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Continental Scale Antarctic Deposition of Sulphur and Black Carbon from Anthropogenic and Volcanic Sources

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Continental Scale Antarctic Deposition of Sulphur and Black Carbon from Anthropogenic and Volcanic Sources Atmos. Chem. Phys., 10, 2457–2465, 2010 www.atmos-chem-phys.net/10/2457/2010/ Atmospheric © Author(s) 2010. This work is distributed under Chemistry the Creative Commons Attribution 3.0 License. and Physics Continental scale Antarctic deposition of sulphur and black carbon from anthropogenic and volcanic sources H.-F. Graf1, S. V. Shirsat1, C. Oppenheimer1, M. J. Jarvis2, R. Podzun3, and D. Jacob3 1University of Cambridge, Geography Department, Cambridge, UK 2British Antarctic Survey, Cambridge, UK 3Max-Planck-Institute for Meteorology, Hamburg, Germany Received: 8 October 2009 – Published in Atmos. Chem. Phys. Discuss.: 11 December 2009 Revised: 1 March 2010 – Accepted: 5 March 2010 – Published: 11 March 2010 Abstract. While Antarctica is often described as a pristine largest with a population of around 1000 people during the environment, there is an increasing awareness of the potential austral summer (November to March) and of 250 during win- threats from local pollution sources including tourist ships ter (April to October). The history of tourism in Antarctica and emissions associated with scientific activities. However, also dates back to the 1950s. In 2000 an international organi- to date there has been no systematic attempt to model the im- zation was created (IAATO, www.iaato.org) to monitor and pacts of such pollutants at the continental scale. Indeed, until regulate tourist activity in the region. Their reports reveal a very recently there was not even a sulphur emission budget strongly increasing number of tourist visits from 12 248 to available for Antarctica. Here we present the first compre- about 46 000 between the 2001/2002 and the 2007/2008 sea- hensive study of atmospheric pollution in Antarctica using a sons, with an anticipation of further growth. Most of the limited area chemistry climate model, and a monthly emis- tourists (98%) are ship borne. sions inventory for sulphur from maintenance of research Several prior studies have investigated pollution due to stations, ground and air traffic, shipping and the active Ere- research activity at stations. PM10 abundance measured in bus volcano. We find that ship emissions, both sulphurous McMurdo during the austral summer routinely exceeds lev- and black carbon, dominate anthropogenic pollution near the els found in remote coastal regions of the continent (Lu- ground. Their prevalence is likely to rise dramatically if re- gar, 1993; Mazzera et al., 2001). Another study (Wolff cent trends in tourism continue. and Cachier, 1998) conducted during 1992–1995 measured Black Carbon (BC) at Halley research station and found a mean background atmospheric level of approximately 1 ng BC m−3, and spikes of several hundred ng BC m−3 350– 1 Introduction 400 m downwind of the generators. It was also suggested that the annual cycle of BC from its timing appears to be The remote and mostly uninhabited continent of Antarctica controlled by biomass burning in the tropics, strongly mod- was discovered in the late 18th century but forsaken except ulated by the efficiency of transport to Antarctica. In a more for sporadic expeditions until the International Geophysical recent study Stohl and Sodemann (2010) assessed long-range Year in 1957/1958 when a number of permanent research transport of BC towards Antarctica excluding any loss pro- stations were established. Today, 37 year-round and 16 cesses along the transport path. They conclude that it is “un- summer-only research bases operate in Antarctica, of which likely for air from these continents to reach Antarctica on McMurdo (managed by the US Antarctic Program) is the time scales relevant for aerosols and many short-lived trace gases”. This makes local sources of pollution especially rel- Correspondence to: H.-F. Graf evant. ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. 2458 H.-F. Graf et al.: Continental scale Antarctic deposition of sulphur and black carbon oxidises to SO2 and, ultimately, to sulphate in the atmo- Table 1. Emissions from sulphur inventory (6) in Mg SO2 month−1. sphere. Estimates of source strength range between 1.4 and 2.7 Tg S yr−1 for the Southern Ocean (Berresheim, 1987; Source Station Ship Aircraft Erebus Curran and Jones, 2000) but their transformation into other sulphur species and subsequent deposition is highly uncer- April 4 – 2229 tain (Boucher et al., 2003). In any case, these sources by far May 4 – 2229 exceed anthropogenic emissions of sulphur species and mask June 4 – 2229 the contribution from anthropogenic sources. In order to de- July 4 – 2229 August 4 – 2229 termine the patterns of anthropogenic sulphur deposition we September 4 – 2229 therefore exclude DMS sources from our study. The mod- October 4 – 2229 elled distributions of sulphur emissions may