Partial Zero Emission Vehicles – PZEV – The temperature of the catalyst is a critical factor in the performance of your car.  When it is cold, it is less efficient then when it is hot.  Further down the line, with your exhaust, is more ceramic substrate catalysts that help further reduce hydrocarbon and NOx.  The only downside to this is the highly expensive cost of the metals used to coat the catalysts, sometimes costing up to $1000/ounce.