Published: 4 February 2013

Aerosol optical depth (AOD) measures total aerosol burden in the atmosphere. The spectral dependence of AOD, typically described by the Angstrom exponent, is also an indicator of particle size. Small Angstrom exponent values (near zero) indicate presence of large particles, and vice versa.

The AOD value-added product (VAP) provides both the wavelength-dependent values of AOD and the Angstrom exponent from five spectrally resolved measurements gathered from the multifilter rotating shadowband radiometer (MFRSR). This VAP uses MFRSR-based algorithms originally developed by Michalsky et al. and applied to more than 10 years of AOD measurements at the well-established ARM Southern Great Plains (SGP) site. These algorithms were tailored for applications at different places around the world with the short-term deployment (typically up to 12 months) of the ARM Mobile Facility (AMF). The AOD VAP is regularly updated with data from each new deployment of the AMF. (See previous data announcements here)

Recently, data from the AMF Gan Island (GAN) and Ganges Valley, India (PGH), deployments were added to the AOD VAP. Clouds were very often present at these two sites, and as a result, the fraction of time with cloud-free AODs is moderately reduced. The figures show examples of AODs collected on a 20-second interval during daylight cloud-free periods.

More information on AOD is available at the VAP web page. To access these data, log in to the Data Archive. (Go here to request an account.)