Optical properties, morphology and elemental composition of atmospheric particles at T1 supersite on MILAGRO campaign

Abstract

Atmospheric particles were sampled at T1 supersite during MILAGRO campaign, in March 2006. T1 was located at the north of Mexico City (MC). Aerosol sampling was done by placing copper grids for Transmission Electron Microscope (TEM) on the last five of an 8-stage MOUDI cascade impactor. Samples were obtained at different periods to observe possible variations on morphology. Absorption and scattering coefficients, as well as particle concentrations (0.01–3 μm aerodynamic diameter) were measured simultaneously using a PSAP absorption photometer, a portable integrating nephelometer, and a CPC particle counter. Particle images were acquired at different magnifications using a CM 200 Phillips TEM-EDAX system, and then calculated the border-based fractal dimension. Also, Energy Dispersive X-Ray Spectroscopy (EDS) was used to determine the elemental composition of particles. The morphology of atmospheric particles for two aerodynamic diameters (0.18 and 1.8 μm) was compared using border-based fractal dimension to relate it to the other particle properties, because T1-generated particles have optical, morphological and chemical properties different from those transported by the MC plume. <br><br> Particles sampled under MC pollution influence showed not much variability, suggesting that more spherical particles (border-based fractal dimension close to 1.0) are more common in larger sizes (<i>d</i><sub>50</sub> = 1.8 μm), which may be attributed to aerosol aging and secondary aerosol formation. Between 06:00 and 09:00 a.m., smaller particles (<i>d</i><sub>50</sub> = 0.18 μm) had more irregular shapes resulting in higher border-based fractal dimensions (1.2–1.3) for samples with more local influence. EDS analysis in <i>d</i><sub>50</sub> = 0.18 μm particles showed high contents of carbonaceous material, Si, Fe, K, and Co. Perhaps, this indicates an impact from industrial and vehicle emissions on atmospheric particles at T1

Real-time aerosol optical properties, morphology and mixing states under clear, haze and fog episodes in the summer of urban Beijing

“…This enhanced absorption in such structure is because of the lensing effect of coated materials (Jacobson, 2001). Field measurements indicate that during transport from the sources, fresh soot becomes internally mixed with sulfate and organics, leading to enhancement in light absorption, which was in agreement with the results of modelling calculation Doran et al, 2007;Carabali et al, 2012). Kleinman et al (2007) observed a doubling in the ratio of aerosol light absorption in aged air masses compared to fresh emissions over the eastern US.…”

Real-Time Aerosol Optical Properties, Morphology and Mixing States under Clear, Haze and Fog Episodes in the Summer of Urban Beijing

“…This enhanced absorption in such structure is because of the lensing effect of coated materials (Jacobson, 2001). Field measurements indicate that during transport from the sources, fresh soot becomes internally mixed with sulphate and organics, leading to enhancement in light absorption, which confirms the modelling calculation (Kleinman et al, 2007;Doran et al, 2007;Carabali et al, 2012). Kleinman et al observed a doubling in the ratio of aerosol light absorption in aged air masses compared to fresh emissions over the eastern U.S. (Kleinman et al, 2007).…”

Characterization of aerosol particles during a high pollution episode over Mexico City

“…The AOD parameter measured by the Aerosol Robotic Network (AERONET) represents the vertically integrated extinction coe cient in the atmospheric column. Simultaneous analyzes of the aerosol morphological properties and their elemental composition is an alternative to characterize them 2,[16][17][18][19] . While particle shape can be associated with their size and optical properties, the elemental composition is related to their origin and mixing state.…”

“…Based on their composition and morphology, urban aerosol particles can be classi ed as soot, tarballs (TB), mineral dust, S-rich and K-rich, sea salt, metallic, among others [20][21][22] . This classi cation can be performed by using Transmission-(TEM) and Scanning electron microscopy (SEM) techniques coupled with the energy dispersed X-ray detector (EDX or EDS) 19,20,23 .…”