• P. 97, L. 1970: The authoring team should consider deleting the clause “aided by U.S. decreases.” This point has already been made in the text.

  • P. 98, L. 1992-1995: This text states that the U.S. GWP-weighted emissions of ODSs have declined by 74% through 2004. However, section 2.1.4.2 (P. 47, L. 973-975) states that U.S. production and consumption data are not available in GWP-weighted form. Both sentences may strictly be true, but U.S. GWP-weighted emissions are only obtainable from detailed knowledge of the production.

CHAPTER 3:
OZONE AND UV

Chapter 3 of the draft SAP represents a good effort at assembling the necessary material into a first draft. The questions are clearly posed, and the topics needed to address these questions are covered. Chapter 3 may be improved with a reorganization of its sections, as suggested in Chapter 2 (Overarching Comments) of this review, and as suggested below.

Major Comments

As suggested in the “Major Comments” for SAP Chapter 1, some of the background information provided in the introduction of SAP Chapter 3 should be moved to SAP Chapter 1 instead. In addition, there could be some useful restructuring within SAP Chapter 3. While recognizing that this suggestion is a preference, it is motivated by the belief that the intended audience will then benefit more from the data. For example, the chemistry to understand processes in Section 3.2.1.2 (P. 121) is not defined until later in Section 3.2.3.2.1, and the text should not have to refer the reader ahead in the text to understand the discussion, which is now necessary in at least two places (e.g., L. 2390 and 2570). At a minimum, the background information should be presented at the beginning of the draft SAP Chapter 3, or in Chapter 1, perhaps defining concepts and incorporating parts of the Key Issues section, before presenting the key findings.

Chapter 3 of the draft SAP is the place to distinguish between the two types of stratospheric ozone loss, including the different photochemical mechanisms (catalytic cycles) associated with the loss processes, for example, causing (1) small ozone loss (in absolute terms relative to column ozone, but large fractional ozone loss) in the upper stratosphere largely at midlatitudes, and (2) the large polar ozone losses in the lowermost stratosphere, as well as the relative roles of transport and chemistry in causing ozone changes in the mid-latitude lower stratosphere. Some mention should be made of the different methods of observing/monitoring ozone loss at these two altitude regimes. Note that the agreement among measurements of ozone trends in the upper stratosphere is better than Figure 3.8 shows (some of the differences are due to differences between trends at fixed pressure and at fixed altitude). Instead of showing a cumulative trend per decade, the authoring team should show the trend as a variation over time (similar to Figure 3.7). While the time series of ozone loss at the poles is shown (Figures 3.5 and 3.7), a similar time series of 40 km ozone amounts is needed (e.g., see Steinbrecht et al.



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