Estimation of the Aitken particle source intensity in rural equatorial Africa

Abstract

Using aircraft measurement methods, the rate of production of Aitken particles of the different types of vegetation found in the equatorial zone (forest, flooded forest and savannah) was estimated. For the savannah, the average diurnal rate in the rainy season is of the order of 4 × 10 3 p cm −2 s −1 . This increases one hundredfold in the dry season as soon as the scrub fires start. In the flooded forest zone, a region with no distinct dry season and which is practically uninhabited, emission is roughly constant throughout the year at 2 × 10 4 pcm −2 s −1 . In the other forests the production varies with the season from 3 to 7 × 10 4 pcm −2 s −1 . A preliminary estimation on the scale of the Congo shows that in the wet season 99 % of the Aitken particles have a natural origin whereas in the dry season 90% are due to human activity — mainly scrub fires. For the Congo, this corresponds to a total production of 6.5 × 10 19 particles s −1 in the wet season and 6 × 10 20 particles s −1 in the dry season.