Preliminary results from AWARE

Description

As part of the DOE/NSF AWARE (ARM West Antarctic Radiation Experiment) campaign, the AMF II Aerosol Observing System (AOS) was deployed at McMurdo station on the southern tip of Ross Island in Antarctica in November 2015. The AMF II suite of aerosol instruments includes a Cloud Condensation Nuclei Counter (CCN), a Condensation Particle Counter (CPC), a Humidified Tandem Differential Mobility Analyzer (HT-DMA) and a Nephelometer. A preliminary analysis of the data gathered by these instruments was performed to get an early overview of the local aerosol properties. The measured aerosol particle number concentration is characterized by a low and relatively steady baseline usually below 500 1/cm3 with numerous sharp peaks that can reach over 10 000 1/cm3. Similar features are observed in the aerosol optical scattering data measured by the Nephelometer, however, the sharp peaks do not always coincide between the two instruments and tend to be narrower and more clearly defined in case of the Nephelometer. The sampled aerosol is also relatively hygroscopic. The activated aerosol particle number concentration as measured by the CCN reaches a maximum at 0.8-1% supersaturation, roughly matching the total particle number concentration measured by the CPC. The HT-DMA, operating at 90% RH, shows steady aerosol growth factor of 1.6-1.7, regardless of the particle selection size, which is varied by the instrument between 50 and 250 nm. Some sources of high peaks in the CPC and Nephelometer data have been traced to on-site activity as observed by the local technicians. They have reported ground work near the site and heavy traffic on a nearby road coinciding with the increase in the number of peaks in the CPC and Nephelometer data time series. Dust in the inlet lines of the AOS has been observed, as well. However, the dust from the ground is expected to be mineral by composition and thus not be hygroscopic, which does not explain the observed particle hygroscopicity. Dust particles could become hygroscopic if covered by organics, but no such source has been identified. It is likely that there are several sources of local aerosol and something else besides the mineral dust is present. A good candidate for that is sea salt, which is hygroscopic and readily dispersed by the ocean waves. However, further analysis is needed to ascertain the composition and the origins of the local aerosol.