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En los últimos años se ha confirmado, a través de multitud de estudios, la existencia de perjuicios graves en la salud de las personas derivados de una mala calidad del aire, lo que ha fomentado el interés en diferentes áreas para su mejora. Previamente, en el año 1987, y sus revisiones en 1997 y 2005, la Organización Mundial de la Salud [OMS) ya indicaba los principales contaminantes en el aire exterior y sus efectos adversos para la salud de las personas. Más tarde, en 2010, publicaba las directrices para espacios interiores. Establecidos estos, la organización estimaba, en 2016, que este factor es el causante de la muerte prematura de 4,2 millones de personas en el mundo. En el ámbito nacional, el estudio de la evaluación de la calidad del aire en España de 2020 constata que estos indicadores, entre los que destacan la materia particulada PM2,5 y PM1 O o el Ü 3, superaban ampliamente los valores límite recomendados por la OMS. Es por ello por lo que, el Consejo General de la Arquitectura Técnica de España ha realizado un estudio de la concentración de CO2 en viviendas, analizando diferentes factores que puedan influir en este indicador. En este caso, se presenta la relación de la concentración de CO2 con la apertura de la puerta durante el periodo nocturno, atendiendo a la exposición del usuario en el dormitorio, lo que ha permitido evaluar la diferencia de concentraciones entre los que duermen con la puerta abierta y los usuarios que lo hacen con la puerta cerrada, un factor que a priori puede parecer irrelevante, pero como veremos en los resultados tiene una gran importancia. Abstract In recent years, numerous studies have confirmed the existence of serious damage to people's health resulting from poor air quality, which has fostered interest in different areas for its improvement. Previously, in 1987, and its revisions in 1997 and 2005, the World Health Organization [WHO] already indicated the main pollutants in outdoor air and their adverse effects on people's health. Later, in 2010, it published the guidelines for interior spaces. Established these, the organization estimated, in 2016, that this factor is the cause of the premature death of 4.2 million people in the world. At the national level, the study of the evaluation of air quality in Spain in 2020 confirms that these indicators, among which particulate matter PM2.5 and PM1 O or Ü3 stand out, exceeded widely the limit values recommended by the WHO. That is why the General Council of Technical Architecture of Spain has carried out a study of the concentration of CO2 in homes, analyzing different factors that may influence this indicator. In this case, the relationship between the concentration of CO2 and the opening of the door during the night is presented, considering the exposure of the user in the bedroom, which has made it possible to evaluate the difference in concentrations between those who sleep with the door open. open and the users who do it with the door closed, a factor that may seem irrelevant at first, but as we will see in the results it is of great importance.

The Earth CO2 is constantly changing. During photosynthesis CO2 is assimilated and immobilized in the form of organic matter. In the other way around, under the action of chemical and biochemical processes, the CO2 of the organic matter is released again into the atmosphere. The current concentration of CO2 in the atmosphere is about 390 ppm. Based on information from the literature, it is possible to estimate the amount of organic matter produced from the CO2 available in the atmosphere. On the other hand, by incinerating all the plant and animal organic matter on the Earth, it is possible to estimate the amount of CO2 produced and released to the atmosphere. In order to test these hypotheses, mathematical models were developed. By the models it is possible to estimate that if all CO2 in the atmosphere is assimilated via photosynthesis, it would produce 296 Mg.ha-1 of organic matter. On the other hand, by incinerating all vegetable and animal organic matter from the Earth, excluding petroleum, coal and other carbon sources, and considering an average value of 100 Mg.ha-1 the CO2 concentration in the atmosphere would increase by 131.8 ppm. This value added to the existing 390 ppm would raise CO2 concentration to 521.8 ppm. According to the models and results presented, forests may not be as important as carbon accumulators, making the environment conducive to life on Earth, but according to literature they are essential in the formation of rainfalls and maintenance of humidity, especially in areas far from the oceans and seas.

The objective of this study was to evaluate gas exchange in the massai grass during establishment and regrowth cycles in a greenhouse, using five nitrogen (N) fertilization levels. A completely randomized split-plot design of five nitrogen levels (0; 150; 300; 450 and 600 mg N•dm-3 of soil) was employed with the N levels as plots, and the cycles (establishment, regrowth 1 and 2) as subplots, evaluated with five replicates. We evaluated leaf transpiration (E), leaf temperature (TFOL), leaf photosynthesis rate (A), leaf carbon dioxide concentration (Ci), stomatal conductance (gs), photosynthesis/transpiration ratio (A/E), photosynthesis/conductance ratio (A/gs), chlorophyll relative index (CRI), and nitrogen sufficiency index (NSI). Growth cycles influenced all physiological characteristics, except for NSI. N fertilization levels affected TFOL, A, CRI and NSI variables, whereas for gs, E, Ci, A/E and A/gs it did not occur. A increased from 6.38 to 10.33 µmol•m-2.s-1, at levels 0 and 600 mg N•dm-3 of soil, respectively. Gas exchange in the massai grass was favored by nitrogen fertilization, since the cycles amended these characteristics of the grass.