Arctic air pollution : future perspectives

Chères et chers collègues,

Atmospheric pollution (ozone, aerosols and their precursors) in the Arctic originates primarily from mid-latitude emission regions but also has local sources which are likely to increase in the future due to global warming and economic drivers. It is important to quantify their impacts on regional air quality and climate.

The contribution of different sources to Arctic pollution still remains uncertain despite significant advances, in particular, as a result of field campaigns which took place during the International Polar Year in 2008 (e.g. POLARCAT-France, ARCTAS, ISDAC), and subsequent analysis/data collection that is still on-going (e.g. ANR-CLIMSLIP - http://www.latmos.ipsl.fr/index.php/fr/tact/themes-de-recherche/climslip, LIA YAK-AEROSIB, https://yak-aerosib.lsce.ipsl.fr/doku.php ) involving groups from several laboratories (LATMOS, LaMP, LSCE, LGGE, LMD). Local anthropogenic emissions in the Arctic may be playing a more significant role (direct and indirect effects) than previously appreciated, and are likely to increase substantially in the near to mid-term future. Changing natural aerosols as well as methane also need to be taken into consideration.

With this in mind, we have identified 2 research areas which we feel merit further discussion in the French community as part of the Chantier Arctique prospective:

Local Arctic Pollution:
Given the very rapid nature of climate change in the Arctic and global economic pressures, accelerated industrialization in the Arctic is already underway with summer maritime sea routes along the Northern Sea Route already open, and strong interest in oil/gas and mineral exploration in Alaska, Greenland and northern Eurasia. Construction of polar class ships, which can penetrate summer sea-ice across the North Pole, has already been evoked. Local emissions already appear to be influencing atmospheric composition and climate in the Arctic (e.g. flaring and domestic combustion emissions of black carbon in Eurasia, cruise shipping in Svalbard). Significant growth in local sources, together with increased growth in infrastructure, industrialization and/or urbanization, are likely to impact concentrations of trace gases and aerosols and thus, regional air quality and/or climate.

Given the significant uncertainties which exist in quantifying current and future emissions from shipping, oil/gas extraction, metal smelting, mining, domestic combustion as well as boreal/agricultural fires in the Arctic, a combination of local-scale and regional modelling, analysis of existing data (e.g. from EU ACCESS project (www.access-eu.org), ground-based, satellite) and new field data is needed. In particular, an aircraft campaign, using an aircraft from the French fleet, could be used to improve quantification of local emissions and regional budgets. The aircraft, equipped with a full aerosol and trace gas payload, could be based in, for example, northern Scandinavia/ Spitzbergen. It will also be important to take into consideration unique Arctic photochemistry, such as the presence of halogens or snow emissions, which can influence the Arctic oxidising capacity, particularly in the boundary layer where local emissions are occurring. An aircraft equipped with remote sensing instruments (radar and lidar) could also be used for aerosol and cloud studies. A campaign with the Russian YAK aircraft could also be dedicated to these issues since some of the largest uncertainties surround local emissions in Siberia and northern Russia (e.g. fires, smelting, flaring, domestic emissions). New data would be used to improve the representation of emissions and aerosol/trace gas processing in regional/global models as well as to improve emission inventories used for predicting future composition and climate. These data will also help to better understand the impact of pollution on clouds and radiative processes.

Air Pollution Sources in the High Arctic:
Significant changes are currently underway in the Arctic Ocean, in particular, the decline of the summer sea-ice with significant reductions in volumes/extend reported. The role of pollutants, and in particular aerosols, in Arctic warming is currently poorly quantified due to a lack of knowledge about important processes and their treatment in models. In particular, there is a lack of information about the vertical distribution of trace gases, aerosols and their speciation as well as cloud microphysics in the high Arctic (>75N) with previous airborne campaigns focusing largely on more southerly Arctic latitudes. Cloud properties related to pollution aerosols are also poorly quantified and new field experiments would benefit from up to date microphysical and remote sensing airborne measurements recently developed in France. A combination of airborne radar/lidar measurements could be used to document aerosols and mixed-phase clouds. Satellite data (e.g. CALIPSO-CloudSat, EarthCare, IASI, GOSAT) can provide additional information (up to 82N for CALIPSO), including regions of pollutant import, but further work is required on retrievals at high latitudes. New developments, as part of the Equipex IAOOS project (http://www.iaoos-equipex.upmc.fr/, 2011-2019), are also underway such as the addition of aerosol micro-lidars to ocean-atmosphere buoys that will be deployed in the Arctic Ocean from 2014/15 and can provide contextual information about cloud/aerosol distributions. Other new approaches could also be envisaged, such as the use of unmanned aerial vehicles (UAVs), as well as the development of new airborne sensors.

