Development and testing of a modernised Programmable Ion Mobility Spectrometer

The atmosphere is made slightly electrically conductive by cosmic rays and natural radioactivity, which generate ions. Air conductivity is a key component of the global electric circuit and influences droplet and cloud charging [1]. Further, atmospheric ions may affect the radiative balance through particle formation and infra-red absorption [2], [3]. Both considerations motivate the need for accurate atmospheric ion measurements. The Programmable Ion Mobility Spectrometer (PIMS) is a computer-controlled instrument based on the Gerdien measurement principle in which a cylindrical capacitor, across which a voltage is applied, is aspirated to sample air ions [4]. Computer control of a switchable multimode electrometer [5] offers the capability to measure ions in two modes, offering self-calibration, which removes the difficulties with providing a well-characterised environment for calibration [6]. The PIMS can independently monitor internal leakage currents which can be a significant source of thermally dependent error, especially in outdoor use. First developed in the early 2000s, the PIMS has recently been modernised with a new electrometer and advanced microcontroller, leading to significantly miniaturised electronics and opportunities for more sophisticated interfacing. The modernised PIMS was tested at Nagycenk Geophysical Observatory (47.632°N,16.718°E), Hungary in summer 2022, alongside a full range of meteorological and atmospheric electrical measurements for comparison.

 

References

[1]      R. G. Harrison and K. A. Nicoll, “The electricity of extensive layer clouds,” Weather, vol. 77, no. 11, pp. 379–383, Nov. 2022, doi: 10.1002/wea.4307.

[2]      K. L. Aplin, “Composition and measurement of charged atmospheric clusters,” Space Sci Rev, vol. 137, no. 1–4, 2008, doi: 10.1007/s11214-008-9397-1.

[3]      K. L. Aplin and M. Lockwood, “Cosmic ray modulation of infra-red radiation in the atmosphere,” Environmental Research Letters, vol. 8, no. 1, 2013, doi: 10.1088/1748-9326/8/1/015026.

[4]      K. L. Aplin and R. G. Harrison, “A computer-controlled Gerdien atmospheric ion counter,” Review of Scientific Instruments, vol. 71, no. 8, 2000, doi: 10.1063/1.1305511.

[5]      R. G. Harrison and K. L. Aplin, “Multimode electrometer for atmospheric ion measurements,” Review of Scientific Instruments, vol. 71, no. 12, 2000, doi: 10.1063/1.1327303.

[6]      K. L. Aplin and R. G. Harrison, “A self-calibrating programable mobility spectrometer for atmospheric ion measurements,” Review of Scientific Instruments, vol. 72, no. 8, 2001, doi: 10.1063/1.1382634.