Other Species Targets

The availability of other species in the atmosphere will be determined by the 
spectral region that the detector will target and the resolution of measurement.  
The visible region of interest (400-800 nm) contains such possible targets as 
H2O, O2, NO2 and NO3, according to HITRAN 1992 in this spectral region.  
Specific wavelengths used in the detection of a particular species are usually 
contaminated by other atmospheric constituents.  A full spectral range allows 
better separation amongst atmospheric constituents, including aerosols, and does 
not necessarily rely on unique spectral signatures.

Simultaneous in situ measurements of radicals and other representatives from the 
important chemical family, NOx, will provide valuable information to aid in the 
interpretation of the ozone trend in this region. The source of stratospheric 
NO2 is mainly N2O, which has seen significant increase in recent years from 
industrial pollutants. Determining the NO2 trend will help to develop more 
insight into the effects of its source.  

Several species undergo large diurnal variations.  The conversion from NO to NO2 
at night is a rapid process, while the photolysis rate of NO3 is large enough 
that NO3 is nearly immeasurable during the day.  The object of our stellar 
occultation method is to determine vertical profiles of these nighttime species.  
Both NO2 and NO3 have strong absorption features within the spectral range of 
400-700 nm.  From studies at the tangent altitude of 24 km, NO2 suffers at least 
an estimate 7% loss in transmission at 431 nm (without scattering).  The 
resolution of our instrument will be assessed, and the availability of other 
species which are available for retrieval will be determined.