Spatial and temporal variations in inhalable CuZnPb aerosols within the Mexico City pollution plume
2008
Moreno, T. | Querol, X. | Pey, J. | Minguillón, M. C. | Pérez, N. | Alastuey, A. | Bernabé, R. M. | Blanco, S. | Cárdenas, B. | Eichinger, W. | Salcido, A. | Gibbons, W.
We report on the CuPbZn content of PM₁₀ and PM₂.₅ samples collected from three sites (urban T0, suburban T1 and rural T2) during the Mexico City MILAGRO campaign of March 2006. Daytime city centre concentrations of ∑CuZnPb(PM₁₀) were much higher (T0 > 450 ng m⁻³) than at the suburban site (T1 < 200 ng m⁻³). Rural site (T2) ∑CuZnPb(PM₁₀) concentrations exceeded 50 ng m⁻³ when influenced by the megacity plume but dropped to 10 ng m⁻³ during clean northerly winds. Nocturnal metal concentrations more than doubled at T0, as pollutants became trapped in the nightly inversion layer, but decreased at the rural site. Transient spikes in concentrations of different metals, e.g. a “copper event” at T0 (CuPM₁₀ 281 ng m⁻³) and “zinc event” at T1 (ZnPM₁₀ 1481 ng m⁻³) on the night of March 7–8, demonstrate how industrial pollution sources produce localised chemical inhomogeneities in the city atmosphere. Most metal aerosols are <2.5 μm and SEM study demonstrates the dominance of Fe, Ti, Ba, Cu, Pb and Zn (and lesser Sn, Mo, Sb, W, Ni, V, As, Bi) in metalliferous particles that have shapes including spherical condensates, efflorescent CuZnClS particles, cindery Zn, and Cu wire. Metal aerosol concentrations do not change in concert with PM₁₀ mass, which is more influenced by wind resuspension than industrial emissions. Metalliferous particles can induce cell damage, and PM composition is probably more important than PM mass, with respect to negative health effects, so that better monitoring and control of industrial emissions would likely produce significant improvements in air quality.
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