Knowledge Bank

The reaction of $OH+NO2\to HNO3$ is a critical sink of $HOx$ and $NOx$ radicals in the atmosphere. The unstable intermediate HOONO has long been proposed as a minor channel. Because HOONO is predicted to be bound by kcal/mol, it would thermally decompose to reactants and would not serve as a sink for OH radicals; hence, its formation would reduce the rate of stable nitric acid formation. We report direct detection of this adduct at $3280cm-1$ by IR cavity ring-down spectroscopy in a discharge flow cell, and present a study of its relative yield and significance in the troposphere and stratosphere.