Importance of biogenic precursors to the budget of organic nitrates: observations of multifunctional organic nitrates by CIMS and TD-LIF during BEARPEX 2009

Alkyl and multifunctional organic nitrates, molecules of the chemical form RONO2, are products of chain terminating reactions in the tropospheric HOx and NOx catalytic cycles and thereby impact ozone formation locally. Many of the molecules in the class have lifetimes that are long enough that they can be transported over large distances. If the RONO2 then decompose to deliver NOx to remote regions they affect ozone production rates in locations distant from the original NOx source. While measurements of total RONO2 (Sigma ANs) and small straight chain alkyl nitrates are routine, measurements of the specific multifunctional RONO2 molecules that are believed to dominate the total have rarely been reported and never reported in coincidence with ambient Sigma ANs measurements. Here we describe observations obtained during the BEARPEX 2009 experiment including Sigma ANs and a suite of multifunctional nitrates including isoprene derived hydroxynitrates, oxidation products of those nitrates, 2-methyl-3-buten-2-ol (MBO) derived hydroxynitrates, and monoterpene nitrates. At the BEARPEX field site, the sum of the individual biogenically derived nitrates account for two-thirds of the Sigma ANs, confirming predictions of the importance of biogenic nitrates to the NOy budget. Isoprene derived nitrates, transported to the site, are a much larger fraction of the Sigma ANs at the site than the nitrates derived from the locally emitted MBO. Evidence for additional nitrates, possibly from nocturnal chemistry of isoprene and alpha-pinene, is presented.