Limestone, dust and the I-35 corridor
Parts of Hays County sit on limestone, and construction and quarry activity in the region puts a lot of fine mineral dust into the air. Winds can lift it from graded lots, and it settles on window sills, air handler filters and return grilles. On the other hand, the area also has Ashe juniper, which sends heavy pollen into the air in winter.
Residents who drive I-35 to work see these dust and pollen conditions every year. At home, that shows up as filters that darken faster than expected and a fine residue at registers. Cleaning helps remove what accumulated, while a snug filter and sealed return joints keep the problem from returning quickly.

