Observation of isoprene hydroxynitrates in the southeastern United States and implications for the fate of NO<sub><i>x</i></sub>

Abstract

Abstract. Isoprene hydroxynitrates (IN) are tracers of the photochemical oxidation of isoprene in high NOx environments. Production and loss of IN have a significant influence on the NOx cycle and tropospheric O3 chemistry. To better understand IN chemistry, a series of photochemical reaction chamber experiments was conducted to determine the IN yield from isoprene photooxidation at high NO concentrations (> 100 ppt). By combining experimental data and calculated isomer distributions, a total IN yield of 9(+4/−3) % was derived. The result was applied in a zero-dimensional model to simulate production and loss of ambient IN observed in a temperate forest atmosphere, during the Southern Oxidant and Aerosol Study (SOAS) field campaign, from 27 May to 11 July 2013. The 9 % yield was consistent with the observed IN/(MVK+MACR) ratios observed during SOAS. By comparing field observations with model simulations, we identified NO as the limiting factor for ambient IN production during SOAS, but vertical mixing at dawn might also contribute (~ 27 %) to IN dynamics. A close examination of isoprene's oxidation products indicates that its oxidation transitioned from a high-NO dominant chemical regime in the morning into a low-NO dominant regime in the afternoon. A significant amount of IN produced in the morning high NO regime could be oxidized in the low NO regime, and a possible reaction scheme was proposed.

The lifetime of nitrogen oxides in an isoprene-dominated forest

“…This is in the middle of the range of branching ratios for isoprene (0.09-0.15) found in recent experiments (e.g. Paulot et al, 2009;Teng et al, 2015;Xiong et al, 2015).…”

“…The effects of boundary layer growth are not accounted for, but are unlikely to be important after 10:00 (e.g. Xiong et al, 2015). The 55 % uncertainty constrains the average ANs production rate to between 50 and 145 ppt h −1 .…”

Controlled nitric oxide production via O(<sup>1</sup>D) + N<sub>2</sub>O reactions for use in oxidation flow reactor studies

“…Fig. 5 suggests this compound is a secondgeneration oxidation product that is formed after two reactions with OH, one RO 2 + NO termination reaction, and one RO 2 + HO 2 termination reaction (Xiong et al, 2015). The signal observed at m/Q = 288, C 5 H 10 N 2 O 8 , is a second- Figure 5.…”

Decadal changes in summertime reactive oxidized nitrogen and surface ozone over the Southeast United States

“…For isoprene, α is 9 ± 4 % (for ISOPN) according to a recent study (Xiong et al, 2015). For monoterpenes, specifically α-pinene, α ranges from 1 to 26 % (Rindelaub et al, 2015;Nozière et al, 1999;Aschmann et al, 2002).…”

“…Biogenic RONO 2 species are mainly produced from the oxidation of BVOCs by OH in the presence of NO x during daytime and by the nitrate radical (NO 3 ) during nighttime. Laboratory and field studies show a wide range of RONO 2 yields from their BVOC precursors (Browne et al, 2014;Fry et al, 2014;Lockwood et al, 2010;Paulot et al, 2009;Rindelaub et al, 2015;Rollins et al, 2009;Lee et al, 2014;Xiong et al, 2015Xiong et al, , 2016Teng et al, 2015). Another uncertainty lies in the fate of RONO 2 ; i.e., recycling RONO 2 into NO x or converting it to HNO 3 has important implications for the NO y budget and thus ozone production (Fiore et al, 2005;Horowitz et al, 2007;Ito et al, 2009;Perring et al, 2013;Paulot et al, 2012).…”