Although data is a key part in smart cities, traditionally there has been no systematic effort to enable the sharing of data in a trustworthy manner among applications or services. In order to promote sharing of data, mechanisms need to be put into place to provide the different actors - data producers, data consumers, etc. means to control and visualize how their data or requests are being processed and used. In this paper we deal with a key issue involved in trust which is usage control, i.e., how data is used once access to it has been granted. We propose a Data Usage Control Model (DUPO) to capture the diversity of obligations and constraints that data providers impose on the use of their data. Based on the DUPO model and semantic technologies, we propose a trustworthy data sharing platform which enhances transparency and traceability of data usage in smart cities. Lastly a proof-of-concept is developed to evaluate our solution and results show that the performance of the added trust does not impact negatively on the system