Environ. Sci. Technol. 1983, 27, 2478-2405
Atmospheric Chemistry of Unsaturated Alcohols Danlel Grosjean,’ Eric Grosjean, and Edwin L. Wllliams I1 DGA, Inc., 4526 Telephone Road, Suite 205, Ventura, California 93003
The atmospheric oxidation of the unsaturated alcohols [allyl alcohol (CHz=CHCHzOH), 3-buten-1-01(CHz=CHCHzCHzOH), and cis-3-hexen-1-01(CH&HzCH=CHCH2CH20H)I has been studied in experiments involving unsaturated alcohol-ozone-cyclohexane mixtures in the dark and involving unsaturated alcohol-nitric oxide mixtures in the sunlight. Major carbonyl products of the ozone-unsaturated alcohol reaction, with cyclohexane added to scavenge OH, included formaldehyde and hydroxyacetaldehyde from allyl alcohol (yields 0.50 f 0.03 and 0.30 f0.03, respectively);formaldehyde from 3-buten1-01(yield 0.37 f 0.09); and propanal, methylglyoxal, and acetaldehyde from cis-3-hexen-1-01(yields 0.59 f 0.12, 0.17 f 0.05 and 0.13 f 0.02, respectively). The corresponding reaction mechanisms are outlined with focus on formation and decomposition pathways for hydroxyalkylsubstituted Criegee biradicals. Carbonyl and peroxyacyl nitrate products of the alcohol-NO reaction in sunlight have been identified and their concentrations measured. Their formation is discussed in terms of pathways initiated by reaction with the hydroxyl radical. Peroxypropionyl nitrate [PPN, CH~CHZC(O)OONOZI was a major product of cis-3-hexen-1-01and accounted for 14-20 % of the initial NO. Atmospheric persistence of unsaturated alcohols and implications for the formation of propanal and PPN from biogenic emissionsof cis-3-hexen-1-01are briefly discussed. Introduction Biogenic hydrocarbons play a critical role in ozone production and aerosol formation in the atmosphere (1, 2). While many studies have been carried out to elucidate the atmospheric oxidation of isoprene and of monoterpenes (refs 3-6 and references cited therein), little is known regarding the atmospheric persistence and fate of other biogenic compounds. Yet it has been known for some time that biogenic emissions also include oxygenated compounds such as alcohols and esters (7-12). Among these, unsaturated alcohols appear to constitute an important category of biogenic emissions. For example, cis3-hexen-1-01,CH~CHZCH=CHCHZCHZOH, long known as leaf alcohol, has been identified as a major component of emissions from trees, grass, and agricultural plants (711). In the same way, the unsaturated alcohol linalool, a structural homologue of the terpene myrcene, has been recently identified as a major component of emissions from orange blossoms and has been detected in ambient air (12). As more selective and sensitive sampling and analytical methods become available, other unsaturated alcohols may be identified along with isoprene and terpenes as important biogenic emissions to the atmosphere. Unsaturated alcohols are predicted to be oxidized in the atmosphere in pathways initiated by their reactions with ozone, with the hydroxyl radical, and at night, with the nitrate radical (13, 14). These reactions produce carbonyls, carboxylic acids, and, in the presence of oxides
* Corresponding author. 2478
Environ. Scl. Technol., Vol. 27,
No. 12,
1993
of nitrogen, peroxyacyl nitrates (13,14). Indeed, in a recent exploratory study involving sunlight irradiation of cis-3hexen-1-01 and nitric oxide in purified air, we have identified the carbonyl propanal (CH3CH2CHO) and the peroxyacyl nitrate peroxypropionyl nitrate [CH~CHZC(O)OONOz, hereafter called PPNI as reaction products (15). Carbonyls including propanal react rapidly with OH, thus “fueling” atmospheric oxidation processes (13, 14). Peroxyacyl nitrates including PPN are phytotoxic (16) and play an important role in the long-range transport of odd reactive nitrogen (17). Thus, information on the atmospheric oxidation of unsaturated alcohols, including the nature and yields of their reaction products, is important in the context of assessing the role and impact of biogenic hydrocarbon emissions. In this study we have investigated, in laboratory experiments carried out under conditions that are relevant to the atmosphere, the oxidation of the unsaturated alcohols cis-3-hexen-1-01,3-buten-1-01,and allyl alcohol. cis-3-Hexen-1-01was selected for its abundance in biogenic emissions (7-11). The monosubstituted compound 3-buten-1-01 (CH~=CHCHZCHZOH) was included as a simpler structural homologue (both compounds bear the hydroxyethyl substituent) to assess the general applicability of unsaturated alcohols atmospheric oxidation pathways. The simplest unsaturated alcohol, allyl alcohol, has a number of industrial applications and was included for consistency and to compare the hydroxyethyl and hydroxymethyl substituents. Two types of experiments have been performed, one involving sunlight irradiations of unsaturated alcoholNO mixtures and the other involvingthe reaction of ozone with the unsaturated alcohol in the dark in the presence of cyclohexane. The unsaturated alcohol-NO-sunlight experiments provide information on oxidation pathways initiated by reaction with OH (reaction with ozone also takes place after the NO-NO2 crossover);they also provide information on the formation of peroxyacyl nitrates and other nitrogen-containing reaction products. The unsaturated alcohol-ozone-cyclohexane experiments provide information on alcohol oxidation initiated by reaction with ozone under conditions that minimizethe role of OH, which has been recently shown to be a product of the reaction of ozone with olefins including alkenes (18-20), isoprene (18,21) and terpenes (18). Cyclohexane, whose reaction with ozone is negligibly slow (131, acts as a “scavenger”for OH, thereby allowing us to obtain unambiguous product data for the ozone-unsaturated alcohol reaction, Experimental Methods Sunlight Irradiation of NO-Unsaturated Alcohol Mixtures. Sunlight irradiations of mixtures of nitric oxide with cis-3-hexen-1-01(AldrichChemical Co., purity = 98 % ) or 3-buten-1-01 (Aldrich, purity = 99%) in purified air (relative humidity = 55 f 10%)were carried out at ambient temperature and atmospheric pressure in a 3.7-m3 allTeflon collapsible chamber constructed from 200A FEP Teflon film (4, 6, 15, 20). Purified, particle-free air was 0013-936X/93/0927-2478$04.00/0
