In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 23 ( 2021-12-02), p. 17513-17528
Abstract:
Abstract. Aerosol–cloud interactions contribute to the large uncertainties in current
estimates of climate forcing. We investigated the effect of aerosol particles
on cloud droplet formation by model calculations and aircraft measurements
over the Amazon and over the western tropical Atlantic during the
ACRIDICON–CHUVA campaign in September 2014. On the HALO (High
Altitude Long Range Research) research aircraft,
cloud droplet number concentrations (Nd) were measured near the
base of clean and polluted growing convective cumuli using a cloud combination
probe (CCP) and a cloud and aerosol spectrometer (CAS-DPOL). An adiabatic
parcel model was used to perform cloud droplet number closure studies for
flights in differently polluted air masses. Model input parameters included
aerosol size distributions measured with an ultra-high sensitive aerosol
spectrometer (UHSAS), in combination with a condensation particle counter
(CPC). Updraft velocities (w) were measured with a boom-mounted Rosemount
probe. Over the continent, the aerosol size distributions were dominated by
accumulation mode particles, and good agreement between measured and modeled
Nd values was obtained (deviations ≲ 10 %)
assuming an average hygroscopicity of κ∼0.1, which is consistent
with Amazonian biomass burning and secondary organic aerosol. Above the
ocean, fair agreement was obtained assuming an average hygroscopicity of
κ∼0.2 (deviations ≲ 16 %) and further
improvement was achieved assuming different hygroscopicities for Aitken and
accumulation mode particles (κAit=0.8, κacc=0.2; deviations ≲ 10 %), which may reflect
secondary marine sulfate particles. Our results indicate that Aitken mode
particles and their hygroscopicity can be important for droplet formation at
low pollution levels and high updraft velocities in tropical convective
clouds.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-21-17513-2021
DOI:
10.5194/acp-21-17513-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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