Chemosphere 57 (2004) 931–942

www.elsevier.com/locate/chemosphere

Characterising sources and sinks of rural VOCin eastern France

Agnes Borbon a,*, Patrice Coddeville b, Nadine Locoge b, Jean-Claude Galloo b

a Laboratoire Interuniversitaire des Systemes Atmospheriques, Faculte des Sciences et Technologies,

Universite Paris XII, 61, avenue du General de Gaulle, 94010 Creteil Cedex, Franceb Departement Chimie et Environnement, Ecole des Mines de Douai, BP 838, 941, rue Charles Bourseul,

59508 Douai Cedex, France

Received 9 October 2003; received in revised form 21 June 2004; accepted 13 July 2004

Abstract

Fifty non-methane hydrocarbons (NMHC) and seventeen carbonyl compounds were measured at a French rural site

from 1997 to 2001, as part of the EMEP programme. Data handling was based on an original source–receptor

approach. First, the examination of the levels and trends was completed by the comparison of the seasonal distribution

of rural and urban VOC/acetylene ambient ratios. This analysis has shown that most of the compounds derived from

mixing and photochemical transformation of mid-range transported urban pollutants from the downwind urban area.

Then, identified sources and sinks were temporally apportioned. Urban air masses mixing explains, at least, 80% of the

wintertime levels of anthropogenic NMHC and isoprene. In summer, photochemistry dominates the day-to-day distri-

bution of anthropogenic NMHC whilst summertime isoprene is also controlled by in-situ biogenic emissions. Then, the

results of C1–C3 carbonyls were discussed with respect to their direct biogenic and anthropogenic emissions and pho-

tochemical production through the {carbonyl/auto-exhaust tracers} emission ratio. Diluted vehicle exhaust emissions

mainly contribute to the total content of lower aldehydes in winter while other processes control lower ketones. Sec-

ondary production is predominant in summer with at least a 50% high intensity. Its dependence upon temperature

and radiation is also demonstrated. Finally, the importance of the primary and secondary biogenic production of ace-

tone and formaldehyde is assessed. In particular, biogenic contribution would explain 37 ± 25% of acetone levels in

summer.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Source–receptor relationships; VOC ratios; Vehicle exhaust emissions; Biogenic; Photochemistry; Dispersion and transport

1. Introduction

During the last decade, a large fraction (10–40%) of

the European population, at rural locations in particu-

0045-6535/$ - see front matter � 2004 Elsevier Ltd. All rights reserv

doi:10.1016/j.chemosphere.2004.07.034

* Corresponding author. Fax: +33 1 45 17 15 19.

E-mail address: borbon@lisa.univ-paris12.fr (A. Borbon).

lar, was exposed to ground-level ozone concentrations

above the health-protection-based target level (Larssen

et al., 2002). For that reason, the question of the rela-

tionships between ozone and its precursors still remains

an issue of special concern. In particular, the contribu-

tion that volatile organic compounds (VOC) make to

the exceedence of environmental criteria for ozone is

now well recognised (Seinfeld, 1986). The distribution

ed.

932 A. Borbon et al. / Chemosphere 57 (2004) 931–942

of VOC is the result of three major combined processes:

(1) primary and secondary formation process, (2) re-

moval process and (3) mixing process.

(1) Sources of primary VOC are both of anthropogenic

and biogenic origin. Major anthropogenic sources

are related to fossil fuel combustion (vehicle exhaust

emissions, combustion boilers), storage and distri-

bution of fuels (petrol evaporation) and solvent

use (Friedrich and Obermeier, 1999). Carbonyls

are not only primary but also secondary pollutants

produced by the photooxidation of VOC (Alts-

huller, 1993). Biogenic emissions also contribute to

the presence of highly photoreactive VOC, especially

in rural atmospheres. Isoprene is one of the most

abundant biogenic hydrocarbons (Fuentes et al.,

2000). Acetone has also been identified as a direct

emitted biogenic compound (Singh et al., 1994)

and to a lesser extent aldehydes (Kesselmeier and

Staudt, 1999).

(2) Mechanisms of VOC oxidation are mainly induced

by the hydroxyl radical OH in daytime, by the

NO3 at night, and by ozonolysis for unsaturated

compounds (Atkinson, 1994). Either photolysis or

reaction with OH radical constitutes a carbonyl

sink. Finally, water-soluble carbonyls may be scav-

enged by airborne aqueous droplets.

(3) Mixing processes, closely related to meteorological

conditions within the mixing boundary layer, tend

to redistribute the pollutants through advective

and convective transport at a regional or long-range

scale, especially for long residence time species

(ethane, acetone).

The consideration of the relative importance of these

factors can provide relevant insights for a better under-

standing on VOC impact on tropospheric chemistry. In-

deed, the chemical mechanisms involved are complicated

and there are still uncertainties as to how reductions

should be made cost effective.

This is the objective of the present work to assess and

apportion sources and sinks of rural VOC on a temporal

basis. To do so, a specific source–receptor methodology

was developed. Here, non-methane hydrocarbons

(NMHC) and carbonyl data, collected at one French

rural location, were used in the framework of the EMEP

programme (Co-operative programme for monitoring

and evaluation of the long-range transmission of air pol-

lutants in Europe).

