Seasonal and Frontal Variation in Antarctic Aerosol Concentrations

Abstract

Total aerosol concentrations have been observed twice daily at the South Pole since January 1974, using a Pollak photoelectric nucleus counter. The aerosol size distribution has been approximated using the Rich diffuser denuder and Spurny membrane filter techniques. These observations show the seasonal variation in aerosol concentration at the surface to be of large relative amplitude. The concentrations reach a very low value, with monthly averages of less than 15 cm⁻³, beneath the strong nocturnal inversion in winter. The mean concentration begins to rise near the time of astronomical sunrise, and attains monthly average values of 100–200 cm⁻³ during summer months. Variations in aerosol concentration and size accompany meteorological events. Extreme sky clarity and subsequent lowering of temperature and strengthening of the near-surface inversion in winter months are accompanied by nearly unmeasurable aerosol concentrations of 3–5 cm⁻³; winter warming is sometimes accompanied by increases in aerosol concentration to 50 cm⁻³. Frontal passage aloft (at the 500 mb level) during summer months, and/or strong subsidence of dry air, is often accompanied by large increases in aerosol in the smaller size classes. Advection of warm moist air from the Wedell Sea and frontal passage at lower levels are accompanied by an increase in aerosol particles in the larger size classes. Several case studies are included to illustrate these phenomena. Recent flight data indicates that the moist layer, just above the surface inversion at 650–550 mb over the South Pole, is relatively rich in particulate material. Mixing of this air downward can then be the source of increased aerosol concentration at the surface and increased particle precipitation to the ice cap.