0
1993 American Chemical Soclety
obtained by passing ambient air through large cartridges containing activated carbon, silica gel, and molecular sieves and contained less than 1 ppb of reactive hydrocarbons, ozone and oxides of nitrogen, less than 0.1-0.5 ppb of formaldehyde, acetaldehyde, and propanal; and less than 0.05-0.1 ppb of peroxyacyl nitrates including PPN and peroxyacetyl nitrate [CH3C(O)OON02, hereafter called PAN]. Ozone was measured by ultraviolet photometry using a calibrated Dasibi 1103continuous analyzer. Oxides of nitrogen were measured by chemiluminescence using a Monitor Labs 8840 continuous analyzer calibrated using the diluted outputs of a certified cylinder of NO in nitrogen and of a certified NO2 permeation tube maintained at 30.0 f 0.1 "C. Ozone-Unsaturated Alcohol Reaction. Ozone produced by the built-in generator of the ozone analyzer was introduced in a 3.5-m3all-Teflon chamber identical to that described above and covered with black plastic film. The experiments were carried out at ambient temperature and atmospheric pressure in purified, humid air (RH = 55 f 10%). Once the desired ozone concentration was obtained, the ozone generator was turned off and the ozone concentration was monitored to verify the absence of olefinsor other ozone-consuming impurities. Cyclohexane (Aldrich, purity >99.9 7%)was introduced in the chamber by injecting microliter aliquots of the liquid into a threeway 200-cm3glass bulb and by flushing the contents of the glass bulb into the chamber using purifiedair as the carrier gas. The absence of ozone-consuming impurities in cyclohexanewas verified in separate experiments involving ozone (500 ppb) and cyclohexane (400 ppm) in purified air. The rate loss of ozone in these experiments was 1.1 f 0.1 X lo4 s - ~ . The unsaturated alcohol (cis-3-hexen1-01,3-buten-1-01,or allyl alcohol; Aldrich, purity = 99%) was injected last using the same method as for cyclohexane. The rate of loss of ozone by diffusion to the chamber walls was measured in separate experiments involvingppb levels of ozone in purified air and was 0.9 f 0.1 x 10-6 s-l. This value is consistent with literature values for other chambers constructed from the same type of Teflon film (22). Carbonyl Measurements. Carbonyl products were isolated as their 2,4-dinitrophenylhydrazonesby sampling the reaction mixture through small CIScartridges coated with twice recrystallized 2,4-dinitrophenylhydrazine (DNPH) as described previously (20,23,24).To minimize ozone-induced sampling artifacts, carbonyl samples were collected near the completion of the ozone-unsaturated alcohol experiments when the ozone concentration had decreased to less than 10 ppb. The sampling flow rate was 0.52 L/min, and the sampling duration was 40-60 min. Following collection, the cartridges were eluted with HPLC-grade acetonitrile, and aliquots of the acetonitrile extracts were analyzed by liquid chromatography with ultraviolet detection (23). The carbonyl 2,4-dinitrophenylhydrazones were separated on a Whatman Partisphere CIS column, 110 X 4.7 mm, with 5545 by volume CHsCN-HzO eluent (both HPLC-grade) at a flow rate of 1 mL/min. The liquid chromatograph components included a solvent delivery system equipped with 0.2-pm pore size Teflon filters, a SSI 300 pump, a 20-pL injection loop, a Whatman Partisphere CIS guard cartridge, and a PerkinElmer LC75 UV-visible detector. The detection wavelength was 360 nm. Confirmation of the presence of monofunctional or difunctional carbonyl derivatives was obtained by measuring their 4301360 nm absorbance ratio. The 2,4-
dinitrophenylhydrazones of aliphatic dicarbonyls absorb with a maximum at 430 nm; those of aliphatic compounds containing only one carbonyl group absorb with maxima of about 360 nm (20, 23, 24). In this way, positive identification could be made by matching retention times and 4301360 nm absorbance ratios of peaks in the chromatograms of the samples to those of reference standards synthesized in our laboratory and for which structure confirmation had been obtained independently by chemical ionization mass spectrometry (25). For additional structure confirmation, 190-600 nm spectra were recorded using a diode array detector (23) for one carbonyl sample in each experiment. These samples were also analyzed by chemical ionization mass spectrometry (25)with selective ion monitoring at the appropriate mass/ charge ratio, e.g., 211 amu for formaldehyde-DNPH (MW = 2101, 239 amu for propanal-DNPH (MW = 238), 279 amu for cyclohexanone-DNPH (MW = 278), and so on. The hydroxycarbonyl product 1-hydroxypropanal, CH2OHCHzCHO, could not be positively identified due to the lack of a reference standard for comparison. Indirect evidence for its formation as a product was indicated by the presence of acrolein-DNPH (as verified by comparison of retention time, UV spectrum, and mass spectrum with those of a reference standard) in the carbonyl samples collected in the cis-3-hexen-l-ol-ozone, cis-3-hexen-l-01NO, 3-buten-l-ol-ozone, and 3-buten-l-ol-NOX experiments. Acrolein was not,present as an impurity (this was verified experimentally) and is not expected to form in the oxidation of either