  We present a study of the properties of dusty warm absorbers and point to
some important consequences for the resulting X-ray absorption spectra of AGN.
Pronounced effects of the presence of dust in warm material are (i) an apparent
flattening of the observed X-ray spectrum in the ROSAT band due to a sequence
of absorption edges and a shift to lower gas ionization, (ii) the presence of a
strong carbon edge at 0.28 keV, and (iii) the expectation of increased time
variability of the warm absorber parameters. The first two effects can be
drastic and may completely hamper an X-ray spectral fit with a dusty warm
absorber even if a dust-free one was successfully applied to the data. In order
to demonstrate facets of the dusty warm absorber model and test the recently
reported important, albeit indirect, evidence for dusty warm material in the
Narrow-Line Seyfert 1 galaxy IRAS 17020+4544 we have analyzed ROSAT PSPC and
HRI observations of this galaxy. The X-ray spectrum can be successfully
described by a single powerlaw with index Gamma_x = -2.4 plus small excess cold
absorption, or alternatively by a steeper intrinsic powerlaw (G_x = -2.8)
absorbed by a dusty warm absorber. The findings are discussed in light of the
NLSy1 character of IRAS 17020 and consequences for NLSy1s in general are
pointed out. In particular, the presence of dusty warm gas results in a steeper
intrinsic powerlaw than observed, thus exaggerating the `FeII problem'. It also
implies weaker potential warm-absorber contribution to high-ionization Fe
coronal lines.
