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Atmospheric Environment 41 (2007) 3360–3372

www.elsevier.com/locate/atmosenv

The use of CFC-12, CFC-11 and CH3CCl3 to trace terrestrialairborne pollutant transport by land–sea breezes

Bing-Sun Leea,�, Chung-Biau Chioub

aDepartment of Biotechnology, ChungChou Institute of Technology, Yuanlin, Changhua, Taiwan 510, ROCbDepartment of Automatic and Control Engineering, ChungChou Institute of Technology, Yuanlin, Changhua, Taiwan 510, ROC

Received 6 August 2006; received in revised form 2 December 2006; accepted 8 December 2006

Abstract

Time-series observations of the atmospheric concentrations of the halocarbons, trichlorofluorocarbon (CFC-11),

dichlorofluorocarbon (CFC-12), 1,2-trichlorofluoroethane (CFC-113), methyl chloroform (CH3CCl3) and carbon

tetrachloride (CCl4) were conducted at a site in Lukang, in Central Taiwan between April and August 2004. Fluctuations

in atmospheric concentrations of CFC-11, CFC-12 and CH3CCl3 were generally driven by diurnal land–sea breeze and

anthropogenic activity in this area. Elevated levels of CFC-11, CFC-12, and CH3CCl3 frequently occurred when the air

was stagnant and the prevailing seaward land breeze was dominant. Atmospheric concentrations of CFC-113 and CCl4were much less variable relative to CFC-11, CFC-12 and CH3CCl3 during the same period, indicating that emissions of

these two species from anthropogenic activities were small. The time-series distributions of atmospheric levels of CFC-12,

CFC-11, CH3CCl3 and CO were characterized as a diurnal cycle with an elevated level at night and a low level during the

daytime for most of the observed periods. As CFC-12, CFC-11 and CH3CCl3 behave as traffic- and industry-derived

airborne pollutants in the urban atmosphere, they provide as a useful tracer in the application for the study of terrestrial

airborne pollutants transport across the coastal area driven by land–sea breezes in this area.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Time-series; Land–sea breezes; Diurnal cycle

1. Introduction

Two of the most critical environmental issuesover the last 40 yr are the South Antarctica ozonedepletion and global warming. Anthropogenictrichlorofluorocarbon (CFC-11), dichlorofluorocar-bon (CFC-12), 1,2-trichlorofluoroethane (CFC-113), methyl chloroform (CH3CCl3) and carbontetrachloride (CCl4) have been well documented as

e front matter r 2007 Elsevier Ltd. All rights reserved

mosenv.2006.12.025

ing author. Tel.: +886 4 7841762;

4070.

ess: bslee@dragon.ccut.edu.tw (B.-S. Lee).

playing an important role in the depletion of theglobal stratospheric ozone layer and the augmenta-tion in global warming in the troposphere. It hasbeen estimated that these 5 species contribute morethan 80% of ozone-depletion substances in thestratosphere and more than 20% of warmingpotential in the troposphere (Houghton, 1990). Inaddition, CH3CCl3 and CCl4 have also beenrecognized as human carcinogens and thus havebeen regulated for use in most developed countries.Because of the serious environmental impacts ofthese compounds, the 1987 Montreal Protocol andsubsequent amendments have endeavored to halt

.

ARTICLE IN PRESSB.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–3372 3361

the growth of the atmospheric concentrations ofhalocarbons and gradually phase out the release ofthese species in the atmosphere via worldwideregulation. After implementation of the 1987Montreal Protocol and subsequent amendmentsover �15 yr, the current atmospheric levels of thesehalocarbons have started to decline. Some specieswith relatively short lifetimes (e.g. CH3CCl3) havedeclined dramatically (Prinn et al., 2000).

Prior to the initiation of atmospheric monitoringprograms, estimates of the evolution of thesehalocarbons in the atmosphere have been derivedfrom estimates of emission rates with corrections forloss based on their atmospheric lifetimes. With thelongest atmospheric lifetime of 100 yr among thesespecies, the current atmospheric level of CFC-12,after leveling off for several years, is slightlydecreasing due to stringent worldwide regulationon usage of this species. On the other hand, with theshortest atmospheric lifetime (�4.8 yr), the concen-trations of atmospheric methyl chloroform havedecreased much faster than the other halocarbonsover the last decade.

