Late one night in September 1999, ZL, travelling the inland road between the Station and West Light, encountered a distinct pocket of acrid air accumulated in a low sheltered hollow along the road. ZL returned to the Station to report to the Station manager, and both then travelled between West Light and the west end of the island to investigate. Although air having the very strong chemical smell could be found only in several low points along the inland road, the smoky plume from the Thebaud platform was clearly visible and extended across the western end of the island. The atmosphere of the Scotian Shelf region is affected, to some degree, by activity associated with the offshore energy industry. Exploration and production installations, supply and seismic vessels, and helicopters produce various air emissions, including: combustion products from engine exhaust and flares aerosol from incomplete combustion and/or physical-chemical reactions volatile and semi-volatile organic compounds (VOCs) from incomplete combustion and fugitive emissions Some of the above emissions (e.g. combustion products such as oxides of nitrogen) are greenhouse gases. Although none has been reported, hydrogen sulfide (H₂S) gas, from "sour" well developments, is also a potential airshed pollutant. While MSC's greenhouse gases program on Sable Island addresses continental and global pollution sources and impacts, the primary focus of the airshed monitoring program is to measure and identify sources of ambient air emissions in the Scotian Shelf region. The Sable Island site is one of ten air monitoring installations in Nova Scotia which provide ambient air quality indexes relevant to human health. Also, the data from Sable Island improves the overall accuracy of air quality predictions, and helps in identification of air quality concerns within the region and implementation of management strategies to address those concerns. The quality of the air we breathe is dependent on the rate that pollutants are emitted into the atmosphere and the ability of the atmosphere to disperse these pollutants. The movement and dispersion of air pollutants is controlled by wind, temperature, turbulence and the changes in these elements caused by local topography and/or oceanography. To gain a better understanding of possible sources and behaviours of pollutants, the interpretation of the data is supported by basic meteorological measurements of parameters that affect the transport and dispersion of emissions. Measurements collected at the Sable Island Station in support of the airshed monitoring program are: wind speed and direction; temperature; solar radiation; and relative humidity. Atmospheric modelling, which relies on meteorological and aerological data collected at Sable Island and other stations, enables researchers to generate back-trajectories for air parcels, and provides a tool for study of circulation of atmospheric pollutants. Thus, if the airshed monitoring program on Sable Island detects a pollution event, researchers would be able to generate a back-trajectory indicating an origin of the polluted air.
Back-trajectory for air parcels at Sable Island at 0600 hrs GMT on June 9th, 2004 (Meteorological Service of Canada).



This plot, generated back to June 5th shows the routes travelled by air parcels, west to east across the North American continent, arriving at Sable Island on June 9th. The red, blue and green lines show the tracks of air at three different pressure levels, corresponding to different altitudes. The red line represents air flows at approximately 3000 meters, the blue line shows air flows at approximately 1500 meters, and the green line shows air flows closest to the ground. These flows move across the continent, but also move up and down due to topography, temperature changes, and the movement of pressure patterns. For example, the low level flow represented by the green line was at a pressure of 925 millibars. This corresponded to 100 meters above sea level at its western start, but at 750 meters above sea level over Sable Island.

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The airshed monitoring program on Sable Island was initiated by the Canada-Nova Scotia Offshore Petroleum Board and sponsored by the Environmental Studies Research Fund, a funding source provided by the offshore energy industry. Also participating are the Meteorological Service of Canada, and the Nova Scotia Department of Environment and Labour.

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