The doping of He droplets by Al atoms and their reactions with H2O and O-2 at T = 0.37 K was investigated. It was found that at high doping concentrations, the incorporated Al atoms do not aggregate to form clusters. They rather remain as separated atoms inside of the He droplets. Mass spectrometry and the recently developed depletion method have been applied to study the reactions. It was found that single Al atoms react with single O-2 molecules. The dominant product of this reaction occurring inside of the He droplets is AlO2. The reaction between Al and O-2 clusters has also been detected. The Al clusters react with single H2O molecules or clusters. While single Al atoms react with H2O clusters, no reaction of single Al atoms with a single water molecule was found.