Publications by Karen Aplin

Atmospheric condensation nuclei formation and high-energy radiation

Journal of Atmospheric and Solar-Terrestrial Physics 63 (2001) 1811-1819

RG Harrison, KL Aplin

Considerable controversy exists over a proposed link between cosmic radiation and clouds in the apparent absence of a microphysical mechanism between ionisation and particle formation. New atmospheric experimental data which supports previous laboratory evidence of radiolytic particle formation is presented, showing increases in surface condensation nuclei (CN) which correlate positively with increases in surface ionisation. Correlations between physically-displaced Geiger counters are used to attribute some of the ionisation events to cosmic radiation, above a background noise level determined by Monte Carlo simulations of the detector system. When cosmic ionisation events are more frequent, ionisation maxima are followed by increases and then decreases in CN concentration. Some of the variability in atmospheric CN may therefore be attributable to processes initiated by cosmic ionisation. © 2001 Elsevier Science Ltd. All rights reserved.

Tropospheric ion measurements


KL Aplin, RG Harrison

A self-calibrating programable mobility spectrometer for atmospheric ion measurements

Review of Scientific Instruments 72 (2001) 3467-3469

KL Aplin, RG Harrison

Ion measurements in atmospheric air allow atmospheric ion-aerosol charge exchange to be investigated, which is thought to be important in cloud processes. Classical aspiration ion measurement techniques have been significantly improved by the use of electronic switching systems to permit the selection of different mobilities, with adjacent instruments using the combination of Voltage Decay and ion current techniques used for calibration. An integrated programable ion mobility spectrometer using the same collection electrodes in both modes is described here, with which high-resolution measurements (1 s sampling) of ion concentration fluctuations have been made. Mobility spectrum information has also been extracted by varying the bias voltage under full computer control. The integrated system can determine small ion concentrations to ±1%, to a minimum mobility μ∼0.1 cm2 V-1 s-1 (corresponding to a particle radius of ∼2 nm). © 2001 American Institute of Physics.

Multimode electrometer for atmospheric ion measurements

Review of Scientific Instruments 71 (2000) 4683-4685

RG Harrison, KL Aplin

A computer-controlled electrometer capable of either high impedance voltage measurements or femtoampere current measurements has been developed. It is intended for use with a Gerdien ion counter in atmospheric temperatures. Temperature variations can cause significant thermal errors arising from offset voltage and bias current changes that compromise the measurements. Use of high impedance switching permits the offset voltage and input bias currents of the electrometer to be measured, and allows regular software compensations to be applied in both modes. © 2000 American Institute of Physics.

A computer-controlled Gerdien atmospheric ion counter

Review of Scientific Instruments 71 (2000) 3037-3041

KL Aplin, RG Harrison

Accurate measurements of atmospheric ions are desirable in order to investigate atmospheric aerosol processes. A cylindrical capacitor ion counter is described which has a flexible computerized control system, to allow selection of ion mobility by changing the bias voltage across the capacitor. Ion measurements obtained correlate well with the ionization rate measured with an adjacent Geiger counter in clean air. Measurements of air ions using the device in current and voltage decay modes show consistent results. The collecting electrode is exposed directly in the air stream to be sampled, eliminating diffusive losses in intake tubes. The system can measure ion concentrations from 20 ions cm-3 (including typical atmospheric concentrations) and can sample ions rapidly. These characteristics enable comprehensive air conductivity measurements to be made. © 2000 American Institute of Physics.

Femtoampere current reference stable over atmospheric temperatures

Review of Scientific Instruments 71 (2000) 3231-3232

RG Harrison, KL Aplin

Calibration of ultralow current ammeters deployed in atmospheric ion counters requires stable current references operating at high source impedance. Using standard precision components, this current reference generates equal bipolar currents of nominally ±500fA, cyclically for 32 s each. The currents were found to be stable to 2 fA over the temperature range - 20 to 20°C, typical of atmospheric conditions. The output current is delivered via a capacitor, and by arranging for the capacitor to be guarded at ground potential when the system is not generating a current, the reference can be permanently connected to an electrometer with minimal leakage. © 2000 American Institute of Physics.



RG Harrison, KL Aplin

Radioactivity and atmospheric condensation nuclei

Journal of Aerosol Science 31 (2000)

RG Harrison, KL Aplin

Multimode ion counter

Journal of Aerosol Science 31 (2000)

KL Aplin, RG Harrison

The interaction between air ions and aerosol particles in the atmosphere

ELECTROSTATICS 1999 163 (1999) 411-414

KL Aplin, RG Harrison

An electrical method of urban pollution measurement

Journal of Aerosol Science 29 (1998)

KL Aplin, RG Harrison, S Wilkinson