•Introduction•Physics and chemistry of air ions•Development of instrumentation•Measurements of atmospheric ions•Research of ion-induced nucleation•Atmospheric ions a factor of climate

Air ion research2003-2006+

•Introduction•Physics and chemistry of air ions•Development of instrumentation•Measurements of atmospheric ions•Research of ion-induced nucleation•Atmospheric ions a factor of climate

Hannes.Tammet@ut.eeUniversity of Tartu, Estoniahttp://ael.physic.ut.ee/tammet/

Air ion research2003-2006+

The collection of papers used when compiling the review consists of about 30 papers per year:a little more than four years ago.

Main reason of the increase is the high research activity in the field of aerosol nucleation, which is a vulnerable factor of the Earth's climate.

•Atmos. Chem. and Phys. (15 papers), •J. Geophys. Res. (11 papers),•Atmos. Environ. (10 papers), •J. Aerosol Sci. (6 papers), •J. Atmos. Solar. Terr. Phys. (5 papers), •Atmos. Res. (5 papers).

Leading international journals 2003-2006:

New leader in publishing atmospheric ion research:

15 atmospheric ionresearch papers

during 2003-2006

A new center of atmospheric ion research: the University of Helsinki, Finland. The Helsinki research group leaded by Prof. Markku Kulmala is a top-ranked center of aerosol research. Atmospheric ion research was commenced there due to the need to estimate the role of ions in aerosol nucleation. About 25 scientific papers and abstracts about atmospheric ions were published in the Finnish journal:

Report Series in Aerosol Science during 2003-2006.

PHYSICS AND CHEMISTRYOF AIR IONS

Froyd and Lovejoy measured the stepwise growth of cluster ions by means of a mass spectrometer and calculated the thermodynamic parameters of growth reactions.

The results can be applied to assess ion-induced nucleation in the atmosphere. According to authors, significant aerosol nucleation on the sulphur acid-based cluster ions can be expected only in the stratosphere and upper troposphere.

Nadykto and Yu developed a model of ion cluster formation from two-component polar vapors.

The dipole-charge interaction decreases the size of critical clusters and when the highly polar vapors are nucleating, the actual size of small binary ion clusters may deviate significantly from the size predicted by the classical Kelvin-Thomson theory.

Iinuma et al. developed a new method for the analysis of air ion mobility distribution, which is expected to be composed of few Gaussian components. The method is based on the dynamic equilibrium theory and makes use of the reaction matrix. The method is examined analyzing the composite mobility spectra of the of hydrated ammonium cluster ions using simultaneously the results of mobility and mass measurements. The new method improves the understanding of the formation of cluster ion mobility spectra although a large uncertainty of the experimental data complicates the quantitative analysis.

NB: The single air ion paper in J. Atmos. Electr. during 4 years!

DEVELOPMENTOF INSTRUMENTATION

Harrison and Wilding designed a new high-tech ion mobility spectrometer for balloon-borne measurements. The voltage of the aspiration condenser is electronically controlled and the induced current is compensated using a compensation capacitor.

Kremer et al. published an intriguing paper describing an "electrostatic lens", which collimates the air ions at the atmospheric pressure.

However, the collimation is apparent and useless in aspirating instruments, because an increase in the ion concentration in the electric field is physically impossible. The claimed effect of collimation is valid only for the ion current density and explained by the increase in the field strength along the ion trajectories in the described instrument.

Labowsky and Mora developed several novel mobility analyzers for the cluster and intermediate ion mobility range, having in view applications in aerosol research. Differing from the traditional aerosol instruments, the new analyzers are isopotential: their inlet and outlet are at the same voltage. This makes it possible to apply them in atmospheric ion research.

The main advantage of the new analyzers is the high mobility resolution of 1–2%.

Airel Ltd. started developing and manufacturing air ion mobility spectrometers for atmospheric research. The instruments AIS(Air Ion Spectrometer)and NAIS, designed byDr. Aadu Mirme, take advantage of the multichannel technique.

