Characteristics of new-particle formation at three SMEAR stations

We analyzed the size distributions of atmospheric aerosol particles measured during 2013-2014 at Varrio (SMEAR I) in northern Finland, Hyytiala (SMEAR II) in southern Finland and Jarvselja (SMEAR-Estonia) in Estonia. The stations are located on a transect spanning from north to south over 1000 km and they represent different environments ranging from subarctic to the hemi-boreal. We calculated the characteristics of new-particle-formation events, such as the frequency of events, growth rate of nucleation mode particles, condensation and coagulation sinks, formation rate of 2 nm and 3 nm particles, and source rate of condensable vapors. We observed 59, 185 and 108 new-particle-formation events at Varrio, Hyytiala and Jarvselja, respectively. The frequency of the observed events showed an annual variation with a maximum in spring. The analysis revealed size dependence of growth rate at all locations. We found that the growth rate and source rate of a condensable vapor were the highest in Jarvselja and the lowest in Varrio. The condensation sink and particle formation rate were of a similar magnitude at Hyytiala and Jarvselja, but several times smaller at Varrio. Tracking the origin of air masses revealed that the number concentration of nucleation mode particles (3-25 nm) varied from north to south, with the highest concentrations at Jarvselja and lowest at Varrio. Trajectory analysis indicated that new-particle-formation events are large-scale phenomena that can take place concurrently at distant stations located even 1000 km apart. We found a total of 26 days with new-particle-formation events occurring simultaneously at all three stations.Peer reviewe

Quiet New Particle Formation in the Atmosphere

Atmospheric new particle formation (NPF) has been observed to take place in practice all around the world. In continental locations, typically about 10-40% of the days are so-called NPF event days characterized by a clear particle formation and growth that continue for several hours, occurring mostly during daytime. The other days are either non-event days, or days for which it is difficult to decide whether NPF had occurred or not. Using measurement data from several locations (Hyytiala, Jarvselja, and near-city background and city center of Budapest), we were able to show that NPF tends to occur also on the days traditionally characterized as non-event days. One explanation is the instrument sensitivity towards low number concentrations in the sub-10 nm range, which usually limits our capability to detect such NPF events. We found that during such days, particle formation rates at 6 nm were about 2-20% of those observed during the traditional NPF event days. Growth rates of the newly formed particles were very similar between the traditional NPF event and non-event days. This previously overlooked phenomenon, termed as quiet NPF, contributes significantly to the production of secondary particles in the atmosphere.Peer reviewe

Dataset of air ion and aerosol measurements. Tahkuse 2004-2014

The present dataset of air ion mobility and aerosol particle size distributions is a follow-up of the dataset Tahkuse_1993_1994, http://datadoi.ut.ee/handle/33/22. It makes available results of routine measurements in Tahkuse Air Monitoring Station from 01.01.2004 to 31.12.2014. The station is located in the Sepa farmhouse in Tahkuse village about 27 km northeast of the city of Pärnu, Estonia. Geographical coordinates are 58º31'28"N, 24º55'32"E, 24 m a.s.l. The farmhouse is surrounded with flat open landscape with some tree groups, grassland and agricultural land. The level of air pollution is typical for atmospheric air at a sparsely populated rural area. The dataset includes results of simultaneous measurements of positive and negative air ions and neutral aerosol particles. The small air ions are charged molecules and clusters up to 1.6 nm, the intermediate and large air ions are charged fine aerosol particles of size 1.6 – 70 nm. The air ion spectrometers are the same as used in Tahkuse during 1993 – 1994. Important upgrades of the instrumentation are taking into use the aerosol particle size spectrometer EAS and the AlphaGUARD radon monitor. The spectrometers are installed in the attic of the building. The air intake is at a height of 5 m above the ground. The continued measurements of wind speed, wind direction, air temperature, relative humidity, and concentration of NO2 are complemented with measurements of air pressure, sun radiation and radon activity concentration. The detailed description of the landscape, station, and instruments is presented in the thesis by Hõrrak, U. (2001) Air ion mobility spectrum at a rural area, https://dspace.ut.ee/handle/10062/50218. The measurements are saved into 11 yearly files as a tab-separated ANSI text. The zip-package of files should be downloaded from the present website, unpacked and operated in the personal computer of the scientist. The data can be immediately opened and analyzed using MS Excel as well as by means of different computer programs, which are able to process the ANSI text. Every file consists of a table with 114 columns and 8761 or 8785 rows. The columns correspond to variables and rows to measurement hours. The data are written without omissions for 24 hours per day even when the measurements were stopped or failed and the values of variables are unknown. The missing values are marked with the code –99. The data is accompanied with an instruction for the user Tahkuse_data_2004–2014_guide.pdf and a presentation of data preparation algorithms Tahkuse_data_2004–2014_supplement.pdf. The authors acknowledge Aadu Mirme for great work designing the original instrumentation