Air pollution tutorial should show path to "vectorization"

The air polution tutorial has a "vectorized" function to calculte the AIQ (IIRC). This can be vectorized using searchsorted (which is a bit much work, but not too tricky).
I am also almost completely certain that it can also be replaced with a single call to np.interp1d.

Having the "vectorize" version seems good, but doesn't fully leverage the concepts that NumPy provides. I think it would be great arc to keep it, but then also show the final interp and maybe even the searchsorted idea. (I honestly don't like stopping at vectorize becuzse it makes seems that vectorize is a common approach, when I consider it more of a fallback solution – whether used a lot in practice or not.)

大気汚染チュートリアルから始め、AQI の計算に使用されている既存のベクトル化関数を見つけます。チュートリアルで、searchsorted と補間の考え方と並べて vectorize アプローチをどのように提示できるかを比較します。チュートリアルがこれらの代替手段を説明し、vectorize が唯一の方法であると示唆しなければ完了です。