CleanAirKits - Triple Exhalaron (3-fan)

The PureZone mini has such a tiny CADR (10 cfm for dust at the highest speed, which is ridiculously noisy for how small this thing is!) that it serves as a false sense of security more than anything, especially if you're going to use it anywhere other than a small car. I'd recommend the Clean Air Kits Exhalaron (92 cfm for the 2-fan one and 128 cfm for the 3-fan one) or the AirFanta 3Pro (430 cfm at the highest setting, which is very noisy) if you have some extra space to spare (it's not as small as the Exhalaron but it is highly portable)

If you're driving a car that you own, then upgrade the cabin air filter to a HEPA filter if you haven't already. Keep the car's fan running as it brings it quite a bit of fresh air. I've seen this ventilation keep the interior's CO2 levels near outdoor air levels or just above even with 2-3 people in the vehicle. Then I've used a Clean Air Kits Exhalaron in the middle of the back seat to mix/filter the air that's farther away from the vents.