unsaturated alcohol. Literature data for other hydroxycarbonyls and their DNPH derivatives, e.g., authentic samples of 3-hydroxybutanal, 5-hydroxypentanal and 5-hydroxy-2-pentanone (251,indicate facile loss of water for these compounds. Thus, by analogy, our observation of the DNPH derivative of acrolein may be indicative of the presence of 1-hydroxypropanal followed by the CHzOHCHzCHO H2O + CH2=CH-CHO and/or CH20HCH2CHO-DNPH H2O + acroleinDNPH pathways. Quantitative analysis involved the use of external standards (23)for which calibration curves, i.e., absorbance (peak height) vs concentration, were constructed. These calibration curves were constructed over the concentration range that bracketed those found in the samples collected in the experiments. The slopes of these calibration curves, i.e., response factors, were used to calculate the concentrations of the carbonyl products. Retention times, 430/ 360 nm absorbance ratios and response factors are listed in Table I for a number of carbonyls relevant to this study. Examples of calibration curves have been given previously for the 2,4-dinitrophenylhydrazonesof these carbonyls and dicarbonyls (4,20,23,24). Alimitation of the carbonyl measurement method employed in this work is that P-hydroxycarbonyls and the corresponding dicarbonyls could not be resolved if formed as products in the same experiment. Thus, attempts to synthesize the DNPH derivative of hydroxyacetaldehyde yielded the DNPH derivative of glyoxal, presumably due to acid-catalyzed oxidation of the P-hydroxycarbonyl during the derivatization step (20). Peroxyacyl Nitrates. Peroxyacyl nitrates were measured by electron capture gas chromatography using SRI 8610 gas chromatographs equipped with Valco 140 BN detectors (26-29). The columns used were 70 x 0.3 cm Teflon-lined stainless steel columns packed with 10% Carbowax on Chromosorb P, which was acid-washed and
--
Environ. Sci. Technol., Vol. 27, No. 12, 1993
2470
~
Table I. Summary of Parameters for Carbonyl 2,4-DinitrophenylhydrazineDerivatives
carbonyl formaldehyde acetaldehyde propanal hvdroxv- acetaldehydeb glyoxal cyclohexanone methylglyoxal
carbonyl-DNPH response factor, retention peak height absorbtime, (mm, attenuation ance relative to setting 7) ratio, that of for 1pg/mL formaldehyde- 4301360 carbonyla nm DNPH" (1.00) 1.24 f 0.01 1.70 f 0.04 2.94 f 0.16* 2.90 f 0.12 3.17 f 0.06 4.37 f 0.25
0.15 0.21 0.21 2.08 2.30 0.28 2.1
8.45 f 2.7 56.0 2.7 37.8 f 2.7 10.0 f 1.0
*
Mean f 1SD from data for multiple injections of the carbonylDNPH standards. Oxidized to glyoxal-DNPH, see text.
DMCS-treated. The column and detector temperatures were 36 and 6OoC, respectively, and the carrier gas was ultrahigh-purity nitrogen. The column flow rate was 58 mL/min. Air from the Teflon chamber was continuously pumped through a short section of 6-mm-diameter Teflon tubing connected to a 6.7-mL stainless steel sampling loop housed in the GC oven and was injected every 30 min using a timer-activated 10-port sampling valve. To calibrate the EC-GC instrument, PAN and PPN were synthesized in the liquid phase as described before (27, 28) using commercially available anhydrides as starting materials. Parts per billion levels of PAN and PPN in the gas phase were obtained by dilution, with purified air, of the output of diffusion vials containing solutions of PAN or PPN in n-dodecane and maintained at 2OC (27,281.A silica gel trap was inserted upstream of the diffusion vial to minimize water condensation. Calibration involved colocated readings with the EC-GC instrument and with a calibrated chemiluminescent NO, analyzer,which employs a molybdenum surface converter to reduce oxides of nitrogen to NO and, therefore, responds quantitatively to peroxyacyl nitrates including PAN and PPN (27, 28). Results and Discussion Ozone-Unsaturated Alcohol Reaction. Cyclohexane as a Scavenger of OH. Cyclohexanone is, along with cyclohexanol, a major product of the OH-cyclohexane reaction (18, 19). Cyclohexanone was identified as a product in unsaturated alcohol-ozone-cyclohexane mixtures, thus indicating that OH was indeed formed as a product of the ozone-unsaturated alcohol reaction. The fraction of OH that is scavenged by its reaction with cyclohexane can be estimated from the relative concentrations of cyclohexane and of the unsaturated alcohol and from the OH-cyclohexane and OH-unsaturated alcohol reaction rate constants: -d [OHlldt = [OH] (k,[Cl + ku,[UAI) (la) where [Cl and [UAI are the initial cyclohexane and unsaturated alcohol concentrations, respectively, and k , and kUA are the corresponding organic hydroxyl radical reaction rate constants. The room temperature rate constant k , is 7.5 X 10-12 cm3 molecule-' s-1 (13). The rate constants kUA have not been measured but can be estimated from structure-reactivity relationships for structural homologues (30,311 to be approximately 30 x cm3 molecule-l s-l for the monosubstituted comEnviron. Scl. Technol., Vol. 27, No. 12. 1993
+ RkO + RCHO
---> OH
--a0
---> CHz = C(R)OOH
CH, = C(R)OOH ---> (RC(O)CH~OH)+ ---> RC(O)CH~OH ---> Hz + RCOCHO ---> R ~ + O
*
22.5 1.8 14.4 f 0.8 6.9 f 0.5
a
2480
R H C ~ O ~---> ) RCOOH
---> OH
+
CH,OH
RC(O)CH,
EH,OH +
0, ---> HO, + HCHO REO ---> ---> products including RC(O)C(O)R RC(0)kHz ---> ---> products including RC(0)CHO
Figure 1. Slmplified scheme for the reaction of ozone with the unsaturatedalcohols: allyl alcohol (R1 = CHpOH, R2 = H), 3-buten-1-01 (R1 = CHpOHCHp-,R2 = H), and cls-3-hexen-l-0l (R1 = CHpOHCHp-, R2 = CH3CHz-). Adapted from the ozone-alkene reaction scheme given In ref 20. The monosubstituted Criegee blradlcals RCHpCHOO Include R = CHzOH (3-buten-l-ol), R = CH3, or R =: CHpOH (cis-3hexen-1-01) and R = OH (allyl alcohol).
