O3 reaction: influence of particle acidity on aerosol yields and products

ARTICLE IN PRESS

Atmospheric Environment 38 (2004) 761–773

Aerosol-chamber study of the a-pinene/O3 reaction: influence of particle acidity on aerosol yields and products . Yoshiteru Iinuma, Olaf Boge, Thomas Gnauk, Hartmut Herrmann* Leibniz-Institut fur e.V. (IfT), Permoserstr. 15, Leipzig D-04318, Germany . Tropospharenforschung . Received 1 August 2003; received in revised form 30 September 2003; accepted 6 October 2003

Abstract a-Pinene ozonolysis was carried out in the presence of ammonium sulfate or sulfuric acid seed particles in a 9 m3 Teflon chamber at the mixing ratios of 100 ppbv for a-pinene and about 70 ppbv for ozone. The evolution of size distribution was measured by means of a differential mobility particle sizer (DMPS). The resulting secondary organic aerosol (SOA) was sampled by a denuder/quartz fiber filter combination for the determination of the total organic carbon concentration (TOC) in the particle phase, using a thermographic method and by a denuder/PTFE filter combination for the analysis of individual chemical species in the particle phase using capillary electrophoresiselectrospray ionization-mass spectrometry (CE-ESI-MS). cis-Pinic acid (m=z 185) and another species tentatively identified at m=z 171 and 199 were the major particle phase species for both seed particles although the product yields were different, indicating the influence of seed particle acidity. A thermographic method for the determination of TOC showed an increase of particle phase organics by 40% for the experiments with higher acidity. CE-ESI-MS analysis showed a large increase in the concentration of compounds with Mw > 300 from the experiments with sulfuric acid seed particles. These results suggest that the seed particle acidity enhances the yield of SOA and plays an important role in the formation of larger molecules in the particle phase. Our results from direct particle phase chemical analysis suggest for the first time that condensation of smaller organics takes place by polymerization or aldol condensation following the formation of aldehydes, such as pinonaldehyde from the terpene ozonolysis. r 2003 Elsevier Ltd. All rights reserved. Keywords: a-Pinene ozonolysis; SOA; Acidic seed particles; Chamber experiment; CE-MS

1. Introduction Biogenic organic compounds are emitted to a substantial amount to the atmosphere mainly from the terrestrial vegetation. The total global biogenic organic emissions are estimated to range from 491 to 1150 Tg year 1, exceeding the estimated anthropogenic emissions by as much as an order of magnitude (Muller, . *Corresponding author. Tel.: +49-341-235-2446; fax: +49341-235-2325. E-mail address: [email protected] (H. Herrmann).

1992; Guenther et al., 1995). Together with methane and isoprene, the terpenes are the organic compounds with the highest global emission. Monoterpenes rapidly undergo oxidation initiated by ozone or OH and NO3 radicals to form multifunctional oxidation products (Arey et al., 1990; Aschmann et al., . 1998; Berndt and Boge, 1997; Calogirou et al., 1999; Hakola et al., 1994; Hallquist et al., 1999; Nozie" re et al., 1999; Winterhalter et al., 2000). The products of these reactions are likely to be of low volatility and hence might lead to particle formation. Went (1960) first postulated that terpenes are responsible for the blue

1352-2310/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2003.10.015

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

762

transformations of gaseous or semi-volatile organic compounds in atmospheric particles or at their surface. For instance, the acid-catalyzed reactions of carbonyl compounds can contribute to SOA formation via hydration, polymerization or aldol condensation (R1–R3). A similar effect of aerosol acidity on SOA yields in different reaction systems (mostly aldehydes) was shown very recently (Jang and Kamens, 2001; Jang et al., 2002, 2003a, b; Czoschke et al., 2003).

haze above forests, due to oxidative particle formation. In laboratory and smog chamber studies, it has been shown that terpene oxidation processes can in fact lead to aerosol formation (Griffin et al., 1999; Hoffmann et al., 1997; Kamens et al., 1999; Koch et al., 2000). Only a few studies have been performed to determine the composition of the secondary organic aerosol (SOA) and the yields of particulate and gaseous products (Hatakeyama et al., 1989; Hoffmann et al., 1998; Jang and Kamens, 1999; Yu et al., 1999a; Glasius et al., 1999, R

R

H+ O

+

H R

R O

H

R'' O

R'

H

OH

R

R

H

C

OH

OH

R H

C

+

H

R

+

(R1)

OH

R'

R'

n

OH

H2O

O

C O n-1

OH

R'

O

H+ +

+ H

(R2) OH

R'''

2000; Larsen et al., 2001; Jaoui and Kamens, 2001, 2003a, b; Jaoui et al., 2003). SOA formation from the oxidation of biogenic compounds (mostly terpenes) contributes a considerable amount to the total atmospheric aerosol burden, estimated by different researchers ranging from 13 to 24 Tg year 1 (Griffin et al., 1999) or even from 30 to 270 Tg year 1 (Andreae and Crutzen, 1997). Very recently photo-oxidation products of monoterpenes, such as pinonaldehyde, pinonic acid, nor-pinonic acid, pinic acid etc., were detected in the gas and particulate phase in a forest atmosphere (Kavouras et al., 1998, 1999; Yu et al., 1999b; Pio et al., 2001; Kavouras and Stephanou, 2002). The contribution of secondary organic carbon (SOC) to the measured organic aerosol concentration remains a controversial issue. The SOC content in the tropospheric particles is highly variable and its composition and formation mechanisms are not well understood (Pandis et al., 1992; Turpin et al., 2000). Because of the big influence of particulate organic compounds on thermodynamic, microphysical and chemical properties (e.g. Turpin et al., 2000), a quantitative description of the impact of organic compounds to aerosol formation is needed. The SOA yields of secondary organic products have been normally explained by condensation or partitioning theory (Pankow, 1994; Odum et al., 1996; Hoffmann et al., 1997; Kamens et al., 1999; Kamens and Jaoui, 2001). However, there is also the possibility of further

H2O

(R3)

R'''

R

The purpose of the present study is to determine the influence of seed particle acidity on the particle phase yield following the gas-phase ozonolysis of a-pinene. The possible change in the distribution of semi-volatile products and the possible appearance of products unknown until now in acidic aerosols are also studied.

