Reibun
？。

Just how much of the yellow dust — which is smaller than pollen — can you actually block with a mask? It seems even more of a pest than pollen to me.

Literal

Pollen [than-よりも] smaller-is yellow-dust [obj-を] mask [by-で] how-much block [nominalizer-こと] [subject-が] can-do [question-のか]? Pollen [than-よりも] much-more troublesome-one [like-のように] think.

An observation about Japanese air-quality concerns. 黄砂 ('yellow dust') is the fine sand particles carried on winds from the Gobi and Taklamakan deserts into Japan each spring, a major health concern. 花粉 ('pollen') is the other spring air-quality nuisance — pollen allergies (花粉症) affect huge numbers of Japanese. 厄介者 ('troublesome thing/person') is a fixed noun for something bothersome. よりも is the comparison particle よ​り reinforced with も for emphasis.