distributions of c2–c6 hydrocarbons over the western north pacific and eastern indian ocean

Atmospheric Environment 34 (2000) 4373}4381

Distributions of C2}C

6hydrocarbons over the

western North Paci"c and eastern Indian Ocean

T. Saito!, Y. Yokouchi", K. Kawamura!,*

!Institute of Low Temperature Sciences, Hokkaido University, N19, W8, Kita-Ku, Sapporo 060-0819, Japan"National Institute for Environmental Studies, Tsukuba, Japan

Received 15 July 1998; received in revised form 7 December 1999; accepted 7 January 2000

Abstract

Atmospheric nonmethane hydrocarbons (NMHCs: C2}C

6) were measured over the western North Paci"c and eastern

Indian Ocean between 253N and 403S during oceanographic cruise from December 1996 to February 1997 usinga fused-silica-lined stainless-steel canister and GC technique. Averaged mixing ratios of individual NMHCs were0.61 ppbv (ethane), 0.42 ppbv (ethylene), 0.17 ppbv (acetylene), 0.24 ppbv (propane), 0.60 ppbv (propylene), 0.07 ppbv(i-butane), 0.13 ppbv (n-butane), 0.04 ppbv (i-pentane), 0.06 ppbv (n-pentane), and 0.06 ppbv (n-hexane). Although thereare few reported data available for comparison in these regions of marine boundary layer, mixing ratios of the NMHCsare within the range of previous results reported in the similar latitudes from the Atlantic and Paci"c Ocean. NMHCswith lifetimes more than a week (C

2}C

4alkanes and acetylene) showed a signi"cant latitudinal decrease from north to

south in the Northern Hemisphere, suggesting an important source strength in East Asian region. In contrast, NMHCswith lifetimes less than a week (alkenes and C

5}C

6alkanes) did not show any signi"cant latitudinal trends. Based on

a comparison with the results of the backward trajectories for 2 days, light alkenes were suggested to be derived fromocean surfaces. ( 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Nonmethane hydrocarbons; Marine atmosphere; Western North Paci"c; Eastern Indian Ocean; Long-range transport

1. Introduction

There has been a growing interest on nonmethanehydrocarbons (NMHCs) because they are important pre-cursors of tropospheric ozone and organic aerosols(Chameides et al., 1992; Kawamura et al., 1996). NMHCsare emitted to the atmosphere from a variety of anthro-pogenic and natural sources. In the last few decades,studies on NMHCs in the marine atmosphere and insurface sea water suggested that C

2}C

6NMHCs are in

part derived from oceanic sources (e.g., Swinnerton andLamontagne, 1974). Based on the published data of dis-solved C

2}C

4hydrocarbons in the surface ocean waters,

Plass-DuK lmer et al. (1995) reported that the emission

*Corresponding author.E-mail address: [email protected]

(K. Kawamura).

rates of C2}C

4hydrocarbons from the global ocean is

2.1]1012 g yr~1. They suggested that the oceanic sourceplays a minor role in the global budgets of NMHCs.Nevertheless, in the remote marine atmosphere the oceanis a major emission source of highly reactive alkenes suchas ethylene and propylene which have an impact on thelocal photochemistry (Donahue and Prinn, 1993).

Asian continent and Southeast Asian islands areimportant source regions of NMHCs as well asphotochemical pollutants such as O

3and NO

x(Akimoto

et al., 1994). These pollutants can be transported over thewestern North Paci"c and eastern Indian Ocean by long-range atmospheric transport. However, measurements ofNMHCs have rarely been carried out in the marineatmosphere over these oceans (Blake et al., 1997).

To better understand the distributions, atmospherictransport and photochemical transformation ofNMHCs, we collected 22 air samples using canisters overthe western North Paci"c and eastern Indian Ocean.

1352-2310/00/$ - see front matter ( 2000 Elsevier Science Ltd. All rights reserved.PII: S 1 3 5 2 - 2 3 1 0 ( 0 0 ) 0 0 2 4 9 - 1

Fig. 1. Cruise track of R/< Hakuho Maru and canister samplinglocation (triangles) in the western North Paci"c and easternIndian Ocean.

Here, we report distributions of C2}C

6hydrocarbons

and discuss their source regions and source strength.Based on NMHCs compositions, we further discuss thephotochemical and transport processes in the atmo-sphere from the marginal and remote ocean.

