Abstract :
[en] Free tropospheric HCN columns have been derived from infrared solar spectra recorded with the National Solar Observatory Fourier transform spectrometer on Kitt Peak, Arizona (31.9ºN latitude, 111.6ºW longitude, 2.09 km altitude) between May 1978 and May 2000. The time series show up to a factor of 2.4 enhancement during the strong El Ninos of 1982-1983 and 1997-1998, the most intense since 1970. The observations provide confirmation that HCN is a sensitive tracer of biomass burning emissions transported to the free troposphere. No statistically significant long-term trend in the HCN-free tropospheric column has been detected over the 22-year measurement period. The results illustrate the importance of long-term spectroscopic measurements for quantifying climate and atmospheric chemistry-related atmospheric changes.
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