のっぱmeans tall, addingさ for degree of - i.e. height.

Not sure height of air makes sense though... do you have any more context on what the text is about?

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Note added at 42 mins (2012-12-20 06:57:32 GMT)
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That would be ぽ, of course...

Pulmonary function tests are a group of tests that measure how well the lungs take in and release air and how well they move gases such as oxygen from the ...
www.nlm.nih.gov/medlineplus/ency/article/003853.htm

I'm afraid something is missing between "の" and "っぽさ".

Ex.空気の"ほこり"っぽさ(the extent how the air is dusty) 、空気の"湿"っぽさ(humidity of the air),etc...

I suppose you need to make sure if the source sentences are correct.

context or source please... rendering this expression depends so much on that factor.... (scientific, poetic, fiction, news paper article, blog?)

Could this be: the 'essential quality of'? the '~(ish) ness of'?
and っぽさ the noun for Adj.suffix っぽいas in: 子供っぽい、東京っぽい,... ?

This would make it: 'a scale to measure the ....

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Note added at 1 day26 mins (2012-12-21 06:41:21 GMT)
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"atmosphere' whether nature's or of a social gethering

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Note added at 1 day27 mins (2012-12-21 06:41:54 GMT)
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Oops! sorry for the typo!


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Note added at 4 days (2012-12-24 12:37:23 GMT)
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Reflecting on Terry's remark, I realise teh following :
a) my initial suggestion did not render the unfavourable connotation that ～っぽさ conveys. b) that negative connotation may be mild but is so definite that ~っぽい alone without any specific attribute to qualify it can still work, as in this uncommon case. c) if so, the simplest way to render it would be in generic terms, dropping the suffix 'ishness' and replacing it with a noun like "the unpleasant quality of" (the air) (whatever the cause(s) of it). d) the context in which this mention crops up is not known to us. If it appeared in a scientific article, however, reference to that scale must have been thought justified if the idea behind it sounded odd enough to raise a few eyebrow: "How could a scale be divised to measure something as subjective as human perceptions?" for this reason, I conclude that an acceptable way to translate this sentence would be to refer to a scale to rate (not measure) the unpleasant quality of the air.

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Note added at 4 days (2012-12-24 12:40:05 GMT)
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oops! apologies once more for those few typos.