Evidence of traffic-generated air pollution in Havana

In Havana, transport is blamed as a likely source of pollution issues, which is usually supported on arguments referring to a vehicle fleet mainly made of old cars (i.e., most models are American from the 1950s or Russian from the 1980s) with poor technical conditions. Most of the existing studies are based on measurements from passive samplers collected for 24 h, which may not be representative of conditions where pollutant concentrations (particles or gases) fluctuate or are not homogeneous, such as transport-related pollution. The goal of this paper is to explore the transport-generated pollution by examining short-time correlations between traffic flows, pollutant concentrations and meteorological parameters. To do that, statistical relationships among all variables were analyzed, which revealed that PM10, NO2 and SO2 concentration levels are influenced by vehicular traffic, mainly with low-speed winds blowing perpendicular to the street axis. Furthermore, southeast and northeast winds force drag pollution from sources other than traffic. These conclusions depend on the specific conditions of the summer season at the measurement area. A more complete analysis could be conducted when more data becomes available for each season

CFD modeling and evaluation of a bi-stable micro-diverter valve

ABSTRACT Micro-diverter valves are innovative and efficient devices used to generate microbubbles that can significantly enhance process efficiency in industry. Micro-diverter valves have been experimentally tested and modeled using CFD in previous works. However, a detailed CFD modeling evaluation of these valves has not been performed employing detailed turbulence modeling at transient and steady state. This article presents a three-dimensional CFD simulation and performance evaluation of a bi-stable diverted valve for microbubble generation. In the model, transient and steady state approaches were used to quantify the behavior in the valve. The K - ε standard and k - ε RNG turbulence models were used and compared. Different mesh configurations, mesh generation methods, and both turbulence models were evaluated to find the best set-up to simulate this valve. A brief analysis of the time-step size using the Courant number approach was also performed. Operation conditions at low Reynolds (3800) and high frequency (200 Hz) were used to assess possible industrial applications, thus setting the base for further studies. The results of this work show that at low Reynolds numbers and high frequencies, the valve is able to divert the fluid and thus it may have wider industrial applications.RESUMEN Las válvulas de micro- desviación son dispositivos innovadores y eficientes que se utilizan para generar microburbujas que pueden mejorar significativamente la eficiencia de un proceso en la industria. Las válvulas de microdesviación han sido probadas experimentalmente y modeladas usando CFD en trabajos previos. Sin embargo, hasta el momento no se había llevado a cabo una evaluación del modelado en CFD de éstas válvulas utilizando un modelo detallado de turbulencia en estado transitorio y estable. Este artículo presenta una simulación tridimensional de CFD y la evaluación del rendimiento de una válvula desviada biestable para la generación de microburbujas. En el modelo, fueron utilizados aproximaciones en estado estable y transitorio para cuantificar el desempeño de la válvula. Los modelos k - ε estándar y de turbulencia k - ε RNG fueron utilizados y comparados. Fueron evaluados diferentes métodos de generación y configuraciones de malla y ambos modelos de turbulencia para encontrar la mejor configuración para simular esta válvula. Además se realizó un breve análisis del tamaño del paso de tiempo utilizando el enfoque del número Courant. Fueron evaluadas las condiciones de operación a bajo Reynolds (3800) y alta frecuencia (200 Hz) para posibles aplicaciones industriales, sentando así la base para estudios posteriores. Los resultados de este trabajo muestran que a bajos números de Reynolds y altas frecuencias, la válvula puede desviar el fluido y, por lo consiguiente puede servir en una amplia cantidad de aplicaciones industriales

Air quality variations in Northern South America during the COVID-19 lockdown

Lockdown measures led to air pollution decrease in several countries around the world such as China and India, whereas other regions experimented an increase in pollutant concentrations. Northern South America (NSA) was one of those areas where pollution changed during lockdown due to high fire activity. This study aims to analyze, for the first time in NSA, the behavior of selected criteria air pollutants during the implementation of the SARS-CoV-2 lockdown in two high populated cities of the region: Bogotá and Medellín in Colombia. A set of tools including surface measurements, as well as satellite and modeled data were used. 24-hour average concentrations of PM , PM , and NO were collected from air quality stations for the lockdown period ranging from February 21 to June 30, 2020. The Copernicus Atmosphere Monitoring Service (CAMS) was used to analyze the fire flux OC as a biomass burning (BB) indicator, and tropospheric NO concentrations were retrieved from TROPOMI. The HYSPLIT model was used to analyze back trajectories and fire data were obtained from MODIS sensor measurements. Our analysis shows short-term background NO , PM , and PM concentration reductions of 60%, 44%, and 40%, respectively, for the strict lockdown; and 62%, 58%, and 69% for the relaxed lockdown. Corresponding long-term reductions were of 50%, 32%, and 9% for the strict lockdown; and 37%, 29%, and 19% for the relaxed lockdown. Regional BB increased PM concentrations by 20 μg/m during the strict lockdown, and the Saharan dust event increased PM concentrations up to 168 μg/m in Bogotá, and 104 μg/m in Medellín, bringing an additional risk of morbidity and mortality for population. Regional BB has several causes that need to be properly managed to benefit local air quality improvement plans. Future cleaner transport policies equivalent to reduced lockdown mobility could bring pollution close to WHO guidelines. 10 2.5 2 2 2 10 2.5 2.5 10 3 3