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2016: A Stratospheric HCN Oddity

Last year, an unprecedented amount of hydrogen cyanide (HCN) was emitted from Southeast Asia into the upper troposphere and lower stratosphere.

Since the lifetime of HCN in this region is relatively long, on the order of months to years, the emitted HCN was then transported by the general circulation from the tropics to polar latitudes. By early 2016, the daily mean concentrations of HCN in the lower stratosphere at all latitudes, as measured by the ACE-FTS instrument, were consistently the largest on record for the region, on the order of 50-90% greater than the climatological mean, and ~30% greater than the 2007 El Niño-driven values. By October 2016, levels of polar HCN in the lower stratosphere were still consistently the largest on record, on the order of 20% greater than the climatological mean. This study will examine the only available satellite measurements of HCN in the upper troposphere - lower stratosphere and will discuss likely emission sources.