OBSERVATION ON ION DYNAMICS Urmas Hõrrak, Hannes Tammet
Institute of Environmental Physics, University of Tartu, 18 Ülikooli St., 50090 Tartu, Estonia.
E-mail: Urmas.Horrak@ut.ee
ESTONIA
T a l l i n n
Location of Tahkuse Observatory
Measurements
Location: Tahkuse Observatory (58°31'N 24°56'E), a sparsely populated rural region.
Instrumentation: three original multichannel aspiration spectrometers (second-order differential mobility analyzers). Method: particle classification by electrical mobilities.
Mobility range: 0.00041–3.14 cm2V–1s–1,
logarithmically divided into 20 intervals.
Mobility spectra of positive and negative ions are measured in every 5 minute.
Height of measurements: 5 m above the ground.
The database consists of 8900 hourly average spectra measured during the period Sept. 1993 – Oct. 1994.
Diagram of the measuring system
and the small air ion spectrometer (cross-section).
E is electrometer,
HVS is high voltage supply VS is voltage supply.
External dimensions of the cylindrical aspiration
spectrometer:
height 695 mm, diameter 122 mm.
Classification of air ions
Average spectra of air ions at Tahkuse. Sept.1993 - Oct.1994.
Particle diameter (nm)
Mobility of fractions (cm 2 V -1 s -1 )
Fraction concentration (cm-3 ) 79 52 34 22 15 11 7.4 4.8 3.2 2.3 2.0 1.8 1.60 1.42 1.24 1.03 0.85 0.70 0.56 0.45 0.36
1 2 46 10 20 4060 100 200 400600 1000
0.00041 0.00087 0.00192 0.0042 0.0091 0.016 0.034 0.074 0.15 0.25 0.32 0.40 0.50 0.63 0.79 1.02 1.28 1.60 2.01 2.51 3.14
Small ions Intermediate ions
Large ions
Positive ions Negative ions
Cluster ions Aerosol ions
Classification of air ions and aerosol particles
Class of air ions Mobility range cm2 V–1 s–1
Diameter range*
Class of particles Small cluster ions 1.3 – 3.2 0.36 – 0.85 Clusters Big cluster ions 0.5 – 1.3 0.85 – 1.6 Clusters Intermediate ions 0.034 – 0.5 1.6 – 7.4 Nanometer
particles Light large ions 0.0042 – 0.034 7.4 – 22 Ultrafine
particles Heavy large ions 0.00087 – 0.0042 22 – 79 Aitken
particles
* Estimates of equivalent diameter ranges assume single charged particles.
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.
Atmospheres 105, 9291–9302.
Small or cluster ions
Particle diameter (nm)
Electrical mobility (cm 2 V -1 s -1 )
Fraction concentration (cm-3 )
90 26 7.6 2.0 0.36
0 100 200 300 400 500 600
0.00032 0.0032 0.032 0.32 3.2
Positive ions Negative ions
Small ions Large ions
Intermediate ions
Aerosol ions Cluster ions
Average spectra of air ions. Sept. 1993 - Oct. 1994. Tahkuse Observatory
Average characteristics of small ions (means and standard deviations) Parameter Small ions,
cm–3 Mean mobility, cm2 V 1 s1
Conductivity of small ions, fS m1 Polarity (+) 274 96 1.36 0.06 6.0 2.1 Polarity (–) 245 88 1.53 0.10 6.0 2.1 Ratio (+/–) 1.13 0.07 0.89 0.04 1.00 0.05
Particle diameter (nm)
Mobility (cm 2 V -1 s -1 ) Fraction concentration (cm -3 )
2.3 2.0 1.8 1.6 1.4 1.24 1.0 0.85 0.7 0.56 0.45 0.36
0 10 20 30 40 50 60 70 80
0.25 0.50 0.79 1 1.3 1.6 2 2.5 3.14
Positive ions Negative ions
Average mobility spectra of small ions. Sept. 1993 – Oct. 1994. Tahkuse.
