Photochemical sensitivity to emissions and local meteorology in Bogotá, Santiago, and São Paulo: An analysis of the initial COVID-19 lockdowns

This study delves into the photochemical atmospheric changes reported globally during the pandemic by analyzing the change in emissions from mobile sources and the contribution of local meteorology to ozone (O3) and particle formation in Bogotá (Colombia), Santiago (Chile), and São Paulo (Brazil). The impact of mobility reductions (50%–80%) produced by the early coronavirus-imposed lockdown was assessed through high-resolution vehicular emission inventories, surface measurements, aerosol optical depth and size, and satellite observations of tropospheric nitrogen dioxide (NO2) columns. A generalized additive model (GAM) technique was also used to separate the local meteorology and urban patterns from other drivers relevant for O3 and NO2 formation. Volatile organic compounds, nitrogen oxides (NOx), and fine particulate matter (PM2.5) decreased significantly due to motorized trip reductions. In situ nitrogen oxide median surface mixing ratios declined by 70%, 67%, and 67% in Bogotá, Santiago, and São Paulo, respectively. NO2 column medians from satellite observations decreased by 40%, 35%, and 47%, respectively, which was consistent with the changes in mobility and surface mixing ratio reductions of 34%, 25%, and 34%. However, the ambient NO2 to NOx ratio increased, denoting a shift of the O3 formation regime that led to a 51%, 36%, and 30% increase in the median O3 surface mixing ratios in the 3 respective cities. O3 showed high sensitivity to slight temperature changes during the pandemic lockdown period analyzed. However, the GAM results indicate that O3 increases were mainly caused by emission changes. The lockdown led to an increase in the median of the maximum daily 8-h average O3 of between 56% and 90% in these cities

Aerosoles secundarios en Santiago de Chile: estado y tendencias

Tesis para optar al grado de Magíster en Meteorología y ClimatologíaA pesar de la reducción de las concentración de partículas, total (MP2.5) y parcialmente (MP10) respirables, observadas en Santiago de Chile desde mediados de los años 1990, informes recientes de la Organización mundial de la Salud (OMS), muestran que la ciudad de Santiago aún se mantiene entre las áreas urbanas más contaminadas del mundo. Los planes de descontaminacíon implementados desde 1997 han enfatizado medidas destinadas a frenar las actividades responsables de la emisiones primarias de aerosoles, pero, hasta ahora, poca atención se ha prestado a la contaminación fotoquímica. Sin embargo, las razones de mezcla de ozono (O3) en el este de Santiago regularmente exceden 110 ppbv en verano, mientras que en invierno las razones de mezcla a menudo alcanzan máximos de 90 ppbv. Además, la suma de O3 y dióxido de nitrógeno (NO2), denominada Ox (Ox = O3 + NO2) y utilizada como un estimador de la actividad fotoquímica atmosférica, muestra una tendencia creciente de más de 3.5 ppbv por década en 5 de 8 estaciones en Santiago, donde se dispone observaciones de estas especies. Esta tendencia es impulsada por el aumento de NO2, posiblemente asociado a las crecientes tasas de motorización en Santiago. A falta de datos de la especiación química a largo plazo para aerosoles, este trabajo utiliza la traza de monóxido de carbono (CO) como indicador de aerosoles primarios y los máximos diarios de ozono (O3max) como indicador de la formación de aerosoles secundarios. Esto con el fin de generar una estimación empírica de la fracción secundaria de MP2.5. Esta estimación es comparada con la provista por un modelo de dispersión y transporte químico de última generación (EMEP). Ambas aproximaciones son comparables y evidencian una fracción de aerosoles secundarios, que alcanza una contribución cercana al 50\% en el total de MP2.5 en los últimos años. Todo esto muestra la necesidad en la toma de nuevas medidas enfocadas a controlar la contaminación fotoquímica en el plan de descontaminación regional. Esto es relevante por los impactos sobre la salud y el clima regional

PM2.5 forecasting in Coyhaique, the most polluted city in the Americas

Coyhaique is a southern Chilean city with a population of approximately 64,000 habitants. In spite of its small size, Coyhaique has been identified as the city with highest annual PM2.5 concentrations of the Americas (including south America, central America and north America). Episodes of high pollution are concentrated on the fall- winter season when meteorological conditions do not favor atmospheric particle dispersion and extended use of wood stoves is responsible for more than 99% of the emissions. In Chile, the 24 h average of PM2.5 concentration is classified in four ranges: fair, bad, very bad and critical. We have developed a neural network model and a linear model aimed to forecast the maximum of the 24 h moving average one day in advance. Input variables for the models are hourly values of PM2.5 at 18 h and 19 h of the present day, measured and forecasted temperature, wind speed and precipitation and measured values of NO2, CO and O3 concentrations. The neural network model is slightly more accurate than the linear model. We are able to anticipate the observed range in 75% of the cases, and critical days in 84% of the cases

Forecasting of hourly PM2.5 in south-west zone in Santiago de Chile

© Taiwan Association for Aerosol Research. We present the results of a neural network model designed for the forecasting of hourly PM2.5 concentrations in Santiago, Chile. The study focuses on the observed values at two of the monitoring stations, which are located in the south-west zone of the city and are among the stations that register the highest concentrations during the period between April and August. This is the season when air quality is very often in ranges that are harmful to the population and some restrictions on emissions become useful. The forecasting model is a multilayer neural network. The input variables are observed values of hourly PM10 and PM2.5 concentrations measured at the station of interest and at a neighboring station at 7 PM of the present day and some observed and forecasted meteorological variables. NO2 concentrations during the morning and afternoon hours, which may be associated with secondary particle formation, are also used as input. The implemente

Evaluation of anthropogenic air pollutant emission inventories for South America at national and city scale

International audienceThe changing composition of the atmosphere, driven by anthropogenic emissions, is the cause of anthropogenic climate change as well as deteriorating air quality. Emission inventories are essential to understand the contribution of various human activities, model and predict the changing atmospheric composition, and design cost-effective mitigation measures. At present, national emission inventories in South America (SA) focus on Greenhouse Gases (GHG) as part of their obligation to the United Nations Framework Convention for Climate Change (UNFCC) within the framework of their national communications. Emission inventories other than GHG in SA focus mainly on growing urban areas and megacities. Therefore, studies examining air quality at national, regional or continental scales in SA depend on (down-scaled) global emission inventories. This paper examines the emission estimates of air pollutants from various global inventories for five SA countries, namely Argentina, Brazil, Chile, Colombia and Peru. A more detailed analysis is conducted for the EDGAR and ECLIPSE emission inventories, in particular comparing local city-scale inventories of a major city in each country. Although total emissions between down-scaled global inventories and local city inventories are often comparable, large discrepancies exist between the sectoral contributions. This is critical, as the mitigation of poor air quality will depend on addressing the right sources. Potential sources of discrepancies between global and local inventories include the spatial distribution proxies, difference in emission factors used and/or the use of generic statistical country data when estimating emissions. This highlights the importance of using local information when generating national emission inventories, especially for air quality modeling and development of effective mitigation measures. This study represents the first step towards an increased understanding of the strengths and weaknesses of emissions information in SA