This is just a guess, but considering how wet it's been in the spring/summer the last few years (last year in particular), I suspect that the majority of poplar fluff has been taken off the trees by rain and washed down sewers, lessening the allergen significantly. But this year, we haven't had a good rain in a few weeks, which has allowed the fluff to accumulate and annoy the crap out of people with allergies.
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