Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
Laboratory tests for the development of a new
high uptake rate passive sampler for nitrogen
dioxide measurements
A. Minguy, H. Plaisance, J.-C. Galloo & R. Guillermo
Ecole des Mines de Douai, Diparternent Chimie et Environnement,
Frnnce
Abstract
Outdoor measurements provided by continuous monitors are inappropriate to
assess nitrogen dioxide personal exposure because people spend most of their
time in indoor environments. A passive sampler is a good alternative.
Unfortunately, it can only provide an integrated concentration measure due to the
long sampling time required to obtain reliable results.
The department developed a new passive sampler which is 45 times as
sensitive as a Palmes tube and can provide reliable measures on a very short
sampling period (in the order of one hour).
Uptake rate and environmental factors affecting this sampler performances
(such as wind speed, temperature, humidity) have been determined thanks to an
exposure chamber.
It was tested in a first pilot study involving volunteers in order to assess
NO2 personal exposure of city-dwellers living in a big city in northern France.
1 Introduction
Nitrogen dioxide is a very ubiquitous pollutant, which is produced in outdoor
environments as well as in indoor environments. Health effects of the air
pollution depend on the concentration to which people are exposed. Previous
studies have shown that personal exposure to NO, depends on indoor
environment characteristics (ventilation, indoor source presence such as gascookers or cigarette smoke ...) rather than on outdoor NOz levels [l]: [2].
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
Consequently, it seems that personal sampling should be preferred for
personal NO, exposure assessment. Passive sampling is a good means but this
easy to use method needs a long exposure time to provide reliable measures.
The department has designed a new type of passive sampler which is able
to perform reliable measures on very short sampling periods (in the order of one
hour) and hence to distinguish different rnicroenvironnlents in personal
exposure.
This sampler was developed in laboratory conditions by means of an
exposure chamber experimental system. Uptake rate as well as wind speed,
temperature, and relative humidity effects have been e\duated. Then, this
passive sampler was used in a first pilot study to assess NOz personal exposure
of city-dwellers living in Lille, a big city in northern France.
2 Alaterials and methods
2.1 The new passive sampler
Passive sampling is performed by a concentration gradient existing from the
absorption media (concentration is assumed to be equal to zero) to the sampler
exterior (ambient air concentration). The ambient concentration can be
calculated according to the first Fick law integration with the following equation:
C : coilcentration measured by passive sampler ( ~ g . r n . ~ )
Q : amount of absorption product present in the sampler (p:)
d , : uptake rate (m3.s~')
t : sampling time (S)
The new passive sampler is composed of a porous plece impregnated \i.ith
the trapping solut~onand placed in a cylindrical protection box with caps at its
t n o extremities (see fig. 1). Each cap is drilled 1~1tha screm- tlircad in its centre.
The superior cap IS screwed on a detachable transversal bar. The inferior cap is
screu-ed on a fixed transversal bar. The porous plecr is manufactured in highdensit). polyethylene and is equipped ~ v i t ha thread allowmp it to be screlhed on
the detachable superior bar.
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
Two cap types have been studied. They are both circular with a central
proti-usion to maintain a 4 mm calibrated space. The second type presents a
c~rcularedge designed to reduce the wind effect on the sampling. Thus, two
sa~nplerversions were sh~died(with and without circular edges on the caps).
The porous piece is impregnated with a TEA (triethanolaimine) aqueous
solution to trap h-0,(10% (WV)TEA and 0.3?0 (V V) Brij 35 (polyoxyethylene
dodecyl ether)) and then preserved in test tubes hernletically sealed before and
after exposure.
This nelv passive sampler has two circular openings at its extremities and a
large absorption surface (porous piece surface) which allow to have a high
uptake rate. The porous piece cylindrical shape limits the extraction volume used
to desorb the reaction products and therefore increases the method sensitivity.
The extraction is perfonned in test tubes adding 5 rnL of ultra pure \vater.
The NO, sampled inolecules are detected as nitrite ions in the TEA solution.
xibite ions are analysed by ion chromatography. This technique was preferred to
the c o ~ ~ m ~ o used
n l y spectrophotometry method on account of better sensitivity
PI.
Several analytical parameters were optimised:
X 10 nxno1.L.' sodium hydroxide eluent is used to obtain a good
separation of nitrite and chlorite peaks;
A large 500 uL injection loop is used to decrease the analysis detection
limit.
Chromatograms of an exposed porous piece and of an unexposed one
(blank) are presented in figure 2.
F15ure l : Cross sectlon of the passive sampler. The second cap \.ersion \\.it11
circular edges is represented in dotted line.
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
Figure 2: At the top: unexposed sampler analysis. at the bottom: analysis of a
'
for 4 hours. The nitrite measured
sampler exposed at 67 p g . ~ n - KOl
concentrations are 0.009 mg.L-' for the unexposed sampler and 0.147
m g L ' for the exposed sampler.
