Infrared Photometric Properties of Inner and Outer Parts of HII regions
  The fact that infrared ring nebulae (IRRNs) are frequently associated with
HII regions, provides us the opportunity to study dust at the interface between
ionized and neutral gas. In this paper, we analyze the infrared radiation in
the range from 8 to 500~$\mu$m in outer and inner parts of 32 IRRNs showing
round shape. We aim to determine the morphology of these objects and possible
dust evolution processes on the base of the comparison of IR radiation towards
the ionized and neutral regions. We calculate six slopes between adjacent
wavelengths in their spectral energy distributions to trace the difference in
the physical conditions inside and outside ionized regions. Using the data on
these 32 objects we show that their morphology is likely 3D spherical rather
than 2D plane-like. The slope between 70 and 160~$\mu$m is the most appropriate
tracer of the dust temperature in the outer envelope. The larger 8-to-24~$\mu$m
intensity ratio is associated with smaller intensities at mid-IR indicating
that the PAHs may indeed be generated due to larger grain destruction. These
data are important for the subsequent theoretical modeling and determining the
dust evolution in HII regions and their envelopes.