The AIS has 42 physical channels and provides both negative and positive air ion fraction concentrations for 26 uniform fractions on logarithmic scale in the mobility range of 0.0013–2.4 cm2V−1s−1. The inlet air flow rate is 1 l/s. http://www.airel.ee

AIS and NAIS have provided data for several atmospheric aerosol nucleation research projects

A more specific instrument manufactured by Airel Ltd. is the Balanced Scanning Mobility Analyzer (BSMA). The BSMA allows to measure 16 mobility fractions, which are logarithmically uniformly divided over the range of 0.032–3.2 cm2V−1s−1. The high inlet air flow of about 50 l/s reduces the time of ion passage to 60 ms and the heating of the air in the analyzer to 0.2 K, which suppresses a possible transformation of ions inside the instrument. The instrument is used for routine measurements at the Universities of Helsinki and Tartu.

MEASUREMENTSOF ATMOSPHERIC IONS

Hõrrak et al. analyzed data consisting of 8900 hourly average mobility distributions measured in the mobility range of 0.00041–3.2 cm2V–1s–1 (diameter 0.36–79 nm) at Tahkuse, Estonia, in 1993–1994. The average variation is typical for continental stations. The size distribution of intermediate and light large ions in the size range of 1.6–22 nm is strongly affected by nucleation bursts of nanometer particles. The concentration of heavy large ions (charged Aitken particles) is enhanced in the afternoon, which is explained by the bursts of nanometer particles and the subsequent growth of particles by condensation and coagulation.

Tahkuse

AIR INLETAIR INLET

AEROSOLSPECTROMETER

AIR ION MOBILITYSPECTROMETERS

Laakso studied ions having in view applications in the modeling of aerosol nucleation. He claimed the ion measurements offer a way to study small particles below the size detection limit of traditional aerosol instruments. Atmospheric ions were measured in a boreal forest at the Hyytiälä forest station, Finland. Ion counters were used during the first period, and later, the air ion spectrometers AIS and BSMA. A combination of kinetic and ion-based nucleation was found to be the most probable particle formation mechanism in the atmosphere.

This is the single air ion research thesispublished during 2003-2006

Laakso et al. studied the ion production rates in a boreal forest at the Hyytiälä forest station. Two different methods were used simultaneously:

1) cluster ion and particle concentration measurements,

2) external radiation and radon concentration measurements.

The average ionization rate calculated from aerosol particle size distribution and air ion mobility distribution measurements was 2.6 ion pairs cm−3s−1, and based on external radiation and radon measurements, 4.5 ion pairs cm−3s−1. The discrepancy of the results remained without sound explanation.

Hyytiälä,

Finland

Tammet et al. introduced a new mathematical model describing the air ion balance including the effect of the dry deposition of ions onto the forest canopy. The model was tested with specific air ion measurements carried out simultaneously at two heights at the Hyytiälä forest station, Finland. The results explain the discrepancy in the former research by Laakso et al. [2004] as a consequence of neglecting the dry deposition of ions.

The ionization rate during a 16-hour measuring campaign was 5.6±0.8 cm−3s−1 at the height of 2 m and 3.9±0.2 cm−3s−1 at the height of 14 m, between the tree tops. The recombination sink of cluster ions on the ions of opposite polarity made up 9–13%, the sink on aerosol particles 65–69%, and the sink on the forest canopy 18–26% of the total sink of cluster ions. The average lifetime of cluster ions was about 130 s for positive and about 110 s for negative ions. At the height of 2 m, about 70% of the space charge of the air was carried by aerosol particles, and at the height of 14 m, about 84%.

According to this paper, the total ion production rate varied in the range of 4.2–17.6 ion pairs cm–3 s–1. The fraction of 222Rn contribution in the ion production varied in the range 0–0.43, with average fraction 0.11 +/- 0.07. The ion production was explained mostly by the external radiation .

A hard problem: uncertainty in measurements of the ionization rate.

