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NO2 INTERCOMPARISON AT THE EUPHORE SIMULATION CHAMBERS DURING THE FIONA CAMPAIGN
M. Ródenas1, A. Muñoz1, M. Vázquez1, E. Clemente1, F. Alacreu1, P. Mikuška2, Z. Večeřa2, D.S. Venables3, J. Chen3, M. Daniels4, S. Ball4, A.A. Ruth3, H-P. Dorn5, R. Varma6
1Instituto Universitario CEAM - UMH, Spain, 2Institute of Analytical Chemistry AS CR –Brno, Czech Republic, 3Chemistry Dept., Physics Dept., Environmental Research Institute, University College Cork, Ireland, 4University of Leicester, UK,
5Forschungszentrum Jülich, ICG-2, Germany, 6National Institute of Technology - NIT Calicut, Rep. of India
contact: [email protected]
Nitrogen dioxide plays a vital role in atmospheric chemistry, with important implications for climate change and air quality. NO2 is mainly emitted by combustion processes and by natural sources like lightning and soil, and plays a key part in the
production of tropospheric ozone which is both a greenhouse gas and a component of poor air quality that is particularly harmful to biological systems. In addition, the reaction of NO2 with OH forms nitric acid, one of the main components of acid rain.
This work reports results from experiments carried out during the FIONA (Formal Intercomparison of Observations of Nitrous Acid) campaign held at the EUPHORE simulation chambers in May 2010. Whilst the primary aim of the campaign was to
compare HONO measurement methods, several of the instruments deployed at FIONA were also able to accurately quantify NO2. Here we present a comparison of NO2 datasets obtained by differential optical absorption spectroscopy (1 instrument),
broadband cavity-enhanced absorption spectroscopy (3 instruments with different configurations), a commercial NO-O3 Chemiluminescence monitor and a NO2 – luminol Chemiluminescence monitor.
A general description of the FIONA experiments is provided, and the NO2 datasets are compared and examined for possible interferences based on the working principles of the instruments.
EUPHORE DESCRIPTION
Daytime reactions Photooxidation
Nocturnal
reactions
EUPHORE (Valencia, Spain) is one of the major outdoor smog
chambers existing for the study of photochemical processes
that take place in the atmosphere. EUPHORE consists of two
identical half-spherical FEP (fluorine-ethene-propene) foil
chambers, mounted on aluminum floor, that is transparent to
sunlight in more than 80% above 300 nm. An air drying and
purification system supplies the chamber with clean air. This
allows simulating real conditions with a low ratio of wall-effects
due to the large volume and shape of the chambers.
INSTRUMENTS
DOAS CEAM
The DOAS (Differential Optical Absorption Spectroscopy) device consists of a Xenon short-arc lamp together with a telescope that collimates
the light into a narrow beam. This beam passes through a White type f/53.3 multi-reflection cell and is received by a Newton telescope,
focusing the light on the entrance slit of a f/6.9 Czerny-Turner spectrograph with 0.5 m focal length (Acton Spectra Pro 5).
In the FIONA experiments a spectral resolution of FWHM 0.7 nm was selected, and mirrors with special dielectric coating were mounted
allowing an optical path length of 898 m (base path 8 m). The analysis of the spectra was done in the range 336-373 nm allowing the
simultaneous analysis of several species. DOASIS was used for this purpose together with an improved software developed at CEAM.
Fig. 1: EUPHORE simulation chambers
The chamber used for the experiments described here has a volume of approximately 195 m3 and two mixing fans to ensure homogeneity of the
reaction mixtures within less than 2 min. A number of ports situated on the floor of the chamber are available for the introduction and sampling of
reaction mixtures. A retractable steel housing surrounds the chamber is used to control the time of exposure to sunlight.