The frequency distributions (histograms) of the mean mobility of positive and negative small ions
Mean mobility (cm 2 V -1 s -1 )
No of obs
0 200 400 600 800 1000 1200
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Small negative ions Small positive ions Normal approximation
Diurnal variation in the concentration of small ions (0.5–
3.14 cm2V1s1) and wind speed. August 21 – August 30, 1994.
Day
Small ions (cm-3 ) Wind speed (m s-1 )
0 2 4 6 200
400 600 800 1000 1200
21 22 23 24 25 26 27 28 29 30
Positive ions Negative ions
Average diurnal variation in small (or cluster) ion concentration
Average diurnal variation of positive cluster ion concentration in the warm season (Sept.1993, May – Sept. 1994) and in the cold season (Nov. 1993 – April 1994).
Statistics: median, box (25% and 75%) and whiskers (10% and 90% quantiles).
LST (hour)
Small ions (cm-3 ) Small ions (cm-3 )
200 300 400 500 600 700
100 200 300 400
0 2 4 6 8 10 12 14 16 18 20 22 24
median, warm season median, cold season
Variation in the activity concentration of radon at Tahkuse.
August 19 - September 18, 1998.
Day Radon activity concentration (Bq m -3 )
0 5 10 15 20 25 30 35
19/08 20/08 21/08 22/08 23/08 24/08 25/08 26/08 27/08 28/08 29/08 30/08 31/08 1/09 2/09 3/09 4/09 5/09 6/09 7/09 8/09 9/09 10/09 11/09 12/09 13/09 14/09 15/09 16/09 17/09 18/09 19/09
Radon, Tahkuse 19.08 - 18.09.1998
Correlation coefficients (in percent) between positive air ion mobility fractions. November 1, 1993 – Aprill 30, 1994.
Diameter (nm)
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P1: 0.36–0.45 100 67 64 59 49 38 33 29 24 19 20 20 21 20 16 8 -5 -17 -24 -32 P2: 0.45–0.56 67 100 95 85 66 47 36 16 4 2 3 3 2 -1 -7 -16 -30 -43 -52 -60 P3: 0.56–0.70 64 95 100 94 79 61 45 19 2 -1 0 -1 -2 -5 -13 -22 -38 -52 -61 -69 P4: 0.70–0.85 59 85 94 100 94 81 62 29 8 3 2 1 0 -3 -11 -21 -38 -54 -64 -73 P5: 0.85–1.03 49 66 79 94 100 95 77 43 17 12 8 8 7 4 -4 -14 -32 -49 -59 -68 P6: 1.03–1.24 38 47 61 81 95 100 89 57 29 20 16 16 15 12 6 -4 -22 -39 -51 -60 P7: 1.24–1.42 33 36 45 62 77 89 100 79 54 43 37 37 37 36 30 19 0 -21 -36 -45 P8: 1.42–1.60 29 16 19 29 43 57 79 100 81 69 66 66 67 67 62 51 31 9 -8 -18 P9: 1.6–1.8 24 4 2 8 17 29 54 81 100 79 80 80 82 82 77 66 47 26 10 1 P10: 1.8–2.0 19 2 -1 3 12 20 43 69 79 100 79 80 78 74 65 53 37 21 10 4 P11: 2.0–2.3 20 3 0 2 8 16 37 66 80 79 100 99 93 83 69 51 32 17 6 1 P12: 2.1–3.2 20 3 -1 1 8 16 37 66 80 80 99 100 95 84 68 50 31 16 6 1 P13: 3.2–4.8 21 2 -2 0 7 15 37 67 82 78 93 95 100 95 81 61 39 21 9 3 P14: 4.8–7.4 20 -1 -5 -3 4 12 36 67 82 74 83 84 95 100 93 76 51 29 13 6 P15: 7.4–11.0 16 -7 -13 -11 -4 6 30 62 77 65 69 68 81 93 100 91 71 44 24 15 P16: 9.7–14.8 8 -16 -22 -21 -14 -4 19 51 66 53 51 50 61 76 91 100 91 67 43 29 P17: 15–22 -5 -30 -38 -38 -32 -22 0 31 47 37 32 31 39 51 71 91 100 89 66 51 P18: 22–34 -17 -43 -52 -54 -49 -39 -21 9 26 21 17 16 21 29 44 67 89 100 89 75 P19: 34–52 -24 -52 -61 -64 -59 -51 -36 -8 10 10 6 6 9 13 24 43 66 89 100 91 P20: 52–79 -32 -60 -69 -73 -68 -60 -45 -18 1 4 1 1 3 6 15 29 51 75 91 100 The absolute value of critical correlation coefficient at a confidence level of 95% is 3%.