A combined approach, based on new field measurements, regional/global modelling and analysis of satellite data, is needed to improve our understanding about the role of pollutants (aerosols, ozone) and feedback processes in the high Arctic. An aircraft campaign using the French aircraft fleet, based in Spitzbergen or Greenland, for example, could be used to collect data on vertical distributions over the Arctic Ocean, in the vicinity of pollutant import regions linking to the IAOOS buoy network and to validate satellite data. The data would be used to improve our understanding about radiative effects and impacts on clouds, and the treatment of such processes in models leading to improved climate predictions. Such an initiative could also contribute to international plans under development as part of the International Polar Initiative (IPI) (http://internationalpolarinitiative.org/) focusing on improving seasonal and climate predictability in the Arctic.

We look forward to discussing these ideas in the French community and welcome any comments or feedback.

Kathy Law, Gerard Ancellet, Jacques Pelon, Jennie Thomas, Jean-Christophe Raut, Cyrille Flamant, Francois Ravetta, Claire Granier, Cathy Clerbaux, Julien Delanoë, Sébastien Payan
LATMOS (CNRS-UPMC-UVSQ/IPSL)

Contribution du Laboratoire de Météorologie Physique (LaMP,
CNRS-UBP Clermont II, OPGC).





Les modèles de climat suggèrent
que les rétroactions liées aux nuages et l’absorption par le carbone suie contribuent
fortement au réchauffement climatique observé en arctique. En effet des
observations montrent que la modification des propriétés des nuages a joué un
rôle prépondérant dans la fonte de la banquise en 2007 (Kay and Gettelman,
2009). Néanmoins, les incertitudes associées à la représentation des nuages et
des aérosols dans les modèles de climat engendrent de grandes incertitudes dans
la prédiction du changement climatique en arctique. La complexité des interactions entre les
aérosols et les nuages doit être mieux appréhendée afin de résoudre les
divergences entre les modèles de climat et les mesures. L’évaluation de
l’impact radiatif des nuages est conditionnée par une compréhension et une
caractérisation détaillée de la phase thermodynamique, des propriétés
microphysiques, optiques et géométriques des nuages. D’autre part, la forte
variabilité saisonnière des propriétés physico-chimiques des aérosols (plus de
CCN en hiver et au début du printemps, plus d’IN en Mai qu’en Octobre) modifie de façon significative les
propriétés microphysiques des nuages
(par exemple les concentrations respectives de gouttelettes d’eau et de
cristaux de glace au sein d’un nuage en phase mixte). La plupart des études
menées sur l’impact des aérosols (CCN) sur les propriétés des nuages se sont
concentrées sur les nuages en phase liquide. La phase thermodynamique des
nuages jouant un rôle primordial sur les propriétés radiatives, il est
nécessaire de considérer de façon plus adéquate l’effet des aérosols sur la partition
eau/glace des nuages dans les modèles. L’étude de l’interaction aérosols-nuages
en arctique passe donc par une quantification de la variabilité saisonnière, de
la distribution verticale des propriétés physico-chimiques des aérosols et des
nuages. Il apparait donc primordial de disposer d’observations coordonnées des
propriétés des aérosols et des nuages en particulier au début du printemps
(concentration élevée des aérosols et apparition du soleil) ainsi qu’en Mai
(début de la fonte et efficacité du forçage maximale).


Différentes campagnes de mesures
aéroportées réalisées en collaboration avec l’AWI (ASTAR 2004, 2007, SORPIC
2010) au large du Spitzberg ont mis en évidence l’intérêt de la plateforme de
mesures aéroportées du LaMP pour caractériser les propriétés microphysiques et
optiques in situ des nuages arctiques. L’apport du RADAR et du LIDAR (RALI)
aéroportés du LATMOS lors de POLARCAT 2008 a apporté une dimension
supplémentaire pour la documentation des propriétés nuageuses selon la
verticale. D’autre part, dans le cadre de l’ANR CLIMSLIP des mesures in situ
des nuages de basse altitude ont été réalisées en synergie avec des mesures des
propriétés physiques des aérosols pendant 3 mois à la station du Mont Zeppelin
(Ny-Alesund) en 2012 . Ces différentes campagnes nous ont permis de mieux
documenter certaines composantes des processus microphysiques nuageux. Néanmoins, il serait nécessaire d’effectuer
des campagnes de mesures aéroportées au large du Spitzberg avec un avion équipé
de la plateforme microphysique du LaMP (Falcon) en nuage coordonnées avec des
mesures in situ de la composition et des propriétés physiques des aérosols proches
du nuage ainsi que des mesures réalisées par la plateforme RALI (sur l’ATR-42).


