Final Report Summary - NANODYNAMITE (Quantifying Aerosol Nanoparticle Dynamics by High Time Resolution Experiments)
The project “nanoDynamite” aimed at the characterization of aerosol nanoparticles and their dynamical behavior. To this end we have developed new experimental tools that provide appropriate sensitivity for statistical signal evaluation at unprecedented time resolution, and allow in-situ characterization of airborne nanoparticles. Furthermore, we performed heterogeneous nucleation studies in which atomic ions were used as seed particles and we investigated the effect of temperature and relative humidity on the heterogeneous nucleation of a working fluid commonly used in condensation particle counters (CPCs). A summary of major breakthroughs is given below.
One of the major achievements of this project was the development of the DMA train. It uses six differential mobility analyzers (DMAs) in parallel that all operate at individual but fixed sizes. This way we can study nanoparticle dynamics in the 1.8 – 10 nm size range from statistical analysis of individual particle counts. The DMA train closes an important gap in the sizing of aerosol nanoparticles that could not be captured by any other technique so far. The combination of sizing instruments covering the sub-2 nm range and the range above 10 nm with the DMA train now allows the complete retrieval of size distributions emerging directly from the gas phase. The DMA train was so far mainly used in nanoparticle formation studies in the CLOUD project at CERN, Geneva, and provided detailed insights to growth mechanisms of organic particles. First ambient measurements were conducted lately in collaboration with the ERC grant A-LIFE where the DMA train measured sub-10 nm particle dynamics in Cyprus. Apparently, the DMA train reveals new particle formation events that frequently stay undiscovered in regular particle sizers.
Besides electrical mobility based particle sizing we have made substantial progress in the in-situ characterization of airborne nanoparticles by using small-angle x-ray scattering (SAXS). SAXS has been used in the past to study nucleation phenomena and aerosol synthesis in flames; however, these measurements typically required low pressures (few kPa) or particle concentrations as high as 10^13 /cc. In this project we managed to merge operating ranges of conventional aerosol techniques (CPCs, DMAs) with SAXS by applying a differential background subtraction procedure and taking several precautions for improved signal-to-noise ratios. Accordingly, we could monitor SAXS signals at ambient pressure and particle concentrations in the range of 10^6 /cc which allowed the parallel operation of conventional aerosol instruments. Remarkably, the SAXS signals not only provided information on the size and number concentration but also on the shape of the particles. This information can be used to study formation mechanisms of nanoparticles in-situ.
Another major part of the project was dedicated to fundamental studies of heterogeneous nucleation. To this end we have used a size analyzing nuclei counter (SANC) to investigate effects of seed particle size, charge, temperature and humidity on the heterogeneous nucleation of n-butanol. Using a high resolution parallel plate DMA we succeeded in performing heterogeneous nucleation experiments on atomic ions with diameters below 0.5 nm which is the smallest seed size detected so far. Also we could demonstrate that a reduction of the nucleation temperature in heterogeneous nucleation of n-butanol increases the counting efficiency of CPCs significantly shifting the cut-off diameter of these instruments to the sub-2 nm size range. Similarly, we could demonstrate that humidity plays an important role in the detection of nanoparticles composed of hygroscopic materials.
One of the major achievements of this project was the development of the DMA train. It uses six differential mobility analyzers (DMAs) in parallel that all operate at individual but fixed sizes. This way we can study nanoparticle dynamics in the 1.8 – 10 nm size range from statistical analysis of individual particle counts. The DMA train closes an important gap in the sizing of aerosol nanoparticles that could not be captured by any other technique so far. The combination of sizing instruments covering the sub-2 nm range and the range above 10 nm with the DMA train now allows the complete retrieval of size distributions emerging directly from the gas phase. The DMA train was so far mainly used in nanoparticle formation studies in the CLOUD project at CERN, Geneva, and provided detailed insights to growth mechanisms of organic particles. First ambient measurements were conducted lately in collaboration with the ERC grant A-LIFE where the DMA train measured sub-10 nm particle dynamics in Cyprus. Apparently, the DMA train reveals new particle formation events that frequently stay undiscovered in regular particle sizers.
Besides electrical mobility based particle sizing we have made substantial progress in the in-situ characterization of airborne nanoparticles by using small-angle x-ray scattering (SAXS). SAXS has been used in the past to study nucleation phenomena and aerosol synthesis in flames; however, these measurements typically required low pressures (few kPa) or particle concentrations as high as 10^13 /cc. In this project we managed to merge operating ranges of conventional aerosol techniques (CPCs, DMAs) with SAXS by applying a differential background subtraction procedure and taking several precautions for improved signal-to-noise ratios. Accordingly, we could monitor SAXS signals at ambient pressure and particle concentrations in the range of 10^6 /cc which allowed the parallel operation of conventional aerosol instruments. Remarkably, the SAXS signals not only provided information on the size and number concentration but also on the shape of the particles. This information can be used to study formation mechanisms of nanoparticles in-situ.
Another major part of the project was dedicated to fundamental studies of heterogeneous nucleation. To this end we have used a size analyzing nuclei counter (SANC) to investigate effects of seed particle size, charge, temperature and humidity on the heterogeneous nucleation of n-butanol. Using a high resolution parallel plate DMA we succeeded in performing heterogeneous nucleation experiments on atomic ions with diameters below 0.5 nm which is the smallest seed size detected so far. Also we could demonstrate that a reduction of the nucleation temperature in heterogeneous nucleation of n-butanol increases the counting efficiency of CPCs significantly shifting the cut-off diameter of these instruments to the sub-2 nm size range. Similarly, we could demonstrate that humidity plays an important role in the detection of nanoparticles composed of hygroscopic materials.