Scatterplot: the concentrations of small positive ions (0.5–3.2 cm2 V1 s1) versus heavy large ions (52 –79 nm).
Heavy large ions (cm -3 )
Small ions (cm -3 )
0 100 200 300 400 500 600
0 400 800 1200 1600 2000 2400
Nonlinear regression coeff. - 0.77
n = 3306 * N - 0.4226
n - small ion concentration N - large ion concentration
Heavy large ions (cm -3 )
Small ions (cm -3 )
0 200 400 600 800 1000 1200
0 400 800 1200 1600 2000 2400
Linear correlation Correlation coeff. - 0.23
Cold season (Nov. 1993 – April 1994),
Warm season (May–Sept. 1994).
Evolution of cluster ion mobility spectra
in wintertime
Evolution of negative air ion mobility spectra. January 9, 1994.
Mobility of fractions (cm 2 V -1 s -1 )
Fraction concentration (cm-3 )
1 2 46 10 20 4060 100 200 400600 1000
0.00041 0.00087 0.00192 0.0042 0.0091 0.016 0.034 0.074 0.15 0.25 0.32 0.40 0.50 0.63 0.79 1.02 1.28 1.60 2.01 2.51 3.14
4 - 5 LST 6 - 7 LST 8 - 9 LST 16 - 17 LST
Evolution of positive air ion mobility spectra. January 9, 1994.
Mobility of fractions (cm 2 V -1 s -1 )
Fraction concentration (cm-3 )
1 2 46 10 20 4060 100 200 400600 1000
0.00041 0.00087 0.00192 0.0042 0.0091 0.016 0.034 0.074 0.15 0.25 0.32 0.40 0.50 0.63 0.79 1.02 1.28 1.60 2.01 2.51 3.14
4 - 5 LST 6 - 7 LST 8 - 9 LST 16 - 17 LST
The effect of aerosol particle concentration on the mobility distribution of cluster ions
Evolution of cluster ion mobility spectra
in summertime
Evolution of negative air ion mobility spectra. August 17, 1994.
Mobility of fractions (cm 2 V -1 s -1 )
Fraction concentration (cm-3 )
1 2 46 10 20 4060 100 200 400600 1000
0.00041 0.00087 0.00192 0.0042 0.0091 0.016 0.034 0.074 0.15 0.25 0.32 0.40 0.50 0.63 0.79 1.02 1.28 1.60 2.01 2.51 3.14
5 - 6 LST 8 - 9 LST 14 - 15 LST 20 - 21 LST
Evolution of positive air ion mobility spectra. August 17, 1994.
Mobility of fractions (cm 2 V -1 s -1 )
Fraction concentration (cm-3 )
1 2 46 10 20 4060 100 200 400600 1000
0.00041 0.00087 0.00192 0.0042 0.0091 0.016 0.034 0.074 0.15 0.25 0.32 0.40 0.50 0.63 0.79 1.02 1.28 1.60 2.01 2.51 3.14
5 - 6 LST 8 - 9 LST 14 - 15 LST 20 - 21 LST
The combined effect of the concentration aerosol particles and radon (Rn 222)
on the mobility
distribution of cluster ions
Small and big cluster ions
It is rational to subdivide cluster ions (0.5–0.14 cm2V1s1) into two classes of small and big cluster ions
(with the boundary at 1.3 cm2V–1s–1 for negative ions and 1.0 cm2V1s1 for positive ions).
