Have you noticed your coolant level going down over time?
If they white smoke is constant or consistent, and does not go away after the vehicle warms up, you may have a failing head gasket.
Best thing to do would be to contact a local shop for a confirmation diagnosis!
http://repairpal.com/volvo-within-10-miles-of-arcadia-california-91006
RepairPal Certified shops can diagnose and repair your 1997 Volvo 850. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.