Isoprene, atmosphere

Yu, J., H. E. Jeffries, and R. M. Le Lacheur, Identifying Airborne Carbonyl Compounds in Isoprene Atmospheric Photooxidation Products by Their PFBHA Oximes Using Gas Chromatography/ Ion Trap Mass Spectrometry, Environ. Sci. Technol., 29, 1923-1932 (1995). 

Carmichael, G. R., D. G. Streets, G. Calori, M. Amman, M. Z. Jacobson, J. Hansen and H. Ueda (2002) Changing trends in sulfur emissions in Asia Implications for acid deposition, air pollution, and climate. Environmental Sciences and Technology 356, 4707-4713 Carroll, J. J. and A. E. Mather (1992) The system carbon dioxide-water and the Krichevsky-Kasarnovsky equation. Journal of Solution Chemistry 21, 607-621 Carlton, A. G., C. Wiedinnyer and J. H. Kroll (2009) A review of secondary organic aerosol (SOA) formation from isoprene. Atmospheric Chemistry and Physics 9, 4987-5005 Carslaw, K. S., O. Boucher, D. V Spracklen, G. W. Mann, J. G. L. Rae, S. Woodward and M. Kulmala (2010) A review of natural aerosol interactions and feedbacks within the Earth system. Atmospheric Chemistry and Physics 10, 1701-1737... 

In a polluted or urban atmosphere, O formation by the CH oxidation mechanism is overshadowed by the oxidation of other VOCs. Seed OH can be produced from reactions 4 and 5, but the photodisassociation of carbonyls and nitrous acid [7782-77-6] HNO2, (formed from the reaction of OH + NO and other reactions) are also important sources of OH ia polluted environments. An imperfect, but useful, measure of the rate of O formation by VOC oxidation is the rate of the initial OH-VOC reaction, shown ia Table 4 relative to the OH-CH rate for some commonly occurring VOCs. Also given are the median VOC concentrations. Shown for comparison are the relative reaction rates for two VOC species that are emitted by vegetation isoprene and a-piuene. In general, internally bonded olefins are the most reactive, followed ia decreasiag order by terminally bonded olefins, multi alkyl aromatics, monoalkyl aromatics, C and higher paraffins, C2—C paraffins, benzene, acetylene, and ethane. 

A. C. Fewis, K. D. Bartle and F. Rattner, High-speed isothermal analysis of atmospheric isoprene and DMS using online two-dimensional gas cliromatogr aphy . Environ. Sci. Technol. 31 3209-3217 (1997). 

Another interesting applieation of MDGC is in the rapid determination of isoprene (the most reaetive hydroearbon speeies) and dimethyl sulfide (DMS) (the major souree of sulfur in the marine troposphere and a preeursor to eloud formation) in the atmosphere (16). The deteetion limits were 5 and 25 ng 1 respeetively. 

Another approach for producing isoprene is the dimerization of propylene to 2-methyl-1-pentene. The reaction occurs at 200°C and about 200 atmospheres in the presence of a tripropyl aluminum catalyst combined with nickel or platinum. 

Apart from CO2, CH4, and CO there are many gases containing carbon present in the atmosphere, terpenes, isoprenes, various compovmds of petrochemical origin and others. We will not discuss them further, although some, like dimethylsulfide (DMS, (CH3)2S), are of great importance in the biogeochemical cycles of other elements. The total amount of atmospheric carbon in forms other than the three discussed is estimated at 0.05 Pg C (Freyer, 1979). 

Trees and shrubs contain a group of fragrant compounds called terpenes. The simplest terpene is isoprene. All other terpenes are built around carbon skeletons constructed from one or more isoprene units. Plants emit terpenes into the atmosphere, as anyone who has walked in a pine or eucalyptus forest will have noticed. The possible effect of terpenes on the concentration of ozone in the troposphere has been the subject of much debate and has led to careful measurements of rates of reaction with ozone. 

The formation of peroxyacetyl nitrate from isoprene (Grosjean et al. 1993a) and of peroxy-propionyl nitrate (Grosjean et al. 1993b) from ctT-3-hexen-l-ol that is derived from higher plants, illustrate important contributions to atmospheric degradation (Seefeld and Kerr 1997). 

