One could argue that air has no weight, but it does have mass. At sea level and at 20 °C, dry air has a density of approximately 1.2 kg per cubic meter. Moisture actually makes it just a bit...
A cubic foot of lead weighs 321 kgs or 708 lbs at room temp. There are 27 cubic feet in a cubic yard, therefore, a cubic yard of lead weighs 8,667 kgs or 19,116 lbs at room temp.