Illumination d'eau
de mer synthétique, permettant l'étude de la photochimie
à l'interface
air/mer © Ircelyon
first detected abiotic source of isoprene
(September 30, 2015) Lyon/
Leipzig. The oceans seem to produce significantly more isoprene, and
consequently affect stronger the climate than previously thought. This emerges
from a study by the Institute of Catalysis and Environment in Lyon (IRCELYON,
CNRS / University Lyon 1) and the Leibniz Institute for Tropospheric Research
(TROPOS), which had studied samples of the surface film in the laboratory. The
results underline the global significance of the chemical processes at the
border between ocean and atmosphere, write the researchers in the journal
Environmental Science & Technology.
Isoprene is a gas that is formed by both the vegetation and
the oceans. It is very important for the climate because this gas can form
particles that can become clouds and then later affect temperature and
precipitation. Previously it was assumed that isoprene is primarily caused by
biological processes from plankton in the sea water. The atmospheric chemists
from France and Germany, however, could now show that isoprene could also be
formed without biological sources in surface film of the oceans by sunlight and
so explain the large discrepancy between field measurements and models. The new
identified photochemical reaction is therefore important to improve the climate
models.
The oceans not only take up heat and carbon dioxide from the
atmosphere, they are also sources of various gaseous compounds, thereby
affecting the global climate. A key role is played by the so-called surface
microlayer (SML), especially at low wind
speed. In these few micrometers thin layer different organic substances such as
dissolved organic matter, fat and amino acids, proteins, lipids are
accumulating as well as trace metals, dust and microorganisms.
For the now published study, the research team took samples
from the Norther Atlantic Ocean. The
surface film was collected in the Raunefjord near Bergen in Norway. For
this purpose, a glass plate is immersed in water and then again carefully
pulled from the water. The 200 micron thin film sticks to the glass and is then
scraped off with a wiper. The sample thus obtained is analyzed in the
laboratory later. At the Institute of Catalysis and Environment in Lyon
(IRCELYON), which belongs to the French research organization CNRS and the
University of Lyon 1, the team investigated its photochemical properties during
which collected samples were irradiated with light and the gases were
analyzed: it became clear that isoprene
was produced in magtnetudes that were previously attributed solely to plankton.
"We were able for the first time trace back the production of this
important aerosol precursor to abiotic
sources, so far global calculations
consider only biological sources," explains Dr. Christian George from
IRCELYON.