2. Experimental 2.1. Description and instrumentation of the reaction chamber The experiments were carried out in an aerosol chamber made of Teflon FEP film type 500A (Du Pont) by Vector GmbH Bremen (Germany). The chamber has a volume of 9 m3 and a surface/volume ratio of 3 m 1. A tent-shaped chamber is held with an aluminum frame. The FEP covered plywood platform (80 cm above ground) has a hatch to enter the chamber. In the center of the hatch, a hole covered by a Teflon shield is installed for in- and outlets. The chamber was filled with particle-free air with a flux of up to 20 m3 h 1. The hatch was opened with a small slit to let escape the air stream during flushing. The chamber was equipped with a humidifier, an ozone and a particle generator. The humidifier consists of a battery of 12 horizontal assembled glass tubes filled by half with Milli-Q grade water (Millipore, Bedford, USA). Relative humidities (RHs) above 50% can be

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

obtained even with a flow rate of 19 m3h 1. An injection port allowed to add gaseous compounds or particles to the air stream and to carry them along into the chamber. Ozone was produced by an UV lamp in an oxygen stream of 2 l min 1. Polydisperse aerosols were generated by atomizing aqueous solutions of either (NH4)2SO4 or H2SO4. Aliquots of an a-pinene/He mixture were added by means of a mass flow controller from a storage bulb. The chamber was equipped with a fan to ensure sufficient mixing of reactants during introduction into the chamber. Probes for temperature and RH were introduced by special inlets. Outlets are connected with a condensation particle counter (CPC), a continuous monitoring ozone analyzer (Monitor Labs ML 9812) and a particle sampling filter device with a fixed integrated annular denuder to avoid gaseous contamination of the deposited particles during sampling. The denuder is the same dimension as described by Wyers et al. (1993). The inside wall of the denuder is coated with Apiezon L (Fluka, Germany). The size distributions of particles in the reaction chamber as a function of time were measured by a differential mobility particle sizer (DMPS) and an ultrafine differential mobility particle sizer (UDMPS). The DMPS consists of a differential mobility analyzer (DMA) with and a TSI 3010 CPC and the UDMPS consists of a long DMA with a TSI 3025A ultra-fine condensation particle counter (UCPC). Both DMPS and UDMPS are connected to the same sampling inlet through a bipolar charger. The DMPS was operated with 0.5 l min 1 sample flow and 5 l min 1 sheath flow. The UDMPS was operated with 2 l min 1 sample flow and 20 l min 1 sheath flow. The scanned size range of UDMPS and DMPS are 3–22.09 and 22.09–900 nm, respectively. At the beginning of each scan, 22.09 nm was measured by both the UDMPS and the DMPS to check the performance. Raw data were smoothed and inverted for corrections. A whole scan of size distribution from 3 to 900 nm takes 14 min. 2.2. Experimental run Before starting a run, the chamber was flushed overnight with purified air. Subsequently, the humidifier was connected to the air stream. At RHs >45%, ozone was introduced until a mixing ratio of about 65–75 ppb was obtained in the chamber. The particle generator was activated next to introduce seed particles until a number concentration reached approximately 25,000– 30,000 cm 3. The chamber was closed after the introduction of particles for the experiment. a-Pinene was introduced within 1 min after the closing of the hatch by an air volume of about 300 l to obtain a concentration of about 100 ppbv, 4 min later the fan was stopped and the reaction was run for 150 min. At the end of the reaction time, filter samples were taken on 47 mm PTFE or

763

quartz filters by an air stream of 30 l min 1 (optimal efficiency for the integrated denuder) up to 2 m3. The air stream passed through the filter was returned to the chamber to avoid large volume losses. This was carried out for the all filter samplings to minimize the sample to sample bias, as this might change the partitioning of products between the gas and the particle phase and possibly underestimation of particle phase products. At the end of sampling, the chamber was flushed again with particle-free clean air until the next experiment. The obtained quartz filter samples were analyzed for organic carbon (OC) and the PTFE filter samples for single organic compounds. Blank filter samples were produced by the abovedescribed procedure without the addition of a-pinene to the chamber. 2.3. Sample collection and analysis 2.3.1. Organic carbon Particle samples from quartz filters were analyzed for their carbon content using a gas evolution method (VDI 2465 Part 2, 1999). Assuming that the particulate carbon found under these experimental conditions can be only OC, no separation procedure between OC and EC (elemental carbon) was needed in the present experiments. Samples were burned for 8 min at 650 C under oxygen atmosphere using a carbon analyzer C-mat 5500 . (Strohlein GmbH, Germany). The produced CO2 was quantified by an NDIR detector calibrated with an external potassium hydrogen phthalate standard. In repeated measurements of ambient high-volume quartz filter sample aliquots, the coefficient of variation of the method with the C-mat 5500 analyzer was found to be 4.5%. 2.3.2. Organic compounds The samples were collected on a PTFE filter (47 mm diameter, 3 mm pore size). The filters were wetted by 0.2 ml of methanol and 1.0 ml of Milli-Q water was added to extract the samples. The resulting solution was ultrasonicated 10 min for CE-MS analysis. The samples were frozen after the extraction and they were thawed shortly prior to the analysis. CE separations were carried out on an Agilent 3DCE instrument (Agilent, Germany) coupled to an Esquire 3000 plus ion trap mass spectrometer (Bruker Daltonics, Germany) equipped with an electrospray ionization source (Agilent, Germany). A fused silica capillary with an internal diameter of 50 mm, an outer diameter 360 mm and a total length of 55 cm was used for the CE separation. The separation voltage was set at 30 kV and capillary temperature was kept at 25 C. Sample injection was carried out by hydrodynamic injection (50 mbar for 10 s). The sheath liquid (water/isopropanol 1:1, volume) was delivered to electrospray ionization source by a micro-syringe pump

