The implementation of confinement and physical distancing measures to restrict people's activities and transit in the midst of the COVID-19 pandemic allowed us to study how these measures affect the air quality in urban areas with high pollution rates, such as Santiago, Chile. A comparative study between the concentrations of PM10, PM2.5, NOx, CO, and O3 during the months of March to May 2020 and the corresponding concentrations during the same period in 2017–2019 is presented. A combination of surface measurements from the air quality monitoring network of the city, remote satellite measurements, and simulations of traffic activity and road transport emissions allowed us to quantify the change in the average concentrations of each pollutant. Average relative changes of traffic emissions (between 61% and 68%) implied statistically significant concentrations reductions of 54%, 13%, and 11% for NOx, CO, and PM2.5, respectively, during the pandemic period compared to historical period. In contrast, the average concentration of O3 increased by 63% during 2020 compared to 2017–2019. The nonlinear response observed in the pollution levels can be attributed to the changes in the vehicular emission patterns during the pandemic and to the role of other sources such as residential emissions or secondary PM.

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Pollen is one of the primary causes of allergic rhinoconjunctivitis in urban centers. In the present study, the concentrations of 39 different pollens in the Santiago de Chile metropolitan area over the period 2009–2013 are characterized. The pollen was monitored daily using Burkard volumetric equipment. The contribution of each type of pollen and the corresponding time trends are evaluated. The concentrations of the pollens are compared with the established threshold levels for the protection of human health. The results show that the total amount of pollen grains originating from trees, grasses, weeds and indeterminate sources throughout the period of the study was 258,496 grains m-3, with an annual average of 51,699 ± 3,906 grains m-3 year-1. The primary source of pollen is Platanus orientalis, which produces 61.8% of the analyzed pollen. Grass pollen is the third primary component of the analyzed pollen, with a contribution of 5.82%. Among the weeds, the presence of Urticacea (3.74%) is remarkable. The pollination pattern of the trees is monophasic, and the grasses have a biphasic pattern. The trends indicate that the total pollen and tree pollen do not present a time trend that is statistically significant throughout the period of the study, whereas the grass pollen and weed pollen concentrations in the environment present a statistically significant decreasing trend. The cause of this decrease is unclear. The pollen load has doubled over the past decade. When the observed concentrations of the pollens were compared with the corresponding threshold levels, the results indicated that over the period of the study, the pollen concentrations were at moderate, high and very high levels for an average of 293 days per year. Systematic counts of the pollen grains are an essential method for diagnosing and treating patients with pollinosis and for developing forestation and urban planning strategies.

Artículo de publicación ISISin acceso a texto completoThe relationships between ozone (O-3) and its precursors, nitrogen oxides (NO (x) ) and volatile organic compounds (VOCs), were investigated in the VIR region (34A degrees 10' S, 71A degrees 36' W), referred to as Libertador General Bernardo O'Higgins of Chile. Observations were obtained from a field study performed at four monitoring sites, which represented different environmental conditions, i.e., rural-coastal (Marchihue, MA), urban (Rancagua, RA, and Rengo, RE), and semi-urban (Codegua, CO) during the summer (between Feb 1 and Mar 12, 2010). Overall, greater O-3 concentrations were identified at the urban sites compared with the semi-urban and rural sites. In addition, the O-3 precursor concentrations were high in the early morning hours as a consequence of fresh vehicular emissions (from 11 to 40 ppbv for NO (x) and from 15 to 36 ppbC for VOC). The total VOC/NO (x) ratios at the study sites indicated that the formation of O-3 was limited by VOCs. Most O-3 was formed from ethene, isoprene, propene, 2-methylpropene, m- and p-xylenes, and toluene. These VOCs accounted for more than 50 % of the O-3 formation. The m- and p-xylene/ethylbenzene ratio confirmed the reception of aged air masses at the CO site. In contrast, at the RA site, the impact of pollution was primarily local. Control measures should be implemented to prevent O-3 exceedances of the National Ambient Air Quality Standard (NAAQS), despite the fact that the current O-3 concentrations do not exceed the current 8-h standard of 61 ppbv. These measures should include the control of VOC emissions and their chemical reactivity.Chilean Ministry of the Environment Scholarships-Chile CONICYT Facultad de Ciencias of the Universidad de Chile CONICYT/FONDECYT 1113017

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AbstractsQuadrupole moments, dipole quadrupole polarizability A, and quadrupole polarizability C values have been obtained for a set of organic molecules, in both the ground and first singlet excitedstates, by means of Rayleigh-Schrodinger perturbation theory. Computations for T systems have been carried out using the PPP-SCF procedure. Results are discussed through the paper and compared with available experimental and theoretical information. Quadrupole moments are shown to be very sensitive to the quality of the wave functions, and the A and C polarizabilities are highly dependent on geometries.On a obtenu les moments quadrupolaires, les polarisabilites dipolaires-quadrupolaires et les polarisabilites quadrupolaires dans un ensemble de moltcules organiques, pour I'ttat fondamental et le premier Ctat excitt singulet, utilisant la thtorie de perturbation d e Rayleigh-Schrodinger. Pour les calculs relatifs aux systkmes r on a utilise la mtthode PPP-SCF. Les resultats sont discutes et compares avec I'information theorique et exptrimental de la literature. Les moments quadrupolaires se sont montrts trks sensibles a la qualite de la fonction d'onde et les polarisabilites A et C sont fortement dependantes d e la geometrie.Quadrupolmomente, Dipol-Quadrupol-Polarisierbarkeiten A und Quadrupol-Polarisierbarkeiten C sind fur eine Reihe von organischen Molekulen im Grundzustand und in den ersten angeregten Singulettzustanden mittels Rayleigh-Schrodinger-Storungstheorie berechnet worden. Die Berechnungen fur die r-Systeme sind mit dem PPP-scF-Verfahren ausgefuhrt worden. Die Ergebnisse werden diskutiert und mit zuganglichen experimentellen und theoretischen Daten verglichen. Es zeigt sich, dass die Quadrupolmomente von der Qualitat der Welienfunktion sehr stark abhangen, wahrend die Polarisierbarkeiten sehr von der Geometrie abhangen.