Variations of Large Ions Concentration in the Air above Athens

Large ions (positive and negative) concentration of air was regularly monitored at the NOA (National Observatory of Athens) atmospheric electricity station for a long period from 19691980. At the Laboratory of Climatology, University of Athens, Panepistimioupolis, measurements of large ions concentration has been performed regularly since June 2002 using the same type of instrumentation. At both stations, measurements of meteorological parameters (temperature, pressure, humidity, etc.) are performed on a daily basis. This paper presents the preliminary results of the new recordings of the large ions concentration performed at Panepistimioupolis station. Their variations of the large ions concentration and their diurnal course presented almost the same pattern as those at NOA station. More research is needed in order to have a clear understanding of the behaviour of large ions concentration requiring, thus, more recordings. INTRODUCTION The concentration of small ions in the air depends on the rate of production and destruction of these ions. When a small ion attaches itself to an uncharged nucleus, the product is characterized as a large ion. This ion has evidently much reduced mobility. In Athens – Greece measurements of both positive and negative large ions have been made regularly since 1969 at the National Observatory of Athens (NOA). NOA (φ=37°58' N, λ=23°43'E, h=107m) is located on the rather flat top of Nymphs Hill in the centre of Athens, facing Acropolis, about 30m higher than surrounding city. The variations of large ions concentration at NOA station and the effects of air pollution (smoke, SO2, ozone) and meteorological parameters have been studied by Retalis [1983], Retalis D. and Retalis A. [1992, 1998]. They showed that large ions concentration is highly correlated with smoke, SO2 (positive trend) and ozone (negative trend), while large ions concentration and wind speed are anti-correlated. At the Laboratory of Climatology (φ=37°58' N, λ=23°47' E, h=243m), University of Athens, Panepistimioupolis, measurements of large ions concentration has been performed regularly since June 2002. The instruments used are of the same type as those used for the NOA recordings. At NOA a meteorological station has been working for more than 145 years. The annual values of specific elements for the period 1951-1980 (30-years mean) are: mean air temperature 17.7 °C, relative humidity 62%, wind speed 2.4m/s, sunshine 2919 hours. Thunderstorm activity in Greece is very weak. During a 16-year period (1965-1980), 282 thunderstorm days were observed, i.e. 17.6 days per annumn. We note that the mean annual number of thunderstorm days, for a period of 80 years, in Athens, is 18 days [Retalis D. and Retalis A., 1992]. At Panepistimioupolis station systematic measurements of meteorological parameters (i.e. temperature, pressure, humidity, etc.) are also performed on a daily basis. In this study the preliminary results of the new recordings of both positive and negative large ions concentration performed at the Laboratory of Climatology at Panepistimioupolis are presented and discussed to the relative recordings recorded at NOA station. INSTRUMENTATION AND METEOROLOGICAL CONDITIONS Large ions concentration is measured by an ionic current, which is composed by a charged plate capacitor, through which an air current of known velocity flows. Owing to the reduced mobility of large ions a plate capacitor was used instead of a cylindrical one aluminium plates of length L = 0.5 m form a 12-surface capacitor with d = 4 mm. With a flux through a surface 49.65 cm and a flux volume M0 = 0.625 l/sec, the flux velocity is only v ≈ 12.6 cm/sec. The relationship k⋅V = d⋅v/L = 0.0403⋅10 m/sec exists between the voltage V of the capacitor and the mobility k. Using a voltage of 161 volts, we are able to measure all large ions including those with mobility 2.5 × 10 m/V⋅sec [Retalis, 1983]. The instruments used have been constructed at the Laboratory of Physics at Aarau, Switzerland by Saxer and Sigrist [1966]. The mean values of the meteorological parameters for October 2002 at Panepistimioupolis and NOA station respectively, are presented in Table 1. As shown it is evident that the meteorological conditions prevailing at both stations present some small variations concerning wind direction and precipitation height. Table 1. Climatic data for October 2002 at Panepistimioupolis (PAN) and NOA stations, respectively. Precipitation Absolute Maximum Temperature Absolute Minimum Temperature Absolute Mean Temperature Wind Speed (m) Wind Direction Relative Humidity (%) (Days) (mm) PAN 27.3 10.5 18.1 2.3 SE 65.4 4 38.8 NOA 27.8 11.2 19.8 2.7 N 67.0 4 69.0 DATA DESCRIPTION DISCUSSION At the Laboratory of Climatology of the University of Athens (Panepistimioupolis), measurements of positive and negative large ions concentrations have been performed since July 2002. Systematic measurements have started since September 2002. Due to limitation of space needed for the purposes of this paper we are presenting only the results for October 2002, which are representative of the whole recording period. These measurements (daily courses) are presented in Figure 1a. Figure 1a