Eric Grosjean

Liquid Chromatography Analysis of Carbonyl (2,4-Dinitrophenyl)hydrazones with Detection by Diode Array Ultraviolet Spectroscopy and by Atmospheric Pressure Negative Chemical Ionization Mass Spectrometry

The (2,4-dinitrophenyl)hydrazones of carbonyls are separated by liquid chromatography and detected by ultraviolet spectroscopy (diode array detector) and by atmospheric pressure negative chemical ionization mass spectrometry. Results are presented for 78 carbonyls including 18 1-alkanals (from formaldehyde to octadecanal), 16 other saturated aliphatic carbonyls (5 C(4)-C(7) aldehydes and 11 C(3)-C(9) ketones), 16 unsaturated aliphatic carbonyls (9 C(3)-C(11) aldehydes and 7 C(4)-C(9) ketones), 13 aromatic carbonyls (including hydroxy- and/or methoxy-substituted compounds), 10 C(2)-C(10) aliphatic dicarbonyls, 3 aliphatic carbonyl esters, and 2 other carbonyls. Isomers were observed for α,β-unsaturated ketones and saturated carbonyls that bear other oxygen-containing substituents, e.g. methoxyacetone, 2-furaldehyde, and the 3 carbonyl esters. For all but two of the carbonyls studied, the base peak in the negative APCI mass spectrum was the M - 1 ion (NO(2))(2)C(6)H(3)NN [Formula: see text] CR(1)R(2) (R(1) = H for aldehydes), where M is the molecular mass of the carbonyl (2,4-dinitrophenyl)hydrazone derivative. The dicarbonyls 2,4-pentanedione and succinic dialdehyde reacted with DNPH to yield predominantly other products. Concentrations measured by ultraviolet spectroscopy (peak area) and by mass spectrometry (abundance of M - 1 ion) were in good agreement. Applications described include the measurement of 34 C(1)-C(18) carbonyls at levels of 0.015-14 parts per billion (ppb) in urban air and the identification of carbonyls at ppb concentrations as reaction products in laboratory studies of the atmospheric oxidation of unsaturated organic compounds.

Ambient levels of gas phase pollutants in Porto Alegre, Brazil

Abstract Air samples have been collected using electropolished canisters in downtown Porto Alegre, Brazil, where ethanol is used as a vehicle fuel and methyl-tert-butyl ether (MTBE) is used as a vehicle fuel additive. The 150 volatile organic compounds (VOC) identified by GC-FID and GC-MS included 46 alkanes, 30 alkenes, 22 aromatics, 17 carbonyls, 3 alcohols, 8 bicyclic aromatics, 11 halogenated hydrocarbons and 13 other compounds. The most abundant VOC on a mass concentration basis (after CO2, CH4 and CO) included acetylene, MTBE, ethanol, the alkanes propane, n-butane, n-pentane, isopentane, n-hexane, 2-methylpentane and indane, the alkenes ethylene and propene, and the aromatics benzene, toluene, ethylbenzene and (m+p) xylene. During the ca. one-year period studied, 20 March, 1996–16 April, 1997, ambient concentrations of VOC correlated well with those of carbon monoxide, for which vehicle exhaust emissions account for ca. 99% of total emissions in Porto Alegre. Two VOC photochemical reactivity rankings are presented: one involves reaction with OH (product of VOC concentration and VOC–OH reaction rate constant) and the other involves production of ozone (product of VOC concentration and VOC maximum incremental reactivity coefficient). Reaction with OH is dominated by CO followed by 2-methyl-2-butene and by several other alkenes. Ozone production is dominated by ethylene and CO (about equal contribution) followed by several alkenes, alkylbenzenes and aldehydes. The two fuel oxygenates, ethanol and MTBE, play only a minor role as photochemical precursors (reaction with OH and production of ozone) in the atmosphere of Porto Alegre.

