Compositional data analysis (CoDA) as a tool to evaluate a new low-cost settling-based PM₁₀ sampling head in a desert dust source region

Abstract

Abstract. This paper presents a new sampling head design and the method used to evaluate it. The elemental composition of aerosols collected by two different sampling devices in a semi-arid region of Tunisia is compared by means of compositional perturbation vectors and biplots. This set of underused mathematical tools belongs to a family of statistics created specifically to deal with compositional data. The two sampling devices operate at a flow rate of about 17 L min−1, with a cut-off diameter of 10 µm. The first device is a low-cost laboratory-made system, where the largest particles are removed by gravitational settling in a vertical tube. This new system will be compared to the second device, a brand-new standard commercial PM10 sampling head, where size segregation is achieved by particle impaction on a metal surface. A total of 44 elements (including rare earth elements or REE, together with Al, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Rb, S, Sc, Se, Sr, Ti, Tl, U, V, Zn, and Zr), was analysed in sixteen paired samples, collected during a two-week field campaign in Tunisian dry lands, close to source areas, with high levels of large particles. The contrasting meteorological conditions encountered during the field campaign allowed a broad range of aerosol compositions to be collected, with very different aerosol mass concentrations. No compositional differences were observed between samples collected simultaneously by the two devices. The mass concentration of the particles collected was estimated through chemical analysis, and results for the two sampling devices were also very similar to those obtained from an on-line aerosol weighing system, TEOM (tapered element oscillating micro-balance), installed next to them. Results suggest that the commercial PM10 impactor head can therefore be replaced by the decanter, without any measurable bias, for the determination of chemical composition, and for further assessment of PM10 concentrations in source regions.

Sediment quality and environmental risk assessment in a Mediterranean coastal system using geochemical and multivariate statistical analyses: the case of Boughrara Lagoon (southeastern Tunisia)

“…For this purpose, the compositional data analysis (CoDA) was applied with the chemical element concentrations analyzed in the surficial sediments (Cu, Zn, Co, Cd, Pb, Mn, Fe, Al and P) by using RStudio software. Indeed, CoDA is a statistical method useful for simultaneous analysis of several elemental ratios by reducing a large number of variables to a few unrelated components (Aitchison, 1982;Xu-Yang et al, 2021).…”