2.2 The exposure chamber system
The exposure chamber is cylindrical and composed of borosilicated glass. Its
volume is 30 L. It comprises a detachable cap to facilitate the sampler placing
and withdra~ving.It contains a tray to lay the samplers and three fans connected
to a variable voltage generator to produce wind speeds from 0 to 2.23 m.s-l in the
chamber. The latter is placed in a thermostatic enc1osu1.e which can reach
temperatures between 0 and 40°C (see Fig. 3). The air is produced by a
compressor and is purified by a zero air supply. A first air flow consists of a high
NO, concentration bottle dilution operated by a blender . A second air flow
coming from the zero air supply runs through a \vater fitted bubbler to provide a
hunlidih saturated air at a rate regulated by a mass flou contl-oller. The t\vo
flows are mixed at the exposure chamber intake. generating a NO1 concentration
and humidity controlled air tlow. Relative humidity mhich can be reached is
included betneen 0 and 90?6.A probe is inserted into the chamber to measure
wind speed. temperature and relative h ~ ~ n i i d iduring
h,
the tests.
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
Voltmeter
Monltor
H g h NO: concentration
bottle
Figure 3: Schema of the exposure chamber system
3 First tests
3.1 U p t a k e rates
The sampler uptake rates \\ere estmated under the f o l l o n ~ n gc o n d ~ t ~ o nIns
the e\posure chamber a temperature of 20uC. a relatl\ e h u l n l d ~ hof 50' O. an
a\elage \ ~ ~ nspeed
d
of 0 S m s '. as recommended 111 the European standard
ploject prEn 13528 [-L] and s e ~ e r a samplers
l
n e r e mtroduced In the chamber for
d~tferentNO1 concentlatlons for a p e r ~ o do f 4 hours The results obtamed f o ~the
trio m n p l e ~belslons ale plesented In table 1
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
Table 1. Uptake rate for the two sampler versions
/
1
\I ltliout edge
!
Lession
Edge eqmpped /
Lerslon
1
Number of
measures
Mean uptake rate
jcm'.s-')
20
1 62
9
0 95
95% confidence
interval (cm5.s-')
1
50073
1
i 0 128
3.2 Wind speed effect
B) changing the voltage provided to the exposure chamber fans, different wind
speeds could be obtained. Many positions on the chamber t r q were selected to
expose the passive sampler to a large range of wind speeds. Samplers were
exposed at these positions under the following conditions: a relative humidity of
50 %. a temperature of 20°C and a NO2 concentration close to 50 pg.m-' for 3
hours. The results obtained are shown in figure 1.The experimental points
follow a In-shaped curve: which had already been demonstrated for Pahnes tubes
and badges in previous studies [j]:[ 6 ] .
The edges equipping the caps seem to limit the wind speed effect
efficiently. Above 0.3 m.s", the edge equipped version uptake rate appear not to
be dependent on the wind speed anymore.
The wind speed effect remains particularly important for weak wind speeds
(3976 increase between 0.08 and 0.30 1n.s-l).
-
-
p
-
* V 1t11o~1t
edge \ ession
" Edge equipped
\elSIOIl_~
-
P
-
F ~ ~ L 4:
I I -LVind
e
speed effect on the snn~plingrate for the tmo types of samplers.
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
3.3 Temperature influence
Tests were made at 5°C. 2OCCand 30°C.Other parameters were maintained
constant; relative humidity of 50%, wind speed of 0.5 m.s" and KO2
concenh-ation close to 50 pg.m-' for a period of 4 hours.
A similar incl-ease of about 214 per degree C was o b s e ~ ~ efor
d the tu.0
passive sampler versions. This increase seems to be linear.
3.4 Humidity influence
Samplers were tested at 20%, 35%, 4094,5056 and 80% RH. All tests were
proceeded at a temperature of 20°C and at an average wind speed of 0.5m's and
lasted 4 hours. XO, concentration was set on aa-erage at 50 pg.m~'.The sampling
rate is constant for the two sampler versions for relative humidities superior to
50%. There is a decrease of the uptake rate for the two sanlpler versions for
relative humidities below 40°4.This decrease seems to be more limited for the
edge equipped passive sampler version.
4 Application example
The edge equipped passive sampler was tested on 13 volunteers living in greater
Lille. a big city in northern France.
Thls feasibility study was carried out to know if real time personal
exposure measures were possible in all n~icroenaironmentswith this passive
sampler.
