Build charcoal fire or preheat gas grill. Remove silver skin from back of ribs, if desired. Set up the grill for indirect heat and if using wood chips, place soaked chips directly on charcoal, or in smoking box of gas grill. Rub the cut lemons over front and back of ribs squeezing to release as much juice as possible. Set aside for 5 minutes. Rub ribs liberally with spice rub and let sit, covered, for 15 to 20 minutes.
Place ribs (bone side down) in the center of the cooking grate or in a rib holder/rack over direct medium Low heat, making sure they are not over a direct flame. Grill covered (at about 325 degrees F, if your grill has a thermometer) for 1 1/2 to 2 hours or until meat is tender and has pulled back from the ends of the rib bones.
Do not open the grill for the first 30 minutes--this means no peeking; especially important if using wood chips. If the ribs start to burn on the edges, stack them on top of one another in the very center of the grill and lower your fire slightly. Twenty minutes before serving, unstack ribs, if necessary and brush with barbecue sauce. Remove ribs from grill and let rest 10 minutes before cutting into individual or 2 to 3 rib portions. Warm remaining sauce in a saucepan and serve on the side, if desired.
Combine paprika, salt, sugar, brown sugar, cumin, chili powder, pepper, cayenne, onion powder, garlic powder, celery salt and oregano in bowl; mix well. For a smoother rub, puree ingredients in a spice grinder until well combined and all pieces are uniform (the rub will be very fine and tan in color). This step is important if adding to any homemade barbecue sauce.
Extra rub can be stored in an airtight container for up to 6 months.
Recipe courtesy of Elizabeth Karmel, Girls at the Grill