Dust particles from a blasting operation rise up in the atmosphere to a height of 500 m. The viscosity of air is \( 1.80 \times 10^{-5}\ \text{kg}\,\text{m}^{-1}\,\text{s}^{-1} \). Assume the particles have quiescent settling (no turbulence) in atmosphere. Neglecting air density, the settling time, in days, of a dust particle of 2.5 \(\mu\)m diameter and 3600 \( \text{kg}\,\text{m}^{-3} \) density is . (rounded off to two decimal places)