El Niño affects the HCN content of the tropical stratosphere
Zonal mean HCN anomalies (in ppbv) as a function of altitude and time, as measured by MLS, MIPAS, and ACE-FTS. In the El Niño years 2002/2003, 2006/2007, 2009/2010 and particularly 2015/2016 increased mixing ratios of HCN were measured.The cause of the increased stratospheric HCN concentrations is enhanced biomass burning activity. During El Niño years equatorial Asia is particularly dry and thus favorable for biomass burning. Often the exhaust is transported rapidly into the stratosphere where its ascent creates a tape recorder-like signal.
For more information see: https://www.atmos-chem-phys.net/18/691/2018/