Using starlight to measure greenhouse gases

Astronomers of the University of Warwick, in partnership with institutions in Spain, show how astronomy tools, which are generally used to study stars, can be reused as climatic sensors, helping us follow how the earth’s atmosphere changes in the face of global warming.

During her journey to earth, the light of the stars can change when she interacts with the particles in the regions containing gas and dust. This effect is particularly visible when light crosses our atmosphere because the atmosphere introduces lines (like its own “barcode”) in the light patterns observed from stars (stellar spectra).

These lines, known as revealing lines, are a nuisance for astronomers, who seek to “decontaminate” their observations by eliminating these undesirable characteristics, but a new algorithm called astroclimes, developed at the University of Warwick, aims to measure the abundance of molecules in the earthly atmosphere) Dioxide (Co₂), water vapor (h₂o).

Marcelo Aron Fetzner Keniger, a doctorate of the Warwick Prize. The student of the Warwick Astronomy and Astrophysics Group and Astroclime Algorithm Developer said: “Monitoring the abundance of GES is necessary to quantify their impact on global warming and climate change. Using revealing lines to measure the abundance of GHGS in the earthly atmosphere. Can be done only during the day, so astroclimes can, hopefully, fill the gap with night measurements.

In this spirit, an observation campaign was carried out last July at the Astronomical Observatory of Calar Alto (CAHA) in Almería, Spain, in collaboration with the University of Warwick, the University of Almería and the Spanish Meteorological Agency (AEMET).

The main objective of this campaign is to demonstrate the unique potential to combine solar measures (during the day) and the measurements of other stars (at night, using astroclimes) to study the carbon cycle, the role of GHGs in the current context of global warming and the strengthening of observation systems for these gases.

Diurnal spectra were measured using a portable Ftir spectrometer (EM27 / Sun) from the Coccon-Spain network, temporarily installed at the Calar Alto Observatory. During the night, Starlight was analyzed using the astroclime algorithm on the data from the Carmenes spectrograph on the 3.5 m telescope of the observatory. The COCCON instrument can derive from atmospheric GHG concentrations that are calibrated and tied with literature standards and are used to calibrate the abundances measured with astroclime algorithm.

Marcelo Aron added: “If we can successfully calibrate astroclimes using Coccon measures, he could provide a new network to measure the abundances of GHGs, completing current networks with night measures.”

Diurnal observations taken by EM27 / SUN at around 2,100 m were completed by a second instrument at sea level at the University of Almería (UAL). Joaquín Alonso Montesinos, University Professor and UAL representative in the Coccon-Spain project, said: “We are grateful to Aemet for having counted on us for such an important project, which, in our view, will be a reference in the energy transition.”

“The National Coccon-Spain network aims to approach the latent lack of atmospheric GHG observations in Spain thanks to the implementation of a network of measurement stations on a national scale. (AEMET-CIAI), network coordinator.

Jesús Aceituno, director of the observatory, concludes: “Calar Alto, with its photovoltaic factory and its biomass boiler, aims to reach energy sustainability. These greenhouse gas detections made with Carmenes demonstrate that an astronomical observatory can also be used to monitor the climate of our planet.”