2. Experimental

2.1. Site description

Data sets used in this study correspond to samples

collected at the rural station of Donon belonging to both

French MERA (MEsure des Retombees Atmospheri-

ques) and EMEP networks (Fig. 1). This site is charac-

terised by a high-density coniferous forest coverage

(100%). The site is 58 km west downwind the densely

populated urban centre of Strasbourg.

2.2. VOC sampling and analysis

Measurements were performed from April 1997 to

December 2001. As recommended by EMEP (1990),

measured compounds comprise fifty NMHC (C2–C9)

and seventeen carbonyl compounds (C1–C7). Sampling

is carried out twice a week around 12:00 UT during

4 h, generally on Tuesdays and Thursdays.

2.2.1. Non methane hydrocarbons

Stainless steel canisters (6L) provide the collection of

NMHC samples according to the well-established TO-14

method for many non polar VOCs (US EPA, 1997), so

used in the EMEP network. Since 2001, NMHC sam-

pling has been using the ambient volatile organic canis-

ter sampler (AVOCs) from Andersen Instruments Inc.

NMHC analysis uses the Auto TCT/CP9000-GC

(VOCAA from Chrompack). Separation is performed

by a dual capillary column system equipped with a

switching device. The analytical conditions were de-

scribed in details by Locoge and Galloo (1998). The

ambient air sampling because of low concentrations, dic-

tates the need for thorough QA/QC. Four main steps

constitute the QA/QC programme which are based on

the TO-14 method (1997):

(1) The establishment of standard operating proce-

dures,

(2) Canister cleaning and certification (<0.02 ppbv),

(3) Sampling system cleaning and lab certification,

(4) In-situ tests with collocated samplers in field.

2.2.2. Aldehydes and ketones

Carbonyls are determined using 2,4-DNPH silica car-

tridges and HPLC analysis following DNPH derivatiza-

tion (Coddeville et al., 1998). During sampling (300 l),

an ozone KI-scrubber is placed upstream of the

cartridge.

3. Results and discussion

3.1. Levels and trends

The number of observations since 1997 at Donon

equals 495 with a high recovery of about 97%. The med-

ian concentrations reported in Fig. 2(a) are in good

agreement with the ones at other EMEP stations

Fig. 1. The sampling area.

A. Borbon et al. / Chemosphere 57 (2004) 931–942 933

(http://www.nilu.no/projects/ccc/reports.html). Except

for isoprene, the hierarchical distributions of VOC at

Donon and in French urban atmospheres are consistent,

indicating the dominating anthropogenic origin of rural

VOC. 1,3-butadiene, butenes, pentenes, higher alkanes

(>C7), trimethylbenzenes and higher carbonyls have, at

least, 30% of their concentration levels below detection

limits (DL). While these compounds are generally well-

detected in urban environments (>0.05 ppbv) they do

not survive to transport due to their high reactivity.

Finally, higher rural levels of isoprene mirror its well-

known biogenic origin.

As already observed in rural or remote environments

worldwide (Solberg et al., 1996; Hagerman et al., 1997;

Sharma et al., 2000), VOC exhibit pronounced seasonal

cycles (Fig. 2(b)). The cycle of anthropogenic NMHC

(e.g. ethane and benzene) with wintertime maxima and

summertime minima not only reflects enhanced photo-

chemically driven processes in summer but also emission

strengthening in winter. For instance, wintertime heat-

ing function and vehicle ‘‘cold start’’ effect may be

responsible for higher emissions of combustion related

products (acetylene, ethylene, propene) and C2–C4 alka-

nes. For the latter group (e.g. ethane), significant back-

ground levels persist in summer due to their relatively

long atmospheric residence time (several days). For

shorter lived species (few hours), summertime concen-

trations are sometimes close to DL. What should be

noted is the clear decrease of benzene levels from 1999

in relation with its 1% volume-limitation in fuel (direc-

tive 98/70/EC). Finally, isoprene and carbonyls (e.g. for-

maldehyde) show a clear opposite cycle indicating the

contribution of summertime biogenic emissions for iso-

prene and acetone and intensified VOC photooxidation

processes that lead to the secondary formation of

carbonyls. The additional biogenic emissions of ace-

tone will be discussed in details later (Section 3.4.3;

Fig. 6(b)).

As time series reveal the superimposition of various

processes, another way to analyse VOC data is to work

with their ambient ratios.

