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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2016-1128
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
23 Jan 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Tropospheric NO2 concentrations over West Africa are influenced by climate zone and soil moisture variability
Ajoke R. Onojeghuo1, Heiko Balzter1,2, and Paul S. Monks3 1University of Leicester, Centre for Climate Research, University Road, Leicester, LE1 7RH, UK
2National Centre for Earth Observation, University of Leicester, University Road, Leicester, LE1 7RH, UK
3University of Leicester, Department of Chemistry, University Road, Leicester, LE1 7RH, UK
Abstract. The annual cycles of soil moisture and NO2 have been analysed across the climate zones of West Africa using two satellite data sets (OMI on AURA and ASCAT on MetOp-A). Exploring the sources and sinks for NO2 it is clear that the densely populated urban cities including Lagos and Abuja had the highest mean NO2 concentrations (> 1.8 × 1015 molecules cm−2) indicative of the anthropogenic urban emissions. The data analysis shows that rising soil moisture levels may influence the sink of NO2 concentrations after the biomass burning. The results also show significant soil moisture changes in areas of high humidity especially in the east equatorial monsoon climate zone where most of the Niger delta is located (4 %/yr.). A decline in NO2 (0.9 %/yr.) was also observed in this climate zone. Beyond seasonal linear regression models, climate based Granger’s causality tests show that tropospheric NO2 concentrations from soil emissions in the arid steppe (Sahel) and arid desert climate zones of West Africa are significantly affected by soil moisture variability (F > 10, p < 0.01). The arid steppe and arid deserts regions showed no significant changes in soil moisture levels but significant increase in tropospheric NO2 concentrations (> 0.8 %/yr). The results demonstrate the critical sensitivity of the West African emissions of NO2 on soil moisture and climate zone.

Citation: Onojeghuo, A. R., Balzter, H., and Monks, P. S.: Tropospheric NO2 concentrations over West Africa are influenced by climate zone and soil moisture variability, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2016-1128, in review, 2017.
Ajoke R. Onojeghuo et al.
Ajoke R. Onojeghuo et al.
Ajoke R. Onojeghuo et al.

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Short summary
This research focused on the identifying seasonality and linear trends of NO2 and soil moisture across West Africa using satellite data. A strong effect of soil moisture on tropospheric NO2 variations in arid steppe and desert zones has been shown. Recent increasing trends in NO2 over arid steppe/desert areas are more likely connected to fertilizer induced afforestation from the Sahel green wall initiative than soil moisture variations.
This research focused on the identifying seasonality and linear trends of NO2 and soil moisture...
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