Air Ion Research in Atmospheric Electricity Hannes.Tammet@ut.ee

1. Hyytiälä 2005 Air Ion ResearchinAtmospheric Electricity Hannes.Tammet@ut.ee Institute of Environmental Physics, University of Tartu

2. Hyytiälä 2005 CONTENTS: • Discovery and Nature of Air Ions • Air Ion Measurements Until 1963 • World Data Centre • Dataset ATMEL1 • Air Ion Measurements at Tahkuse

3. Discovery and Nature of Air Ions Hyytiälä 2005 Air electrical conductivity: Richmann 1744 Coulomb 1785 1834:William Whewell. Letter to Michael Faraday 5 May: ... For the two together you might use the term ions. 1834:Michael Faraday. Philosophical Transactions of the Royal Society. CXXIV. 79:....Finally, I require a term to express those bodies which can pass to the electrodes … I shall call them ions. Greek ion, something that goes, neuter present participle of ienai, to go. Thomson, J.J. (1898) Discharge of Electricity Through Gases, Westminster. Nobel Prizes: Thomson Rutherford Lenard Wilson Hess 1906 1908 1905 1927 1936

4. Discovery and Nature of Air Ions Hyytiälä 2005 Elster, J., Geitel, H. (1899) Über die Existenz elektrischer Ionen in der Atmosphäre.Terr.Magn.Atmos.Electr.4, 213-234. (Terrestrial Magnetism was grounded 1996, renamed to Terrestrial Magnetism and Atmospheric Electricity1899and to Journal of Geophysical Research 1949) 3.8 d 3 min 27 min 20 min <1 ms 23 y 5 d 138 d 222Rn →218Po →214Pb →214Bi →214Po →210Pb → 210Bi →210Po →206Pb 5.5 MeV 5.2 Mev 7.7 MeV 5.3 MeV 56 s 0.2 s 1 h 183 s 220Rn →216Po →212Bi →208Tl →208Pb 6.3 MeV 6.8 MeV 6 MeV Langevin, P. (1905) Sur les ions de l’atmosphère. C. R. Acad. Sci. 140, 232-234. Pollock, J.A. (1915) A new type of ion in the air. Phil. Mag. 29, 636-646. ........ ........ Israël, H. (1970) Atmospheric Electricity. Jerusalem.

5. GD AS AE Expanding research fieldsand the position of air ionsas a common research subject Hyytiälä 2005 AS – Aerosol Science AIR IONS GD – Gas Dischargeand Plasma Physics AE – Atmospheric Electricity

6. Air Ion Measurements Until 1963 Hyytiälä 2005 Measured quantities: Air conductivity Concentration of small air ions Concentrations of few ion groups Mobility distribution of air ions During the first period of the increased activity in1904...1914, air conductivity was routinely measured at a large number of stations. Both conductivity and small ion concentration were systematically measured at about 10 locations in Europe and South America. The original data of old measurements are often lost or stored in archives inaccessible for the wide community of scientists. A large amount of work in recovering and analysing retrospective data has been done by Giles Harrison in Reading, UK. } Mobility and size of small air ions