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

764

ammonium sulfate seed aerosol and (ii) sulfuric acid seed aerosol. The pure sulfuric acid seed particle is chosen to demonstrate the importance of heterogeneous reactions to the aerosol yield even it is too acidic compared to typical ambient particles. Table 1 shows the initial mixing ratios of ozone as well as the experimental conditions for the two sets of experiments. Parameters influencing the SOA formation process, such as RH, temperature, ozone mixing ratio, a-pinene concentration or seed aerosol particle number concentration were held nearly constant in all experimental runs. Table 1 summarizes experimental conditions and aerosol yield (DTOC). The obtained average SOA masses and their standard deviations (95% confidence interval) were 52.478.5 and 72.3714.2 mg m 3 for ammonium sulfate seed aerosol and sulfuric acid seed aerosol, respectively. Sulfuric acid particles yield almost 40% more OC compared with ammonium sulfate seed particles. It should be noted that the wall effects are not taken into account into the aerosol yields for both systems and this might lead to the underestimation of the aerosol yields, especially for the sulfuric acid seed particle experiments as demonstrated by Czoschke et al. (2003).

(Cole-Parmer, USA) at 3 ml/min. The capillary voltage of the MS was 4.5 kV and electrospray current was kept under 300 nA. The electrospray was operated at the negative mode to detect deprotonated compounds (Mw 1). Mass ranges scanned were from m=z 50–500 for the detection and quantification and estimation of smaller molecules (Mw o300) and m=z 300–1500 for the detection of macromolecules. MSn experiments were carried out for the possible structural elucidation of detected compounds. A buffer system containing 20 mm ammonium acetate/10% methanol at pH 9.1 (adjusted by NH4OH) was used. All substances used except norpinonic acid were the highest purity available commercially and were bought from Sigma-Aldrich (Munich, Germany). cis-Norpinonic acid was synthesized by oxidative cleavage of verbenone in two-phase procedure as described by Cella (1983). Stock solutions of cis-pinic acid, cis-pinonic acid, trans-norpinic acid and cis-norpinonic acid were prepared by dissolving appropriate amount in Milli-Q water. Although a transstructure is not formed from the a-pinene ozonolysis the trans-norpinic acid was included in the standard solution for the comparison as cis-norpinic acid was not available from a manufacturer and cannot be synthesized easily. The standard solutions (1, 5, 10, 20 and 40 mm) were prepared by diluting an appropriate volume of stock solution with Milli-Q water (Millipore, Bedford, USA). The buffer, stock and standard solutions were stored in the refrigerator until they were required. Calibration was carried out by injecting the known amount of standard solution. Linear calibration curves with R2 above 0.999 were found for all standard compounds.

3.2. Chemical analysis The products formed in the a-pinene/ozone/ammonium sulfate seed particle system and the a-pinene/ ozone/sulfuric acid seed particle system as well as the filter samples with only ammonium sulfate seed particles and sulfuric acid seed particles were analyzed as blanks and no contamination was found from the seed particles and filters. It has been reported that some products from a-pinene ozonolysis form acetate adducts in an HPLCESI-MS study (Glasius et al., 1999). This was not observed with the CE-ESI-MS configuration and all m=z reported here are not adducts. Since the separation of CE relies on the ionic mobility, compounds that are not readily ionized in the water such as pinonaldehyde are

3. Results and discussion 3.1. OC measurements Two sets of experiments were carried out. a-Pinene ozonolysis was performed in the presence of (i)

Table 1 Initial conditions and TOC yields found in particles from the ozonolysis of a-pinene with H2SO4 and (NH4)2SO4 seed particles Date

Particle

Ozone0 (ppb)

RH (%)

T ( C)

DTOC (aerosol yield) (mg/m3)

05/11/2002 25/11/2002 26/11/2002 29/11/2002 28/11/2002 10/01/2003 14/01/2003 16/01/2003 20/01/2003

H2SO4 H2SO4 H2SO4 H2SO4 H2SO4 (NH4)2SO4 (NH4)2SO4 (NH4)2SO4 (NH4)2SO4

75 68 72 62 71 63 61 67 70

45 41 43 42 43 50 52 49 48

17.6 22.9 20.7 18.7 19.2 17.8 17.7 18.7 20.2

54.9 83.3 66.6 84.5 PTFE-Filter 62.2 47.1 47.8 PTFE-Filter

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

not separated and detected at the electroosmotic flow (EOF); hence, they were not quantified in this study. Fig. 1A and B show typical base peak mass electropherograms of products formed with the ammoIntens . x106

187_ 3 171_ 1

0.8

Cis-pinic acid (185_3)

199_2+231_3 199_1

0.6

171_2 0.4 157

0.2

183_3

(A) 0.0 x106 0.8

185_2 Cis-pinic acid (185_3)

171_1 185_1+201_3 199_2

0.6

199_1

0.4

171_2

157

0.2 183_3

(B)

185_2

0.0 0

1

2

3

4

5

6

7

Time [min]

Fig. 1. Base peak electropherograms for the experiments with (A) ammonium sulfate seed particles and (B) sulfuric acid seed particles. Peaks are labeled with m=z peak no.

