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Laboratory tests reveal insights to the collection of particles onto filters

Laboratory tests reveal insights to the collection of particles onto filters

Correction factors were determined for quartz filters when filtering liquid solutions containing soot.

Soot are particles that are very efficient in absorbing solar radiation. Once at a snow surface the particles accelerate and increase snowmelt. A common measurement technique for soot in snow collects the particles onto filters via filtration of the melted snow.

In a recent study, laboratory experiments were conducted to better understand quartz filters optical response to soot particles sampled in air and in liquid. When comparing the quartz filters to other standard filters (Pallflex) widely used in atmospheric absorption photometers a 20% scattering enhancement for the quartz filters was observed. A multiple-scattering correction factor for the quartz filter was estimated to be ~3.4.

Once the particles were mixed in water solutions, the particles showed a greater attenuation of light compared to the airborne deposition of particles. The reason for this was the greater penetration of the soot particles in the filter media for the liquid filtrations. This penetration depth looks to be even greater when the liquid solution is sonicated before filtration. In summary, applying these correction factors decrease previously published absorption coefficients, which will assist researchers to more accurate estimate soot's impact on snow.

Further information:

Researcher Jonas Svensson, Finnish Meteorological Institute,

Senior researcher Aki Virkkula, Finnish Meteorological Institute,

Full citation of publication:

Svensson, J., Ström, J., and Virkkula, A.: Multiple-scattering correction factor of quartz filters and the effect of filtering particles mixed in water: implications for analyses of light absorption in snow samples, Atmos. Meas. Tech., 12, 5913–5925,, 2019.

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