NO 2 INTERCOMPARISON AT THE EUPHORE SIMULATION CHAMBERS DURING THE FIONA CAMPAIGN

1. EUROCHAMP 2 Exp. 18.05.2010: m-nitrite, isopropyl nitrate *1 Exp. 20.05.2010: isoprene, a-pinene Exp. 24.05.2010: t-buthylnitrite *2 NO2 INTERCOMPARISON AT THE EUPHORESIMULATION 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: mila@ceam.es 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 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. 2:DOAS set-up at EUPHORE 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). 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 particle systems are used to follow the reactions. Also, physical properties are monitored (P, t, humidity, solar radiation) for a better characterization of the chemical processes. 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. 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. DESCRIPTION OF EXPERIMENTS 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. 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: Fig. 3: Schematic of the Open path -IBBCEAS UCC 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. • CONCLUSIONS • The FIONA campaign allowed the intercomparison of several instruments for the measurement of NO2. • There is a good agreement among the optical systems (except for the BBCEAS-UCC), that did not show interferences within the different scenarios tested. • 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. • 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. • 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. • 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. RESULTS Fig. 4: NO2 temporal profiles Fig. 6: NO2 temporal profiles *1: from 10:15 to 15:04 *2: from 6:50 to 11:32 . K.H. Becker: The European Photoreactor EUPHORE, Final Report of the EU project, EV5V-CT92-00591996 .J. Chen and D. S. Venables, A broadband optical cavity spectrometer for measuring weak near-ultraviolet absorption spectra of gases, Atmos. Meas. Tech. Discuss., 3, 4571-4602, 2010. .J.M. Langridge, S.M. Ball and R.L. Jones, A compact broadband cavity enhanced absorption spectrometer for detection of atmospheric NO2 using light emitting diodes Analyst, 131, 916-922, 2006. .P. Mikuška, Večeřa, Z. (1992). Determination of nitrogen dioxide with a chemiluminescent aerosol detector. Anal. Chem. 64, 2187-2191 .P. Mikuška, Večeřa, Z. (2000). Effect of Complexones and Tensides on Selectivity of Nitrogen Dioxide Determination in Air with Chemiluminescence Aerosol Detector. Anal. Chim. Acta 410, 159-165 .M. Ródenas. et al (2006). Avances en la aplicación de técnicas DOAS. DEA U. Valencia  .M. Ródenas (2008). Improvements in Spectroscopy data processing: Faster production and better reliability of lab data . ESF-INTROP Report .S.M. Ball and R.L. Jones Broadband cavity ring-down spectroscopy, Cavity ring-down spectroscopy: Techniques and applications, edited by Giel Berden and Richard Engeln, Blackwell Publishing Ltd, 2009. Fig. 5: NO2 temporal profiles Table 1: NO2 correlations vs DOAS Acknowledgements: Generalitat Valenciana, EUROCHAMP-2, CONSOLIDER –INGENIO 2010 (GRACCIE) and Fundación Bancaja, for supporting this work European Geosciences Union (EGU) General Assembly 2011 Vienna 3-8th April 2011