When we breathe in smoke from a wood fire we may be breathing in toxic amounts of isocyanic acid. Isocyanic acid is the simplest molecule to contain all four of the most common elements in organic compounds. It has the formula HNCO and was first discovered by Wohler in 1830.

Using a specially designed mass spectrometer to measure gases in the atmosphere researchers from the University of Colorado have reported that isocyanic acid is produced in the smoke from biomass fires. Initially they detected it in controlled fires in a laboratory where the amount was up to 600 parts per billion by volume (ppbv).  However they were also able to show that it was produced during the recent forest wild fires that occurred near Boulder, Colorado. What surprised them was not only that it was present in the smoke but it was also detected in the atmosphere several miles away. They have also found isocyanic acid in the urban atmosphere in Los Angeles and the level is higher during the day suggesting that it may be formed as a secondary pollutant in photochemical smogs (see Option E, Assessment statement E.10.2 ). Isocyanic acid has also been detected in tobacco smoke (relevant for Option D, Assessment statement , D.5.3).

Isocyanic acid is known to be toxic to humans. It is soluble in blood and if levels exceed 1 pppv then it may contribute to health problems such as cardiovascular disease and arthritis. Isocyanic acid is related chemically to methyl isocyanate, the compound that caused the deaths in the Bhopal tragedy (see separate blog on Chemistry and politics). The team at Colorado University have produced the following video on isocyanic acid in smoke  .