Once upon a time, google was obsessed with aggregating the worlds data. Today, google is all about AI generated or sourced data. And building a complex model to estimate pollen levels is definitely what they’d do.

(Plus the cost of those sensors would not be justified for such a small product).

Or use an open-data approach from the millions of hobby/scientific weather stations.

That would make it harder to sell the data though so why bother ?

I think crowdsourcing data's more of an open source thing. I don't think Google's ever been into that? Their approach is more "we're gonna scan all the books in the library/photograph every street in the world". (Interested to hear counterexamples).

crowdsourcing data is exactly what the Googs does. CAPTCHA to train it's models of data of dubious origins is the SEP (someone else's problem) nobody wants to talk about

They’ve crowdsourced a lot of their Maps data for information on specific businesses through the Local Guides program.

Also we local guides provide streetview maps where there previously were none.