  Smog, as a form of air pollution, poses as a serious problem to the
environment, health, and economy of the world[1-4] . Previous studies on smog
mostly focused on the components and the effects of smog [5-10]. However, as
the smog happens with increased frequency and duration, the smog pattern which
is critical for smog forecast and control, is rarely investigated, mainly due
to the complexity of the components, the causes, and the spreading processes of
smog. Here we report the first analysis on smog pattern applying the model of
dynamical networks with spontaneous recovery. We show that many phenomena such
as the sudden outbreak and dissipation of smog and the long duration smog can
be revealed with the mathematical mechanism under a random walk simulation. We
present real-world air quality index data in accord with the predictions of the
model. Also we found that compared to external causes such as pollution
spreading from nearby, internal causes such as industrial pollution and vehicle
emission generated on-site are more critical to the health of the whole
network. Most strikingly, we demonstrate that spreading out the pollution
sources by moving them to nearby suburban areas, a common practice for smog
control, will degrade the overall health of system under certain conditions