765

nium sulfate seed particles and sulfuric acid seed particles, respectively. Both electropherograms show very similar patters except the difference in intensities of detected m=z: Figs. 2 and 3 summarize the estimated particle phase concentrations (mg m 3) of the detected m=z for the a-pinene/ozone/ammonium sulfate seed particle and the a-pinene/ozone/sulfuric acid seed particle system, respectively. cis-Pinic acid (m=z 185), cis-pinonic acid (m=z 183) and cis-norpinonic acid (m=z 169) were positively identified and quantified by comparing to the authentic standards. Since the standards of other a-pinene oxidation products are not readily available or cannot be synthesized, the concentrations of other detected compounds are estimated using calibration curves obtained from the standard compounds. The lowest concentration stands for a calibration curve with the least sensitive slope, the highest concentration stands for the most sensitive and the average concentration stands for the average of all four calibration curves. A bar chart in the left represents the particle phase concentrations of resolved and unresolved OCs in the total organic carbon (TOC). The right tables summarize the estimated concentration ranges of each detected compound. The

80

70

60

50 Unresolved

-3

Conc. (µgm )

ESI ( -)

Conc . lowest a ( µgm-3 )

Conc . ave b. ( µgm-3 )

Conc. highest c ( µgm-3 )

Pinic acid* (186_3)

185

12.20

12.20

12.20

172_1

171

1.86

3.84

6.55

200_1

199

1.64

3.42

5.85

232_3

231

0.57

1.28

2.25

158

157

0.49

1.09

1.90

200_2

199

0.46

1.04

1.83

184_3

183

0.33

0.77

1.37

216_1

215

0.31

0.76

1.36

188_3

187

0.29

0.71

1.26

216_2

215

0.24

0.62

1.12

232_2

231

0.22

0.59

1.07

188_4

187

0.14

0.41

0.75

216_4

215

0.12

0.38

0.72

Norpinonic acid* (170)

169

0.35

0.35

0.35

202_5

201

0.10

0.33

0.63

202_3

201

0.05

0.23

0.45

188_2

187

0.05

0.21

0.43

186_2

185

0.05

0.21

0.42

172_2

171

0.05

0.20

0.41

202_1

201

0.03

0.19

0.39

216_3

215

0.01

0.16

0.35

Pinonic acid* (184_1)

183

0.12

0.12

0.12

232_4

231

<0.01

0.10

0.25

184_2

183

<0.01

0.09

0.22

202_2

201

<0.01

0.08

0.21

198

197

<0.01

0.06

0.17

Compound (M w_Peak No.)

40

30

20 Resolved 10

0 With Ammonium Sulfate Seed

Rest

<0.1

<0.2

0.95

Total

19.80

29.64

43.57

Fig. 2. Quantified and estimated particle phase concentration of detected compounds for the experiment with ammonium sulfate seed particles. ( Quantified with an authentic standard; tentatively identified compounds are estimated from (a) the lowest response calibration curve, (b) the average of all calibration curves and (c) the highest response calibration curve obtained from the standard compounds.)

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

766 110

100 Compound (Mw_PeakNo.)

ESI ( -)

Conc. Lowest a (µgm -3)

Conc. Ave b . (µgm -3)

Pinic acid* (186_3)

185

13.07

13.07

13.07

172_1

171

2.98

6.10

10.37

200 _1

199

1.61

3.36

5.75

200 _2

199

0.53

1.20

2.10

184_3

183

0.43

0.98

1.72

188_4

187

0.37

0.87

1.53

202_3

201

0.31

0.75

1.35

186_1

185

0.22

0.56

1.02

90

80

Conc. ( µgm-3 )

70

60

Unresolved

50

40

30

20 Resolved 10

0 With Sulfuric Acid Seed

Conc. Highest c (µgm-3 )

158

157

0.20

0.50

0.91

216_2

215

0.18

0.50

0.92

188_3

187

0.18

0.48

0.87

252

251

0.09

0.34

0.66

202_5

201

0.08

0.28

0.54

232_3

231

0.06

0.28

0.55

186_2

185

0.07

0.27

0.51

216_1

215

0.05

0.24

0.48

Norpinonic acid* (170)

169

0.22

0.22

0.22

172_2

171

0.05

0.21

0.41

198

197

0.02

0.17

0.35

258

257

<0.01

0.15

0.35

232_2

231

<0.01

0.14

0.31

216_4

215

<0.01

0.13

0.30

216_3

215

<0.01

0.12

0.27

184_2

183

<0.01

0.10

0.2 3

202_1

201

<0.01

0.09

0.23

Pinonic acid* (184_1)

183

<0.01

0.02

Area less than 0.5%

<0.1

<0.35

1.35

Total

20.90

31.48

46.40

0.02

Fig. 3. Quantified and estimated particle phase concentration of detected compounds for the experiment with sulfuric acid seed particles. ( Quantified with an authentic standard; tentatively identified compounds are estimated from (a) the lowest response calibration curve, (b) the average of all calibration curves and (c) the highest response calibration curve obtained from the standard compounds.)

