If you place the unit inside a sealed car, the oxygen will be depleted in short order, and the ozone output will drop to zero, stopping the process.
You want to place the ozone machine outside the car, and blow it into the car, via a taped up window. This will maximize the ozone concentration, also minimizing the treatment time.
Placing the unit in the car, with a cracked window will take much longer to treat the car, as there is no impetus for any in-and-out air movement, and you will both be relying on oxygen to "meander" into the car, as well you will be releasing ozone before it gets a chance to interact with malodorous substances inside the car.
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Ducting the ozone in to a confined space is the same principle used for "ozonation rooms", designed to treat objects off-site. You want the ozone machine in the clean (most oxygen laden) air, to make the ozone generation the most efficient.