If the asteroid hits on land, there would be a huge amount of dust thrown up into the atmosphere. If it hits in water, then there would be an increase in water vapor in the atmosphere. This would result in an increase in rain resulting in landslides and mudslides.
Regionally there might be earthquakes, hurricanes and tsunamis due to the increase in kinetic energy. If the asteroid is large enough, these could be global in impact.
The asteroid belt is a big highway in a circle around the Sun.
Asteroids can be a few feet to several hundred miles wide. The belt probably contains at least 40,000 asteroids that are more than 0.5 miles across.