A wide variety of instruments ranging from spectroscopic, monitors, chromatography and
systems
are
used
toinfollow
Also,
May particle
18th 2010: Clean
conditions:
HONO
/ NOx
dark andthe
sunlitreactions.
chamber
physical properties are monitored (P, t, humidity, solar radiation) for a better characterization
of the chemical processes
Scheduling Chamber
Motivation.
- HONO/NOx addition.
- Open roof after to form OH.
- m-nitrite and water
Afternoon-1
- Open roof
Morning
The FIONA campaign took place at the EUPHORE chambers in May 2010. A
description of the campaign can be found in the poster EGU2011-8736 (XY164) and
oral AS3.1 at 11:45h 6th May 2011.
Ten experiments were conducted. Here we show the results obtained in three of them,
addressing different scenarios:
35
10
10:00
12:00
14:00
25
20
16:00
10
5
8:00
10:00
12:00
Lum Chem-IACH
DOAS-CEAM
Monitor-CEAM
Fig. 4: NO2 temporal profiles
NO2 H2O
Isoprene NO
a-Pinene
Close
O3
Open
NO2 Concentration [ppb]
18:00
BBCEAS-U.Cork
BBCEAS-U.Leicester
Open IBBCEAS-U.Cork
DOAS-CEAM
Flushing
80
Monitor-CEAM
BBCEAS-U.Cork
Lum Chem-IACH
BBCEAS-U.Leicester
Open IBBCEAS-U.Cork
60
40
20
0.627
0.663
1.082
1.004
1.100
1.739
5.328
-4.340
1.120
0.711
0.9384
0.9878
0.9569
0.9976
0.9851
10:00
Monitor-CEAM
BBCEAS-U.Leicester
12:00
Time [hh:mm]
BBCEAS-U.Cork
Open IBBCEAS-U.Cork
14:00
Lum Chem-IACH
DOAS-CEAM
Fig. 5: NO2 temporal profiles
European Geosciences Union (EGU) General Assembly 2011 Vienna 3-8th April 2011
16:00
Monitor-CEAM
BBCEAS-U.Cork
BBCEAS-U.Leicester
Open IBBCEAS-U.Cork
0.157
0.645
0.937
0.972
3.267
3.265
-0.416
1.827
0.3334
0.9769
0.9978
0.993
Table 1: NO2 correlations vs DOAS
• 2-nitrophenol produced an interference in the optical systems since it absorbs in the UV. Those instruments
that used its reference in the data analysis avoided this interference.
• The commercial Monitor-CEAM showed a negative interference with nitrites and its products, as well as low
concentrations that should be studied further given its implications as a widely used instrument in both field
and laboratories.
• The interference with H2O shown by the Lum Chem-IACH Monitor is most probably due to the location of
the instrument in the chamber: close to the system of addition of H2O.
• Although the amount of interfering species added to the chambers was much greater than expected in the
ambient atmosphere, more agreement was expected among the techniques. Further studies are required on
this work.
Exp. 24.05.2010: t-buthylnitrite *2
8:00
IBBCEAS UCC
The U. College Cork instrument was an IBBCEAS system similar to that previously reported (J.Chen and D.S.Venables, 2010). Light from a LED was focused into a 2 m optical
cavity. Chamber air was sampled at 2 L min-1. Sampled gas had a residence time of 160 s in the cavity. Light leaking out of the cavity was bandpass filtered (Semrock 365/44)
and coupled into one end of a high UV transmission Y fibre bundle connected to a 163 mm focal length spectrograph with a CCD detector (Andor SR-163 and iDUS 420A BU).
The spectrograph resolution was ca. 0.3 nm. The concentration of NO2 was quantified using the DOASIS spectral analysis package over the window 352 - 373 nm.
During the campaign, the reflectivity of the cavity mirrors had a value of 0.9992 at 365 nm. The instrument was located on the ground floor of the CEAM facility, requiring a
sample inlet line of about 4 to 5 m. The large thermal gradients occurring during some experiments resulted in some misalignment of the optical cavity.