7. Analysis of retrospective data by Harrison: Hyytiälä 2005 F. Märcz and R.G. Harrison (2005) Further signatures of long-term changes in atmospheric electrical parameters observed in Europe. Annales Geophysicae 23. Harrison R.G. and Ingram W.J. (2004) Air-earth current measurements at Kew, London, 1909-1979. Atmos. Res., doi: 10.1016. Harrison, R.G. (2004) Long-range correlations in measurements of the global atmospheric electric circuit. J. Atmos. Solar-Terr. Phys., 66, 1127-1133. Harrison R.G. (2004) Long term measurements of the global atmospheric electric circuit at Eskdalemuir, Scotland, 1911-1981. Atmos. Res.70 (1), 1-19. Harrison R.G. and Aplin K.L. (2003) Nineteenth century Parisian smoke variations inferred from Eiffel Tower atmospheric electrical observations. Atmos. Environ.37, 5319-5324. Märcz F. and Harrison R.G. (2003) Long-term changes in atmospheric electrical parameters observed at Nagycenk (Hungary) and the UK Observatories at Eskdalemuir and Kew. Annales Geophysicae21, 2193-2200. Harrison R.G. (2003) Twentieth century atmospheric electrical measurements at the observatories of Kew, Eskdalemuir and Lerwick. Weather58, 11-19. Harrison R.G. (2002) Twentieth century secular decrease in the atmospheric electric circuit. Geophysical Research Letters, 29(14) DOI 10.1029/2002GL014878, Harrison R.G. and Aplin K.L. (2002) Mid-nineteenth century diurnal smoke concentrations at Kew, London. Atmos. Environ.36, 25 4037-4043. Harrison R.G. (2004) Twentieth century air pollution near London: a reconstruction from measurements of atmospheric electricity. Childhood Leukaemia: Incidence, causal mechanisms and prevention, London 6th-10th September 2004, 4-6. Harrison R.G. (2003) Climate change and long-term variations in the atmospheric electrical system. Proc.12th International Conference on Atmospheric Electricity, Versailles, vol2, 703-706, 2003. Harrison R.G. (2003) Long-term changes in aerosol and the electrical conductivity of oceanic air. Proc. 14th annual conference, The Aerosol Society, Reading, 2nd-3rd April 2003, 22-25. Harrison R.G. and Aplin K.L. (2002) Aerosol variations inferred from historical atmospheric electrical data. Proc. XIIIth Annual Conference The Aerosol Society, Lancaster, April 2002, 113-116.

8. Concentration of few ion groups Hyytiälä 2005 Early thirties: H. Israël and L. Schulz (Ph.D. thesis 1933 “Beiträge zur Kenntnis der Luftionen”) initiated measurement of four ion groups (ultralarge, Langevin, large intermediate, small intermediate) in many locations in Europe. 4-10 measurements were made in one location. The results are resumed in the book by Israël (1970). Systematic measurements were made by J. Reinet in Tartu during full year 1951. Events of increased concentration of intermediate ions (charged nanometer particles) were discovered. P. Prüller carried out 3 year measurements in Tartu 1960-1963. The concentrations of ion groups were recorded 4-8 times every day. Early fifties: Christian Junge showed that the measurements of large and intermediate ions contain unique information about atmospheric aerosol:

9. Mobility distribution of air ions Hyytiälä 2005 First high resolution measurementof atmospheric ion mobility distribution: Yunker, E.A. (1940) The mobility spectrum of atmospheric ions.Terr. Magn. Atmos. Electr. 45, 127-132. Episodic measurements have been performed since 1950 in Japan by Misaki, Sekigava, Suzuki, Kojima, Nagato, ...

10. World Data Centre Hyytiälä 2005 The World Data Centre for Atmospheric Electricity operated within the Main Geophysical Observatory, St. Petersburg, Russia 1965-1993. The data for 1964-1989 were published as monthly reports "Results of ground observations of atmospheric electricity". Kolokolov, V.P. (1981) On activity of World Data Centre for Atmospheric Electricity (in Russian). Meteorologya i Gidrologya, N2, 119-120. Gordyuk, V.P. and Tammet, H. (1992) Modernization of the World Data Center for Atmospheric Electricity. Proc. 9th Int. Conf. on Atmospheric Electricity, St. Petersburg, 1, pp. 46–49. Dolezalek, H. (1992) The World Data Centre for Atmospheric Electricity and global change monitoring. European Science Notes Information Bulletin. 92-02. Office of Naval Research, European Office, 1-37.

