Inherited Smoking Tenant of 10 years

[Mitch Howard]

It's our first deal, just closed. A duplex. Upper unit is vacant. Lower unit occupied by tenant of 10 years, on a month to month lease. Lower unit is being rented significantly below market value, almost 50% of market value. Lower unit tenant smokes inside, lower unit has heavy smoke odor. 

Do I even give the opportunity of signing a new lease requiring he stop smoking inside or do I just give a notice to vacate? I hate to do it in the middle of winter, he's an older guy and the old owner of the property said he's always on time with payment but the smoke smell is very heavy.