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The SMEAR Estonia station (58.277663 N, 27.308266 E, 36 m a.s.l.) was established in south-east of Estonia at the Järvselja Experimental Forestry in 2012 to investigate the atmosphere-biosphere interactions and atmospheric aerosol formation and growth.In summer 2019, the gamma-radiation monitor GammaTRACER XL2-3 (Saphymo GmbH) was set up at Järvselja station and the rain sensor DRD11A (Vaisala Oyj) in autumn 2019. These devices enable to measure the gamma-radiation dose rate and precipitation intensity, which affect the ionization rate of atmospheric air close to ground, with high accuracy and time resolution, and complement our measurement system of atmospheric ions and aerosol particles.The gamma-radiation dose rate measurements at about 1.2 m above the ground reveled on relatively steady background about 70 nSv/h occasional events with increase up to about 110 nSv/h, which correlated well with rainfall intensity. Commonly such events last 3-4 hours, but in specific meteorological situation with continuous long-lasting rain and air mass movement from southerly directions the effect can last 2-3 days, resulting in gradual increase in gamma-radiation dose rate level during about 24 h.Such a phenomenon is known to occur due to wet deposition of radioactive aerosol particles during rain, namely due to the radon (222 Rn) short-lived daughter progeny products (Po-218, Pb-214, Bi-214) attached to atmospheric aerosol particles. The radon (222 Rn) daughter progeny involvement is confirmed by simultaneous gamma-spectrometric measurements with SARA AGS711F (Envinet GmbH) at Tõravere station (58° 15' 52,9" N, 26° 27' 42,1", 72 m), located about 50.3 km west from the Järvselja SMEAR station. The gamma dose rates showed very similar temporal behavior when both stations were affected by the same air mass with precipitation zone passing over the stations.To our best knowledge, the details of rain-induced enhancement of gamma-radiation dose rate and atmospheric processes behind the phenomenon are not well known and are worth future investigations. The events of rain induced gamma-radiation dose rate enhancement at Järvselja SMEAR and Tõravere station are analyzed and discussed in more detail in the presentation and the spatial representativity of the phenomenon is estimated based on the gamma-radiation monitoring network data of Estonian Early Warning System.

New Particle Formation (NPF) is a process in which a large number of particles is formed in the atmosphere via gas-to-particle conversion. Previous research shows the important role of formation of new particles for atmosphere, clouds and climate (Kerminen, V.-M. et al. 2018). There exist measurements from different parts of the world which show that NPF is happening worldwide (Kerminen, V.-M. et al. 2018). Measurements at SMEAR II station in Hyytiälä, Finland (Hari P. and Kulmala M., 2005), show that NPF is a common process in Finland’s boreal forests. However, measurements at Zotto station in Siberia, Russia, show that NPF events are very rare in that area (Wiedensohler A. et al., 2018). Measurements in Siberian boreal forests are sparse. We have conducted new measurements at Fonovaya station near Tomsk (Siberia, Russia) using Neutral cluster Air Ion Spectrometer (NAIS), Particle Size Magnifier (PSM), Differential Mobility Particle Sizer (DMPS) and the Atmospheric Pressure interface Time-Of-Flight mass spectrometer (APi-TOF). Those instruments measure aerosol particle number size distribution (NAIS, DMPS), ion number size distribution (NAIS), size distribution of small particles (PSM) and chemical composition of aerosol particles (APi-TOF). The novelty of this work is that such complex measurements have not been done in Siberia before. Here we report the first results of our research on NPF phenomenon in Siberian boreal forest. We present detailed statistics of NPF events, as well as formation rates (J) and growth rates (GR) of aerosol particles. The results from Fonovaya station are compared with those from SMEAR II station and from SMEAR Estonia station in Järvselja, Estonia. Literature[1] Kerminen V.-M. et al. “Atmospheric new particle formation and growth: review of field observations”. In: Environmental Research Letters 10 (2018), p. 103003. [2] Wiedensohler A. et al. “Infrequent new particle formation over the remote boreal forest of Siberia”. In: Atmospheric Environment 200 (2019), pp. 167–169. [3] Dada L. et al. “Long-term analysis of clear-sky new particle formation events and nonevents in Hyytiälä”. In: Atmospheric Chemistry and Physics 10 (2017), pp. 6227–6241.