Global networks of monitoring stations in remotelocations were established in the 1970s and haveprovided detailed records of the background atmo-spheric levels of halocarbons. Data from thesestations have been used to evaluate the degree ofcompliance with the 2000 Montreal Protocol. Fornon-background regions, observations of atmo-spheric halocarbons are fairly sporadic. Studies onevolution of these atmospheric halocarbons inurban environments have been carried out byseveral research groups (Frank et al., 1991a–c;Keene et al., 1999; Grosjean et al., 1999; Wanget al., 2000; Yamamoto et al., 2000; Chang et al.,2001; Glavas and Moschonas, 2002; Rivett et al.,2003). Most observations of these halocarbons weremade by national agencies in industrial areas,focusing on possible health effects due to occupa-tional exposure.

To evaluate the degree of compliance with theregulation on use of these halocarbons in urbanareas, the most effective strategy currently taken isvia time-series observations of atmospheric concen-trations of these halocarbons at sites in proximity topotential emission areas. Each halocarbon species inthe urban environment has a different emissionstrength, which can be estimated by the amount ofthe variability in its measured atmospheric concen-trations (Wang et al., 1998). In general, thevariability of atmospheric concentrations of halo-

carbons in urban area is primarily modulated by theatmospheric lifetime of the halocarbon, anthropo-genic emission and meteorological parameters suchas atmospheric inversion height, wind speed andwind direction (Derwant et al., 1998; Chang et al.,2001; Rivett et al., 2003). Halocarbons with shortatmospheric lifetime usually have large concentra-tion spread and vice versa (Wang et al., 2000; Changet al., 2001; Rivett et al., 2003). As the emissionsources for these halocarbons are mobile and/orstationary, atmospheric levels of halocarbons in theurban atmosphere are usually sensitive to winddirection and wind speed and have differentbehaviors. For instance, CFC-12 was used asaerosols and a refrigerant for air conditioners,especially, in old vehicles and thus its sources wererecognized as mobile and/or stationary patterns inthe pre-protocol era. CFC-11 was used as arefrigerant in large central conditioning systemsfor buildings and as a foam blowing agent formanufacture of a variety of products and thus itsemission sources usually exhibited stationary andarea-dependent behavior. CFC-113 was mainly usedas a deflux agent in the electronics industry,therefore its emission sources primarily displayed astationary pattern in the pre-protocol era. Methylchloroform and carbon tetrachloride were com-monly used as clean solvents in conventionalindustry and usually exhibited stationary patterns.

Carbon monoxide (CO) is a natural troposphericconstituent with a background level of �0.1 ppbv. Itis produced by incomplete combustion of organicsubstances and as an intermediate in the tropo-spheric oxidation of substances such as methane.The background value of CO is small comparedwith the polluted levels in the urban air. Incompletecombustion of fossil fuel can lead to local levels ofCO greatly in excess of the background level. COconcentrations in urban air can be higher than thosein unpolluted areas by a factor of ten to severalthousands. The major sinks for CO in the tropo-sphere are uptake in soil, followed by microbialoxidation to CO2, (Bartholomew and Alexander,1982; Conrad, 1996) and by atmospheric oxidationby hydroxyl radical in the troposphere.

In addition to anthropogenic contributions, localair circulation patterns in the atmosphere also playan important role in modulating the atmosphericlevels of airborne pollutants. For inland areas,transport of terrestrial airborne pollutants duringthe daytime is driven by air convection near theground. As the ground is heated by solar radiation,