compounds without authentic standards are expressed as molecular weight followed by a migration order of that particular molecular mass in the electropherogram. The three most abundant compounds found from both seed particle systems are the same, i.e. cis-pinic acid (m=z 185), 172 1 (m=z 171) and 200 1 (m=z 199). cis-Pinic acid has been observed before by a number of researchers from a-pinene ozonolysis (Hoffmann et al., 1998; Christoffersen et al., 1998; Glasius et al., 1999; Jang and Kamens, 1999; Yu et al., 1999a, b; Koch et al., 2000). The migration time of 172 1 (m=z 171) suggests a hydroxy-monocarboxylic acid (e.g. pinolic acid, C9H16O3), which cannot be explained by the reaction mechanisms at this moment. The possibility of a dicarboxylic acid with a molecular weight of 172 (cisnorpinic acid) cannot be excluded as the MS2 of m=z 171 1 produced only the [M–CO2] fragment. The migration time of both 200 1 and 200 2 (m=z 199) suggests a C10 hydroxy-monocarboxylic acid (C10H16O4). A strong fragment of [M–H2O] from both m=z 199 also supports a possible hydroxy-monocarboxylic acid. Certain mass to charge ratios are only seen either with the ammonium sulfate seed particles or sulfuric acid seed particles. For example, the concentra-

tions of m=z 215, 231 and pinonic acid are much higher with the ammonium sulfate seed particles, whereas m=z 157, 171 1 and 185 1 are much higher with sulfuric acid seed particles. It is evident that the properties of the seed particle played an important role in the yield of produced compounds. However, at this stage, it is not clear which exact mechanisms of interaction between the seed particles and produced compounds made the difference in the yield. Table 1 summarizes the MS2 experiments of detected m=z for both experiments with ammonium sulfate and sulfuric acid seed particles with MS2 precursors and resulting fragmentations. Most of compounds show the loss of H2O( 18), CO2( 44) or H2O+CO2( 62). It is interesting to note that there are three different types of fragmentation patterns with MS2: (a) the strong or medium loss of CO2( 44) with weak or no loss of H2O( 18) and H2O+CO2( 62); (b) the strong loss of H2O( 18) with various loss of other masses and (c) a group which does not belong to (a) and (b). This fragmentation information together with the precursor’s mass to charge ratio suggests type (a) is a mono or dicarboxylic acids and type (b) is a hydroxy carboxylic acid.

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

767

Intens. x107 0.8 0.6

EOF

0.4 0.2

a1 a2

(A)

0.0 x107 0.8

EOF

0.6

b2

0.4

b1

0.2 0.0

(B) 0

1

2

3

4 Time [min]

5

6

7

Fig. 4. Extracted ion electropherograms for the experiments with (A) ammonium sulfate seed particles and (B) sulfuric acid seed particles (m=z 300–1500).

Intens. 4 x10

a1

2.7-3.0min

1.5

1.0 583 627 0.5 335 401

495 737

799 885

1010

1115

1232

1410

0.0 400

600

800

1000

1200

1400

m/z

Fig. 5. Background subtracted mass spectrum of peak a1 in Fig. 4A.

The same samples were further analyzed with MS parameters optimized for m=z 300–1500. Fig. 4A and B show the extracted ion electropherograms (m=z 300– 1500) of a-pinene ozonolysis with ammonium sulfate seed particles and sulfuric acid seed particles, respectively. Two broad peaks are found between 2.7 and 3.2 min in both the Fig. 4A and B. A significant difference in intensity was observed between the peak a1 to b1 and a2 to b2 with higher intensities for the experiment with sulfuric acid from both peaks. Figs. 5–8 show the background subtracted average mass spectra of peak a1, a2, b1 and b2 in Fig. 4, respectively. The averaged mass spectra show that the peak a1 (Fig. 5) and b1 (Fig. 7) consist of compounds with mainly m=z 300–1200 with the maximum intensity

around m=z 550, possibly a result of polymerization or aldol condensation under the acidic conditions. It is interesting to note that the experiment with ammonium sulfate also showed small peaks in this mass range although the intensities are much lower than the experiment with sulfuric acid (Fig. 4), and it showed different m=z from the sulfuric acid experiment (Figs. 5 and 7). The obtained mass spectrum of the peak b1 from the experiment with sulfuric acid is similar to that of fluvic acid identified by ESI-MS (Pfeifer et al., 2001). MSn experiments were carried out to obtain further clues on the structures of macro-molecules detected from the experiments with sulfuric acid. However, no meaningful MSn spectra were obtained and hence these data are not shown.

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

768 Intens.

a2

x105

3.0-3.2min

0.8

0.6

0.4

0.2

0.0

522

983 1032

617

400

600

800

m/z

1000

1200

1400

Fig. 6. Background subtracted mass spectrum of peak a2 in Fig. 4A.

Intens . x10 4

b1

2.7-3.0min

1273

1413

1.5 553 525 569

1.0

599 371

0.5

799 733 920 1117

0.0 400

600

800

1000

1200

1400

m/z

Fig. 7. Background subtracted mass spectrum of peak b1 in Fig. 4B.

Intens. x10 5 0.8

b2

3.0-3.2min

369

0.6

0.4

0.2 465

581

739

845

1031

0.0 400

600

800

1000

1200

1400

m/z

Fig. 8. Background subtracted mass spectrum of peak b2 in Fig. 4B.

The peaks a2 and b2 show the compounds with smaller m=z ranging from m=z 300–700 with an intensive peak at m=z 369, followed by m=z 353 for the peak b2

but not a2. Further MSn experiments were carried out in order to obtain qualitative information on functional groups of the m=z 369. Fig. 9 shows the example of MS2

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773 Intens . x10 4

769

-MS2 (369)

185.0

2.5 2.0

167.1

1.5 169.1 1.0 351.1

141.2 123.1

0.5

199.0

0.0 50

100

150

200

250

300 m/z

350

400

450

Fig. 9. MS2 mass spectrum of m=z 369. Table 2 Summary of MSn for compounds detected in the particle phase from ozonolysis of a-pinene with (NH4)2SO4 and H2SO4 seed particles Name

MS2 precur.

MS3 precur.

