A study of elemental composition of PM2.5 samples collected at the main campus of the Universidad Nacional Autónoma de México, comprising data from 2015, 2016, and 2019, is described. X-ray fluorescence analysis was employed to measure concentrations of up to 19 elements, complemented with ion chromatography for eight ionic species (for samples of 2015 and 2016), and thermo-optical analysis for organic and elemental carbon (for samples of 2015). Positive matrix factorization (PMF) was applied to develop receptor models for each year, to identify polluting sources and their contributions to total mass. Five sources were identified in every case. With the aid of PMF, the influence of biomass burning on a major episode in May, 2019, was recognized. Comparisons with previous studies in this or nearby sites are also presented. It should be noted that only limited compositional data in this site are available since 2005 for the aerosol fine fraction.

Two sets of experiments were performed for collected particulate mass emitted directly from the exhaust of diesel engines burning diesel and biodiesel fuels: First, a diesel truck was used in the field, and in the second test, a similar diesel engine was used in the laboratory. The mass of particles and polycyclic aromatic hydrocarbons (PAH) was determined. No reduction was observed in the mass of particles per min using biodiesel relative to that produced when burning diesel. Pyrene and phenanthrene showed the highest mass concentrations in diesel and biodiesel in both tests. Reductions in these PAHs greater than 80% (in the truck field test) and 35% AE 11% (in the engine laboratory test) were observed when using biodiesel in any mixture thereof, with respect to diesel. The mean AE standard deviation of the ratios of BaA/(BaA þ Chry) and (BbF þ BkF)BghiP for diesel emissions were consistent with the literature. Four ratios amongst PAHs were proposed, with relative standard deviation < 10%, which suggests that these ratios could be used as emission markers for diesel and animal biodiesel blends (

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Mass attenuation coefficient is a fundamental parameter of radiation interaction, from which the other radiological parameters like half Value Layer [HVL], tenth Value Layer [TVL], total atomic and electronic cross-sections, mass energy absorption coefficient, KERMA, CT number and effective atomic number are deduced. These parameters are extensively required in a number of fields such as diagnostic radiology, gamma ray spectroscopy, fluorescence analysis and reactor shielding. In the present work, mass attenuation coefficients are determined experimentally for some organic compounds at 122 keV incident photons using narrow-beam transmission geometry to establish a relation between effective atomic number (Z eff) and other deduced parameters. The experimental data for all these parameters are compared with the values deduced from WinXcom software package and are found to agree within experimental estimated errors. This study gives some insight about the photon interaction in some organic compounds whose effective atomic numbers match with some human body fluids.

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