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

Jonathan Taylor, Thomas Choularton, A. M. Blyth , Michael Flynn, Paul I Williams, Gillian Young, Keith Bower, Jonathan Crosier, Martin Gallagher, James Dorsey, Zixia Liu, P. D. Rosenberg

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    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 2–3 μgm-3 (corrected
    to standard cubic metres at 1013.25 hPa and 273.15 K), 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 150–280 cm-3 at
    0.1% and 400–500 cm-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 500 cm-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.
    Original languageEnglish
    Pages (from-to)11687–11709
    JournalAtmospheric Chemistry and Physics
    Issue number18
    Publication statusPublished - 21 Sept 2016


    • Aerosols
    • CCN (cloud condensation nuclei)
    • Ice nucleation
    • Marine aerosol
    • Aerosol chemistry


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