Better check to see if your Oxygen sensor is working. There may be loose connections in the wiring sometimes. Or may be the Oxygen sensor is too old and worn out now. (when did u last change ur oxygen sensor?)
"The sensor is part of the emissions control system and feeds data to the engine management computer. The goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible."
Reference- http://auto.howstuffworks.com/question257.htm
Changing the oxygen sensor if its old and broken, will definitely improve exhaust emissions.
Take your vehicle to panchikawatta and you should be able to locate an oxygen sensor to replace with the original.
Post your findings. Let us know what caused the failure at the emission tests.
