Citizen science participation in research in the environmental sciences: key factors related to projects' success and longevity.

The potential impacts of citizen science initiatives are increasing across the globe, albeit in an imbalanced manner. In general, there is a strong element of trial and error in most projects, and the comparison of best practices and project structure between different initiatives remains difficult. In Brazil, the participation of volunteers in environmental research is limited. Identifying the factors related to citizen science projects' success and longevity within a global perspective can contribute for consolidating such practices in the country. In this study, we explore past and present projects, including a case study in Brazil, to identify the spatial and temporal trends of citizen science programs as well as their best practices and challenges. We performed a bibliographic search using Google Scholar and considered results from 2005-2014. Although these results are subjective due to the Google Scholar's algorithm and ranking criteria, we highlighted factors to compare projects across geographical and disciplinary areas and identified key matches between project proponents and participants, project goals and local priorities, participant profiles and engagement, scientific methods and funding. This approach is a useful starting point for future citizen science projects, allowing for a systematic analysis of potential inconsistencies and shortcomings in this emerging field.