• Changes in the path length of the BBCEAS-UCC instrument occurred due to thermal instabilities of the
system during the experiments. This fact, together with the use of a long sampling line would help to explain
the differences encountered.
R2
ax-b
a
b
2
R
1
ax-b
a
b
Monitor-CEAM
0.530
1.819
0.8545
Exp. 18.05.2010: m-nitrite, isopropyl nitrate *
BBCEAS-U.Cork
0.399
7.690
0.3719
Monitor-CEAM
0.530
1.819
0.8545
Lum
Chem-IACH
0.665
3.103
0.4873
BBCEAS-U.Cork
0.399
7.690
0.3719
BBCEAS-U.Leicester
1.045
-1.737
0.9846
Lum Chem-IACH
0.665
3.103
0.4873
Open
IBBCEAS-U.Cork
1.171
-1.142
0.9845
BBCEAS-U.Leicester
1.045
-1.737
0.9846
Open IBBCEAS-U.Cork
1.171
-1.142
0.9845
2
R
ax-b
a
b
Exp. 20.05.2010: isoprene, a-pinene
100
0
6:00
16:00
Fig. 6: NO2 temporal profiles
NO2 intercomparison. FIONA. 20.05.10
120
14:00
Time [hh:mm]
BBCEAS-U.Cork
Open IBBCEAS-U.Cork
Fig. 3: Schematic of the Open path -IBBCEAS UCC
Open-Path IBBCEAS UCC
The open-path incoherent broadband cavity-enhanced absorption spectroscopy setup (see Fig. 3) consisted of a transmitter unit and a
receiver unit, each containing one of the cavity mirrors (R=0.999 at 375 nm, r = -7m). Both units were placed into the EUPHORE
chamber thereby forming a cavity of length d = 664 cm. The transmitter unit housed two temperature stabilized UV LEDs, whose output
was combined by means of a branched (Y-shaped) light guide to cover a spectral range from ~350-400 nm. The receiver unit housed
the monochromator/CCD assembly with a spectral resolution of 0.2 nm. A purge of 10 dm3 /min was applied to both cavity mirrors. The
analysis was based on a singular value decomposition linear least square fit procedure ,applied to stray light- and pressure-corrected
spectra.
• Since the main aim of FIONA was the study of HONO, the instruments were optimized to measure HONO,
and not NO2. Also, the experiments were chosen to test HONO interferences, therefore other specific NO2
interfering compounds should be studied.
15
0
6:00
-5
ECO Physics Monitor CEAM
NOx-ECO Physics -Alppt 77326 (NO, NO2 and NOx, ppb): This monitor measures the NO, NO2 and NOx (ppb) concentration directly from the chamber. It has two independent
units: the analyzer CLD 770 Alppt and the photolytic converter PLC 760. The principle of operation of the CLD 770 Alppt analyzer is the gas phase chemiluminescent reaction of
nitric oxide (NO) with ozone (O3). The photolytic converter PLC 760 performs a selective conversion of NO2 to NO through photo-dissociation with a xenon lamp.
• There is a good agreement among the optical systems (except for the BBCEAS-UCC), that did not show
interferences within the different scenarios tested.
30
Time [hh:mm]
Monitor-CEAM
BBCEAS-U.Leicester
Flush Stop
Close
Flush
H2O2
20
8:00
Stop 2-Nitrophenol
Flush
Open
IACH Monitor
IACH monitor of NO2 operates on the principle of the chemiluminescent reaction of NO2 with an alkaline solution of luminol (Mikuška and Večeřa, 1992). The composition of
luminol solution was optimised to minimise interference by gaseous co-pollutants (Mikuška and Večeřa, 2000). Time resolution of the measurement is 1 s. The detection limit of
NO2 was 0.025 ppb (v/v) (S/N=3) and the calibration graph was linear in the range from 3 to 665 ppb of NO2, RSD is 3.5 % at 0.5 ppb.
