A product study of the isoprene+NO<sub>3</sub> reaction

Abstract

Abstract. Oxidation of isoprene through reaction with NO3 is a significant sink for isoprene that persists after dark. The products of the reaction are multifunctional nitrates. These nitrates constitute a significant NOx sink in the nocturnal boundary layer and they likely play an important role in formation of secondary organic aerosol. Products of the isoprene+NO3 reaction will, in many locations, be abundant enough to affect nighttime radical chemistry and to persist into daytime where they may represent a source of NOx. Product formation in the isoprene+NO3 reaction was studied in a smog chamber at Purdue University. Isoprene nitrates and other hydrocarbon products were observed using Proton Transfer Reaction-Mass Spectrometry (PTR-MS) and reactive nitrogen products were observed using Thermal Dissociation–Laser Induced Fluorescence (TD-LIF). The organic nitrate yield is found to be 62±6% and the combined yield of MACR+MVK is found to be ~10%. Additional hydrocarbon products, thought to be primarily C4 and C5 carbonyl compounds, were observed by the PTR-MS at various m/z ratios and their yields quantified. These other oxidation products are used as additional constraints on the reaction mechanism.

Isoprene oxidation by nitrate radical: alkyl nitrate and secondary organic aerosol yields

“…Table 2 summarizes the results of studies in the literature that report quantifying the yield of total alkyl nitrates from the isoprene + NO 3 reaction. Our observation of alkyl nitrate formation (70±8%) is equivalent to previously reported yields (65%-80%), within the combined experimental errors (Skov et al, 1992;Perring et al, 2009). The fact that multiple experiments conducted under different conditions (concentrations of isoprene and oxidants differing by more than a factor of 100) have all produced high yields of alkyl nitrates implies that the yield is robust and relatively insensitive to the peroxy radical chemistry, and supports findings that the isoprene + NO 3 reaction is possibly the single strongest source of alkyl nitrates in the atmosphere (Horowitz et al, 2007).…”

“…Kwok et al (1996) yields of 3.5% for both MVK and MACR. Perring et al (2009) observed a 7% yield of the sum of MVK and MACR using PTR-MS. Skov et al (1992) and Perring et al (2009) measured product yields by adding isoprene to a chamber that was initially charged with ppm levels of N 2 O 5 . Kwok et al (1996) added isoprene first as we did, but then injected N 2 O 5 in ppm steps.…”

“…However, other studies (Barnes et al, 1990;Skov et al, 1992;Ng et al, 2008;Perring et al, 2009) have distinguished hydroxynitrates, carbonylnitrates, and peroxynitrates as the majority of the oxidation products. In Fig.…”

Real Time In Situ Detection of Organic Nitrates in Atmospheric Aerosols

“…Specific individual gas phase RONO 2 molecules have been observed using gas chromatography (e.g. (2)(3)(4)(5)(6)) and chemical ionization mass spectrometry (7)(8)(9), and the total of gas and aerosol RONO 2 (total Alkyl Nitrates, ΣAN) has been observed by Thermal Dissociation Laser Induced Fluorescence (TD-LIF) (1,(10)(11)(12). Recently there has been growing interest in understanding the partitioning of RONO 2 to atmospheric particles (13)(14)(15)(16)(17)(18).…”

Quantum Yields for Photochemical Production of NO2 from Organic Nitrates at Tropospherically Relevant Wavelengths

“…Difunctional organic nitrate compounds can form when NO3 reacts with unsaturated hydrocarbons in air, and the chemistry of these processes was discussed by Barnes et al 10 Reaction of NO3 with isoprene is an important example, 11 producing products such as nitrooxy carbonyls and, in principle, organic dinitrate species. For example, in a chamber study, Rollins et al 12 observed dinitrate species produced in the reaction of primary isoprene nitrates with NO3.…”