Grosjean D, EL Williams II, E Grosjean (1993a) Atmospheric chemistry of isoprene and its carbonyl products. Environ Sci Technol 27 830-840. 

It is somewhat endothermic, AH°f (g) +75.7kJ/mol, 1.11 kJ/g. In absence of inhibitors, isoprene absorbs atmospheric oxygen to form peroxides which do not separate from solution. Although the solution is not detonable, the gummy peroxidic polymer obtained by evaporation can be detonated by impact under standard conditions. 

Pentane and ethane (end products of n-6 and n-3 polyunsaturated fatty acid peroxidation, respectively) in expired air are useful markers of in vivo lipid peroxidation. Nevertheless, when gas chromatography is used to measure hydrocarbons, some technical difficulties may be experienced because chromatographic resolution of pentane from isoprene and isopentane is extremely difficult to achieve. Another possible problem could be the presence of these gases as contaminants in atmosphere. Furthermore, the production of hydrocarbon gases depends on the presence of metal ions to decompose lipid peroxides. If such ions are only available in limited amounts, this index may be inaccurate. 

The most widely used gas-phase chemiluminescence reagent is ozone. Analytically useful chemiluminescence signals are obtained in the reactions of ozone with NO, SO, and olefins such as ethylene and isoprene, but many other compounds also chemiluminesce with ozone. Ozone is conveniently generated online at mixing ratios of =1-5% by electrical discharge of air or 02 at atmospheric pressure [14]. 

Isoprene, the most abundant hydrocarbon emitted to the atmosphere by plants, can also be measured using ozone chemiluminescence. As discussed above, al-kenes react with ozone to produce formaldehyde in its A2 electronic state, in addition to several other chemiluminescent products. In a fast isoprene detector manufactured by Hills Scientific (Boulder, CO), the chemiluminescence is detected using a blue-sensitive PMT to maximize the sensitivity for isoprene detec-... 

The cycloaddition of dienes to imines to form tetrahydropyridines (equation 46) has been investigated extensively40. Ordinary imines are not sufficiently reactive to add to dienes they have to be activated by the presence of electron-withdrawing substituents. Thus the triester 70 adds to cyclopentadiene under atmospheric pressure to form 71 (equation 47). The reactions with other dienes (cyclohexadiene, isoprene or 2,3-dimethylbuta-l,3-diene) require high pressures41. 

Rasmussen, R. A. Isoprene Identified as a forest-type emission to the atmosphere. Environ. Sci. Technol. 4 667-671, 1970. 

These processes are both natural and manmade. In fact, the Los Angeles basin was called by the early Native American inhabitants the land of the smokes, and salt spray from oceans is a major source of Cl in the atmosphere. In many situations people have only exaggerated the natural chemicals and reactions that were present before we and our technology arrived. The Smoky Mountains are an example of natural smog caused by chemicals such as isoprene (the natural mbber monomer) and terpenes, which are emitted by trees. 

In addition, in the nighttime atmosphere, reaction of the R02 radicals with N03 may occur as discussed earlier. As a result, the products of the isoprene-N03 reaction in the atmosphere will depend on the concentrations of NO, N03, H02, and R02. 

Biesenthal, T. A., and P. B. Shepson, Observations of Anthropogenic Inputs of the Isoprene Oxidation Products Methyl Vinyl Ketone and Methacrolein to the Atmosphere, Geophys. Res. Lett., 24, 1375-1378 (1997). 

Gutbrod, R., E. Kraka, R. N. Schindler, and D. Cremer, Kinetic and Theoretical Investigation of the Gas-Phase Ozonolysis of Isoprene Carbonyl Oxides as an Important Source for OH Radicals in the Atmosphere, J. Am. Chem. Soc., 119, 7330-7342 (1997a). 

Paulson, S. E., R. C. Flagan, and J. H. Seinfeld, Atmospheric Photooxidation of Isoprene. 1. The Hydroxyl Radical and Ground State Atomic Oxygen Reactions, hit. J. Chem. Kinet., 24, 79-101 (1992a). 

Silver, G. M and R. Fall, Characterization of Aspen Isoprene Synthase, an Enzyme Responsible for Leaf Isoprene Emission to the Atmosphere, J. Biol. Chem., 270, 13010-13016 (1995). 

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