2. Experimental procedure

2.1. Air sampling

Fresh air samples were taken in two types of stainless-steel canisters with a metal bellows pump (pressurized toplus 0.3}plus 1 kgf cm~2) and a Te#on inlet line (1/4AOD,(1 m long) during a cruise of R/V Hakuho Maru on20 December 1996}February 1997 (see Fig. 1). Eighteenair samples of total 22 samples were taken in 6-l fused-silica lined stainless-steel canisters (SiliconCan, RestekCo., Ltd) and four samples (sample nos. 1}4, see Table 1)were taken in 3-l electrochemical bu$ng (ECB) stain-less-steel canisters (Ultra"nish Technology Co., Ltd). Airsampling was made on upper deck of the ship (ca. 14 mabove the sea surface) when winds were coming fromthe ship bow to avoid the contamination from shipengine exhaust. The canisters were carefully prepared inthe laboratory by lincing with the humidi"ed ultra puregrade nitrogen and evacuating at elevated temperature ofca. 1003C. These steps were repeated 3 times. Air sampleswere collected over the western North Paci"c and easternIndian Ocean between 253N; 1343E and 403S; 1093E. Allthe canister samples (total 22 samples) were shipped tothe laboratory for the analysis.

2.2. Chemical analysis

NMHCs were measured using a gas chromatography(Hewlett-Packard 5890 SERIES II) equipped with aAl

2O

3/KCl porous layer open tubular (PLOT) column

(50 m long]0.32 mm ID; Chrompack) and a #ame ioniz-ation detector. Aliquot (500 cm3) of the air sample wastaken from each canister using a metal bellows pump anda mass #ow controller. The sample was then passedthrough a 7 cm long glass tube "lled with a magnesiumperchlorate [Mg(ClO

4)2] to remove moisture.

NMHCs in the air were preconcentrated using a two-stage cryofocusing system (DKK GAS-30). In the "rststage, NMHCs were condensed in a 1/8A stainless-steeltube packed with a combination of Carboxen 1000 (car-bon molecular sieve, 60/80 mesh) and CarbopackB (graphitized carbon, 60/80 mesh) at !103C usinga liquid CO

2. Both ends of the stainless-steel tube were

plugged with a silanized glass wool. The adsorbedNMHCs were thermally desorbed at approximately2503C, and introduced to the GC column by #ushingwith helium as a carrier gas through the trap at a #owrate of 2.0 ml min~1. In the second stage, the transferred

NMHCs were cryofocused at the head of GC columncooled down to !1503C by #ushing a liquid nitrogen,and then the GC column head was rapidly heated to1503C, so that an early peak broadening in GCchromatogram was avoided. The GC oven temperaturewas programmed from 303C (for 4 min) to 2003C at 103Cmin~1, and then held at 2003C for 20 min.

Calibration for determining NMHC concentrationswas performed using a gravimetrically prepared standardmixture (Taiyo Toyo Sanso Co., Ltd.) in the same man-ner as an air sample except for sampling volume. Thestandard gas was diluted using a dilution system (DKKGAS-2BM) to several di!erent levels from 10 ppbv to0.001 ppbv. Excellent linearity was obtained in the rangeof 0.01}10 ppbv each for individual compounds in thestandard (r'0.999). The relative standard deviationfor "ve measurements of diluted standard at 0.01 ppbvwere 2.1% for ethane, 1.6% for ethylene, 9.4% for acety-lene, 2.7% for propane, 2.8% for propylene, 3.3% fori-butane, 1.4% for n-butane, 1.0% for i-pentane, 0.6% forn-pentane, and 1.2% for n-hexane. The detection limit atsignal-to-noise ratio of 3 was estimated from the repeatedintegration of the smallest chromatographic peaks; thedetection limit for a 500 ml sample was approximately

4374 T. Saito et al. / Atmospheric Environment 34 (2000) 4373}4381

Tab

le1

Con

centr

atio

nsof

mea

sure

dN

MH

Cs

(ppbv)

ove

rth

ew

este

rnP

aci"

can

dea

ster

nIn

dia

nO

cean

NM

HC

s

Dat

eN

o.

Lat

itude

Long

itude

Eth

ane

Pro

pan

ei-Buta

nen-

But

ane

i-Pen

tane

n-P

enta

ne

n-H

exan

eEth

ylen

ePro

pyl

ene

Ace

tyle

ne

21/1

2/96

1253N

1343

E1.

660.

740.

140.

280.

090.

110.

030.

930.

430.

5421

/12/

962

223N

1323

E0.

920.

580.

110.

200.

070.

090.

050.

270.

420.

1822

/12/

963

193N

1313

E1.

030.

640.

170.

240.

140.

200.

120.

341.

490.

