Black carbon pollution simulations: a RegCM4 model projection and assessment during the boreal winter and summer over West Africa region

Abstract

The increasing sources of black carbon (BC) emission into the atmosphere have made BC a major air pollutant that could contribute significantly and alter the global atmospheric radiation budget. A perturbed global radiation budget will have profound effect on rainfall cycle and dependent socioeconomic activities. In this paper, RegCM version 4.7, a regional climate model, has been used to simulate back carbon (BC) pollution over West Africa. Pollution-radiation feedback option in the model was activated to determine the effect of radiative properties of BC on climate parameters (rainfall, temperature and wind speed). The study attempted to capture the effect of radiative properties of BC on those climate parameters by activating and de-activating radiation feedback option (RFB) of the model under two RCP2.6 and 8.5. When RFB was turned off, both scenarios showed a decrease in the mean monthly rainfall of up to 2 mm/month in the north and 1.2 mm/month in the south of the West African region. Temperature increased by a factor of 2 K/month in the north and south of the region. For the entire region, the temperature projection in the near future (at the end of twenty-first century) showed an increase of about 3 K/month wind speed and slows down generally in the north and south up to a factor of 0.6 ms−1/month under both RCPs. However, when RFB was turned on, rainfall decreases by a factor 0.9 mm/month in the south and 0.8 mm/month in the north under RCP2.6 and 8.5, respectively. In summary, results show that elevated BC concentration in the atmosphere will lead to increase in temperature and decrease in rainfall in the near future relative to historical records and these changes could be exacerbated through BC interactive radiation feedback with the atmospheric variables.