369

351 141 167 169 185 351

353 123 167 169 185 335

Pinonic acid

Pinic acid

157 171 171 183 183 185 185 185 187 187 187 187 197 199 199 201 215 215 231 251

Frag. ( 18)

1 2 1 3 1 2 3 1 2 3 4 1 1 2 3 1 2 3

167 333 335

Frag. ( 44)

165

w w w

Frag. 5

123

s

141 307

s w

Frag. 6

185

s

123

s

185

w

123

m

167

Frag. 7

Frag. 8

169

m

167

s

141

w

169

w

167

s

123

w

m

155

m

169

m

143

m

s s m m

157 145

s s

s

w

m

167 169 169 169 169

m s w s s

181 181 183

s s s

213

Frag. ( 62)

w

123 167

Frag. ( 60)

w

113 127 127 139 139

s s w m m

141 141 143

s s w

153 155 155 157

187 207

127 127 127 127

s s m m

s m m m

s w

125

m

125 125

s s

141 145 145 145

137 137

m m

157 157

m m

153

s

199 199 167

m m s

s: strong fragment, m: medium fragment, w: weak fragment. MS2 precursors are labeled with m/z peak no. in the electropherogram.

and Table 2 summarizes the fragmentation patterns of MS2 and MS3 for m=z 369 and 353 among other detected compounds. The fragmentation patterns show

strong fragments at m=z 167 and 185 followed by a weaker fragment of m=z 169 for m=z 369, and a strong fragment of m=z 167 followed by weaker fragments of

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

770

m=z 185 and 169 for m=z 353. MS2 and MS3 results suggest that both compounds consist of the same structural groups. Reactions (R4)–(R6) show the possible formation pathways of m=z 353 and 369 using hydration (R1) and polymerization (R2) from pinonaldehyde and hydroxyl pinonaldehyde. A possible hydration and polymerization of pinonaldehyde under acidic condition is also suggested by Czoschke et al. (2003). Although the MSn experiments give a good insight of function group present in the target compounds, it is difficult to determine the exact structure of target compounds only from the fragmentation pattern. However, the absence of these m=z with the ammonium sulfate seed particles, fast migration time of the compounds and no co-eluting compounds at this migration time suggest that the sulfuric acid seed particle catalyzed the formation of compounds with molecular weight over 300.

Time zero is the initial size distribution of seed particles. For both experiments, the overall shape of the size distribution was still unchanged at the second scan (13 min after a-pinene injection) although the mean geometric particle diameter (Dpg ) were shifted slightly to larger diameters (43.8–52.5 nm with ammonium sulfate seed and 73.7–84.5 nm with sulfuric acid seed). The size distributions from both experiments changed significantly by 30 min after the a-pinene injection due to the growth by a condensation process. The Dpg increased from 43.8 (0 min) to 105.2 nm (27 min) with an ammonium sulfate seed particle and 73.7 nm (0 min) to 104.8 nm (27 min) with the sulfuric acid seed particle. As the mode diameter of the ammonium sulfate seed particle was smaller than that of the sulfuric acid seed particle, the particles grew much faster. The size distribution continued to evolve after 30 min although the change was not as significant as the initial 30 min. O

O +

+

H

H2O

OH

(R4)

O

OH

Pinonaldehyde C10H16O2 Mw: 168.1

C10H18O3 Mw: 186.1 O

O

O

O

H+ +

(R5)

OH

OH

O

O

OH

C10H18O3 Mw: 186.1

OH

C20H34O5 Mw: 354.2

C10H16O2 Mw: 168.1 OH

O

O HO

O

H+ +

O

e.g.

e.g.

OH

C10H18O3 Mw: 186.1

(R6)

OH

OH O

OH Pinonaldehyde C10H16O3 Mw: 184.1

3.3. Size distributions The change of the size distributions from secondary aerosol formation as a function of time was monitored with a DMPS system. Fig. 10A and B show the example of change in the particle number distribution (dN/dlogD) for the ammonium sulfate seed experiment and sulfuric acid seed experiment, respectively.

O OH

C20H34O6 Mw: 370.2

No significant change in terms of the shape of the size distributions was observed after 1 h although the Dpg kept shifting to larger diameters. Although the evolution of size distributions is similar for both seed particle experiments, bulk phase reactions contributed significantly to the final aerosol yield of sulfuric acid experiments as higher DTOC was achieved with lesser mode diameter increase. The final Dpg for the ammonium sulfate seed system (168.6 nm) was slightly larger

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773 50000

100000 00:00 00:13 00:27 01:06 01:59

60000

00:00 00:13 00:27 01:06 01:59

40000 dN/dlogDp (cm-3)

80000 dN/dlogDp (cm-3)

771

40000

30000

20000

10000

20000

0 10

(A)

100 Dp (nm)

10

1000

(B)

100 Dp (nm)

1000

Fig. 10. The evolution of size distributions for the experiments with (A) ammonium sulfate seed particles and (B) sulfuric acid seed particles. The legends show the elapsed time from the a-pinene injection.

than that of the sulfuric acid seed system (156.2 nm). It is interesting to note that a small second mode started to evolve after 30 min for the experiments with ammonium sulfate seed particles (DpgB80 nm), but not for the experiments with sulfuric acid particles. The nature of this mode is unclear and further study is needed in order to characterize this mode.

Acknowledgements We would like to thank H. Puxbaum, Vienna for helpful discussions. This work was supported by the BMBF within the atmospheric research program AFO 2000 under FKZ 07ATF25, BEWA.