172/

12/9

64

163N

1293

E0.

930.

420.

070.

140.

040.

070.

040.

401.

570.

1829

/12/

965

83S

1153

E0.

400.

180.

030.

110.

040.

090.

040.

821.

110.

1430

/12/

966

93S

1153

E0.

250.

230.

040.

130.

030.

070.

030.

811.

240.

1430

/12/

967

103S

1173

E0.

300.

180.

040.

100.

040.

080.

041.

541.

690.

172/

1/97

8173S

1143

E0.

220.

090.

040.

060.

020.

040.

030.

310.

360.

142/

1/97

9203S

1133

E0.

210.

070.

020.

030.

010.

02n.

d0.

250.

270.

153/

1/97

10263S

1123

E0.

240.

180.

020.

090.

010.

050.

010.

690.

730.

0913

/1/9

711

423S

1123

E0.

230.

160.

020.

090.

010.

060.

010.

471.

160.

0815

/1/9

712

403S

1093

E0.

420.

210.

180.

150.

070.

100.

050.

360.

780.

0718

/1/9

713

303S

1093

E0.

190.

080.

040.

050.

020.

020.

010.

170.

100.

0919

/1/9

714

293S

1093

E0.

230.

100.

050.

060.

040.

040.

030.

200.

150.

1121

/1/9

715

183S

1053

E0.

250.

130.

250.

500.

060.

060.

080.

310.

360.

1223

/1/9

716

93S

1023

E0.

170.

070.

050.

050.

020.

020.

010.

220.

190.

1026

/1/9

717

0933E

0.49

0.09

0.05

0.09

0.03

0.04

0.02

0.28

0.32

0.08

28/1

/97

1873

N893E

0.81

0.22

0.04

0.04

0.02

0.02

n.d

0.14

0.10

0.14

29/1

/97

1973

N893E

0.81

0.18

0.06

0.09

0.08

0.06

0.07

0.16

0.16

0.16

30/1

/97

20113N

923E

1.00

0.23

0.06

0.07

0.04

0.03

0.03

0.19

0.16

0.24

31/1

/97

2193

N943E

1.15

0.30

0.08

0.10

0.03

0.02

0.01

0.18

0.20

0.30

1/2/

9722

113N

923E

1.40

0.29

0.05

0.06

0.01

0.02

n.d

0.11

0.12

0.29

Ave

rage

0.61

0.24

0.07

0.12

0.04

0.06

0.03

0.42

0.60

0.17

S.D

.0.

450.

190.

060.

100.

030.

040.

030.

340.

030.

10

T. Saito et al. / Atmospheric Environment 34 (2000) 4373}4381 4375

5 pptv for ethane, ethylene, and acetylene; 3 pptv forpropane and propylene; 2 pptv for i-butane and n-bu-tane; and 1 pptv for the other heavier NMHCs. We donot report benzene data here, because of an appearanceof sporadic contamination probably derived from carbonadsorbents.

Reproducibility of the NMHC measurements in theanalytical procedures was tested from canister samplingto GC analysis. Two SilicoCans that were "lled with theair outside the Institute of Low Temperature ScienceBuilding were used for this experiment. Duplicate analy-sis of the samples showed that the standard deviationswere within 15% of the mean concentrations. To evaluatethe preservation of the NMHCs during a storage of canis-ter samples, another two SilicoCan samples were analyzedin 2 h after sampling and then in 1, 2, 3 and 4 months. Themeasured concentrations of NMHCs did not show anincreasing/decreasing trend with time. The standard de-viation for "ve measurements were within 15% of meanvalues. The storage tests for NMHCs were not concludedin ECB canister. However, Yokouchi et al. (1999) re-ported that storage stabilities for isoprene and DMS inECB canisters were better than those in SilicoCans.

Analyses of the canister samples collected during thecruise were completed within 4 months after the samplecollection.

3. Results and discussion

Ten NMHC species ranging from ethane to n-hexanewere detected in the marine atmosphere. Table 1 givestheir concentrations. Averaged concentrations of alkenes(ethylene and propylene) in our samples were a littlehigher than those from previous studies based on in situmeasurements (e.g., Donahue and Prinn, 1993). Singhet al. (1988) have shown that alkene concentrations slow-ly increased with the storage of canisters. Ramacher et al.(1997) suggested that propylene was formed on the canis-ter's inner surface. However, as discussed above, theconcentrations of alkenes did not increase during storageof the fused-silica-lined stainless-steel canisters over4 months. Atlas et al. (1993) reported that concentrationsof alkenes did not increase in the stainless-steel canistersprepared in NCAR laboratory at least for 2 months ofstorage of air samples. Thus, discrepancies in the samplestorage tests between the previous studies (Singh et al.,1988; Ramacher et al., 1997) and our study may be causedfrom the di!erence in the types of inner surface of canis-ters (electropolished or fused-silica coated) and/or thedi!erence of the preparation procedure of canisters.Many previous studies have used the electropolishedstainless-steel canisters but the use of `fused-silica linedastainless-steel canisters are only recent. We believe thatthe fused-silica-lined canisters do not have any signi"cantproblems during the storage of air samples for NMHC

