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We present the effects of the confinement and physical distancing policies applied during the COVID-19 pandemic on the concentrations of PM10, PM2.5, NO, NO2 and O3 in 16 cities in central and southern Chile. The period between March and May in 2020 was compared with the corresponding months during 2017–2019, using surface data and satellite information. The relative percent changes in the concentration of atmospheric pollutants, and the meteorological variables observed between these two periods were used to quantify the effects of the lockdowns on the local air quality of the urban areas studied. The results showed statistically significant changes in 11 of the 16 cities. Significant relative changes between +14% and –33% were observed for PM10 in 9 cities; while statistically significant changes between –6% and –48% were evident for PM2.5 in 10 cities. Significant decreases between –27% and –55%, were observed in 4 cities in which NO2 data were available; while significant increases in O3, between 18% and 43%, were found in 4 of the 5 cities with available data. The local meteorological variables did not show significant changes between both periods. In all the cities studied, one of the main PM sources is wood burning for residential heating. Although the quarantine imposed during the health emergency could have induced an increase in residential emissions, these were compensated with the reductions in vehicular and/or industrial emissions. Therefore, these results should be carefully interpreted and should inspire new research considering the social, cultural, and economic factors that could alter the common emission patterns and air quality of urban centers.

The mass concentration of particulate matter (PM) has been systematically used in epidemiological studies as exposure indicator, to relate airborne concentrations with a wide variety of human health effects, which can be hardly explained by using this single parameter. In fact, PM is a “particle cocktail” that includes a complex mixture of compounds with a wide range of sizes, chemical compositions and emission sources. Current research hypothesizes that many of the adverse health effects are derived from oxidative stress in biological systems caused by the deposition of PM into the lungs. This emerging hypothesis is called the oxidative stress paradigm. In this commentary article we analize how this new paradigm could help to answer the as-of-yet unanswered questions related to the mechanism of action of PM pollution on human health. Acellular oxidative potential (OP) assays have been emerged as a promising approach to quantify the PM potential to induce oxidative stress and to relate it with the chemical composition and size distribution of PM. Recent researches have shown that the OP is related to the presence of metals, organic carbon, polyaromatic hydrocarbons and quinones. However, the association between PM and particle-induced toxicity is still largely unknown. Therefore, additional research is needed to identify the specific PM characteristic(s), such as its specific size, emission source or chemical content, which contribute the most to its redox activity. Thus, the OP measurements provide information that allows us to evaluate and integrate the toxic potential of PM in a unique parameter, whose relationships with emission sources, size distribution and/or chemical composition should be faced in the near future.

To improve the current understanding of the ammonia distribution in the major urban area of Chile, measurements of atmospheric NH3 were collected in Santiago during three sampling periods (25 April to 27 May, 11 to 26 June and 27 June to 31 July 2008). Additionally, air quality and meteorological data as well as NH4 + , NO3 – , SO4 = and Ca +2 concentrations in fine particles were collected during the same period. NH3 concentrations for the different sites in the three sampling periods varied from 7.7 ± 2.0 µg/m 3 to 19.8 ± 2.1 µg/m 3 . The results of one-way ANOVA and cluster analysis suggest that were no significant differences between the three sampling periods, but significant differences in NH3 concentrations were detected between the sampling sites. Furthermore, two clusters were found with a pronounced difference between sampling sites located in the eastern part of the city and those located in the western part of the city. The results suggest that the distribution of ammonia in the western part of the city is due to the emissions of ammonia by agricultural areas, wetlands and the large sewage treatment plants, while in the eastern part of the city, ammonia emissions are governed by vehicular emissions. Fine particles (PM2.5) chemical speciation showed NH4 + /SO4 = and NO3 – /SO4 = molar-equivalents ratios of 5.7 ± 0.3 and 1.8 ± 0.1, respectively. The results show that during the sampling period, complete neutralisation of H2SO4 and HNO3 occurred in the presence of excess of NH4 + and NH3. Therefore, the atmosphere of Santiago can be considered to be ammonia-rich in the gas phase. Abundant NH3 was present to neutralise the acid components, such as H2SO4 and HNO3, and to form fine particulate ammonium salts, such as (NH4)2SO4, NH4NO3 and others. Relatively high humidity and low temperatures in the cold season support the formation of particulate ammonium nitrate.

The Valparaiso Region is characterized by the presence of air sheds that modulate the general atmospheric circulation with local winds. The ozone concentration in the region increases from the west coast toward the mountainous area, where the concentrations of ozone precursors are lower. In this study, surface ozone (O3), nitric oxide, nitrogen dioxide, nitrogen oxide (NO x ), and volatile organic compounds (VOCs) were measured at four sites, including two upwind urban sites (Vina del Mar (VM) and Villa Alemana (VA)), an upwind suburban site (Quillota (QU)) and a downwind semirural site (Los Andes (LA)) during 01 March–07 April 2010. The purpose of this study is to improve our understanding of the photochemistry of ozone in urban and semirural areas of the Valparaiso Region and the transport of ozone pollution in downwind rural areas. The results show that, in the VM and VA sites, higher concentrations of ozone precursors, NO x , and VOCs, are observed in the early morning hours, which is related to emissions from vehicle traffic, while comparatively lower ozone precursor concentrations are observed in QU and LA. In contrast, higher ozone concentrations are found in LA and QU, and lower concentrations are found in VM and VA. VOC analysis was performed by gas chromatography, and the results show that the VOC composition in the studied sites is similar to and coincident with vehicle emissions. An ozone formation regime limited by VOCs is found in the area. The leading contributors to the ozone-forming potential were ethene, propene, xylene, and toluene, which are also anthropogenic species and account for more than 70 % of O3 formation. Thus, benzenes–toluene–xylenes played the most important role in O3 formation, followed by alkenes, alkanes, aromatic, biogenic, and alkynes during the study periods. The m-, p-xylene/ethylbenzene relation confirms the reception of aged air masses in LA. The results of the present study demonstrate that ozone pollution is a regional problem and that O3 regional transport is associated with such pollution. Finally, the results indicate the need to adopt mitigating measures for ozone pollution that consider the reactivity characteristics of VOCs.

Ammonia, one of the ambient gasses that require environmental monitoring, is typically measured using a passive sampling method. The present work presents an evaluation of the uncertainty according to the Guide to the Expression of Uncertainty in Measurement for the measurement of the atmospheric ammonia concentration as determined by an Ogawa passive sampler, using a colorimetric method. The analytical results report the uncertainty only as a standard deviation of repeated measurements, but not all sources of uncertainty are considered. In this work, the major sources of uncertainty in the measurements are identified as contributions to the linear least-square regression lines, repeatability and recovery. The result, including the expanded uncertainty (k = 2) at a level of confidence of 95%, is 39.2%. The aforementioned results indicate that the Ogawa sampler can be successfully deployed to estimate the atmospheric NH3 and could find wide application in environmental monitoring. However, to obtain correct conclusions, the uncertainty in the measurements must be considered.

Electrostatic precipitators, fabric filters, and certain types of scrubbers appear to be the only commercially available devices that have the capacity to meet current emission standards for incinerators. The design, advantages and disadvantages of each of these mechanisms is briefly discussed, and factors to be considered in the selection of control systems are noted. Initial cost, operating cost, reliability, and efficiency of pollutant removal are considered. Energy requirements are said to represent the single most important difference between systems, with scrubbers having by far the greatest requirement of the three systems. (JTE)