On formation, growth and concentrations of air ions

Aerosol particles have effect on climate, visibility, air quality and human health. However, the strength of which aerosol particles affect our everyday life is not well described or entirely understood. Therefore, investigations of different processes and phenomena including e.g. primary particle sources, initial steps of secondary particle formation and growth, significance of charged particles in particle formation, as well as redistribution mechanisms in the atmosphere are required. In this work sources, sinks and concentrations of air ions (charged molecules, cluster and particles) were investigated directly by measuring air molecule ionising components (i.e. radon activity concentrations and external radiation dose rates) and charged particle size distributions, as well as based on literature review. The obtained results gave comprehensive and valuable picture of the spatial and temporal variation of the air ion sources, sinks and concentrations to use as input parameters in local and global scale climate models. Newly developed air ion spectrometers (Airel Ltd.) offered a possibility to investigate atmospheric (charged) particle formation and growth at sub-3 nm sizes. Therefore, new visual classification schemes for charged particle formation events were developed, and a newly developed particle growth rate method was tested with over one year dataset. These data analysis methods have been widely utilised by other researchers since introducing them. This thesis resulted interesting characteristics of atmospheric particle formation and growth: e.g. particle growth may sometimes be suppressed before detection limit (~ 3 nm) of traditional aerosol instruments, particle formation may take place during daytime as well as in the evening, growth rates of sub-3 nm particles were quite constant throughout the year while growth rates of larger particles (3-20 nm in diameter) were higher during summer compared to winter. These observations were thought to be a consequence of availability of condensing vapours. The observations of this thesis offered new understanding of the particle formation in the atmosphere. However, the role of ions in particle formation, which is not well understood with current knowledge, requires further research in future.Aerosolihiukkaset vaikuttavat ilmastoon suorasti sirottamalla ja absorboimalla auringon valoa, sekä epäsuorasti muodostamalla pilvipisaroita ja vaikuttamalla pilvien ominaisuuksiin. Tämän hetkisen tiedon mukaan aerosolihiukkasten vaikutus ilmastoon on viilentävä. Aerosolihiukkaset vaikuttavat myös ilman laatuun ja ihmisten terveyteen. On siis tarpeen tutkia mistä ja miten näitä hiukkasia muodostuu, kasvaa ja poistuu ilmakehässä, jotta voisimme paremmin arvioida aerosolihiukkasten vaikutusta jokapäiväiseen elämäämme. Tässä työssä saimme laajan käsityksen ilman ionien (varattuja molekyylejä, klustereita ja hiukkasia) lähteiden, nielujen ja pitoisuuksien ajallisesta ja paikallisesta vaihtelusta. Tässä työssä tutkittiin myös hiukkasten muodostumista ja kasvua ilmakehässä uusilla mittalaitteilla. Näin ollen työssä kehitettiin analyysimenetelmä varattujen hiukkasten muodostumistapahtumien luokitteluun, sekä testattiin hieman aiemmin kehitettyä hiukkasten kasvunopeuden määritysmenetelmää. Havainnot hiukkasmuodostuksesta ja kasvusta olivat erittäin mielenkiintoisa: esimerkiksi hiukkasten kasvu voi joskus pysähtyä ennen kuin (~ 3 nm) ne havaittaisiin perinteisillä mittalaitteilla, hiukkasmuodostus voi tapahtua niin päivällä kuin illallakin, alle 3-nm hiukkasten kasvu oli tasaista vuoden ympäri mutta 3-20-nm hiukkasten kasvu oli nopeampaa kesällä kuin talvella. Näiden havaintojen uskottiin johtuvan tiivistyvien höyryjen saatavuudesta ilmakehässä. Työssä kehiteltyjä ja käytettyjä analyysimenetelmiä on laajamittaisesti hyödynnetty niiden julkaisemisesta lähtien. Tehdyt havainnot tarjoavat laajan tietopaketin, jota voidaan hyödyntää ilmastomalleissa. Tulevaisuudessa kuitenkin tarvitaan lisää tutkimuksia ionien roolista hiukkasmuodostuksessa, joka ei nykytiedoilla ole täysin selvä, sekä mittaushavaintoja esimerkiksi hiukkasmuodostukseen ja kasvuun osallistuvista höyryistä

Measurements of positive ions and air-earth current density at Maitri, Antarctica

