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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers | Copyright
https://doi.org/10.5194/amt-2018-164
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 01 Jun 2018

Research article | 01 Jun 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Measurement Techniques (AMT).

Instrument Artifacts Lead to Uncertainties in Parameterizations of Cloud Condensation Nucleation

Jessica A. Mirrielees and Sarah D. Brooks Jessica A. Mirrielees and Sarah D. Brooks
  • Texas A&M University, College Station, TX 77843

Abstract. The concentrations of cloud condensation nuclei (CCN) modulate cloud properties, rainfall location and intensity, and climate forcings. This work assesses uncertainties in CCN measurements and the apparent hygroscopicity parameter (κapp) which is widely used to represent CCN populations in climate models. CCN measurements require accurate operation of three instruments: the CCN instrument, the differential mobility analyzer (DMA), and the condensation particle counter (CPC). Assessment of DMA operation showed that varying the ratio of aerosol to sheath flow from 0.05 to 0.30 resulted in discrepancies between the κapp values calculated from CCN measurements and the literature value. Discrepancies were found to increase from effectively zero to 0.18 for sodium chloride, and from effectively zero to 0.08 for ammonium sulfate. The ratio of excess to sheath flow was also varied, which shifted the downstream aerosol distribution towards smaller particle diameters (for excess flow < sheath flow) or larger particle diameters (for excess flow > sheath flow) than predicted. For the CPC instrument, undercounting occurred at high concentrations, resulting in calculated κapp lower than the literature values. Lastly, undercounting by CCN instruments at high concentration was also assessed, taking the effect of supersaturation on counting efficiency into account. Under recommended operating conditions, the combined DMA, CPC, and CCN uncertainties in κapp are 1.1% or less for 25 to 200nm diameter aerosols.

Jessica A. Mirrielees and Sarah D. Brooks
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Jessica A. Mirrielees and Sarah D. Brooks
Jessica A. Mirrielees and Sarah D. Brooks
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Latest update: 16 Oct 2018
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Short summary
Particles in the air, called aerosols, can participate in cloud formation and affect cloud properties. One way to study these particles is by determining their ability to uptake water, called hygroscopicity. Apparent hygroscopicity is one such measurement. This study evaluates how errors can arise in determining apparent hygroscopicity, and how to avoid or minimize them when collecting data.
Particles in the air, called aerosols, can participate in cloud formation and affect cloud...
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