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List of Abstracts 57Contact: visahini.kanthasamy@mail.mcgill.caFormaldehyde is the highest concentration aldehyde in the atmosphere with typical concentration rangingfrom 0.3 to 2 ppbv in Canada. It is an important intermediate in the gas-phase methane oxidation chain andplays an important role in the chemistry of troposphere by influencing its hydroxyl radical (HOx) budget,and thus its oxidative capacity. It can be produced anthropogenically and biogenically and can also betransferred from the ocean. Weather the ocean is the source or sink of the formaldehyde is of interest toscientists in order to completely understand the chemical processes happening in the ocean/air interface. Wedevelop a method for determining formaldehyde in ambient air using solid phase microextraction method(SPME), a facile, low-cost, versatile technique. The formaldehyde is derivatized on the SPME fiber to itspentafluorobenzyl oxime using 1, 2, 3, 4, 5-pentafluorobenzylhydroxylamine (PFBHA) and then analyzedwith gas chromatography with flame ionization detector (GC-FID). We herein present the methodologydeveloped, the calibration curves, and some results from outdoor/indoor samplings. We also present an intercomparisonof this method with DNPH derivatization with HPLC method.P-Interfaces.34 ID:4346 15:35Effects of coupling and relative humidity on HONO mixing ratios in a spruce forestMatthias Sörgel 1 , Ivonne Trebs 2 , Andrei Serafimovich 3 , Alexander Moravek 2 , Franz X. Meixner 2 ,Cornelius Zetzsch 11 University of Bayreuth, Atmospheric Chemistry Research Laboratory2 Max Planck Institute for Chemistry, Biogeochemistry Department3 University of Bayreuth, Department of MicrometeorologyContact: i.trebs@mpic.deWe made HONO measurements using two long path absorption photometers (LOPAPs) at a field sitelocated in the Fichtelgebirge mountains in north-eastern Bavaria, Germany (50°09’N, 11°52’E, 775m abovesea level) within the framework of the project “ExchanGE processes in mountainous Regions” (EGER).HONO was measured simultaneously close to the forest floor (0.5 m above ground) and at 24.5 m height(just above the spruce forest canopy top) from 13 to 26 September 2007 using two long path absorptionphotometers (LOPAPs). Diel cycles of HONO and mixing ratio differences between above canopy and closeto the forest floor are discussed in view of the coupling between canopy and the air above and are related tothe dependency of HONO mixing ratios on relative humidity. Since HONO is rapidly photolyzed duringdaytime, it typically featured a pronounced diel cycle with low levels (50 to 100 ppt) around noon and higherlevels (up to 500 ppt) at nighttime during a dry period (20-25 Sep.). The shading from the forest canopyreduces photolysis in the trunk space to about 4-10% of the values measured above the canopy. Thus, theHONO lifetime ranges from 70 to 200 minutes below the canopy and is about 10 minutes above the canopyaround noontime on a clear sky day. Despite this, the differences of the measured HONO mixing ratios areabout zero (± 20 ppt) from 8:00 to 13:00 CET. This is attributed to an enhanced vertical mixing within theforest canopy during daytime as indicated by the coupling regimes calculated from turbulence measurementsof horizontal and vertical wind components and sonic temperature using sonic anemometers according toThomas and Foken [1]. In the early afternoon, starting about 13:00 CET, a trend towards higher HONOmixing ratios in the trunk space was detected, which considerably increases at 17:00 CET one hour beforesunset, when the coupling regime changes. Coinciding with the increasing HONO mixing ratios, the relativehumidity increases below the canopy.[1] C. Thomas and T. Foken; Flux contribution of coherent structures and its implications for the exchangeof energy and matter in a tall spruce canopy; Boundary-Layer Meteorology;123; 2007; 317-337iCACGP-IGAC 2010 12 July, 2010