Annual-Report-2019

INTERLINKAGES IN THE CHEMISTRIES OF THE
TROPOSPHERE AND STRATOSPHERE: IMPACTS OF
NITROUS OXIDE ON EARTH SYSTEM
The mission of the project lays out the key needs to better understand the
role of nitrous oxide in the Earth’s climate and ozone layer depletion, and
information needed to make any policy to curb N 2
O emissions. The major
need is to quantify the budget of nitrous oxides- i.e., quantification of various
source, both natural and anthropogenic, and loss processes.
Earth, Ecology & Environment Sciences 2019
74
Prof. Akkihebbal
Ravishankara
From: Colorado State University - US
In residence at: Institute of Combustion
Aerothermal Reactivity and Environment
(ICARE) - Orléans
Nationality: American
Dates:
LE STUDIUM Research Professor
Smart Loire Valley General Programme
Ravishankara currently is a Professor in the
Departments of Chemistry and Atmospheric Science
at Colorado State University. He chairs the US
National Academy’s Board on Atmospheric Science
and Climate, serves on the Editorial Board of the
Proceedings of the National Academy of Science
(USA), and a member of the Science Advisory Panel
of the Climate Clean Air Coalition of UNEP. In 2019,
Prof. Ravishankara was elected a Foreign Member
of the Royal Society (London). Before that he was the
Director of the National Oceanic and Atmospheric
Administration’s Chemical Sciences Division of Earth
System Research Laboratory where he served for
nearly 30 years in Boulder, CO. Prof. Ravishankara’s
work relates to stratospheric ozone depletion, climate
change, and regional air quality. His measurements in
the laboratory and in the atmosphere have contributed
to deciphering the ozone layer depletion, including the
ozone hole; to quantifying the role of chemically active
species on climate; and to advancing understanding of
the formation, removal, and properties
of pollutants.
Dr Abdelwahid Mellouki
Host scientist
June 2017 to July 2017
May 2018 to July 2018
May 2019 to July 2019
Dr Abdelwahid Mellouki graduated from the
Universities of Tours, Orleans and Paris 7 (France).
He spent two years as a Research Associate at the
National Oceanic and Atmospheric Administration’s
Aeronomy Laboratory (Boulder-Colorado). Dr Mellouki
is currently a Research Director at ICARE in Orleans
(France). His research focused on many aspects of
atmospheric chemistry, including the studies of the
atmospheric oxidation mechanisms of anthropogenic
and biogenic carboncontaining species and halogen
chemistry. He has conducted a large number of
experimental studies on the atmospheric fate of
chlorofluorocarbons (CFCs) substitutes, as well as on
CH 4
and N 2
O which are considered to be important
greenhouse gases (GHGs). is an Editor of the Journal of
Geophysical Research, the premier journal in this field.
The goal of this proposed work is to provide that information on all the
loss processes through a combination of laboratory studies, chemical
calculations, field measurements, and atmospheric modeling.
The laboratory studies of the reaction of OH with N 2
O were completed and
manuscript describing this work was published. Theoretical studies were
carried out in collaboration with a scientist from Lille in order to provide an
explanation for the non-reactivity of N 2
O with the OH radical. It was realized
that we should also explore the potential reaction of N 2
O with the ubiquitous
NO 3
radical.
This work was carried out using a unique experimental system that was
assembled in ICARE that utilized the cavity ring-down spectroscopy to detect
NO 3
radicals at very low concentrations (part per trillion). Furthermore,
quantum calculations were carried out examine the potential reaction of NO 3
with N 2
O.
Based on the results from these
three studies, we have been
able to rule out any significant
tropospheric chemical loss of N 2
O.
This work greatly improves our
understanding of the atmospheric
lifetime of N 2
O.
While the experimental work was ongoing, we also undertook a quantum
mechanical theoretical study of the reaction of NO 3
radicals with N 2
O.
The study showed that the reaction of NO 3
with N 2
O is very slow. Further
calculations showed that this pathway would not be very viable in Earth’s
atmosphere.
In addition, with Prof. Valery Catoire, we started a project looking at the
vertical profiles of nitrous oxide in the stratosphere. Observations going back
to 1970s were collected, quality controlled, and analyzed.
In collaboration with Dr Douglas Kinnison of the National Center for
Atmospheric Research at Boulder, CO, USA, the community global model
was used to calculate the vertical profiles of N 2
O and compare them with
observations. This work was done in collaboration with a post-doctoral
researcher, Dr Vanessa Brocchi, of Orleans.
Some of the results this study was presented at the European Space Agency
symposium in Essen, Germany, in the summer of 2019.
A laboratory study of the reaction of OH radicals with HNO 3
, a product of N 2
O
degradation in the stratosphere, continued at ICARE in collaboration with Drs
Yuri Bedjanian and Mellouki.
These experiments were completed, and the results being analyzed.
Furthermore, theoretical calculations of this reaction are being planned.