measurements. The problems of the di!erence in thealkene concentrations between in situ measurements andthose from canister samples are still remained, as claimedby Donahue and Prinn (1993). However, such problemswould have little e!ect on our discussion based on therelative abundances of alkenes.

3.1. Latitudinal distribution of light alkenes

The measured mixing ratios of ethylene are plotted inFig. 2a as a function of latitude. Ethylene mixing ratioswere found to distribute at a similar concentration levelaround 0.3 ppbv in both Hemispheres, except for severalsamples collected at 253N, 8, 9, 10 and 263S (sample Nos.1, 5, 6, 7, and 10, respectively), which showed relativelyhigh mixing ratios of ethylene (0.8}1.6 ppbv). Becauselifetime of ethylene in the atmosphere is quite short(2 days at OH concentration of 7]105 molecules cm~3;Blake et al., 1996), it is unlikely that ethylene survivesduring long-range transport. We conducted 2 daysback-trajectory analysis at 500 m at height for all airsamples to discuss the in#uence of continental emissions.The back trajectory at 263S showed that the air mass hada contact with the coastal zone of the western Australia,suggesting a continental origin of ethylene. On the con-trary, back trajectory for the air sample collected at 253Nshowed no contact with any continents, suggesting thatethylene was derived from oceanic sources. Previousstudies showed that substantial amounts of ethylene andpropylene are emitted from the oceans (Bonsang et al.,1988; Plass et al., 1992; Plass-DuK lmer et al., 1993, 1995).Although back-trajectory analysis for 8, 9 and 103S wasnot available, the samples could be a!ected by continen-tal sources because they were collected near Indonesia(see Fig. 1).

Fig. 2b shows a latitudinal pro"le of propylene whosedistribution seems to be similar to that of ethylene. Againseveral higher concentrations of propylene suggest a con-tinental in#uence. This is consistent with the results ofback trajectories. Although propylene is approximately3 times more reactive than ethylene in the atmosphere(Atkinson, 1997), concentrations of propylene wereslightly higher than those of ethylene in the samples,suggesting an in#uence from a speci"c continental sourcesuch as industrial process emissions (Nelson et al., 1983).Similar results were shown in the sample observed nearHawaii islands during shipboard in situ measurements(Donahue and Prinn, 1993). On the other hand, continen-tal origin of two samples collected near 403S, which alsoshowed higher concentrations of propylene (and alsoethylene), can be ruled out, because the back trajectoriesshowed no contact with any continents. In fact,Yokouchi et al. (1999) suggested that the elevated iso-prene concentrations (ca. 0.2 ppbv) observed near 403Swas caused by the high biological productivity in australsummer in the Southern Ocean. Thus, these two alkene


Fig. 2. Latitudinal distributions of NMHCs (ppbv) over the western North Paci"c and eastern Indian Ocean.

measurements might re#ect the signi"cant oceanic emis-sions of alkenes to the atmosphere.

3.2. Latitudinal distributions of light alkanes (C2}C4)

The measured mixing ratios of ethane, propane,i-butane and n-butane are plotted in Fig. 2c}f as a func-

tion of latitude. In contrast to ethylene, mixing ratio ofethane clearly shows a latitudinal decrease from north tosouth, being consistent with the previously publishedresults in the Atlantic and Southern Paci"c Ocean (Singhand Salas, 1982; Rudolph and Johnen, 1990; Bonsangand Lambert, 1985). For ethane, there is strong inter-hemispheric gradient with an averaged north/south ratio


Fig. 3. Lantitudinal distributions of (a) ethane/propane, (b)ethane/i-butane, and (c) ethane/n-butane concentration ratiosfor the air samples collected from western North Paci"c andeastern Indian Ocean. The horizontal lines mean the averagedvalues calculated from the previous reported urban results (seeTable 2).

of 4.0. A drastic decrease from 1.66 to 0.30 ppbv wasfound between 253N and 103S; however, there was nosigni"cant latitudinal gradient between 10 and 423S. Thetrend in a latitudinal distribution for other light alkanes(propane, i-butane and n-butane) is somewhat similarto that for ethane, but an interhemispheric gradient ofpropane is more pronounced than that of ethane, (seeFig. 2c}f ).

