# Accurate Estimation of Air Pollution in Outdoor Routes for Citizens and Decision Making
## 2 Related Work  
Citizens' route choice decisions are often about minimising travel time, although in many situations, the risk of illness causes citizens to apply other criteria, such as reducing air pollution, particularly when the citizen suffers from respiratory diseases or allergies. In a study by [8], it was found that cyclists could opt for alternative routes with approximately 20% less exposure to pollution (given by nitrogen and carbon oxides) compared to shorter routes in a Danish city. Similarly, in [9] it is demonstrated that pedestrians in California could reduce PM2.5 exposure, around 40%, by choosing appropriate routes. Additionally, in [10] a web application for cyclists is shown which can help to find alternative routes with 4% less pollution. Furthermore, numerous previous studies examining exposure at the route level, such as [11], have consistently demonstrated that different routes within cities exhibit different levels of air pollution.  
From a different point of view, regarding the trade-off between emissions and exposure to pollution, in [12], the feasibility of utilising emission and exposure metrics as benchmarks for assessing real-world policy is considered. The authors propose, based on the type of vehicle used, air pollution tolls given by time, taking into account the emission costs. However, the specific trade-off between the impact of exposure as a factor in route choice has not been extensively evaluated. In this line, in [13], an application is presented that does not systematically reduce travel distance or travel time, when CO\({}_{2}\) emissions are considered as a vehicle cost factor.  
In [14], the authors present a population-based assessment, carried out in Helsinki (Finland), of multiple environmental exposures for active commuting, allowing urban-scale exposure analyses to inform exposure levels. It highlights that cyclists have more noise exposure and pollution, which exceed healthy thresholds. In [15], the authors show a summary of different studies focusing on main air pollutants and their impact on cyclists. In [16] is detailed the Green Paths software (v.1), an open-source routing method (based on shortest path algorithm) and exposure assessment tool for a route planner for Helsinki which takes into account exposure metrics given by air quality, noise, and greenery. This software uses OpenStreetMap, both with walking and cycling street network maps, with pre-calculated exposure cost attributes assigned to the network edges.  
In addition, it is worth mentioning several commercial platforms that offer you AQ information in your route, such as AirNow [17], BreezoMeter [18], and PlumeLabs [19]. Their use can be beneficial although they are not open-source. Aimow provides only AQ at the source and destination, and is constrained to North America and limited to specific roads, considering only O\({}_{3}\) and PM as pollutants. BreezoMeter shows AQ index (AQI) only at the monitoring spots and is limited to specific roads. Finally, PlumeLabs analyses the AQ in your location. As we can see, the information provided by these platforms is constrained to the source or destination, as well as the locations with monitoring systems, but it does not include information for your whole route. As we can see, the information that these platforms report is simpler than our approach.  
In summary, we have seen that there are different initiatives to improve citizens' mobility and assess air pollution in order to assist them in their daily trips, but from a different point of view and using less accurate air pollution estimation techniques, which are neither focused on official AQ monitoring measurements nor assess the citizen's profile (medical history). We have not found alternatives that can provide a detailed and accurate air pollution estimation along a specified route, taking into account this profile and the WHO AQG. This is our goal and the research gap we aim to fill.