Sensor datasets on the Web are becoming increasingly available, and there is a need for making them discoverable and accessible, so that they can be reused despite their heterogeneity. While RDF and Linked Data provide fundamental principles for sharing data on the Web, it is evidenced that they have limitations for efficiently transmitting and archiving sensor data. In this paper we identify some of the main challenges for engineering semantic sensor data archives, and we present an abstract architecture for such type of infrastructure. The proposed approach is based on a mix of RDF metadata and raw sensor archives with RDF mappings, so that data can be RDF-ized on demand. We use a real sensor deployment for air quality monitoring as a motivating use case and running example, and we show preliminary results on RDF transformation, compared with a representative data compression algorithm.