There's been plenty of technical progress made since this publication dated 2013.
"We investigated exhaled breath cannabinoid concentrations following controlled cannabinoid smoking. There is strong interest in finding alternatives to urine and blood for identifying recent drug use. To date, oral fluid is the most studied and promising alternative matrix for DUID programs. However, THC is detected in oral fluid for 48hrs in chronic smokers during sustained abstinence. Exhaled breath may offer an alternative to oral fluid testing as cannabinoid detection in this matrix may better coincide with impairment." - Marilyn Huestis PhD