When the wind kicks up dust and sand, the dust grains are charged. the small grains tend to get a negative charge, and the large grains a positive charge. the small grains are lifted higher by the wind.?

Explanation:

Small grains are negatively charged by the wind while big grains is positively charged and remains at the ground . This process creates an electric field due to the presence of oppositely charged particles.

When ever electric field exists it is directed from a positive charge to a negative charge so the here electric field is towards an upwards direction.