Report Series in Aerosol Science, 81, 180-185, 2006

Hõrrak et al. measured the mobility distribution of air ions during rainfall and in laboratory experiments. The splashing of water drops generates negative particles with the dominating size of 2-3 nm.

RAINRAIN

RESEARCH OF ION-INDUCED NUCLEATION

Vana et al. compared the formation of intermediate ions and nanometer aerosol particles at three stations (Hyytiälä and Värriö in Finland and Tahkuse in Estonia) considering the air mass trajectories and meteorological data. The analysis shows that the bursts of intermediate ions and the nucleation events are synoptic-scale phenomena occurring in the horizontal extent of more than 1000 km.

Eisele et al. measured mass identified ion cluster distributions in the near ground air and compared the results with the model predictions. The measurements suggest that the ion-induced mechanism did not contribute significantly to new particle production or growth during these events. This does not rule out the possibility that ion-induced nucleation could contribute significantly to the atmospheric new particle formation under very different atmosphere conditions such as in the areas with much lower temperatures and higher ion concentrations.

Iida et al. investigated new particle formation events near Boulder, Colorado. Typically, the charged fractions of freshly nucleated particles were below the stationary-state values, indicating that neutral nucleation was dominant. Sometimes the asymmetry between negative and positive charge was observed, which could not be explained unless positive or negative ion-induced nucleation occurred to some extent. However, the average contribution of ion-induced nucleation to the fresh particle formation was estimated less than 1%.

Kazil et al. investigated the formation of sulfate aerosol in the marine troposphere from neutral and charged nucleation using a box model of neutral and charged aerosol processes on a grid covering the oceans. Neutral binary nucleation contributes only marginally to the aerosol production. This highlights the importance of other mechanisms, including charged binary and ternary, and neutral ternary nucleation for aerosol formation. However, the effect in radiative forcing was estimated smaller than the concurrent variation of total solar irradiance.

Yu developed a new model, which explicitly treats the evaporation of neutral and charged clusters and describes the evolution of the size spectra and composition of both ions and neutral particles ranging from clusters molecules to particles of several micrometers in diameter. The results suggest that under favorable conditions,

the ion-mediated nucleation of H2SO4–H2O can lead to a significant

production of new particles in the lower atmosphere. It has been shown that the freshly nucleated particles of few nanometers in size can grow by the condensation of low volatile organic compounds to the size of cloud condensation nuclei.

ATMOSPHERIC IONS AS A FACTOR OF CLIMATE

A review by Gavin Schmidt:

?

Usoskin et al. calculated the time-variable spatial distribution of cosmic ray-induced ionization of the lower atmosphere using a model. They calculated the 3D (geographical coordinates and altitude) equilibrium ion concentration in the lower atmosphere as a function of time for the period of 1951–2000. The calculated cosmic ray-induced ionization reproduces in general the observed altitudinal and latitudinal profiles of the ion concentration. The results provide a basis for a quantitative study of the solar–terrestrial relationships on long time scales.

Tinsley and Yu analyzed the changes in cloud properties that correlate with the 11-year cycles in space particle fluxes. Two mechanisms are proposed as possible explanations for these links.

The ion-induced or ion-mediated nucleation.

The electroscavenging of aerosol particles, which act as cloud condensation nuclei and ice forming nuclei.

Electroscavenging is controlled by atmospheric ions and atmospheric electric vertical current, which depend on the flux of cosmic rays and the solar wind.

Geophys. Monogr., 2004, vol. 141, pp. 321-340

Harrison and Stephenson analyzed the weather data including diffuse solar radiation. BADC datasets and the Colorado neutron monitor data 1951-2000 were used. Diffuse radiation increases in days of high cosmic ray flux by 2.0±0.3 %. The decrease of diffuse solar radiation was reliably detected for the Forbush event days, which proves the cosmic ray as the factor of solar radiation.

Aplin and McPheat showed on the basis of laboratory experiments that the cluster ions absorb infra-red radiation in the water vapor continuum region between 4 and 14 mm. Under clear-sky conditions or periods of enhanced atmospheric ionization, such as solar proton events, the infra-red absorption by atmospheric ions may affect climate through the radiative balance.

