Black carbon and total carbon measurements at urban and rural sites in Kenya, East Africa

Abstract

This paper reports measurements of black carbon (BC) and total carbon (TC) (TC=BC+organic carbon) in the lower troposphere in Nairobi and the towns of Nanyuki and Meru in Kenya. The rural sites of Nanyuki and Meru are both located on the equator on the northwestern and northeastern slopes of Mount Kenya, respectively. Particles were collected for 24 h on glass fibre filters using a dichotomous impactor. The content of TC and BC was analysed using a carbon–hydrogen–nitrogen analyser and a black smoke reflectometer. The mean TC concentration in Nanyuki was found to be two times higher than that of Meru, 14±2 and 7±1 μg m −3, respectively. The measured BC concentration in Meru (1.4±0.1 μg m −3) was twice that of Nanyuki (0.72±0.06 μg m −3). The organic carbon (OC) concentration was estimated from the difference between the measured TC and BC. The obtained mean concentrations were lower than those found in the literature for Asia and USA but higher than those of some European cities. The local burning of biomass was seen as the main source of carbonaceous aerosols at all measurement sites. The Nanyuki site exhibited OC concentrations comparable to those of the urban site in Nairobi. Nairobi had the highest concentration of both TC and BC. Vehicular and waste burning emissions in Nairobi may have enriched the carbonaceous aerosols.