ATom: World Survey of the Atmosphere: Long History of Using Aircraft to Understand the AtmosphereJuly 26th, 2016 by Steve Wofsy
In the last two weeks, we’ve wrapped up the test flights and major preparations for NASA’s ATom mission. ATom is an airborne science experiment aboard the DC-8 flying laboratory that will study the most remote parts of the Earth’s atmosphere. We want to learn how much pollution reaches areas most people would consider untouched by human influence, and to understand how pollutant chemicals in these distant regions affect things we care about.
I’m Steve Wofsy, an atmospheric scientist at Harvard University and ATom’s Principal Investigator. I couldn’t be more excited to get underway. ATom is the realization of an idea to sample cross-sections of the world’s atmosphere that I have dreamed about for more than 20 years. The idea for ATom started in the 1990’s, when I participated in a series of aircraft missions that characterized the chemistry of the Earth’s stratosphere, spanning from the Arctic to the Antarctic. Our images of global chemical changes were immensely powerful in helping us to understand depletion of stratospheric ozone. Together with my colleagues in those stratospheric missions, Paul Newman of NASA’s Goddard Space Flight Center and Michael Prather of University of California, we started to think about how we might undertake such a study in the troposphere, where we all live.
The chemistry of the atmosphere is very important for human beings and for all creatures on Earth. In the ATom study we want to understand air pollution and climate change. Air pollution has immediate and long-term consequences for human health, agriculture, and ecosystems. Climate change in the era of fossil fuel emissions and industry is being driven mostly by the gases we pump into the atmosphere.
To understand the chemistry of the atmosphere, we have to be able to measure many different chemicals in tiny amounts. The only way to do that is by going out in the atmosphere itself. We can’t make the measurements only at the ground, because the atmosphere extends far above the surface. Some measurements can be made using satellites that look down into the atmosphere, but many measurements must be made directly in the air, because the concentrations of many important gases are far too small, and the patterns we need to observe are too fine, to be measured from space.
Scientists have been using airplanes to sample the atmosphere since the 1940’s, when Britain’s Royal Air Force flew missions to understand the occurrence of contrails, which are simply water vapor that condenses behind an aircraft in certain atmospheric conditions. Today’s modern flying laboratories take sophisticated instrumentation throughout the atmosphere, in locations remote and nearby, polluted and nearly unpolluted. It is a very exacting, challenging endeavor, but one that pays off for both our understanding of the planet and for protecting it and the people on the ground.
Some of the most daring measurements of atmospheric chemistry were made in the stratospheric missions I mentioned before, between 1985 and 2000. We used the high-flying ER-2 aircraft carrying extremely sensitive instruments to measure very reactive “free radical” chemical species – in particular the chemicals responsible for the hole in stratospheric ozone that was forming each year over Antarctica. The measurements cannot be done by capturing air and taking it back to the lab – these chemicals are constantly generated by sunlight, and then they react and vanish in seconds, minutes, or hours.
The insights scientists were able to gain because of those data sets led to huge societal changes, including the Montreal Protocol, the international treaty banning a whole class of industrial chemicals that were harming Earth. The amazing global consensus to ban these chemicals could not have happened without the ER-2 aircraft measurements.
Those data did not come easily. Scientists had to develop a whole new class of instruments that had to operate autonomously, since only the pilot is on board the ER-2. The plane had to go to the limit of its capability to sample in very inhospitable locations. Pilots, engineers and scientists worked very closely together to ensure safe execution of these flights.
The equipment on board the DC-8 in ATom likewise has to be very carefully engineered to be both safe and exquisitely sensitive and accurate. Because the chemistry of the troposphere is much more complex than that of the stratosphere, the number of independent instruments has multiplied to 22. The crew has to manage this very complex payload, with many possible hazards. The plane will often be flying very low to the ocean surface, and it will cross some of the most remote and inhospitable areas on the planet. Many of the instruments in ATom have their heritage in those flights of the ER-2.
The preparation of the DC-8 and the science payload has been meticulous. The planning of flights and logistics around the globe for our ten stopovers was undertaken to meet multiple constraints of safety, cost, and science objectives. We don’t know yet what we’ll see, but it will be the most detailed slice of the atmosphere we’ve ever measured. We hope to find out how human beings are changing the global atmosphere, what are the effects on climate, and what these changes may mean for the health and welfare of human beings and global ecosystems. We are confident in our readiness, eager to head out on our adventure, and ready to report back.