3.2. VOC vs. acetylene regression

Our approach to the data has been to work with the

daily concentration ratios VOC/acetylene by the use of

simple regression analysis (Derwent et al., 2000). Here,

acetylene has been chosen as a reference compound of

vehicle exhaust emissions (Borbon et al., 2001b). The ap-

proach involves the visual exploration of the seasonal

0.12 0.13

0.06

0.511.060.62

2.10

0.01

0.10

1.00

10.00

form

alde

hyde

acet

alde

hyde

prop

anal

met

hacr

olei

ne

acet

one

benz

alde

hyde E

VK

median µg,m

-3

1.67

0.14

0.03

0.110.18

0.52

0.04

0.37

0.040.04

0.19

0.63

0.08

0.40

0.24

0.24

0.65

0.01

0.10

1.00

10.00

acet

ylen

e

benz

ene

isob

utan

e

n-bu

tane

etha

ne

ethy

lene

ethy

lben

zene

n-he

xane

isop

enta

ne

n-pe

ntan

e

prop

ane

prop

ene

tolu

ene

1,2,

3-T

MB

m,p

-xyl

ene

o-xy

lene

isop

rene

med

ian

ppb

vrural (this study)

urban (Strasbourg) *urban (Lille) **

(a)

* ASPA (Association pour la Surveillance et l'étude de la Pollution atmosphérique en Alsace)

Personal communication.

** Borbon et al., 2002

ethane

0.0

1.0

2.0

3.0

4.0

5.0

Ap

r-97

Jul-9

7O

ct-9

7Ja

n-98

May

-98

Au g

-98

Nov

-98

Mar

-99

Jun-

99S

ep

-99

Dec

-99

Ap

r-00

Jul-0

0O

ct-0

0Ja

n-01

May

-01

Au

g-0

1N

ov-0

1

ppbv

formaldehyde

0

2

4

6

Ap

r-97

Jul-9

7O

ct-9

7Ja

n-98

May

-98

Aug

-98

Nov

-98

Mar

-99

Jun-

99S

ep

-99

Dec

-99

Ap

r-00

Jul-0

0O

ct-0

0Ja

n-01

May

-01

Aug

-01

No

v-01

µg,m

-3

isoprene

0.0

1.0

2.0

3.0

4.0

Ap

r-97

Jul-9

7O

ct-9

7Ja

n-98

May

-98

Au

g-9

8N

ov-

98M

ar-9

9Ju

n-99

Se

p-9

9D

ec-9

9A

pr-

00Ju

l-00

Oct

-00

Jan-

01M

ay-0

1A

ug

-01

No

v-01

ppbv

benzene

0.0

0.2

0.4

0.6

0.8

1.0

Ap

r-97

Jul-9

7O

ct-9

7Ja

n-98

May

-98

Au

g-9

8N

ov-9

8M

ar-9

9Ju

n-99

Se

p-9

9D

ec-9

9A

pr-0

0Ju

l-00

Oct

-00

Jan-

01M

ay-0

1

Aug

-01

No

v-01

ppbv

(b)

Fig. 2. (a) Rural air mass composition at Donon station for the 20 major VOCs (5-year median) and comparison to urban air masses

on a log-scale (units in ppb and lg m�3). (b) Typical VOC time series at Donon station. Black curves correspond to 15-day moving

averages.

934 A. Borbon et al. / Chemosphere 57 (2004) 931–942

ambient ratio distributions (Fig. 3) to underline sink and

source contributions other than vehicle exhausts (as de-

signed by rural).

Similar scatterplots (as designed by urban) have been

constructed from NMHC data collected at the suburban

station ‘‘STG-West’’ (STGw) of Strasbourg city by the

local Air Quality Monitoring Network (ASPA). NMHC

collection at STGw consists of an automated on-line

sampling and analysis performed by the Turbomatrix/

Autosystem-GC from Perkin Elmer.

The similarity of distribution patterns (Fig. 3) indi-

cates that anthropogenic NMHC at Donon mainly de-

rive from mixing and transforming of the mid-range

transported urban plume from Strasbourg (Fig. 1). Ex-

cept for isoprene, lower rural slopes illustrate the hete-

rogeneity of photochemical removal and mixing.

formaldehyde_ruralµg.m-3

0.0

2.0

4.0

6.0

0.0 1.0 2.0 3.0 4.0

rural

0

5

10

15

0.0 1.0 2.0 3.0 4.0

ethy

lene

ppb

v

rural

0

3

6

9

12

0.01 .0 2.03 .0 4.0

etha

ne p

pbv

acetone_ruralµg.m-3

0

2

4

6

8

10

12

0.0 1.0 2.0 3.0 4.0

rural

0.00.51.01.52.02.53.03.54.0

0.0 1.0 2.0 3.0 4.0

isop

rene

ppb

v

urban

0

3

6

9

12

0.0 2.0 4.0 6.0

urban

0

4

8

12

16

0.0 2.0 4.0 6.0

urban

0.0

0.1

0.2

0.3

0.4

0.02 .0 4.06 .0

rural

0.0

0.5

1.0

1.5

2.0

0.0 1.0 2.0 3.0 4.0

isop

enta

ne p

pbv urban

0

1

2

3

4

5

0.0 2.0 4.0 6.0

methacroleine-ruralµg.m-3

0.0

0.1

0.2

0.3

0.4

0.5

0.0 1.0 2.0 3.0 4.0

EVK-ruralµg.m-3

0.0

1.0

2.0

3.0

4.0

0.0 1.0 2.0 3.0 4.0

Fig. 3. Seasonal scatterplots of VOC vs. acetylene concentrations (x-axis) in rural (Donon) and urban atmosphere (Strasbourg, STGw)

in ppbv. Black points and grey points correspond to wintertime (November–March) and summertime (April–October) data sets,

respectively.