Rate constants for the gas-phase reaction of ozone with unsaturated oxygenates

The gas-phase reaction of ozone with a series of unsaturated oxygenates and with 1-pentene has been studied at ambient T (287–296 K) and p=1 atm. of air. Reaction rate constants, in units of 10−18 cm3 molecule−1 s−1, are 0.22±0.05 for 2 (5H)-furanone, 1.08±0.20 for methacrolein, 1.74±0.20 for crotonaldehyde, 5.84±0.39 for methylvinyl ketone, 1.05±0.15 for methyl acrylate, 3.20±0.47 for vinyl acetate, 59.0±8.7 for cis-3-hexenyl acetate, 154±30 for ethylvinyl ether, ≥(315±23) for linalool, and 10.9±1.4 for 1-pentene. The results are compared to literature data for the compounds studied and for other unsaturated oxygenates, and are discussed in terms of reactivity toward ozone as a function of the nature, number, and position of the oxygen-containing substituents (SINGLEBOND)CHO, (SINGLEBOND)C(O)R, (SINGLEBOND)C(O)OR, and (SINGLEBOND)OC(O)R. Atmospheric implications are briefly examined.

Ambient Levels of Formaldehyde and Acetaldehyde in Atlanta, Georgia

Ambient levels of formaldehyde and acetaldehyde have been measured at four locations in the Atlanta, Georgia, area during July and August 1992. Location-averaged concentrations were 2.7 - 3.0 ppb for formaldehyde and 2.6 - 3.2 ppb for acetaldehyde (2 hr - samples). The highest concentrations measured were 8.3 ppb for formaldehyde and 8.4 ppb for acetaldehyde. On the average, ambient aldehyde concentrations measured at two elevations (6 m and 30 m) at a near-downtown location were similar; those recorded at a predominantly upwind site were slightly lower, and those recorded at a predominantly downwind site were slightly higher. The formaldehyde/acetaldehyde concentration ratio (ppb/ppb) ranged from 0.2 to 3.3 and averaged 1.04 ± 0.46 (217 samples). A brief discussion of the data is presented and includes method performance evaluation, diurnal variations, examination of the acetaldehyde/formaldehyde concentration ratio, and comparison with literature data for other urban areas.

The reaction of unsaturated aliphatic oxygenates with ozone

The reaction of ozone with unsaturated aliphatic oxygenates has been studied at ambient T (287–297 K) and p = 1 atm. of air (RH = 55 ± 10%) with sufficient cyclohexane added to scavenge the hydroxyl radical. Reaction rate constants, in units of 10-18 cm3 molecule-1 s-1, are 10.7 ± 1.4 for methyl trans-3-methoxy acrylate, 63.7 ± 9.9 for 4-hexen-3-one (predominantly the trans isomer), 125 ± 17 for trans-4-methoxy-3-buten-2-one, ≥148 ± 13 for cis-4-heptenal, ≥439 ± 37 for 3- methyl-2-buten-1-ol and ≥585 ± 132 for (cis + trans)-ethyl 1-propenyl ether. The influence of the oxygen-containing substituents on reactivity toward ozone is examined. Unsaturated ethers react with ozone faster than their alkene structural homologues; the reverse is observed for unsaturated esters and unsaturated carbonyls. Major reaction products have been identified by liquid chromatography with ultraviolet detection (LC-UV), particle beam-mass spectrometry (PB- MS) and gas chromatography-mass spectrometry (GC-MS) and are methyl formate and methyl glyoxylate from methyl trans-3-methoxy acrylate, acetaldehyde and 2-oxobutanal from 4-hexen-3-one, propanal and succinic dialdehyde from cis-4-heptenal, hydroxyacetaldehyde and acetone from 3-methyl-2-buten-1-ol, and ethyl formate and acetaldehyde from (cis + trans)-ethyl 1-propenyl ether. PB-MS and GC- MS were also employed to identify new reaction products and to confirm the structure of products tentatively identified in a previous study of the reaction of ozone with five unsaturated oxygenates (Grosjean and Grosjean, 1997a): formic acid and methyl glyoxylate from methyl acrylate, formic acid and formic acetic anhydride from vinyl acetate, 2-oxoethyl acetate and 3-oxopropyl acetate from cis-3-hexenyl acetate, ethyl formate and formic acid from ethyl vinyl ether, and methyl formate from trans-4-methoxy-3- buten-2-one. The nature and formation yields of the reaction products are consistent with (and supportive of) the reaction mechanism: O3 + R1R2C=CR3X → α(R1COR2 + R3C(X)OO) + (1 - α)(R3COX + R1C(R2)OO), where R1, R2 and R3 = H or alkyl, X is the oxygen-containing substituent, R1COR2 and R3COX are the primary products and R1C(R2)OO and R3C(X)OO are the carbonyl oxide biradicals. The variations of the coefficient α, which ranges from 0.25 to 0.61, are discussed in terms of the number and nature of alkyl and oxygen-containing substituents. Subsequent reactions of the alkyl-substituted biradicals R1C(R2)OO and of the biradicals R3C(X)OO that bear the oxygen-containing substituent are discussed. For the biradical CH3CHOO, the ratio ka/kb for the competing pathways of rearrangement to acetic acid (CH3CHOO → CH3C(O)OH, reaction (a) and formation of an unsaturated hydroperoxide (CH3CHOO → CH2=CH(OOH), reaction (b) is <0.25 for ethyl 1-propenyl ether and <0.27 for 4-hexen-3-one. Concentrations measured in co- located samples, one downstream of a water impinger and the other without water impinger, show the uptake in water impingers to be high (from 83.2 to >99.9%) and comparable to that for formaldehyde (98.4%) for formic acetic anhydride and for difunctional oxygenated compounds. Uptake in water impingers was lower (19–78%) for monofunctional aldehydes and ketones.

