Evaluating magnetic properties of atmospheric particulate matter (PM10) at Brasília bus station, central Brazil

Abstract

This study analyzes the Saturation Magnetization (M_S) in PM₁₀ particles collected at a central bus station in Brasília from 2018 to 2019, exploring its relationship with chemical elements (total metals - Fe, V, Cu, Mn, Sr, Cd - and ions - Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl⁻, NO₃⁻, SO₄²⁻) and meteorological variables (relative humidity and global radiation). M_S was measured using a S700X SQUID magnetometer and modeled with the Langevin equation, yielding values between 0.114 and 1.407 Am²/kg (n = 13), with a standard deviation of 0.01–0.1. Statistical analysis revealed similar median values between M_S and the studied variables, indicating shared sources of PM₁₀. The higher total concentrations of metals (Fe > Sr > Mn) and ions (Ca²⁺ = 30 %, Na⁺ = 23 % of total ions) suggest a natural origin of PM₁₀, likely from soil minerals. In contrast, metals (Cu, V, Cd, Ni, Co and Zn) and ions (SO₄²⁻, NO₃⁻) of anthropogenic origin were associated with vehicle emissions and road dust. FTIR spectroscopy identified magnetite as the dominant magnetic carrier in PM₁₀, with absorption peaks at 570 and 390 cm⁻¹, and particle sizes ranging from 8.5 to 11 nm, although a broader size range (8–33 nm) was also observed. This supports the formation of heterogeneous particles through mineral-metal or carbonaceous adsorption, as confirmed by morphological data. The temporal distribution of M_S in PM₁₀ samples showed peak values during the rainy season, despite no direct correlation with the studied variables, suggesting that iron solubility in minerals may influence the saturation magnetization.