Il serait également judicieux de
prolonger les observations précédemment effectuées au Mont Zeppelin
(Ny-Alesund) en renforçant la caractérisation des propriétés physico-chimiques,
IN et CCN des aérosols avec une instrumentation plus sophistiquée disponible au
LaMP. L’apport de la plateforme portative BASTA (RADAR-LIDAR) du LATMOS
permettrait également de documenter la distribution verticale des propriétés
des nuages de couche limites.


L’ensemble de ces observations
couplées aux outils de modélisation de microphysique détaillée (DESCAM-3D)
devrait permettre une étude optimale de l’interaction aérosols nuages en
arctique.





Olivier
Jourdan, Alfons Schwarzenböck, Karine Sellegri, Evelyn Freney, Wolfram Wobrock
(LaMP), Julien Delanoë (LATMOS)

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 local 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.


Evelyn
Freney, Karine Sellegri, Olivier Jourdan, Aurelie Colomb, Alfons Schwarzenböck
(LaMP).

Atmospheric black carbon and ozone precursors typically released by human activities at mid-latitude industrialized regions of the Northern Hemisphere are quickly moved over long distances by atmospheric transport and can reach the Arctic. Black carbon, tropospheric ozone and several other species has become of increasing concern because they can change atmospheric chemistry and air quality in the Arctic and change the radiate balance of the Arctic area. In addition, emissions from forest fires in Siberia and by prescribed agricultural fires in Southern Siberia, Kazakhstan and Ukraine in spring and summer are large sources of trace gases such as aerosols and gas pollutants to the Arctic.
YAK-AEROSIB (https://yak-aerosib.lsce.ipsl.fr) aims at tackling these issues by organizing new aircraft campaigns to better document these phenomena and better understand influences on Arctic radiative balance. Aircraft can reach the intercontinental pathways and source areas in Siberia and the Arctic ocean coastal environment. Currently the aircraft is equipped to measure CO, O3, CO2, CH4, and has limited observation capacity for BC and aerosol size distribution. Future campaigns should have an enhanced instrumental package
1- to better resolve the vertical structure of aerosols
2- to better observe O3 precursors transport, NOy including NOx and reservoir species (PAN), and
3- to better characterize concentrations, size distribution, chemical and optical properties of aerosols, especially black carbon and organic carbon.
Regarding point 1 a microLIDAR is being prepared for following campaigns.
Points 2 and 3 would require new in-situ instrumentation. This would possibly include SP2 for black carbon, and an AMS for a better characterization of aerosol size and chemical composition. Few observation techniques detailing total reactive nitrogen are available for aircraft, but chemiluminescence type analysers could be flown to have access to NOx and NOy and possibly CIMS for PAN.

Effectivement, la spatialisation des données est une des clefs pour comprendre le rôle des différentes sources dans la pollution à grande
échelle du bassin Arctique. N'oublions pas que le phénomène d'arctique haze, étudié depuis les années 70 et évoqué par les pilotes de l' USAF
dès les années 50, est un phénomène ancien. La pollution de l'Arctique n'est donc pas une donnée nouvelle en soi. En revanche, il est clair que la structure
de cette pollution ait très probablement évolué au cours du temps (avec la notable décroissance des concentrations en sulfate ou du plomb par exemple).
L'urbanisation, le transport, l'exploitation à l'intérieur même du bassin Arctique est effectivement un élément à prendre en compte tout comme, la forte
industrialisation de l'asie ou les politiques de régulation des émissions polluantes. Ce changement de structure au cours du temps est forcément enregistré
dans les neiges.

Il conviendrait donc de s'intéresser tout autant aux dépôts neigeux qu'aux différents compartiments de l'atmosphere Arctique (MBL, FT, UTLS).
L'étude des enregistrements glaciologiques s'imposent aussi comme outil pertinent d'étude de l'évolution spatio-temporelle de cette pollution à l'échelle
décennale et du bassin Arctique. Les changements des signatures isotopiques en azote des sédiments des lacs de l'amérique du Nord ou des glaces
du groenland depuis la révolution industrielle sont les témoins de ces modifications des sources, cependant le sens de ces modifcations est à l'opposé de ce qui
est attendu par l'augmentation des émissions anthropiques. Le simple schéma d'une augmentation des émissions anthropiques qui s'imprimerait telles quelles
dans les neiges et l'atmosphère Arctique ne fonctionne pas. N'oublions pas de même que les études de cette dernière décennie ont révélé à quel point
la neige pouvait constituer un réacteur chimique efficace capable de jouer aussi le rôle d'émetteur et non uniquement de receptacle. Dans cette optique,
l'analyse de la neige et des flux de matière associés est essentielle à la compréhension de l'anthropisation de l'Arctique. Il serait intéressant d'effectuer des études
latitudinales du couvert neigeux et d'en comprendre son anthropisation.