The FIONA campaign allowed the intercomparison of several instruments for the measurement of NO2.
40
t-bNitrite HONO t-bNitrite
Flush
BBCEAS U.Leicester
Broadband cavity enhanced absorption spectroscopy (BBCEAS) is a continuous-wave variant of cavity ring-down spectroscopy [Langridge et al., 2006; Ball & Jones, 2009].The
University of Leicester’s LED-BBCEAS instrument uses the output from a light emitting diode (LED) to pump a high finesse optical cavity. The reflectivity of the cavity mirrors used
for the FIONA campaign (Rmax = 99.98%) enabled path lengths of up to 3.5 km (baseline length = 77 cm). DOAS is then applied to separate the spectral contributions of the
various over-lapping molecular absorption features.
For the FIONA campaign, the LED-BBCEAS operated with a spectral bandwidth of 363 - 401nm. Typical detection limits were 0.4 ppbv for NO2 (1 minute integration time).
CONCLUSIONS
NO2 intercomparison. FIONA. 24.05.10
NO2 Concentration [ppb]
NO2 Concentration [ppb]
May 18th 2010: Clean conditions: HONO / NOx in dark and sunlit chamber
Scheduling Chamber
Motivation
- HONO/NOx addition.
Morning
Photolytic reformation of the HONO/NOx system
- Open roof after to form OH.
- m-nitrite and water
Hydrolysis of methyl nitrite on wet surfaces.
Afternoon-1
- Open roof
Study of interferences.
Formation of nitrite from organic nitrates in the
Afternoon-2 - Isopropyl nitrate
aqueous samplers
May 20th 2010: Isoprene nitrates in gas phase and heterogeneous phase
Scheduling Chamber
Motivation
Morning
- Flushed, dark and humid
chamber (RH: 40%).
Isoprene oxidation by photolytically formed OH
- Add isoprene and NO.
leading to organic
nitrates
in gas phase.
NO
intercomparison.
FIONA.
18.05.10
2
- Open roof after to form OH.
Afternoon
- -pinene ozonolysis to generate Study influence of particle-bound organic nitrates.
40
NO2 HONO Flush Stop Open Close
Stop m-Nitrite
Close
particles.
Flush
H2O
H2O
Open
isop-Nitrate
Flush
May 24th 2010: Photolysis of nitrophenols
Scheduling 30 Chamber
Motivation
Morning
- t-butyl nitrite
Interference test optical systems
- HONO addition
Afternoon
- Photolysis of 2-nitrophenol
Interference against nitrophenols
0
6:00
Photolytic reformation of the HONO/NOx system
Hydrolysis of methyl nitrite on wet surfaces.
Study of interferences.
Formation of nitrite from organic nitrates in the
Afternoon-2 - Isopropyl nitrate
aqueous samplers
May 20th 2010: Isoprene nitrates in gas phase and heterogeneous phase
Scheduling Chamber
Motivation
Morning
- Flushed, dark and humid
chamber (RH: 40%).
Isoprene oxidation by photolytically formed OH
- Add isoprene and NO.
leading to organic nitrates in gas phase.
- Open roof after to form OH.
Afternoon
- -pinene ozonolysis to generate Study influence of particle-bound organic nitrates.
particles.
May 24th 2010: Photolysis of nitrophenols
Scheduling Chamber
Motivation
Morning
- t-butyl nitrite
Interference test optical systems
- HONO addition
Afternoon
- Photolysis of 2-nitrophenol
Interference against nitrophenols
DESCRIPTION OF EXPERIMENTS
R
E
S
U
L
T
S
Doas scheme
Fig. 2: DOAS set-up at EUPHORE
*1: from 10:15 to 15:04
*2: from 6:50 to 11:32
Acknowledgements:
Generalitat Valenciana, EUROCHAMP-2, CONSOLIDER –INGENIO 2010 (GRACCIE) and Fundación Bancaja, for supporting this work
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