Abstract:
Black carbon is one of the primary aerosols directly emitted from biomass
known to have strong absorbing properties. The INDAAF and PASMU observational
field campaigns which took place (2018) in Abidjan (urban area)
and Lamto (rural area) allow the analysis of Black carbon concentration at
different time scales through real-time measurements using an analyzer
named Aethalometer AE-33. Results presented here show at Lamto: 1) for the
diurnal scale an average of 1.71 ± 0.3 μg·m−3 (0.34 ± 0.09 μg·m−3) in the dry
(wet) season; 2) for the monthly scale an average of 1.14 ± 0.84 μg·m−3; 3) on
the seasonal scale, an average of 2.2 ± 0.02 μg·m−3 (0.6 ± 0.19 μg·m−3) in the
dry (wet) season. The black carbon variation at Lamto is seasonal with an
amplification factor of 85.6. Regarding the urban area of Abidjan, due to
sampling issues, our analyses were limited to daily, diurnal and weekly time
scales. We observed: a) at a daily scale an average of 5.31.± 2.5 μg·m−3, b) diurnal
scale, an average ranging from 6.87 to 13.92 μg·m−3. The analysis indicated
that emissions from urban areas are more related to social and economic
activities, with weekday concentrations (7.24 μg·m−3) higher than concentrations
over the weekend (e.g. Saturday 6.59 μg·m−3 and Sunday 6.00
μg·m−3). Moreover, BC concentration in Abidjan is quite noticeable compared
to that of rural areas (Lamto). The ratio between the maximum values of the
two areas is of the order of 5.86. In addition, concentrations in some urban
areas are slightly above the daily threshold set by the WHO (10 μg·m−3).
Therefore, the levels of urban BC concentrations are alarming whilst rural BC
concentrations remain below daily WHO thresholds and are of the same
magnitude as those of West African megacities. This study underlies that BC concentrations at Lamto are mainly related to biomass combustion sources
while those from urban areas are related to traffic sources. The latter is permanently
active, unlike those in rural Lamto, which is seasonal.
