Model studies on the sensitivity of upper tropospheric chemistry to heterogeneous uptake of HNO3 on cirrus ice particles

A chemistry box model is applied to investigate potential chemical perturbations in the midlatitude upper troposphere caused by the reactive and nonreactive uptake of trace gases on cirrus ice particles. Chemical implications of denoxification caused by heterogeneous reactions with HNO3 as a product...

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Bibliographic Details
Published in:Journal of Geophysical Research - Atmospheres 2002-12, Vol.107 (D23), p.ACH 9-1-ACH 9-16
Main Authors: Meier, Andreas, Hendricks, Johannes
Format: Article
Language:English
Subjects:
Aerosols and particles
Atmospheric Composition and Structure
cirrus clouds
Cloud physics and chemistry
Constituent sources and sinks
denitrification
heterogeneous chemistry
ozone
upper troposphere
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Summary:A chemistry box model is applied to investigate potential chemical perturbations in the midlatitude upper troposphere caused by the reactive and nonreactive uptake of trace gases on cirrus ice particles. Chemical implications of denoxification caused by heterogeneous reactions with HNO3 as a product and adsorption of gas phase HNO3 on ice surfaces are the special focus. The role of denitrification due to gravitational settling of ice particles is investigated. The simulations suggest that cirrus cloud chemistry has the potential to induce strong local reductions in upper tropospheric HNO3 and NOx. Because of NO reduction the OH/HO2 ratio and the OH concentration decrease. As a consequence of these effects a significant reduction in the net ozone production rate is modeled. Sensitivity studies were performed varying the HNO3 adsorption efficiency, the particle sedimentation efficiency, and the ambient NOx concentration. The sensitivity experiments reveal that the modeled cirrus cloud impacts are mainly driven by the nonreactive uptake of HNO3 on ice particles and the subsequent particle sedimentation. The effects strongly depend on the efficiency of HNO3 adsorption. If a very efficient uptake of HNO3 is assumed, decreases in the ozone mixing ratio up to 14% are modeled. The simulations also suggest that the cirrus cloud impact on ozone is sensitive to the ambient NOx concentration. The heterogeneous reactions on ice with HNO3 as a product appear to be of secondary importance in the upper troposphere. Chlorine activation due to heterogeneous reactions on cirrus ice particles has a minor effect on model ozone chemistry under the conditions regarded. The model calculations further suggest that chemical perturbations caused by the uptake of OH, HO2, and H2O2 on ice are potentially significant only in periods of high cirrus cloud activity. Since observational data on cirrus chemical impacts in the upper troposphere are currently too sparse to perform a detailed model validation, it remains unclear whether the potentially large chemical perturbations caused by HNO3 adsorption on cirrus ice particles are of relevance for the real atmosphere.
ISSN:0148-0227
2156-2202
DOI:10.1029/2001JD000735