References 4. Summary and conclusion In this study, the comparison of the SOA yield and the particle phase composition from a-pinene ozonolysis in the presence of ammonium sulfate seed particle and sulfuric acid seed particles were carried out by means of a thermographic method and CE-EIS-MS. Compared to the experiments with ammonium sulfate particles, almost 40% increase in measured OC concentration was observed from the experiments with sulfuric acid particles. Yields for the identified products in the particle phase have been determined or estimated by CE-ESI-MS. cis-Pinic acid was the major ozonolysis product from both ammonium sulfate and sulfuric acid particles. A number of compounds with Mw > 300 have been detected from the experiments with sulfuric acid seed particles. A subsequent MSn study along with an increase in SOA yield observed by a thermographic method suggests sulfuric acid catalyzed the formation of larger molecules in the particle phase. This result suggests that particle acidity of atmospheric aerosols plays an important part in the heterogeneous reaction of SOA and may explain an unresolved fraction of organic aerosols in the atmosphere. Although mass spectrometry provides useful information for the product study, a new analytical approach is desirable in order to elucidate the structure or the process leading to the formation of these compounds.

Andreae, M.O., Crutzen, P.J., 1997. Atmospheric aerosols: biogeochemical sources and role in atmospheric chemistry. Science 276, 1052–1058. Arey, J., Atkinson, R., Aschmann, S.M., 1990. Product study of the gas-phase reactions of monoterpenes with the OH radical in the presence of NOx. Journal of Geophysical Research 95, 18539–18546. Aschmann, S.M., Reissell, A., Atkinson, R., Arey, J., 1998. Products of the gas phase reactions of OH radical with a- and b-pinene in the presence of NO. Journal of Geophysical Research 103, 25553–25561. . Berndt, T., Boge, O., 1997. Products and mechanism of the gasphase reaction of NO3 radicals with a-pinene. Journal of Chemical Society, Faraday Transaction 93, 3021–3027. Calogirou, A., Larsen, B.R., Kotzias, D., 1999. Gas-phase terpene oxidation products: a review. Atmospheric Environment 33, 1423–1439. Cella, J.A., 1983. A convenient procedure for preparative scale oxidation of enones. Synthetic Communications 13, 93–98. Christoffersen, T.S., Hjorth, J., Horie, O., Jensen, N.R., Kotzias, D., Molander, L.L., Neeb, P., Ruppert, L., Winterhalter, R., Virkkula, A., Wirtz, K., Larsen, B.R., 1998. Cis-pinic acid, a possible precursor for organic aerosol formation from ozonolysis of alpha-pinene. Atmospheric Environment 32, 1657–1661. Czoschke, N.M., Jang, M., Kamens, R.M., 2003. Effect of acidic seed on biogenic secondary organic aerosol growth. Atmospheric Environment 37, 4287–4299. Glasius, M., Duane, M., Larsen, B.R., 1999. Determination of polar terpene oxidation products in aerosols by liquid

ARTICLE IN PRESS 772

Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773

chromatography-ion trap mass spectrometry. Journal of Chromatography A 833, 121–135. Glasius, M., Lahaniati, M., Calogirou, A., Di Bella, D., Jensen, N.R., Hjorth, J., Kotzias, D., Larsen, B.R., 2000. Carboxylic acids in secondary aerosols from oxidation of cyclic monoterpenes by ozone. Environmental Science and Technology 34, 1001–1010. Griffin, R.J., Cocker, D.R., Seinfeld, J.H., Dabdub, D., 1999. Estimate of global atmospheric organic aerosol from oxidation of biogenic hydrocarbons. Geophysical Research Letters 26, 2721–2724. Guenther, A., Hewitt, C.N., Erickson, D., Fall, R., Geron, C., Graedel, T., Harley, P., Klinger, L., Lerdau, M., McKay, W.A., Pierce, T., Scholes, B., Steinbrecher, R., Tallamraju, R., Taylor, J., Zimmerman, P., 1995. A global model of natural volatile organic compound emissions. Journal of Geophysical Research 100, 8873–8892. Hakola, H., Arey, J., Aschmann, S.M., Atkinson, R., 1994. Product formation from the gas-phase reactions of OH radicals and O3 with a series of monoterpenes. Journal of Atmospheric Chemistry 18, 75–102. Hallquist, M., W.angberg, I., Ljungstr.om, E., Barnes, I., Becker, K.H., 1999. Aerosol and product yields from NO3 radicalinitiated oxidation of selected monoterpenes. Environmental Science and Technology 33, 553–559. Hatakeyama, S., Izumi, K., Fukuyama, T., Akimoto, H., 1989. Reactions of ozone with a-pinene and b-pinene in air: yields of gaseous and particulate products. Journal of Geophysical Research 94, 13013–13024. Hoffmann, T., Odum, J.R., Bowman, F., Collins, D., Klockow, D., Flagan, R.C., Seinfeld, J.H., 1997. Formation of organic aerosols from the oxidation of biogenic hydrocarbons. Journal of Atmospheric Chemistry 26, 189–222. Hoffmann, T., Bandur, R., Marggraf, U., Linscheid, M., 1998. Molecular composition of organic aerosol formed in the alpha-pinene/O3 reaction: implications for new particle formation processes. Journal of Geophysical Research 103, 25569–25578. Jang, M., Kamens, R.M., 1999. Newly characterized products and composition of secondary aerosols from the reaction of a-pinene with ozone. Atmospheric Environment 33, 459–474. Jang, M., Kamens, R.M., 2001. Atmospheric secondary organic aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol. Environmental Science and Technology 35, 4758–4766. Jang, M., Czosche, N.M., Lee, S., Kamens, R.M., 2002. Heterogeneous atmospheric aerosol production by acid catalyzed particle-phase reactions. Science 298, 814–817. Jang, M., Lee, S., Kamens, R.M., 2003a. Organic aerosol growth by acid-catalyzed heterogeneous reactions of octanal in a flow reactor. Atmospheric Environment 37, 2125–2138. Jang, M., Carroll, B., Chandramouli, B., Kamens, R.M., 2003b. Particle growth by acid-catalyzed heterogeneous reactions of organic carbonyl on preexisting aerosols. Environmental Science and Technology 37, 3828–3837. Jaoui, M., Kamens, R.M., 2001. Mass balance of gaseous and particulate products analysis from a-pinene/NOx/air in the presence of natural sunlight. Journal of Geophysical Research 106, 12541–12558.