pounds allyl alcohol and 3-buten-1-01and 65 X 10-l2cm3 molecule-l s-1 for the disubstituted compound cis-3-hexen1-01. Thus, with initial unsaturated alcoholconcentrations of 1-2 ppm and initial cyclohexane concentrations of 200400 ppm, at least 98% of the OH formed was scavenged by reacting with cyclohexane. In the same way, the reaction of OH with products of the ozone-unsaturated alcohol reaction that are reactive toward OH, e.g., aldehydes, was negligible in the presence of excess cyclohexane. In turn, we estimate from the measured cyclohexanone concentration, from the OH-alcohol reaction rate constants given above, and from the ozone-alcohol reaction rate constants (32)that the small fraction of OH that did react with the unsaturated alcohols contributed only 2-5 % of the total alcohol reaction, i.e., 9598% of the unsaturated alcohol was removed by its reaction with ozone. Carbonyl Products and Reaction Mechanism. Carbonyl products identified and their concentrations are listed in Table I1 along with the corresponding average molar yields. Carbonyl products that could not be identified due to the lack of reference standards are also listed in Table I1 which includes, for each unknown carbonyl, the retention time relative to that of formaldehyde, the abundance relative to that of formaldehyde, and the 430/360 nm absorbance ratio. These parameters did not match those of 40 carbonyl-DNPH standards previously synthesized and characterized in our laboratory (23-25). The reaction of ozone with unsaturated alcohols is expected to involve steps identical to those of the reaction of ozone with other olefins. The major features of the ozone-olefin reaction in the gas phase have been established in a number of studies (refs 13and 33, and references cited therein). These features are summarized in Figure 1 and include electrophilic addition on the unsaturated carbon-carbon bond followed by unimolecular decomposition of the 1,2,3-trioxolane adduct into a carbonyl and an energy-rich Criegee biradical. Recent experimental product studies (18-20, 34-37) indicate that, under conditions relevant to the atmosphere, subsequent reactions of monosubstituted Criegee biradicals RlCHOO
Table 11. Unsaturated Alcohol-Ozone-Cyclohexane Experiments: Summary of Initial Conditions and Carbonyl Products cis-3-Hexan-1-01 experimental no. 2
1
carbonyl samtde no. 2 1
1
initial alcohol, ppm initial ozone, ppb initial cyclohexane, ppm carbonyls, ppb formaldehyde acetaldehyde propanal hydroxyacetaldehyde and/or glyoxal, as glyoxal methylglyoxal 2-butanone or n-butanal, as 2-butanone cyclohexanone
2
4.8 490 200 14 52 228 6.8 50 5 30
av carbonyl yield, % a
1.2 98 200
4.5 16 69 3.1 24 3 4.3
12
51 226 7.6 50 5 35
4.1 15 70 2.1 25 3 3.6
3.5 f 1.0 13.1 f 2.5 58.7 f 12.0 2.1 f 1.0
17.6 f 5.0 2.0 f 1.0 5.3 f 1.5
3-buten-1-01 experiment no. 2 carbonyl sample no. 3 1
1
2
1
initial alcohol, ppm initial ozone, ppb initial cyclohexane, ppm carbonyls, ppb formaldehyde acroleinb hydroxyacetaldehyde and/or glyoxal, as glyoxal cyclohexanone
1.7 170 200 49 4.7 9.6
1 1
34 3.1 5.7
23 4.2 3.1
+
109 6.1 14.1
+
Allyl Alcohol exueriment no. 2 carbonyl sample no. 2
+
3 I _
3
0
1.75 174 400
1.75 175 400
93 56 13 0.8
87 58 12 1.5
92 52
+
-
av carbonyl yield, % a
2
3.4 180 200
200
+
2.0 200
initial alcohol, ppm initial ozone, ppb initial cyclohexane, ppm carbonyls, ppb formaldehyde hydroxyacetaldehyded acetaldehyde acetone cyclohexanone
1
1.0 110
54 4.7 8.9
+
3
12
7.2
+
37.3 f 19.0 2.8 f 1.0 5.3 f 2.0
111
5.7 12.8
+
C
av carbonyl yield, % a
50 f 3 30 f 3 6.5 i 0.5 1.7 f 1.0 c
Unidentified Carbonyls unsaturated alcohol 3-buten-1-01 cis-3-hexen-1-01
retention timee
Tlf
peak heighte
4.55 f 0.04 6.12 f 0.07 0.85 0.01 4.28 f 0.05 8.36 0.08 7.2 f 0.1
6 (6) 6 (6) 2 (4) 4 (4) 3 (4) 2 (3)
0.07 f 0.06 0.07 f 0.02 0.17 f 0.02 0.11 f 0.05 0.06 f 0.01 0.06 f 0.01
* *
430/360 nm absorbance ratio 0.28 0.19 0
0.50
-
0.19 allyl alcohol a Mean f 1 SD, from the measured ozone reacted and assuming a 1:l reaction stoichiometry. Possibly from 1-hydroxypropanal HzO + acrolein, see text. Observed but not measured. Measured as glyoxal, see text; concentration reported as hydroxyacetaldehyde using the ratio of the response factors given in Table I. e Relative to that of formaldehyde. f Number of samples in which unidentified carbonyl was present; total number of samples in parentheses.
