Ambient air particle mass concentrations in the urban area of the capital city of Yaoundé (Cameroon, Central Africa): monthly and seasonal behaviour

Abstract

ABSTRACT Two size fractions of particulate matters (PM2.5, PM10-2.5) were sampled for 1 year at an urban site of Yaoundé from March 2018 to February 2019 to describe PM2.5, PM10-2.5 and PM10 pollution variations and determine their main sources. Samples were collected for 24 h on grease-coated filters using a Gent sampler. The analyses were carried out by Gravimetric and statistical methods. The highest monthly average level of the three size fractions were observed in the Long Dry season. Particularly in February (17 ± 13 µg/m3) for PM2.5, in December (51 ± 28 µg/m3) for PM10-2.5 and in January (65 ± 30 µg/m3) for PM10. Whilst the lowest in the Long Rainy season especially in September (5 ± 3 µg/m3) and October (5 ± 4 µg/m3) for PM2.5, in August (6 ± 3 µg/m3) and September (6 ± 3 µg/m3) for PM10-2.5, and in September for PM10 (11 ± 5 µg/m3). Compared to WHO limits, the annual mean was slightly lower for PM2.5 (9 ± 3 µg/m3) and exceedingly higher for PM10 (30 ± 8 µg/m3). However, that pollution level was in line with the lowest WHO Annual Interim Target limits. The correlation between PM2.5 and PM10 varied depending on the seasons. The PM2.5/PM10 ratio was higher in the Long Rainy season and lower in the Long Dry season. The annual ratio was 0.38 ± 0.18 and reflect that coarse particles are more abundant. Thus, the PM pollution in Yaoundé was dominated by dust sources and was close to that of some relatively less polluted developing country capitals around the world. It can also be ranked as the eleventh most airborne polluted African capital.