Relationships of major ions in snow fall and rime at Sonnblick Observatory (SBO, 3106 m) and implications for scavenging processes in mixed clouds

Snow fall and rime samples have been collected at the Sonnblick Observatory (SBO, 3106 m) during a four year time period and have been analyzed for major ions (Cl-, NO3-, SO42-, H+, NH4+, Na+, K+, Ca2+, Mg2+) as well as for S(IV) and H2O2. We applied the Brantner el ol. (1994) snow/cloud mass balance model for estimating the relative mass of rime droplets attached on ice crystals. From this estimate the mass of rime droplets attached on snow crystals is on the yearly average approximately 20%. There is little seasonal variation except for fall with a slight increase of the rimed mass. There is indication for considerable gas phase scavenging of SO2, HNO3 and H2O2 directly on respectively during growth of the ice crystals. 'Crustal and "sea salt" elements (Ca, Mg, Na, K, Cl) appear to become scavenged predominantly via ice nucleation. Our tentative estimates: indicate that as a lower limit NO3- in snow fall is derived to more than 35% From direct gas phase scavenging onto ice crystals and crustal elements in snow are derived more than 60% from ice nucleation scavenging. (C) 1998 Elsevier Science Ltd. All rights reserved.