Detection of Saharan dust and biomass burning events using near-real-time intensive aerosol optical properties in the north-western Mediterranean
The study of Saharan dust events (SDEs) and biomass burning (BB) emissions are both topics of great scientific interest since they are frequent and important polluting scenarios affecting air quality and climate. The main aim of this work is evaluating the feasibility of using near-real-time in...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/12567/2016/acp-16-12567-2016.pdf |
| Summary: | The study of Saharan dust
events (SDEs) and biomass burning (BB) emissions are both topics of great
scientific interest since they are frequent and important polluting scenarios
affecting air quality and climate. The main aim of this work is evaluating
the feasibility of using near-real-time in situ aerosol optical measurements
for the detection of these atmospheric events in the western Mediterranean
Basin (WMB). With this aim, intensive aerosol optical properties (SAE:
scattering Ångström exponent, AAE: absorption Ångström
exponent, SSAAE: single scattering albedo Ångström exponent and <i>g</i>:
asymmetry parameter) were derived from multi-wavelength aerosol light
scattering, hemispheric backscattering and absorption measurements performed
at regional (Montseny; MSY, 720 m a.s.l.) and continental (Montsec; MSA,
1570 m a.s.l.) background sites in the WMB. A sensitivity study aiming at
calibrating the measured intensive optical properties for SDEs and BB
detection is presented and discussed.
<br><br>
The detection of SDEs by means of the SSAAE parameter and Ångström
matrix (made up by SAE and AAE) depended on the altitude of the measurement
station and on SDE intensity. At MSA (mountain-top site) SSAAE detected
around 85 % of SDEs compared with 50 % at the MSY station, where
pollution episodes dominated by fine anthropogenic particles frequently
masked the effect of mineral dust on optical properties during less intense
SDEs. Furthermore, an interesting feature of SSAAE was its capability to
detect the presence of mineral dust after the end of SDEs. Thus, resuspension
processes driven by summer regional atmospheric circulations and dry
conditions after SDEs favoured the accumulation of mineral dust at regional
level having important consequences for air quality. On average, SAE, AAE and
<i>g</i> ranged between −0.7 and 1, 1.3 and 2.5 and 0.5 and 0.75
respectively during SDEs.
<br><br>
Based on the aethalometer model, BB contribution to
equivalent black carbon (BC) accounted for 36 and 40 % at MSY and MSA
respectively. Linear relationships were found between AAE and %BC<sub>bb</sub>,
with AAE values reaching around 1.5 when %BC<sub>bb</sub> was higher than
50 %. BB contribution to organic matter (OM) at MSY was around 30 %.
Thus fossil fuel (FF) combustion sources showed important contributions to
both BC and OM in the region under study. Results for OM source
apportionment showed good agreement with simultaneous biomass burning
organic aerosol (BBOA) and hydrocarbon-like organic aerosol (HOA) obtained by applying a positive matrix factorization model (PMF) to simultaneous Aerosol Chemical Speciation Monitor (ACSM) measurements. A wildfire episode was identified at
MSY, showing AAE values up to 2 when daily BB contributions to BC and OM
were 73 and 78 % respectively. |
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| ISSN: | 1680-7316 1680-7324 |