include four pathways: rearrangement to a carboxylicacid, decomposition to 0 + carbonyl, decomposition to OH + RCO and hydroxyperoxide formation by intramolecular H-atom abstraction. In turn, the hydroperoxide rearranges into an energy-rich hydroxycarbonyl, followed by the four pathways of collisional stabilization (yielding the hydroxycarbonyl), decomposition into a dicarbonyl + H2, unimolecular decomposition yielding RCO + CHzOH, and
decomposition into RCOCH2 + OH. Under the conditions of our study, i.e., in the absence of NO, the RCOCH2 and RCO radicals are expected to lead to products that include the corresponding dicarbonyls RCOCHO and RCOCOR, respectively (20). A comparison of expected and measured carbonyl products is given below for each unsaturated alcohol studied, with emphasis on carbonyl yields as a measure of Envlron. Scl. Technol.. Vol. 27, No. 12, 1993 2481
the relative importance of some of the pathways listed above and outlined in Figure 1.
most likely present as an impurity (or oxidation product thereof’). The reactions of interest are
3-Buten-1-01, Carbonyl products of the reaction of 3-buten-1-01with ozone were formaldehyde (yield = 0.37 f 0.19) and hydroxyacetaldehyde (yield = 0.12 f 0.05) and/ or glyoxal (yield = 0.05 f 0.02), along with small amounts of three unidentified carbonyls (17 % of formaldehyde on a peak height basis). The carbonyl l-hydroxypropanal could not be positively identified due to the lack of a reference standard. The reactions of interest are (see Figure 1)
CH,CH,CH=CHCH,CH,OH 0, CH,CH,CHO + CH,OHCH,CHOO + CH,OHCH,CHO + CH,CH,CHOO (10)
-
CH, = CHCH,CH,OH + 0, HCHO CH,OHCH,CHOO + H,COO + CH,OHCH,CHO (1)
+
followed by reactions of the hydroxyethyl-substituted Criegee biradical: CH,OHCH,CHOO
--
CH,OHCH,C(O)OH
(2)
OH + CH,OHCH,CO
(3)
0 + CH,OHCH,CHO
(4)
- -
followed by reactions of the two Criegee biradicals. The reactions of the hydroxyethyl-substituted biradical have been discussed above for 3-buten-1-01,see reactions 1-9. The ethyl-substituted biradical evolves as follows: CH,CH,CHOO
---
CH,OHCH=C(H)OOH
--*
(CH,OHCHOHC(H)O)’
-
hydroxycarbonyl
H,
+ CH,OHC(O)CHO
(7) OH + CH,OHCHCHO (8) HCO + CH,OHCHOH (9a) CH,OH
+ CHOHCHO
(9b) Two unimolecular decomposition pathways are possible, one leading to hydroxyacetaldehyde (reaction 9a) and the other to formaldehyde and glyoxal (reaction 9b). The carboxylic acid hydroxypropionic acid expected to form in reaction 2 was not measured. The 0-hydroxydicarbonyl products postulated to form in reactions 6 and 7 (as well as in reactions subsequent to reaction 9) were not observed due to the lack of reference standards. The yields of formaldehyde and of hydroxyacetaldehyde and/or glyoxal are not inconsistent with preferential formation of themore substituted Criegee biradical, CH20HCH2CHOO. cis-3-Hexen-1-01. Major carbonyl products of the ozone-cis-3-hexen- 1-01reaction included propanal (yield 0.59 f0.121, methylglyoxal(yield0.17 f0.051,acetaldehyde (yield 0.13 f 0.021, and glyoxal and/or hydroxyacetaldehyde (yield 0.02 f 0.01 as glyoxal). The carbonyl l-hydroxypropanal could not be positively identified. Also detected were small amounts of 2-butanone or n-butanal,
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Environ. Sol. Technol., Vol. 27. No. 12, 1993
(11)
+ CH,CH,CO
(12)
0 + CH,CH,CHO
(13)
CH,CH=C(H)OOH
(14)
OH
- -
-
-
CH,OHCHOHCHO (6)
CH,CH,C(O)OH
CH,CH=C(H)OOH (CH,CHOHCHO)’
-
CH,OHCH=C(H)OOH (5)
followed by the hydroperoxide products sequence of reactions:
-
+
CH,CHOHCHO (15) H,
+ CH,COCHO
(16) HCO + CH,CHOH (17) OH + CH,CHCHO
(18) The CH3CHOH radical formed in reaction 17 reacts with oxygen to form HO2 and acetaldehyde. The acetaldehyde yield indicates that unimolecular decomposition, reaction 17, may account for 13 f 2% of the overall reaction of the CH3CH2CHOO biradical. The CH3CHCHO radical formed in reaction 18leads to methylglyoxal and other products. The carboxylic acids hydroxypropionic acid and propionic acid expected to form in reactions 2 and 11, respectively, were not measured. More cyclohexanone (and therefore more OH) was formed from the more reactive (disubstituted) compound cis-3-hexen-1-01 than from the monosubstituted unsaturated alcohols,in qualitative agreement with recent considerations regarding OH yield vs olefin reactivity for simple alkenes (19). Allyl Alcohol. Carbonyl products of the reaction of allyl alcohol with ozone were formaldehyde (yield 0.50 f 0.03), hydroxyacetaldehyde (yield 0.30 f 0.03), and an unidentified monofunctional carbonyl formed in low yield (peak height = 6 f 1% of that of formaldehyde). Small amounts of acetaldehyde and acetone were also present, presumably as impurities (or oxidation products thereof‘). The relevant reactions are
-
CH,=CHCH,OH + 0, HCHO + CH,OHCHOO
+ H,COO +
CH,OHCHO (19) followed by reactions of the hydroxymethyl-substituted Criegee biradical: CH,OHCHOO
-- + - +
CH,OHCOOH 0 CH,OHCHO
(20) (21)
OH CH,OHCO (22) The carboxylic acid hydroxyacetic acid postulated to form in reaction 20 was not measured. Our carbonyl product data do not provide clues as to the possible formation of
RCH = CHCH~CH~OH + OH -->
Table 111. Sunlight Irradiation of NO-Unsaturated Alcohol Mixtures: Summary of Initial Conditions and Product Concentrations cis-3hexen-l-olo 1 2
3-buten-1-01 1 2 initial organic, ppm initial NO, ppm initial organic/NO ratio, PPm C/PPm NO-NO2 crossover time, min from to concentration, ppb. maximum concentrations, ppb ozone PAN PPN carbonyl samples start, min from to sampling duration, min carbonyl concentrations, ppb formaldehyde acetaldehyde propanal hydroxyacetaldehyde/ glyoxal, as glyoxal methylglyoxal unidentified carbonyls retention timeb peak heightb 0
2.0 0.57 14
2.0 0.24 33
0.22
135 200 29
1.0
BO2
55 110
65 214
RCH(OH)C(~)HCH~CH,OH --->
1.1
88 4.4
CH~OHCH~CHO +H O ~ Figure 3. Simplified scheme for the reaction of the hydroxyl radical with the unsaturated alcohols (RCH = CHCH2CH20H)3-buten-1-01 (R
+
= H), and cis-3-hexen-1-01 (R = CH3CH2-).R 0 2 NO RO O2reactions omitted for clarity, see text.