This may be detectable in the atmospheric longwave radiationat 12.3 and 9.1 m under cloud-free conditions.

Kulmala, M. & Tammet, H. 2007Finnish–Estonian air ion and aerosol workshops. Boreal Env. Res. 12: 237–245.

The introductory overview of the special issue consists of a brief summary of the motivation, history and main achievements in air ion research. This special issue presents main achievements in a set of 14 original papers.

6 issues a year, Impact Factor 2006 : 1.188

Appendix

Laakso, L., Grönholm, T., Kulmala, L., Haapanala, S., Hirsikko, A., Lovejoy, E. R., Kazil, J., Kurtén, T., Boy, M., Nilsson, E. D., Sogachev, A., Riipinen, I., Stratmann, F. & Kulmala, M. 2007: Hot-air balloon as a platform for boundary layer profile measurements during particle formation. Boreal Env. Res. 12: 279–294.

The concentration of freshly-formed 1.5–2 nm negative ions was several times higher than the concentration of positive ions. The nucleation during one of the days, 13 March 2006, was a combination of neutral and ion-induced nucleation. Simulations of boundary layer dynamics showed that particles are formed either throughout the mixed layer or in the lower part of it, not at the top of the layer.

Hirsikko, A., Yli-Juuti, T., Nieminen, T., Vartiainen, E., Laakso, L., Hussein, T. & Kulmala, M. 2007: Indoor and outdoor air ions and aerosol particles in the urban atmosphere of Helsinki: characteristics, sources and formation. Boreal Env. Res. 12: 295–310.

New particle formation was observed indoors almost every day, and four times outdoors. Indoors, the observed growth rates were 2.3–4.9 nm h–1 for 1.3–3 nm ions, 6.5–8.7 nm h–1 for 3–7-nm ions and 5.1–8.7 nm h–1 for 7–20-nm ions. Outdoor ions (3–7 nm) grew at rates as large as 15.4 nm h–1. Outdoor ion and particle number concentrations were dependent on the wind direction, whereas indoor concentrations were dependent on ventilation conditions.

Tiitta, P., Miettinen, P., Vaattovaara, P., Laaksonen, A., Joutsensaari, J., Hirsikko, A., Aalto, P. & Kulmala, M. 2007: Road-side measurements of aerosol and ion number size distributions: a comparison with remote site measurements. Boreal Env. Res. 12: 311–321.

The average cluster ion concentrations were quite low (around 320 cm–3 and 280 cm–3 for negative and positive ions). Negative intermediate ions (1.8–7.5 nm) reached maximum concentrations of 620 cm–3, while the average concentrations were in the range 60–80 cm–3 depending slightly on the wind direction. Positive intermediate ion concentrations were lower. Straightforward impact of traffic was observed when the wind blew from the road: an increase in the traffic density increased concentrations of large ions.

Komppula, M., Vana, M., Kerminen, V.-M., Lihavainen, H., Viisanen, Y., Hõrrak, U., Komsaare, K., Tamm, E., Hirsikko, A., Laakso, L. & Kulmala, M. 2007: Size distributions of atmospheric ions in the Baltic Sea region. Boreal Env. Res. 12: 323–336.

Number size distributions of air ions and aerosol particles were measured at three sites in the Baltic Sea region in spring 2004. One site was on the island of Utö in the Baltic Sea and the two other sites, Hyytiälä and Tahkuse, had a more continental location not far away from the coast of the Baltic Sea. The concentrations of cluster ions were about three times smaller at the Utö island as compared with those at the Hyytiälä mainland site in Finland, although the particle concentrations were at about the same level at these two sites.

Lihavainen, H., Komppula, M., Kerminen, V.-M., Järvinen, H., Viisanen, Y., Lehtinen, K., Vana, M. & Kulmala, M. 2007: Size distributions of atmospheric ions inside clouds and in cloud-free air at a remote continental site. Boreal Env. Res. 12: 337–344.

