| Abstract | Sodium chloride (NaCl) plays an important role both in the laboratory as a calibration aerosol and in nature as a component of sea-spray particles. Despite their ubiquity, NaCl particles show significant variation in their shape depending on the drying rate. This work builds on the current literature by establishing the influence of drying rate on the distribution of effective density and dynamic shape factor of laboratory generated NaCl particles. A calibration factor is first established using a spherical aerosol composed of Santovac (polyphenyl ether), to account for instrumental uncertainties. A total of three different drying rates were tested: −97 RH/s (slow), −260 RH/s (intermediate), and −506 RH/s (fast). The effective density and dynamic shape factor results (in the transition regime) shows that slow dried particles attained a distinct cube-like shape (ρeff ≈ 2200–1600 kg/m³, χ ≈ 1–1.15), intermediate particles achieved much rounded corners while still showing some cube-like features (ρeff ≈ 2200–1800 kg/m³, χ ≈ 1.00–1.08), and fast dried particles retained its spherical morphology (ρeff ≈ 2200–2000 kg/m³, χ ≈ 1.00–1.02). The range of shapes observed is also influenced by particle size; smaller particles (<50 nm) were more spherical regardless of the drying rate. Additionally, bidimensional effective density analysis revealed shape variability within particles of the same size, suggesting a distribution of morphologies, especially for the slow drying case. These results are validated using TEM images at three approximately different mobility sizes − 100, 200 and 400 nm. |
|---|
