Characterisation of anthropogenic aerosols and their interactions with clouds in the Arctic.

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Characterisation of anthropogenic aerosols and their interactions with clouds in the Arctic.

Message  EJFreney le Mar 30 Avr - 16:09

Contributions from the
Laboratoire de Meteorologie physiques (LaMP).

Several recent studies have
highlighted that the Arctic is warming twice as fast as the rest of the Earth. This
has resulted in the shrinking of the Arctic ice sheet and thereby opening up
new shipping channels that were not previously available. The increase in shipping
channels and the consequent
urbanization results
in an increase in local emissions that can have important implications on
aerosol properties and their interactions with clouds (liquid and ice phase).
It is thought that aerosol
direct (absorption by black carbon) and indirect (aerosol cloud interactions) effects
are likely to play a large role in the rapidly changing Arctic climate. In
addition to lo
cal sources, polluted air masses are transported over long-distances
that lead to the formation of the Arctic Haze, containing high concentrations
of absorbing aerosol particles.

Predictions of climate warming
in the Arctic from models are considerably lower than observations, thereby
highlighting the need to carry out experiments dedicated to understanding the influence
of anthropogenic emissions in the Arctic environment, and how these emissions
affect the interactions between aerosol particles and clouds. Although there are
an increasing number of ground-based studies, few aircraft observation studies
have performed detailed chemistry measurement of aerosol particles in the Arctic.
Aircraft studies are one of the most efficient methods to characterize the
influence of different air-masses and local sources on the Arctic environment,
characterising the evolution of aerosol particles as they leave the source and
mix with background air-masses. In addition, they provide a means to
characterize the vertical profile of the chemical and physical properties of
both gas and aerosol particles.

The LaMP has three airborne
racks that are equipped with a suite of ATR-42 (SAFIRE) certified
instrumentation including the C-ToF-AMS (particle chemistry), SMPS and CPC
(size distribution measurements), volatility measurements, and impactor stages
for offline analysis with electron microscopy. This combination of instruments
allows us to characterize the chemical and physical properties of aerosol
particles with timescales of less than 1 minute. The combination of CPCs and
SMPS provides us with aerosol particle number concentration of aerosol particles
as small as 5 nm, providing important information on new particle formation
events (NPF). NPF events (nucleation) can contribute up to 50% to cloud condensation
nuclei in the atmosphere, making it essential to characterize the meteorological
conditions under which they form. Electron microscopy can provide detailed
information on aerosol composition, morphology, and mixing state which is
essential to understand aerosol cloud interactions, and is especially useful in
understanding the formation of ice crystals.

In addition to airborne
measurements, ground based in-situ measurements of aerosol particle chemical
and physical properties, together with cloud condensation nuclei measurements can
provide a means to carry out extended studies using additional instrumentation that
can not be airborne. This extended set-up will allow for process studies in the
very specific conditions of the arctic environment. In particular, ship
emissions containing high content of sulfur can lead to large numbers of new particles,
that in turn may influence cloud optical properties.

Freney, Karine Sellegri, Olivier Jourdan, Aurelie Colomb, Alfons Schwarzenböck


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Date d'inscription : 30/04/2013

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