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Volume 16, issue 18 | Copyright
Atmos. Chem. Phys., 16, 11687-11709, 2016
https://doi.org/10.5194/acp-16-11687-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Sep 2016

Research article | 21 Sep 2016

Aerosol measurements during COPE: composition, size, and sources of CCN and INPs at the interface between marine and terrestrial influences

Jonathan W. Taylor1, Thomas W. Choularton1, Alan M. Blyth2, Michael J. Flynn1, Paul I. Williams1,3, Gillian Young1, Keith N. Bower1, Jonathan Crosier1,3, Martin W. Gallagher1, James R. Dorsey1,3, Zixia Liu1, and Philip D. Rosenberg4 Jonathan W. Taylor et al.
  • 1Centre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
  • 2National Centre for Atmospheric Science, University of Leeds, Leeds, UK
  • 3National Centre for Atmospheric Science, University of Manchester, Manchester, UK
  • 4School of Earth and Environment, University of Leeds, Leeds, UK

Abstract. Heavy rainfall from convective clouds can lead to devastating flash flooding, and observations of aerosols and clouds are required to improve cloud parameterisations used in precipitation forecasts. We present measurements of boundary layer aerosol concentration, size, and composition from a series of research flights performed over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) of summer 2013. We place emphasis on periods of southwesterly winds, which locally are most conducive to convective cloud formation, when marine air from the Atlantic reached the peninsula. Accumulation-mode aerosol mass loadings were typically 2–3µgm−3 (corrected to standard cubic metres at 1013.25hPa and 273.15K), the majority of which was sulfuric acid over the sea, or ammonium sulfate inland, as terrestrial ammonia sources neutralised the aerosol. The cloud condensation nuclei (CCN) concentrations in these conditions were  ∼ 150–280cm−3 at 0.1% and 400–500cm−3 at 0.9% supersaturation (SST), which are in good agreement with previous Atlantic measurements, and the cloud drop concentrations at cloud base ranged from 100 to 500cm−3. The concentration of CCN at 0.1% SST was well correlated with non-sea-salt sulfate, meaning marine sulfate formation was likely the main source of CCN. Marine organic aerosol (OA) had a similar mass spectrum to previous measurements of sea spray OA and was poorly correlated with CCN.

In one case study that was significantly different to the rest, polluted anthropogenic emissions from the southern and central UK advected to the peninsula, with significant enhancements of OA, ammonium nitrate and sulfate, and black carbon. The CCN concentrations here were around 6 times higher than in the clean cases, and the cloud drop number concentrations were 3–4 times higher.

Sources of ice-nucleating particles (INPs) were assessed by comparing different parameterisations used to predict INP concentrations, using measured aerosol concentrations as input. The parameterisations based on total aerosol produced INP concentrations that agreed within an order of magnitude with measured first ice concentrations at cloud temperatures as low as −12°C. Composition-specific parameterisations for mineral dust, fluorescent particles, and sea spray OA were 3–4 orders of magnitude lower than the measured first ice concentrations, meaning a source of INPs was present that was not characterised by our measurements and/or one or more of the composition-specific parameterisations greatly underestimated INPs in this environment.

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We present measurements of boundary layer aerosol concentration, size and composition from research flights performed over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) of summer 2013. We compare case studies of aerosol in cleaner marine air from the Atlantic with anthropogenic pollution from the UK. These measurements are then used to investigate the possible sources of CCN and IN in the region.
We present measurements of boundary layer aerosol concentration, size and composition from...
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