Jaoui, M., Kamens, R.M., 2003a. Mass balance of gaseous and particulate products from b-pinene/O3/air in the absence of light and b-pinene/NOx/air in the presence of natural sunlight. Journal of Atmospheric Chemistry 43, 101–141. Jaoui, M., Kamens, R.M., 2003b. Gaseous and particulate oxidation products analysis of a mixture of a-pinene+ b-pinene/O3/air in the absence of light and a-pinene+ b-pinene/NOx/air in the presence of natural sunlight. Journal of Atmospheric Chemistry 44, 259–297. Jaoui, M., Leungsakul, S., Kamens, R.M., 2003. Gaseous and particle products distribution from the reaction of b-caryophyllene with ozone. Journal of Atmospheric Chemistry 45, 261–287. Kamens, R.M., Jaoui, M., 2001. Modeling aerosol formation from a-pinene+NOx in the presence of natural sunlight using gas-phase kinetics and gas-particle partitioning theory. Environmental Science and Technology 35, 1394–1405. Kamens, R.M., Jang, M., Chien, C.J., Leach, K., 1999. Aerosol formation from the reaction of a-pinene and ozone using a gas-phase kinetics-aerosol partitioning model. Environmental Science and Technology 33, 1430–1438. Kavouras, I.G., Stephanou, E.G., 2002. Direct evidence of atmospheric secondary organic aerosol formation in forest atmosphere through heteromolecular nucleation. Environmental Science and Technology 36, 5083–5091. Kavouras, I.G., Mihalopoulos, N., Stephanou, E.G., 1998. Formation of atmospheric particles from organic acids produced by forests. Nature 395, 683–686. Kavouras, I.G., Mihalopoulos, N., Stephanou, E.G., 1999. Formation and gas/particle partitioning of monoterpenes photo-oxidation products over forests. Geophysical Research Letters 26, 55–58. Koch, S., Winterhalter, R., Uherek, E., Kolloff, A., Neeb, P., Moortgat, G.K., 2000. Formation of new particles in the gas-phase ozonolysis of monoterpenes. Atmospheric Environment 34, 4031–4042. Larsen, B.R., Di Bella, D., Glasius, M., Winterhalter, R., Jensen, N.R., Hjorth, J., 2001. Gas-phase of oxidation of monoterpenes: gaseous and particulate products. Journal of Atmospheric Chemistry 38, 231–276. Muller, . J.F., 1992. Geographical distribution and seasonal variation of surface emissions and deposition velocities of atmospheric trace gases. Journal of Geophysical Research 97, 3787–3804. Nozi"ere, B., Barnes, I., Becker, K.H., 1999. Product study and mechanisms of the reactions of a-pinene and pinonaldehyde with OH radicals. Journal of Geophysical Research 104, 23645–23656. Odum, J.R., Hoffmann, T., Bowman, F., Collins, D., Flagan, R.C., Seinfeld, J.H., 1996. Gas/particle partitioning and secondary organic aerosol formation. Environmental Science and Technology 30, 2580–2585. Pandis, S.N., Harley, R.A., Cass, G.R., Seinfeld, J.H., 1992. Secondary organic aerosol formation and transport. Atmospheric Environment 26A, 2269–2282. Pankow, J.F., 1994. An absorption model of the gas/aerosol partitioning involved in the formation of secondary organic aerosol. Atmospheric Environment 28, 189–193. Pfeifer, T., Klaus, U., Hoffmann, R., Spiteller, M., 2001. Characterisation of humic substances using atmospheric

ARTICLE IN PRESS Y. Iinuma et al. / Atmospheric Environment 38 (2004) 761–773 pressure chemical ionisation and electrospray ionisation mass spectrometry combined with size exclusion chromatography. Journal of Chromatography A 926, 151–159. Pio, C., Alves, C., Duarte, A., 2001. Organic components of aerosols in a forested area of central Greece. Atmospheric Environment 35, 389–401. Turpin, B.J., Saxena, P., Andrews, E., 2000. Measuring and simulating particulate organics in the atmosphere: problems and prospects. Atmospheric Environment 34, 2983–3013. VDI 2465 Part 2, 1999. Measurement of soot (ambient air) thermographic determination of elemental carbon after thermal desorption of organic carbon. VDI/DIN-Handbuch . Reinhaltung der Luft 4, VDI-Publisher Dusseldorf. Went, F.W., 1960. Blue hazes in the atmosphere. Nature 187, 641–643.

773

Winterhalter, R., Neeb, P., Grossmann, D., Kolloff, A., Horie, O., Moortgat, G., 2000. Products and mechanism of the gas phase reaction of ozone with b-pinene. Journal of Atmospheric Chemistry 35, 165–197. Wyers, G.P., Otjes, R.P., Slanina, J., 1993. A continuous-flow denuder for the measurement of ambient concentrations and surface-exchange fluxes of ammonia. Atmospheric Environment 27A, 2085–2090. Yu, J., Cocker III, D.R., Griffin, R.J., Flagan, R.C., Seinfeld, J.H., 1999a. Gas-phase ozone oxidation of monoterpenes: gaseous and particulate products. Journal of Atmospheric Chemistry 34, 207–258. Yu, J., Griffin, R.J., Cocker, D.R., Flagan, R.C., Seinfeld, J.H., Blanchard, P., 1999b. Observation of gaseous and particulate products of monoterpene oxidation in forest atmospheres. Geophysical Research Letters 26, 1145–1148.