11. List of 37 stations, which have been sent the data to WDC Hyytiälä 2005 Aachen (FRG) Kara-Dag (Ukraine) Porto (Portugal) Auckland (N-Zealand) Kew (UK) Potsdam (Germany) Athens (Greece) Kiev (Ukraine) Sacushima (Japan) B-Elan (Russia) Kirov (Russia) Soccoro (USA) Brest (France) Lisbon (Portugal) Swider (Poland) Budapest (Hungary) Lerwick (UK) Tashkent (Uzbekistan) Dourbes (Belgium) Macherata (Italy) Toronto (Canada) Eskdalemuir (UK) Memambetsu (Japan) Uccle (Belgium) Dusheti (Georgia) Montreal (Canada) University Park (USA) Helsinki (Finland) Murmansk (Russia) Venice (Italy) Irkutsk (Russia) Nivot Ridge (USA) Verkhnee Dubrovo (Russia) Kakioka (Japan) Odessa (Russia)Voeikovo (Russia) Yuzhno-Sakhalinsk (Russia)

12. A page of WDC monthly brochure Hyytiälä 2005

13. A sample of original WDC data written in YaOD Hyytiälä 2005 599307096 4 1 9999999 8 796121200120150 29999 599307096 4 110999999 7 696999999999999999999 599307096 4 111999999 7 696999999999999999999 599307096 4 112999999 7 69610 084000100 39999 599307096 4 113999999 5 596999999999999999999 599307096 4 114999999 4 496999999999999999999 599307096 4 115999999 6 69610 084000 90 49999 599307096 4 116999999 6 5969999999999999972 2 599307096 4 117999999 6 5969999999999999972 1 599307096 4 118999999 6 59610 882020 90 472 1 599307096 4 119999999 6 5969999999999999972 1 599307096 4 120999999 5 4969999999999999972 1 599307096 4 121999999 3 596101088002 90 672 1 599307096 4 122999999 4 4969999999999999972 1 599307096 4 123999999 3 5969999999999999972 2 599307096 4 124999999 5 696101088002110 573 1 599307096 4 2 1999999 5 6969999999999999973 2 599307096 4 2 2999999 6 6969999999999999973 2 599307096 4 2 3999999 7 796101088220120 373 1

14. Dataset ATMEL1 Hyytiälä 2005 Stations: 13 Quantities: 51 Variables: 158 Diurnal series: 456 105 Data format: Diary (DataDiurna) Bytes: 42 922 325 LatitudeLongitudeAltitude Station 59.97 30.3 72 Voeikovo near St. Petersburg (former Leningrad) 52.27 104.32 467 Irkutsk near Baikal See 42.08 44.7 910 Dusheti near Tbilisi 56.8 60.63 237 Verhnee Dubrovo near Jekaterinenburg (former Sverdlovsk) 46.48 30.63 42 Odessa 46.95 142.72 22 South-Sakhalinsk (Japanese name Toyohara) 41.27 69.27 477 Tashkent 47.5 11.15 1780 Wank Peak: R.Reiter's station near Garmish-Partenkirchen 59.93 17.58 10 Marsta Meteorological Observatory (University of Uppsala) 59.436 24.757 10 Viru: City centre of Tallinn (Estonia) 58.55 26.38 40 Saarejärve: EMEP station in Estonia 59.53 25.88 5 Lahemaa: EMEP station in Estonia 58.39 21.84 5 Vilsandi: EMEP station in Estonia

15. ATMEL1 quantities Hyytiälä 2005 Type of quantity # Cloud characteristic 8 Weather type 3 Condensation nuclei 3 Concentrations of gases 6 Humidity 2 Electric field 3 Electric current 2 Air conductivity 3 Concentration of small air ions 2 Space charge 1 Air pressure 1 Optical radiation (incl. UV) 4 Air temperature 6 Richardson number 1 Wind 5 Visibility 1

