This overview compiles the actual knowledge of the biogenic emissions of some volatile organic compounds (VOCs), i.e., isoprene, terpenes, alkanes, alkenes, alcohols, esters, carbonyls, and acids. We discuss VOC biosynthesis, emission inventories, relations between emission and plant physiology as well as temperature and radiation, and ecophysiological functions. For isoprene and monoterpenes, an extended summary of standard emission factors, with data related to the plant genus and species, is included. The data compilation shows that we have quite a substantial knowledge of the emission of isoprene and monoterpenes, including emission rates, emission regulation, and biosynthesis. The situation is worse in the case of numerous other compounds (other VOCs or OVOCs) being emitted by the biosphere. This is reflected in the insufficient knowledge of emission rates and biological functions. Except for the terpenoids, only a limited number of studies of OVOCs are available; data are summarized for alkanes, alkenes, carbonyls, alcohols, acids, and esters. In addition to closing these gaps of knowledge, one of the major objectives for future VOC research is improving our knowledge of the fate of organic carbon in the atmosphere, ending up in oxidation products and/or as aerosol particles.

Biogenic Volatile Organic Compounds (VOC): An Overview on Emission, Physiology and Ecology

Veterinary pharmaceuticals (VPs) are used in large amounts in modern husbandry. Due to their use pattern, they possess a potential for reaching the soil environment. To assess their mobility in soil, the literature on sorption of chemicals used as VPs is reviewed and put into perspective of their physicochemical properties. The compilation of sorption coefficients to soil solids (Kd,solid) demonstrates that these chemicals display a wide range of mobility (0.2 < Kd,solid < 6,000 L/kg). Partition coefficients for association of tetracycline and quinolone carboxylic acid VPs to dissolved organic matter (Kd,DOM) vary between 100 and 50,000 L/kg. The variation in Kd,solid for a given compound in different soils can be significant. For most of the compounds, the variation is not considerably lower for the organic carbon-normalized sorption coefficient Koc. In addition, prediction of log Koc by log Kow leads to significant underestimation of log Koc and log Kd,DOM values. This suggests that mechanisms other than hydrophobic partitioning play a significant role in sorption of VPs. A number of hydrophobicity-independent mechanisms such as cation exchange, cation bridging at clay surfaces, surface complexation, and hydrogen bonding appear to be involved. These processes are not accounted for by organic carbon normalization, suggesting that this data treatment is conceptually inappropriate and fails to describe the sorption behavior. Moreover, prediction of log Koc based on the hydrophobicity parameter log Kow is not successful.

Sorption of veterinary pharmaceuticals in soils: a review.

. Kinetic and mechanistic data relevant to the tropospheric degradation of volatile organic compounds (VOC), and the production of secondary pollutants, have previously been used to define a protocol which underpinned the construction of a near-explicit Master Chemical Mechanism. In this paper, an update to the previous protocol is presented, which has been used to define degradation schemes for 107 non-aromatic VOC as part of version 3 of the Master Chemical Mechanism (MCM v3). The treatment of 18 aromatic VOC is described in a companion paper. The protocol is divided into a series of subsections describing initiation reactions, the reactions of the radical intermediates and the further degradation of first and subsequent generation products. Emphasis is placed on updating the previous information, and outlining the methodology which is specifically applicable to VOC not considered previously (e.g. a - and b -pinene). The present protocol aims to take into consideration work available in the open literature up to the beginning of 2001, and some other studies known by the authors which were under review at the time. Application of MCM v3 in appropriate box models indicates that the representation of isoprene degradation provides a good description of the speciated distribution of oxygenated organic products observed in reported field studies where isoprene was the dominant emitted hydrocarbon, and that the a -pinene degradation chemistry provides a good description of the time dependence of key gas phase species in a -pinene/NOX photo-oxidation experiments carried out in the European Photoreactor (EUPHORE). Photochemical Ozone Creation Potentials (POCP) have been calculated for the 106 non-aromatic non-methane VOC in MCM v3 for idealised conditions appropriate to north-west Europe, using a photochemical trajectory model. The POCP values provide a measure of the relative ozone forming abilities of the VOC. Where applicable, the values are compared with those calculated with previous versions of the MCM.

