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.
The steep slopes, highlands, and valleys of the Andes mountain chain are inhabited throughout its formidable length. This unique characteristic does not repeat in any other mountain region. The Andes shape weather and climate in South America. However, proper understanding of atmospheric phenomena influenced by a daunting altitudinal gradient is still behind what is needed to produce detailed and consistent climate projections. Despite significant advances, global models misrepresent key precipitation and circulation processes that are influenced by complex topography. Along with a lack of coordinated observations, the result is limited information to design preparedness measures, particularly to face extreme climate events. Of equal concern is the issue of air quality in densely urbanized countries that face decarbonization challenges and share a legacy of social inequity and political unrest. The complexity of the Andes region magnifies risks within all nations that share their influence. Thus, urgent action is needed to improve climate and air quality assessments with the direct purpose of strengthening policy-making processes.
Despite the decline in partially (PM 10) and fully (PM 2.5) inhalable particles observed in recent decades, Santiago in Chile shows high levels of particle and ozone pollution. Attainment plans have emphasized measures aimed at curbing primary and, to some extent, secondary particles, but little attention has been paid to photochemical pollution. Nevertheless, ozone hourly mixing ratios in Eastern Santiago regularly exceed 110 ppbv in summer, and in winter maximum mixing ratios often reach 90 ppbv. Moreover, the sum of ozone and nitrogen dioxide shows an increasing trend of more than 3.5 ppbv per decade at 5 out of 8 stations. This trend is driven by increasing NO 2 , possibly associated with increasing motorization but also with changes in photochemistry. To estimate the fraction of secondary particles in PM 2.5 and due to the lack of long-term speciation data for particles, we use carbon monoxide as a proxy of primary particles and ozone daily maxima as a proxy for secondary particle formation. We find a growing fraction of secondary particles due to an increase in the oxidizing capacity of Santiago's atmosphere. This stresses the need for new curbing measures to tackle photochemical pollution. This is particularly needed in the context of a changing climate.
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