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

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

Plain electrode effect

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.

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, 31-45. 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, 8453-8469.

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

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.

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

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

Comparison of BSMA1 and BSMA2

BSMA2 near the aerosol cottage AIS inlet BSMA2

BSMA2 near the aerosol cottage and BSMA1 in old cottage

BSMA2 on the top of tower measuring the vertical gradient

Vertical profile of mobility?

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.

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.

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