Atmospheric chemistry of olefins: a product study of the ozone-alkene reaction with cyclohexane added to scavenge hydroxyl radical.

Carbonyl and carboxylic acid products of the ozone-olefin reaction, in which the hydroxyl radical is produced, have been identified and measured for eight alkenes in the presence of excess cyclohexane, i.e., ruder conditions that minimize subsequent reactions of OH with the alkenes and with their carbonyl product. The carbonyls expected to form directly, i.e., alkene+ozone→1,d,3-trioxolane adduct→two carbonyls+two Criegee biradicals, were observed as major product (e.g., formaldehyde and d-butanone from d-methyl-1-butene). Their yields ranged from 9±2% for 1,3-butadiene to 88±4% for 2,3-dimethyl-d-butene. For alkenes that lead to two Criegee biradicals, carbonyl yields were consistent with preferential formation of the more substituted biradical

Gas-phase reaction of ozone with trans-2-hexenal, trans-2-hexenyl acetate, ethylvinyl ketone, and 6-methyl-5-hepten-2-one

The gas-phase reaction of ozone with the unsaturated oxygenates trans-2-hexenal, trans-2-hexenyl acetate, ethylvinyl ketone, and 6-methyl-5-hepten-2-one, which are components of biogenic emissions and/or close structural homologues thereof, has been investigated at atmospheric pressure and ambient temperature (286–291 K) and humidity (RH = 55 ± 10%). Reaction rate constants, in units of 10−18 cm3 molecule−1 s−1, are 1.28 ± 0.28 for trans-2-hexenal, 21.8 ± 2.8 for trans-2-hexenyl acetate, and 394 ± 40 for 6-methyl-5-hepten-2-one. Carbonyl product formation yields, measured with sufficient cyclohexane added to scavenge the hydroxyl radical, are 0.53 ± 0.06 for n-butanal and 0.56 ± 0.04 for glyoxal from trans-2-hexenal, 0.47 ± 0.02 for n-butanal and 0.58 ± 0.14 for 1-oxoethyl acetate from trans-2-hexenyl acetate, 0.55 ± 0.07 for formaldehyde and 0.44 ± 0.03 for 2-oxobutanal from ethylvinyl ketone, and 0.28 ± 0.02 for acetone from 6-methyl-5-hepten-2-one. Reaction mechanisms are outlined and the atmospheric persistence of the compounds studied is briefly discussed.