During the late autumn 2004, aerosol and air ion number size distributions inside and outside clouds and cloud droplet number size spectra were measured in Pallas, northern Finland. The concentrations of cluster ions were substantially lower, roughly by an order of magnitude, inside clouds as compared with cloud-free air. Very few intermediate ions (1.6–7.4 nm diameter) were present during the cloudy periods, indicating that processes capable of generating intermediate ions were rather inactive inside clouds during the measurement campaign.

Venzac, H., Sellegri, K. & Laj, P. 2007: Nucleation events detected at the high altitude site of the Puy de Dôme Research Station, France. Boreal Env. Res. 12: 345–359.

Aerosol and ion number size distributions were measured at the top of the Puy de Dôme (1465 m above the sea level) for a three-month period. Concentrations of cluster ions varied typically between 100 and 1000 cm–3. Intermediate ion (1.4–6 nm) concentrations were usually lower than 500 cm–3 but could exceed 3000 ions cm–3 during nucleation events.

Vartiainen, E., Kulmala, M., Ehn, M., Hirsikko, A., Junninen, H., Petäjä, T., Sogacheva, L., Kuokka, S., Hillamo, R., Skorokhod, A., Belikov, I., Elansky, N. & Kerminen, V.-M. 2007: Ion and particle number concentrations and size distributions along the Trans-Siberian railroad. Boreal Env. Res. 12: 375–396.

Concentrations of positive and negative intermediate and large ions were of the same order of magnitude as in previous studies made in boreal forests. Concentrations of intermediate ions were often a few ions cm–3, but their concentration increased during nucleation, rain and snowfall events. Concentrations of positive and negative cluster ions were sometimes very high, reaching values of about 5000 cm–3 in case of negative ions. Occasionally the ion production rate reached 30 s–1 cm–3 due to 222-radon decay.

Virkkula, A., Hirsikko, A., Vana, M., Aalto, P. P., Hillamo, R. & Kulmala, M. 2007: Charged particle size distributions and analysis of particle formation events at the Finnish Antarctic research station Aboa. Boreal Env. Res. 12: 397–408.

Approximately 23% of the days were particle formation event days. It was observed a clear positive correlation between the wind speed and cluster and intermediate ion concentrations, which suggests that ions were produced by friction processes in fast moving snow and ice crystals during the periods with strong winds. The average positive and negative cluster ion concentrations were 557 and 587 cm–3, respectively.

Parts, T.-E., Luts, A., Laakso, L., Hirsikko, A., Grönholm, T. & Kulmala, M. 2007: Chemical composition of waterfall-induced air ions: spectrometry vs. simulations. Boreal Env. Res. 12: 409–420.

The ion size spectrum near a waterfall permanently differs from that in ordinary tropospheric air. A simulation series of air small negative ion evolution was carried out, proposing that falling water increases the concentration of OH– cluster ions, which were employed as an extra input for the ion evolution model. The presence of additional OH– ions resulted in a decrease of typically model-provided NO3

– and/or HSO4

– cluster ion concentrations and an increase of the abundance of HCO3

– cluster ions.

Tammet, H. & Kulmala, M. 2007: Simulating aerosol nucleation bursts in a coniferous forest. Boreal Env. Res. 12: 421–430.

The dry deposition of ions and freshly nucleated particles onto tree needles was included into a numerical model of atmospheric aerosol nucleation bursts. The dry deposition is estimated using the Churchill-Bernstein approximation, which is adapted from the theory of heat transfer. The model includes an improved submodel of the sink of ions and nucleation mode particles onto large particles of the background aerosol. The examples show that the dry deposition of ions and nanometer scale particles onto the conifer needles has a considerable effect on the air ion concentrations.

CONCLUSIONS:

Activity in the research of atmospheric ions has slightly increased when compared with the previous four-year review period.

Considerable progress was achieved in the studies of ion-induced nucleation and the mobility distribution of atmospheric ions.

Atmospheric ions are recognized as a factor having an influence on the Earth's climate.

Thank You