From: Brian Toon
Organization: University of Colorado

Research Area: CHEMISTRY

Mission Scenario: Clouds/Aerosols/Chemistry -- Interactions of cirrus clouds, and aerosols in the upper troposphere

The issues: Due to their high altitudes cirrus remain the least understood clouds in the atmosphere. The radiative properties of cirrus are difficult to evaluate. Particle shapes in cirrus are difficult to treat radiatively. Since cirrus are often optically thin they can have positive or negative net radiative forcing. Likewise, our understanding of aerosols in the upper troposphere is poor. Some of these serve as ice nuclei, but we don't understand which ones, or their sources. Long range tranport of pollution occurs at high levels. Finally heterogenous chemistry either on aerosols, or on cirrus may significantly impact the nitrogen, sulfur, and ozone cycles. The HIAPER will undoubtedly be of value in furthering our understanding of these issues.

Candidate missions: Numerous missions could be flown. The emphasis would be on the region within a few kilometers of the tropopause. At midlatitudes a 50000 ft max. altitude would cover the range well, though in the tropics some clouds might not be possible to explore. As an example mission, it would be of great interest to explore cirrus in the Northern and Southern Hemisphere to determine the aerosols that have served as ice nuclei in them. Likewise the chemical composition of the ice and of the surrounding air would be of value to explore. I include below a candidate list of instruments. This list includes instruments that are rather large. However, the sizes continue to fall with time. A mission such as this requires that the aircraft be readily deployed to the Southern Hemisphere. It also requires long duration flights to reach regions of cloudiness. An eight hour flight duration would be sufficient.

Candidate instruments
Measurement Typical Technique
(alternate techniques are possible)
Aerosol composition Laser mass spectrometry , ion chromatography, electron microscopy
BrO, ClO, UV fluorescence
HNO3 CIMS
aerosol /cloud particle size and concentration
nm - 100 µm 		laser scatter, CN counters, holography
CO2, N2O, CH4 IR absorption
O3 UV absorption
water vapor TDL absorption, lidar
Photolysis rates UV-vis spectrometer
NOy, NOx Chemiluminescence, TF-LIF
CH2O, HOOH, CH3OOH, OH, HO2 fluorescence, ammonia, acetone
SO2, H2SO4 CIMS
Cloud morphology Eye safe-forward scanning lidar Under-belly camera
Temperature, pressure, winds
Light absorbing material optical
PAN, hydrocarbons
Ice nuclei at T<-40C
Radiative fluxes Vis and Ir radiometers-preferrably spectrally resolving
Ice water content Cvi, Gerber probe
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