The esperiment was carried out for a weekday and for a v, eekend day. Four
m~croenvii-oilmelitswere considered: house. other indoor places (workplace or
other collective buildings), transport (car, motorbike, b i c ~ d e ,train. bus or
suburban trip) and outdoors. Each volunteer was provided a sampler with four
pal-ous pieces (one for each microenaironment type). and tu.0 questionnaires: the
first one about home and workplace characteristics and the second one to fill out
during the sampling about activities (time-activity diary). They \Tore the sampler
for 23 hours (from 12:OO to 12:OO) and changed the porous piece each time they
changed of n~icroenviro~ment.
They carried over each porous piece change on
1112 time-activity diary and noted particular situations (if they were standing nest
to smokers for example).
Concentl-ation levels in the different mlcroenvironments considered are
shon.11 in figure 5. The highest concentrations n.ere found ln transport and
outdooi-S. often esceeding 100 pg.m-" Differences are observed betr-een
n-eekday and n-eekend day transport and outdoor concentrations. This can be
easlly explained by the fact that eaffic is denser and consequently generates
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
more pollution on weekdays. Concentrations measured in houses are weak
(around 20 pg.m-3) and similar for the weekday and the weekend day. Weekday
traffic increase does not seem to affect house concentration levels.
Concentrations are hlgher in other indoor places. The possible explanations are: a
better isolation in houses due to the energy control policy, whlch limits the
pollutant penetration into houses; the presence of environmental tobacco smoke
in collective indoor places (restaurants and cafes) and, in some cases, special
c o o l n g processes (such as barbecues in restaurants which represents the highest
recorded level). Personal exposure levels are close to indoor concentrations (see
figure 5) due to the high part of time spent in these microenvironrnents (more
than 90% of total time). The indoor environments contribute on average for more
than 80% to personal exposure, whereas transport and outdoor places appear to
have a minor importance (see fig.6).
5 Conclusion
The new passive sampler developed can provide reliable measures on a very
short sampling time (one hour). Sampling rate as well as temperature, wind speed
and humidity effects have been determined for the ks.0 passive sampler versions.
The edge equipped cap version is less sensitive but less wind speed influenced
than the simple cap equipped version.
It will be necessary to correct the passive sampler measures with the
relations deduced from the exposure chamber tests, particularly in case of
extreme meteorological conditions (weak relative humidities, weak wind speeds
and hot or cold temperatures).
The edge equipped version was found to be 45 times as sensitive as a
Palmes tube. This version was retained to lead a personal exposure campaign on
volunteers living in greater Lille, a big city in northern France. Highest
concentrations were found in transport and outdoors. In these
microenvironrnents, concentrations differed betueen weekdays and weekend
days, whereas it was not the case for house microenvironment. For the latter
microenvironment, weekday traffic increase had no influence on NO2
concentration. Personal exposure levels were close to indoor concentrations.
Indoor NOz levels were found to be deciding for personal exposure.
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
Type of microenvironment
Figure 5 : Medians, minima and maxima of the :oncentrations ineasured ill the
Outdoors
Transpo~t
C3 Other indoor places
3 House
v, eekday
v, eekend day
to personal exposure.
Figr~re6: Contributions of the different microell\-~ro~ullents
Transactions on Ecology and the Environment vol 47, © 2001 WIT Press, www.witpress.com, ISSN 1743-3541
References
[ l ] Fischer, P., Bmnekreef, B. Pc Boleij, J.S.M. Indoor NO, pollution and
personal exposure to NO, in two areas with different outdoor NOZ pollution.
E m ~ i ~ . o i z i ~ wMoniforing
~tnl
and Assessrnenr, 6 , pp. 22 1-229, 1986.
[2] Monn, C.. Brandli; 0..
Schindler, C. et al. Per-sonal exposure to nit~ogen
dioxide in Switzerland. The Science ofthe Total Envi~~oninent,
215, pp. 243251, 1998.
[3] Millel-. D.P. Ion chromatographic analysis of Palmes tubes for nitrite.
At~nospl~ei~ic
Environment, 18 (1),pp. 891-892, 1984.
[ 3 ] European standard project prEn 13528 : Ambient alr quality-Diffusive
samplers for the detemination of the concentmtions of gases and vapoursRequirements and tests methods. 1999.
[ j ] Yanagisawa, Y., Hemphill, C P . ? Spengler. J.D. & Ryan, B. Wind effect on
adsol-ptlon rate of NO, passive sampler, palmes tube and filter badge. Proc.
of the
A111711d Meeting of the Air Polhtion Control Asso~icltioiz:
Miilneapolis, Minnesota, pp 1- 13, 1986.
[6] Plaisance, H. & Minguy, A. Etude des perfornmlces en chambre d'exposition
n c ela
des tubes a diffusion NO2.. rapport Laboratoire Centml de S ~ ~ r ~ e i l l n ci'e
QuniirP de l'llir. Ecvle des Mines de Douai. 1. 2000.