16. ATMEL1 quantities page 1: Hyytiälä 2005 Stat. Quantity From To Irk Cl-low 19890101 19970331 Ode Cl-low 19890101 19940831 Sakh Cl-low 19890101 19940630 Tash Cl-low 19890101 19951231 Ural Cl-low 19890101 19961210 Vo Cl-low 19890101 19970331 Irk Cl-mid 19890101 19970331 Ode Cl-mid 19890101 19940831 Sakh Cl-mid 19890101 19940630 Tash Cl-mid 19890101 19951231 Ural Cl-mid 19890101 19961210 Vo Cl-mid 19890101 19970331 Irk Cl-nim 19890101 19970331 Ode Cl-nim 19890101 19940831 Sakh Cl-nim 19890101 19940630 Tash Cl-nim 19890101 19951231 Ural Cl-nim 19890101 19961210 Vo Cl-nim 19890101 19970331 Wank Cl-R 19810613 19831231 Irk Cl-str 19890101 19970331 Stat. Quantity From To Ode Cl-str 19890101 19940831 Sakh Cl-str 19890101 19940630 Tash Cl-str 19890101 19951231 Ural Cl-str 19890101 19961210 Vo Cl-str 19890101 19970331 Irk Cl-tot 19890101 19970331 Ode Cl-tot 19890101 19940831 Sakh Cl-tot 19890101 19940630 Tash Cl-tot 19890101 19951231 Ural Cl-tot 19890101 19961210 Vo Cl-tot 19890101 19970331 Irk Cl-upp 19890101 19970331 Ode Cl-upp 19890101 19940831 Sakh Cl-upp 19890101 19940630 Tash Cl-upp 19890101 19951231 Ural Cl-upp 19890101 19961210 Vo Cl-upp 19890101 19970331 Irk Cl-ver 19890101 19970331 Ode Cl-ver 19890101 19940831 Sakh Cl-ver 19890101 19940630

17. ATMEL1 quantitiespage 2: Hyytiälä 2005 Stat. Quantity From To Tash Cl-ver 19890101 19951231 Ural Cl-ver 19890101 19961210 Vo Cl-ver 19890101 19970331 Dush C-MGO 19670101 19801231 Irk C-MGO 19890101 19970331 Ode C-MGO 19890101 19940831 Sakh C-MGO 19890101 19940630 Tash C-MGO 19890101 19951231 Ural C-MGO 19740101 19961231 Vo C-MGO 19660101 19970331 Wank CNR1:cm-3 19720801 19831231 Wank CNR2:cm-3 19720801 19831231 Wank CNR3:cm-3 19720801 19831231 Viru CO:mg/m3 19940725 19990731 Wank E:inv/h 19720801 19831231 Dush E:V/m 19670101 19801231 Irk E:V/m 19890101 19970331 Marsta E:V/m 19930203 19981203 Ode E:V/m 19890101 19940831 Sakh E:V/m 19890101 19940630 Stat. Quantity From To Tash E:V/m 19890101 19951224 Ural E:V/m 19740101 19961210 Wank E:V/m 19720801 19831231 Vo E:V/m 19660101 19970331 Marsta Eflct:V/m 19930205 19981203 Marsta H2O:g/kg 19940531 19980923 Wank H2O:g/kg 19720801 19831231 Marsta j:pA/m2 19930204 19981130 Wank j:pA/m2 19720801 19831231 Wank jp:pA/m2 19740103 19820704 Dush L-:fS/m 19670101 19801231 Irk L-:fS/m 19890101 19970331 Marsta L-:fS/m 19930204 19981130 Ode L-:fS/m 19890204 19940831 Sakh L-:fS/m 19890101 19910815 Ural L-:fS/m 19740101 19951001 Wank L-:fS/m 19730724 19831130 Vo L-:fS/m 19660103 19970331 Dush L+:fS/m 19670101 19801231 Irk L+:fS/m 19890101 19970331

