Erkki Siivola

Particle Size Magnifier for Nano-CN Detection

A new particle size magnifier (PSM) for detection of nano-CN as small as ∼1 nm in mobility diameter was developed, calibrated and tested in atmospheric measurements. The working principle of a PSM is to mix turbulently cooled sample flow with heated clean air flow saturated by the working fluid. This provides a high saturation ratio for the working fluid and activates the seed particles and grows them by condensation of the working fluid. In order to reach high saturation ratios, and thus to activate nano-CN without homogeneous nucleation, diethylene glycol was chosen as the working fluid. The PSM was able to grow nano-CN to mean diameter of 90 nm, after which an ordinary condensation particle counter was used to count the grown particles (TSI 3010). The stability of the PSM was found to be good making it suitable for stand-alone field measurements. Calibration results show that the detection efficiency of the prototype PSM + TSI 3010 for charged tetra-alkyl ammonium salt molecules having mobility equivalent diameters of 1.05, 1.47, 1.78, and 2.57 nm are 25, 32, 46, and 70%, respectively. The commercial version of the PSM (Airmodus A09) performed even better in the smallest sizes the detection efficiency being 51% for 1.47 nm and 67% for 1.78 nm.

Surface-atmosphere interactions over complex urban terrain in Helsinki, Finland

Long-term measurements of fluxes of sensible heat (H), latent heat (LE) and carbon dioxide (Fc) were made from December 2005 to August 2006 over an urban landscape in Helsinki, Finland using the direct micrometeorological eddy covariance technique. Three distinguished sectors of land-use cover (vegetation, roads and buildings) allowed comparisons of fluxes over different urban surfaces. The normalized standard deviation of wind and scalars as a function of atmospheric stability were typical for rough surfaces, as were turbulence spectra and cospectra. Footprint analysis was performed by a boundary-layer one and half-order closure model allowing for discrimination of surface and canopy sinks/sources and complex topography. Fluxes were analysed as average diurnal courses over winter, spring and summer periods. H exceeded LE reaching 300 W m-2 over urban and road surfaces in the summer and it was close to 100 W m-2 in the winter. LE was highest in the summer over vegetation cover attaining 150 W m-2. The emission rate of CO2 was high over road sector [20 μmol (m2s)-1] [Correction added after online publication 16 Oct 2007: 30 μmol changed to 20 μmol] while in the vegetation sector it remained below 5 μmol (m2s)-1 and at summertime reached even −10 μmol(m2 s)-1 [Correction added after online publication 16 Oct 2007: wording of sentence altered]. Effluxes from soil measured by chambers were 1- 3 μmol (m2s)-1. Fc correlated with traffic density and a background non-vehicle flux was 1 μmol (m2s)-1 [Correction added after online publication 16 Oct 2007: 2 μmol changed to 1 μmol].

Relaxed Eddy Accumulation System for Size-Resolved Aerosol Particle Flux Measurements

Abstract A novel relaxed eddy accumulation (REA) system for aerosol particle flux measurement has been developed and tested. The system consisted of a fast-response sonic anemometer, a flow system, and software for operating the valves and the concentration analysis system. The prototype was used during September–October 2001 at the SMEAR II station of the University of Helsinki. The REA system was operated with a varying threshold for valve switching determined by the running mean standard deviation of the vertical wind speed. Such a varying threshold made the flux proportionality coefficient β independent of observation conditions. Using temperature as a tracer, β was determined to be 0.392 ± 0.002. The system was validated by comparing the carbon dioxide fluxes estimated by REA with the ones measured by the eddy covariance technique. The system was used subsequently for flux measurements of 50-nm aerosol particles and deposition velocity estimation. Observed deposition velocities over a pine forest dur...

