E. Tamm

Electrical aerosol spectrometer of Tartu University

The electrical aerosol spectrometer (EAS) of the parallel measuring principle at Tartu University is an efficient instrument for rapid measurement of the unstable size spectrum of aerosol particles. The measuring range from 10 nm to 10 μm is achieved by simultaneously using a pair of differential mobility analyzers with two different particle chargers. The particle spectrum is calculated and measurement errors are estimated in real time by using a least-squares method. Experimental calibration ensures reliability of measurement. The instrument is well suited for continuous monitoring of atmospheric aerosol.

Comparative study of nucleation mode aerosol particles and intermediate air ions formation events at three sites

[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 <500 nm. At Tahkuse the charged fraction of nucleation mode particles estimated through comparison of aerosol size distribution and air ion mobility distribution turned to be much higher than steady state charging probability of a single charge on the particle. Analysis of air mass trajectories and meteorological data indicated that the nucleation events are synoptic-scale phenomenon occurring in horizontal extent more than 1000 km.

Statistical characteristics of aerosol in Baltic Sea region

The article presents the results of the aerosol measurements carried out on the eastern coast of the Baltic Sea during 1986 – 1993. Aerosol size distributions in the diameter range of 0.01–10 μm have been measured with the electric aerosol spectrometer (EAS). A short description of EAS is given. The majority of number distributions obtained by measurements were of monomodal shape. Modal diameter varied at 0.01–0.1 μm. Seven percent of all number distributions were of bimodal shape with modes at 0.010 – 0.032 μm and at 0.032 – 0.1 μm, separated with a minimum at 0.018 – 0.056 μm. The majority of aerosol mass distributions were of bimodal shape and consisted of an accumulation mode varying at 0.18 – 1.0 μm and of a coarse particle mode at 1.8 – 10 μm separated by a minimum varying at 0.56 – 3.2 μm. Parameters of the Junge distribution and the 4-parameter KL distribution have been obtained. The variability of aerosol concentrations and the stability of aerosol at a fixed site have been studied analyzing the time sequences of aerosol number distributions. The variability of concentrations depended on particle size. The variability was about 0.7 at 0.1 – 0.3 μm and rose toward both the smaller and larger diameters up to values 1.4 at 0.01 μm and 1.7 at 10 μm.

Air ion measurements as a source of information about atmospheric aerosols

The mobility spectra of air ions recorded in the course of routine atmospheric electric measurements contain information about atmospheric aerosols. The mobility spectrum of air ions is correlated with the size spectrum of aerosol particles. Two procedures of conversion (and conversion errors) are considered in this paper assuming the steady state of charge distribution. The first procedure uses the fraction model of the aerosol particle size distribution and algebraic solution of the conversion problem. The second procedure uses the parametric KL model of the particle size distribution and the least square fitting of the mobility measurements. The procedures were tested using simultaneous side-by-side measurements of air ion mobilities and aerosol particle size distributions at a rural site during a monthly period. The comparison of results shows a promising agreement between the measured and calculated size spectra in the common size range. A supplementary information about nanometer particles was obtained from air ion measurements.

Comparison of sequential and parallel measurementprinciples in aerosol spectrometry

Abstract The dynamic measurement errors of the sequential aerosol spectrometers are analyzed.In the case of TSI 3030 the random dynamic error of a measured spectrum fraction concentration may twice exceed its real variability. In the case of a parallel aerosol spectrometer the only dynamic error - smoothing of the quick changes of the spectrum can be minimized by decreasing the measurement time.

Electrically Produced Standard Aerosols in a Wide Size Range

Non-uniformly charged particles cause a major problem in electrical methods for producing standard aerosols, imposing strict limitations on the usability of the obtained standard aerosols. This article gives a quick overview of this problem, examining the ways how differently charged particles affect the generation of standard aerosols, and presenting a new method for producing standard aerosols and avoiding the effects of multiply charged particles, with the key idea that the probability for small particles to have more than one charge is very low. A two-stage aerosol generator is used. Small silver particles (d< 40 nm) generated by homogeneous nucleation of silver vapors obtain in bipolar charger not more than one elementary charge. These condensation nuclei are enlarged by a condensational growth device. Big particles are now also not more than singly charged, and narrow size distribution can be obtained by electrical separation. Properties of standard aerosols produced experimentally by both the conventional and the new method, are compared and the validity of the new idea behind the new method is confirmed.

Age estimation of atmospheric black carbon over Finland from combined aerosol size distribution and radon progeny measurements

Data on aerosol particle size distributions between 0.01 and 10 um were combined with 222Rn and 210Pb particle activities to analyze black carbon characteristics. The activity ratio 210Pb/222Rn was applied to estimate the aerosol and black carbon age. Aerosol with high concentration in the size range of 0.100–0.320 um was related to high black carbon levels with an estimated 2.8 d residence time, and easterly continental winds. Aerosol in the nanometer size range, 0.010–0.032 um, was associated with low black carbon levels, polar winds and 2.0–4.4 d residence time. Aerosol number concentrations varied between 2000-25,000 cm−3, 222Rn activity concentrations between 0.3–13 Bq/m3, radon progeny 210Ph between 110–315 μBq/m3, and black carbon levels between 50–700 ng/ms. Observed mass ratio of black carbon to total aerosol mass in the size range 0.010–10 μm was on average 0.64%, which is substantially smaller than at other remote sites. A near constant ratio of black carbon to the 0.100–0.180 um aerosol fraction is proposed to represent an equilibrium state in an aged aerosol.

Small-particle concentration fluctuations at a coastal site

Abstract 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.

Derivation of the size spectrum of aerosol particles from a mobility spectrum

Publisher Summary Air–ion mobility spectrum is a traditional subject of atmospheric electric research. The electric mobility is well correlated with the particle size in the range of intermediate and large air ions. Correspondingly, a mobility spectrum can be transformed into a size spectrum and the atmospheric electric measurements can be used as a source of information about the atmospheric aerosol particle size-distribution. The mobility spectra of air ions measured in atmospheric electrical research give essential information about atmospheric aerosols. The air–ions and aerosol particles were simultaneously measured during a monthly period at a rural site, and the aerosol particle size-spectrum was derived from the air ion measurements. The comparison of results shows satisfactory agreement between the measured size spectra at the common size subrange and essential supplementary information about nanometer particles extracted from air ion measurements.

Electrical classification as a basis of the aerosol standard

Abstract An attempt is made to develop a general theory of the electrical classification method of aerosol particles for aerosol standard purposes. Ideal conditions in the classifier are considered.