[EN] There is an increasing interest to study the interactions between atmospheric electrical parameters and living organisms at multiple scales. So far, relatively few studies have been published that focus on possible biological effects of atmospheric electric and magnetic fields. To foster future work in this area of multidisciplinary research, here we present a glossary of relevant terms. Its main purpose is to facilitate the process of learning and communication among the different scientific disciplines working on this topic. While some definitions come from existing sources, other concepts have been re-defined to better reflect the existing and emerging scientific needs of this multidisciplinary and transdisciplinary area of research., This paper is based upon work from the COST Action "Atmospheric Electricity Network: coupling with the Earth System, climate and biological systems (ELECTRONET)," supported by COST (European Cooperation in Science and Technology). AO received funding from Poland Ministry of Science and Higher Education for statutory research of the Institute of Geophysics, Polish Academy of Sciences (Grant No 3841/E-41/S/2019).

Atmospheric new particle formation (NPF) is an important phenomenon in terms of global particle number concentrations. Here we investigated the frequency of NPF, formation rates of 10 nm particles, and growth rates in the size range of 10–25 nm using at least 1 year of aerosol number size-distribution observations at 36 different locations around the world. The majority of these measurement sites are in the Northern Hemisphere. We found that the NPF frequency has a strong seasonal variability. At the measurement sites analyzed in this study, NPF occurs most frequently in March–May (on about 30% of the days) and least frequently in December–February (about 10% of the days). The median formation rate of 10 nm particles varies by about 3 orders of magnitude (0.01–10 cm􀀀3 s􀀀1) and the growth rate by about an order of magnitude (1–10 nm h􀀀1). The smallest values of both formation and growth rates were observed at polar sites and the largest ones in urban environments or anthropogenically influenced rural sites. The correlation between the NPF event frequency and the particle formation and growth rate was at best moderate among the different measurement sites, as well as among the sites belonging to a certain environmental regime. For a better understanding of atmospheric NPF and its regional importance, we would need more observational data from different urban areas in practically all parts of the world, from additional remote and rural locations in North America, Asia, and most of the Southern Hemisphere (especially Australia), from polar areas, and from at least a few locations over the oceans.

We performed a more comprehensive test of a new NPF parameter estimator published recently. The estimator considers measurements as test data and automatically adjusts the values of its physical control parameters according to the criterion of best fit. The parameters estimated within this procedure include nucleation rate, particle growth rate, birth size of nanoparticles etc. We analyzed all new particle formation events recorded during a measurement campaign at Hyytiala, Finland. The results show a good performance in reproducing the time series of the concentrations of small air ions and aerosol nanoparticles in the diameter interval of 2.8–8.6 nm. The numerically estimated values of the parameters are in accordance with the results known from certain other studies carried out at Hyytiala. We conclude the new method may appear useful in the analysis of several air ion and atmospheric aerosol measurements during new particle formation events.

We use a previously published simulator of aerosol new particle formation (NPF) events as the core component of the new method for automated estimation of its input parameters. The simulator has a large number of physical input parameters (e.g., nucleation and growth rates), and it yields results about the dynamics of particle concentrations and their size distributions as its output. Our new method automatically solves the inverse problem. It estimates the physical input parameters by recurrent simulations according to the criterion of best fit of the simulated output parameters with the known data. The method is implemented as a computer program that includes the previous simulator as a subroutine. The method enables the estimation of several physical parameters, e.g., the nucleation rate, particle growth rate, contribution from ion-induced and neutral nucleation, and particle charging state. The program was tested using the results of two NPF events measured at Hyytiala, Finland. The measured time series of the concentration of atmospheric ions and nanoparticles in the diameter interval of 2.8–8.6 nm were well reproduced by our method. The estimated values of the analyzed input parameters are in agreement with the results known from many other studies carried out at Hyytiala. The proposed method of inverse simulator may appear useful in the analysis and interpretation of air ion and atmospheric aerosol measurements during new particle formation events.

