Isoprene nitrates: preparation, separation, identification, yields, and atmospheric chemistry

Abstract

Isoprene is an important atmospheric volatile organic compound involved in ozone production and NO<sub>x</sub> (NO+NO<sub>2</sub>) sequestration and transport. Isoprene reaction with OH in the presence of NO can form either isoprene nitrates or convert NO to NO<sub>2</sub> which can photolyze to form ozone. While it has been shown that isoprene nitrate production can represent an important sink for NO<sub>x</sub> in forest impacted environments, there is little experimental knowledge of the relative importance of the individual isoprene nitrate isomers, each of which has a different fate and reactivity. In this work, we have identified the 8 individual isomers and determined their total and individual production yields. The overall yield of isoprene nitrates at atmospheric pressure and 295 K was found to be 0.070(+0.025/–0.015). Three isomers, the (4,3)-IN, (1,2)-IN and Z-(4,1)-IN represent 90% of the total IN yield. We also determined the ozone rate constants for three of the isomers, and have calculated their atmospheric lifetimes, which range from ~1–2 h, making their oxidation products likely more important as atmospheric organic nitrates and sinks for nitrogen

Determination of Semivolatile Organic Nitrates in Ambient Atmosphere by Gas Chromatography/Electron Ionization–Mass Spectrometry

“…The common isomers of isoprene hydroxy nitrates include 1-hydroxy-2-nitrooxy isoprene, 2-hydroxy-1-nitrooxy isoprene, 4-hydroxy-3-nitrooxy isoprene, 3-hydroxy-4-nitrooxy isoprene, E/Z-1-hydroxy-4-nitrooxy isoprene, and E/Z-4-hydroxy-1-nitrooxy isoprene. They have been separated and identified by GC-ECD/CIMS or GC-MS in the laboratory from synthetic mixtures of isoprene hydroxy nitrates [5,35,38]. Xiong et al [5] measured the total concentration of isoprene hydroxy nitrates in the atmosphere in the southeast United States with the CIMS.…”

Isomerization of the Isoprene Hydroxy Nitrates and Formation of Orthonitrite Compounds

“…1 Isoprene is the second most emitted hydrocarbon to Earth's atmosphere 2 and because of this ISOPNs represent significant NOx reservoirs as well as chain-terminating free radical sinks. [3][4][5][6] Branching between nitrate stabilization vs. chemically activated fragmentation to alkoxyl radicals is a key parameter in atmospheric chemical mechanisms, and has been studied extensively for isoprene. 7 Likewise, the photochemical degradation of ISOPNs is also important, and key atmospheric sinks such as the reaction with OH have been widely investigated.…”

“…7 Earlier studies report total ISOPN yields anywhere from 4 to 14 %. 3,4,[9][10][11][12] When considering the individual ISOPN isomers -of which there are eight -Paulot et al 3 estimated yields of 6.7 % for those with β-hydroxy functionality compared to 24 % for those with δ-hydroxy groups. The source of this variability remains unclear.…”