Study of Particle Size Distribution of Harmattan Dust in Maiduguri, Borno State

Harmattan dust, transported from the Sahara Desert into northern Nigeria during the dry season, significantly degrades air quality and solar resource availability across the North East geopolitical zone. Maiduguri in Borno State is among the cities most severely affected by harmattan episodes, with visibility frequently reduced to below 1 kilometre during peak events. This study characterises the particle size distribution of harmattan dust collected in Maiduguri during the 2022 to 2023 harmattan season using laser diffraction particle size analysis. Bulk dust samples are collected at three sites using sedimentation traps over weekly intervals from November to February. Sub-samples are dispersed in ethanol and analysed using a Mastersizer 3000 instrument. Results indicate volume-median particle diameters ranging from 18 to 47 micrometres, with the coarse sand fraction (greater than 63 micrometres) comprising 12 to 28 percent of the total by volume. Clay-sized particles below 2 micrometres constitute less than 5 percent of the bulk. Temporal analysis reveals progressive coarsening of particle size distribution as the harmattan season intensifies in January. The fine particle fraction contains quartz, feldspar, and kaolinite identified by XRD analysis. Particle size data are relevant for respiratory health risk assessment and aerosol radiative forcing estimation in North East Nigeria. Keywords: harmattan dust, particle size, Maiduguri, laser diffraction, aerosol