AEROCLO-sA PEGASUS aerosol particle carbonaceous composition in the PM1 fraction

The AEROCLO-sA field campaign took place from 21 August to 13 September 2017 at the Sam Nujoma Marine and Coastal Resources Research Centre (SANUMARC) of the University of Namibia at Henties Bay (Formenti et al., 2019). This sampling site, operated on the long-term as described by Formenti et al. (2018) and Klopper et al. (2020).
During the campaign, aerosol samples of particles smaller than 1 µm in diameter (hereafter named PM1 size fraction) were collected both during day (approximately 07:00-17:00 UTC) and night time (approximately 17:30-06:30 UTC). The sampling duration was marginally adapted in real-time to the nature and the aerosol load of air masses using the readings of the local wind speed and direction and of the aerosol mass concentration, also measured online. Air sampling was performed from the PortablE Gas and Aerosol Sampling UnitS (PEGASUS; https://pegasus.aeris-data.fr/) facility with two high-volume aerosol inlets delivering approximately 450 L min-1 each. At wind speeds between 5 to 10 m s 1, typical for coastal Namibia, sampling is almost isokinetic for particles up to 40 µm in aerodynamic diameter (Rajot et al., 2008). The total sampled flow rate was distributed to various instruments, including a 4-stage Dekati® PM10 impactor operated at 10 L min-1. This sampler was operated with 25-mm polycarbonate membranes on three impactor stages (> 10 µm, 10-2.5 µm and 2.5-1 μm) while the final filter stage, where the PM1 fraction is collected, was a quartz filter (Pall, 2500QAT-UP Tissuquartz, 47-mm filter diameter). In total, 31 PM1 samples (including blanks) were collected from 26 August to 12 September 2017.
Organic carbon (OC) and elemental carbon (EC) were measured using a thermo-optical carbon analyser (Sunset Laboratory Inc.) on a 1.5 cm2 filter following the EUSSAR-II protocol (Cavalli et al., 2010). The Sunset analyzer was calibrated using a sucrose solution (purity > 99.5 %) in the concentration range between 0.42 µg cm-2 and 40 µg cm-2. The limit of quantification for total carbon and organic carbon is henceforth estimated to be equal to 0.42 µg cm-2. An instrumental blank and a control point with a sucrose solution at 10 µg cm-2 were done at the beginning of each day of analysis. OC and EC concentrations are automatically calculated with the software OCBC835 (Sunset Laboratory). The optical split point was manually verified to ensure their assignment.