+
-
RON02 and
substantially faster than that of the less reactive monosubstituted compound 3-buten-1-01. OH-Unsaturated Alcohol Reaction Mechanism. Under the conditions of this study, the oxidation of unsaturated alcohols is initiated by their reaction with the hydroxyl radical. Reaction with ozone becomes important only after the NO-NOz crossover;reaction with atomic oxygen is of minor importance at the reactant concentrations employed;reaction with the nitrate radical, which photolyzes rapidly in sunlight, is also unimportant. By analogy with other alkenes (13),the OH-unsaturated alcohol reaction is expected to involve addition on the unsaturated carbon-carbon bond as is shown in Figure 3 (H-atom abstraction may also be possible as a minor pathway for unsaturated alcohols that, for example, contain a weak tertiary C-H bond). Following OH addition, the two P-hydroxyalkylradicals react with oxygen (R + 02 ROz) followed by reaction of the corresponding peroxy radicals with NO (RO2 NO RO + NOd and by unimolecular decomposition of the alkoxy radicals, both of which yield HOz and two carbonyls, one hydroxyalkylsubstituted and the other not. In the reaction scheme shown in Figure 3, we have omitted the ROz + NO RON02 reaction, which competes with alkoxy radical formation and yields two dihydroxynitrates, and the RO + 02 reaction, which competes with RO unimolecular decomposition and yields two dihydroxyketones. These c4 (from 3-buten-1-01) and c6 (from cis-3-hexen-1-01) products were not observed. The RO + 0 2 reaction, which is unimportant for other P-hydroxyalkoxy radicals (381, is probably also negligible for unsaturated alcohols. The ROz + NO RON02 reaction, again by analogy with literature data for simple hydrocarbons (39),is expected to increase in importance with substituent length and may therefore be negligible for the C4 compound 3-buten-1-01 but not for the c6 compound cis-3-hexen-1-01. cis-3-Hexen-l-ol-OHReaction. As is shown in Figure 3, the OH-initiated oxidation of cis-3-hexen-1-01leads to propanal and to l-hydroxypropanal:
-
.
-
A02
160 110
0
CH,OHCHOO
+ 02 ---> .+ 0 2 - 4
27
2oo
40
B
A O ~+ NO ---> R C H ( O H ) C ( ~ ) H C H ~ C H ~ O H
goo)
0
A
2.0 0.46 26
See ref 15. Relative to that of formaldehyde.
1 lo0i
RCH(OH)~HCH~CH~OH (A)
+ R ~ H C H ( O H ) C H ~ C H ~ O H(6)
+
-
-
-
-
CH,CH,CH=CHCH,CH,OH + OH -+ CH,CH,CHO + CH,OHCH,CHO (24) Propanal was indeed a major reaction product. Hydroxypropanal could not be positively identified. The peroxyacyl nitrate PPN was also a major reaction product Environ. Sci. Technol., Vol. 27, No. 12, 1993
2483
~~
Table IV. Estimates of Atmospheric Persistence for Unsaturated Alcohols cis-3allyl 3-buten1-01 hexen-1-01 alcohol reaction rate constants, cm3 molecule-' s-l ozone (32) OH, measured (13) OH, estimated0 half-life, days 08 = 100 ppb OH = 1.0 X lo6 molecule cm4 a
14.4 X 10-l8 4.9 X 2.6 X 10-l' 4.3 X 10-11 3.3 X 0.23 0.18
0.66 0.24
CH,COCHO
7.2 X
-
0.03 0.11
Usinn h e a r free-enerw relationshbs (31).