A. Borbon et al. / Chemosphere 57 (2004) 931–942 935

• The long-lived species ethane and propane are char-

acterised by diffuse scatterplots (e.g. ethane), as intro-

duced by Derwent et al. (2000), with no significant

seasonal differences between the slopes. In Northern

Hemisphere, ethane and propane are principally

related to natural gas exploitation. Their intercept

either in urban or rural atmosphere is statistically dif-

ferent from zero indicating their important back-

ground levels.

• Ethylene illustrates the behaviour of combustion

derived products (propene, 1,3-butadiene) with a uni-

form pattern and a relatively constant annual ratio

with acetylene. Traffic exhaust is their major emission

source.

• Isoprene/acetylene pairs are characterised by a multi-

form distribution. The wintertime urban uniform dis-

tribution indicates its vehicle exhaust origin (Borbon

et al., 2001a) while the diffuse summertime pattern

and greater ratios are related to its dominant bio-

genic origin.

• Butanes and C5–C9 NMHC pairs (e.g. isopentane)

are characterised by diffuse scatterplots and higher

summertime slopes. It is particularly pronounced in

the urban environment but still detectable at the rural

site of Donon. It illustrates the potential increase of

petrol evaporation completed by a solvent contribu-

tion for aromatics (toluene, xylenes). The persistent

diffuse characteristic of the scatterplots in winter

(e.g. isopentane) reveals the presence of wintertime

evaporative sources for pentanes as suggested by

Borbon et al. (2003a,b).

Finally, scatterplots of carbonyls are characterised by

a multiform distribution. In summer, data points signi-

ficantly lie away from the typical uniform wintertime

distribution except for acetone. In winter, carbonyl con-

centrations at the receptor site mostly reflect vehicle ex-

haust emissions from some distance away rather than

secondary formation. The wintertime satellite distribu-

tion of acetone–acetylene pairs with a few scattered

points indicates its other man-made origin as a com-

monly used solvent (Singh et al., 1994). On the contrary,

the diffuse summertime distributions indicate that car-

bonyls are mainly controlled by secondary formation:

a more efficient oxidation of precursors and/or higher

biogenic emissions.

3.3. Source and sink apportionment of non-methane

hydrocarbons

VOC/acetylene scatterplots have shown that rural

VOC distribution is mainly impacted by aged urban

936 A. Borbon et al. / Chemosphere 57 (2004) 931–942

air masses and/or local emissions. Here, our purpose is

to temporally apportion those contributions.

3.3.1. Method

We have established the concentration of a given

hydrocarbon (HC) at the receptor ([HC]receptor) as

following:

½HC�receptor ¼ ½HC�0 � ½HC�photochemistry � ½HC�dynamics

ð1Þ

where

• [HC]0 is the initial concentration at time of emission:

½HC�0 ¼ ½HC�source ¼ ½HC�STGw ð2Þ

• [HC]photochemistry is the concentration removed by

photochemical process. Considering that photo-

chemical removal is mainly driven by hydroxyl

radical (OH) reactions, the photochemical decay

[HC]photochemistry can be determined:

½HC�photochemistry ¼ ½HC�0 � ½HC�0 expð�kOH½OH�tÞð3Þ

where [OH] is the temporal and spatially averaged

OH concentration as reported by Spivakovsky

et al. (2000), kOH is the second-order rate constant

of reaction between HC and OH (Atkinson, 1994)

and t the source–receptor time of transport depend-

ing on the source–receptor distance (58 km) and

wind speed.

• [HC]dynamics is the concentration due to dynamical

processes and air mass mixing in particular. Accord-

ing to the photochemical age of air masses and their

high or low polluted level, [HC]dynamics could either

be negative or positive depending on the sign of the

term ‘‘[HC]source � [HC]receptor’’. While a positive

‘‘[HC]source � [HC]receptor’’ term is an indicator of

air mass dilution (designed by mix�), a negative

‘‘[HC]source � [HC]receptor’’ term points out an air

mass enrichment during transport (designed by

mix+). Such an enrichment is the result of important

local or regional emissions that overlap dilution proc-

ess. Regarding Eqs. (1) and (3), a rough estimate of

the relative contribution of photochemical decay,

urban air mass transport and local emissions to the

variation of NMHC concentration from source to

receptor can be obtained. Equations were applied

to each observation from 1997 to 2001. The value

of photochemical process contributions depends on

[OH] levels. The influence of [OH] values upon the

exponential term of Eq. (3) was examined for the

unreactive acetylene and the highly-reactive 1,3-but-

adiene. While the photochemical decay of acetylene

is not affected within an OH range of 0.01–10

molecules cm�3, the one of 1,3-butadiene can be

clearly affected when OH values become greater

than 0.1 molecules cm�3 (i.e. during seasons outside

of winter). Consequently, the uncertainty of the

photochemical contribution was estimated for 1,3-

butadiene, which corresponds to the maximum

uncertainty that can be expected for the target

NMHC. During the warm season, the maximum

uncertainty equals 30% and is inferior to 10% during

the cold season.

Results are presented in Fig. 4 for the most relevant

NMHC.

