Light absorption measurements

Particle light absorption has long been measured using a custom built soot photometer operating using a green light sources with a wavelength of 550 nm. The attenuation of the light through the filter is not only due to absorption by the particles, but due to scatteringof the light by the particles. Corrections for this are made with the aid of the Nephelometer light scattering measurements (see light scattering for more info on those measurement). The measurements are continuous, but integration is typically performed over 1 hour intervals.

Since 2014 we measure lightabsorption with the 5012 Multiangle Absorption Photometer. The MAAP uses multiple detectors to simultaneously measure the transmitted and scattered light though the filters so for this data the scattering correction is made by the instrument itself.

The amount of light absorbing particles very well follows the intrusions of polluted air into the Arctic. The highest values are found in spring during so called Arctic Haze events. During clean periods the amount calculated in equivalent amount of soot usually are below 10 ng m-3. During Arctic Haze the concentrations can be almost hundred times higher. An interesting question is how soot is mixed with other compounds.