Latitudinal distributions of ethane/propane, ethane/i-butane, and ethane/n-butane ratios are plotted in Fig.3a}c. The ethane/propane ratios show an increase from2 at around 253N to 5}6 at the equator. These ratios arewell above the urban value (ca. 1.4) as listed in Table 2.These features are also seen for the other light alkanes. Ingeneral, variation of mixing ratios for alkanes with shor-ter atmospheric lifetimes are greater than those of lon-ger-lived alkanes. Since propane and n-/i-butanes reactwith OH radical faster than ethane does (Atkinson, 1997),ethane/propane and ethane/n-/i-butane ratios should in-crease with increasing the transport time from the sourceregions, depending on OH radical mixing ratios. Fur-thermore, it is well known that these light alkanes aremainly emitted from various anthropogenic sources suchas natural gas and car exhausts in large cities of theNorthern Hemisphere (e.g., Rudolph, 1995). Thus, thelatitudinal structures for light alkane composition inthe North Paci"c marine troposphere might be caused bytransport from urban areas in Asian continent to thetropical region. If the alkane ratios could linearly in-crease with an increase in the distance from the majorsource regions, we would attribute the major sourceregion of the light alkanes to the urban or industrialareas at 25}303N (Fig. 3). This region in East Asia (e.g.south part of China) is characterized by rapidly growinganthropogenic emissions to the atmosphere (Akimotoet al., 1994).

For ethane/propane ratios, high values around 5}6were obtained at the north edge of the intertropicalconvergence zone (ITCZ). This is consistent to the pre-viously reported results (5}10) in the Atlantic Ocean(Rudolph and Johnen, 1990; Koppmann et al., 1992).However, the ethane/propane ratios (av. 2) obtained at8}423S are signi"cantly lower than the result (ca. 8)reported by Clarkson et al. (1997) at Baring Head (NewZealand) and Scott Base (Antarctica) for 1990}1996.Because the ratios generally depend on source type suchas fossil fuel emissions (ca. 1.5; Hough, 1991) and emis-sions from biomass burning (range: 1}5, av. 2; Rudolph etal., 1995), this di!erence may be caused by di!erentsources which have di!erent ethane/propane ratios. Thissuggests that our results are substantially in#uenced bycontinental alkane emissions. Alternatively, ocean maybe the source of the alkanes detected in our samples. Infact, the ratios of ethane/propane emitted from the oceanare 1.2 in the North Sea (Broadgate et al., 1997), 1.6 in theopen ocean (Plass-DuK lmer et al., 1995), and 3.7 in the

Atlantic (Plass-DuK lmer et al., 1993). These ratios areconsistent with the observed low ratios (av. 2) in thisstudy.

Transport of the NMHCs from their source regionto the remote marine atmosphere should be accom-panied with a decrease in their concentrations due to adispersion and photochemical destruction. As pointed by


Table 2Average mixing ratios (ppbv) of NMHCs at various urban sites

NMHCs

Ethane Propane i-butane n-butane i-pentane n-pentane n-hexane Ethylene Propylene Acetylene

Tulsa! 4.5 3.1 3.1 12.5 13.2 8.2 2.4 3.4 1.0 4.5Upland" 25.5 16.0 7.5 22.0 * 9.4 * 20.0 4.7 21.5Sydney# 7.5 5.9 4.7 7.4 9.0 5.0 2.1 * 7.4 10.1Houston$ 12.5 17.0 8.2 16.0 13.4 7.6 3.3 * 5.7 7.5Philadelphia$ 6.5 9.7 5.2 11.5 8.4 5.4 2.2 * 3.3 3.0Boston$ 4.0 3.0 3.0 7.2 7.0 3.2 1.5 * 1.3 4.5Milwaukee$ 4.5 3.3 1.7 7.0 4.6 2.4 1.1 * 1.0 2.5Baltimore$ 5.5 4.7 3.3 10.3 10.4 4.8 1.5 * 2.3 5.5Washington$ 6.0 3.7 3.0 9.3 10.8 4.6 1.2 * 2.7 7.0Newark$ 10.5 7.3 5.5 12.0 11.0 5.6 1.8 * 3.0 5.0Lancaster% 27.1 4.1 10.2 4.2 16.2 2.2 1.7 21.2 3.3 5.2Tokyo& 2.6 4.0 1.2 2.2 1.9 1.4 1.3 3.1 0.5 2.039 U.S. cities' 11.7 7.8 3.7 10.1 9.1 4.4 * 10.7 2.6 6.5Budapest) 10.7 4.4 2.9 4.7 9.1 5.2 5.0 29.5 3.3 *

