Ozone monitoring

Average ozone declines have been measured over much of Canada using ground-based Brewer spectrophotometers [1]. Since 1980 a statistically significant decrease of about 6% has been found by all five long-term Canadian stations including Toronto (44°N, 79°W). Ozone sonde measurements show that most of the decline has occurred in the lower stratosphere.

Ozone at Arosa, Switzerland since 1926

The decrease in Arctic ozone is most severe in the spring as can be seen from the ground and from satellites. The total ozone column obtained from satellite-based TOMS instruments shows this decrease (averaged over the entire polar region) in the month of March. In March 1997, the ozone column was 21% less than normal and in a small region near the pole the decrease was 40% [2]. Although dynamics plays a major role in redistributing ozone in the Arctic stratosphere, it seems clear that chemical loss of ozone due to heterogeneous chemistry is playing a major role. In fact, several recent publications have indicated that much of the chemical loss in the winter and springtime Arctic is often masked by transport of ozone-rich air from above [3-6]. Specifically Muller et al. (1997) estimate that 120-160 DU of ozone were chemically destroyed between January and March 1996 overwhelming the putative dynamical increase leading to a net loss of about 50 DU. This chemical loss is greater than that which was occurring over Antarctica when the ozone hole was first observed in 1985 [7].

TOMS total ozone

The major goal of ACE is to address the question of Arctic ozone loss and, by means of modeling and measurements (both atmospheric and laboratory), to attempt to quantify the contributions from dynamics and chemistry. Since sulphate aerosol and PSCs play a major role in ozone loss in the Arctic , distinguishing between PSCs, aerosols and cirrus and other clouds is important. There is an important role for laboratory measurements. The role of modeling, either forward modeling or data assimilation, is also critical. A variety of atmospheric models ranging from simple box models for the chemistry to atmospheric global circulation models (AGCMs) are used to interpret our data.The ACE mission is also put in context with existing Canadian and international satellite instruments for atmospheric chemistry. ACE has excited substantial international interest and partners from the United States, Europe and Japan partners work together for the mission. One of our strengths is the financial commitment that our partners have made to ACE. Given the constraints on funding science in Canada , such leveraging of resources is of vital importance.

References

1. Ozone Science: A Canadian Perspective on the Changing Ozone Layer, D.I. Wardle, J.B. Kerr, C.T. McElroy and D.R. Francis, eds., Environment Canada, 1997.
2. Newman, P.A. et al., Anomalously low ozone over the Arctic, Geophys. Res. Lett., 24, 2689-2692, 1997.
3. Müller, R., Crutzen, P.J., Grooss, J.-U., Bruhl, C., Russell III, J.M., Gernandt, H., McKenna, D.S. and Tuck, A., Severe chemical ozone loss in the Arctic during the winter of 1995-96, Nature , 389 , 709-712, 1997.
4. Rex, M. et al. , Prolonged stratospheric ozone loss in the 1995-1996 Arctic winter, Nature, 389, 835-838, 1997.
5. Knudsen, B.M. et al. , Ozone depletion in and below the Arctic vortex for 1997, Geophys. Res. Lett. , 25 , 627-630, 1998.
6. Lefevre, F., Figarol, F., Carslaw, K.S. and Peter, T., The 1997 Arctic ozone depletion quantified from three-dimensional model simulations, Geophys. Res. Lett. , 25 , 2425-2429, 1998.
7. Farman, J. C., Gardiner, B.G., and Shanklin, J.D., Large losses of total ozone in Antarctica reveal seasonal ClO_x/NO_x interaction, Nature , 315 , 207-210, 1985.