ARTICLE IN PRESSB.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–33723362

the polluted air near the surface becomes warmerand more buoyant. Subsequently, the cooler anddenser upper air over the ocean moves towards theland to replace the buoyant air. Without effectiveinfluence of lateral wind, airborne pollutants canbuild up in the near-ground atmosphere of theinland urban area at night due to restricted verticaldissipation process, especially when the atmosphereis under a nocturnal temperature inversion. Nearcoastal areas, transport of polluted air mass isadditionally driven with diurnal land–sea breezesand thus the atmospheric level of air pollutant issensitive to wind speed and direction and usuallyshows a diurnal cycle (Biraud et al., 2002; Younget al., 2005). Diurnal land–sea breezes are created byspecific heat difference between seawater and land.As the specific heat of seawater is larger than that ofland, land temperature is more changeable andhigher than seawater temperature under sunlightheating during the daytime. Consequently, theground air is heated by land more quickly thanthe marine air by seawater during the daytime. Atnight, seawater temperature decreases more slowlythan land temperature and thus marine air iswarmer than land air. As a result, the atmosphericpressure in marine air is relatively higher than thatin land air during the daytime and this circumstancereverses at night. The dynamic temperature gradientbetween land air and marine air generates thediurnal land–sea breeze system near the coastalarea. In general, the airborne pollutants in land airare conveyed over the coastal area to the sea withthe seaward land breeze at night and the landatmosphere is refreshed by fresh marine air duringthe daytime. Diurnal time-series distributions ofairborne pollutants near the coast area are usuallycharacterized with a diurnal cycle driven by land–sea breezes. In this study, we investigate the diurnalvariability of atmospheric levels of halocarbons(CFC-12, CFC-11 and CH3CCl3) and CO at twocoastal urban sites and interpret the variationpattern of each species with meteorological para-meters, anthropogenic emission and diurnal land–sea breezes.

2. Experimental

2.1. Site description

The field observation site for halocarbons waslocated at our laboratory in Lukang, in CentralTaiwan. The region in which the monitoring site is

located is in the largest plain terrain of TaiwanIsland (Fig. 1a). About 3 and 1 km away fromthe monitoring site are the Changhua CoastalIndustrial Park and the Fusing Industrial Parksituated to the north and the south respectively(Fig. 1b). A Taiwan EPA monitoring site measuringSO2, NO, NO2, CO, O3, etc. is located in the urbanenvironment of Hsienshi (Fig. 1b) of which theCO data were incorporated with halocarbonsfor discussion in this study. The Taiwan Strait islocated to the west of these two monitoringsites. These monitoring sites, which usually experi-ence landward sea breezes during the daytimeand seaward land breezes at night in spring andsummer, provide a natural laboratory for theobservation of diurnal cycles of terrestrial airbornepollutants.

2.2. Instrumentation

An automated cryogenic purge-and-trap gaschromatographic system modified from the systemdeveloped by Bullister and Weiss (1988) wasdeployed in the laboratory to monitor atmospherichalocarbons. In order to monitor the variability ofatmospheric halocarbons, hourly measurements ofhalocarbons at this site were carried out over a4-month period between April and August 2004. Airsamples were taken with an automated air samplingsystem consisted of an air sampling pump (AirCadet Model 7530-40) and lengths of air intake lineof 3/8 in o.d. Dekabon tubing (Samuel Moore Co.).The inlet end of the air sampling line was mountedat the top of the building at a height of �30m abovethe ground. Ambient air was drawn continuouslythrough the inlet line into the laboratory at a rate of9 lmin�1 for 10min before loading to the system.An in-line backpressure regulator was used tomaintain the pressure downstream of the pump atabout 0.7 atm above ambient. A stream of air(�100 cm3min�1) was split from the main streamand directed through a desiccant tube and then via a10 port selector valve (Valco, TX) into 10 and 3 cm3

1/800 s.s. sample loops mounted on two consecutive2-way 6 port switching valves. The halocarbon-freeultra pure N2 stream was directed through thesample loop and the halocarbons of interest in airsample in the sample loop were cryogenicallycollected on a cold (�45 1C) trap and separatedfrom gases with lower boiling points. The trap wasmade with a piece of 1/8 in. o.d. s.s. tubing packedwith 4 cm Porapak N (80/100 mesh) and 4 cm

ARTICLE IN PRESS

N

N

Changhua C oastal

Changhua

Lukang

Industrial Park

Fusing Industrial ParkMt. Ba Gua

Taiwan Strait

Hsienshi

Fig. 1. (a) Satellite mapping of Taiwan Island. The Changhua

County is marked in the rectangle area. Darker green and lighter

green represent mountainous areas and the plain terrain

respectively. (b) The enlarged satellite mapping of the Changhua

County as marked in the rectangle area (Fig. 1a). The monitoring

sites for halocarbons in Lukang and CO in Hsienshi are marked

with a symbol ‘‘�’’.

