10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Air Ions – the Key in Understating Features in the Surface Atmospheric Electric Field in Relation to Aerosol Processes in the Lower Atmosphere
XUEMENG CHEN, Susana Barbosa, Antti Mäkelä, Jussi Paatero, Veli-Matti Kerminen, Tuukka Petäjä, Markku Kulmala, University of Helsinki, Finland
Abstract Number: 808 Working Group: Aerosol Physics
Abstract Under fair weather conditions, an electric field in the order of 100-150 Vm-1 exists in the Earth’s atmosphere (e.g. Tinsley 2008). It was shown based on averaged data that the fair-weather electric field follows an alike diurnal pattern, known as the Carnegie curve, in different measurement locations around the globe (e.g. Harrison 2013). The global variations in thunderstorm activities have been believed to be the cause of this diurnal behaviour in the Carnegie curve (Whipple 1929), following the proposal of the global circuit concept by C. T. R. Wilson (Wilson 1921). In the global circuit concept, the Earth’s surface and the ionosphere serve as the two electrodes of a capacitor that gets recharged by lightning activities while leaks under fair weather conditions through the flow of air ions.
Air ions are created by ionising radiation. In the lower atmosphere, air ions interact with aerosol particles. Atmospheric new particle formation, for instance, is one of the main aerosol processes that significantly changes the number size properties of air ions (Kulmala and Kerminen 2008). Air ion properties are altered by aerosol processes whereas the presence of air ions modifies atmospheric electric field. Investigations have been dedicated to understand the relations of air ions to aerosol processes and to atmospheric electric properties, respectively. Yet, there is little effort put in studies characterising the connection between atmospheric electricity and aerosol processes. To understand how atmospheric electric field varies with aerosol processes, air ions, being the medium connecting atmospheric electric properties and aerosol processes, are the paramount parameter.
During June-November, 2017, a measurement campaign was carried out at Hyytiälä SMEAR II station (61°51 ́N, 24°17 ́E, 181 m above sea level), which situates in a boreal forest in southern Finland (Hari and Kulmala 2005). We measured atmospheric electric field together with soil radon concentration, atmospheric radioactivity as well as air ion and aerosol number size distributions. The number size distribution data of air ions and aerosol particles is part of the routine measurement system at the station. Moreover, the station also provides access to meteorological parameters to further assist our analysis.
In the presentation, we will focus on features in electric fields in relation to aerosol processes, such as atmospheric new particle formation and wet scavenging. Our preliminary results showed that aerosol formation processes introduce variations in the fair-weather atmospheric electric field that blurs the Carnegie pattern and the washout of airborne radon progeny along with the wet scavenging of aerosol particles can result in a temporary increase in air ion production that modifies atmospheric electric field. With the advantages of our air ion and aerosol measurements, we will elucidate how air ion dynamics are reflected in patterns in the atmospheric electric field in relation to aerosol processes.
References: [1] Hari, P. and Kulmala, M. (2005). Boreal Environ. Res. 10:315-322. [2] Harrison, R. G. (2013). Surv. Geophys. 34:209-232. [3] Kulmala, M. and Kerminen, V.-M. (2008). Atmos. Res. 90:132-150. [4] Tinsley, B. A. (2008). Rep. Prog. Phys. 71:066801. [5] Whipple, F. J. W. (1929). Q. J. R. Meteorol. Soc. 55:1–18. [6] Wilson, C. T. R. (1921). Philos. Trans. R. Soc. London A. 221:73-115.