Osaka* 4.8 4.7 2.9 6.1 3.5 2.0 1.0 9.6 0.7 4.8Yokohama+ 3.6 5.3 4.4 12.1 9.6 8.8 2.1 3.9 0.4 3.0Takasaki+ 1.8 2.4 1.3 2.5 1.6 1.0 0.8 1.7 0.1 3.4Karuizawa+ 1.8 2.7 1.5 2.6 2.3 1.4 1.0 2.0 0.1 4.4Sapporo, 3.2 6.0 1.9 3.3 0.9 0.5 0.3 4.2 1.7 2.0

!Arnts and Meeks (1981)."Singh et al. (1981), geometric mean.#Nelson et al. (1983), geometric mean.$Sexton and Westberg (1984), arithmetic mean.%Colbeck and Harrison (1985), arithmetic mean.&Uno et al. (1985), average.'Seinfeld (1989), median.)Haszpra et al. (1991), arithmetic mean.*Tanaka et al. (1995), average.+Satsumabayashi (1996), 29 July 1983.,This study, 1 April 1998, data were obtained at Oodori in Sapporo City.

Roberts et al. (1984), concentration ratios of two com-pounds derived from same source depend on a di!erencein their photochemical oxidation rates. Fig. 4 givesa log}log plot for n-butane/ethane ratios versus i-bu-tane/ethane ratios together with the data from the urbanarea (see Table 2). All the points plotted for the NorthernHemisphere show smaller values than those of urbansamples. The correlation coe$cient of the regression linedrawn for the points for the Northern Hemisphere is high(R"0.92). Further, the regression line pass througha group of the points for the urban measurements, sug-gesting that these light alkanes were transported frompolluted urban regions. On the other hand, the correla-tion coe$cient (0.65) of the regression line drawn for thepoints for the Southern Hemisphere lower than that forthe Northern Hemisphere. The samples taken in theSouthern Hemisphere might be in#uenced by varioussources which have di!erent alkane ratios from urban.

3.3. Distributions of other NMHCs

The distribution of acetylene showed some of the fea-tures which can be seen in the light alkane pro"les. Thehighest acetylene value (0.5 ppbv) was found at 253Nwhereas the minimum (0.07 ppbv) was at 403S.

In general, the mixing ratio of i-pentane is higher thanthat of n-pentane in the urban atmosphere (see Table 2).Both pentanes have similar lifetime against OH oxida-tion (Atkinson, 1997). Despite the similar atmosphericreactivity and the relative concentrations of i-/n-pentanein some source regions, the averaged mixing ratio ofn-pentane is slightly higher than that of i-pentane (seeTable 1). These alkanes did not show a signi"cant di!er-ence in the interhemispheric distribution. Further, theirlatitudinal structures are in some aspect similar to thoseof light alkenes such as ethylene. Broadgate et al. (1997)reported oceanic #ux of n-pentane to be higher than


Fig. 4. Logarithm plot of the i-butane/ethane versus n-bu-tane/ethane concentration ratios. The solid and open circlesindicate the data from the Northern Hemisphere and from theSouthern Hemisphere, respectively. The open triangles indicatethe plots of the previously published urban results (see Table 2).The solid line is a linear least-squares "t for the solid circles.

those of i-pentane. Thus, the presence of both iso andnormal pentanes in the marine atmosphere might beexplained by the local emissions from the ocean itself.

The mixing ratios of n-hexane varied around 0.03 ppbvwhich is comparable to the value reported in the equato-rial Paci"c by Greenberg and Zimmerman (1984).

4. Conclusions

Atmospheric concentrations of several NMHCs wereobtained in December 1996 to February 1997 over thewestern Paci"c and eastern Indian Ocean. Spatial distri-butions of light alkenes (i.e. ethylene and propylene)suggested that they are emitted from the ocean ratherthan continental sources. Backward trajectory analysissupported this interpretation.

In the Northern Hemisphere, the latitudinal distribu-tions of light alkanes (ethane, propane, i-/n-butane)showed a north-to-south decrease in their concentra-tions. The alkane concentration ratios suggested thatthese latitudinal structure is caused by their transportfrom East Asian source regions to ITCZ. On the otherhand, the concentration ratios of alkanes in the SouthernHemisphere were speci"c sources (e.g., ocean) which arecharacterized by lower alkane ratios. Alkane composi-tion in the Northern Hemisphere is suggested to be morea!ected by the anthropogenic emissions than in theSouthern Hemisphere.

