Unique microphysical properties of small boundary layer ice particles under pristine conditions on Dome C, Antarctica

The Antarctic plateau, one of the coldest and cleanest regions of our planet, experiences almost exclusively frozen precipitation. Understanding the microphysical properties of inland Antarctic boundary layer ice particles with sizes below a few hundred micrometers is essential to improve atmospheric models and accurately validate remote sensing data for this region. Currently, only a small number of in situ atmospheric measurements exist for particle sizes smaller than 100 µm on the Antarctic plateau, performed over short measurement times. We present the first multi-week study of optical in situ measurements of boundary layer ice particle size, shape and morphological complexity for sizes down to 11 µm with a temporal resolution in the order of minutes, including a multi-day ice fog event. Classifying ice fog events with a lidar system, we found mean particle sizes smaller than 11 µm for ice fog events and of about 70 µm for cirrus precipitation and diamond dust events. The mean particle concentration of the ice fog at Dome C (3.9 L⁻¹) is found to be lower than in parametrisations of Arctic ice fog and lower than the concentration of anthropogenically influenced urban ice fog measured at Fairbanks, Alaska during a three-year study with the same instrument (90 L⁻¹). Moreover, ice fog particles at Dome C are found to be more pristine than at Fairbanks. Our findings show that Antarctic boundary layer ice particles may need to be parametrised differently than their Arctic counterparts due to distinct conditions on the Antarctic plateau.