Quote:

Ed Workman
That 'cloud of dust' is just as likely the edge of the smog.
The north winds typically enter the basin thru Cajon and Newhall Passes.
When they are sufficiently strong the San Gabriel and Pomona Valleys will be cleared, in time.
When not, the edge of smog may hang roughly on the I5 alignment on the east edge of the SFV,
or near the Arroyo Seco, leaving Pasadena still and smoggy.

I beg to differ with you as smog is held in place (in Southern California) by an inversion layer which would hold the smog between it and the ground. On the other hand, you may be correct after viewing the CSUN discussion of inversion layer scenario in Southern California. I grew up in the San Fernando Valley in the 60's and 70's. While in elementary school in Van Nuys, I recall some days when visibility was noticeably decreased and physical exercise left one with lots of coughing.