Abstract
Abstract. Measurements of atmospheric ions in the size range 0.8–42 nm were conducted at the environmental research station of the University of Crete at Finokalia from April 2008 to April 2009 in the frame of the EUCAARI project. Both positive and negative atmospheric ions were found to have a clear annual cycle, with minimum concentrations in summer. Their concentrations were found to vary with the prevailing meteorology and the abundance of aerosol particles in the atmosphere. High concentrations of ions were observed during new particle formation events. There were 53 nucleation events recorded. It was found that under certain atmospheric conditions enhanced ion concentrations can be observed during night. Overall, 39 night-time events were observed, all of them observed for the negatively charged particles while only 21 were observed for the positively charged particles. Night-time enhanced ion concentrations were more frequent during spring and autumn and no such events were recorded from July to September. A strong anti-correlation was found between air ion concentrations, especially at cluster sizes (1.25–1.66 nm), and condensation and coagulation sinks. Enhanced ion concentrations at night were found to be more frequent when air masses had traveled over the island of Crete, indicating possible association with local biogenic sources.
Highlights
Atmospheric ions have been measured at different sites around the world (Kulmala and Tammet, 2007)
We studied the dependence of night-time increased ion concentrations on the origin of air masses, since from the previous analysis it was obvious that the concentration of small air ions is strongly dependent on atmospheric composition, which in turn significantly depends on air mass history at Finokalia
The maximum values for the positive air ions were observed in winter and in March for the negative ones with secondary maxima in June and November
Summary
Atmospheric ions (charged molecular clusters or particles) have been measured at different sites around the world (Kulmala and Tammet, 2007). Hirsikko et al (2007) found that the Air Ion Spectrometer (AIS) could detect particle formation events that were suppressed, due to low concentrations of condensing vapours or high condensation and coagulational sink by pre-existing aerosol particles, before the DMPS (detection limit 3 nm) detected any particles. Lehtipalo et al (2011) showed that the night-time events in Hyytialaare seen frequently for neutral particles, and that the night-time concentrations of sub-3 nm particles and ions have a clear connection to oxidized organic molecules Another aim of this study is to explore the night-time ion behavior in a completely different environment (coastal Mediterranean area) by checking for a link with day-time nucleation events
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