Received: 19 Dec 2016 – Accepted for review: 17 Jan 2017 – Discussion started: 23 Jan 2017
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.
How to cite. 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. [preprint], https://doi.org/10.5194/acp-2016-1128, 2017.
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...