3.3.2. Isoprene

During the warm season, transported isoprene is

mainly controlled by in-situ biogenic emissions (as de-

signed by mix+ in Fig. 4) and photochemistry. In sum-

mer, in-situ biogenic emissions dominate at least 80%

of isoprene. In winter (from January), more than 90%

of residual rural isoprene generally comes from urban

air mass mixing (as designed by mix� in Fig. 4).

3.3.3. Anthropogenic NMHC

Urban air mass mixing and photochemistry mainly

control anthropogenic NMHC during their transport.

Their relative intensity depends on the atmospheric

reactivity of each compound. This time, the occurrence

of in-situ emissions (as designed by mix+ in Fig. 4) is

exceptional.

In winter, the distribution of rural NMHC is mostly

caused by meteorological processes that dilute pollut-

ants from nearby urban sources, even for the highly

photoreactive C4–C5 alkenes (e.g. 1,3-butadiene). Photo-

chemistry process does not exceed 20% before the 60th

day. After the 60th day (March) photochemistry be-

comes significant until summertime maxima. In summer,

photochemistry is responsible for 80–100% of pentenes

and butenes decay, 20–40% of aromatic decay (e.g. tol-

uene) excepted benzene and no more than 20% of C4–

C5 alkane decay (e.g. butane and isopentane). Indeed,

wintertime NMHC chemical lifetimes are prolonged

due to the low concentrations of OH and weaker UV

radiation compared to summer. For alkenes, the contri-

bution of photochemical removal should be viewed as a

lower limit as the model does not consider their removal

by ozone. Finally, air mass mixing mostly explains the

distribution of the stable acetylene, benzene and ethane.

For the latter, background levels (corresponding to the

regression slope intercept with acetylene in Fig. 3) repre-

sent 60% of its levels.

3.4. Source and sink apportionment of carbonyls

The regression analysis VOC vs. acetylene (Fig. 3)

has pointed out the two principal primary and second-

ary pathways that lead to carbonyl presence at Donon

isoprene

0%

20%

40%

60%

80%

100%

1 18 34 48 62 81 102

116

132

147

163

181

201

216

230

245

259

273

289

307

333

364

julian day

cont

ribut

ion

mix +mix -photochemistry *

isopentane

0%

20%

40%

60%

80%

100%

1 18 33 47 61 75 93 107

122

139

154

168

189

208

223

237

254

268

284

298

313

327

342

356

julian day

cont

ribut

ion

mix +mix -photochemistry *

ethylene

0%

20%

40%

60%

80%

100%

16 32 46 60 74 91 105

119

139

154

168

188

208

222

237

254

270

285

300

317

333

347

363

julian day

cont

ribut

ion

mix +mix -photochemistry *

0%

20%

40%

60%

80%

100%

1 18 33 47 61 75 93 107

122

140

156

172

191

209

223

237

252

266

282

296

310

324

340

354

julian day

cont

ribut

ion

mix -

photochemistry *

ethane

0%

20%

40%

60%

80%

100%

1 18 33 47 61 75 93 107

125

144

160

174

194

212

226

242

256

270

285

299

314

329

345

358

julian day

cont

ribut

ion

mix +mix -background

n-butane

0%

20%

40%

60%

80%

100%

1 16 32 46 60 72 86 100

112

126

140

156

170

184

198

212

226

240

254

268

282

296

310

324

julian day

cont

ribut

ion

mix +mix -photochemistry *

mix +mix -photochemistry *

benzene

0%

20%

40%

60%

80%

100%

1 18 33 47 61 75 93 107

122

139

154

168

188

207

221

235

249

263

278

292

306

320

334

349

363

julian day

cont

ribut

ion

mix +photochemistry *mix -

1,3-butadienemix -

photochemistry *

toluene

0%

20%

40%

60%

80%

100%

1 18 33 47 61 75 93 107

122

139

154

168

188

207

221

235

249

265

280

294

308

322

338

352

julian day

cont

ribut

ion

mix+mix -photochemistry *

* Monthly average concentrations of OH in 105 molecules cm-3 (zone: 44°N-52°N / 900-1000 mbar): January: 0.06 / April: 0.70 / July: 1.30 / October: 0.30 (Spivakovsky et al., 2000)

Fig. 4. Day-to-day variations of the contribution of photochemical removal and air mass mixing to NMHC levels at Donon station.

A. Borbon et al. / Chemosphere 57 (2004) 931–942 937

station. This is the objective of this last section to esti-

mate the relative temporal contribution of their direct

and indirect formation.

