09 Feb 2021

09 Feb 2021

Review status: this preprint is currently under review for the journal ACP.

The impact of aerosol size-dependent hygroscopicity and mixing state on the cloud condensation nuclei potential over the Northeast Atlantic

Wei Xu1,2, Kirsten N. Fossum1, Jurgita Ovadnevaite1, Chunshui Lin1,2, Ru-Jin Huang2, Colin O'Dowd1, and Darius Ceburnis1 Wei Xu et al.
  • 1School of Physics, Ryan Institute’s Centre for Climate and Air Pollution Studies, National University of Ireland Galway, Galway, Ireland
  • 2State Key Laboratory of Loess and Quaternary Geology and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China

Abstract. We present an aerosol cloud condensation nuclei (CCN) closure study over the Northeast Atlantic Ocean using six approximating methods. The CCN number concentrations (NCCN) were measured at four discrete super-saturations (SS, 0.25, 0.5, 0.75 and 1.0 %). Concurrently, aerosol number size distribution, sub-saturation hygroscopic growth factor and bulk PM1 chemical composition were obtained at matching time resolution and after a careful data validation exercise. Method A used a constant bulk hygroscopicity parameter κ of 0.3; method B used bulk PM1 chemical composition measured by an aerosol mass spectrometer (AMS); method C and D utilized a single size (165 nm) growth factor (GF) measured by humidified tandem differential mobility analyzer (HTDMA); method C utilized size-dependent GFs measured at 35, 50, 75, 110 and 165 nm; method E divided the aerosol population into three hygroscopicity modes (near-hydrophobic, more-hygroscopic and sea-salt modes) and the total CCN number in each mode was cumulatively added up; method F used the full size scale GF probability density function (GF-PDF) in the most complex approach. The studied periods included high biological activity and low biological activity seasons in clean marine and polluted continental air masses to represent and discuss the most contrasting aerosol populations.

Overall, a good agreement was found between estimated and measured NCCN with a linear regression slopes ranging from 0.64 and 1.6. The temporal variability was captured very well with Pearson's R value ranging from 0.76 to 0.98 depending on the method and air mass type. We further compared the results of using different methods to quantify the impact of size-dependent hygroscopicity and mixing state and found that ignoring size-dependent hygroscopicity induced overestimation of NCCN by up to 12 %, and ignoring a mixing state induced overestimation of NCCN by up to 15 %. The error induced by assuming an internal mixing in highly polluted cases was largely eliminated by dividing the full GF-PDf into three conventional hygroscopic modes while assuming an internal mixing in clean marine aerosol did not induced significant error.

Wei Xu et al.

Status: open (until 06 Apr 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Wei Xu et al.

Data sets

Cloud condensation nuclei and hygroscopic growth measurement at Mace Head from 2009 to 2010 Wei Xu, Kirsten Fossum, Darius Ceburnis, Jurgita Ovadnevaite, and Colin O'Dowd

Wei Xu et al.


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Short summary
Could condensation nuclei (CCN) is an important topic in atmospheric studies, especially for evaluating the climate impact of aerosol. Here in this study, CCN closure study by using chemical composition based on aerosol mass spectrometer (AMS) and hygroscopicity growth measurements based on humidified tandem differential mobility analyzer (HTDMA) in the Mace Head Atmospheric Research Station.