Optical and Microphysical Properties of Trajectory-Clustered Aerosols at an AERONET site in West Africa

O.G. Fawole, X. Cai & A.R. Mackenzie.

Sources and composition of atmospheric aerosols play prominent roles in their properties and, hence, their global warning tendencies. Black carbon (BC), a product of incomplete combustion and principal light-absorbing specie in ambient aerosol, has been identified as the second major contributor to global warming after CO2 (Santos et al., 2014). Using a 7-day back trajectory from the AERONET site over a ten-year period, clusters of aerosol were created. At the AERONET site, the four major sources of aerosol considered in the cluster analysis are two big cities (CC) (Lagos – 6.58 oN, 3.75 oE and Ibadan 7.4 oN, 3.92 oE), Desert Dust (DD) (13.9 – 18.8 oN; 6.2 – 17.0 oE) and Biomass Burning (BB) in Central Africa (12.0 – 17.7 oS; 21.5 – 33.5 oE). Seven clusters; DD, CC, GF, GF-DD-CC, GF-CC, GF-DD and DD-CC were identified from the trajectory analysis. The optical and microphysical properties of these clusters show that the GF aerosol are made up of a larger percentage of fine black carbon (BC) particulate, with AAE (440-870 nm) = 0.99 (0.26) and EAE (440-870 nm) = 1.2 (0.25). The urban (CC) aerosol comes next in terms of BC content but more coarse with AAE (440-870 nm) = 1.27 (0.46) and EAE (440-870 nm) = 0.58 (0.38).


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