Modeling investigation of light-absorbing aerosols in the Amazon Basin during the wet season
We use a global chemical transport model (GEOS-Chem) to interpret observed light-absorbing aerosols in Amazonia during the wet season. Observed aerosol properties, including black carbon (BC) concentration and light absorption, at the Amazon Tall Tower Observatory (ATTO) site in the central Amaz...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/14775/2016/acp-16-14775-2016.pdf |
| Summary: | We use a global chemical transport model (GEOS-Chem) to
interpret observed light-absorbing aerosols in Amazonia during the wet
season. Observed aerosol properties, including black carbon (BC)
concentration and light absorption, at the Amazon Tall Tower Observatory
(ATTO) site in the central Amazon have relatively low background levels but
frequently show high peaks during the study period of January–April 2014. With
daily temporal resolution for open fire emissions and modified aerosol
optical properties, our model successfully captures the observed variation
in fine/coarse aerosol and BC concentrations as well as aerosol light
absorption and its wavelength dependence over the Amazon Basin. The source
attribution in the model indicates the important influence of open fire on
the observed variances of aerosol concentrations and absorption, mainly from
regional sources (northern South America) and from northern Africa. The
contribution of open fires from these two regions is comparable, with the
latter becoming more important in the late wet season. The analysis of
correlation and enhancement ratios of BC versus CO suggests transport times
of < 3 days for regional fires and ∼ 11 days for African
plumes arriving at ATTO during the wet season. The model performance of
long-range transport of African plumes is also evaluated with observations
from AERONET, MODIS, and CALIOP. Simulated absorption aerosol optical depth
(AAOD) averaged over the wet season is lower than 0.0015 over the central
Amazon, including the ATTO site. We find that more than 50 % of total
absorption at 550 nm is from BC, except for the northeastern Amazon and the
Guianas, where the influence of dust becomes significant (up to 35 %).
The brown carbon contribution is generally between 20 and 30 %. The
distribution of absorption Ångström exponents (AAE) suggests more
influence from fossil fuel combustion in the southern part of the basin (AAE
∼ 1) but more open fire and dust influence in the northern
part (AAE > 1.8). Uncertainty analysis shows that
accounting for absorption due to secondary organic aerosol (SOA) and primary
biogenic aerosol (PBA) particles could result in differences of
< 8 and 5–40 % in total absorption, respectively. |
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| ISSN: | 1680-7316 1680-7324 |