Out of Africa: High aerosol concentrations in the upper troposphere over Africa

[摘要] In the year 2000, six flights (three southbound and three northbound) of the CARIBIC projectwere conducted between Germany and two destinations in the southern hemisphere(Windhoek, Namibia and Cape Town, South Africa).In the present report, results on particlenumber concentrations are discussed in three size ranges (>4 nm, >12nm, and >18 nm particle diameter) during the unique transequatorial Africa flights.The flights covered a totalof about 80 h in May, July, and December.Thus, no claim can be made for long-termrepresentativeness of the aerosol data.Nevertheless, they are the first upper systematictropospheric transequatorial aerosol profiles over Africa.The average aerosol results show abroad maximum, roughly symmetrical to the equator, which compares well in latitudinalextent to a maximum of CO concentrations measured on the same flights.This export ofcontinental surface aerosol to the upper troposphere will be dispersed on a global scale bothwith the easterly flow near the equator and with the westerlies in the adjacent subtropicalregions.There was strong evidence of recent new particle formation before aerosol arrival atflight level, in particular during the time periods between 9:00 and 13:00 local time overAfrica.Direct and indirect climate effects of the respective particulate matter remain to beinvestigated by future flights with the ongoing extension of the CARIBIC payload towardssize-resolved measurements above 100 nm particle diameter.At the same time globalchemical transport models and aerosol dynamics models need to be extended to be able toreproduce the CARIBIC findings over Africa.

[学科分类] 大气科学