B.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–3372 3363

Porapak T (80/100 mesh) and 1 cm glass beads werepacked on both ends and 1 cm glass wool waspacked in between the different sorbents. Duringdesorbing, the trap was rapidly heated up to 140 1Cwithin seconds and then the sample was immedi-ately transferred by the halocarbon-free N2 gasstream through the precolumn and onto the mainGC column. After desorption, the pre-concentratedhalocarbons of interest were separated in theprecolumn from more slowly eluting higher mole-cular weight compounds which were vented to theatmosphere later by back flushing gas stream. Theprecolumn used for CFCs and halocarbons analyseswas a wide-bore DB-624 fused silica capillarycolumn (J&W, 35m� 0.53mm o.d. 3 mm film).After being eluted from the precolumn, the gasstream containing the halocarbons passed into a75m main column of the same material as theprecolumn. Separation of halocarbons occurred inthe GC main column held at 40 1C in the oven of theHewlett Packard 4890 gas chromatograph equippedwith 63Ni Electron Capture Detector.

A representative chromatogram for an air sampleat this site was shown in Fig. 2. The hourly cycleconsisted of the analysis of a system blank followedby one standard and four consecutive air samples.Concentrations of halocarbons (CFC-12, CFC-11,CFC-113, CH3CCl3 and CCl4) in our workingstandard were calibrated by National OceanicAtmospheric Administration, PMEL Laboratoryrelative to SIO 98 calibration scale (Walker et al.,2000), which is based on primary standardsprepared in the laboratory by volumetric dilution.Varying volumes of standard gas (covering a rangeof concentrations found in air) were injected togenerate a calibration curve. The multi-pointcalibration curve was constructed by varying thesize of the injected volume. Analysis of the standardgas was performed on the hourly basis to offset anychanges in detector sensitivity for each halocarbon.Polynomial expressions are obtained by leastsquares fitting to the calibration data. Overall theleast squares fitting for each halocarbon usuallyhave R240.995 in this study (Bullister and Weiss,1988; Lee et al., 1999).

Calibration curves were run once 1 or 2 weeks.The measurement uncertainty based on the stan-dard deviation of replicate analysis of our standardgases is �1% for CFC-12, CFC-11, CFC-113, �3%for CH3CCl3 and CCl4.

Meteorological data were obtained from Depart-ment of Environmental Monitoring and Information

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Table 1

Statistics for observed atmospheric halocarbons (pptv) at Lukang site and under advanced global atmospheric gases experiment

(AGAGE) project and the NOAA/CMDL chromatograph for atmospheric trace species (CATS) Program in the Northern Hemisphere in

2004

Compound Site Maximum

concentration

Minimum

concentration

Mean

concentration

Relative standard

deviation (%)

Lukang 1998.1 532.6 593.3 14.0

CFC-12 AGAGE 555.0 532.0 541.4 1.1

CATS 536.3 535.6 536.0 0.5

Lukang 490.6 249.1 264.8 6.4

CFC-11 AGAGE 265.0 247.0 254.6 1.4

CATS 255.6 254.7 255.2 0.2

Lukang 90.2 78.3 82.2 2.1

CFC-113 AGAGE 83.5 76.5 79.2 2.0

CATS 81.6 80.8 81.1 0.4

Lukang 600.6 21.6 33.0 117.0

CH3CCl3 AGAGE 28.0 21.1 23.8 6.7

CATS 24.0 22.4 23.1 1.0

Lukang 123.1 90.0 96.4 3.4

CCl4 AGAGE 100.7 92.1 95.9 1.8

CATS 97.0 96.5 96.7 0.2

counts

1

2

10000

9000

8000

7000

6000

5000

4000

3000

0 5

3

4 5

67

10

Minutes

15 20 25

Fig. 2. Typical chromatogram from the in-situ hourly measurements. The reported compounds are (1) CFC-12, (2) CFC-11, (3) CFC-113,

(4) CHCl3, (5) CH3CCl3, (6)CCl4, and (7) CHCl ¼ CCl2.

B.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–33723364

Management (Taiwan EPA website 2004) for thelocal surface station located in Hsienshi.