3.4.1. Method

The general method is based on the one developed by

Borbon et al. (2003b) in an urban environment of north-

ern France. A first step consists in estimating the mean

wintertime {carbonyl/auto-exhaust tracer} ratio (Table

1) thought to be representative of the vehicle exhaust

emission ratio (Figs. 3; Section 3.2). Five other com-

pounds, which have appeared as potential auto-exhaust

tracers (Section 3.2) have been retained in addition to

acetylene: ethylene, propene, isopentane, benzene and

toluene. They were compared to their homologues

Table

1

Summary

ofcarbonylsvs.auto-exhaust

tracerratiosfrom

ambientruralobservations(D

onon)anddirectem

issionmeasurements

Tracer

Form

aldehyde/tracer

Acetaldehyde/tracer

Propanal/tracer

Acetone/tracer

MBK/tracer

EVK/tracer

Ambienta

Emissionb

Ambient

Emissionb

Ambienta

Emissionb

Ambienta

Emissionb

Ambienta

Emissionb

Ambienta

Emissionb

Acetylene

1.06±0.65

0.92±0.29

0.77±0.45

0.29±0.11

0.15±0.13

0.063±0.023

1.91±1.28

0.094±0.031

0.062±0.041

0.0072±0.0026

0.47±0.27

0.048±0.014

Ethylene

0.85±0.60

0.43±0.16

0.62±0.43

0.14±0.06

0.11±0.10

0.029±0.012

1.56±1.31

0.044±0.017

0.049±0.035

0.0034±0.0014

0.38±0.29

0.022±0.007

Propene

2.89±2.15

1.02±0.37

2.04±1.32

0.33±0.14

0.37±0.25

0.070±0.028

5.18±4.26

0.105±0.039

0.167±0.129

0.0081±0.0032

1.30±1.02

0.053±0.017

Benzene

1.07±0.62

0.88±0.29

0.78±0.47

0.28±0.11

0.14±0.12

0.060±0.023

1.93±1.23

0.091±0.031

0.063±0.040

0.0070±0.0026

0.48±0.28

0.046±0.014

Isopentane

1.22±0.93

0.90±0.27

0.89±0.76

0.29±0.10

0.16±0.12

0.061±0.021

2.18±1.85

0.092±0.029

0.070±0.055

0.0071±0.0024

0.54±0.42

0.047±0.013

Toluene

1.16±0.99

0.41±0.13

0.82±0.68

0.13±0.05

0.15±0.13

0.028±0.010

2.05±1.9

0.042±0.014

0.066±0.051

0.0032±0.0011

0.51±0.45

0.021±0.006

aRatiosderived

from

185wintertim

eobservationsin

w/w

atDononsite.

bData

from

Fontaine(2000)andFontaineandGalloo(2002).Theratiocalculationusesthefollowingform

:

ratio¼

0:85�

P jðE

Fcarbonyl;j�f j

"# p

assenger

car

þ0:15�

EFcarbonyl;diesel

�� co

mmercialcar

8 < :9 = ;

0:85�

P jðE

Fauto-exhaust

tracer;j�f j

"# p

assenger

car

þ0:15�

EFauto-exhaust;diesel

�� co

mmercialcar

8 < :9 = ;

,

whereEF(N

MHC,j)is

theEF

ofa

given

NMHC

forthemotortypej,

f jis

thefraction

in%

ofthe2000

urban

mileagerunning

by

themotortypej,

with

f non-catalyst

petrol

cars=30%,

f catalyst

petrolcars=31%,f non-catalyst

dieselcars=24%,f catalyst

dieselcars=15%.

938 A. Borbon et al. / Chemosphere 57 (2004) 931–942

derived from vehicle exhaust emissions (Table 1). Vehic-

ular emission data are part of a comprehensive pro-

gramme establishing the emission factors (EF, in

mg km�1) of about 200 VOC from the French running

passenger and commercial car (Fontaine, 2000; Fon-

taine and Galloo, 2002). Emission ratio calculation

(Borbon et al., 2003a) corresponds this time to the end

of the year 2000 and integrates the percentage of com-

mercial vehicles (15%) and catalyst diesel cars, which

are important emitters of carbonyl compounds (Fon-

taine and Galloo, 2002). While the ambient and emission

aldehydes/tracer ratios are in good agreement whatever

the considered tracer, ambient ketones/tracer ratios are

greater than the emission ones suggesting other forma-

tion processes in winter for ketones. Especially, atmos-

pheric oxidation of alkanes (propane, isobutane,

isopentane) would be an important source of acetone

in temperate Northern Hemisphere outside summer (Ja-

cob et al., 2002). Moreover, the chemical lifetime of ace-

tone is sufficient (P30 days) for mixing over large areas

contributing to elevated background levels. Conse-

quently, the apportionment of ketones will be based

on the vehicular emission ratios (Table 1), which sup-

ports other ratio values reported in the literature (Kirch-

stetter et al., 1999). On the contrary, the estimation

of anthropogenic aldehydes will use the ambient

wintertime ratios which are representative of realistic

conditions.

A second step is to apply the established ratio to

the tracer concentrations in order to calculate carbonyl

concentrations due to direct vehicle exhausts ([carbo-

nyl]modelled). Finally, the relative contribution of primary

and secondary formation is defined by comparing

[carbonyl]modelled to [carbonyl]measured. This approach in-

volves three main assumptions:

(1) the absence of sources other than traffic exhaust in

winter for both tracers and carbonyls,

(2) the non-heterogeneity of removal process (photo-

chemistry and mixing) during the transport of urban

air pollutants,

(3) an unchanged emission ratio all over the year.

Those assumptions remain arguable since:

• other sources might contribute to VOC presence in

winter,

• samples taken at different times of the year represent

air plumes with different histories,

• compounds have different chemical and physical

characteristics determining their atmospheric fate.

