On-line analysis of gas and particle composition during the AEROCLO-SA campaign in Henties Bay (Namibia).

The AEROCLO-sA project (Aerosol, Radiation and CLOuds in southern Africa)investigates the role of aerosols on the regional climate of southern Africa. The regionis characterized by high atmospheric aerosol loadings originated from biomassburning, mineral dust and marine sea salt. In addition it is influenced by strongmarine biological emissions by the Benguela upwelling and a semi-permanent andextended stratocumulus cloud deck. This area therefore provides an exceptionalnatural laboratory for studying the full range of aerosol physico-chemical properties,aerosol-radiation and aerosol-cloud interactions and their perturbations of the Earth’sradiation budget. AEROCLO-sA is based on a field campaign conducted for a month in August-September2017 at the coastal Henties Bay experimental site (22˚ 6’ S, 14˚ 17’ E). An instrumentedmobile station was implemented at ground over coastal Namibia in order to document fog,clouds, aerosols, volatile organic compounds and other traces gases at the ocean-atmosphereinterface. State of the state-of-the-art instrumentation for the measurement of volatilecompounds as proton-transfer-reaction mass spectrometer and retrieval of chemical andphysical properties of aerosol as time of flight aerosol mass spectrometer, scanningmobility particle sizer, particle counters, cloud condensation nuclei counter weredeployed. Here we present results from on-line AMS data analysis of the sub-micrometer aerosolwhich is dominated by sulphate, sea salt followed by organic compounds. Marine biogenicemissions strongly enhanced concentrations of short-chain aldehydes, alcohols, carboxylicacids and sulphur-containing compounds in the gas phase, and strongly influenced PM1composition, while diurnal cycles of iodide and MSA species were observed along the wholecampaign. Source apportionment analysis has been run for both the organic gas phase andaerosol fraction. Additional information from on-line analysis on water-soluble fraction onTSP (PILS-IC) and off-line analysis (filters and TEM grids) will complete our view of theaerosol chemical composition in this region. The full set of data will improve ourunderstating of emissions and mechanisms occurring at the ocean-atmosphere interface inthis region. [ABSTRACT FROM AUTHOR]