Here's the scoop:

Spec AUS 32 is contained in ISO 22241. If you search for it on-line..you'll get this abstract:

ISO 22241-1:2006 specifies the quality characteristics of the NOx reduction agent AUS 32 (aqueous urea solution) which is needed to operate converters with selective catalytic reduction, so-called SCR (Selective Catalytic Reduction) converters, in motor vehicles with diesel engines. SCR converters are particularly suitable for selectively reducing the nitrogen oxide (NOx) emissions of diesel engines.

If you want to purchase DEF other than BMW, the Fleetguard product (a Cummins company) can be found at Cummins Distributor branches.
Pricing over the counter is:

1 Gallon - $6.04

2.5 Gallon - $17.40

5 Gallon - $30.25

It's been my opinion that if your dealer fills both tanks, 6.5 gallon total, you should be able to make it between oil change, and have BMW pay for your refil. However, I think that the early warning messages that several of us have seen is most likely do to only having the active tank filled at delivery, not the larger tank that would take the bulk of the fluid. It's unfortunate that there is no way to get iDrive to check on the DEF fluid level.

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