Douglass, A. R.

Stolarski, R. S.

English

NASA Technical Reports Server

7(91-71518
L'ncsrtoint" C^lculsticns snd Th^ir Re^ Bt^onsh^p
to the Problem of Early Detection of Ozone Change
R. S. Stolarski
Code 616
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
and
A. R. Douglass
Applied Research Corporation
8201 Corporate Drive
Landover, MD 20785
Laboratory measurements of rate coefficients for chemical reactions are
usually input to stratospheric photochemistry models as single "best" values
for each reaction. In general, a laboratory measurement is done numerous
times and our best knowledge is actually a central value and a distribution
about that value. We have done a Monte-Carlo calculation of uncertainty
propagation through a stratospheric photochemistry model in an attempt to
include the full range of information concerning chemical reaction rate
coefficients. The result of such a calculation is the prediction of
probability distributions for the concentrations of stratospheric species and
for.the, changes in ozone and other species due to specified perturbations.
These probability distributions can be used in'several ways to attack the
problem of model-measurement intercomparison and the search for the best way
to detect future changes. We have examined several possibilities for using
measurements to reduce the uncertainty range of model predictions. A study of
the calculated present-atmosphere ozone concentration versus altitude
indicates that it has little predictive capability for changes in the ozone
column induced by chlorine perturbations. This probability distribution for
ozone concentration at 40 and 50 km did overlap the data with the model being
generally below the data. At 30 km the model was consistently higher than the
data. In none of the more than 300 cases run did the model fall within the
one-sigma variability range of the data at all three altitudes. The 50 or so
cases which showed the best fit with the data showed no preference for either
high or low ozone depletion predictions.
The best correlations for ozone depletion predictions was with lower
stratospheric parameters. It was found that sets of reaction rate
coefficients which predict high ozone depletions for small chlorine injections
tend to yield larger disagreements with data than do other cases.
Specifically, the model predicts lower stratospheric CIO concentrations which
are on the high side of measurements. Since the ambient C10/C1X is one of the
best predictors of chlorine perturbation efficiency, models with low initial
CIO are favored by the data. This eliminates virtually all cases which give
more than 10% ozone change for continued release of fluorocarbons at their
present rate. Examination of NO and NO^ data indicates that the model tends
to yield concentrations pretty much in the center of the measurement range.
The measurements thus indicate that models on both extremes of the range of
odd nitrogen compounds should be discarded. This procedure eliminates a
https://ntrs.nasa.gov/search.jsp?R=19910073963 2020-03-17T14:52:57+00:00Z
number of low ozone depletion cases (when odd nitrogen is high) and also a
number of high ozone depletion cases (many of the same cases as discarded on
the basis of disagreement with CIO). When all three of these are taken
together, 125 of 329 cases remain with an ozone depletion of 3±2% for steady-
state at the present fluorocarbon flux. This is contrasted with 6±5* before
screening with the measurements.
An interesting poor correlation is that of the change in ozone due to a
chlorine perturbation with the lower stratospheric hydroxyl radical
concentration. We have begun examining the correlations of column ozone
change with a number of measured parameters and are attempting to determine a
strategy for the best method of early detection of change as well as for an
identification of the cause of change.


Uncertainty calculations and their relationship to the problem of early detection of ozone change

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server