Deposition processes of ionic constituents to snow cover

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Atmospheric deposition is an important removal process of aerosol particles and gases from the atmosphere. To elucidate the relative contributions of wet and dry processes and in-cloud and below-cloud scavenging based on deposition amounts in winter at Mt. Tateyama, central Japan, we obtained daily samples (December, 2006–March, 2007) of size-segregated aerosol particles and precipitation at Senjyugahara (SJ; 475 m a.s.l.) and vertical samples of spring snow cover at Murododaira (MR, 2450 m a.s.l., 13 km distance from SJ) on the western flank of Mt. Tateyama. The NH 4 + and nssSO 4 2− in aerosols were mostly found in the fine fraction (<2 μm), although Na +, NO 3 −, and nssCa 2+ were mainly detected in the coarse fraction (>2 μm). Average ionic concentrations (μg g −1) in precipitation at SJ were higher about 3.8 for Na + and nssCa 2+, 3.4 for NO 3 −, 3.7 for NH 4 +, 2.5 for nssSO 4 2− than those at MR, whereas cumulative precipitation amounts at SJ and MR were, respectively, 84 and 175 cm of water equivalent. Wet and dry deposition amounts during the study period were estimated for sites using size-segregated aerosol data, winter averages of HNO 3, NH 3, and SO 2 concentrations, and dry deposition velocities. Particle-dry deposition comprised about 3% (Na +) to 11% (NH 4 +) of the total deposition at MR. The maximum amounts of gas dry deposition were estimated, respectively, as 4, 13, and 3% of the total deposition at MR for NH 4 +, NO 3 −, and nssSO 4 2−. The relative contributions of below-cloud scavenging (BCS) between MR and SJ were estimated as considering the wet only deposition amount at MR. Higher contributions of BCS were obtained for Na + (56%) and nssCa 2+ (45%), whereas BCSs for NH 4 +, NO 3 −, and nssSO 4 2− were lower than 28%. Ionic constituents existing predominantly in the coarse fraction showed a large contribution of BCS.