Complex sentence: The Sahara and drylands around the Arabian peninsula are the main terrestrial sources of airborne dust, with some contributions from Iran, Pakistan and India into the Arabian Sea, and China's significant storms deposit dust in the Pacific.
Split into simpler sentences: The Sahara and drylands around the Arabian peninsula are the main terrestrial sources of airborne dust. Also with some contributions from Iran, Pakistan and India into the Arabian Sea, and China's significant storms deposit dust in the Pacific.