In:
Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 102, No. D5 ( 1997-03-20), p. 5979-5991
Abstract:
Results from the Intergovernmental Panel on Climatic Change (IPCC) tropospheric photochemical model intercomparison (PhotoComp) are presented with a brief discussion of the factors that may contribute to differences in the modeled behaviors of HO x cycling and the accompanying O 3 tendencies. PhotoComp was a tightly controlled model experiment in which the IPCC 1994 assessment sought to determine the consistency among models that are used to predict changes in tropospheric ozone, an important greenhouse gas. Calculated tropospheric photodissociation rates displayed significant differences, with a root‐mean‐square (rms) error of the reported model results ranging from about ±6–9% of the mean (for O 3 and NO 2 ) to up to ±15% (H 2 O 2 and CH 2 O). Models using multistream methods in radiative transfer calculations showed distinctly higher rates for photodissociation of NO 2 and CH 2 O compared to models using two‐stream methods, and this difference accounted for up to one third of the rms error for these two rates. In general, some small but systematic differences between models were noted for the predicted chemical tendencies in cases that did not include reactions of nomnethane hydrocarbons (NMHC). These differences in modeled O 3 tendencies in some cases could be identified, for example, as being due to differences in photodissociation rates, but in others they could not and must be ascribed to unidentified errors. O 3 tendencies showed rms errors of about ±10% in the moist, surface level cases with NO x concentrations equal to a few tens of parts per trillion by volume. Most of these model to model differences can be traced to differences in the destruction of O 3 due to reaction with HO 2 . Differences in HO 2 , in turn, are likely due to (1) inconsistent reaction rates used by the models for the conversion of HO 2 to H 2 O 2 and (2) differences in the model‐calculated photolysis of H 2 O 2 and CH 2 O. In the middle tropospheric “polluted” scenario with NO x concentrations larger than a few parts per billion by volume, O 3 tendencies showed rms errors of ±10–30%. These model to model differences most likely stem from differences in the calculated rates of O 3 photolysis to O( 1 D ), which provides about 80% of the HO x source under these conditions. The introduction of hydrocarbons dramatically increased both the rate of NO x loss and its model to model differences, which, in turn, are reflected in an increased spread of predicted O 3 . Including NMHC in the simulation approximately doubled the rms error for O 3 concentration.
Type of Medium:
Online Resource
ISSN:
0148-0227
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1997
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