• Subdividing leads to more distinct shape of the diurnal variation in the concentration of these ion classes.
• The ratio of the concentrations of small and big cluster
ions is closely correlated with the mean mobility of cluster ions (the correlation coefficients are 97% and 95% for
positive and negative small ions, respectively).
Diurnal variation in the median concentration of positive and negative small cluster ions and big cluster ions in
the warm season (Sept. 1993, May – Sept. 1994).
LST (hour)
Small cluster ions (cm-3 ) Big cluster ions (cm-3 )
0 50 100 150 200 250 300
0 50 100 150 200 250 300
0 2 4 6 8 10 12 14 16 18 20 22 24
Small positive clusters
Small negative clusters
Big positive clusters Big negative clusters
Average diurnal variation of the natural mean mobility of small positive and negative ions in the warm season (Sept. 1993, May – Sept. 1994).
Statistics: median, box (25% and 75%) and whiskers (10% and 90% quantiles).
LST (hour) Mean mobility (cm2 V-1 s-1 )
1.2 1.3 1.4 1.5 1.6 1.7
0 2 4 6 8 10 12 14 16 18 20 22 24
Negative ions Positive ions
Variations in the mean mobility of negative and positive small ions and air temperature at Tahkuse, September 1–30, 1993.
Negative ions Positive ions
Day
Mean mobility ( cm2 V-1 s-1 ) Temperature (°C)
0 10 20
1.1 1.2 1.3 1.4 1.5 1.6 1.7
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Variations in the mean mobility of negative and positive small ions and air temperature at Tahkuse. December 23, 1993 - January 31, 1994
Day
Mean mobility ( cm2 V-1 s-1 ) Temperature (°C)
-16 -8 0 8
1.3 1.4 1.5 1.6 1.7 1.8
23 25 27 29 31 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Negative ions Positive ions
Variations in the mean mobility of negative and positive small ions and accumulation mode aerosol particle (100–500 nm)
concentration at Tahkuse from April 14 to May 16, 1994.
Negative ions Positive ions
Day
Mean mobility ( cm2 V-1 s-1 ) Aerosol (cm-3 )
0 1000 2000 3000 4000
1.1 1.2 1.3 1.4 1.5 1.6 1.7
14 16 18 20 22 24 26 28 30 2 4 6 8 10 12 14 16
Conclusions
• The average diurnal variation of cluster ions at Tahkuse had the ordinary shape for the continental stations of high latitude.
• The results are in accordance with the hypothesis that radon is the main ionizing agent, which causes the variation in the ionization rate, and therefore in the concentration of cluster ions near the ground.
• The different behavior of small and big cluster ions during diurnal cycle causes the diurnal variation in the natural mean mobility of small ions.
• The diurnal variation of the mean mobility was considerable only in the warm season while
in the cold season the mean mobility was mainly correlated with the changes in air masses.
The factors of the mobility distribution of cluster ions
We suppose that the changes in the mobility distribution of cluster ions are due to the changes in
• the chemical composition and the concentration of some trace gases or vapors in the air, probably
generated by photochemical reactions;
• the changes in the ionization rate and
• the concentration of aerosol particles.
The last two factors have an effect on the lifetime of cluster ions.
