Stratospheric Aitken particles

The nature and sources of stratospheric Aitken particles have remained highly uncertain in spite of considerable research by various groups. Most of the field studies of these particles have been performed by using condensation nucleus counters and by impactors. Numerous theoretical studies have been made of their formation, transport, and fate. This article reviews and analyzes the results. This analysis strongly indicates that the Aitken particles in the stratosphere below 20 km in altitude are usually of tropospheric origin and like the larger particles consist to a major extent of impure sulfuric acid. Above 20 km they may contain a considerable fraction of Aitken particles of meteoric origin.