18. ATMEL1 quantitiespage 3: Hyytiälä 2005 Stat. Quantity From To Marsta L+:fS/m 19930203 19981203 Ode L+:fS/m 19890204 19940831 Sakh L+:fS/m 19890101 19910815 Ural L+:fS/m 19740101 19951001 Wank L+:fS/m 19730724 19831130 Vo L+:fS/m 19660102 19970331 Wank NC-:cm-3 19720801 19831231 Wank NC+:cm-3 19720801 19831231 Saare NO:ug/m3 19971231 19990620 Vils NO:ug/m3 19950418 19990630 Viru NO:ug/m3 19940725 19990731 Saare NO2:ug/m3 19971122 19990620 Vils NO2:ug/m3 19950418 19990630 Viru NO2:ug/m3 19940725 19990731 Saare NOX:ug/m3 19971122 19990620 Wank NOX:ug/m3 19740308 19830729 Vils NOX:ug/m3 19950418 19990630 Viru NOX:ug/m3 19940725 19990731 Lahe O3:ug/m3 19940615 19990731 Saare O3:ug/m3 19971112 19990620 Stat. Quantity From To Vils O3:ug/m3 19940528 19990630 Viru O3:ug/m3 19960605 19990731 Marsta p:mb 19940531 19981130 Dush Ph-code 19670101 19801231 Irk Ph-code 19890101 19970331 Ode Ph-code 19890101 19940831 Sakh Ph-code 19890101 19940630 Tash Ph-code 19890101 19951231 Ural Ph-code 19740101 19961231 Vo Ph-code 19660101 19970331 Dush Ph-int 19670101 19801231 Irk Ph-int 19890101 19970331 Ode Ph-int 19890101 19940831 Sakh Ph-int 19890101 19940630 Tash Ph-int 19890101 19951231 Ural Ph-int 19740101 19961231 Vo Ph-int 19660101 19970331 Wank Rad:W/m2 19720801 19831231 Marsta RH% 19940531 19980923 Wank RH% 19720801 19831231

19. ATMEL1 quantitiespage 4: Hyytiälä 2005 Stat. Quantity From To Sakh Wind:deg 19890101 19940630 Tash Wind:deg 19890101 19951231 Ural Wind:deg 19890101 19961210 Wank Wind:deg 19720801 19831231 Vils Wind:deg 19951231 19960720 Vo Wind:deg 19890101 19970331 Irk Wind:m/s 19890101 19970331 Lahe Wind:m/s 19970219 19990731 Ode Wind:m/s 19890101 19940831 Sakh Wind:m/s 19890101 19940630 Tash Wind:m/s 19890101 19951231 Ural Wind:m/s 19890101 19961210 Wank Wind:m/s 19720801 19831231 Vils Wind:m/s 19951231 19960720 Vo Wind:m/s 19890101 19970331 Marsta Wind08:m/s 19940531 19981130 Marsta Wind10:m/s 19940531 19981130 Wank Vis:km 19750109 19831231 Stat. Quantity From To Marsta Ri 19940531 19981130 Marsta SC:pC/m3 19930204 19981130 Wank SC:pC/m3 19730724 19831231 Wank Sky:W/m2 19770205 19831231 Saare SO2:ug/m3 19971231 19990620 Vils SO2:ug/m3 19940528 19990630 Viru SO2:ug/m3 19940726 19990731 Wank Sun% 19730729 19831231 Wank T:C 19720801 19831231 Marsta T08:C 19940531 19981130 Marsta T10:C 19940531 19981130 Wank Tepot:K 19730703 19831231 Marsta Tgr:K/m 19940531 19981130 Wank Tpot:K 19730703 19831231 Wank UV:mW/m2 19740307 19831231 Marsta Wflct:m/s 19940531 19981130 Irk Wind:deg 19890101 19970331 Lahe Wind:deg 19970218 19990731 Marsta Wind:deg 19940531 19981130 Ode Wind:deg 19890101 19940831

