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Persistent URL http://purl.org/net/epubs/work/43567
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Record Id 43567
Title Water vapour changes and atmospheric cluster ions
Abstract Properties of small ions in atmospheric air have been investigated using a modern ion spectrometer with co-located meteorological and atmospheric electrical measurements, in urban air at Reading during May and June, (days 147-154) 2005. The ion spectrometers programmed measurement sequence determined the mean ion currents and their variability, permitting derivation of positive and negative ion number concentrations, and their associated mean mobilities, on a ~30 minute cycle. The ion measurements were validated by comparing the derived air conductivity with the nearby atmospheric electrical potential gradient, and both these independently measured parameters correlated closely under fair weather conditions. Histograms of the mean mobility for positive (mu+) and negative (mu-) ions across the 7 days of measurement showed mu->mu+, i.e. that the negative ion mass was less than that of positive ions. Adjacent air humidity measurements were used to analyse the mobility data. Using the median water vapour pressure of 4.1hPa as a threshold, the mean mu+ was found to be significantly lower when vapour pressures were above the threshold, but there was no significant change in mu- with vapour pressure. As the effect on positive ions remains present in strong sunlight, weak sunlight, and darkness, it is unlikely to be solely of photochemical origin but, more probably, related to changes in ion hydration. There is therefore an asymmetric response of positive and negative ions to water vapour. This will influence the aerosol electrification in fogs and clouds, and modify the radiative response of hydrated ion clusters.
Organisation SSTD , STFC
Keywords 93.30.Ge (Geophysical observations, instrumentation or techniques, Europe) , 36.40.Wa (Charged clusters) , 92.60.Pw (Atmospheric electricity, lightning) , Physics , 92.60.Mt (Atmospheric aerosols) , Natural environment , 92.60.Jq (Water in the atmosphere)
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Language English (EN)
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Journal Article Atmospheric Research 85, no. 2 (2007): 199-208. doi:10.1016/j.atmosres.2006.12.006 2007