Andreas StohlNorwegian Institute for Air Research (NILU)

and

E. Andrews, T. Berg, J. F. Burkhart, A. M. Fjæraa, C. Forster, A. Herber, S. Hoch, Ø. Hov, D. Kowal, C. Lunder, T. Mefford, W. W. McMillan, J. A. Ogren, S. Oltmans, S. Sharma, M. Shiobara, D. Simpson, S. Solberg,

N. Spichtinger, K. Stebel, R. Stone, J. Ström, R. Treffeisen, K. Tørseth, K. Virkkunen, C. Wehrli, and K. E. Yttri

Some current science problems regarding Arctic air pollution

Aerosol radiative forcing

Aerosol direct radiative forcing is different from any other place• large solar zenith angles• pronounced haze layers• high surface albedo (snow, ice, stratus cloud decks)lead to multiple scattering/reflection between haze layers and the surface and enhance the relevance of light absorption

Aerosol indirect radiative forcing could be positive in the Arctic• no solar radiation in winter• Arctic clouds so thin that they are greybodies in the

longwave, making them susceptible to aerosol effects in the longwave (thermal radiation)

Thus, positive forcing, opposed to the shortwave effects

Some current science problems regarding Arctic air pollution

Albedo effects

Black carbon important light absorber in the atmosphere, but also when deposited on the ground, as it reduces the albedo of snow/ice surfaces.

The efficacy of this effect is about twice as large as that of CO2, thus leading to pronounced effects on the surface temperatures and sea ice melting.

Some current science problems regarding Arctic air pollution

Uncertain sources of Arctic air pollution

One study (Koch and Hansen, 2005) suggests South Asia as the main source of Black Carbon, another (Stohl, 2006) rejects this hypothesis – quite heavily debated just recently in a workshop on Arctic climate forcing.

Stohl (2006) suggests a ”new” source of Black Carbon to be dominant in summer: biomass burning (esp. boreal forest fires)

Pyro-convection can inject aerosols into the high-latitude stratosphere

Some current science problems regarding Arctic air pollution

Ozone depletion events

In springtime, ozone can disappear almost completely at surface stations

”Bromine clouds” responsible, but unclear where the bromine originates

Satellites and models have problems in the Arctic

Satellites

• No data from geostationary satellites • No light in winter – no observations in the shortwave• Large solar zenith angles in summer – still problems• High albedo of snow and ice – aerosol optical depth

unreliableModels

• Highly stable atmosphere – thin layers that cannot be resolved

• Many global models use a latitude/longitude grid – singularity at the pole, which may lead to incorrect transport in large parts of the Arctic

IASOA observatories

December,the darkest month

- lowest 100 mof the atmosphere

Stohl (2006): J. Geophys. Res. 111, D11306, doi:10.1029/2005JD006888.

Intercontinental transport

July January

Time spent continuously north of 70°N - Lowest 100 m of the troposphere

Note the different scales!!!

Average age of air north of 80°N

Stohl (2006): Characteristics of atmospheric transport into the Arctic troposphere. J. Geophys. Res. 111, D11306, doi:10.1029/2005JD006888.

Continental BC contributions in dependence of time from a FLEXPART tracer model simulation– no chemistry, no removal, only transport using BC emission inventory from T. Bond

Lower troposphere Total column

Continental BC contributions in dependence of time

BC inventories from T. Bond and D. Lavoue (boreal fires)

Lower troposphere Total column

• 2004 was the most severe burning season in Alaska

• Strong fires also in western Canada

• > 5 million hectare burned

Pan-Arctic enhancements of light absorbing aerosol concentrations

due to North American boreal forest fires during summer 2004Stohl et al. (2006): JGR, 111, D22214, doi:10.1029/2006JD007216.

Pyro-Cb

Damoah et al. (2006):

Atmos. Chem. Phys. 6, 173-185.

FLEXPART Tracer Simulation:Total CO column

Barrow

Alert

80°N

90°N

Comparison model / satellite image

5. July 2004

FLEXPART Total Column MODIS satellite image

Barrow

Alert

Barrow, Alaska

• Aerosol Optical Depth (AOD) measurements(symbols) and FLEXPART CO column(line)

Source analysis

”normal” value

• EBC measurements(black line) and FLEXPART CO tracerat the surface(colors give the ”age” sinceemission)

Barrow, Alaska

Source analysis

using a FLEXPART backward calculation

Barrow

Emission sensitivity

Summit, Greenland

• Aerosol Optical Depth (AOD) measurements(symbols) and FLEXPART CO column (line)

• EBC measurements(black line) and FLEXPART CO tracerat the surface(colors give the ”age” sinceemission)

”normal” value

Zeppelin, Spitsbergen

• CO and EBC measurements from May til September

◀ CO ▶Anomaly

Zeppelin, Spitsbergen

• Aerosol Optical Depth (AOD)-measurements(symbols) and FLEXPART CO column(line)

◀ fog, rain ▶

◀ CO anomaly ▶

• EBC measurements(black line) and FLEXPART CO tracerat the surface(colors give the ”age” sinceemission)

”normal”

value

Effects on the albedo of snow

Albedo at Summit, Greenland

Fresh snowSnow drift

Arctic smoke – record high air pollution levels in the European Arctic due to agricultural fires in

Eastern EuropeStohl et al. (2006): Atmos. Chem. Phys. Discuss. 6, 9655–9722.

Fire detections in April/May 2006

Record warmth in the European Arctic

Temperature at Ny Ålesund, Spitsbergen in April and May 2006

Warmth ”dismantles” the polar dome and creates effectivepathway into the Arctic!

Transport of fire emissions into the European Arctic

Extreme pollution

Picture courtesy: Ann-Christine Engvall

Extreme pollution

At Zeppelin, new records were set for practically all measured compounds

Ozone, aerosol optical depth (both measured for about 15 years!)

Carbon monoxide,particulate matter, etc.

Ozone formationwas highly efficient!

Extreme pollution

At Iceland, a new ozone record was set, 15 ppb higher thanany previously measured value

Polluted snow at Holtedahlfonnaobserved by John Burkhart

Snowmobile track←

Polluted

snow

Ion chromatographic analysis of snow samples confirms BB source.

POLARCATPolar Study using Aircraft, Remote Sensing, Surface

Measurements and Models, ofClimate, Chemistry, Aerosols, and Transport

http://www.nilu.no/polarcat

Contact me: AST@NILU.NO

How? When? Where?Major Campaigns

1. March/April 2007: 2 aircraft based in Longyearbyen, Svalbard2. February-May 2008: Approximately 5 aircraft, based at various

locations throughout the Arctic, plus a ship cruise from North America to the Norwegian Sea

3. June-August 2008: Up to 10 aircraft based in Canada, Russia, Europe, Greenland, etc.; measurements with a railway carriagealong the Transsiberian railroad

Surface stationsZeppelin, Barrow, Summit, etc.: long-term monitoring, plus intensive campaigns

Satellite dataRetrievals will be made in near-real time for flight planning, and for post-mission analyses; algorithm validation and improvement

ModelsA variety of chemistry-climate, chemistry-transport, and pure transport models will be used

Some of the POLARCAT platforms ....