# A Crowdsensing Platform for Monitoring of Vehicular Emissions: A Smart City Perspective
## 1 Introduction
This range of possibilities allows the population itself to cooperate in the construction of smart cities. In addition to mobile devices, there are other robust systems that are capable of providing relevant data for creating more sustainable urban environments, and one of them is the automobile. Currently, automobiles have advanced electronic and computer systems interconnected by a complex communication network. These devices offer the most varied information about the vehicle, such as engine temperature and rotation, mass air flow, and speed, among others [23]. Data captured by the mass air flow sensor can be used to measure the pollution emitted by the vehicle [24], for example. It should be noted that the emission of vehicular gases is one of the largest contributors to air pollution in large urban centers, with pollution indices similar to the industry [25]. Vehicle emissions are generated through the chemical reactions that occur inside the combustion chamber of the engines. These compounds are mainly responsible for the degradation of atmospheric air, which results in a loss of quality of life for all city inhabitants; such pollution can cause, for example, respiratory problems and degradation of city structures. These problems occur mainly in large urban centers, where the number of vehicles is high [26]. The polluting gases generated by vehicles are also responsible for problems of greater magnitude related to climate change [27; 28]. As an example, the city of Natal, the capital of the state of Rio Grande do Norte in northeast Brazil, has the following situation in relation to the vehicular fleet: it presents one of the largest fleets in the northeast of the country, with the proportion of approximately two vehicles for every five inhabitants in the city. At a national level, it is the 16 th capital with the largest fleet [29]. It is estimated that every year, the number of vehicles is increasing by about 5.5%. Currently, the estimated vehicle fleet is approximately 387,400 vehicles, of which 341,751 are considered light vehicles (gasoline-, alcohol-, or Vehicular Natural Gas (VNG)-powered cars), and only 34,801 are heavy vehicles (diesel-powered cars), according to the State Department of Traffic of Rio Grande do Norte [30] and the National Department of Transit [29]. In this sense, as a consequence of the growing number of vehicles in urban centers, there is also the increase of the air pollution caused by them. In order to corroborate this perspective, a study by the Environmental Protection Agency (EPA) of the United States of America has surprisingly concluded that a passenger vehicle using gasoline as fuel generates an average of four tons of carbon dioxide (CO\({}_{2}\)) per year [31]. This indicates how alarming the issue of urban vehicular pollution is. Several countries have projects and goals to reduce vehicle emissions. In Brazil, the Program for the Control of Air Pollution by Automotive Vehicles was created by the National Council for the Environment (CONAMA), composed of: PROCONVE (cars, trucks, buses, and road and agricultural machinery) and PROMOT (motorcycles and similar) [32]. These initiatives defined deadlines, emission limits, and technologies for domestic and imported vehicles, which are important references when planning to reduce air pollution in urban areas. As an example for vehicles with a specific mass of up to 1700 kg, the emission limit is 2 g/km of CO. For vehicles with a mass superior to 1700 kg, the limit is 6.2 g/km [32]. In the last few decades, CO\({}_{2}\) was pointed out as one of the main gases responsible for the greenhouse effect, which results in the significant elevation of the temperature of our planet. Among the damages caused to the environment are the acidification of rivers and forests, climatic changes, acid rain, and the melting of the polar caps, together with rising sea levels, thus hindering the life of animals and the development of flora [33]. The effects on human health are mainly caused by the particles of this pollutant suspended in the air.