you may be right...i'm thinking about the same reason becuase the self absorption increases in the UV range and oygen spectrum lies in the UV...another thing is that may be the air itself gets too thick near plasma it may also absorb the radiations as u have said
my question is why oxygen lines does not appear in metal oxides spectrum taken at 532nm wavelength of Nd:YAG laser at atmospheric pressure. and what is the criteria for selecting emission lines for analysis?