Cattle and cars along Highway 91 north of Smithfield. Air quality issues.BLACK BACKGROUND VERSION. In this panoramic series of four photographs, traffic speeds past a herd of cattle along Highway 91 north of Smithfield. The debate over how much pollution the cattle are causing is apparently over. Air quality issues. Photo by Trent Nelson; 7.22.2004Cattle and cars along Highway 91 north of Smithfield. Air quality issues.Cattle and cars along Highway 91 north of Smithfield. Air quality issues.Cattle and cars along Highway 91 north of Smithfield. Air quality issues.Cattle and cars along Highway 91 north of Smithfield. Air quality issues.