PLTDEV DSNDED BELOW ASSIGNED ALT.

Narrative

CTLR WANTED US TO ACCEPT A VISUAL APCH IN THE WORST WAY - - FOR HIS BENEFIT. WE COULD SEE PARALLEL RWY; THE ONE WE WEREN'T GOING TO; BUT AN OBSCURATION PREVENTED US FROM SEEING THE RWY OF INTENDED LNDG. WE TOLD CTLR OF OBSCURATION SO HE DSNDED US FROM 3000 FT MSL TO 2500 FT MSL. WE LEVELED OFF; THEN WERE TOLD TO LOOK FOR RWY AND ANOTHER ACFT. I WAS HAND FLYING AND LET ALT GET TO 2200 FT BEFORE I NOTICED AND CLBED BACK TO 2500 FT. BY NOW; WE KNEW WE HAD NO CHANCE OF A VISUAL AND FINALLY GOT THAT MESSAGE THROUGH TO THE VERY BUSY CTLR WHO GAVE US A CLB AND SOME TURNS FOR THE ILS TO THE SAME RWY -- THE VERY APCH WE DID ASK FOR TO BEGIN WITH; BUT NOT FORCEFULLY ENOUGH TO GET THE CTLR'S ATTN. HE WAS FIXED ON THE RPTED VISIBILITY AND OTHER ACFT ACCEPTING A VISUAL APCH TO A BRIGHT SPOT IN THE OBSCURATION. ON THE SUBSEQUENT ILS WE DIDN'T SEE THE RWY CLRLY UNTIL 400 FT AGL. THE ARPT OFFICIALLY WENT IFR A LITTLE WHILE AFTER WE LANDED. THE OBSCURATION I REFER TO WAS CAUSED BY VERY COLD DENSE AIR CARRYING INDUSTRIAL STEAM/SMOKE ACROSS THE FINAL APCH COURSE OF FIRST ONE RWY; WITHOUT APCH LIGHTS; THEN THE RWY WITH APCH LIGHTS.