How are cold, dry air masses formed?

Question

over land in polar regions

over water in tropical zones

over water in polar regions

over land in tropical areas

Answer 1

Cold, dry air masses are typically formed over land in polar regions. In these areas, the air is able to cool significantly, and with limited moisture sources (as opposed to over water), the air becomes both cold and dry. This is in contrast to areas over water, where air masses are generally more humid.