1. DOAS AS AN COMPLEMENTARY TOOL FOR LIDAR MEASUREMENTS R. Jimenez, I.Balin, H.van den Bergh and B. Calpini Laboratory for Air and Soil Pollution (LPAS) Swiss Federal Institute of Technology (EPFL) CH. 1015. LAUSANNE bertrand.calpini@epfl.ch A new DOAS TE 2000 system -Differential Optical Absorption Spectroscopy – is continuously developed at LPA-EPFL laboratory. Measurements of O 3, NO 2 and SO 2 were validated during many field campaigns by comparison with many point monitor measurements and a OPSIS DOAS system. Reference spectra studies and measurements were also performed for BTEX, HONO, CH 2 O and NO 3. Based on the UV-VIS high-frequency structure of molecular absorption spectra (differential spectra), DOAS is a relatively new method to measure the concentration of the trace gases in the atmosphere The average field concentration is retrieved by a multiple regression of the differential field spectra fitting the sum of the differential reference spectra. DA =  D C L DOAS 2000 System Method Where DA= A- F n is the differential absorbance (A) Fn = polynomial filter of degree n [C i ] = concentration of the “i” compound L = optical path  i = multiple regression coefficients  D =  - F n is the differential UV-VIS cross section DOAS 2000 Optical Layout Advantages: - -multi-compound measurement -“in situ” monitoring technique - integrated-path measurements -fenceline and flux measurements - non-contact measurements - relatively low maintenance costs DOAS 2000 Technical Parameters Coaxial Cassegrain of 8” telescope ~ 1ppb detection limit L = 50-2000 m Optical Path Xe Lamp 150W Light Source 33 Hz Vibrating Slit 250 to 650nm spectral range 40 nm analytical windows PMT detection device DOAS 2000 Specificity DOAS CH 2 O MEASUREMENTS DOAS BTEX MEASUREMENTS POINT MONITOR and DOAS COMPARISON Region of measurements and simulation domain CH 2 O Measurements 2D O 3 and CH 2 O Simulation 13 th May 1998 O 3 and CH 2 O Model and Measurements Seregno on the 13 th May 1998 AB CD A. O 3 at 10:00. B. HCHO at 10:00. C. O 3 at 16:00. D. HCHO at 16:00 [ppb] DOAS on the waste water treatment plant Vidy: Lausanne Switzerland, Sept’99 Oxygen Interference Problem DOAS BTEX and FID NMHC comparison DOAS BTEX measurement serie DOAS ground measurement for LIDAR profile O3O3 NO 2 CONCLUSION This new DOAS TEI 2000 system is currently used to measure the criteria gases (NO 2, O 3, SO 2 ) and take usually part in the tropospheric air pollution measurements campaign (e.g. Milan-Italy 1998, Grenoble- France 1999 and Lausanne –Switzerland 1999). The new developments are on going to improve and validate the BTEX, CH 2 O, NO 3 and HONO measurements. The DOAS ground measurements (e.g. O 3 ) complete the O 3 LIDAR vertical profiles. Acknowledgements: Thermo Environmental Instruments (TEI) Franklin –USA and STEP-Vidy, Lausanne- Switzerland ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE Logo optimisé par J.-D.Bonjour, SI-DGR 13.4.93 DOAS TEI 2000 UV-VIS beam Seregno-Italy, 1999 http://lpas.epfl.ch/lidar/ 20th International Laser Radar Conference Vichy, FRANCE July 10-14, 2000