http://joenschem.com/yahoo_site_admin/assets/docs/atkinson2000r.93190106.pdf

Atmospheric chemistry of VOCs and NOx

Atmospheric degradation of volatile organic compounds

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.

/pdf/protocol-for-the-development-of-the-master-chemical-21efizove5.pdf

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

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

As part of a larger experiment that provides a comprehensive set of observations to be used for testing air quality models for organic air pollutant transport and reaction, ambient air samples have been collected using DNPH-coated C18 cartridges at four urban locations and one background location in the Los Angeles area and have been analyzed for carbonyls as their DNPH derivatives. Twenty-three carbonyls have been identified and their concentrations measured:  14 aliphatic aldehydes (from formaldehyde to tetradecanal), two aromatics (benzaldehyde and m-tolualdehyde), three ketones (acetone, 2-butanone, and cyclohexanone), one unsaturated carbonyl (crotonaldehyde), and three dicarbonyls (glyoxal, methylglyoxal, and biacetyl). Another 19 carbonyls have been tentatively identified including 11 low molecular weight (MW) and intermediate MW carbonyls (of which four may be due to reactions of ambient NO, NO2, and ozone with DNPH on the sampling cartridge), four C4−C6 dicarbonyls present at trace levels, and fo...

Air Quality Model Evaluation Data for Organics. 2. C1−C14 Carbonyls in Los Angeles Air

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

Carbonyls can be toxic and highly reactive in the atmosphere. To quantify trends in carbonyl emissions from light-duty (LD) vehicles, measurements were made in a San Francisco Bay area highway tunnel bore containing essentially all LD vehicles during the summers of 1999, 2001, and 2006. The LD vehicle emission factor for formaldehyde, the most abundant carbonyl, did not change between 1999 and 2001, then decreased by 61 ± 7% between 2001 and 2006. This reduction was due to fleet turnover and the removal of MTBE from gasoline. Acetaldehyde emissions decreased by 19 ± 2% between 1999 and 2001 and by the same amount between 2001 and 2006. Absent the increased use of ethanol in gasoline after 2003, acetaldehyde emissions would have further decreased by 2006. Carbonyl emission factors for medium- (MD) and heavy-duty (HD) diesel trucks were measured in 2006 in a separate mixed-traffic bore of the tunnel. Emission factors for diesel trucks were higher than those for LD vehicles for all reported carbonyls. Diesel...

Carbonyl and Nitrogen Dioxide Emissions From Gasoline- and Diesel-Powered Motor Vehicles

Emissions of carbonyls by motor vehicles are of concern because these species can be hazardous to human health and highly reactive in the atmosphere. The objective of this research was to measure carbonyl emission factors for California light-duty motor vehicles. Measurements were made at the entrance and exit of a San Francisco Bay area highway tunnel, in the center bore where heavy-duty trucks are not allowed. During summer 1999, approximately 100 carbonyls were identified, including saturated ahphatic aldehydes and ketones, unsaturated ahphatic carbonyls, ahphatic dicarbonyls, and aromatic carbonyls. Concentrations were measured for 32 carbonyls and were combined with NMOC, CO and CO2 concentrations to calculate by carbon balance emission factors per unit of fuel burned. The measured carbonyl mass emitted from light-duty vehicles was 68 +/- 4 mg L^-1. Formaldehyde accounted for 45% of the measured mass emissions, acetaldehyde 12%, toluadehydes 10%, benzaldehyde 7.2%, and acetone 5.9%. The ozone forming potential of the carbonyl emissions was dominated by formaldehyde (70%) and acetaldehyde (14%). Between 1994 and 1999, emission factors measured at the same tunnel for formaldehyde, acetaldehyde, and benzaldehyde decreased by 45-70%. Carbonyls constituted 3.9% of total NMOC mass emissions and 5.2% of NMOC reactivity. A comparison of carbonyl emissions with gasoline composition supports previous findings that aromatic aldehyde emissions are related to aromatics in gasoline. Carbonyl concentrations in liquid gasoline were also measured. Acetone and MEK were the most abundant carbonyls in unburned gasoline, 8 other carbonyls were detected and quantified.

/pdf/on-road-measurement-of-carbonyls-in-california-light-duty-2d2k2wr4qr.pdf

Eric Grosjean

Papers

Atmospheric chemistry of isoprene and of its carbonyl products

Air Quality Model Evaluation Data for Organics. 2. C1−C14 Carbonyls in Los Angeles Air

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

Carbonyl and Nitrogen Dioxide Emissions From Gasoline- and Diesel-Powered Motor Vehicles

On-Road Measurement of Carbonyls in California Light-Duty Vehicle Emissions - eScholarship