(40-65 ppb, i.e., 14-20% of the initial NO concentration). The presence of PPN was verified using the followingtests. Its retention time on two EC-GC instruments matched those of PPN synthesized in the liquid phase and those of PPN prepared in situ by sunlight irradiation of propanal-NO mixtures in pure air. The compound decomposed when passing the reaction mixture through a tube heated to 17OOC. The compound also decomposed upon addition of excess NO, and this at a rate that matched well that of pure PPN (40). PPN forms readily and in high yields from propanal in a sequence of reactions initiated by the reaction of propanal with OH. This reaction involves H-atom abstraction from the carbonyl carbon: CH,CH,CHO
CH,CH,C(O)OO
+ OH
-
CH,CH,CO
+ H,O
(25)
+ NO, e CH,CH,C(O)OONO,
(PPN) (27)
PPN was not observed to form until after the NO-NO2 crossover. In the presence of excess NO, P P N rapidly decomposes via the reverse reaction of equilibrium 27 followed by reaction of NO with the peroxypropionyl radical, leading to products including acetaldehyde (40): CH,CH,C(O)OO
- + + + + -
+ NO
CH,CH,C(O)O
CH,CH,C(O)O CH,CH,
CH,CH,O,
CO,
0,
NO
CH,CH,
CH,CH,O, CH,CH,O
+ NO,
(28) (29) (30) (31)
CH,CH,O 0, CH,CHO + HO, (32) In turn, acetaldehyde leads to peroxyacetyl nitrate by a sequence identical to that shown above for propanal (reactions 25-27). Indeed, acetaldehyde and PAN were identified as reaction products (see Table 1111,with PAN/ PPN concentration ratios of 0.34 f 0.1 and acetaldehyde/ propanal concentration ratios of 0.20 f 0.05. Formaldehyde was also identified and is a product of PAN thermal decomposition (401, acetaldehyde oxidation, and other reaction pathways. After the NO-NO, crossover, ozone accumulates in the system and competes with OH for removal of cis-3-hexen1-01. As discussed earlier, the reaction of ozone with cis3-hexen-1-01also yields propanal as a major product, see reaction 10. With NO, now present in the system, the propanal produced in the ozone-cis-3-hexen-1-01 reaction 2484
Envlron. Scl. Technol., Vol. 27, No. 12, 1993
-
+ OH H,O + CO + CH,CO CH,COCHO + hu HCO + CH3C0 CH,CO + 0, CH,CO(O,) CH,CO(O,) + NO, s CH,C(O)OONO, (PAN)
105 X
10-11
leads to PPN via reactions 25-27. Acetaldehyde and methylglyoxal, the other carbonyl products of the ozonecis-3-hexen-1-01reaction, both lead to PAN and acetaldehyde via reactions identical to reactions 25-27 and methylglyoxal by reaction with OH and by photolysis (13, 14): (33) (34) (35) (36)
3-Buten-l-ol-OH Reaction. The OH-initiated oxidation of 3-buten-1-01 leads to formaldehyde and to l-hydroxypropanal (see Figure 3): CH,=CHCH,CH,OH
+ OH
--*
HCHO
-+
+ CH,OHCH,CHO
(37)
Formaldehyde was identified as the major carbonyl product; hydroxypropanal could not be positively identified. Propanal and PPN, which do not form from 3-buten-1-01,were not detected. This indicated that cis3-hexen-1-01 or other olefins whose oxidation lead to propanal (e.g., l-butene) were not present as impurities in 3-buten-1-01. However, small amounts of PAN and of its precursors acetaldehyde and methylglyoxal were detected, presumably due to impurities in 3-buten-1-01. In a recent study of isoprene chemistry (4), we have discussed the possible formation of hydroxy-PAN [CHzOHC(O)OONOZ]from hydroxyacetaldehyde. Similarly here, hydroxy-PPN [CHzOHCH~C(O)OONO~I may be postulated to form from l-hydroxypropanal in the cis-3hexen-l-ol-NO and 3-buten-l-ol-NO systems. We did not observe hydroxy-PPN, which may not be stable, may decompose or may otherwise go undetected under the conditions we employed to measure PPN and PAN. Atmospheric Implications. The atmospheric persistence of unsaturated alcohols can be estimated from kinetic data. Major removal processes in the atmosphere include reactions with ozone and with the hydroxyl radical. Ozone-unsaturated alcohol reaction rate constants have been recently measured (32). Rate constants for the OHalcohol reaction have been reported (13,411 but only for saturated alcohols and for one unsaturated compound, allyl alcohol. Those for other unsaturated alcohols can be estimated from the measured ozone reaction rate constants and using linear free-energy relationships (31). These measured and estimated rate constants are listed in Table IV along with atmospheric half-lives calculated for typical atmospheric conditions, ozone = 100 ppb and OH = 1.0 X lo6 molecule cm-,. For the most reactive compound studied, cis-3-hexen-1-01,which is a major component of biogenic emissions (7-121, half-lives against removal by reaction with ozone or removal by reaction with OH are comparable and are only 1-3 h. Therefore, cis-3-hexen1-01 emitted by biogenic sources is rapidly oxidized to propanal, PPN, and other products. The rapid reaction of ozone with cis-3-hexen-1-01 may contribute to the formation of OH radicals at night. Our results indicate a biogenic contribution to propanal, which has been previously used as an indicator of anthropogenic pollution (42). In the same way, while PAN has been shown to form from biogenic hydrocarbons such as isoprene ( 4 ) and several terpenes (61,our results underline the possibility
of a biogenic source for PPN as well.
