Atmospheric photooxidation of isoprene part I: The hydroxyl radical and ground state atomic oxygen reactions

Abstract

The OH reaction with isoprene is studied. Methyl nitrite photolysis experiments were carried out in an outdoor smog chamber in a n attempt to identify as completely as possible OHisoprene product distribution. Emphasis was placed on identification and quantification of oxygenated products. A Tenax-based cryo-trap thermal desorber used to trap, concentrate, and dry chamber samples for identification on a GC/MS is described. Analysis of the products revealed that O(3P) can form in reaction systems designed to study OH reactions that include high concentrations of NO, and consequently NOz, hence, this reaction is also examined. The yields of methacrolein and methyl vinyl ketone are determined as 25 t 3 and 35.5 t 4%, respectively, with an additional 4 t 2% as 3-methyl furan, totaling 65 t 4%. These results, combined with those of previous studies allow 80% of isoprene's products to be explicitly identified, and the general structure of the remaining products to be ascertained. The O(3P) reaction produces 84 5 8% epoxides, and 8 t 3% species which result in production of HOa, and subsequently, OH. A heretofore unidentified product of the O(3P) reaction, 2-methyl2-butenal, is identified. The rate constant of the N02-isoprene reaction is measured.

Isoprene emissions in Africa inferred from OMI observations of formaldehyde columns

“…Model values are much higher than observed at 11-13 • N and 7-8 • N, reflecting a local overestimate of E ISOP in MEGAN (Ferreira et al, 2010;Murphy et al, 2010). MVK and MACR are first-stage C 4 isoprene oxidation products, with HCHO produced from the additional carbon atom (Paulson et al, 1992). The tightness of the isoprene-(MVK + MACR) relationship in Fig.…”

Observations of elevated formaldehyde over a forest canopy suggest missing sources from rapid oxidation of arboreal hydrocarbons

“…The laser was originally fabricated to emit near 5.7 µm, which is the ν 2 band of HCHO (C=O stretch mode: 1746 cm −1 Perrin et al, 2003). However, the active lasing surface used in this experiment emitted closer to 1721 cm −1 , and the thermoelectric cooling system was not able to cool the laser mount below −10 • C at typical ambient room temperature, limiting the tuning range to ∼2 cm −1 .…”

“…Isoprene (Isop) is attacked by OH to form isoprene peroxy radical (Isop-O 2 ). Isop-O 2 then reacts with NO to produce Isop-O radical with the yield of 90% (Reaction R2a in Appendix C) and subsequently to produce HCHO, MVK, and MACR (Reactions R5a, b in Appendix C) with a yield of 63%, 35%, and 24%, respectively, in high-NO x conditions (Tuazon and Atkinson, 1990;Paulson et al, 1992;Ruppert and Becker, 2000;Paulot et al, 2009;Miyoshi et al, 1994;Sprengnether et al, 2002;Karl et al, 2006). On the other hand, Isop-O 2 also competitively reacts with RO 2 to produce HCHO, MVK, and MACR with a yield of 34%, 16%, and 20%, respectively, via Isop-O (Reaction R4a in Appendix C) under NO x -free conditions (Ruppert and Becker, 2000;Miyoshi et al, 1994).…”

Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): tropospheric degradation of non-aromatic volatile organic compounds

“…The degradation of isoprene leads to the generation of a series of carbonyl compounds as major first generation products (Tuazon and Atkinson, 1990;Paulson et al, 1992;Miyoshi et al, 1994;Ruppert and Becker, 2000). These include formaldehyde (HCHO), the C 4 unsaturated carbonyls methacrolein (MACR, CH 2 =C(CH 3 )CHO) and methyl vinyl ketone (MVK, CH 3 C(O)CH=CH 2 ), and the isomeric C 5 unsaturated hydroxy aldehydes, HOCH 2 C(CH 3 )=CHCHO and HOCH 2 CH=C(CH 3 )CHO.…”