Simultaneous measurements of the small-, intermediate- and large- positive ions and air earth current density made at a coastal station, Maitri at Antarctica during January to February 2005, are reported. Although, small and large positive ion concentrations do not show any systematic diurnal variations, variations in them are almost similar to each other. On the other hand, variations in intermediate positive ion concentrations are independent of variations in the small/large positive ions and exhibit a diurnal variation which is similar to that in atmospheric temperature on fair weather days with a maximum during the day and minimum during the night hours. No such diurnal variation in intermediate positive ion concentration is observed on cloudy days when variations in them are also similar to those insmall/large positive ion concentrations. Magnitude of diurnal variation in intermediate positive ion concentration on fair weather days increases with the lowering of atmospheric temperature in this season. Scavenging of ions by snowfall and trapping of Alha - rays from the ground radioactivity by a thin layer of snow on ground, is demonstrated from observations. Variations in intermediate positive ion concentration are explained on the basis of the formation of new particles by the photolytic nucleation process.Comment: 38 pages, 11 figure and 2 tabl

Waterfalls as sources of small charged aerosol particles

In this study, we measured the mobility distributions of cluster and intermediate ions with an ion spectrometer near a waterfall. We observed that the concentration of negative 1.5–10 nm ions was one-hundred fold higher than a reference point 100 m away from the waterfall. Also, the concentration of positive intermediate ions was found to be higher than that at the reference point by a factor of ten. This difference was observed only at the smallest sizes; above 10 nm the difference was insignificant

Identification and classification of the formation of intermediate ions measured in boreal forest

International audienceWe have measured the size distributions of air ions (0.42?7.5 nm in diameter) with the Balanced Scanning Mobility Analyzer in boreal forest, in Southern Finland since spring 2003. The size range covers the size range of cluster ions (approximately 0.42?1.6 nm) and naturally charged nanometre aerosol particles (1.6?7.5 nm) or intermediate air ions. Based on the measurements from April 2003 to March 2006 we studied the characteristics of charged aerosol particle formation by classifying each day either as a particle formation event, undefined or non-event day. The principal of the classification, as well as the statistical description of the charged aerosol particle formation events are given. We found in total 270 (26% of the analysed days) and 226 (22% of the analysed days) particle formation days for negative and positive intermediate ions, respectively. For negatively charged particles we classified 411 (40% of the analysed days) undefined and 348 (34% of the analysed days) non-event days whereas for positively charged particles 343 (33% of the analysed days) undefined and 460 (45% of the analysed days) non-event days. The results were compared with the ordinary classification based on the Differential Mobility Particle Sizer (DMPS) measurements carried out at the same place. The above-presented values differed slightly from that found from the DMPS data, with a lower particle diameter of 3 nm. In addition, we have found the rain-induced intermediate ion bursts frequently. The rain effect was detected on 163 days by means of negative ions and on 105 days by positive ones. Another interesting phenomenon among the charged aerosol particles was the appearance and existence of intermediate ions during the snowfall. We observed this phenomenon 24 times with negatively charged particles and 21 times with positively charged ones during winter months (October?April). These intermediate air ions were seen during the snowfall and may be caused by ice crystals, although the origin of these intermediate ions is unclear at the moment

Ambient sesquiterpene concentration and its link to air ion measurements

International audienceAmbient air ion size distributions have been measured continuously at the Finnish boreal forest site in Hyytiälä since spring 2003. In general, these measurements show a maximum of air ions below 1.0 nm in diameter. But this physical characterization does not provide any information about the ion's chemical composition, which is one key question regarding the explanation of nucleation events observed. In this study we propose a link of the observed maximum of negative air ions between 0.56 and 0.75 nm to the so-called stabilised Criegee biradical, formed in the reaction of biogenic sesquiterpenes with ozone and predominantly destroyed by its reaction with ambient water vapour. Calculations of the electron and proton affinities of 120 kJ mol?1 (1.24 eV) and of 960 kJ mol?1 support this link. Other possible candidates such as sulphuric acid derived clusters are unable to explain the observations made. By using this approach, we are able to calculate the ambient concentration of sesquiterpenes at the air ion instrument inlet with a high time resolution on the daily and seasonal scale. The estimated concentration is found to reveal the same seasonal pattern as emission measurements conducted at shoot level. As expected for biogenic VOCs, the concentration is obtained highest during summer (maximum values of about 100 pptv) and smallest during winter (minimum less than 1 pptv). Because of the sesquiterpenes high reactivity and its low ambient concentrations, this approach can be a first step in understanding their emission and their impact on atmospheric chemistry in more detail. The findings presented are highly relevant for emission budgets too, since boreal forests are extended over large areas of the globe