Wet deposition of nitrogen and sulfur in Guangzhou, a subtropical area in South China

Understanding the exchange mechanism between stratosphere and troposphere is one of the most important concerns of meteorologists and climatologists for decades. Different methods are being adopted to study those mechanisms. One of those methods is the study upon the tropospheric concentration of conserve or passive entities with stratospheric origin. One of those passive entities is ⁷Be that is produced upon the incident of cosmic rays on light atmospheric nuclei in the stratosphere. The availability of 5 years observations of ⁷Be concentration in surface air in Tehran (35°41^′ N, 51°18^′ E) encouraged us to investigate meteorological condition effect on the surface concentration of ⁷Be. Also, the intention was to see if there was any intrusion of stratospheric air into the troposphere at the time of high surface concentration of ⁷Be and scavenging mechanism when the concentration was low. During the course of this study, it has been found that ⁷Be concentration is high whenever there is a jet stream over Tehran. Since high-level jet streams normally form near tropopause folding, it could be interpreted as a sign of the intrusion of stratospheric air into the troposphere. It was also found that high concentration of ⁷Be in the Tehran surface air in summer is associated with an upper ridge on 500 hPa surface located east of the city, and low concentration in winter is associated with an upper trough. The latter normally is seen whenever there is precipitation that suggests wet scavenging could be the reason for that observed low concentration.