CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

AVIATION AND ENVIRONMENT
2.3.2 Simulations of the plume dilution and its impact on the atmosphere (D.
Cariolle, O. Thouron, R. Paoli)
The space industry now provides an important component of the societys infrastructure and economy.
It plays a key role in several sectors such as telecommunications, broadcasting, or earth observation.
Rockets are the vectors of space activities with the rocket launch being the most visible manifestation
of a space mission. During a launch, the burning of massive amounts of propellants within minutes leads
to vast emissions of chemically and/or climate-forcing (i.e. radiatively active) gases and particles into the
atmosphere, resulting in perturbations of atmospheric chemical composition and radiative balance. Gases
and particles are emitted either directly from engines or produced as secondary products of processes
occurring in rocket plumes. The principal compounds emitted by the european launcher Ariane 5, Vega,
Soyuz are carbon dioxide (CO 2 ) and water vapour (H 2 O), chlorine compounds (HCl, chlorine radicals)
for Ariane and Vega, nitrogen oxides (NO and NO 2 , jointly referred to as NOx), carbon monoxide (CO),
aluminium oxide (Al 2 O 3 ) particles for Ariane and Vega and soot particles for Soyuz.
CO 2 and H 2 O are powerful greenhouse gases. The other exhaust products are not climate forcers but they
play an influential role in atmospheric chemistry, especially chlorine and nitrogen oxides who are involved
in the production and destruction of ozone, an important climate forcer.
In a ’clean’ atmosphere without anthropogenic emissions, ozone is mainly produced by photodissociation
of molecular oxygen and the main reactions that control its concentration are the following :
O 2 + hν → O( 3 P) + O( 3 P) (λ < 242nm)
O( 3 P) + O 2 → O 3
O( 3 P) + O 3 → O 2 + O 2
When reactive emissions are introduced, like the chlorine species from propergol combustion, the ozone
content is reduced by the following catalytic cycle :
Cl + O 3 → ClO + O 2
ClO + O → Cl + O 2
Bilan : O 3 + O → 2O 2
In that context we have studied the impact on stratospheric ozone of a launch of a rocket using propergol,
like Ariane, Vega or the U.S. Titan. Emphasis has been placed on the regional impact above the launch site
and on the ozone destruction within a few hours after the launch. This period is critical since the rocket
exhausts are still very large and their impact on ozone is maximum. To this end we have developed a
transport-chemistry model which computes the chemical composition of the plumes during their dispersion
phase. The transport is introduced with a diffusion model in cylindric geometry. The chemical scheme is
composed of 29 species and about 80 reactions which account for the main reactions of the Ox, NOx, Clx
and HOx species. The models solves the system :
dC i /dt = ... − div(K.grad(C i )) − KC j C i + ... (2.1)
where C i are the concentrations and K the diffusion coefficient. The resulting set of equations is integrated
using the chemical solver described in section 3.1. Fig. 2.5 shows the ozone evolution after Titan 4 launch
at midnight at 15 et 40 km. At sunrise, at 6 am, the ozone is rapidly destroyed within the launcher plume.
The ozone destruction reaches about 70% at 15 km and almost all the ozone is removed within the plume at
40 km. Those pictures are in good agreement with in-situ measurements in the lower stratosphere obtained
by aircraft in the plume after a Titan 4 launch. The local ozone destruction persists over a day before it is
completely mixed with the surrounding atmosphere.
This work is still in development, next steps will focus on the initialisation of the radical concentration using
outputs from the AVBP code (see section 2.3.1), on the atmospheric impact of rockets that use kerosene and
on the improvement of the representation of transport processes by atmospheric turbulence.
CERFACS ACTIVITY REPORT 185