Ozone climatology, trends, and substances that control ozone

Ozone decline observed in the stratosphere over the past three decades has resulted from the accumulation of chlorine‐ and bromine‐containing ozone‐depleting substances (ODSs) in the atmosphere. Production of most of these gases is regulated by the Montreal Protocol and its Amendments and Adjustments. The latest observations show a decline in major ODSs in the troposphere as a result of these regulations. Observed changes in global ozone are in line with those expected based on changes in stratospheric levels of chlorine and bromine. A change in the rate of ozone decline was observed in the mid‐1990s. This paper gives a brief overview of the present knowledge of distribution, variability, and long‐term trends in column ozone and ozone profiles, with a focus on observational results and particularly on Canadian data analysis.