifying these changes, and making sensible predictions on the state of our future home, is incredibly difficult. Not only does it require a thorough understanding of the chemical and physical processes shaping our entire planet, but it requires detailed knowledge of every industrial, agricultural, or other practice which impacts upon it. Whilst our understanding of these natural processes is improving daily, built over centuries of experimentation, our world is undeniably complex. Add to that the myriad different ways that we as a species are influencing the environment around us and you have a recipe for intricacy on a truly universal scale.
Measuring greenhouse gases such as carbon dioxide and methane isn’t easy. They are both invisible to the naked eye, and present in the atmosphere at relatively low concentrations (albeit far higher than in pre-industrial times). In the case of methane, there are approximately two molecules for every million molecules of air – a proper needle in a haystack situation! The atmosphere is also a dynamic system – molecules are subject to both physical transport, like being carried by the wind, or chemical changes, through reaction with other species. To put it lightly, finding these molecules is not always easy!
However, greenhouse gas scientists aren’t always interested in the absolute number of molecules of methane. We’re often more interested in the total number of molecules being emitted from a particular source. In scientific terms, this is referred to as an emission flux (for example, in kg per second), the amount, or mass, of gas (in kg) released per unit time (in seconds). Imagine, if you will, a stream – the flowing water represents the dynamism of the atmosphere, with currents and eddies just like the swirling of the wind. Now imagine that somewhere within that stream, there’s a steady drip of a dye the exact same colour as water. Imagine how difficult it is to find the dye, given that the stream can take it pretty much anywhere. Once you do find it, you may be able to measure its concentration at a single point, but that’s not enough. You can’t know exactly how much of the dye was put into the stream from a single measurement – maybe you’ve found a spot where it’s really concentrated, or maybe you’ve found a spot where it’s really dilute and the rest of the dye is somewhere else. Furthermore, as the currents in the stream change, you could measure the concentration at that same point several seconds later and find that it has changed completely!
This is our fundamental challenge. The atmosphere is dynamic. Single point measurements, or snapshots of the atmosphere, are not always representative of what’s really happening. How can we measure multiple points, in three dimensions?
Drones
You’ve guessed it, this is where the drones come in. Really, drones shouldn’t be called drones at all, that’s just what everyone refers to them as. More technically, they’re called unmanned aerial vehicles, or UAVs, a term with which many millennials who grew up playing Call of Duty should be familiar. However, our UAVs don’t monitor the locations of enemy players, and hopefully nobody wants to shoot them down either. We’ll continue to use the word drones for now to avoid using tedious acronyms.
With a drone we’re able to fly through a large volume of the atmosphere relatively quickly, sampling methane (or in reality, any gas we like so long as a portable sensor exists), and identifying areas of higher concentration over the background concentration (the concentration of methane in the atmosphere is never zero). Drone measurements are made downwind of the greenhouse gas emission source, in our case, downwind of the hydraulic fracturing site. The drone is flown in a sampling vertical plane, perpendicular to the wind direction.
Drones can only reach the lowest parts of our atmosphere, just below where planes are allowed to fly. In the UK, small drones (of less than 20 kg) are limited to flying to 400 feet above the surface. Aircraft must fly above 500 feet so there’s little risk of a crash if operated responsibly and competently. Drones are versatile, agile and can hover in the air, much like a helicopter. They are also cheap to run – a single drone flight in the UK costs less than 10p withstanding wear, tear and replacement costs. However, the difficulty comes with finding somewhere to fly. Regulations state that drones must be at least 50 metres away from any buildings and cannot fly in the traffic zone for any airports. You also need to stay well away from open air assemblies (such as crowds of people). This means that flying over Glastonbury to get a glimpse of the headline act would not be allowed (unless you have special permission of course).
There is a wide variety of different drones on the market. Their prices can range from about £50 (at the time of writing) to well into the millions, depending on what you may need your drone to do. The power and payload of the drone can limit the flight endurance. Our research group uses an 8 kg drone (which we lovingly named Amanda), worth approximately £10,000. She is battery powered and can fly for just 10 minutes, although recent developments have allowed solar powered drones to fly for days on end. She carries instruments on-board to measure wind speed, wind direction, position and altitude (using satellite data), temperature, pressure, and humidity. When measuring gases, including methane, we connect a long tube from Amanda to a methane sensor on the ground. We then fly downwind of our target methane source, such as a fracking site or landfill, or if we fancy it, a barn filled with lactating cattle.
However, there are some limitations. Flying a drone in the first place requires suitable winds and weather. A drone cannot fly in too wet or too windy weather, nor can it fly in winds faster than its maximum flight speed (otherwise it can’t fight against the wind to return to its take-off position and could be blown away!). For example, Amanda can only fly in winds gusting at up to 25 miles per hour. If the winds are stronger than this, then flying is a no-go. This poses a bit of a dilemma for us as atmospheric monitoring is often easier in high winds – slow winds lead to stagnation and build-up of local pollution, which can confuse our measurements.
Piloting a drone can be both exciting and nerve wracking – you’re in total control of a £10,000 flying robot and one wrong move could send it hurtling into the embracing arms of a nearby tree. Despite the associated drawbacks (standing in a muddy field in December for hours on end?), drones pose a useful tool for atmospheric scientists as we seek to understand the world around us. Their use as a measurement platform is relatively new, but innovations continue to be made every year. Who knows, maybe the future of atmospheric science is drones, maybe the future is more like the opening scene of a Star Wars film than we know.