The charging state of aerosol populations was determined using an Ion-DMPS in Helsinki, Finland between December 2008 and February 2010. We extrapolated the charging state and calculated the ion-induced nucleation fraction to be around 1.3 % ± 0.4 % at 2 nm and 1.3 % ± 0.5 % at 1.5 nm, on average. We present a new method to retrieve the average charging state for a new particle formation event, at a given size and polarity. We improve the uncertainty assessment and fitting technique used previously with an Ion-DMPS. We also use a new theoretical framework that allows for different concentrations of small ions for different polarities (polarity asymmetry). We extrapolate the ion-induced fraction using polarity symmetry and asymmetry. Finally, a method to calculate the growth rates from the behaviour of the charging state as a function of the particle diameter using polarity symmetry and asymmetry is presented and used on a selection of new particle formation events.

Coastal nucleation events and behavior of cluster ions were characterized through the measurements of air ion mobility distributions at the Mace Head research station on the west coast of Ireland in 2006. We measured concentrations of cluster ions and charged aerosol particles in the size range of 0.34–40 nm. These measurements allow us to characterize freshly nucleated charged particles with diameters smaller than 3 nm. The analysis shows that bursts of intermediate ions (1.6–7 nm) are a frequent phenomenon in the marine coastal environment. Intermediate ion concentrations were generally close to zero, but during some nucleation episodes the concentrations increased to several hundreds per cm 3 . Nucleation events occurred during most of the measurement days. We classified all days into one of seven classes according to the occurrence and type of new particle formation. Nucleation events were observed during 207 days in 2006, most prominently in the spring and summer months. Rain-induced events, in turn, were observed during 132 days. Particle formation and growth events mostly coincided with the presence of low tide. Also small cluster ions (0.34–1.6 nm) were characterized. Average concentrations of small ions were 440 cm − 3 for the negative ions and 423 cm − 3 for the positive ions. Average mean mobilities of small ions were 1.86 cm 2 V − 1 s − 1 and 1.49 cm 2 V − 1 s − 1 for the negative and positive polarities, respectively. Concentrations of small ions were observed to be strongly dependent on the variations of meteorological parameters including wind speed and direction.

Atmospheric aerosol formation is known to occur almost all over the world, and the importance of these particles to climate and air quality has been recognized. Although almost all of the processes driving aerosol formation take place below a particle diameter of 3 nanometers, observations cover only larger particles. We introduce an instrumental setup to measure atmospheric concentrations of both neutral and charged nanometer-sized clusters. By applying the instruments in the field, we come to three important conclusions: (i) A pool of numerous neutral clusters in the sub–3 nanometer size range is continuously present; (ii) the processes initiating atmospheric aerosol formation start from particle sizes of ∼1.5 nanometers; and (iii) neutral nucleation dominates over the ion-induced mechanism, at least in boreal forest conditions.

The LAPBIAT measurement campaign took place in the Värriö SMEAR I measurement station located in Eastern Lapland in the spring of 2003 between 26 April and 11 May. In this paper we describe the measurement campaign, concentrations and fluxes of aerosol particles, air ions and trace gases, paying special attention to an aerosol particle formation event broken by a air mass change from a clean Arctic air mass with new particle formation to polluted one approaching from industrial areas of Kola Peninsula, Russia, lacking new particle formation. Aerosol particle number flux measurements show strong downward fluxes during that time. Concentrations of coarse aerosol particles were high for 1–2 days before the nucleation event (i.e. 28–29 April), very low immediately before and during the observed aerosol particle formation event (30 April) and increased moderately from the moment of sudden break of the event. In general particle deposition measurements based on snow samples show the same changes. Measurements of the mobility distribution of air ions showed elevated concentrations of intermediate air ions during the particle formation event. We estimated the growth rates in the nucleation mode size range. For particles

Ions can speed up the formation of aerosol particles. The former studies have mainly concerned on the role of the ion charge itself. We have studied the possible (additional) role of the actual small air ion spectrum shape, and the quantitative role of ion–ion recombination pathway. By means of our ion evolution model, formation of new species (H 2 SO 4 ) n (NH 3 ) m (HNO 3 ) k via ion–ion recombination was investigated. The model shows how the generation rate of the new species depends on the concentrations of H 2 SO 4 and NH 3 , and how it depends on the tropospheric background aerosol situation. The rate can be up to a few new neutral complexes per cubic centimeter and per second. New particle generation via ion–ion recombination provides an extra channel, especially for the clean atmosphere. Former results have shown that such situations are often present in Antarctica. Our aerosol spectrum measurements reveal a number of similar non-Antarctic results. Sometimes, such situations are followed by aerosol bursts, which may be (partly) due to an ion–ion recombination channel.