3. Results and discussion

Statistics for the measured CFC-12, CFC-11,CFC-113, CH3CCl3 and CCl4 at the Lukang siteduring the period between April and August 2004

are listed in Table 1. The relative standard devia-tions (1s) of the data set for CFC-12 (593.3714.0%), CFC-11 (264.876.4%) and CH3CCl3(33.07117.0%) are large relative to the measure-ment precision. On the contrary, the absolutestandard deviations of the data set for both CFC-113 (82.272.1%) and CCl4 (96.473.4%) are smallrelative to the measurement precision.

ARTICLE IN PRESSB.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–3372 3365

Time-series distributions of halocarbons areshown in Fig. 3 for CFC-12, CFC-11, and CH3CCl3and in Fig. 4 for CFC-113 and CCl4. Largevariability was seen for CFC-12, CFC-11 andCH3CCl3 and very little for CFC-113 and CCl4which have small standard deviations. The baseline(minimal) value for each species observed in thisarea was not very different from its contemporarynorthern hemispheric background value (Table 1).The concentration spread for each halocarbon,providing a useful indicator of relative emissionstrength and lifetime of these halocarbons, follows asequence of CFC-124CFC-114CH3CCl34CCl44CFC-113 (Fig. 5). This phenomenon indicates thatusages of CFC-12, CFC-11 and CH3CCl3 were stillin existence and were trivial for CFC-113 and CCl4in this area. Observations of these halocarbonsmade in a variety of non-background environmentsin northern Taiwan during the period of 1996–1998(Wang et al., 1998; Wang et al., 2000; Chang et al.,2001) revealed that the emission strength of thesespecies generally followed a sequence of CFC-124CH3CCl34CFC-114 CFC-1134CCl4. CFC-12 was the halocarbon with the highest emissionstrength in northern Taiwan during the period of

600

500

[CFC

-11]

and

[C

H3C

C13

] (p

ptv)

400

300

200

100

0

Date Tim

2004

/4/1

0 2:

05

2004

/4/1

2 20

:14

2004

/4/1

8 13

:02

2004

/4/2

2 12

:27

2004

/4/2

5 22

:15

2004

/4/3

0 12

:18

2004

/5/1

7 7:

04

2004

/5/2

1 22

:00

2004

/5/2

5 2:

27

2004

/5/2

9 7:

14

2004

/6/1

8:4

7

2004

/6/4

13:

13

2004

/6/1

1 4:

21

Fig. 3. Time-series distributions of atmospheric conc

1996–1998 and in this area in 2004. With theshortest lifetime among these halocarbons,CH3CCl3 displayed moderate emission strength innorthern Taiwan and at the Lukang site. Both CFC-113 and CCl4 showed very little emission strength innorthern Taiwan and this area. The concentrationspread of CFC-113 was somewhat narrower at theLukang site, where main manufacturing processeswere conventional industrial processes than that innorthern Taiwan where part of samples were takenin electronic industrial (Chang et al., 2001). It isnoted that less demand and stringent regulation forusage of CFC-113 and CCl4 in Taiwan are effectivein phase-out of these two compounds during the lastdecade.

Wang et al. (1998) reported that the distributionof atmospheric concentration of CFC-11 was quiteconstant and its emission strength was smaller thanCH3CCl3 in northern Taiwan, which is somewhatdifferent from our result at the Lukang site. Thisinconsistency could be due to the spatial andtemporal variation in CFC-11 usage. Moreover,the previous on-site in situ continuous observationswere usually made with duration of less than 2weeks and part of results were via discrete flask

2500

2000

1500

1000

500

0

[CFC

-12]

(pp

tv)

CFC-12

CFC-11

CH3CC13

e

2004

/6/1

4 8:

47

2004

/6/1

7 10

:20

2004

/6/2

2 20

:47

2004

/6/2

6 0:

44

2004

/6/2

9 5:

10

2004

/7/1

7 2:

00

2004

/7/2

0 3:

33

2004

/7/2

3 8:

04

2004

/7/2

7 10

:26

2004

/7/3

0 18

:22

2004

/8/3

20:

38

entrations of CFC-12, CFC-11, and CH3CCl3.