Burst events of intermediate ions (charged nanometer particles ) in the atmospheric air
Average spectra of air ions. Sept. 1993 - Oct. 1994. Tahkuse Observatory
Particle diameter (nm)
Electrical mobility (cm 2 V -1 s -1 )
Fraction concentration (cm-3 )
90 26 7.6 2.0 0.36
0 100 200 300 400 500 600
0.00032 0.0032 0.032 0.32 3.2
Positive ions Negative ions
Small ions Large ions
Intermediate ions
Aerosol ions Cluster ions
Variation in the concentration of positive intermediate ions, air temperature, and relative humidity at Tahkuse, Sept. 11–27, 1993.
Day
Intermediate ions (cm-3 ) Temperature (°C)
0 10 20
0 100 200 300 400
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Relative humidity (%)
40 60 80 100
Rainy days Rainy days
Time series of the concentration of positive intermediate ions, air temperature, relative and absolute humidity. Tahkuse, Oct. 10 - 28, 1994.
Day
Intermediate ions (cm-3 ) Relative humidity (%)
20 40 60 80 100
0 100 200 300 400 500
10 12 14 16 18 20 22 24 26 28
Day
Air temperature (°C) Absolute humidity (g m-3 )
0 2 4 6 8 10
-5 0 5 10 15 20
10 12 14 16 18 20 22 24 26 28
Temperature Abs. humidity
Variation in the concentration of positive intermediate ions, air temperature, relative and absolute humidity. Tahkuse, November 5 - 18, 1993 relative
and
Day
Intermediate ions (cm-3 ) Relative humidity (%)
20 40 60 80 100
0 100 200 300 400 500
5 6 7 8 9 10 11 12 13 14 15 16 17 18
Day
Air temperature (°C) Absolute humidity (g m-3 )
0 1 2 3 4 5 6
-20 -16 -12 -8 -4 0 4
5 6 7 8 9 10 11 12 13 14 15 16 17 18
Temperature Abs. humidity
Time variation of the concentration of aerosol particles (100 - 560 nm) and intermediate ions (1.6 - 7.4 nm). Tahkuse 14.04 - 16. 05. 1994. and
Date
Aerosol particles (cm-3 ) Intermediate ions (cm-3 )
0 200 400 600 800 0
1000 2000 3000 4000 5000
14/04 16/04 18/04 20/04 22/04 24/04 26/04 28/04 30/04 02/05 04/05 06/05 08/05 10/05 12/05 14/05 16/05
Aerosol particles (100 - 560 nm) Intermediate ions (1.6 - 7.4 nm)
Variation in the concentration of positive intermediate ions, the mean mobility of negative and positive small ions and relative humidity. Sept. 11–27, 1993.
Day
Intermediate ions (cm-3 ) Small ion mobility (cm2 V -1 s-1 )
1.2 1.3 1.4 1.5 1.6 1.7
0 100 200 300 400
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Negative ions Positive ions
Rel. humidity (%)
40 60 80 100
Rainy
days Rainy
days
Scatterplot of the mean mobility of small ions versus intermediate ion concentration. Sept. 1993 – Oct.1994.
Concentration of intermediate (-) ions (cm -3 )
Mean mobility of (-) small ions (cm2 V-1 s-1 ) 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
0 100 200 300 400 500 600 700 800 900 1000
Concentration of intermediate (+) ions (cm -3 )
Mean mobility of (+) small ions ( cm2 V-1 s-1 ) 1.1 1.2 1.3 1.4 1.5 1.6
0 100 200 300 400 500 600 700 800 900
Contour plot of the evolution of air ion spectrum at Tahkuse. October 20, 1994
10 20 60 80 100 200 300 400 500 600 above
LST (hour)
Particle diameter (nm)
0.36 0.45 0.56 0.70 0.85 1.03 1.24 1.421.6
1.8 2.0 2.3 3.2 4.8 7.4 11 15 22 34 52 79
6 8 10 12 14 16 18 20 22 24 2 4 6 8 -3 Air ion concentration in cm
Evolution of positive air ion mobility spectra. Oct. 20, 1994
.