In this work, the charging state of atmospheric nanoparticles was estimated through simultaneous measurements of aerosol size distribution and air ions mobility distribution with the aim to elucidate the formation mechanisms of atmospheric aerosols. The measurements were performed as a part of the QUEST 2 campaign at a boreal forest station in Finland. The overlapping part of the measurement ranges of the particle size spectrometers and air ion mobility spectrometers in the mass diameter interval of 2.6–40 nm was used to assess the percentage of charged particles (charging probability). This parameter was obtained as the slope of the linear regression line on the scatterplot of the measured concentrations of total (neutral + charged) and charged particles for the same diameter interval. Charging probabilities as a function of particle diameter were calculated for different days and were compared with the steady state charging probabilities of the particles in the bipolar ion atmosphere. For the smallest particles detectable by the particle size spectrometers (2.6–5 nm), the high percentages of negatively charged particles were found during the nanometer particle concentration bursts. These values considerably exceeded the values for the steady charging state and it was concluded that negative cluster ions preferably act as condensation nuclei. This effect was found to be the highest in the case of comparatively weak nucleation bursts of nanoparticles, when the rate of the homogeneous nucleation and the concentration of freshly nucleated particles were low. The nucleation burst days were classified according to the concentration of the generated smallest detectable new particles (weak and strong bursts). Approximately the same classification was obtained based on the charge asymmetry on particles with respect to the charge sign (polarity). The probabilities of negative and positive charge on the particles with the diameter of 5–20 nm were found to be nearly equal and they approximately agree with the values corresponding to the steady state charge distribution for negative particles known from lab experiments. It means that the steady charging state was reached during the growing time of particles up to 5 nm. The natural charging state of particles with a diameter between 2.5 and 4.5 nm was estimated by means of a special DMPS setup. Results were found to be in good correlation with the data by the particle size spectrometers and air ion mobility spectrometers.

Aerosol size spectra ( d= 10 nm–10 μm) were measured with an electrical aerosol spectrometer (EAS) at Mace Head on the west coast of Ireland. Several small aerosol particle (diameter 10–32 nm) concentration bursts were observed during the measurement period. Relationships between the events, air mass trajectories, tide height, and meteorological parameters are examined. Series of bursts were observed when a spectral transformation due to subsequent particle growth from 10 to 56–100 nm can be identified in an Eulerian experiment. Particle growth rates of between 1 and 3 nm/h were determined. These bursts appear in cold and comparatively clean arctic or polar air masses with temperature and relative humidity fluctuations, and do not correlate with low tide in some cases. These episodes, similar to those frequently found in the continental boundary layer, are thought to occur over a wide area and, for clear detection, require stable airflow for a few days. Elevated small-particle concentration events are more common during low tide or shortly after, and are typically associated with low wind speeds. Here, the increased shore exposure during low tide is thought to influence the nucleation and the subsequent growth of these aerosol particles. The occurrences of the bursts are found to depend on local wind direction. The highest d= 10–32 nm particle concentrations appeared for wind sectors furthest from the tidal regions when the wind direction was 150–160°(south-easterly). Most of the events occurred during daytime when solar irradiation is most intense.

Area of representativeness (AR) of atmospheric aerosol measurements and horizontal dimensions of a cloud of particles are estimated by time series of aerosol particle size number spectrum measured simultaneously at two locations. The distances between sampling points are varied, 7, 30, 50, 100 or 375 km. The spectrum in form of 12 fraction concentrations is measured every 10 or 15 min during five 2–4 week measurement campaigns in Estonia. During one measurement campaign one measurement point was in Estonia (Tahkuse) and the other in Finland (Hyytiala). Two electrical aerosol spectrometers (EAS) designed at University of Tartu, having diameter range 10 nm–10 μm, were used. At Hyytiala, the particle size spectrum ( d=3–500 nm ) was measured by two Hauke type differential mobility analysers (DMA). The transport of the submicron fraction ( d=60 nm –1 μm ) of atmospheric aerosol is investigated during the time intervals when an air mass moves from the one measurement point towards the other or crosswise to this direction. Sample cross-correlation functions (SCCF) are calculated between prewhitened time series. The time lag corresponding to the mode of these functions are found to be 3–5 h for upwind–downwind case and zero for crosswind case. This time lag should indicate the mean time of pollution transport for upwind–downwind case. A certain minimal distance between sampling points should exist, when statistically significant correlation between the time series cannot be found. Considering this circumstance, the half-width of the AR is estimated. It is found to be more than 100 km but less than 375 km when the sampling points are located on the same line with the wind direction; and more than 50 km but less than 100 km when the sampling points are located on a straight line crosswise to the wind direction. The pollutant concentrations in the limits of AR are estimated by regression analysis. To support these results, the dispersion calculations by HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectories) model are used.

