The specific surface area of fresh dendritic snow crystals

Abstract

Abstract:The surface area to mass ratio or speci®c surface area (SSA) is an often neglected characteristic of the snowpack that varies substantially with time, and with the shape of the individual snow crystal for fresh snow. The SSA for the dendritic shape of snow crystals was computed using a series of images photographed by W. A. Bentley. The speci®c images were dendritic crystals (P1d, P1e, P1f) and crystals that take a partial dendritic form and have ends or extensions (P2a, P2b, P2d, P2e, P2f, P2g) according to the Magono and Lee snow crystal classi®cation. Image analysis, using known geometric relationships between length and width, and particle size distributions, examined the spatial properties of 50 sample snow crystals. Probability distribution functions were derived for SSA and these compared well with measured and other computed estimates of fresh snow SSA. For the non-rimed condition, the average SSA was 0 . 182 m 2 /g with a range from 0 . 09 to 0 . 33 m 2 /g. The presence of rime is discussed, and depending on the shape of the rime particles and the degree of surface coverage, the SSA can be doubled (20% coverage for needle or plate shaped rime). Fractal analysis was performed to determine various geometric relationships that characterize the dendritic form of snow crystal.

Influence of Snow and Ice Crystal Formation and Accumulation on Mercury Deposition to the Arctic

“…If we make a simple assumption that mercury concentration is proportional to SSA, and that samples are collected before other terms in eq 1 can alter the initial concentration, then the high concentrations found for diamond dust make sense. The SSA of diamond dust, which consists of particles not much bigger than a mote, is far higher than the ∼1500 cm 2 /g reported as the maximum values for freshly fallen snow (32) and rimed dendritic crystals (33). Airborne cloud ice particles, the progenitors of diamond dust, have even higher SSAs than diamond dust.…”

“…Because of the Kelvin effect and vapor density gradients , by the time we collected diamond dust from the trays, the crystals were slightly larger. Regardless, these were the smallest crystals we collected, and therefore we can assume they had the highest specific surface area (SSA ), the surface area of a mass of snow or ice that is available to exchange with a gas , . The diamond dust crystals were also the youngest crystals collected (excluding 2 m pole condensation).…”

Snow‐Induced Perturbations in Nitrous Acid (HONO) Levels: Insights Into Heterogeneous Reactions During Wintertime in Mid‐Latitude Regions

“…Gas adsorption measurements indicate that freshly deposited snow typically exhibits SSA values ranging from 100 to 3,000 cm 2 g −1 , with a characteristic value of several hundred cm 2 g −1 for fresh natural snowpack (Domine et al., 2007; Hoff et al., 1998). In contrast, morphological analyses and microscopy methods reveal that snow crystals can attain SSAs reaching thousands or even up to 10,000 cm 2 g −1 (Fassnacht et al., 1999; Wergin et al., 1995). This discrepancy arises from the structural preservation of ice frameworks in atmospheric suspension versus their gravitational collapse in terrestrial accumulation (Grannas et al., 2007), suggesting that morphological estimates better represent the true SSA of atmospheric snowflakes.…”

Transport and deposition of heavy metals in the Ross Sea Region, Antarctica

“…However, at sites where rime ice growth is prevalent, it can be a major contributor to trace element concentration due to its high scavenging efficiency [ Duncan , ; Schwikowski et al , ]. Rime forms in clouds as droplets of supercooled water that impact snowflakes and can increase the specific surface area of the snowflake by 20% or more [ Fassnacht et al , ; Makkonen , ; Rango et al , ], increasing the potential for particulate scavenging. Rime also forms at the snow surface where supercooled cloud droplets impact the surface topography and the accumulation of droplets can lead to needle or plate‐like growth with low densities and high‐specific surface areas [ Berg et al , ; Fassnacht et al , ; Macklin , ].…”

“…Rime forms in clouds as droplets of supercooled water that impact snowflakes and can increase the specific surface area of the snowflake by 20% or more [ Fassnacht et al , ; Makkonen , ; Rango et al , ], increasing the potential for particulate scavenging. Rime also forms at the snow surface where supercooled cloud droplets impact the surface topography and the accumulation of droplets can lead to needle or plate‐like growth with low densities and high‐specific surface areas [ Berg et al , ; Fassnacht et al , ; Macklin , ]. Extensively rimed snow crystals have been found to be more acidic than unrimed crystals and have higher ion concentrations [ Puxbaum and Tscherwenka , ].…”