Thanks for the advice everyone. Here's what I tried: Testors model master acryl grey primer sprayed with the airbrush. Thinned it 3:1. Low odour, good coverage and cheap.
Until now I've used either Tamiya or TEstors enamel primer from a spray can (mostly because it's a time saver). Never thought about how beneficial the airbrush is over the spray can! The spray can provides a much wider spray (so a lot more paint becomes airborne).