Particulate pollution transport is estimated by means of cross-correlation and regression analyses. The aerosol particle size number spectrum in the form of 12 fraction concentrations is measured in units cm−3 (particles per cm3) every 10 minutes during three approximately 20-day measurement campaigns simultaneously in two measurement points in Estonia. The distance between these points is approximately 100 km for two campaigns, and 7 km for the third campaign. Two electrical aerosol spectrometers designed at Tartu University, having a wide particle diameter range (10 nm–10 μm), are used. The spectrometer's record is the mean particle spectrum for the 10 min measurement time. The air pollution transport is investigated during the time intervals when the air mass moves from one measurement point towards the other. The time series of aerosol size fraction concentrations for both locations are prewhitened to eliminate auto-correlation and to achieve stationary series of the ARIMA residuals. Then the cross-correlation function of these two series of residuals is calculated. The time lag corresponding to the mode of this function is treated as the mean time of pollution transport from the windward measurement point to the leeward one. For the submicron aerosol fraction (d=60 nm–1 μm) 3–5 h time lags are found. Mostly these time lags coincide with the mean wind velocities on some of the pressure levels (ground, 850 and 700 hPa) available in the study. In cross-wind cases the fraction concentrations measured in two points separated by 100 km were uncorrelated, but for the two points separated by 7 km there was quite a high correlation with zero time lag. The part of local and distant sources in the formation of the particle concentration in the leeward location is estimated by regression analysis.

In this paper, we summarize recent observations of nighttime nucleation events observed during 4 yr, from 2003 to 2006, at the SMEAR II station in Hyytiälä, southern Finland. Formation of new atmospheric aerosol particles has been frequently observed all around the world in daytime, but similar observations in nighttime are rare. The recently developed ion spectrometers enabled us to measure charged aerosol particles and ion clusters to diameters

An analysis of particle formation (PF) events over a subarctic mire in northern Sweden was performed, based on number–size distributions of atmospheric aerosol particles (10–500 nm in diameter) and ions (0.4–40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005–September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis includes calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm h -1 ) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions, repeated particle formation events were observed within 1 d, with differences in onset time of a few hours. These high growth rates were only observed when the condensation sink was higher than 0.001 s -1 . DOI: 10.1111/j.1600-0889.2008.00351.x

This review is based on ca. 260 publications, 93 of which included data on the temporal and spatial variation of the concentration of small ions (−3. However, concentrations up to 5000 cm−3 have been observed. The results are in agreement with observations of ion production rates in the atmosphere. We also summarised observations on the conversion of small ions to intermediate ions, which can act as embryos for new atmospheric aerosol particles. Those observations include the formation rates (J2[ion]) of 2-nm intermediate ions, growth rates (GR[ion]) of sub-3 nm ions, and information on the chemical composition of the ions. Unfortunately, there were only a few studies which presented J2[ion] and GR[ion]. Based on the publications, the formation rates of 2-nm ions were 0–1.1 cm−3 s−1, while the total 2-nm particle formation rates varied between 0.001 and 60 cm−3 s−1. Due to small changes in J2[ion], the relative importance of ions in 2-nm particle formation was determined by the large changes in J2[tot], and, accordingly the contribution of ions increased with decreasing J2[tot]. Furthermore, small ions were observed to activate for growth earlier than neutral nanometer-sized particles and at lower saturation ratio of condensing vapours.

