“Though” when you mean “because”:
The company also cites data collected by a state air pollution monitor at Washington High School, about two-thirds of a mile southeast of the Burley Avenue terminal.
The monitor has recorded no violations of the federal standard for particulate matter since at least 1993, though prevailing winds typically don’t blow toward the monitor from the KCBX site.
This is common journalese. Writer wants to question something, tosses in oppositional clause, making it an argument against something. But there’s no opposition. Both things can happen. There’s nothing in one to prevent the other.
Both do happen, of course. So what? So the one may mean little, in view of the other. “Because” says more than the writer wants; he wants to hint at it, not say it outright.
Which leads to the question whether he should say it at all — unless he can fine-tune the refutational nature of the second, so that (a) it’s clear and (b) it does not ask or require the reader to supply more than he’d care to come up with on a nice July morning.
Blithe Spirit 