Dear Colleagues,

Air pollution is the world’s single greatest environmental risk to health. Some 6.5 million people across the world die prematurely every year from exposure to outdoor and indoor air pollution, and nine out of ten people breathe outdoor air polluted beyond acceptable WHO guidelines levels.

Megacities (metropolitan areas with populations over 10 million) present a major global environmental challenge. Rapid population growth, unsustainable urban development, and increased energy demand by transportation, industrial, commercial, and residential activities, have led to large amounts of emissions to the atmosphere that subject the residents to the health risks associated with harmful pollutants, and impose heavy economic and social costs.

The aim of this Special Issue is to present original research articles and reviews in assessing air pollution in metropolitan areas and megacities, including both experimental and monitoring studies and mathematical/numerical modeling studies. Topics to be covered include gases pollutants and urban aerosol observations, including particulate matter chemical characterization and human exposure assessment.

Dr. Thiago Nogueira
Dr. Taciana Toledo De Almeida Albuquerque
Dr. Rodrigo J. Seguel
Dr. Manousos Ioannis Manousakas
Dr. Néstor Y. Rojas
Guest Editors

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1. Title: Use of low-cost sensors for environmental health surveillance: wildfire-related particulate matter detection in Brasília, Brazil

Authors: Patrick Joseph Connerton¹, Thiago Nogueira¹, Prashant Kumar², Helena Ribeiro¹

1. University of São Paulo, School of Public Health
2. University of Surrey, Department of Civil and Environmental Engineering

Abstract: Ambient air quality is the most important environmental factor affecting human health, estimated by the WHO to be responsible for 4.2 million deaths annually. Having timely estimates for air quality is critical for implementing public policies that can limit anthropogenic emissions, reduce human exposure and allow for preparation and interventions in the health sector. In Brazil, wildfires constitute an important source of particulate matter emission, particularly in the North and Mid-West regions, areas that are underserved in terms of air quality monitoring infrastructure. In the absence of regulatory-grade monitoring networks, low-cost sensors offer a viable alternative for generating real-time, publicly-available estimates of pollutant concentrations. Here, we examine data from two low-cost sensors deployed in Brasília, in the Federal District of Brazil, during the 2022 wildfire season and use NOAA’s HYSPLIT model to investigate the origin of a particulate matter peak detected by the sensors. There was high agreeability of the data from the two sensors, which showed that daily average PM₁₀ and PM_2.5 concentrations reached peak values of 60 ug/m³ and 41 ug/m³, respectively. This study demonstrates the value of low cost sensors and their possible application in real-time scenarios for environmental health surveillance purposes. 

2. Title: Air Quality in the Megacity of Belo Horizonte: Characterization, Trend Analysis and Future Perspectives

Authors: Amanda Karine Chaves Ribeiro¹, Elson Silva Galvão^2,3, Taciana Toledo de Almeida Albuquerque^1,2,4

¹ Programa de Pós-Graduação em Saneamento, Meio Ambiente e Recursos Hídricos, Universidade Federal de Minas Gerais, Av. Pres. Antônio Carlos, 6627, 31270-901, Belo Horizonte, Brasil.

² Programa de Pós-Graduação em Engenharia Ambiental, Universidade Federal do Espírito Santo, Av. Fernando Ferrari, 514, Vitória, Espírito Santo, Brasil.

³Departamento de Engenharia Ambiental, Universidade Federal do Espírito Santo, Av. Fernando Ferrari, 514, Vitória, Espírito Santo, Brasil.

⁴Departamento de Engenharia Sanitária e Ambiental, Universidade Federal de Minas Gerais, Av. Pres. Antônio Carlos, 6627, 31270-901, Belo Horizonte, Brasil

Abstract: This study aimed to investigate the air quality characterization and the trend of air pollutants concentrations in the Metropolitan Area of Belo Horizonte (MABH), the third most populous Brazilian metropolitan area. It created air quality trends using measurements from monitors located across the MABH from 1995 to 2021, using data on pollutants MP₁₀, MP_2,5, NO₂, O₃, SO_2, and CO. The methodology consisted in checking the trend and the characterization of MABH's air quality following the World Health Organization (WHO) guidelines and interim targets. The results showed a trend of stability in the concentrations of air pollutants in the MABH, with no prospect of improvement or worsening. The Mann-Kendall test was used to check the possibility of tendency statistically. However, the historical characterization in the MABH exposed the region's challenge in ensuring good air quality that provides human health, with concentrations that remained higher than WHO guidelines. Furthermore, the results reinforced the importance of the industrial sector for air pollution in the MABH and exposed the need for improvement in air quality management. In this way, it is essential to reverse the current dismantling scenario of public environmental agencies.

3. Title: Wind-Cluster Based Study of Interannual Variations in Air Quality in The City of Buenos Aires

Authors: Caterina Mosto, Andrea Pineda Rojas, Néstor Rojas

Department of Chemical and Environmental Engineering – Universidad Nacional de Colombia

Abstract: In this work, interannual variations in the concentration of nitrogen dioxide (NO2), carbon monoxide (CO), and particulate matter with diameters less than 10 mm (PM10) at the three air quality monitoring stations of the city of Buenos Aires are studied for the period 2010-2019. A simple statistical trend analysis is used, as well as a clustering based on the daily sequence of hourly wind. A significant decrease in the annual mean PM10 concentration of 1.6 mg/m3.yr is observed at the urban background station. Consistently, a reduction in the frequency of daily exceedances of the World Health Organization (WHO) air quality guideline (AQG) level of 1.6 %/yr is also found. Annual and daily NO2 concentrations are frequently above the WHO AQG levels at the three sites, presenting positive trends that could become statistically significant in the future as new data is made available. When the daily hourly wind sequence is used as a classification variable, marked differences in pollutant concentration levels are observed with different wind patterns. While in general these differences are maintained over the years, highlighting the robustness of the classification, in some cases pronounced interannual variations are observed for specific wind clusters. For example, at the most coastal station, an increase in PM10 concentration observed in recent years is considerably higher with NNW winds, suggesting the impact of a new or more intense source coming from that sector. These results portray wind-cluster analysis as a valuable tool to understand sources of interannual variation in air quality.