[1] Growth rates of new particles during coastal and marine secondary aerosol particle formation events were studied in western Ireland, both at the Mace Head atmospheric research station and onboard the R/V Celtic Explorer as part of the Marine Aerosol Production project. Strong new particle formation events are frequently detected at Mace Head caused by the emission of precursor gases from exposed seaweed during low tide. Although these events were usually only detected as a mode of particles at a certain size, we were able to link the size of the mode to the growth time of these particles after the initial formation by combining data from several events measured between January 2006 and November 2007 with an air ion spectrometer. Typically, the early growth rates were extremely high, reaching values of several hundred nanometers per hour during the first seconds. The growth rates rapidly decreased and reached values below 1 nm h−1 within 1 h after nucleation. Our results were reproduced with box model calculations. All the obtained growth rates could be explained by the model either by varying the precursor formation time (typically a few seconds) or allowing multiple precursor vapor additions. From the ship-borne measurements, we report the first observations of purely open ocean new particle formation detected in this region. In total, four events were detected during this period, with three having a variable continental influence. An estimated average growth rate in marine conditions was 3 nm h−1 for these events.

The detailed mechanism of secondary new particle formation in the atmosphere is still under debate. It is proposed that particle formation happens via activation of 1–2 nm atmospheric neutral molecular clusters and/or large molecules. Since traditional instrumentation does not reach these sizes, the hypothesis has not yet been verified. By directly measuring particle size distributions down to mobility diameters of about 1.3 nm with a pulse-height CPC, we provide evidence of the nucleation mechanism in a coastal environment (Mace Head, Ireland) and in a boreal forest (Hyytiälä, Finland). In both places neutral sub-3 nm condensation nuclei (nano-CN) were continuously present, even when no new particle formation was detected. In Mace Head, however, the concentration of the nano-CN was far too low to account for the particle formation rates during particle bursts. Thus the results imply that at coastal sites new particle formation initiates, as previously proposed, via homogenous nucleation from biogenic iodine vapors. In contrast, activation of pre-existing nano-CN remains a possible explanation in the boreal forest, but the observed concentrations are not the limiting factor for the particle formation events.

We present comprehensive results on continuous atmospheric cluster and particle measurements in the size range ~1–42 nm within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) project. We focused on characterizing the spatial and temporal variation of new-particle formation events and relevant particle formation parameters across Europe. Different types of air ion and cluster mobility spectrometers were deployed at 12 field sites across Europe from March 2008 to May 2009. The measurements were conducted in a wide variety of environments, including coastal and continental locations as well as sites at different altitudes (both in the boundary layer and the free troposphere). New-particle formation events were detected at all of the 12 field sites during the year-long measurement period. From the data, nucleation and growth rates of newly-formed particles were determined for each environment. In a case of parallel ion and neutral cluster measurements, we could also estimate the relative contribution of ion-induced and neutral nucleation to the total particle formation. The formation rates of charged particles at 2 nm accounted for 1–30% of the respective total particle formation rates. As a significant new result, we found out that the total particle formation rate varied much more between the different sites than the formation rate of charged particles. This work presents, so far, the most comprehensive effort to experimentally characterize nucleation and growth of atmospheric molecular clusters and nanoparticles at ground-based observation sites on a continental scale.

Aerosol dynamical box model simulations of coastal new particle formation were performed in order to investigate the nucleation and growth mechanisms in this environment. In the simulations the nucleating vapor was assumed to be iodine dioxide (OIO). Both Eulerian and Lagrangian type simulations were made and compared with observations. We tested three nucleation mechanisms: kinetic nucleation of OIO (K x [OIO](2)), activation of clusters by OIO (A x [OIO]) and sulphuric acid-induced activation of clusters containing OIO (B x [OIO] x [H2SO4]). All the nucleation mechanisms provided reasonable results, although the growth of particles due to condensation is inadequate in kinetic nucleation cases as compared with experimental measurements. Growth of newly formed particles could be assisted by any low-volatility vapors should their concentration exceed 10(9) cm(-3). Using the obtained values of coefficients K, A, and B we found that nucleation driven by iodine compounds in remote marine areas is possible, but by OIO and H2SO4 alone, only a minor fraction of newly formed particles is likely to reach detectable sizes. Owing to the scavenging by coagulation with background aerosol particles, few of them will likely reach climatically relevant sizes by acting as seed particles for other low-volatility vapors. In order to elucidate the significance of our results, more detailed measurements of OIO source and photolysis rates, dimensions of precursor areas, and particle chemical composition are needed.

