Abstract

It has been known for many years that the middle atmosphere (10 to 100 km) ozone distribution is controlled in part by catalytic cycles of the kind: X + O₃ → X + O₂ concurrent with XO + O → X + O₂, giving the net result O + O₃ → 2O₂; i.e., a net ozone destruction. The catalyst, X, in these reactions is usually NO, OH, or Cℓ. The reactive N−, H−, and Cℓ− containing gases can be conveniently grouped into chemical families, often referred to as HO_y, NO_y, and CℓO_y, where the main elements are H, OH, HO₂, and H₂O₂ for HO_y; N, NO, NO₂, HNO₃, N₂O₅, and HNO₄ for NO_y; and Cℓ, CℓO, HCℓ, HOCℓ, and CℓONO₂ for CℓO_y. Figure 1 is a simplified chemistry diagram showing catalytic cycles. The time scale for chemical steady state to be established within these families is generally quite short and much less than transport time scales. Thus, theoretical steady-state arguments allow the distribution within a family to be calculated. The odd hydrogen family is important throughout the atmosphere. It dominates the photochemical destruction of ozone above about 45 km, and it is also very important in the lower stratosphere (where the photochemical time scale is long). Furthermore, OH and HO₂ are involved in the production and destruction of the important reservoirs HNO₃, HNO₄, HCℓ, and HOCℓ, which are formed by interactions between chemical families.

© 1990 Optical Society of America