1.   While its petrol-engined equivalent must have unleaded fuel, the diesel catalyser will only become effective when sulphur levels drop.

2.   This includes measures to introduce lead-free petrol, and reduce sulphur levels in both petrol and diesel.

3.   But Siriphan says the good news is that Bangkok no longer has a problem with lead contamination in the air, and sulphur dioxide levels are also falling.

4.   The monitoring nets will report three times a year on water quality, while the acid raid stations will provide data four times a year on sulphur dioxide levels.