DEPOSITION OF SUBMICRON AEROSOL ON SPRUCE NEEDLES; WIND TUNNEL MEASUREMENTS K. LAMPRECHTOV Á, J.HOVORKA Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Benátská 2, Prague 2, Czech Republic  Atmospheric aerosol deposition onto a plant surface is an efficient mechanism of its removal from the atmosphere. Rate of aerosol deposition strongly depends deposited aerosol, on thickness of laminar sublayer covering plant surface. The layer thickness is altered by vegetal surface morphology and by deposited aerosol.  Deposited aerosol may increase stomatal conductance, which lead to an unwanted increase of water transpiration during water stress periods.  Conifers are periodically subjected to water stress during winter, when water supply is blocked due to frozen soil, and increased transpiration may affects conifer winter survival. Study objectives RESULTS  low values of RSD of experimental data proved the tunnel to be suitable for such a kind of experiment  aerosol deposition velocity was on average higher for P.abies than for P.pungens by 40% and 60% respectively, for experiments with and without wax layer respectively  removing epicuticular wax caused 15% decrease of β n for P. punges regardless the aerosol size while for P.abies, probably due to stronger alteration of laminar sublayer, β n changes with aerosol size  repeated deposition of experimental aerosol decreased β n for both the species near to β n values recorded for experiments without wax layer. This could be explained by filling up the wax structure with aerosol particles  repeated deposition of experimental aerosol had no reproducible effect on values of β n for both the species for experiments without wax layer Measurements  closed circulation wind tunnel (Vol.-0,36 m 3,Surface-3,73 m 2, S/V=10.4)  working section (0,5m long, 0,18m 2 cross section)  Stairmand disc: turbulent flow (R e = ), honeycomb: laminar flow (R e = 608)  wind speed 1.14 m/s  testing aerosol : average GMD=0.7 μm,  g = 1.3, N max. = 1200 pt/cm 3 (AGK 2000, Palas)  aerosol size distributions μm, integration time 6s, (APS 3321, TSI)  32 twigs in 8 rows of Picea pungens-glauca or Picea abies  alteration of needle surface by removing epicuticular wax with chloroform (washing for 60s)  basic model: N = N o exp (- βt) where N– actual number of particles, N o – initial number of particles, β - deposition rate constant   =  0 +  n where “ 0”  or “n” coefficient are experiments for empty tunnel or with twigs   = (S 0 + S n ) / V * D/  where S 0, S n is tunnel/needles geometric surface V tunnel volume, D = diffusion coefficient and  = boundary layer thickness  deposition velocity V d = V / S n *  n Top view on closed circulation wind tunel Detail of working section (side view) Contour graph of temporal changes of aerosol number size distributions Regression curves of aerosol size fractions,  determination   values for empty tunnel β for Picea pungens with wax layer and   for empty tunnel β n for Picea pungens with/without wax layer β n for Picea abies with /without wax layer β n for Picea Pungens with a wax layer decreases with growing amount of deposited aerosol on needles ACKNOWLEDGEMENT The study is a part of MSc. diploma work; financial support by the Institute for Environmental Studies, Faculty of Science, Charles University in Prague is greatly acknowledged. *DNW - dry needle weight CONCLUSIONS  experiment = 3 different cycles measured consecutively; each measurement took approx. 90 minutes 1.one control measurement with empty tunnel 2.four consecutive measurements of aerosol deposition rate with conifer twigs in the tunnel 3.three consecutive measurements of aerosol deposition rate with conifer twigs without wax layer Relative Standard Deviations – RSD’s of  values measurements and needle surface between experiments  RSD, Empty tunel (n=14) 7,05 %  RSD, In-cycle (n=12) 3,41 %  RSD, Inter-cycle (n=8) 5,71% Picea abies needle surface RSD, (n=7)7,6% Picea pungens needle surface RSD (n=5)13,4% Picea Pungens 1g DNW*= 73,8cm 2 Particle size [μm] Deposition velocity V d [cm s -1 ] Unwashed twigs (40,1% n=5) Washed twigs (46,6%, n=4) 0,523 5,10E-033,23E-03 0,542 4,75E-033,80E-03 0,583 4,89E-034,29E-03 0,626 5,67E-034,57E-03 0,673 6,19E-035,03E-03 0,723 6,78E-035,22E-03 0,777 6,80E-035,42E-03 0,835 6,92E-035,69E-03 0,898 7,37E-036,58E-03 0,965 8,06E-038,03E-03 1,037 8,48E-031,13E-02 Picea abies 1g DNW*= 87,3cm 2 Particle size [μm] Deposition velocity V d [cm s -1 ] Unwashed twigs (28,9% n=7) Washed twigs (26,6% n=6) 0,523 1,44E-021,88E-02 0,542 1,43E-021,32E-02 0,583 1,39E-021,33E-02 0,626 1,36E-021,34E-02 0,673 1,32E-021,30E-02 0,723 1,20E-021,34E-02 0,777 1,06E-021,36E-02 0,835 8,51E-031,31E-02 0,898 7,97E-031,22E-02 0,965 9,61E-031,34E-02 1,037 1,07E-021,55E-02 Experimental conditions Analysis  to construct and to test closed circulation wind tunnel for the measurements of aerosol deposition under controlled conditions  to quantify differences in aerosol deposition rates between two coniferous species, Picea abies and Picea pungens-glauca  to quantify the influence of needle surface alteration on aerosol deposition β n for Picea pungens without wax varied stochastically with growing amount of deposited aerosol on needles