Particle diameter (nm)
Mobility of fractions (cm 2 V -1 s -1 )
Fraction concentration (cm-3 ) 79 52 34 22 15 11 7.4 4.8 3.2 2.3 2.0 1.8 1.60 1.42 1.24 1.03 0.85 0.70 0.56 0.45 0.36
1 4 8 20 60 100 400 800
0.00041 0.00087 0.00192 0.0042 0.0091 0.016 0.034 0.074 0.15 0.25 0.32 0.40 0.50 0.63 0.79 1.02 1.28 1.60 2.01 2.51 3.14
10 - 11 LST 11 - 12 LST 12 - 13 LST 13 - 14 LST 14 - 15 LST 15 - 16 LST
Evolution of positive ion mobility spectra at Tahkuse. March 22, 1994.
Particle diameter (nm)
Mobility of fractions (cm 2 V -1 s -1 )
Fraction concentration (cm-3 ) 79 52 34 22 15 11 7.4 4.8 3.2 2.3 2.0 1.8 1.60 1.42 1.24 1.03 0.85 0.70 0.56 0.45 0.36
1 4 8 20 60 100 400 800
0.00041 0.00087 0.00192 0.0042 0.0091 0.016 0.034 0.074 0.15 0.25 0.32 0.40 0.50 0.63 0.79 1.02 1.28 1.60 2.01 2.51 3.14
9 - 10 LST 10 - 11 LST 11 - 12 LST 12 - 13 LST 13 - 14 LST 14 - 15 LST
Contour plot of the evolution of air ion spectrum at Tahkuse. May 22, 1996.
10 20 60 80 100 200 400 600 800 1000 1200 1400 above
LST (hour)
Particle diameter (nm)
0.36 0.45 0.56 0.70 0.85 1.03 1.24 1.421.6
1.8 2.0 2.3 3.2 4.8 7.4 11 15 22 34 52 79
0 2 4 6 8 10 12 14 16 18 20 22 24
Air ion concentration in cm-3
Contour plot of positive air ion spectrum. 19.11 - 20.11.1995, Tahkuse
10 20 60 80 100 200 300 400 500 600 above
Local time (hour)
Particle diameter (nm)
0.36 0.45 0.56 0.70 0.85 1.03 1.24 1.421.6
1.8 2.0 2.3 3.2 4.8 7.411 15 22 34 52 79
6 8 10 12 14 16 18 20 22 0 2 4 6 -3 Air ion concentration in cm
Average diurnal variation of positive air ion concentration during the burst events. Tahkuse 1.09.1993 - 27.10.1994.
Local time (hour) Ion fraction concentration (cm-3 )
2 46 10 20 4060 100 200 400600 800
0 2 4 6 8 10 12 14 16 18 20 22 24
Diameter range of fractions
(nm) 2.0 - 2.3 2.1 - 3.2 3.2 - 4.8 4.8 - 7.4 7.4 - 11 9.7 - 15 15 - 22 22 - 34 34 - 52 52 - 79
Local time (hour) Ion fraction concentrations (cm-3 )
0 100 200 300 400 500 600 700
0 2 4 6 8 10 12 14 16 18 20 22 24
Diameter range of fractions
(nm) 2.0 - 2.3 2.1 - 3.2 3.2 - 4.8 4.8 - 7.4 7.4 - 11 9.7 - 15 15 - 22 22 - 34 34 - 52 52 - 79
Diurnal variation in the median concentration of intermediate ions (diameter 2.1–7.4 nm), light large ions (7.4–22 nm) and heavy large
ions (22–79 nm) in the warm season. Sept. 1993, May – Sept.
1994.
LST (hour)
Intermediate ions (cm-3 ) Light large ions (5 cm-3 ) Heavy large ions (cm-3 )
1000 1200 1400 1600 1800
0 50 100 150 200
0 2 4 6 8 10 12 14 16 18 20 22 24
Intermediate ions, bursts Light large ions, bursts Heavy large ions, bursts
Heavy large ions, without bursts
