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Measurements of Trace Gases and Cirrus Cloud Particles in the Subtropical Upper Troposphere and Lower Stratosphere during CRYSTAL-FACE |
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Improved understanding of cirrus cloud processes and development of a diagnostic for stratosphere-to-troposphere exchange of ozone The NASA Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE) mission was conducted from Key West, FL, during July 2002. Measurements of trace gases and cirrus particles were made by members of the NOAA Aeronomy Lab [ About this Lab ] and CIRES. The results have been used to address HNO3 uptake by cirrus clouds and develop a diagnostic for stratosphere-totroposphere exchange of ozone. HNO3 uptake: The redistribution of HNO3 via uptake and sedimentation by cirrus cloud particles is considered an important term in the upper tropospheric budget of reactive nitrogen. Numerous cirrus cloud encounters by the NASA WB-57F high-altitude research aircraft during CRYSTAL-FACE were accompanied by the observation of condensed-phase HNO3 with the NOAA two-channel chemical ionization mass spectrometer. Subtropical cirrus clouds, as indicated by the presence of ice particles, were observed coincident with condensed-phase HNO3 at temperatures of 197 K - 224 K and pressures of 120 hPa - 224 hPa. Maximum levels of condensed-phase HNO3 exceeded the gas-phase equivalent of 1 ppbv. Ice particle surface coverages as high as 1.4·1014 molecules·cm-2 (14 percent of an HNO3 monolayer) were observed. A dissociative Langmuir adsorption model, when using an empirically derived HNO3 adsorption enthalpy of - 11.0 kcal·mol-1, effectively describes the observed molecular coverages to within a factor of 5. The fraction of total HNO3 in the condensed phase ranged from near zero to 100 percent in the observed cirrus clouds. Thus, complete uptake of HNO3 was observed during some cirrus events. With volume weighted mean particle diameters up to 700 µm and particle fall velocities up to 10 m·s-1, some observed clouds have significant potential to redistribute HNO3 in the upper troposphere. Stratospheric Ozone Transport: A chemical ionization mass spectrometry (CIMS) technique was developed for precise in situ measurements of hydrochloric acid (HCl). Aircraft measurements of HCl, ozone, and other gases were made during CRYSTAL-FACE in the summer of 2002 at subtropical latitudes in the upper troposphere and lower stratosphere. Significant abundances of HCl were found in many upper tropospheric air parcels as a result of stratosphere- to-troposphere transport. Minimum upper tropospheric HCl abundances are much lower than model mean estimates. Using the compact linear correlation of HCl with ozone in the lower stratosphere, the amount of stratospheric ozone in the upper troposphere is uniquely distinguished from ozone that originated in the troposphere. This approach will allow the processes affecting stratosphere to troposphere transport to be diagnosed in the atmosphere with greatly increased precision and accuracy. |
CIRES Research Theme Project Personnel Funding Source(s) |
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