The Interstellar Reddening Law within 3kpc from the Sun
  We have investigated the interstellar reddening law of young open clusters
within 3kpc from the Sun using optical, near-IR 2MASS, and Spitzer IRAC data.
The total-to-selective extinction ratio Rv of 162 young open clusters (log
t{age} <= 7.3) listed in the open cluster database WEBDA is determined from the
color excess ratios. The young open clusters in the Sgr-Car arm show a
relatively higher $R_V$, those in the Per arm and in the Cygnus region of the
local arm show a relatively smaller value, and those in the Mon-CMa region of
the local arm show a normal value (Rv ~ 3.1).
