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

Isoprene is an important atmospheric volatile organic compound involved in ozone production and NO_x (NO+NO₂) sequestration and transport. Isoprene reaction with OH in the presence of NO can form either isoprene hydroxyl nitrates ("isoprene nitrates") or convert NO to NO₂ which can photolyze to form ozone. While it has been shown that isoprene nitrate production can represent an important sink for NO_x 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 295K was found to be 0.070(+0.025/?0.015). Three isomers, representing nitrates resulting from OH addition to a terminal carbon, 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.