The Gas Phase Reaction of Unsaturated Oxygenates with Ozone: Carbonyl Products and Comparison with the Alkene-Ozone Reaction

Carbonyl products have been identified and their formation yields measured in the gas phase reaction of ozone with unsaturated oxygenates in experiments carried out at ambient T, p = 1 atm. of purified humid air (RH = 50%) and with sufficient cyclohexane added to scavenge the hydroxyl radical. The compounds studied are the esters methyl acrylate, vinyl acetate and cis-3-hexenyl acetate, the carbonyl crotonaldehyde, the hydroxy-substituted diene linalool, the ether ethylvinyl ether and the keto-ether trans-4-methoxy-3-buten-2-one. The alkene 1-pentene was included for comparison. The nature and formation yields of the carbonyl products from this study and those measured in earlier work under the same conditions are compared to those of alkenes and are supportive of a reaction mechanism that is similar to that for the reaction of ozone with alkenes, i.e. O3 + R1R2C=CR3X → α(R1COR2 + R3XCOO) + (1 − α)(R3COX + R1R2COO), where Ri are the alkyl substituents, X is the oxygen-containing substituent (–CHO for aldehydes; –C(O)R for ketones; –C(O)OR and –OC(O)R for esters; –OH and hydroxyalkyl for alcohols; and –OR for ethers), R1COR2 is the primary carbonyl, R3COX is the other primary product and R1R2COO and R3XCOO are the carbonyl oxide biradicals. The biradicals lead to carbonyls in reactions that are also analogous to those involved in carbonyl formation from biradicals in the ozone-alkene reaction. These features make it possible to predict the nature and formation yields of the major carbonyl products of the reaction of ozone with unsaturated oxygenates that may be components of biogenic emissions.

Ambient levels of the peroxyacyl nitrates PAN, PPN, and MPAN in Atlanta, Georgia

Ambient levels of the peroxyacyl nitrates [RC(O)OONO2] PAN (R = CH3), PPN (R = C2H5-) and MPAN [R = CH2 = C(CH3)-] have been measured in July - August 1992 in downtown Atlanta, Georgia. Ambient levels of PAN reached 2.9 ppb and averaged 0.71 ± 0.53 ppb(n=817). PPN reached 0.37 ppb and averaged 0.14 ±0.14 ppb (n = 119). Diurnal variations of PAN and PPN were similar and included nighttime minimaand late afternoon/early evening maxima. MPAN was observed on only 12 occasions at levels averaging 0.32 ± 0.07 ppb. A brief descriptive analysis of the data is presented together with a documentation of our measurement and calibration protocols and the results of an interlaboratory comparison involving co-located measurements of ambient PAN.

Carbonyl products of the gas-phase reaction of ozone with 1-alkenes

The gas phase reaction of ozone with alkenes, which is of critical importance in atmospheric chemistry, is still poorly understood. Major uncertainties regarding the reaction mechanism include the nature and the formation yields of the carbonyl products, the formation yields of the biradicals R1R2COO, and the subsequent reactions of these biradicals. In this study, the gas phase reaction of ozone with 1-pentene, 1-hexene, 1-heptene, 2,3-dimethyl-1-butene, cyclopentene, and 1-methylcyclohexene has been studied with sufficient cyclohexane added to scavenge OH. Carbonyl products were identified as their DNPH derivatives by liquid chromatography and chemical ionization mass spectrometry. Primary carbonyl formation yields for the 1-alkenes and 2,3-dimethyl-1-butene were close to the value of 1.0 that is consistent with the mechanism O3 + R1R2CCH2 → α(HCHO + R1R2COO) + (1 − α)(R1COR2 + H2COO), where HCHO and R1COR2 are the primary carbonyls. Data for the 1-alkenes, α = ca. 0.50, were consistent with about equal...