In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 18, No. 14 ( 2018-07-19), p. 10255-10274
Abstract:
Abstract. The Amazon Basin is a unique region to study atmospheric aerosols, given
their relevance for the regional hydrological cycle and the large uncertainty of
their sources. Multi-year datasets are crucial when contrasting periods of
natural conditions and periods influenced by anthropogenic emissions. In the
wet season, biogenic sources and processes prevail, and the Amazonian
atmospheric composition resembles preindustrial conditions. In the dry
season, the basin is influenced by widespread biomass burning emissions. This
work reports multi-year observations of high time resolution submicrometer
(10–600 nm) particle number size distributions at a rain forest site in
Amazonia (TT34 tower, 60 km NW from Manaus city), between 2008 and 2010 and
2012 and 2014. The median particle number concentration was 403 cm−3 in the wet
season and 1254 cm−3 in the dry season. The Aitken mode
(∼ 30–100 nm in diameter) was prominent during the wet season, while the accumulation mode
(∼ 100–600 nm in diameter) dominated the particle size spectra during
the dry season. Cluster analysis identified groups of aerosol number size
distributions influenced by convective downdrafts, nucleation events and fresh
biomass burning emissions. New particle formation and subsequent growth was
rarely observed during the 749 days of observations, similar to previous
observations in the Amazon Basin. A stationary 1-D column model (ADCHEM –
Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer
model) was used to assess the importance of the processes behind the observed diurnal
particle size distribution trends. Three major particle source types are
required in the model to reproduce the observations: (i) a surface source of
particles in the evening, possibly related to primary biological emissions;
(ii) entrainment of accumulation mode aerosols in the morning; and (iii)
convective downdrafts transporting Aitken mode particles into the boundary
layer mostly during the afternoon. The latter process has the largest
influence on the modeled particle number size distributions. However,
convective downdrafts are often associated with rain and, thus, act as both a
source of Aitken mode particles and a sink of accumulation mode
particles, causing a net reduction in the median total particle number
concentrations in the surface layer. Our study shows that the combination of
the three mentioned particle sources is essential to sustain particle number
concentrations in Amazonia.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-18-10255-2018
DOI:
10.5194/acp-18-10255-2018-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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