# Accurate Estimation of Air Pollution in Outdoor Routes for Citizens and Decision Making
## 1 Introduction  
According to the World Health Organization (WHO), approximately 90% of the global population is exposed to air containing elevated pollutant concentrations. Recent assessments underscore a distressing fatality count of 7 million individuals annually due to the effects of outdoor and indoor air pollution [1]. People die and suffer many illnesses from exposure to poor air quality (AQ), due to pollutants such as particulate matter (PM2.5 and PM10), carbon monoxide (CO), ozone (O\({}_{3}\)), nitrogen dioxide (NO\({}_{2}\)), and sulfur dioxide (SO\({}_{2}\)) to name a few, mainly due to the burning of fossil fuels. Moreover, of significant concern for public health, 96% of the urban population is exposed to pollution levels surpassing the WHO AQ Guideline (AQG) [2] and in many large cities by more than five times. It is crucial to emphasise that exposure to elevated levels of fine particulate matter and nitrogen dioxide surpassing the WHO's recommendations resulted in an estimated 238,000 and 49,000 premature deaths, respectively, in 2020 [3]. These pollutants have been associated with asthma, heart disease, and stroke. Additionally, chronic exposure to fine particulate matter accounted for 275,000 premature deaths in Europe in 2020, while chronic nitrogen dioxide exposure was responsible for 64,000 deaths, and acute ozone exposure contributed to 28,000 deaths [4]. There is a growing recognition and active involvement of local governments and authorities in addressing the concerns surrounding air pollution. They are implementing control and supervision plans, striving to mitigate the harmful effects. This global publichealth challenge has sparked an accelerated political interest, reflecting a heightened commitment to tackle the issue [1; 5]. The notable increase in the number of cities monitoring air pollution data indicates a growing emphasis on assessing and monitoring air quality. In Europe, air pollution emissions have declined in the last two decades. Despite this positive trend, air pollution remains the most important environmental health risk in this region. The Directive 2008/50/EC of 21 May 2008 on ambient AQ and cleaner air for Europe is one of these AQ measures. According to this directive, the number of sampling points in each zone or agglomeration should be at least one sampling point per 2 million inhabitants or one sampling point per 50,000 km\({}^{2}\), where the latter criterion results in a higher number of sampling points, but not less than one sampling point per zone or agglomeration. For instance, Valencia city (Spain) is an example where these networks are deployed, with a set of AQ official monitoring stations for polluting gases (the network of stations of the Generalitat Valenciana [6]) and the stations deployed in the city of Valencia incorporated into open data, also known as Valencia minute by minute [7]. Figure 1 shows some of these AQ monitoring stations in different cities, such as Burjassot city (SP), Glasgow city (UK), and Valencia city (SP). In this context, our goal is to inform and assist citizens in their daily trips by providing an accurate distribution of pollution along the entire determined or specified route, showing the pollution levels by taking into account his/her profile (health profile or medical history),  
Figure 1: Example of AQ monitoring stations at (**a**): Burjassot city (Spain), (**b**): Glasgow city (United Kingdom), and (**c**): Valencia city (Spain). and to warn about the risks based on the WHO AQG. With this information, the citizen may plan and decide on an alternative route and proactively make informed personal decisions about his/her route choices. For this, we have developed an application based on the information collected from the different official AQ monitoring stations, applying spatial interpolation to estimate the pollutant concentration over the city map. The rest of the paper is structured as follows. In Section 2, we show the related work with regard to pollution exposure and outdoor mobility.