RESUMEN
This paper explores the performance of smartphone cameras as low-cost and easily accessible tools to provide information about the levels and origin of particulate matter (PM) in ambient air. We tested the concept by digital analysis of the images of daily PM10 (particles with diameters 10 µm and smaller) samples captured on glass fibre filters by high-volume aerosol samplers at urban and rural locations belonging to the air quality monitoring network of Extremadura (Spain) for one year. The images were taken by placing the filters inside a box designed to maintain controlled and reproducible light conditions. Digital image analysis was carried out by a mobile colour-sensing application using red, green, blue/hue, saturation, value/hue, saturation, luminance (RGB/HSV/HSL) parameters, that were processed through statistical procedures, directly or transformed to greyscale. The results of the study show that digital image analysis of the filters can roughly estimate the concentration of PM10 within an air quality network, based on a significant linear correlation between the concentration of PM10 measured by an official gravimetric method and the colour parameters of the filters' images, with better results in the case of the saturation parameter (SHSV). The methodology based on digital analysis can discriminate urban and rural sampling locations affected by different local particle-emitting sources and is also able to identify the presence of remote sources such as Saharan dust outbreaks in both urban and rural locations. The proposed methodology can be considered as a useful complement to the aerosol sampling equipment of air quality network field units for a quick estimation of PM10 in the ambient air, through a simple, accessible and low-cost procedure, with further miniaturization potential.
RESUMEN
We have proven the overall applicability of the novel sonoreactor VialTweeter as a tool for a fast, miniaturized and economical extraction of trace elements, namely Cu, Zn, As, Cd, Pb, from soil samples, followed by ICP-MS. The proposed analytical approach applicable in the context of environmental monitoring of elemental soil pollutants, since the selected analytes are relevant pollutants whose presence in soils produces significant effects on their quality affecting animals, plants and humans. The optimum conditions for the extraction of trace metals assisted by the sonoreactor, selected by a Box-Behnken (BBD) experiment design along combined with a response surface methodology were 93% sonication amplitude, 450 s sonication time, 80% HNO3 and a solvent/sample ratio of 0.18 mL/mg. The proposed sonoreactor-assisted extraction methodology provides several advantages of respect to the standard acid digestion taken as comparison term for validation, including a shorter pretreatment time and use of less sample and reagents amounts. However, mixed validation results against the standard acid digestion (taken as a model providing accurate results) were obtained depending on the analyte, with the best results in the case of cadmium that could be measured after US extraction without systematic error respect to the standard acid digestion. Copper and lead can be determined by the proposed US extraction plus ICP-MS only after applying a correction factor based on the slope of the correlation with the standard acid digestion. US treatment for As determination can be only useable by applying a constant correction factor based on the intercept of the correlation line, whereas Zn determination requires a correction based both in the slope and intercept of the correlation line.