Janet Arey

Gas-phase tropospheric chemistry of biogenic volatile organic compounds: a review

Large quantities of non-methane organic compounds are emitted into the atmosphere from biogenic sources, mainly from vegetation. These organic compounds include isoprene, C10H16 monoterpenes, C15H24 sesquiterpenes, and a number of oxygenated compounds including methanol, hexene derivatives, 2-methyl-3-buten-2-ol, and 6-methyl-5-hepten-2-one. In the troposphere these organic compounds react with hydroxyl (OH) radicals, nitrate (NO3) radicals and ozone (O3), and play an important role in the chemistry of the lower troposphere. In this article the kinetics, products and mechanisms of the tropospheric reactions of biogenic organic compounds are presented and briefly discussed.

The formation of nitro-PAH from the gas-phase reactions of fluoranthene and pyrene with the OH radical in the presence of NOx

The products of the gas-phase reactions of the OH radical with fluoranthene and pyrene in the presence of NOx have been studied in a ~6400-l environmental chamber. 2-Nitropyrene was the sole nitro-PAH formed from pyrene, while 2-nitrofluoranthene, together with much smaller amounts of 7- and 8-nitrofluoranthene, were formed from fluoranthene. 2-Nitrofluoranthene and 2-nitropyrene have not been reported to be present in direct combustion-generated emissions nor to be formed during sampling of ambient particulate matter. It is estimated that this daytime OH radical-initiated formation route to 2-nitrofluoranthene, the major mononitro-PAH observed in ambient particulate matter, is comparable in importance to night-time formation via reaction of fluoranthene with N2O5.

Formation of OH radicals in the gas phase reactions of O3 with a series of terpenes

The gas phase reactions of O3 with ethene, isoprene, and a series of monoterpenes have been investigated at 296 ± 2 K and atmospheric pressure of air in the presence of cyclohexane at concentrations sufficient to essentially totally scavenge any OH radicals formed. The expected products of the OH radical-initiated reaction of cyclohexane, cyclohexanone and cyclohexanol, were observed in all cases. From a knowledge of the chemistry of cyclohexane in these reaction systems and as a result of cyclohexanone and cyclohexanol formation yield data obtained in subsidiary experiments, the formation yields of OH radicals in these O3-alkene reactions were derived. The OH radical formation yields obtained from the gas phase reactions of O3 with alkenes were ethene, 0.12; isoprene, 0.27; camphene, ≤0.18; 3-carene, 1.06; limonene, 0.86; myrcene, 1.15; ocimene (a cis-, trans- mixture), 0.63; β-phellandrene, 0.14; α-pinene, 0.85; β-pinene, 0.35; sabinene, 0.26; and terpinolene, 1.03, all with estimated overall uncertainties of a factor of ∼ 1.5. For a-pinene the effect of varying the water vapor concentration was investigated and no change in the OH radical formation yield was observed over the range of (2.5–24) × 1016 molecules cm−3 of water vapor. The experimental conditions were such that formation of OH radicals from HO2 radicals was of minor importance, and the OH radical formation yields given above refer to direct formation of OH radicals and not HO2 radicals.

Product formation from the gas-phase reactions of OH radicals and O3 with a series of monoterpenes

The formation yields of nine carbonyl products are reported from the gas-phase OH radical-initiated reactions (in the presence of NOx) and the O3 reactions with seven monoterpenes. The products were identified using GC/MS and GC-FTIR and quantified by GC-FID analyses of samples collected on Tenax solid adsorbent cartridges. The identities of products from camphene, limonene and β-pinene were confirmed by comparison with authentic standards. Sufficient quantities of products from the 3-carene, limonene, α-pinene, sabinene and terpinolene reactions were isolated to allow structural confirmation by proton NMR spectroscopy. The measured total carbonyl formation yields ranged from non-detectable for the OH radical reaction with camphene and the O3 reactions with 3-carene and limonene to ∼0.5 for the OH radical reaction with limonene and the O3 reaction with sabinene.

Emission rates of organics from vegetation in California's Central Valley

Rates of emission of speciated hydrocarbons have been determined for more than 30 of the most dominant (based on acreage) agricultural and natural plant types found in Californias Central Valley. These measurements employed flow-through Teflon chambers, sample collection on solid adsorbent and thermal desorption gas chromatography (GC) and GC-mass spectrometry analysis to identify more than 40 individual organic compounds. In addition to isoprene and the monoterpenes, we observed sesquiterpenes, alcohols, acetates, aldehydes, ketones, ethers, esters, alkanes, alkenes and aromatics as emissions from these plant species. Mean emission rates for total monoterpenes ranged from none detected in the case of beans, grapes, rice and wheat, to as high as 12–30 μg h−1 g−1 for pistachio and tomato (normalized to dry leaf and total biomass, respectively). Other agricultural species exhibiting substantial rates of emission of monoterpenes included carrot, cotton, lemon, orange and walnut. All of the plant species studied showed total assigned compound emission rates in the range between 0.1 and 36 νg h−1 g−1.