Acknowledgements

We thank Hong-Jun Li of University of Tokyo,S. Narita of University of Keio and the crew of the

R/V Hakuho-Maru for the help in collecting air samples.We would also like to thank the Center of Earth Envi-ronment in the National Institute for EnvironmentalStudies for the courtesy of the computer facility for back-ward trajectory analysis.

References

Akimoto, H., Davis, D.D., Liu, S.C., PEM-West (A) ScienceTeam, 1994. Atmospheric chemistry of the east Asian North-west Paci"c region. In: Prinn R.G. (Ed.), Global Atmo-spheric}Biospheric Chemistry. Plenum Press, New York.

Arnts, R.R., Meeks, S.A., 1981. Biogenic hydrocarbon contribu-tion to the ambient air of selected area. Atmospheric Envi-ronment 15, 1643}1651.

Atkinson, R., 1997. Gas-phase tropospheric chemistry of volatileorganic compounds: 1. Alkanes and alkenes. Journal ofPhysical and Chemical Reference Data 26, 215}290.

Atlas, E., Pollock, W., Greenberg, J., Heidt, L., Thompson, A.M.,1993. Alkyl nitrate, nonmethane hydrocarbons, and halocar-bon gases over the equatorial Paci"c Ocean during Saga 3.Journal of Geophysical Research 98, 16933}16947.

Blake, D.R., Chen, T.-Y., Smith Jr., T.W., Wang, C.J.-L.,Wingenter, O.W., Blake, N.J., Rowland, F.S., 1996. Three-dimensional distribution of nonmethane hydrocarbons andhalocarbons over the northwestern Paci"c during the 1991Paci"c Exploratory Mission (PEM-West A). Journal of Geo-physical Research 101, 1763}1778.

Blake, N.J., Blake, D.R., Chen, T.-Y., Collins Jr., J.E., Sachse,G.W., Anderson, B.E., Rowland, F.S., 1997. Distributionand seasonality of selected hydrocarbons and halo-carbons over the western Paci"c basin during PEM-WestA PEM-West B. Journal of Geophysical Research 102,28315}28331.

Bonsang, B., Lambert, G., 1985. Nonmethane hydrocarbons inan oceanic atmosphere. Journal of Atmospheric Chemistry2, 257}271.

Bonsang, B., Kanakidou, M., Lambert, G., Monfray, P., 1988.The marine source of C

2}C

6aliphatic hydrocarbons. Jour-

nal of Atmospheric Chemistry 6, 3}20.Broadgate, W.J., Liss, P.S., Penkett, S.A., 1997. Seasonal

emissions of isoprene and other reactive hydrocarbon gasesfrom the ocean. Geophysical Research Letters 24,2675}2678.

Chameides, W.L., Fehsenfeld, F., Rodger, M.O., Cardelino, C.,Martinez, J., Parrish, D., Lonneman, W., Lawson, D.R.,Rasmussen, R.A., Zimmerman, P., Greenberg, J., Middleton,P., Wang, T., 1992. Ozone precursor relationship in theambient atmosphere. Journal of Geophysical Research 97,6037}6055.

Clarkson, T.S., Martin, R.J., Rudolph, J., 1997. Ethane andpropane in the southern marine troposphere. AtmosphericEnvironment 31, 3763}3771.

Colbeck, I., Harrison, R.M., 1985. The concentrations of speci"cC

2}C

6hydrocarbons in the air of NW England. Atmo-

spheric Environment 19, 1899}1904.Donahue, N.M., Prinn, R., 1993. In situ nonmethane hydrocar-

bon measurements on SAGA 3. Journal of GeophysicalResearch 98, 16915}16932.


Greenberg, J.P., Zimmerman, P.R., 1984. Nonmethane hydro-carbons in remote tropical continental, and marine atmo-sphere. Journal of Geophysical Research 89, 4767}4778.

Haszpra, L., SzilaH gyi, I., Demeter, A., TuraH nyi, T., BeH rces, T.,1991. Non-methane hydrocarbon and aldehyde measure-ments in Budapest, Hungary. Atmospheric Environment 25,2103}2110.

Hough, A., 1991. Development of a two demensional globaltropospheric model. Journal of Geophysical Research 96,7325}7362.

