The variations of atmospheric carbon dioxide at Alert and Sable Island, Canada

Abstract

It has been observed that atmospheric carbon dioxide (CO 2) is increasing at Alert and Sable Island at a rate of about 1.25 ppm a −1. Seasonal cycles of atmospheric CO 2 are quite evident there, with the occurrence of minimum values in the late summer. Maximum values occur in the late winter at Sable Island in the mid-latitude and in April or May at Alert in the Arctic. Although anthropogenic emissions of CO 2 into the Arctic atmosphere are 2–3 orders of magnitude smaller than those at mid-latitudes, a higher concentration and larger seasonal variation are observed at Alert than at Sable Island. At Alert, a CO 2 minimum in the seasonal cycle in the summer is associated with a lower frequency of atmospheric inversions, and increased occurrence of stratus clouds, precipitation and cyclonic activities. The frequency of occurrence of relatively low values of CO 2 with precipitation and fog during the period of 1981–1985 was 64.3 % at Alert and 62.0% at Sable Island. Air parcel back-trajectory analyses have indicated that at Sable Island relatively low values of CO 2 are associated with air parcels generally coming from the N or SE (oceanic regions) to the site. In contrast, relatively high values are associated with 5-day trajectories arriving from the W or WSW, i.e. from the continent. The 5-year climatology of air parcel trajectories arriving at Alert showed that low values of atmospheric CO 2 concentrations are usually associated with S-SW airflows, while relatively high values of CO 2 are generally associated with a long trajectory originating in the Soviet Arctic. In particular, high values of CO 2 concentrations occur in the late spring under the meteorological conditions of a pronounced temperature inversion, high solar radiation and calm or light winds at the surface. These conditions are favourable for high air pollution potential in the Arctic and for CO 2 episodes at Alert. It is believed that Arctic air pollution is a cause of perturbation in radiation budgets especially during spring.