"nitrous acid" is a chemical compound made up of nitrous oxide and water. It is a type of acid that can be used in certain chemical reactions or as an ingredient in other products. Full definition
Secondhand smoke itself contains TSNAs, but the presence of nitrous acid in (scientificamerican.com)
Destaillats's team reckon that NNK is produced when nicotine from tobacco smoke reacts with nitrous acid in the air. (newscientist.com)
Secondhand smoke itself contains TSNAs, but the presence of nitrous acid in an environment can increase their numbers by several times in the hours after smoking has ceased. (scientificamerican.com)