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

Abstract

Abstract.Isoprene is an important atmospheric volatile organic compound involved in ozone production and NO x (NO+NO 2 ) sequestration and transport. Isoprene reaction with OH in the presence of NO can form either isoprene hydroxy nitrates ("isoprene nitrates") or convert NO to NO 2 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 295 K 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.

Influence of isoprene chemical mechanism on modelled changes in tropospheric ozone due to climate and land use over the 21st century

“…In CheT2, the overall yield of NO x from ISON was increased, in line with recent measurements (Perring et al, 2009), by increasing the ISON photolysis rate and adding an ISON + OH → NO 2 reaction channel. O 3 initiated degradation of ISON was also added based on the evidence of Lockwood et al (2010) -it should be noted, however, that Lee et al (2014) found that Lockwood et al (2010) substantially overestimated the rate of this reaction. Secondly, CheT2 includes the formation of hydroperoxy-aldehydes (HPALDs) from ISO 2 and subsequent rapid release of OH (Peeters et al, 2009).…”

“…Fourth, dry deposition of isoprene nitrates, which may represent an important NO x sink O. J. Squire et al: Influence of isoprene chemical mechanism on modelled tropospheric ozone 5125 in isoprene-rich regions, is also uncertain, with measured deposition velocities ranging from 0.4 cm s −1 (Shepson et al, 1996) to 2.7 cm s −1 (Farmer and Cohen, 2008). Finally, there is evidence for the importance of O 3 -initiated isoprene nitrate degradation (Lockwood et al, 2010) and fast photolysis of isoprene nitrates (Müller et al, 2014). In this study, the isoprene schemes we compare have a range of different parameterisations for isoprene nitrates.…”

Effects of biogenic nitrate chemistry on the NO<sub>x</sub> lifetime in remote continental regions

“…Here we provide a brief overview of the chemical mechanism which is based on RACM2 chemistry Stockwell et al, 2010) with substantial modifications to the RONO 2 and isoprene chemistry. The isoprene chemistry is based on Paulot et al (2009a, b) and uses ozonolysis rates of isoprene-derived nitrates from Lockwood et al (2010). The formation of a hydroperoxyaldehyde (HPALD) from the 1,6 H-shift of isoprene peroxy radicals is included using the rate constant measured by Crounse et al (2011).…”

Thermodynamics and kinetics of the hydrolysis of atmospherically relevant organonitrates and organosulfates

“…Seven different chemically distinct compounds based on the isoprene carbon backbone, containing epoxy, alcohol, nitrate, and/or sulfate functional groups, have now been identified in ambient SOA Claeys et al, 2004;Wang et al, 2005;Surratt et al, 2007;Altieri et al, 2009;Gómez-González et al, 2008;Surratt et al, 2008;Froyd et al, 2010). Some of these compounds are undoubtedly formed from gas phase processing (Perring et al, 2009a, b;Lockwood et al, 2010;Ng et al, 2008), of isoprene, while other compounds (such as organosulfates) clearly indicate that additional chemical processing is occurring on ambient SOA particles themselves (Cole-Filipiak et al, 2010;Paulot et al, 2009;Surratt et al, 2010;Chan et al, 2010;Minerath et al, 2008Eddingsaas et al, 2010;Szmigielski et al, 2010;Nozière et al, 2010;Rudzinski et al, 2009) We recently investigated some of the potential SOA-phase chemistry for isoprene-related compounds, and proposed an overall mechanism (shown in Fig. 1) that can rationalize the existence of five of the seven observed isoprene-derived SOA components (Darer et al, 2011).…”