20. Diary format Hyytiälä 2005 • From data by Reinhold Reiter: • WANK. 06.12.77 • STUNDENWERTE: • T • -00.4 -01.0 -02.2 -02.9 -01.8 -01.7 -00.1 +00.2 +00.7 +00.1 -00.1 -00.4 • -00.4 -00.1 +00.5 -00.2 -00.5 -01.2 -02.0 -02.1 -02.3 -02.7 -02.8 -03.0 • RF • 21.5 21.8 24.2 26.2 22.4 24.0 20.7 22.8 29.8 36.1 41.1 43.8 • 45.9 49.4 47.6 50.6 52.8 58.6 61.2 63.7 76.1 83.8 88.1 89.5 • Modified: • 06.12.77,T(Wank),-0.4,-1.0,-2.2,-2.9,-1.8,-1.7,-0.1,+0.2,+0.7,+0.1, • -0.1,-0.4,-0.4,-0.1,+0.5,-0.2,-0.5,-1.2,-2.0,-2.1,-2.3,-2.7,-2.8,-3.0 • 06.12.77,RF(Wank),21.5,21.8,24.2,26.2,22.4,24.0,20.7,22.8,29.8,36.1, • 41.1,43.8,45.9,49.4,47.6,50.6,52.8,58.6,61.2,63.7,76.1,83.8,88.1,89.5 • Advantages of diary: • adapted for routine environmental measurements • saved as immediately readable text • data manager will be available as freeware

21. A diary standard: DataDiurna Hyytiälä 2005 DDD,ATMEL1,20041230 19950615,Tash,Cl-mid,h0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,1,1 19950615,Tash,Wind:deg,h0,87,103,120,133,147,160,203,247,290,193,97,0,... 19950615,Tash,Wind:m/s,h0,1,2,2,2,1,1,1,1,1,1,0,0,0,0,0,0,1,1,1,1,1,1,1,1 19950615,Marsta,RH%,h0,100.0,100.0,100.0,100.0,100.0,99.6,98.4,98.9,98.2,94.6,... 19950615,Marsta,E:V/m,h0,10,-2,46,72,67,66,-1,164,91,61,59,98,93,93,76,76,84,... 19950615,Marsta,L+:fS/m,h0,23.1,22.9,23.9,24.8,24.5,24.4,24.1,24.2,24.7,25.7,.... 19950615,Marsta,L-:fS/m,h0,13.3,13.8,14.0,15.7,19.5,19.1,20.0,20.6,25.2,24.5,... 19950615,Marsta,SC:pC/m3,h0,3.7,1.3,-0.5,-0.5,-0.5,1.8,-1.0,-0.6,-0.3,-0.3,4.3,8.2,.... 19950615,Marsta,j:pA/m2,h0,0.36,-0.07,1.74,2.92,2.95,2.87,-0.04,7.35,4.54,3.06,.... 19950615,Viru,SO2:ug/m3,h0,3.7,2.9,2.5,2,2.6,3.8,6.1,7.5,7.7,6.7,5.7,5.2,5,2.7,2.1,... 19950615,Vils,NO2:ug/m3,h0,4.1,4.2,4.3,3.1,4.1,9999,0.8,2.1,9999,1.4,3.4,1.8,0.4,... 19950615,Vils,NOX:ug/m3,h0,4.3,4.5,4.5,3.5,4.5,9999,1.1,2.5,9999,1.8,4.3,2.2,0.6,...