Kawamura, K., Kusakabe, H., Barrie, L.A., 1996. Source andreaction pathways of dicarboxylic acids, ketoacids and dicar-bonyls in arctic aerosols: one year of observations. Atmo-spheric Environment 30, 1709}1722.

Koppmann, R., Bauer, R., Johnen, F.J., Plass, C., Rudolph, J.,1992. The distribution of light nonmethane hydrocarbonsover the mid-Atlantic: results of the Polastern cruise ANTVII/1. Journal of Atmospheric Chemistry 15, 215}234.

Nelson, P.F., Quigley, S.M., Smith, M.Y., 1983. Source of atmo-spheric hydrocarbons in Sydney: a quantitative determina-tion using a source reconciliation technique. AtmosphericEnvironment 17, 439}449.

Plass, C., Koppmann, R., Rudolph, J., 1992. Light hydrocarbonsin the surface water of the mid-Atlantic. Journal of Atmo-spheric Chemistry 15, 235}251.

Plass-DuK lmer, C., Khedim, A., Koppmann, R., Johnen, F.J.,Rudolph, J., Kuosa, H., 1993. Hydrocarbon emissions fromthe Atlantic. Global Biogeochemical Cycles 7, 211}228.

Plass-DuK lmer, C., Koppmann, R., Ratte, M., Rudolph, J., 1995.Light nonmethane hydrocarbons in the seawater: an over-view. Global Biogeochemical Cycles 9, 79}100.

Ramacher, B., Rudolph, J., Koppmann, R., 1997. Hydrocarbonmeasurements in the spring Arctic troposphere during theARCTOC 95 campaign. Tellus 49, 466}485.

Roberts, J.M., Fehsenfeld, F.C., Liu, S.C., Bollinger, M.J., Hahn,C., Albritton, D.L., Siever, R.E., 1984. Measurements ofaromatic hydrocarbon ratios and NO

xconcentrations in the

rural troposphere: observations of air mass photochemicalaging and NO

xremoval. Atmospheric Environment 18,

2421}2432.

Rudolph, J., 1995. The tropospheric distribution and budget ofethane. Journal of Geophysical Research 100, 11369}11381.

Rudolph, J., Johnen, F.J., 1990. Measurements of light atmo-spheric hydrocarbons over the Atlantic in regions of lowbiological activity. Journal of Geophysical Research 95,20583}20591.

Satsumabayashi, H., 1996. Photochemical formation and sinkof organic compounds under long-range transport. Ph.D.Thesis, University of Kushu.

Seinfeld, J.H., 1989. Urban air pollution: state of the science.Science 243, 745}752.

Sexton, K., Westberg, H., 1984. Nonmethane hydrocarbon com-position of urban and rural atmosphere. Atmospheric Envi-ronment 18, 1125}1132.

Singh, H.B., Salas, L.J., 1982. Measurement of selected lighthydrocarbons over the Paci"c Ocean: Latitudinal and sea-sonal variations. Geophysical Research Letters 9, 842}845.

Singh, H.B., Martinez, J.R., Hendry, D.G., Ja!e, R.J., Johnson,W.B., 1981. Assessment of the oxidant-forming potential oflight saturated hydrocarbons in the atmosphere. Environ-mental Science and Technology 15, 113}119.

Singh, H.B., Viezee, W., Salas, L., 1988. Measurements of se-lected C

2}C

5hydrocarbons in the troposphere: latitudinal,

vertical, and temporal variations. Journal of GeophysicalResearch 93, 15861}15878.

Swinnerton, J.W., Lamontagne, R.A., 1974. The oceanic distri-bution of low-molecular-weight hydrocarbons. Environ-mental Science and Technology 8, 657}663.

Tanaka, M., Kamiura, T., Warashita, M., Maeda, Y., Uno, I.,Wakamatsu, S., 1995. Vertical distribution of ambient hydro-carbon and carbon monoxide concentrations measured aloftover Kansai area. Environmental Science 8, 387}396.

Uno, I., Wakamatsu, S., Wadden, R.A., Konno, S., Koshio, H.,1985. Envaluation of hydrocarbon reactivity in urban air.Atmospheric Environment 19, 1283}1293.

Yokouchi, Y., Li, H.-J., Machida, T., Aoki, S., Akimoto, H., 1999.Isoprene in the marine boundary layer (Southeast Asian Sea,eastern Indian Ocean, and Southern Ocean): comparisonwith dimethyl sul"de and bromoform. Journal of Geophysi-cal Research 104, 8067}8076.


distributions of c2–c6 hydrocarbons over the western north pacific and eastern indian ocean

Documents