1. OH in the Coastal Boundary Layer of Crete: Measurements and Primary Production Rates During MINOS Harald Berresheim 1, Christian Plass-Dülmer 1, Thomas Elste 1, and Nikos Mihalopoulos 2 1 German Weather Service, Meteorological Observatory Hohenpeissenberg, Albin- Schwaiger-Weg 10, Germany 2 University of Crete - Environmental Chemical Processes Laboratory (ECPL), Heraclion Greece

2. Location of Finokalia Station (35°19‘N, 25°40‘E; 100-130 m asl)

3. C x H y = Hydrocarbons HO 2 RO 2 NO, O 2 Sources and Sinks of OH ν multiple steps Rain O3O3

4. Chemical Ionization Mass Spectrometer (CIMS) in Field Lab

5. CIMS Ionization Reactor MINOS 2001 Station Finokalia Compounds Measured: OH, H 2 SO 4 (gas), MSA (gas) Time Resolution: 30 sec Signal Integration: 5 min Accuracy, Precision, Detection Limit (2σ) : OH: 38 %, 32 %, 2.5 x 10 5 molec cm -3 H 2 SO 4, MSA: 29%, 21 %, < 1 x 10 5 molec cm -3

6. Time-weighted Average, 10 6 cm -3 06-12 August: 4.0 ± 0.6 13-21 August: 5.3 ± 0.9 * Total Period: 4.7 ± 1.0 * * excluding 19 August

9. Primary Production Rate, P(OH), OH Primary Production Ozone-Photolysis  330 nm O 3 + h O( 1 D) + O 2 O( 1 D) + H 2 O 2 OH O( 1 D) + N 2, O 2 O( 3 P) J(O 1 D) (1) (2) (3)

20. Conclusions Mean OH concentration at Finokalia during MINOS: 4.7 x 10 6 molecules cm -3 (Spivakovsky et al., 2000: 2-3 x 10 6 cm -3, same region, July, 700 hPa; 1.5 x 10 6 cm -3, 36°N zonal and monthly average, July, 1000 hPa) Primary production via ozone photolysis and reaction of O( 1 D) with H 2 O was the dominant source of OH (R 2 = 0.8806) Fairly good agreement with present model calculations of the regional OH balance during MINOS (e.g., poster by Baboukas et al., oral presentation by Lawrence et al., this session)

21. Acknowledgement Our sincere thanks to: Jos Lelieveld (MPI), Marian de Reus and the MINOS team, E. Baboukas, M. Lawrence, Pavlos Petsalakis, ECPL staff and students, and Georg Stange (DWD).