1. Hyytiälä 20060315 Hannes.Tammet@ut.ee
Microscale structure of air ion spatial and temporal distribution: some problems
Hyytiälä

2. CONTENT Plain electrode effect Distribution of ionization rate
Distribution of ion concentration
Fluctuations of ion concentration
Measurements in Hyytiälä 2005
Vertical profile of mobility?
What should be measured?
How to start design of an instrument?
A simple example: the integral counter

3. Plain electrode effect

4. Air-Earth vertical current j = lE does not depend on height.
Conductivity near ground l+ is about a half of free air conductivity l+ + l.
Conclusion: Eo  2E . h E E Eo
Free air electric field is about 100 V/m. It follows electric field on the ground surface about 200 V/m.
The difference is created by space charge carried by cluster ions and aerosol particles. h r
A cluster ion in 150 V/m field travels during 2 minutes of its life about 3 m.
s = eoE
100 V/m corresponds to 5.5×105 e/cm2. This is about 1800 e/cm3 distributed to 3 m.

5. The role of aerosol particles in electrode effect: see a paper by Tapio J. Tuomi
Tuomi, T.J. (1980) Atmospheric electrode effect: approximate theory and wintertime observations. PAGEOPH, 119,
Advanced theory including turbulent diffusion: see papers by John C. Willett, e.g.
Willett, J.C. (1983) The turbulent electrode effect as influenced by interfacial ion transfer. JGR, 88,

6. Distribution of ionization rate
Ionizing agents:
cosmic rays
gamma radiation from ground
alpha radiation from air
alpha radiation from surfaces
beta radiation from surfaces

7. Distribution of ion concentration
Concentration of cluster ions depends on the ionization rate and on the ion sinks. The sinks are:
cluster ions of opposite polarity ( 10 – 20%),
aerosol particles ( 50 – 90%),
surfaces like conifer needles ( 0 – 40%).
The distribution of ion concentration in still air is shaped mostly by the profile of the ionization rate.

8. Fluctuations of ion concentration
The ions from local sources are distributed by wind like smoke from fire.
Measurements (July-August 1963) with an aspiration counter providing t = 0.4 s (flow rate 1.5 m3s–1).
Parameters of fluctuations:
These parameters depend on the time step
ti+1 – ti

10. Measurements in Hyytiälä 2005
BSMA1 inlet
The tower is barely visible
BSMA2 inlet
BSMA2 outlet

11. Comparison of BSMA1 and BSMA2

12. BSMA2 near the aerosol cottage
AIS inlet
BSMA2

13. BSMA2 near the aerosol cottage and BSMA1 in old cottage

14. BSMA2 on the top of tower measuring the vertical gradient

16. Vertical profile of mobility?

17. What should be measured?
Cluster ions at height of 14 m are partially originated from forest and partially from upper air. We need additionally measurements at height of 67 m and at different heights inside of forest.
Multipoint measurements with universal mobility spectrometers are expensive and troublesome.
When analyzing the measurements only few integral parameters of mobility distribution are used like the cluster ion concentration and average mobility, concentration of ion of sizes 1.5…3 nm and 3…7.5 nm.
Measuring of 4 parameters is expected to be cheaper than measurement of 16 mobility fractions.

18. How to start design of an instrument?V1
Parameters of analyzer x1, x2, …
Signals y1, y2, …
Quantities to measure z1, z2, … V2
sheat air (?)
V=0 y1 y2
When x is fixed, the regressions zi = fi (y1, y2,…) can be evaluated using existing data set of mobility distribution measurements.
When real measurements and regression estimates are known, a summary error of estimates D can be evaluated.
Next the components of x can be modified and determined the effect of modification on D.
Finally the minimum problem of D on the space of technically possible values of x can be posed and solved. Manufacturing expenses can be included as a factor of objective function.

19. Simple example: the integral countery yn Vx V1 V2 V3 y1 y2 y3 V
Ncluster = yn / (Fe) Zcluster = const / Vx ? = f (y3 – y2)