It will depend on what allegations the officer is making. If he is alleging that drugs were involved also, could change things. I would call Jim Nesci in Tucson. he is one of the top DUI attorneys in the country and is in Tucson. he wrote the Arizona DUI Defense Guide. I am surre he does free consultations and can give you better advice than you can get from a quick posting.
It is hard to answer the question with out a lot more detail. I don't practice in Arizona, so my answer is for informational purposes only. It could be the officer or prosecutor believes they have sufficient evidence of impairment of your driving even though the test result would seem like a pass. You should consult a dui attorney in your area who, armed with more information would be able to answer your questions and assist you in your defense.
First question: were you charged with DUI? Basically, there are five levels of misdemeanor DUI in Arizona. They are: impaired to the slightest degree by drug or alcohol (28-1381 A. 1.), a breath or blood alcohol content of .08 or greater (1381 A. 2.), the presence of an illegal drug in the driver's system (1381 A. 3.), impaired by alcohol above .15 (1382 A. 1.), and impaired by alcohol above a 2.0 (1382 A. 2.). These are also known as "slightest degree," "over 08," "DUI Drugs," "Extreme," and "Super Extreme."
Prosecution in your case-- without knowing any more of the details than a BAC level of .033--is based on the "slightest degree" theory of DUI. Commonly, observations of bad driving, an accident in which you were at fault, or some other evidence that alcohol impaired your ability to operate a motor vehicle safely are used to prove the slightest degree theory to a jury.
Obviously, the facts surrounding your case are extremely important in determing why you are being charged with a BAC well below the non-commercial legal limit.
Now, if you were charged while driving a commericial vehicle, the legal limit is a .04. If you wre observed driviing in some way erratically in this situation, a prosecution makes more sense.
In Arizona, there are what are called "presumptions" in the law, ARS 28-1381. If a BAC is below .05, there is a presumption that the driver was NOT impaired or under the influence of "intoxicating liquor." This applies to you. Other presumptions are: over .05 but under .08, no presumption; .08 or over, presumption of intoxication.
Presumptions are not strict proof. In other words, a .033 is presumed to be non-impairing however a presumption is merely more likely than not. Thus, a presumption can be overcome by evidence presented by the state of the type mentioned above-- observations by the officer, accident, etc.
DUI law is very involved. A lawyer should look at the facts developed by the state to best advise you of what evidence exists against you and what that evidence means to you and your case. There are many defense attorneys who will consult with you briefly (including enough time to gather the pertinent information) and give you an idea of the weight of your case and the evidence in your favor and against you.