Measuring atmospheric hydrogen cyanide (HCN) from space using the MIPAS-E instrument onboard ENVISAT

The potential to detect hydrogen cyanide (HCN) spectral signatures and retrieve HCN volume mixing ratios (VMR) in the Upper Troposphere and Lower Stratosphere (UTLS) from a space-borne infrared limb-sounding spectrometer is assessed. The primary aim of this project is to search for new molecular signatures using the infrared spectrometers and identify a unique tracer of pollution to separate two sources of pollution namely: industrial transport/non-coal emissions and biomass burning. HCN is an important trace gas constituent in the atmosphere and it is suggested as a sensitive tracer of biomass burning. Present knowledge of the sources and sinks of HCN, and its role in atmospheric chemistry and biogeochemistry is highly uncertain. The atmospheric distribution of HCN is variable and previous space-based measurements do not give detailed tropical and sub-tropical distributions of HCN. Atmospheric limb-emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard the ENVIronment SATellite (ENVISAT) has been successfully used to detect spectral signatures of HCN in MIPAS-E spectra. These signatures were detected in the ranges 744.300–744.525 (HCN_0102) and 746.775–747.825 (HCN_0105) cm−1 for a single scan #2 (orbit 08585), for four selected MIPAS-E spectra from different latitude bands and later for the whole month of October 2003 using an automated detection technique. Retrievals of HCN profiles are also promising, particularly at 12 km MIPAS-E nominal altitude. HCN data have been retrieved for October 2003 in 747.350–747.500 cm−1. The HCN data retrieved at 12 km nominal altitude in the tropics appears to be the most successful. In addition, there is a potential to obtain vertical profiles of HCN on a global basis throughout the UTLS. For more accurate detection and retrieval of HCN, methyl chloride (CH3Cl) and dinitrogen pentoxide (N2O5) need to be fitted well enough in both HCN_0102 and HCN_0105 MW (MW) regions.