Preprints  

The exact point at which a given assembly of molecules represent an atmospheric molecular cluster or a particle remains ambiguous. Using quantum chemical methods we here explore the cluster-to-particle transition point. Based on our results, we deduce a property-based criteria for defining “freshly nucleated particles (FNPs)”, that act as a boundary between discrete cluster configurations and bulk particles.

This study examines new particle formation (NPF) in the Bolivian Andes at Chacaltaya mountain (CHC) and the urban El Alto-La Paz area (EAC). Days are clustered into four categories based on NPF intensity. Differences in particle size, precursor gases, and pollution levels are found. High NPF intensities increased Aitken mode particle concentrations at both sites, while volcanic influence selectively diminished NPF intensity at CHC but not EAC. This study highlights NPF dynamics in the Andes.

With the recently developed instrument CIC (cluster ion counter) we can observe dynamics of small air ions and intermediate air ions. Furthermore we can observe condensation sink and formation and growth rates for intermediated ions.

The performances of different particle lung deposited surface area (LDSA^al) measurement methods (Partector, ELPI+, SMPS/DMPS) were compared in ambient conditions. As LDSA^al is a health-relevant metric and rather easy to utilise in air quality monitoring, it is crucial to know how the different methods agree as there are clear differences in their operation. In all, comparison of different methods can be complicated, but, still, the methods agree rather well in terms of local pollution (<400 nm).

Black Carbon (BC) is a pollutant from combustion that affects the climate and is harmful to health. We tested four different small BC sensors with a reference in Helsinki. The sensors compared well with the reference. As a sensor network they were able to capture differences in BC. Changes in temperature (T) and relative humidity (RH) caused error in the measurement. To reduce the effects of T and RH on BC sensors, more robust boxes should be developed or corrections should be applied.

Surface morphology is critical for enhanced performance in thin films. However, there is limited understanding regarding the accurate control of thin film morphology and earlier studies do not give a systematic way of optimizing different parameters to achieve the desired morphologies. This study identifies parameters that are most relevant for controlling thin film morphology. A systematic design schedule for electrosprayed thin films with different surface morphologies has also been developed.

More than 35'000 particle counters designed for the periodic technical inspection of diesel engine exhaust have been placed on the European market in the past few years. This work shows that the counting efficiency of these instruments depend on the properties of the test aerosols, even if all of them are combustion-based soot of similar mobility diameter. The aim of this study is to promote harmonisation of measurement procedures in the field of emission control.

Although spray flame synthesis (SFS) is a promising approach to prepare nano materials with tailored properties, the impurity formation is not fully understood in SFS. To contribute to this topic, maghemite nanoparticles were prepared by SFS, and two complementary experimental approaches were used to investigate the evolution of soot and carbonaceous surface adsorbates. The methodological procedure and the data provided can be used to denote/compare SFS-materials more reliably in the future.

Several papers have reported on electrospray technique and they have shown that uniform thin films with different surface morphologies can be deposited. Nonetheless, the studies do not give a systematic way of designing different surface morphologies and most outcomes are based on a trial-and-error method. Therefore, in this study a systematic way of designing thin films of different surface morphologies using electrospray technique has been developed.