Equivalent black carbon mass concentration measured over coastal Namibia from 2012 to 2019

Surface observations of aerosol particles are conducted at the Henties Bay Aerosol Observatory (HBAO; http://www.hbao.cnrs.fr/), a recent regional station in the Global Atmosphere Watch (GAW) programme of the World Meteorological Organization (WMO). The research centre is located on the Sam Nujoma Marine and Coastal Resources Research Centre (SANUMARC) of the University of Namibia in Henties Bay (22∘ S, 14∘05′ E), Namibia (Fig. 1). Henties Bay is a small town in an arid environment with no vegetation, no industrial activity and very little traffic. Energy usage is predominantly a mix of electricity and gas, with some solid fuel combustion (wood) due to low availability. The monitoring site, situated on the university campus, is located on the coast approximately 100 m from the shoreline. To the east are the Namibian gravel plains, 3 km to the south of the campus is the town of Henties Bay and to the north is the Omaruru riverbed (river mouth approximately 100 m from SANUMARC). The population of Henties Bay ranges between 4600 and 6000 inhabitants, according to the Namibia Population and Housing Census Main Report (available at http://cms.my.na/assets/documents/p19dmn58guram30ttun89rdrp1.pdf.
The particle equivalent black carbon concentration (eBC) in the PM1 fraction was derived from the optical attenuation of light (ATN) measured by a single-wavelength aethalometer (model AE-14U, Magee Sci., Berkeley, CA; Hansen et al., 1984) operating at 880 nm and sampling at 3.5 (± 0.1) L min-1 from a certified inlet (BGI Inc., Waltham, MA). The airflow temperature and relative humidity were ambient. Measurements were performed at a 5-min time resolution. The original data set was screened to eliminate spikes and peaks lasting less than two hours, generally associated with occasional nearby open fires for barbequing meat.
The operational equations linking the measured attenuation (ATN) at 880 nm to the eBC used a correction factor for multiple scattering (C) and shadowing effect (R(ATN)) were fixed to 3.44 (± 0.21) and 0.93, based on Collaud-Coen et al. (2010) and Weingartner et al. (2003). The mass absorption efficiency of eBC was set to 9.0 (± 1.5) m2 g-1.