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0.00

25.00

50.00

75.00

100.00

125.00

150.00

175.00

200.00

225.00

250.00

0.00

25.00

50.00

75.00

100.00

125.00

150.00

175.00

200.00

225.00

250.00

2004

/4/1

0 2:

05

2004

/4/1

3 15

:31

2004

/4/2

0 10

:54

2004

/4/2

5 4:

44

2004

/5/1

0:2

7

2004

/5/1

8 13

:46

2004

/5/2

4 5:

01

2004

/5/2

9 7:

14

2004

/6/2

6:1

2

2004

/6/7

21:

17

2004

/6/1

3 20

:38

2004

/6/1

7 22

:29

2004

/6/2

4 5:

53

2004

/6/2

8 7:

45

2004

/7/1

7 2:

00

2004

/7/2

1 1:

03

2004

/7/2

5 2:

55

2004

/7/3

0 9:

06

2004

/8/4

8:4

7

Date Time

[CFC

-113

] (p

ptv)

CFC-113

CCl4

Fig. 4. Time-series distributions of atmospheric concentrations of CFC-113 and CCl4.

CFC-12 CFC-11 CFC-113 CH3CCl30

500

1000

1500

2000

Con

cent

ratio

n (p

ptv) 14.0%

6.4%

2.1%

117.0%

3.4%

CCl4

Fig. 5. Box-whisker plot of the measured halocarbons. Whiskers define the outlying 5% of the data. The box represents 10–90% of the

data. The notch represents the median, or the 50th percentile. The solid rectangle symbol (’) represents each measured halocarbon air

sample. The 1s relative standard deviation for each species is also shown in percentage.

B.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–33723366

ARTICLE IN PRESSB.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–3372 3367

samples. In this circumstance, episodes of highatmospheric levels of CFC-11 in northern Taiwanmaybe missed. However, hourly measurements ofatmospheric halocarbons in this study were madeover �4 months’ duration, allowing less chance tomiss out on recording episodes of elevated atmo-spheric levels of CFC-11.

Events of elevated atmospheric levels of CFC-12,CFC-11 and CH3CCl3 appeared to be irregular andcomplex as viewed as a time-series (Fig. 3). To gainan insight into the meteorological factors modulat-ing the atmospheric concentration of each halocar-bon in this area, atmospheric concentrations ofCFC-12, CFC-11, CH3CCl3 and CO were plottedversus wind direction (Fig. 6) and wind speed(Fig. 7). It is clear that elevated levels of CFC-11and CH3CCl3 were frequently correlated with windblowing from the 3401–901 sector and sporadicelevated signals of CH3CCl3 were from �1601(Fig. 6). As shown on Fig. 7, high levels of CFC-12, CFC-11, CH3CCl3 and CO arose mostly during

Wind direc

0 60 120 180

0 60 120 180

[CO

] (p

pmv)

0

1

2

Wind direc

[CFC

-11]

(pp

tv)

100

200

300

400

500

CO

CFC-12

Fig. 6. Concentrations versus wind direction f

the wind speed o�3m s�1. Fig. 6 indicated thatelevated atmospheric levels of CFC-11 andCH3CCl3 were from northern Changhua Countywhere categories of coating and printing processesand vehicle re-spraying were the main manufactur-ing processes, which presumably have potential toemit these compounds. The northern ChanghuaCounty is a typical conventional industrial areawhere two large industrial parks (Fig. 1b), theChanghua Coastal Industrial Park and the FusingIndustrial Park, and a number of small-scalefactories are located. Besides, that elevated levelsof CFC-11 and CH3CCl3 frequently appearedduring the period of low wind speed (Fig. 7)indicated that local impact of these compoundswas significant.

As shown on Fig. 6, elevated levels of CFC-12and CO distributed somehow widely as a mobilesource, as compared with those of CFC-11 andCH3CCl3, which, to some extent, concentrated inthe 01–901 sector as a stationary source. It was

tion

240 300 360

240 300 360

[CFC

-12]

(pp

tv)

500

1000

1500

2000

tion

[CH

3CC

l 3]

(ppt

v)

0

100

200

300

400

500

600

CFC-11

CH3CCl3

or CO, CFC-12, CFC-11 and CH3CCl3.

ARTICLE IN PRESS

Wind speed (m sec-1)

0 2 4 86

[CO

] (p

pmv)

0

1

2

[CFC

-12]

(pp

tv)

500

1000

1500

2000

[CFC

-11]

(pp

tv)

100

200

300

400

500

[CH

3CC

l 3]

(ppt

v)

0

100

200

300

400

500

600

CO

CFC-12

CFC-11

CH3CCl3

Wind speed (m sec-1)

0 2 4 86

Fig. 7. Concentrations versus wind speed for CO, CFC-12, CFC-11 and CH3CCl3.

