Activities in congested urban areas all over the world were reduced this spring as a result of the COVID-19 pandemic. Only a few aircraft have continued to fly. As such, Earth's atmosphere is significantly less polluted by emissions from human transport and industrial activities than it was previously. In the BLUESKY mission, scientists are investigating how clean the air has become during the pandemic, and whether the sky actually appears to be bluer. Christiane Voigt of the Institute of Atmospheric Physics at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is heavily involved in the project and is responsible for the scientific deployment of the DLR Falcon 20E. In this interview, she tells us how the Coronavirus pandemic is providing a special opportunity for atmospheric research, how aircraft are able to conduct measurements just three metres above the ground, about instruments that can be controlled by scientists working from home, and about the first trends revealed by the measurements.
Interview by Falk Dambowsky
You have been travelling all over the world for many years to conduct research flights. How does it feel to be coordinating a flight campaign at a time when most aircraft are grounded?
This is actually a very exciting time for atmospheric research. The regulations enacted in response to COVID-19 now mean that there are fewer anthropogenic pollutants in the atmosphere. Being able to study the composition of the atmosphere under these unique conditions for the first time using research aircraft represents a special opportunity for science and is hugely motivating for us as we go about our day-to-day work.
What challenges did you face in preparing for the mission during the pandemic?
Initially, we were largely tied to working from home, so we had to find new ways of completing approval procedures for the instruments and aircraft. DLR Flight Operations accomplished a lot in this area. Luckily for us, many important instruments had already been installed on board HALO and Falcon for other campaigns, so we only had to modify or install a few. In order to get the aircraft into the air as quickly as possible despite the restrictions, while also keeping the number of people present to a minimum, we worked in a daily shift pattern. Even now, in the active phase of the campaign, we are still working with a skeleton staff. One innovation that has resulted from the COVID-19 pandemic is definitely the increased automation of the instruments. The pandemic led to a pressing need to monitor and control instruments from our home offices during the preparations and the research flights.
As the scientific lead for the Falcon flights, you are responsible for the mission and plan the flight routes and measurement programme. What factors do you consider during your planning?
First, we have to find the most promising targets – the places where we can expect particularly significant changes to the composition of the atmosphere due to the COVID-19 regulations. In terms of air traffic, the number of flights over Europe decreased by almost 90 percent in April 2020 when compared to the previous year. We are looking to measure the resulting changes to the concentrations of aerosols and nitrogen oxides at cruising heights over Germany and the North Atlantic flight corridor, so we are planning our routes accordingly. We are also interested in the effects of reduced emissions from industry and road traffic on the ground. For this, we used satellite data during our planning, in order to send the aircraft directly into the atmospheric boundary layer of previously heavily polluted regions like the Ruhr and the area around Milan. Flights in the atmospheric boundary layer below two kilometres present a particular challenge for pilots and crews. Performing low approaches at a height of three metres at Berlin and Frankfurt airports, which are largely free of air traffic, has also been very exciting. During normal times, it would not be possible to deliberately fly so low there.
You have already completed some flights over Germany, all the way to northern Italy and elsewhere in western Europe. Are the measurements showing any particular patterns?
Falcon's first measurements show a slight decrease in aerosol concentrations in the upper troposphere over Germany. The aerosol concentration there is currently as low as in unpolluted air in the southern hemisphere. In addition to various other parameters, the lower aerosol concentrations in the sky are currently making the sky appear bluer, hence the name of the mission, BLUESKY. Aerosols are produced, among other substances, during the combustion of fossil fuels and are small particles finely dispersed in the air. They affect the radiation balance of our atmosphere, as they scatter and absorb solar radiation and thus also have an impact on cloud formation, our climate and the blueness of the sky. The measurements also show that there are significantly fewer contrails than last year. This can seen very clearly from the satellite data and is being reported by the experimenters on the flights.
Falcon and HALO are the first two aircraft in the world to be used for research purposes to study the special characteristics of the atmosphere under the constraints of the Coronavirus pandemic. How do the two aircraft complement each other on this mission?
The aircraft differ in their range of applications. Falcon is very robust and particularly well suited for flights in the troposphere and for low-level flights within the atmospheric boundary layer. It is equipped with instruments for measuring aerosols and cloud properties, and has a smaller range of trace gas instruments. HALO can cover greater distances and ascend to the stratosphere at an altitude of 15 kilometres. The array of instruments on board HALO is more strongly focused on atmospheric chemistry.
Several renowned German scientific organisations are partnering with you on this mission, namely the Max Planck Institute for Chemistry in Mainz, Goethe University in Frankfurt, Forschungszentrums Jülich and the Karlsruhe University of Technology (KIT). How does the cooperation support the common mission?
The Max Planck Institute for Chemistry, under Jos Lelieveld, is providing scientific leadership for the HALO research flights, and it is working alongside Goethe University, Forschungszentrums Jülich and KIT to operate the various aerosol and trace gas instruments on HALO. Our scientific expertise is mutually beneficial, so the BLUESKY mission really prospers due to the cooperation between the two aircraft teams. We work closely together to coordinate the flight plans and to evaluate the extensive data sets. All of the partners have access to earlier series of measurements, which together provide us with a comprehensive picture of the atmosphere both today and before the pandemic.
Which of the planned flights are you particularly looking forward to, and how will the ongoing evaluation of the measurements continue?
I'm especially looking forward to the route that heads out to the North Atlantic. For one thing, these flights present a major logistical challenge, with Falcon making a stopover in Shannon, Ireland. The North Atlantic flight corridor, which is receiving very little traffic at present, also provides an interesting opportunity for us to gain a better understanding of emissions from air traffic. We expect the background air to be cleaner there than over Europe and hope to be able to capture in detail the decline in aircraft emissions due to the reduced volume of air traffic. Over the coming months, we will then conduct extensive quantitative analyses together with the Max Planck Institute for Chemistry and the other partners, in which we will study the differences between the lower atmospheric pollutant levels we have recorded and earlier measurements. We expect the results of these evaluations to be available by around the end of 2020. In addition, we are planning more comparative measurements over the coming year in order to track the increase in emissions after the lockdown is eased.