TORONTO - Smog is down but don't thank the province's Drive Clean emissions testing program, Auditor General Jim McCarter said in his annual report.

More than three-quarters of the drop in air pollution since 1998 can be traced to factors outside the mandatory vehicle emissions tests - particularly better cars and cleaner fuel.

"The ministry of environment should formally evaluate the extent to which the Drive Clean program continues to be an effective initiative in reducing smog," the report recommends.

British Columbia has already announced it will discontinue its version of the program for light-duty vehicles by 2014 as have five US states.

"Vehicle emissions are no longer one of the major contributors to smog in Ontario," McCarter said, suggesting the government could well look at cutting the program's scope.

"The government's view is that it's still making a contribution, but that contribution is significantly less than when the program was developed."