Aare Luts

Mobility spectrum of air ions at Tahkuse Observatory

Mobility spectra of air ions have been measured at a rural site in Estonia during several periods. The annual average mobility spectrum of natural small air ions is presented. The concentrations of two groups of air ions with mobilities 0.32–0.5 cm2/(V s) and 0.5–2.5 cm2/(V s) are not correlated; this fact indicates the different nature of the ions of the two groups. The air ions with mobilities 0.5–2.5 cm2/(V s) are interpreted as cluster ions and the air ions with mobilities 0.32–0.5 cm2/(V s) as charged aerosol particles that can be created in the process of ion-induced nucleation. A half-year average mobility spectrum of the large ions with mobilities 3.2×10−4–1.5×10−1 cm2/(V s) is presented. The spectrum is well interpreted on the basis of the average size distribution of aerosol particles and on the theory of diffusion charging of the particles.

Evolution of negative small air ions at two different temperatures

Abstract In this paper, we simulate the negative ion evolution shape considering 151 different ions, 66 trace gases and 493 ion–molecule reactions. The main attention is paid to the evolution interval from 30 ms to 3 s where the knowledge is most limited. The connections between the evolution shape and temperature have been studied. The simulated results have been compared with the relevant measurements, and the ions most likely responsible for a certain ion evolution shape observed by Nagato and Ogawa (J. Geophys. Res. 103(D12) (1998) 13917) have been revealed. Also, the composition of trace gases likely responsible for the observed shape can be derived. In the studied evolution interval the transformation O2−(H2O)n→CO3−(H2O)m→NO3−×X×Y prevails. At the higher temperature, the ions CO3−(H2O)m are less abundant. In the respective steady (natural) state the most abundant ions are NO3−×X×Y×(HCl)n and NO3−(H2O)m. At the higher temperature, the ions NO3−(H2O)m are dominant.

Temperature variation of the evolution of positive small air ions at constant relative humidity

Abstract The evolution of positive air ions is mathematically simulated considering 150 trace gases and more than a thousand ion-molecule reactions. The main attention is paid to the evolution of near-ground air ions in the age interval from 10 ms to 3 s where the knowledge about ion evolution is most limited. Recently, detailed experimental data about the time variation of the air ion mobility spectrum became available, and the results of mathematical simulation can be compared with the observed transformations. Unfortunately, the ion mobility measurements have not been accompanied by data about concentrations of the trace gases; therefore the mobilities can be interpreted only ambiguously. Nevertheless, the main features of the measured evolution shape of ions can be explained by the results of simulation, and the best agreement is achieved by the assumption of an enhanced concentration of either acetone or pyridine. In this case, the younger ions should be mainly ions H 3 O + (H 2 O) n , while the more aged ions should be either acetone or pyridine family clusters.