Surface Aerosol Observing System

The ARM Mobile Facility (AMF) is equipped to quantify the interaction between clouds and aerosol particles. A counter-flow virtual impactor (CVI) is used to selectively sample cloud drops. The CVI takes advantage of the higher inertia of the cloud drops to draw them through a slight counter-flow into the system while smaller particles are unable to overcome the counter-flow. Downstream of the CVI the cloud drops are evaporated and the resulting cloud condensation nuclei (CCN) are fed to aerosol instrumentation to characterize their optical, chemical, physical (size, number, and shape) and cloud activation properties. In parallel with the CVI system, a second aerosol inlet with an upper cut-off size of five can sample the interstitial aerosol—that is, the particles which have not activated to cloud droplets. The AMF Aerosol Observing System (AOS) is equipped with many additional inlets to enable additional equipment to be added depending on the needs of a specific deployment.

All deployments that employ the baseline instruments for the AMF AOS are:

  1. Integrating Nephelometer (TSI 3563, operated at low RH): The nephelometer measures total scattering (between 7 and 170 degrees) and backscattering (between 90 and 170 degrees) by aerosol particles at three wavelengths: blue (450 nm), green (550 nm) and red (700 nm). This nephelometer is maintained at a humidity of 50%.
  2. Integrating Nephelometer (TSI 3563, operated at RH scanned from ~40-90%): This is a second nephelometer that samples air at a variety of controlled humidities ranging from 20 to 90%**.
  3. Particle/Soot Absorption Photometer (PSAP; Radiance Research, 3-wavelength): The PSAP is a filter-based method that measures light absorption by particles at a single wavelength: green (565 nm). Particles are collected on a filter and light transmission through the filter is monitored continuously.
  4. Condensation Nuclei Counter (CNC; TSI 3010): The CNC measures the total number concentration of condensation particles of diameter in the size range of 10 nm to 3.
  5. Multiple-Supersaturation Cloud Nuclei and Condensation Nuclei Counter (Droplet Measurement Technologies): Measures the total number of cloud condensation nuclei at six different supersaturations. The instrument adjusts the supersaturation over a period of one-half hour through a range similar to set points of 0.18, 0.29, 0.44, 0.58, 0.85, 1.12, and 1.37.

The AMF AOS is similar to the standard ARM AOS and the data are available through the AOS web page.