also be seen as November 26 223 6.4 2229 giving a guide to the potential dispersal of other, potentially December 26 1971 5.6 2229 more toxic chemical species that are emitted concurrently but January 26 769 21.3 2229 not treated in our model. February 26 693 21.2 2229 The weather and climate of Antarctica are dominated by March 26 217 1.3 2229 strong katabatic winds blowing from the continent’s interior towards the open ocean and by strong westerlies with embed- ded synoptic storms encircling the continent between 60◦ S and 40◦ S, making the region extremely windy, cloudy and precipitation rich. Most human activity is concentrated in Other pollutant sources include combustion of fuel for coastal areas with relatively easy access in summer, when transport and energy production, sewage burning (banned af- the prevailing weather conditions tend to hinder transport of ter 1997) and accidental oil spills (Bargagli, 2008), for ex- airborne pollutants towards the interior of the continent. ample from shipping accidents such as befell the Antarctic cruise vessel “Explorer” in 2007 or the “Bahia Paraiso” acci- dent in 1989 where 6×105 l of oil were spilled. Most of these 2 Emission inventory studies concerned point measurements in the proximity of re- search stations (for a comprehensive review on the effects of We use a new emissions inventory (Shirsat and Graf, 2009) in human presence in Antarctica see Tin et al., 2009), and we a model simulation of transport, chemical transformation and are unaware of any study of continental scale contamination. deposition of sulphur compounds and BC (from ship emis- Only very recently was a first comprehensive emission in- sions only) for the year 2004/2005. The emissions from each ventory published for 2004/2005 (Shirsat and Graf, 2009). source (station activity, ground transport, aviation, ships, and Natural sources of pollution include Erebus volcano, emissions from Erebus volcano) were tagged to allow com- whose summit crater reaches 3794 m above sea level on Ross parison of their individual contributions to the total atmo- Island, and which has probably been degassing continuously spheric abundance and deposition. Station activity including from its active lava lake since at least its discovery in 1972 ground transport contributes 158 Mg of SO2 for April 2004 (Giggenbach et al., 1973). Between 1992 and 2005, the to March 2005, only 18 Mg more than an earlier estimate (Boutron and Wolff, 1989). Aircraft operations contribute average of all SO2 flux measurements for the volcano was 61 Mg d−1 (∼1860 Mg month−1; Sweeney et al., 2008) very 56 Mg of SO2 at varying altitudes but exclusively during the similar to measurements made in 2006 (Boichu et al., 2010). Antarctic summer. In December 2003, ultraviolet spectroscopy indicated that By far the highest anthropogenic source during the 2004/2005 summer season is shipping: 3.873 Gg of SO2 and Erebus volcano is also an important source of NOx (Oppen- 14.5 Mg of BC. This is 40 times more SO2 than the esti- heimer et al., 2005). This finding was substantiated by in ◦ situ sampling of the drifting plume with an instrumented air- mated total shipping source south of 60 S in 1989 (Boutron craft, which revealed significant abundances of volcanogenic and Wolff, 1989)! Bond et al. (2007) as quoted by Stohl and Sodemann (2010) estimated the total BC emission from HNO3 and HO2NO2 as well as ozone depletion likely due to ships south of 60◦ S, including fishery activities, as 100 Mg a combination of reactive halogen and NOx chemistry (Op- penheimer et al., 2010). Several sporadically active volca- per year, an amount exceeding our BC emission data by a ∼ noes are located in the outer South Sandwich and Shetland factor of 7. The number of ship visits to Antarctica, in- Islands, but their emissions have not been measured and they cluding scientific missions, support of station operations and are not taken into account here. tourism, is rising. In the Antarctic summer (November to March) 2004/2005, 65% of all ships carried tourists (Shir- Oceanic and coastal biota (mainly penguins) also con- sat and Graf, 2009) and their number rose from 210 trips in tribute to atmospheric pollution as does the emission of NO x 2004/2005 (our study period) to 301 trips in the 2007/2008 from snow pack (Wang et al., 2008). Marine bioactivity austral summer, an increase of 43% within three years. leads to the emission of dimethylsulphate (DMS), which Atmos. Chem. Phys., 10, 2457–2465, 2010 www.atmos-chem-phys.net/10/2457/2010/ H.-F. Graf et al.: Continental scale Antarctic deposition of sulphur and black carbon 2459 Human activity on the continent is highly localised around driven at the lateral boundaries every 6 h by ECMWF ERA40 bases, with the highest populations found on the Antarctic reanalysis data (Uppala et al., 2005) after initialization at all Peninsula, in the Ross Sea area (Ross Island and Terra Nova grid points on 1 April 2004. Gas phase RADM2 (Stockwell Bay), Queen Maud Land and around the Amery Ice Shelf.
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