Polycyclic aromatic hydrocarbon and nitroarene concentrations in ambient air during a wintertime high-NOx episode in the Los Angeles basin

Abstract The ambient concentrations of polycyclic aromatic hydrocarbons (PAH) (including biphenyl) and nitroarenes were measured during a wintertime, high-NOx episode at a location in Southern California. Daytime and night-time ambient air samples were collected using Hi-vol filters, polyurethane foam (PUF) plugs and Tenax-GC solid adsorbent. 2-Nitrofluoranthene was the most abundant particle-associated nitroarene, but higher concentrations of 1- and 2-nitronaphthalene, methylnitronaphthalenes and 3-nitrobiphenyl were observed on the PUF plugs. Our data show that the ambient concentrations of the more volatile PAH and nitroarenes can be far greater than those of the less volatile species, and suggest that the most abundant nitroarenes in ambient air arise from atmospheric transformations of PAH emitted from combustion sources.

The emission of (Z)-3-hexen-1-ol, (Z)-3-hexenylacetate and other oxygenated hydrocarbons from agricultural plant species

Abstract The oxygenated hydrocarbon species identified as emissions from 29 agricultural and natural plant species found in Californias Central Valley are reported. Prevalent as emissions from these agricultural crops were (Z)-3-hexen-1-ol and (Z)-3-hexenylacetate, with the latter compound often the dominant hydrocarbon emission. Quantitative emission rates for (Z)-3-hexen-1-ol and (Z)-3-hexenylacetate are reported for 18 agricultural and two natural plant species, and a brief discussion of the expected atmospheric chemistry of these two compounds is given.

Terpenes emitted from agricultural species found in California's Central Valley

More than a dozen monoterpenes have been identified as emissions from agricultural and natural plant species occupying large acreages in the Central Valley of California, including as dominant emissions camphene, 2-carene, Δ3-carene, limonene, myrcene, trans-ocimene, β-phellandrene, α-pinene, β-pinene, sabinene, γ-terpinene, and terpinolene. Isoprene was not a significant emission from any of the crop species examined but was emitted by a Valley Oak. In addition to the monoterpenes, sesquiterpenes were emitted from approximately one third of the species investigated, in some cases at higher levels than the monoterpene emissions from the same plant. The possible contributions of these biogenic emissions to the ozone exceedances in the Central Valley should be considered in planning future emission control strategies.

The nitroarenes of molecular weight 247 in ambient particulate samples collected in southern california

Abstract In addition to the dominant nitroarenes 2-nitrofluoranthene and 1- and 2-nitropyrene, the less abundant nitroarenes of molecular weight 247 in ambient particles collected during summer and winter pollutant episode conditions in southern California have been identified by gas chromatography/mass spectrometry. The approximate order of abundance of these nitroarenes was: 2-nitrofluoranthene > 1-nitropyrene ∼ 2-nitropyrene > 8-nitrofluoranthene ≳ 3-nitrofluoranthene > 7-nitrofluoranthene > a nitroacephenanthrylene ∼ 4-nitropyrene. The concentrations of 2-nitrofluoranthene, 1- and 2-nitropyrene and, in some cases, 3- and 8-nitrofluoranthene in 12 ambient samples are given. Significant differences in the distributions of these nitroarene isomers were observed among these samples and these are attributed to the varying importance of direct emission and atmospheric formation by reaction of the gaseous parent polycyclic aromatic hydrocarbon with N 2 O 5 and/or the OH radical (in the presence of NO x ). In particular, a very high (≳ 100) 2-nitrofluoranthene/2-nitropyrene concentration ratio appears to be indicative of nitroarene formation through night-time N 2 O 5 reaction.

Hydrocarbon emissions from natural vegetation in California's South Coast Air Basin

Hydrocarbon emissions from ten native plant species with high contributions to the biomass of Californias South Coast Air Basin (SOCAB) were measured using a flow-through chamber enclosure technique. Camphor and cineole and other oxygenated hydrocarbons were observed to be large emissions from certain aromatic sage and sagebrush species. Representative emission rate measurements for these species were difficult to obtain using the enclosure technique. Sesquiterpenes were found to be a high proportion of the emissions from Black Sage plants from late February to April. The isoprene emission rates measured for Interior Live Oak (Quercus wislizenii) and Scrub Oak (Quercus dumosa) were lower than most previously examined Quercus sp. However, estimated emissions of isoprene and terpenes from natural plant species in the SOCAB suggest that it may be difficult to reduce anthropogenic hydrocarbons sufficiently to meet ambient air quality standards for ozone and support the position that stringent controls on NOx as well as hydrocarbons will be required.