B.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–33723368

noted that elevated levels of CFC-12 and COappeared in the �2401–3401 sector where CFC-11and CH3CCl3 levels were low. This phenomenonillustrates that CFC-12 and CO behaved somehowdifferently from CH3CCl3 and CFC-11 in this areaas expected. It is noticed that a certain percentage ofolder vehicles in Taiwan still use CFC-12 as arefrigerant in air conditioners in the post-protocolera and hence this compound is usually recognizedas a mobile source in the urban environments.Hence, some elevated levels of CFC-12 and COfound in the 2401–3401sector corresponding withsea breezes were presumably from vehicular emis-sion on the west coastal express highway. There aresome episodes of intensive elevated levels of CFC-12occurred with the wind from the 1201–1901 sectorwhere a number of car repair shops are located andCFC-12 was very likely emitted from there.

Relatively low levels of CFC-11 and CH3CCl3and part of CFC-12 and CO occurred when the

wind was from the 2401–3401 sector and when thewind speed was 4�3m s�1 (Fig. 7). In fact, lowlevels of halocarbons and CO were usually con-current with the prevailing sea breezes, which werestronger than land breezes (Fig. 8). As comparedwith land air, marine air was less polluted withhalocarbons and CO and its halocarbon and COlevels were usually near background level during thedaytime. The wind system over this coastal areaconsists of relatively strong landward sea breezes(472m s�1) during the daytime and comparativelyweak seaward land breezes (271m s�1) at night formost of the observed period (Fig. 8). Hence,atmospheric levels of halocarbons and CO nearthe coastal area were strongly influenced by land–sea breezes.

Elevated levels of atmospheric halocarbons andCO were likewise correlated with land breezesat night and in the early morning (Fig. 9). Inspring and early summer, a nocturnal temperature

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Local time of day (hours)0 6 12 18 24

Win

d di

rect

ion

0

60

120

180

240

300

360

Local time of day (hours)

0 6 12 18 24

Win

d sp

eed

(m s

ec-1

)

0

2

4

6

8

Fig. 8. Diurnal distributions of wind direction and speed.

B.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–3372 3369

inversion took place when the atmosphere wasstagnant and consequently elevated levels of atmo-spheric pollutants developed in the low atmos-phere (Young et al., 2005). By contrast, elevatedlevels of atmospheric halocarbons and CO seldomoccurred at the wind speed 45m s�1 (Fig. 7). Inthis area, atmospheric levels of halocarbons andCO in polluted urban air reached their highestvalues usually no later than �8:00AM as seabreezes started to influence the land atmos-phere and since then mixing the polluted urban airwith clean marine air got stronger and elevatedlevels of halocarbons were rapidly eroded. Rela-tively low levels of halocarbons and CO lasted forthe rest of the daytime till the evening around5:00 PM.

Periodically, airborne pollutants in the urban airwas transported over the coast to the sea with land

breezes at night and subsequently the pollutedurban atmosphere was further refreshed by freshmarine air during the daytime (Fig. 9). The atmo-sphere was ventilated relatively slowly when thewind speed was low, with the extreme case of atemperature inversion. Consequently, when the airwas stagnant at night, various traffic and industryderived pollutants gradually accumulated in thelower atmosphere until the temperature inversionwas broken as the ground became warmer undersunlit heating. The dynamic system of diurnalland–sea breeze played an important role incontrolling atmospheric levels of anthropogenicairborne pollutants such as CFC-12, CFC-11,CH3CCl3 and CO in this area, i.e. high levels ofthese species developed at night and graduallydecreased to their near background levels duringthe daytime (Fig. 9).

ARTICLE IN PRESS

Local time of day (hours)

0 6 12 18 24

[CO

] (p

pmv)

0

1

2

[CFC

-12]

(pp

tv)

500

1000

1500

2000

Local time of day (hours)

0 6 12 18 24

[CFC

-11]

(pp

tv)

100

200

300

400

500

[CH

3CC

l 3]

(ppt

v)

0

100

200

300

400

500

600

CO

CFC-12

CFC-11

CH3CCl3

Fig. 9. Diurnal distributions of atmospheric concentrations of CO, CFC-12, CFC-11 and CH3CCl3.

