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BACKGROUND AND OBJECTIVES: Atmospheric zinc corrosion in the Mexico City Metropolitan area has long been attributed mainly to the effect of pollutants such as sulfur dioxide. There are changes in the urban atmosphere's chemical composition due to the implementation of air quality policies focused on reducing the emission of sulfur dioxide and other pollutants. This study's objectives were to estimate and map the contribution of nitric acid on zinc's atmospheric corrosion process. METHODS: The impact of nitric acid on zinc is feasible to estimate using a function for a multi-pollutant situation. This function contemplates the sum of two contributions: one of nitric acid and another that includes sulfuric acid and climatic parameters. The multi- pollutant function is suitable to apply in areas without the strong influence of chlorides and tropical and subtropical climates, comparable to the Mexico City Metropolitan area. FINDINGS: The results showed that spatial and temporal estimation of corrosion rates in grams per square meter of zinc was made for 2015-2019, using data modeling in a geographic information system. The maps of corrosion rates allowed us to visualize that, in general, the "southwest" zone has the most significant effects and that the lowest corrosion rates were presented in 2019 as an outcome of the implementation of air quality programs. Furthermore, a contribution of nitric acid up to 32% to the zinc corrosion rate was estimated. CONCLUSION: The construction of corrosion rate maps provides a spatial and temporal estimate that allows visualizing areas where zinc materials are at risk corrosion due to the dispersion of atmospheric pollutants and climatic parameters. Likewise, it can represent a decision-making tool for the implementation of atmospheric corrosion studies of materials. [ABSTRACT FROM AUTHOR]

Optical properties of atmospheric particles at Mexico City (UNAM) and Queretaro (JQRO) were measured with a Photoacoustic Extinctiometer (PAX) at 870 nm. The Mexico City Metropolitan Area has around 21 million inhabitants and Queretaro Metropolitan Area has little more than a million. Observations of meteorological parameters (relative humidity, solar radiation, and wind speed) were used to identify the rainy and dry seasons and explain the daily and seasonal behaviors of particles optical properties. The measurements were made from November 1, 2014 to July 31, 2016. At UNAM, the mean values of the scattering coefficient (Bscat) in cold dry, warm dry, and rainy seasons were 35.8, 27.1, and 31.3 Mm−1, respectively; while at JQRO were 10.9, 11.9, and 15.0 Mm−1. The average values of the absorption coefficient (Babs) at UNAM during the cold dry, warm dry, and rainy seasons were 14.5, 12.7, and 12.7 Mm−1, respectively; whereas at JQRO were 4.9, 4.7, and 3.9 Mm−1. Both absorption and scattering coefficients showed similar diurnal behaviors, but at UNAM they are three times higher than JQRO. Concentrations of criteria gases (O3, NO, NO2 and NOx) were also measured. At UNAM no difference was observed between the seasonal values for the single scattering albedo (SSA); while in JQRO, the rainy season had the highest seasonal value, being 13% higher than in the dry seasons. The Mass Scattering Cross-Section (MSC) values at UNAM were close to 2 m2/g; on the other hand, at JQRO the MSC values were lower than 1 m2/g. The results suggest a seasonal variability in the aerosol optical properties in both sites, which should be verified with more long-term studies. [ABSTRACT FROM AUTHOR]