A well-built fire adds a smoky complexity to grilled food yet also has the potential to aggravate your eyes — causing them to tear. Smoke is full of tiny particles and gasses. The wafting smoke from the grill transports these particles to your eyes, where reflex tears are produced to wash out these impurities. A gas grill tends to produce less smoke than a charcoal one. But if fat, marinades or juices drip into the fire of either one, smoke flares up.
If you want to reduce the amount of smoke that swells up from your grill, trim as much fat from your meat as possible. Cook all items, even vegetables, over indirect heat. When you grill over charcoal, for example, place a drip pan in the center of the lower chamber and pile coals on either side of it. Place meats and vegetables only over the center of the grill — where the drip pan is — so no drippings fall onto the hot coals and create flares and smoke. This method may not produce a significant char or grill marks on your grilled food, though.
References and ResourcesUnited States Environmental Protection Agency: Burn Wise
The Independent: Why Do We Cry: The Science of Tears
Chicago Tribune: No Smoking