  Some magnetic CVs like BY Cam are characterized by unusual CNO line ratios
compared to other polars and non-solar abundances have been suggested to
explain this anomaly. We present here a first attempt to constrain the
elemental abundances in these systems by applying a specific ionisation model
combined with a geometrical description of the accretion column where these
lines are thought to be formed. The line luminosities have been computed using
the CLOUDY plasma code for different ionisation spectra and column extension.
We show here selected results and compare to the values observed in "peculiar"
magnetic CVs. The model applied to BY Cam confirms that ionization models with
solar abundances fail to reproduce the observed line intensity ratios. Assuming
the model to be valid, the induced best abundances imply an overabundance of N
(x25), underabundance of C (:8) and nearly solar O (:2), in line with CNO
reprocessing.