Coastal nucleation events and behavior of cluster ions were characterized through the measurements of air ion mobility distributions at the Mace Head research station on the west coast of Ireland in 2006. We measured concentrations of cluster ions and charged aerosol particles in the size range of 0.4–40 nm. These measurements allow us to characterize freshly nucleated charged particles with diameter below 3 nm. The analysis shows that bursts of intermediate ions (1.6–7 nm) are a frequent phenomenon in marine coastal environment. Nucleation evens occurred during most of the measurement days. We classified the nucleation burst events. Particle formation and growth events mostly coincided with the presence of low tide. Small ions concentrations appear to be strongly dependent on the variations of meteorological parameters including wind speed and direction.

Latitudinal air ion mobility distribution variations were characterized in the marine boundary layer during a cruise over the Eastern Atlantic and Southern Ocean. We measured concentrations of cluster ions and charged aerosol particles in the size range of 0.4–40 nm. The measured ion mobility distributions were characterized and classified according to meteorological conditions and air mass back-trajectories. New particle formation episodes (bursts of intermediate air ions) were observed above the pack-ice region of the Southern Ocean and several times during showers in the tropical marine boundary layer.

[1] Quantitative characteristics of the formation and growth events of nucleation mode aerosol particles occurred at three stations (Hyytiala and Varrio in Finland and Tahkuse in Estonia) have been compared. Aerosol size distributions were measured on all locations and, in addition, air ion mobility distribution at Tahkuse. Among 157 measuring days, nucleation events were identified on 62, 50, and 45 days at Hyytiala, Varrio, and Tahkuse, respectively. Eighteen days were found when nucleation events occurred on all three locations at the same day. The concentration of condensable vapor, its source strength, the growth rate, the total condensation sink, the formation rate of 3 nm particles, the formation rate, and concentration of 1 nm particles were estimated using measured aerosol number size distributions. The estimated growth rates were in the range of 2-9 nm hr -1 . The growth rates found from the measurements of air ion mobility distributions were comparable with that of nanometer particles. The condensable vapor concentrations were 1-12 x 10 7 cm -3 , which is smaller at Hyytiala than at Tahkuse and Varrio. At Tahkuse, source rates 6-55 x 10 4 cm -3 s -1 were estimated, whereas at Hyytiala and Varrio the rates were 2-14 x 10 4 cm -3 s -1 and 1-20 x 10 4 cm -3 s -1 , respectively. The condensation sink values were usually substantially higher at Tahkuse than on the other locations. Tahkuse size distribution data showed 5-10% underestimates in the total condensation sink considering particles in the diameter range

Some properties, sources and effects of natural and anthropogenic atmospheric aerosols in Arctic areas are discussed in this paper. Long-range transport of anthropogenic aerosols, and local biochemical sources that are thought to lead to aerosol formation and growth are also discussed. Current knowledge and questions remaining to be answered clearly indicate that the future research and measurements of atmospheric aerosols are needed in the Arctic. An important issue is to reduce the uncertainties in assessments of the impact of climate change.

In this paper, we summarize recent observations of nighttime nucleation events observed during 4 yr, from 2003 to 2006, at the SMEAR II station in Hyytiala, southern Finland. Formation of new atmospheric aerosol particles has been frequently observed all around the world in daytime, but similar observations in nighttime are rare. The recently developed ion spectrometers enabled us to measure charged aerosol particles and ion clusters to diameters

The formation and growth of atmospheric aerosols depend on several steps, namely nucleation, initial steps of growth and subsequent – mainly condensational – growth. This work focuses on the initial steps of growth, meaning the growth right after nucleation, where the interplay of curvature effects and thermodynamics has a significant role on the growth kinetics. More specifically, we investigate how ion clusters and aerosol particles grow from 1.5 nm to 20 nm (diameter) in atmospheric conditions using experimental data obtained by air ion and aerosol spectrometers. The measurements have been performed at a boreal forest site in Finland. The observed trend that the growth rate seems to increase as a function of size can be used to investigate possible growth mechanisms. Such a growth rate is consistent with a recently suggested nano-Köhler mechanism, in which growth is activated at a certain size with respect to condensation of organic vapors. The results also imply that charge-enhanced growth associated with ion-mediated nucleation plays only a minor role in the initial steps of growth, since it would imply a clear decrease of the growth rate with size. Finally, further evidence was obtained on the earlier suggestion that atmospheric nucleation and the subsequent growth of fresh nuclei are likely to be uncoupled phenomena via different participating vapors.