Experimental study of the “rain effect” on the mobility distribution of air ions. Experiments with water jet. U. Hõrrak, H. Tammet, E.Tamm, A. Mirme. Institute of Environmental Physics, University of Tartu, 18 Ülikooli St., Tartu, Estonia. Pikajärve, June 27–

Aerosol, air ion and precipitation measurements on Intermediate ion ( nm) concentration maximum 2500 cm -3

Experimental imitation of charged nanometer particle generation by rainfall. H. Tammet, May 13, BSMA measured the mobility distribution in the range of cm 2 V -1 s -1, the apparent diameter range is nm. The splashing of rain droplets was imitated using a thin water jet streaming from a nozzle of diameter 2.5 mm. The water stream broke to droplets which hit a vertical ceramic wall in distance of 65 cm from the nozzle. Flow rate: 55 cm3/s, ejection speed: 11 m/s, equivalent rain intensity: 36 mm/h Stream of water droplets

Evolution of negative and positive air ion size distributions. May 12, BSMA data. Experiment with water jet.

Time series of small (or cluster) ions and intermediate ions ( nm). May 12, BSMA data. Experiment with water jet.

Meteorological parameters during the experiment with water jet. May 12, 2005.

Comparison of measurements at Hyytiälä SMEAR station (left) and results of the experiment with water jet (right). Negative ion spectra. Rain event. Hyytiälä Water-jet. Tartu

Comparison of measurements at Hyytiälä SMEAR station (left) and results of the experiment with water jet (right). Positive ion spectra. Rain event. Hyytiälä Water-jet. Tartu

Comparison of the time series of small (or cluster) ions and intermediate ions ( nm) measured at Hyytiälä SMEAR station (left) and results of the experiment with water jet (right). Rain event. Hyytiälä Water-jet. Tartu

Water jet experiment with extended instrumentation. June 17, Balanced Scanning Mobility Analyzer (BSMA) diameter range of singly charged particles: nm Air Ion Spectrometer (AIS5) diameter range of singly charged particles: 0.4 – 43.6 nm Electrical Aerosol Spectrometer (EAS) diameter range: 3.2 nm – 10 µm

Instrumentation. June 17, 2005.

Objectives of the study To get additional information about the behavior of charged particles in the (apparent) size range above 7 nm during splashing of water droplets. Study the evolution of the size distribution of neutralized aerosol particles. To get any information about the real size of intermediate ions (apparent size range 2 – 10 nm) formed during splashing of water droplets.

Three experiments were carried out. Time series of the concentration of light intermediate air ions measured by AIS and BSMA. June 17, Tartu.

Variation of the meteorological parameters during the experiment.

Time series of the concentration of cluster ions measured by AIS and BSMA. June 17, Tartu.

Time series of the concentration of light intermediate air ions measured by AIS and BSMA. June 17, Tartu.

Time series of the concentration of heavy intermediate air ions measured by AIS and BSMA. June 17, Tartu.

Time series of the concentration of light large ions measured by AIS. June 17, Tartu NB! Unipolarity

Time series of the concentration of heavy large ions measured by AIS. June 17, Tartu Original data

Time series of the concentration of light large ions measured by AIS. June 17, Tartu. NB! Corrected data

Mean spectra of positive and negative air ions during the third experiment. AIS5 data.

Mean spectra measured during the third experiment. AIS5 and BSMA2. 20: :20,

Background spectra after the third experiment. AIS5 and BSMA2. 20: :50,

Time series of the concentration of aerosol particles (3.2 – 56 nm) measured by EAS. June 17, Tartu.

Time series of the concentration of coarse aerosol particles (1.8 – 3.2 µm) and intermediate air ions. June 17, 2005.

Time series of the concentration of coarse aerosol particles (1 – 10 µm). EAS data. June 17, Tartu.

Time series of the concentration of submicron aerosol particles (178 – 316 nm) and intermediate air ions. June 17, 2005.

Time series of the concentration of submicron aerosol aerosol particles (100 – 560 nm). EAS data. June 17, Tartu.

Evolution of the size distribution of aerosol particles, background spectra and spectra affected by water jet. Third experiment. EAS data. June 17, Tartu.

Recovery of the size distribution of aerosol particles after stopping of water jet. Third experiment. EAS data. June 17, Tartu.

Conclusions The experiments with water jet indicated that it can be used to simulate the effect of rain to study the generation of intermediate air ions during rainfall. The experiments with water jet showed that the splashing of water drops affects the mobility (size) distribution air ions generating negatively charged particles below the apparent diameter of about 10 nm and with the concentration peak at 2 -3 nm. The mean size of this mode is nearly constant. The particles in the size range above about 8 nm and blow 40 nm are mainly positively charged. The generation of neutral particles in the nucleation mode size range (5.6 – 18 nm) was only few percent (close to measuring uncertainties). The splashing of water drops affects mainly the size distribution of large aerosol particles in the size range above 0.5 µm.