(1) No person shall operate, drive or cause or permit to be driven or operated any motor vehicle on a public way which emits into the atmosphere any visible emission. Excluded from this section are those motor vehicles:
(a) Powered by compression ignition or diesel cycle engines.
(b) By written order of the Department of Environmental Quality pursuant to ORS 449.810.
(2) No person shall operate, drive, or cause or permit to be driven or operated upon a public way a motor vehicle excluded from subsection (1) above, which emits visible emission into the atmosphere:
(a) Of an opacity greater than 40 percent.
(b) Of an opacity of 10 percent or greater for a period exceeding seven consecutive seconds.