Carbonyl concentrations in indoor-outdoor air were measured at three urban sites in the Metropolitan Zone of Mexico Valley (MZMV) during the first period of confinements due to COVID-19; the exposure for people living in indoor environments was also assessed. Indoor and outdoor samples were simultaneously collected sequentially with Sep-Pack DNPH-Silica cartridges. Formaldehyde, acetaldehyde, acetone, propionaldehyde, butyraldehyde and acrolein were quantified according to the US-EPA TO-11A method. Acrolein and acetone were the most abundant carbonyls in indoor air, with average concentrations of 55.5 µg m−3 and 46.4 µg m−3, respectively, followed by formaldehyde (29.1 µg m−3), acetaldehyde (21.4 µg m−3) and butyraldehyde (7.31 µg m−3). Propionaldehyde was not detected. Acetone was the dominant carbonyl in outdoor samples with an average concentration of 8.4 µg m−3, followed by formaldehyde (2.8 µg m−3) and acetaldehyde (0.7 µg m−3). Butyraldehyde and acrolein were not detected in outdoor air. Indoor/outdoor (I/O) ratios showed that indoor sources prevail for most aldehydes. Statistical analysis of simple correlations showed that the measured carbonyls were influenced by the presence of indoor sources. The average cancer risk coefficients (LTCR) for formaldehyde and acetaldehyde and the non-cancer risk coefficients (HQ) for acrolein and formaldehyde were higher than the recommended limits, which should be a cause for public concern.
<p>The estimation of emissions inventories of climate forcing species and air pollutants from activities such as the burning of biomass from cooking food in rural environments in Mexico presents some degree of uncertainty due to the lack of locally obtained emission factors; emissions estimates were generally obtained with other types of biomass and cookstoves. The relevance of these pollutants to Mexico is mainly due to their contribution to air pollution, global warming and negative impacts on human health. This study presents an assembly of a series of theoretical-experimental procedures for the estimation of emission factors in improved stoves and other biomass burning processes. The design is based on the use of a controlled dilution system from which samples are obtained for the determination of PM<sub>2.5</sub>&#160;and the content of organic carbon and elemental carbon. The flow of diluted samples is conditioned for continuous monitoring of polluting gases (NOx, CO, NHMC, and SO<sub>2</sub>), in addition to climate forcing gases such as CO<sub>2</sub>&#160;and CH<sub>4</sub>&#160;with a mobile laboratory equipped with instrumentation for air quality measurements. The new sampling design allows the determination of gaseous and particle matter emission factors through the application of two procedures: carbon mass balance and concentration ratios with respect to CO<sub>2</sub>&#160;and CO. The proposed design was evaluated for three improved cookstoves (Patsari, Onil, Ecoestufa) using a water boiling test protocol and white oak as fuel, the proposed controlled dilution sampling design can be a reliable method for the determination of emission factors from small combustion sources when biomass is used as fuel and also by using the carbon balance to obtain the emission factors, we reduce the inherent uncertainties of the process due to the difficulty associated with the sampling of this type of emissions under isokinetic conditions in low flow exhaust conditions such as those of small emission sources. The final emission factor consists of a weighted range of the factors determined for each species with respect to the amount of oxidized carbon in each of them. The feasibility of the experimental design is demonstrated by an application of using white oak wood as fuel in three improved cookstoves and one three stones. The ranges of emission factors obtained for the three improved cookstoves in g/kg of wood consumed were: CO<sub>2</sub>, 1309-1375; CH<sub>4</sub>, 3-4; EC, 0.16 &#8211; 0.71; OC 1.94-2.89; CO, 63 - 103; y PM<sub>2.5</sub>, 3.17 &#8211; 4.12, while for the three stones the ranges of emission in g/kg of wood consumed were: CO<sub>2</sub>, 1141- 1232; CH<sub>4</sub>, 4.15-4.71; EC, 1.06 &#8211; 1.78; OC, 4.79-6.03; CO, 124 - 170; y PM<sub>2.5</sub>, 7.47 &#8211; 10.18 g/kg.</p>
El conocimiento del perfil vertical de la composición de los compuestos orgánicos volátiles (COVs) en áreas urbanas contaminadas puede ayudar a un mejor entendimiento del impacto de estos compuestos en la calidad del aire y en el desarrollo de mejores estrategias de control. Con el fin facilitar este tipo de mediciones y de que éstas tengan la confiabilidad necesaria, se diseñó e integró un dispositivo de muestreo miniaturizado programable de COVs ligero de bajo costo, que permite el anclaje de varios de ellos a diversos niveles de altura en el cordel de un globo meteorológico cautivo instrumentado, y cuyo arranque y paro de los muestreadores es controlado desde superficie. El muestreo simultáneo asegura que el perfil vertical de los COVs capturados representen con mejor certeza las diferencias esperadas en la concentración de estos compuestos debido a la influencia del dosel urbano y de la actividad urbana. Cada dispositivo de muestreo consiste en un circuito electrónico que recibe la señal de arranque y/o paro de la minibomba de succión de aire de un sistema maestro de control que se ubica en superficie y que comanda la operación por radiofrecuencia. La captura de los COVs es realizada por medio de un cartucho empacado con un medio adsorbente apropiado para este objeto. La aplicabilidad del sistema miniaturizado fue demostrada en una campaña corta de muestreos a los niveles 0 m, 50 m, y 100 m sobre la superficie en un sitio al suroeste de la Zona Metropolitana de la Ciudad de México durante abril de 2017. Los perfiles de las concentraciones de COVs determinadas fueron comparados tanto con registros previos obtenidos a nivel superficie como en perfiles verticales utilizando métodos de muestreo menos dinámicos demostrando así el beneficio de conocer la concentración a diferentes alturas en la interpretación de la química atmosférica asociada a estos perfiles.
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