SEVERE  AIR  POLLUTION  POTENTIAL

-- Contributing Factors  (Note that all but #1 and #6 are meteorological)--

1.  Many sources (or  densely-packed sources)

2.  Deep, stationary high pressure

3.  Light surface winds (weak surface pressure gradient)

4.  Strong subsidence inversion

5.  Shallow mixing layer

6.  Valley topography

7.  Clear skies

8.  Sunlight (for photochemical smog)