# A Crowdsensing Platform for Monitoring of Vehicular Emissions: A Smart City Perspective
## 1 Introduction  
Rampant urbanization coupled with rapid population growth have become major challenges for sustainable development in urban centers. Actually, this complex scenario has fostered research and highlighted the theme of the smart city [1; 2; 3], reinforced by governmental initiatives and the opening of new commercial opportunities. It is therefore necessary to implement intelligent solutions that facilitate planning and decision-making based on strategic information, so as to provide a more effective response to the dynamics of cities [4]. Actually, the concept of the smart city has been evolving as new paradigms are created, and the last few decades have seen a continuous evolution in this sense. While the Internet rapidly became the main player that put computing in its place of relevance for social and economic transformations, fostering the revolutions of mobile and personal computing, the perception of cities and their digital services has also evolved over time, following this development track. The availability of Internet-based services and the spread use of (personal) computing first allowed the construction of digital cities, providing many services from the \"digital world\" to the cities' inhabitants and for improved governance of public services [5]. However, with the development of new information and communication technologiesand paradigms, this scope evolved into what we call smart cities, which integrate data from the cyber and the physical spaces for deeper transformations in urban areas [6], gaining great attention in the few last years. The proposed platform was developed for this complex and data-rich environment of smart cities. Generally speaking, smart cities are formed by combining ubiquitous communications, autonomous management systems, wireless sensor networks installed at points of interest, a robust communication infrastructure, and the integration of various services that make up the core of urban centers (energy, transport, health, etc.) [3; 7; 8; 9]. These systems should be responsible for collecting and integrating a massive amount of data, forming the basis of what is known as the Internet of Things [10]. The analysis of this raw data generates information that can be used in the creation of new applications, offering a range of services that benefit society and the sustainable development of urban centers [11; 12; 13]. As a result, the design of new ideas and the development of applications for smart cities are not restricted to governments. This reality has fostered the creation of a new business model, in which citizens have the freedom to develop and market their solutions [3; 14; 15; 13]. Although the data collected by government agencies are not open to the public, these extractions can be done in a number of other ways, for example through the concept of crowdsensing [16]. In this approach, the sensors are represented by the people themselves, creating a virtual infrastructure parallel to the existing physical infrastructure. Citizens, through their smartphones, watches, cars, and other gadgets, can share information that will power a larger system [17]. In Brazil, for example, the use of the urban environment in order to generate data open to the population is still taking its initial steps [18; 19]. On the other hand, in a number of countries, such as the United States of America, large amounts of data on health, education, and transportation are available to people, allowing such data to be used when developing solutions to problems people face daily in cities [20]. Another point that has contributed to the creation of open databases for cities is the popularization of mobile devices. These devices have great potential for urban crowdsensing, since they are equipped with several sensors capable of collecting data such as temperature, speed, geolocation, and noise, among many others [21]. The expectation is that new sensors will be built into mobile devices in the next few years [22].