No abstract

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 (7)Be that is produced upon the incident of cosmic rays on light atmospheric nuclei in the stratosphere. The availability of 5 years observations of (7)Be concentration in surface air in Tehran (35 degrees 41(') N, 51 degrees 18(') E) encouraged us to investigate meteorological condition effect on the surface concentration of (7)Be. 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 (7)Be and scavenging mechanism when the concentration was low. During the course of this study, it has been found that (7)Be 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 (7)Be 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.

Concentrations of major inorganic ions (NH 4 ,Mg,SO 4 ,NO 3 ,NO 2 ,Na,Ca,HCO 3 ,F,Cl,Br,K), PH, Total Dissolved Solids (TDS), Electrical Conductivity (EC), Total Alkalinity and Total Hardness in bulk precipitation samples collected in the Tehran city of I.R. of Iran were analyzed. Results show that concentrations of the found substances were higher over the Mehrabad station. The mean concentration of ions indicated that, HCO 3 , SO 4 and NO 3 and were the main anions, while Ca ,Na,NH 4 and Mg were the main cations. Measured PH had shown that autumn and winter precipitation were mostly acidic while the spring and summer were mostly alkaline. The pH ranged from 4.6 to 8.1 with a mean of 6.3. The alkaline cations Ca and Mg and also Bicarbonate anion acted as acid neutralizers and buffered the acidity of rain. The Bicarbonate anion had the highest concentration, among all other ions, over both stations and plays an important role in reduction of the acidity of the rain water. Study upon the potential sources of the ions over Tehran by means of Correlation Analysis, Enrichment Factor and Principle Component Analysis indicate that existence of Qom salt lake and desert in the south of the city were the main source of the Ca,Mg,K and Na . There are anthropogenic sources for SO 4 ,NO 3 , NO 2 ,F, Br ion's. The other ions HCO 3 and NH 4 were from anthropogenic and dust origin.