The increased capacity for affordable data processing, the rise of platforms, and facilitated citizen mobilization through social media encourage citizen science. The rise of citizen science may have significant implications for governance and policy. In the prologue of this special issue on citizen science, we outline the potential of citizen science for public organisations and discuss various tensions. This potential includes citizens influencing policies and generating novel insights through unique combinations of data, organisations and individuals. Public organisations may engage in citizen science initiatives for both epistemological and democratic reasons. We conclude that the roles of public organisations and citizen scientists are not well defined, which is, for example, reflected in debates over data ownership. Additionally, we identify tensions, such as differing perspectives among involved actors in citizen science projects regarding what constitutes data quality.

In the Netherlands, citizens often experience concerns or annoyance due to industrial and logistics activities in their immediate living environment. They typically turn to their municipalities as the responsible authorities to address and improve the situation. However, municipalities often perceive no grounds, legal or otherwise, to intervene. For example, because existing environmental standards or granted permits are not being violated. This may lead to distrust of the government, as well as of the science underlying these standards. In response, citizens sometimes initiate their own projects to measure aspects of their environment, also known as citizen science. Despite stemming from frustration or mistrust, these initiatives can provide opportunities for constructive dialogue among stakeholders. In two citizen science cases, ‘Farmers and Neighbours’ and ‘Citizen Measurement Network Rail America’, five elements crucial for trust have emerged, namely: collaboration between scientists and citizens, joint and public data collection, Complementing calculations with measurements, linking sensor/measurement with experiential data, and an involved local government. In this way, citizen science may bridge the gap between citizens, science, and local policy regarding issues in the living environment. To maintain the trust built, it is essential that results of citizen science research are considered in decision-making and policy.

In the pilot project, Smart Emission 1, action research was carried out between 2015 and 2017 by an experimental citizen sensing network in the city of Nijmegen. This network used small sensors to map environmental pollution in the city on a fine-grained scale. A group of citizens actively shared ideas with the project team about where to measure and which local issues, called 'user cases', to tackle and analyse, for a period of little over a year. By holding meetings for citizens and experts to do ‘participatory sense-making’, a joint learning process was encouraged (Volten, 2016). Citizen science requires a significant investment of time from everyone involved. But, at the same time, the dialogue process can build mutual understanding between citizens and professionals from governments and knowledge institutions. By organising the dialogue between citizens and professionals, mutual trust can grow, and a common ‘language’ can develop. In Nijmegen, the city’s alderman concluded about the Smart Emission project that it is a better investment to free up time and money for citizen science than to conduct lengthy lawsuits between citizens and the local government about environmental pollution and perceived nuisance.

Citizen science is a form of scientific research in which ordinary citizens actively participate. Citizen science is part of a larger movement towards a more open society. Governments are also following this ‘openness movement’ by sharing information with citizens to provide more insight into policies. However, it is still unclear how these two sources of information, scientific data from citizens and open government information, relate to each other. They both aim to improve policies and contribute to a more open society. However, the relationship between citizen science and open government has not yet been investigated in practice.
Through a case study on the joint measurement of groundwater levels by a regional water authority with individual citizens and the publication of these levels as ‘open data’, this contribution examines the interaction between open government and citizen science. The case study shows that open government leads to citizen science: when citizens’ experiences do not align with the open data provided by the water board, citizens conduct their own research and engage in discussions with the water board using their own data. Furthermore, the data collected by citizens can also be included in open government portals, thus potentially influencing future policies more broadly.

In this epilogue to the special issue on citizen science, we discuss different forms of citizen science, the different roles of science, the shifting role of governments and tensions between citizens, science and government authorities, based on articles and interviews. Citizen science comes in many forms. We conclude that the motive behind citizen science and the management of the initiative are important dimensions. Motives and direction are also important for the roles science and government play in the initiatives. For example, there roles as a source of legitimacy, knowledge processing and data processing for third parties. Such roles are then crucial for ensuring data quality and data ownership. Both topics require strong organisation of both the initiative itself and between citizens, government and science, especially if the topic is wicked.