22. A diary standard: DataDiurna Hyytiälä 2005 DDS,ATMEL1,20041223 Vo,59.97,30.3,72,Voeikovo near St. Petersburg (former Leningrad) Irk,52.27,104.32,467,Irkutsk near Baikal See Dush,42.08,44.7,910,Dusheti near Tbilisi Ural,56.8,60.63,237,Verhnee Dubrovo near Jekaterinenburg (former Sverdlovsk) Ode,46.48,30.63,42,Odessa stationlabel,latitude,longitude,altitude[,explanations] DDQ,ATMEL1,20041223 T:C,Celsius,1,-90,90,99,Air temperature near the station T08:C,Celsius,2,-90,90,99,Air temperature at height of 0.8 m T10:C,Celsius,2,-90,90,99,Air temperature at height of 10 m Tgr:K/m,K/m,3,-2,2,9,Gradient of temperature (ATMEL1-MARSTA.doc) Tpot:K,Kelvin,1,180,360,999,Potential temperature (ATMEL1-WANK.doc) Tepot:K,Kelvin,1,180,360,999,Equipotential temperature (ATMEL1-WANK.doc) p:mb,millibar,1,100,1200,9999,Air pressure near the station RH%,%,1,0,100,999,Relative humidity quantitylabel,unit,decimals,lowconstraint,highconstraint,missing[,explanations] DDR,ATMEL1,20041228 h0,24,1800,Average during full hour, first period 00:00-01:00 hw,24,0Average during full hour, first period 23:30-00:30 regimelabel,valuesperday,reference[,explanations]

23. Air Ion Measurements at Tahkuse Hyytiälä 2005 Tahkuse is located in a sparsely populated rural region, 27 km northeast of the city of Pärnu. The first measurements of air ions were carried out 1984. The first period of systematic measurement of small natural air ions was June 10, 1985 to June 2, 1986. The average spectrum of positive and negative air ions of mobility 0.32–3.2 cm2V–1s–1at Tahkuseduring June–September 1985.

24. First observations of bursts of intermediate ions at Tahkuse Hyytiälä 2005 Tammet, H., Salm, J. and Iher, H. (1988) Observation of condensation on small air ions in the atmosphere. In Atmospheric Aerosols and Nucleation. Lecture Notes in Physics, Springer-Verlag, Vienna, 309, pp. 239–240. Hourly average 13 June 1985 at 03 a.m. Hourly average 05 September 1985 at 05 p.m.

25. Tahkuse: Hyytiälä 2005

26. Tahkuse today: • An extended instrumentation for measurements of the air ion spectra in a wide mobility range is running from 1988. Main instruments are: • Air ion spectrometer with a mobility range of 0.00032-3.2 cm2V-1s-1, • NO2 concentration meter designed at the University of Turku, • Ozone meter M-83 for measurements of total column ozone, • Pyranometer M-80M, • Sensors of wind, temperature, pressure, and humidity, • Devices for collection of precipitations. • The data are saved as average values every 5 min. Hyytiälä 2005 Selected publications Hõrrak, U., H. Iher, A. Luts, J. Salm, and H. Tammet (1994) Mobility spectrum of air ions at Tahkuse Observatory, J. Geophys. Res., 99, 10679–10700. Hõrrak, U., J. Salm, and H. Tammet (1998) Bursts of intermediate ions in atmospheric air, J. Geophys. Res. Atmospheres,103, 13909-13915. Hõrrak, U., A. Mirme, J. Salm, E. Tamm, and H. Tammet (1998) Air ion measurements as a source of information about atmospheric aerosols, Atmos. Res., 46, 233-242. Hõrrak, U., Salm, J. and Tammet, H. (2000) Statistical characterization of air ion mobility spectra at Tahkuse Observatory: Classification of air ions. J. Geophys. Res. Atmospheres105, 9291–9302. Hõrrak, U., Salm, J., Tammet, H. (2003) Diurnal variation in the concentration of air ions of different mobility classes at a rural area. J. Geophys. Res. Atmospheres, 108(D20), 4653. Hõrrak, U.(2001) Air Ion Mobility Spectrum at a Rural Area. PhD Thesis, University of Tartu.

27. From the thesis by Hõrrak: Hyytiälä 2005 Average mobility spectra of air ions at Tahkuse. Sept. 1993 – Oct. 1994.

28. Tahkuse: comparison of air ion and aerosol instruments Hyytiälä 2005 From: Hõrrak, U., Mirme, A., Salm, J., Tamm, E. and Tammet, H. (1998) Air ion measurements as a source of information about atmospheric aerosols. Atmos. Res.46, 233–242.