Optical properties, morphology and elemental composition of atmospheric particles at T1 supersite on MILAGRO campaign 1Centro de Ciencias de la Atmósfera, UNAM, Ciudad de México, DF, México
14 Mar 2012
2Centro de Investigaciones de Materiales Avanzados, Chihuahua, México
Received: 04 Apr 2011 – Published in Atmos. Chem. Phys. Discuss.: 25 May 2011 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.
Revised: 30 Jan 2012 – Accepted: 17 Feb 2012 – Published: 14 Mar 2012
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 (d50 = 1.8 μm),
which may be attributed to aerosol aging and secondary aerosol formation.
Between 06:00 and 09:00 a.m., smaller particles (d50 = 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
d50 = 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.
Citation: Carabali, G., Mamani-Paco, R., Castro, T., Peralta, O., Herrera, E., and Trujillo, B.: Optical properties, morphology and elemental composition of atmospheric particles at T1 supersite on MILAGRO campaign, Atmos. Chem. Phys., 12, 2747-2755, doi:10.5194/acp-12-2747-2012, 2012.