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

http://www-personal.umich.edu/~sillman/web-publications/Sillmanreview99.pdf

The relation between ozone, NOx and hydrocarbons in urban and polluted rural environments

Indoor air quality and health

The carbonyl products of isoprene, methacrolein (MTA), methyl vinyl ketone (MVK), hydroxyacetaldehyde, and hydroxyacetone have been identified and their concentrations measured in experiments involving sunlight irradiations of 1 ppm organic and 200 ppb NO in purified air. The MTA/MVK yield ratio was 1.4 for isoprene. The hydroxycarbonyljmethylglyoxal yield ratio was 4.3 for MTA and was 1.9 for MVK. The peroxyacyl nitrates PAN [RC(O)OONO 2 , R=CH 3 - ] and MPAN [R=CH 2 C-(CH 3 )-] have been measured. MPAN/PAN concentration ratios were 0.65±0.04 for isoprene and 2.3±0.1 for MTA

Atmospheric chemistry of isoprene and of its carbonyl products

Several gas-phase carbonyl products of two terpenes, β-pinene and D-limonene, and of the sesquiterpene, transcaryophyllene, have been identified and their concentrations measured in experiments involving the reaction of these unsaturated biogenic hydrocarbons with ozone in the dark. Cyclohexane was added as a scavenger for the hydroxyl radical to minimize interferences from OH, which forms as a product of the ozone-hydrocarbon reaction. Carbonyl products were formaldehyde (yield = 0.42) and nopinone (yield = 0.22) from β-pinene, formaldehyde (yield = 0.10) and 4-acetyl-1-methylcyclohexene from D-limonene, and formaldehyde (yield 0.08) from transcaryophyllene. The nature and yields of these products are discussed in terms of the ozone-olefin reaction mechanism. The ozone-β-pinene reaction rate constant, measured in the presence of cyclohexane, is 12.2 ± 1.3 x 10^(-18) cm^3 molecule^(-1) s^(-1) at 22 ± 1 °C. Carbonyl products have also been identified in exploratory experiments with trans-caryophyllene and NO in sunlight.

Atmospheric oxidation of biogenic hydrocarbons : Reaction of ozone with β-pinene, d-limonene and trans-caryophyllene

Environmental persistence of organic compounds estimated from structure-reactivity and linear free-energy relationships. Unsaturated aliphatics

The gas-phase carbonyl products of α-pinene, β-pinene, and d-limonene have been identified and their concentrations measured in experiments involving sunlight irradiations of mixtures of terpene (1-2 ppm) and NO (0.25 ppm) in air. In turn, sunlight irradiations of carbonyl-NO_x mixtures have been carried out for the major high molecular weight carbonyl products of β-pinene (6,6-dimethylbicyclo[3.1.1] heptan-2-one) and d-limonene (4-acetyl-1-methylcyclohexene), and the corresponding carbonyl products have been identified. The nature and yields of these carbonyl products are discussed in terms of oxidation mechanisms involving the OH-terpene, ozone-terpene, OH-carbonyl, and ozone-carbonyl reactions.

Atmospheric oxidation of selected terpenes and related carbonyls: gas-phase carbonyl products

The kinetics of the gas-phase reaction of ozone with unsaturated alcohols, carbonyls, and esters in air have been investigated at atmospheric pressure, ambient temperature (285–295 K), and in the presence of sufficient cyclohexane to scavenge the hydroxyl radical which forms as a product of the ozone-unsaturated compound reaction. The reaction rate constants, in units of 10−18 cm3 molecule−1 s−1, are 0.26 ± 0.05 for acrolein, 1.07 ± 0.05 for 2-ethyl acrolein, 6.0 ± 0.4 for ethyl vinyl ketone, 4.9 ± 0.4 for 3-buten-1-ol, 14.4 ± 2.0 for allyl alcohol, 105 ± 7 for cis-3-hexen-1-ol, 7.5 ± 0.9 for methyl methacrylate, 2.9 ± 0.3 for vinyl acetate, 4.4 ± 0.3 for methyl crotonate, and 8.1 ± 0.3 for the 1,1-disubstituted alkene 2-ethyl-1-butene. Substituent effects on reactivity are discussed by comparison with alkenes and indicate that the reactivity of unsaturated alcohols is the same as that of alkene structural homologues and that the —C(O)OR, —C(O)R, and —CHO groups decrease the reactivity towards ozone as compared to alkyl groups. Estimates are made of the atmospheric persistence of these unsaturated compounds using the kinetic data obtained in this study as input to structure-reactivity and linear free-energy relationships. © 1993 John Wiley & Sons, Inc.

Edwin L. Williams

Papers

Atmospheric chemistry of isoprene and of its carbonyl products

Atmospheric oxidation of biogenic hydrocarbons : Reaction of ozone with β-pinene, d-limonene and trans-caryophyllene

Environmental persistence of organic compounds estimated from structure-reactivity and linear free-energy relationships. Unsaturated aliphatics

Atmospheric oxidation of selected terpenes and related carbonyls: gas-phase carbonyl products

Rate constants for the gas‐phase reactions of ozone with unsaturated alcohols, esters, and carbonyls