The alkali metal emission from materials collected in a PFB biomass gasification pilot plant has been characterized. Samples of SiC filter ash and fluidized bed particles from different operating conditions were subjected to a constant heating rate up to 1000 degrees C in a nitrogen atmosphere, and the alkali metal emission was monitored continuously by a surface ionization technique. For all samples, two characteristic emission intervals are identified. In the range 100-500 degrees C, a small fraction of the alkali metal content is emitted. Above 600 degrees C, the alkali metal release increases sharply and the rise is close to exponential up to 900 degrees C. For fluidized bed particles, the alkali metal emission is significantly lower for agglomerates compared to material used during 1 day, which is attributed to the formation of less volatile compounds. For the filter ash samples, the alkali metal emission is enhanced in samples collected after longer filter cleaning intervals, indicating that the formation of a filter deposit improves the alkali capture efficiency.