Characterization of a Herrmann-type high-resolution differential mobility analyzer

ABSTRACT Aerosol instrument characterization and verification for nanometer-sized particles requires well-established generation and classification instruments. A precise size selection of sub-3-nm charged aerosol particles requires a differential mobility analyzer (DMA), specially designed for the sub-3-nm size range. In this study, a Herrmann-type high-resolution DMA developed at Yale University was characterized in various operation conditions. A relation between sheath flow rate and tetraheptylammonium ion (C28H60N+, THA+, 1.47 nm, mobility equivalent diameter) was established. The maximum particle size that the DMA was able to classify was 2.9 nm with the highest sheath flow rate of 1427 liters per minute (Lpm), and 6.5 nm with the lowest stable sheath flow rate of 215 Lpm, restricted by the maximum and minimum flow rates provided by our blower. Resolution and transmission of DMA are reported for tetrapropylammonium (C12H28N+, TPA+, 1.16 nm), THA+, and THA2Br+ (1.78 nm) ions measured with two different central electrodes and five different sheath flow rates. The transmission varied between 0.01 and 0.22, and the resolution varied between 10.8 and 51.9, depending on the operation conditions. Copyright

Tube transport of water vapor with condensation and desorption

Attenuation and delay of active tracers in tube transport is an important current problem, but its full explanation is still lacking. To this end a model is introduced, where part of a tracer undergoes condensation and evaporation, treated as a diffusion-type process, in addition to Taylor dispersion. Condensation of water was verified by high-speed imaging, and the model solution fitted the breakthrough curves of laboratory measurements with pulses of water vapor of varying relative humidity. The model provides a transfer function whose performance was verified against field measurements.

Sorption-Caused Attenuation and Delay of Water Vapor Signals in Eddy-Covariance Sampling Tubes and Filters

AbstractAdsorption and desorption (together called sorption) processes in sampling tubes and filters of eddy-covariance stations cause attenuation and delay of water vapor signals, leading to an underestimation of water vapor fluxes by tens of percent. The aim of this work was (i) to quantify the effects on sorption in filters and tubes of humidity, flow rate, and dirtiness and (ii) to test a recently introduced sorption model that facilitates correction of fluxes. Laboratory measurements on the transport of water vapor pulses through tubes and filters were carried out, and eddy-covariance field measurements were also used.In the laboratory measurements, the effects of sorption processes were evident, and filters caused a similar attenuation and delay of the signal as tubes. Filters could have a larger impact than a long tube, whereas the flow rate had a much smaller impact on the flux loss than the sorption processes (Reynolds numbers 2120–3360). The sorption model represented well the water vapor pulses...

How to Utilise the Knowledge of Causal Responses

Our physical and physiological theory provides causal explanations of various phenomena in forests. This causal nature of the theory enables versatile applications in forestry and in the research of the interactions between climate change and forests. We treat the effects of thinnings and whole-tree harvesting on wood production and the responses of forest ecosystem to nitrogen deposition in more detail. The forests react to the increasing CO2 concentration and also to temperature increase generating feedbacks from forests to climate change. The changes in the carbon storages in forest ecosystems and in the emission of volatile organic compounds are evidently the most important feedbacks from forest ecosystems to the climate change.

New Particle Formation in Clean Savannah Environment

Southern African savanna background environment lacks previous, continuous long-term combined sub-micrometer aerosol number concentration and gas measurements. We have build a mobile measurement trailer, which contains measurements of aerosol number size distributions 10-840 nm, positive and negative ion size distributions 0.4-40 nm, aerosol mass PM 10 , PM 2.5 , PM 1 , inorganic compound in PM 10 and PM 2.5 , gases like SO 2 , NO, NOx, CO, O 3 and basic meteorology. In addition, we measure periodically VOCs. The trailer is well- protected against thunder storms, electricity breaks and other typical problems. It is connected to internet via GPRS-modem. Preliminary results show that in a clean savanna environment, new particle formation takes place every sunny day, with relatively high nucleation rates and very high growth rates (up to 15 nm/h).