# A Comparative Analysis for Air Quality Estimation from Traffic and Meteorological Data
## 1 Introduction  
Nowadays, air pollution represents a major environmental problem, increasingly worsening and affecting more people every year. This is especially true in urban environments, where the majority of the industries and traffic reside, releasing into the air alarmingly large quantities of pollutants and particulate matter that become a severe health risk from exposure [1]. Recent estimates claim that 4.6 million people die each year from causes directly attributable to air pollution [2], with a total of 300,000 cases in Europe only. These figures appear surprisingly high when compared to other common death causes such as car crashes, which is approximately three times lower [3]. The high incidence of deaths caused by air pollution can be explained by the fact that more than 90% of the world population lives in places where the air quality exceeds the guideline limits established by the World Health Organization (WHO) [4]. Several studies [1, 5, 6] analysed the relation between air pollution and health issues, both on global and local scale over long periods of time, demonstrating for instance augmented risks of respiratory diseases, such as bronchitis and asthma, or even reduced life expectancy [7]. Furthermore, air pollution is one of the major factors contributing to climate change, especially in terms of global warming. Even considering the relatively brief period, average temperatures have already risen by 1.9\({}^{\circ}\)C since 1980 and data records from NASA report that 19 out of 20 warmest years have occurred between 2001 and the present day ([[https://climate.nasa.gov/](https://climate.nasa.gov/)]([https://climate.nasa.gov/](https://climate.nasa.gov/))). Besides the direct effects of greenhouse gases, several subsequent issues are also involved. For instance, warmer periods could increase the ozone (\(O_{3}\)) levels by 1 to 10 ppb during the next years, where drier regions can drastically increase the risk of wildfires, and consequently release significant source of carbon oxides and particulate matter [8]. For these and other reasons, a steadily growing concern from authorities, media and citizens has led to a broad consensus about the need of strong regulations in order to reduce the emissions of major pollutants in the shortest possible time. Together with important international treaties (e.g., Paris agreements ([[https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement](https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement)]([https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement](https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement)))), the European Union established a remarkable set of legislation aimed at setting strict legal limits and target values for the concentrations of major air pollutants to be reached by the Member States within the next decades ([[https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32008L0050](https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32008L0050)]([https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32008L0050](https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32008L0050))). Because of the high population density in the old country, the primary purpose of this document is the safeguard of the human health by setting limits for Particulate Matter (_PM_10 and _PM_2.5), Sulphur Dioxide (_SO_2), Benzene (_C_6H_6), Carbon Monoxide (_CO_), Ozone (_O_3), Nitrogen Oxides (_NOx_), Lead and other toxic heavy metals such as Arsenic and Cadmium. In order to comply to these directives, each country requires a large amount of sensors to be positioned in key areas, mostly depending on the distribution and density of infrastructures and buildings. These monitoring stations can be divided into different groups according to the emission sources, namely: traffic, industrial or background stations, or the region category.