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Volumetric water content 0 and soil electrical conductivity rr may be measured in situ using time domain reflectometry (TDR). The parallel-wire or two-wire transmission line TDR probes currently in field use suffer from unwanted noise and information loss due to impedance mismatch between the probe and the coaxial connecting cable. Here we describe symmetric, multiwire probes designed to minimize these problems and eliminate the need for a balancing transformer between probe and TDR device. Analysis of the electric field distributions around these new probes shows that they emulate a coaxial transmission line, and their measured characteristic probe impedances approach that of coaxial probes. Signals from the new probes permit more reliable and accurate 0 and rr measurement and are superior to those of two-wire probes with balancing transformer. The enhanced signal clarity of the new probes extends to sample diameters of at least 0.2 m. We show that electrical conductivity determined with the new probes is identical to that found with a coaxial cell and substantially different from that measured by a two-wire probe. Our results indicate that values of rr, determined using the Giese-Tiemann thin sample approach and measured characteristic probe impedances of coaxial or multiwire probes, agree with values of rr measured using an ac bridge for both electrolyte solutions and soil samples to within _+ 10%, provided rr exceeds 10 mS m -1 . Finally, we give an example of the use of multiplexed three-wire probes in following rainfall infiltration and redistribution during and after a simulated rainfall event in the field. Infiltrated quantities of water estimated from the TDR water content profiles agreed within _+ 10% with the amount applied. 1. Comparison of TDR signals L=150 , d =4.7, s=30 (mm) -,-J J•-2.7ns ß ß ß ß ß Balum S E S E ß ß ß ß S E S E

Time domain reflectometry (TDR) is widely used for routine field monitoring of water content and salts in soils. Most estimates of water content assume the TDR‐measured apparent relative permittivity, ϵa, is a good approximation for the real component, ϵ′r, of the soil's complex relative permittivity with the magnitude of ϵ′r being determined primarily by water content. We examine this assumption and show that ϵa is influenced by both the real and imaginary components of the relative permittivity. Increases in ϵa resulted from the dc conductivity and dielectric loss arising from the presence of ions in solution and clay content. At water contents above 0.15 m3 m−3 in soils with high clay content and/or salt, specific calibrations are needed for precise determinations of water content from TDR. We use the wave propagation equations to separate the real and imaginary component contributions to ϵa The Giese and Tiemann interpretation for dc conductivity was again shown to be within 10% of that from a conductance meter and this fact was used to propose a method using only TDR data to separate real and imaginary components of the relative permittivity. It was found that the dielectric losses and conductive losses did not differ according to the source of conductivity, whether from clay content in the soil matrix or electrolyte in the soil solution.

Abstract. Biogenic aerosol formation is likely to contribute significantly to the global aerosol load. In recent years, new-particle formation has been observed in various ecosystems around the world but hardly any measurements have taken place in the terrestrial Southern Hemisphere. Here, we report the first results of atmospheric ion and charged particle concentrations as well as of new-particle formation in a Eucalypt forest in Tumbarumba, South-East Australia, from July 2005 to October 2006. The measurements were carried out with an Air Ion Spectrometer (AIS) with a size range from 0.34 to 40 nm. The Eucalypt forest was a very strong source of new aerosol particles. Daytime aerosol formation took place on 52% of days with acceptable data, which is 2–3 times as often as in the Nordic boreal zone. Average growth rates for negative/positive 1.5–3 nm particles during these formation events were 2.89/2.68 nmh−1, respectively; for 3-7 nm particles 4.26/4.03, and for 7–20 nm particles 8.90/7.58 nmh−1, respectively. The growth rates for large ions were highest when the air was coming from the native forest which suggests that the Eucalypts were a strong source of condensable vapours. Average concentrations of cluster ions (0.34–1.8 nm) were 2400/1700 cm−3 for negative/positive ions, very high compared to most other measurements around the world. One reason behind these high concentrations could be the strong radon efflux from the soils around the Tumbarumba field site. Furthermore, comparison between night-time and daytime concentrations supported the view that cluster ions are produced close to the surface within the boundary layer also at night but that large ions are mostly produced in daytime. Finally, a previously unreported phenomenon, nocturnal aerosol formation, appeared in 32% of the analysed nights but was clustered almost entirely within six months from summer to autumn in 2006. From January to May, nocturnal formation was 2.5 times as frequent as daytime formation. Therefore, it appears that in summer and autumn, nocturnal production was the major mechanism for aerosol formation in Tumbarumba.

The simultaneous measurement of water content and electrical conductivity of soils and KCl solutions was achieved using time domain reflectometry (TDR). Coaxial transmission lines varying in length from 90 to 300 mm contained either KCl solutions or soil of varied water and salt content. The water content of soil or dielectric constant of the water solutions was determined from the travel time. The measured dielectric constant of KCl solutions was unchanged from that of pure water (81) at those concentrations where there was sufficient reflected signal for measurement. Two analyses were used for determination of electrical conductivity, one based on signal attenuation after one “round‐trip” and the second based on a thin sample approximation for the signal reflection and attenuation. Reference measurements of conductivity were made on the same samples using low‐frequency conductance bridge measurements. These analyses of the TDR traces showed that for water solution both the thin sample analysis and the analysis after a signal had traversed one round‐trip yielded conductivity in agreement with bridge conductivity values. This indicated that the imaginary part of the complex dielectric constant was negligible. For soils the thin sample analysis was in general agreement with the bridge measurements. From the analysis of signal after one round‐trip in soils there was indication that the imaginary part of the dielectric constant should not be assumed negligible. Further investigation of the frequency dependence of the dielectric constant and attenuation will be required to identify the relative contributions of the real and imaginary parts of the dielectric constant to measurement by TDR. The effect of impedance‐matching transformers on conductivity measurements in the field has yet to be ascertained.