Enhanced tropospheric HCN columns above Kitt Peak during the 1982-1983 and1997-1998 El Nino warm phases

Free tropospheric HCN columns have been derived from infrared solar spectra recorded with the National Solar Observatory Fourier transform spectromete r on Kitt Peak, Arizona (31.9 degreesN latitude, 111.6 degreesW 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 Fl Ninos of 1982-1983 and 19 97-1998, 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 m easurements for quantifying climate and atmospheric chemistry-related atmos pheric changes. Published by Elsevier Science Ltd.