An extract from a CIA document, written around the time of the first Gulf War, states the following (apologies for the all-capitals--it came that way, and I didn't want to retype it):

STABILITY OF IRAQ'S CHEMICAL WEAPONS STOCKPILE

IRAQ HAS A SIZEABLE CW STOCKPILE, AT LEAST SOME OF WHICH CAN SURVIVE SEVERAL YEARS OF STORAGE.

THE UNITARY FORM OF IRAQ'S SARIN - ITS PRINCIPAL NERVE AGENT - HAD A RELATIVELY SHORT SHELF LIFE DURING THE WAR WITH IRAN.

THE IRAQIS HAVE BEEN WORKING ON THIS PROBLEM:

THEY HAVE TRIED TO INCREASE UNITARY SARIN SHELF LIFE BY IMPROVING THE PURITY OF THE PRECURSOR CHEMICALS AND REFINING PRODUCTION PROCESSES.

THEY HAVE DEVELOPED AND TESTED BINARY NERVE AGENT ROUNDS FOR ARTILLERY SHELLS AND BINARY MISSILE WARHEADS AS WELL.

CIA BELIEVES THAT BY NOW IRAQ HAS EITHER INCREASED THE SHELF LIFE OF UNITARY SARIN OR PRODUCED LARGE QUANTITIES OF BINARY MUNITIONS.

DURING THE WAR WITH IRAN, IRAQ USED LARGE QUANTITIES OF CHEMICAL WEAPONS AGAINST IRANIAN GROUND FORCES. THE PRINCIPLE AGENTS USED WERE THE BLISTER AGENT MUSTARD AND THE NONPERSISTENT NERVE AGENT SARIN. THE NONPERSISTENT NERVE AGENT TABUN AND THE PERSISTENT NERVE AGENT GF WERE ALSO USED.

DESPITE THE GENERAL SOPHISTICATION OF IRAQ'S CW PRODUCTION INFRASTRUCTURE, SOME OF IRAQ'S CHEMICAL AGENTS HAD A SHORT SHELF LIFE, MOSTLY OWING TO IMPURITIES IN THE PRECURSOR CHEMICALS. CIA BELIEVES THAT SOME SARIN HAD A SHELF LIFE OF ONLY A FEW WEEKS.

IN 1989 THE IRAQIS DESTROYED 40 OR MORE TONS OF SARIN THAT HAD DECOMPOSED.

EFFORTS TO LENGTHEN SHELF LIFE

IRAQ HAS TRIED TO SOLVE THIS PROBLEM IN TWO WAYS. FIRST, IT ATTEMPTED, WITH FOREIGN ASSISTANCE, TO IMPROVE THE SHELF-LIFE OF ITS UNITARY SARIN BY INCREASING, THE PURITY OF THE PRECURSOR AND INTERMEDIATE CHEMICALS AND-REFINING PRODUCTION PROCESSES.

SECOND, IT BEGAN TO DEVELOP BINARY CHEMICAL WEAPONS. IN A BINARY MUNITION, THE TWO PRECURSOR CHEMICALS ARE STORED SEPARATELY AND ONLY MIXED TO FORM THE CHEMICAL AGENT IMMEDIATELY BEFORE OR WHEN THE ROUND IS IN FLIGHT. THUS, THE SHELF LIFE OF THE AGENT BECOMES IRRELEVANT; MOREOVER, THE MUNITION IS SAFER TO HANDLE AND STORE. BY 1990 IRAQ HAD SUCCESSFULLY TESTED 155-MM ARTILLERY SHELLS AND OTHER BINARY MUNITIONS AND LAUNCHED A BALLISTIC MISSILE WITH A BINARY WARHEAD AS WELL.

CIA HOLDS THAT THE STOCKS OF SARIN MAY REMAIN VIABLE WELL BEYOND MARCH. CIA ANALYSTS BELIEVE THAT THE SHELF LIFE PROBLEM WAS ONLY TEMPORARY AND THAT THE IRAQIS CAN NOW PRODUCE UNITARY AGENTS OF SUFFICIENT QUALITY BY ADDING A STABILIZER OR IMPROVING THE PRODUCTION PROCESS.

CIA ALSO BELIEVES THAT A SUBSTANTIAL PORTION OF IRAQ'S NERVE AGENT STOCKPILE NOW CONSISTS OF BINARY CHEMICAL WEAPONS WHICH WOULD NOT BE SUBJECT TO DEGRADATION.