Consequently, the use of various tracers with differ-

ent chemical characteristics allows to determine the

standard deviation (SD) of the estimated contributions

by taking into account both removal process heteroge-

A. Borbon et al. / Chemosphere 57 (2004) 931–942 939

neity (dry and wet removal, chemical reactivity differen-

tials) and other possible contributions during the trans-

port of air masses (assumptions 2). Its calculation both

integrates the SD of the ratio representative of vehicle

exhaust emissions and the SD between the contribution

values provided by the six tracers. It is comprised be-

tween 16% and 21%. In order to counteract the evapora-

tive component of isopentane and toluene outside winter

(see Fig. 3 and Section 3.2), their concentrations have

been corrected according to the ratio between the sea-

sonal value of their regression slopes with acetylene.

Anyway, our estimate of anthropogenic contribution

to carbonyls should be viewed as an upper limit.

3.4.2. Results

Fig. 5 depicts the time series of the non-auto-exhaust

fraction of the most representative carbonyls.

Here, the non-auto exhaust fraction of lower alde-

hydes is mainly attributed to secondary formation. In-

deed, these compounds do not show a statistically

significant relationship with summertime isoprene. Sec-

ondary lower aldehydes are clearly affected by the sea-

son displaying a summer maximum. From autumn

(November) to early spring (end of March), our model

shows that vehicular exhaust could explain most of

aldehyde levels at Donon station: secondary fraction

is lower than 40% and generally around a 20% mean.

-20%

0%

20%

40%

60%

80%

100%

avr-9

7ju

in-9

7ao

ût-9

7oc

t-97

janv

-98

mar

s-98

mai

-98

août

-98

oct-9

8dé

c-98

mar

s-99

mai

-99

juil-

99se

pt-9

9dé

c-99

févr

-00

avr-0

0ju

il-00

sept

-00

nov-

00fé

vr-0

1av

r-01

juin

-01

août

-01

nov-

01

non-

auto

exh

aust

fra

ctio

n

-5

0

5

10

15

20

25

°C o

r W.m

-2

formaldehyde temperature radiation (values/50)

non-

auto

exh

aust

frac

tion

80%

85%

90%

95%

100%

avr-9

7ju

in-9

7ao

ût-9

7oc

t-97

janv

-98

mar

s-98

mai

-98

août

-98

oct-9

8dé

c-98

mar

s-99

mai

-99

juil-

99se

pt-9

9dé

c-99

févr

-00

avr-0

0ju

il-00

sept

-00

nov-

00fé

vr-0

1av

r-01

juin

-01

août

-01

nov-

01

non-

auto

exh

aust

frac

tion

-5

0

5

10

15

20

25

°C o

r W.m

-2

acetone temperature radiation (values/50)

Fig. 5. Temporal variations of the non-auto-exhaust fraction of carbo

daily mean value ± SD smoothed by the 15-day moving average.

Secondary formation processes become significant in

April and are predominant in summer with at least a

50% high intensity but generally above 80%. Analogous

trends were obtained by Possanzini et al. (2002) and

Bakeas et al. (2003) for the Rome and Athens metro-

politan areas, on the basis of the hourly summertime

and wintertime concentrations of formaldehyde and

acetaldehyde.

On the contrary, the anthropogenic contribution to

ketone levels is weak during the whole year, even in win-

ter. They do not exceed 5% for acetone and 15% for

alkylketones. Other processes dominate their levels dur-

ing the whole year corroborating Goldstein�s results

(2000). For acetone, secondary formation processes is

completed by biogenic emissions, especially in summer,

and other direct man-made emissions.

Whatever the carbonyl, its non-auto-exhaust fraction

is well correlated to ambient temperature and radiation

(Fig. 5): 0.70 6 r 6 0.79 (temperature) and 0.57 6

r 6 0.62 (radiation).

3.4.3. Focus on formaldehyde and acetone

Among the target carbonyls, special attention was

paid on the biogenic production of the well-known car-

cinogenic and irritative formaldehyde and the abundant

acetone.

Formaldehyde (HCHO), methylvinylketone (MVK)

and methacroleine (MACR) are the major products

-20%

0%

20%

40%

60%

80%

100%

avr-9

7ju

in-9

7ao

ût-9

7oc

t-97

janv

-98

mar

s-98

mai

-98

août

-98

oct-9

8dé

c-98

mar

s-99

mai

-99

juil-

99se

pt-9

9dé

c-99

févr

-00

avr-0

0ju

il-00

sept

-00

nov-

00fé

vr-0

1av

r-01

juin

-01

août

-01

nov-

01

-5

0

5

10

15

20

25

°C o

r W.m

-2

acetaldehyde temperature radiation (values/50)

