system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When an infrared non-contact thermometer is pointed at a target, how does it measure the target's temperature and not the temperature of the air column in front of the target?
gpt
I never got a satisfactory understanding of one of them. But regardless of exactly how the work;

They measure temperature by capturing the infrared radiation of whatever they're looking at. How much a thing radiate infrared depends on something called 'emissivity' and i think most of tbose thermometers have a setting to correct for it; its 1 for what we call 'black body' and 0 for mirror like or white things, with most real things somewhere in between.

Now your scenario; air is mostly transparent at the wavelength used by the thermometers, so it would only really see ir radiation from the object it is looking at. Meanwhile the transparency also means that the emissivity is nearly 0; it doesn't radiate much radiation, even if it were hot. More accurately, its just that there are far fewer air molecules flying around to emit anything at all, compared to a solid object; if you clump up enough gasses and heat it up, it would emit like a black body. (Stars! And thats how you tell how hot they are too). Finally, in most measurement scenario, the thing you are trying to measure will be by far the hottest thing within the column of air in the visual field of the object, so even if the air was denser and had higher emissivity, it wouldn't emit much. 

This would be why its not affected by the air temperarure you are looking through.