Gaseous Nitrate Radical: Possible Nighttime Atmospheric Sink for Biogenic Organic Compounds

The gaseous nitrate (NO$_{3}$) radical, which has recently been measured in nighttime ambient atmospheres over the United States and Europe at concentrations up to $\sim $ 350 parts per trillion, has now been shown to react rapidly with the biogenically emitted organic compounds dimethyl sulfide (DMS), isoprene, and several monoterpenes. Computer simulations demonstrate that these reactions can dominate the atmospheric behavior of these organic compounds at night. Thus reaction with NO$_{3}$ radicals may be the unknown, nonphotochemical removal process for DMS recently invoked by Andreae and Raemdonck to explain the absence of a diurnal profile for DMS in maritime air influenced by continental air masses. Similarly, the nighttime reaction of NO$_{3}$ radicals with monoterpenes can be a dominant removal process, leading to very low monoterpene concentrations in ambient atmospheres during the early morning.