80%

85%

90%

95%

100%

avr-9

7ju

in-9

7ao

ût-9

7oc

t-97

janv

-98

mar

s-98

mai

-98

août

-98

oct-9

8dé

c-98

mar

s-99

mai

-99

juil-

99se

pt-9

9dé

c-99

févr

-00

avr-0

0ju

il-00

sept

-00

nov-

00fé

vr-0

1av

r-01

juin

-01

août

-01

nov-

01

non-

auto

exh

aust

fra

ctio

n

-5

0

5

10

15

20

25

°C o

r W.m

-2

MVK EMK temperature radiation (values/50)

nyl compounds at Donon station. Grey curves correspond to the

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%HCHO (other precursors)HCHO (auto-exhaust)HCHO (isoprene)

(a) formaldehyde (HCHO)

0

1

2

3

4

5

6

7

Jan

Jan

Feb

Feb

Mar

Mar

Apr

Apr

May

May

Jun

Jun

Jul

Jul

Aug

Aug

Sep

Sep

Oct

Oct

Nov

Nov

Dec

Dec

months

µg.m

-3

biogenicC3H6OmeasuredC3H6O

(b) acetone (C3H6O)

Fig. 6. Monthly mean contributions to formaldehyde and acetone levels at Donon station. Vertical bars for acetone correspond to the

monthly SD.

940 A. Borbon et al. / Chemosphere 57 (2004) 931–942

identified and quantified in the atmospheric photooxi-

dation of isoprene via OH radical, NO3 radical and O3

(Paulson et al., 1992). In particular an attempt was

made to estimate the concentration of HCHO attribut-

able to isoprene photooxidation ([HCHO]isoprene), the

secondary biogenic pathway. To do so, the method de-

scribed by Duane et al. (2002) was applied:

½HCHO�isoprene ¼ fHCHO�isoprene;

where fHCHO is the total fractional yield of HCHO

from isoprene (0.63) as reported by Carter and Atkin-

son (1996) and Disoprene, the ppbv-concentration of

reacted isoprene, can be obtained from: Diso-prene = 0.5 [MACR]/0.22 + 0.5 [MVK]/0.35 where the

terms 0.22 and 0.35 are the respective photochemical

yields of MACR and MVK determined in smog

chamber.

The monthly mean contributions to formaldehyde

levels are plotted in Fig. 6(a). As it appears, the

proportion of formaldehyde attributed to isoprene

oxidation is maximum in July but does not exceed

10%; anthropogenic precursor photooxidation being

5 times greater. These results are lower than Duane�sfindings in northern Italy (2002). The method is based

on the assumption that MACR, MVK and HCHO

act as a reservoir collecting all the reacted isoprene

but during summertime intense photoreactive episodes

it cannot be excluded that these products are de-

pleted. Consequently, the HCHOisoprene fraction might

be underestimated. Moreover, summertime isoprene

and its oxidation product levels are greater at the

Italian site indicating more favourable oxidative con-

ditions. Finally, formaldehyde levels at Donon station

would be mainly controlled by anthropogenic precur-

sors photooxidation and diluted anthropogenic emis-

sions.

The biogenic impact on acetone mixing ratios at

Donon station can be illustrated by its significant linear

relationship with the biogenic emission tracer isoprene

in summer: [C3H6O] = 1.59 · [C5H8] + 2.45 (r = 0.62).

Consequently, biogenic acetone was determined by the

product of isoprene mixing ratios and the regression

slope (1.59) thought to be representative of acetone/iso-

prene biogenic emission ratio. Results should be viewed

as an upper limit and are reported in Fig. 6(b). As ex-

pected, biogenic acetone is clearly affected by the season

displaying a summer maximum where it represents

37 ± 25% of acetone mixing ratios corroborating Gold-

stein�s estimations in 2000 (45 ± 12%). On the contrary,

the biogenic fraction of acetone is negligible in winter

(5 ± 4%) suggesting that wintertime acetone mixing ra-

tios are mainly controlled by other primary or secondary

processes formation. In spring and autumn the biogenic

fraction respectively reaches 10% (±4%) and 20%

(±19%).

4. Conclusion

The analysis of a 5-year VOC data set has provided

important insights on factors that control the temporal

distribution of volatile organic compounds at rural

scale. The analysis was achieved by a source–receptor

approach that could be easily transposable to other

areas.

A. Borbon et al. / Chemosphere 57 (2004) 931–942 941

(1) From a simple OH-photochemistry based model,

the importance of photochemical removal, in-situ

emissions and dynamics was estimated for C2–C9

NMHC. In winter, most of rural NMHC result

from the dilution of urban air masses whilst, in

summer, photochemical removal generally domi-

nates for the compounds with an atmospheric life-

time of a few hours. Local biogenic emissions also

dominate the distribution of rural isoprene in

summer.

(2) From the ratios of carbonyls with criteria emission

tracers, the relative intensity of their primary

sources (anthropogenic and biogenic) and second-

ary sources was estimated. Their temperature and

radiation dependency was also demonstrated.

The following task in the characterisation of VOC

environmental impact would be the assessment of their

effects on ozone production and, consequently, human

health and ecosystems.

Acknowledgments

This work was financially supported by the French

Ministry of Environment and the environmental agency

ADEME. The authors would like to thank all the sam-

pling operators at Donon station as well as the analyti-

cal laboratory members. We are also grateful to Y.

Sander from the ASPA for the VOC urban data and

Ms Coquelle for her linguistic comments.

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