B.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–33723370

The variability in the atmospheric level of COobserved at Taiwan EPA monitoring site inHsienshi during the same period characterized asimilar diurnal cycles as halocarbons at the Lukangsite. The diurnal variation in the atmosphericconcentrations of CO at the Hsienshi site was atypical case near the coast, where anthropogenicemission from the land, removal process via atmo-spheric oxidation in the troposphere and dilutionvia mixing of land air with marine air took part inthe diurnal cycle of this species. The atmosphericlevels of CO are variable in different air masses. TheCO level in marine air is relatively low due to theaging effect of marine air in which substrates werenearly depleted via prolonged photolysis. By con-trast, the polluted land air rich in a variety ofsubstrates usually contained high level of CO. Nearthe coastal area, strongly influenced by diurnalland–sea breezes and anthropogenic emission,atmospheric levels of CO are variable and sensitive

to the wind direction and speed. CO has a similarbehavior as CFC-12, CFC-11, and CH3CCl3 in theurban atmosphere near the coastal area. CO levelswere relatively high at night since removal of CO viamicrobial oxidation in soil was not fast enough toeliminate excess anthropogenic source, and physicalmixing between land air and marine air wasinefficient under sluggish air circulation at night.Because CO has an average lifetime of 1–2 months;the more vigorous mixing of air in midday shouldsignificantly out weigh the chemical loss due to OH.

4. Conclusions

Time-series observations of these halocarbons inthe urban atmosphere of Lukang over a period of 4months demonstrated that these species have emis-sion strength as follows: CFC-124CFC-114CH3CCl34CCl44CFC-113. With both long atmo-spheric lifetimes for CFC-113 (�80 yr) and CCl4

ARTICLE IN PRESSB.-S. Lee, C.-B. Chiou / Atmospheric Environment 41 (2007) 3360–3372 3371

(�40 yr) and insignificant emissions of these twocompounds, their atmospheric levels were fairlyconstant, which obviously made them limited in theapplication for the study of observations of airbornepollutants transport in this area. These measure-ments also provided the clear evidence that localregulation on usages of CFC-113 and CCl4 waseffective in Taiwan.

Large variability in the atmospheric level wasfound for CFC-12, CFC-11 and CH3CCl3, espe-cially for the former two species whose elevatedlevels occurred rather frequently. Nevertheless,elevated levels of atmospheric CH3CCl3 occurredsporadically and most of its atmospheric levels wereclose to its background level. This phenomenon wasattributed to its relatively short atmospheric lifetime(�5 yr) and less emission strength in this area. Incomparison of the data collected in this area (2004)and in northern Taiwan (1996–1998), emission ofthese halocarbons was reduced at different rates.The emission strength for CH3CCl3 was found todecrease much faster than that for the otherhalocarbons over the last 7 yr in Taiwan and thatfor CFC-12 and CFC-11 was slightly reduced.However, emission strength of CFC-113 and CCl4essentially paralleled their global emission strengthregarding the consistency between their local atmo-spheric levels and global background levels.

The variability in the atmospheric halocarbons,CFC-12, CFC-11, and CH3CCl3, observed inLukang were characterized as a diurnal cycle drivenby diurnal land–sea breezes in spring and summer.High levels of these species usually appeared atnight when the relatively weak land breezes weredominant and low levels of these halocarbonsoccurred during the daytime when the relativelystrong sea breezes were predominant for most of theobserved period. The atmosphere was usuallystagnant at night and that facilitated airbornepollutants to build up in the low atmosphereespecially under a nocturnal temperature inversion.By contrast, the atmosphere was vigorous understrong vertical convection and lateral mixing bystrong sea breezes, therefore elevated levels of thesespecies seldom occurred during the daytime. Thisphenomenon was consistent with the observation ofatmospheric CO made at the Hsienshi site.

Acknowledgements

The authors would like to thank the NationalScience Council of Taiwan for financially support-

ing this research under Contract nos. NCS93-2113-M-235-011, NCS92-2113-M-235-011 and NCS91-2113-M-235-011. They also thank the Departmentof Environmental Monitoring and InformationManagement for providing monitoring data.

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