(15) Grosjean, D.; Williams, E. L., 11; Grosjean, E. Enuiron. Sci. Technol. 1993,27,979-981. Important atmospheric loss processes for PPN include (16) Taylor, 0. C. J. Air Pollut. Control Assoc. 1969, 19, 347351. its thermal decomposition (40) and, possibly, its reaction (17) Ridley, B. A.; et al. J. Geophys.Res. 1990,95,13949-13961. with OH. In the presence of oxides of nitrogen, the major (18) Atkinson, R.; Aschmann, S. M.; Arey, J., Shorees, B. J. reaction products of both loss processes are acetaldehyde Geophys. Res. 1992, 97, 6065-6073. and PAN, which are sources of free radicals, and therefore, (19) Atkinson, R.; Aschmann, S. M. Environ. Sci. Technol. 1993, contribute to ozone production downwind of areas where 27, 1357-1363. (20) Grosjean, D.; Grosjean, E.; Williams, E. L., 11.Atmospheric PPN is produced from the biogenic emissions of cis-3chemistry of olefins: a product study of the ozone-alkene hexen-1-01. In the less polluted troposphere, Le., at lower reaction with cyclohexane added to scavenge OH. Environ. NO, levels, the C2HsC03 (from PPN) and CH3C03 (from Sci. Technol., submitted for publication. PAN) radicals may combine with HO2 and RO2 radicals (21) Paulson, S. E.; Flagan, R. C.; Seinfeld, J. H. Int. J. Chem. Kinet. 1992,24, 103-125. (43) to form acetic acid and propionic acid. In future (22) McMurry, P. H.; Grosjean, D. Environ. Sci. Technol. 1985, experimental studies of the atmospheric chemistry of 19, 1176-1182. unsaturated alcohols, valuable information could be (23) Druzik, C. M.; Grosjean, D.; Van Neste, A.; Parmar, S. S. obtained by measuring the yields of the hydroxycarbonyl Int. J. Environ. Anal. Chem., 1990,38,495-512. products and by exploring the possible formation and (24) Grosjean, D. Environ. Sci. Technol. 1991, 25, 710-715. (25) Grosjean, D. Anal. Chem. 1983,55, 2436-2439. stability of the corresponding hydroxyalkyl-substituted (26) Williams, E. L., 11;Grosjean, D. Atmos. Enuiron. 1990,24A, peroxyacyl nitrates ( 4 ) . 2369-2377. (27) Williams,E. L., 11;Grosjean, D. Environ. Sci. Technol. 1991, 25, 653-659. Acknowledgments (28) Grosjean, D.; Williams, E. L., 11; Grosjean, E. Environ. Sci. Technol. 1993,27, 110-121. Mrs. Denise M. Velez prepared the draft and final (29) Grosjean, D.; Williams, E. L., 11; Grosjean, E. Environ. Sci. Technol. 1993,27, 326-331. versions of the manuscript. This work was supported by (30) Grosjean, D.; Seinfeld, J. H. Atmos. Environ. 1989,23,1733the Southern California Edison Co., Rosemead, CA, by 1747. the coordinating Research Council, Atlanta, GA, as part (31) Grosjean, D. Atmos. Environ. 1992, 26A, 1395-1405. of Project CRC-APRAC-AQ-1-2;and by internal R & D (32) Grosjean, D.; Grosjean, E.; Williams, E. L., 11.Int. J.Chem. funds, DGA, Inc., Ventura, CA. Kinet. 1993, 25, 783-794. (33) Atkinson, R.; Carter, W. P. L. Chem. Rev. 1984, 84, 437470. Literature Cited (34) Niki, H.; Maker, P. D.; Savage, C. M.; Breitenbach, L. P.; (1) Rasmussen, R. A. J. Air Pollut. Control Assoc. 1972, 22, Hurley, M. D. J. Phys. Chem. 1987,91,941-946. 537-543. (35) Martinez, R. I.; Herron, J. T. J. Phys. Chem. 1988,92,4644(2) Chameides, W. L.; Lindsay, R. W.; Richardson, J.; Kiang, 4648. C. S. Science 1988,241, 1473-1475. (36) Martinez, R. I.; Herron, J. T. J . Phys. Chem. 1987,91,946(3) Tuazon, E. C.; Atkinson, R. Int. J. Chem. Kinet. 1990,22, 953. 1221-1236. (37) Grosjean, D. Environ. Sci. Technol. 1990, 24, 1428-1432. (4) Grosjean, D., Williams, E. L. 11, Grosjean, E. Environ. Sci. (38) Carter, W. P. L.; Atkinson, R. J. Atmos. Chem. 1989, 8, Technol. 1993, 27,830-840. 165-173. (5) Hatakeyama, S.; Isumi, K.; Fukuymana, T.; Akimoto, H. J. (39) Atkinson, R.; Carter, W. P. L. J. Atmos. Chem. 1991, 13, Geophys. Res. 1989,94,13013-13024. 195-210. (6) Grosjean, D.; Williams, E. L. 11; Seinfeld, J. H. Environ. (40) Grosjean, D.; Williams, E. L., 11; Grosjean, E. Thermal Sci. Technol. 1992, 26, 1526-1532. decomposition of PAN, P P N and vinyl-PAN. J. Air Waste (7) Graedel, T. E. Chemical compounds in the atmosphere; Manage. Assoc., submitted for publication. Academic Press: New York, 1978. (41) Wallington, T. J.; Dagaut, P.; Liu, R.; Kurylo, M. J. Int. J. (8) Ohta, K. Geochem. J. 1984,18, 135-141. Chem. Kinet. 1988,20,541-547. (9) Isidorov,V. A.; Zenkevich, I. G.; Ioffe,B. V. Atmos. Environ. (42) Shepson, P. B.; Hastie, D. R.; Schiff, H. I.; Polizzi, M.; 1985, 19, 1-8. Bottenheim, J. W.; Anlauf, K.; Mackay, G. I.; Karecki, D. (10) Arey, J.;Winer, A. M.; Atkinson, R.; Aschmann, S. M.; Long, R. Atmos. Environ. 1991,25A, 2001-2005. W. D.; Morrison, C.L. Atmos. Enuiron. 1991, 25A, 1063(43) Madronich, S.; Chatfield, R. B.; Calvert, J. G.; Moorgat, G. 1075. K.; Veyret, B.; Lesclaux, R. Geophys. Res. Lett. 1990,17, (11) Winer,A.M.;Arey,J.;Atkinson,R.;Aschmann,S.M.;Long, 2361-2364. W. D.; Morrison, C.L.; Olszyk, D. M. Atmos. Environ. 1992, 26A, 2647-2659. Received for review February 16, 1993. Revised manuscript (12) Arey, J.; Corchnoy, S. B.; Atkinson, R. Atmos. Enuiron. received June 14, 1993. Accepted July 9, 1993.' 1991,25A, 1377-1381. Abstract published in Advance ACS Abstracts, September 15, (13) Atkinson, R. Atmos. Environ. 1990, 24A, 1-41. 1993. (14) Carter, W. P. L. Atmos. Environ. 1990,24A, 481-518.
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