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Franchin A.,University of Helsinki | Downard A.,California Institute of Technology | Kangasluoma J.,University of Helsinki | Nieminen T.,University of Helsinki | And 11 more authors.
Atmospheric Measurement Techniques | Year: 2016

Reliable and reproducible measurements of atmospheric aerosol particle number size distributions below 10 nm require optimized classification instruments with high particle transmission efficiency. Almost all differential mobility analyzers (DMAs) have an unfavorable potential gradient at the outlet (e.g., long column, Vienna type) or at the inlet (nano-radial DMA), preventing them from achieving a good transmission efficiency for the smallest nanoparticles. We developed a new high-transmission inlet for the Caltech nano-radial DMA (nRDMA) that increases the transmission efficiency to 12 % for ions as small as 1.3 nm in Millikan-Fuchs mobility equivalent diameter, Dp (corresponding to 1.2 × 10-4 m2 V-1 s-1 in electrical mobility). We successfully deployed the nRDMA, equipped with the new inlet, in chamber measurements, using a particle size magnifier (PSM) and as a booster a condensation particle counter (CPC). With this setup, we were able to measure size distributions of ions within a mobility range from 1.2 × 10-4 to 5.8 × 10-6 m2 V-1 s-1. The system was modeled, tested in the laboratory and used to measure negative ions at ambient concentrations in the CLOUD (Cosmics Leaving Outdoor Droplets) 7 measurement campaign at CERN. We achieved a higher size resolution (R Combining double low line 5.5 at Dp = 1.47 nm) than techniques currently used in field measurements (e.g., Neutral cluster and Air Ion Spectrometer (NAIS), which has a R ∼ 2 at largest sizes, and R ∼ 1.8 at Dp = 1.5 nm) and maintained a good total transmission efficiency (6.3 % at Dp = 1.5 nm) at moderate inlet and sheath airflows (2.5 and 30 L min-1, respectively). In this paper, by measuring size distributions at high size resolution down to 1.3 nm, we extend the limit of the current technology. The current setup is limited to ion measurements. However, we envision that future research focused on the charging mechanisms could extend the technique to measure neutral aerosol particles as well, so that it will be possible to measure size distributions of ambient aerosols from 1 nm to 1 μm. © Author(s) 2016.


Wimmer D.,Goethe University Frankfurt | Wimmer D.,University of Helsinki | Lehtipalo K.,University of Helsinki | Lehtipalo K.,Airmodus Ltd | And 13 more authors.
Atmospheric Measurement Techniques | Year: 2013

When studying new particle formation, the uncertainty in determining the "true" nucleation rate is considerably reduced when using condensation particle counters (CPCs) capable of measuring concentrations of aerosol particles at sizes close to or even at the critical cluster size (1-2 nm). Recently, CPCs able to reliably detect particles below 2 nm in size and even close to 1 nm became available. Using these instruments, the corrections needed for calculating nucleation rates are substantially reduced compared to scaling the observed formation rate to the nucleation rate at the critical cluster size. However, this improved instrumentation requires a careful characterization of their cut-off size and the shape of the detection efficiency curve because relatively small shifts in the cut-off size can translate into larger relative errors when measuring particles close to the cut-off size. Here we describe the development of two continuous-flow CPCs using diethylene glycol (DEG) as the working fluid. The design is based on two TSI 3776 counters. Several sets of measurements to characterize their performance at different temperature settings were carried out. Furthermore, two mixing-type particle size magnifiers (PSM) A09 from Airmodus were characterized in parallel. One PSM was operated at the highest mixing ratio (1 L min-1 saturator flow), and the other was operated in a scanning mode, where the mixing ratios are changed periodically, resulting in a range of cut-off sizes. The mixing ratios are determined by varying the saturator flow, where the aerosol flow stays constant at 2.5 L min-1. Different test aerosols were generated using a nano-differential mobility analyser (nano-DMA) or a high-resolution DMA, to obtain detection efficiency curves for all four CPCs. One calibration setup included a high-resolution mass spectrometer (APi-TOF) for the determination of the chemical composition of the generated clusters. The lowest cut-off sizes were achieved with negatively charged ammonium sulfate clusters, resulting in cut-offs of 1.4 nm for the laminar flow CPCs and 1.2 and 1.1 nm for the PSMs. A comparison of one of the laminar-flow CPCs and one of the PSMs measuring ambient and laboratory air showed good agreement between the instruments. © Author(s) 2013. CC Attribution 3.0 License.


Kuang C.,Brookhaven National Laboratory | Kangasluoma J.,University of Helsinki | Wimmer D.,University of Helsinki | Wimmer D.,Goethe University Frankfurt | And 5 more authors.
AIP Conference Proceedings | Year: 2013

A size-resolved condensation particle counter battery (SR-CPCb) was developed to infer the composition of freshly nucleated aerosol down to 1 nm in diameter. This was accomplished by exploiting the strong dependence of CPC counting efficiency on particle composition and CPC working fluid. The SR-CPCb consists of CPCs that are optimized for sub 2 nm particle detection using the following working fluids: diethylene glycol, water, and butanol. Laboratory characterizations of the SR-CPCb were performed for challenge aerosols of various compositions down to 1 nm in diameter. © 2013 AIP Publishing LLC.


Wimmer D.,Goethe University Frankfurt | Wimmer D.,University of Helsinki | Lehtipalo K.,University of Helsinki | Franchin A.,University of Helsinki | And 12 more authors.
AIP Conference Proceedings | Year: 2013

The counting efficiencies of 2 different types of diethylene-glycol (DEG) based Condensation Particle Counters (CPCs) is described and discussed. The development of two laminar flow CPCs, sensitive in the size range below 3 nm is described. The two types used are a modified TSI 3776 laminar diffusion-type CPC operating with DEG instead of butanol (DEG-CPC) and a turbulent mixing Particle Size Magnifier (PSM) A09 from Airmodus. For each of the two types two different systems with slightly different settings have been investigated, respectively. The two laminar flow CPCs were operated at different temperature settings, where one of the mixing type systems was running at a fixed saturation ratio and therefore had a fixed cut-off diameter and the other one was opaerated in scanning mode. Various different test aerosols have been generated to obtain cut-off curves for all four different CPCs. The main focus was on measuring the counting efficiencies under well controlled laboratory conditions. Therefore a high resolution mass spectrometer was used in the setup as well. © 2013 AIP Publishing LLC.


Kangasluoma J.,University of Helsinki | Junninen H.,University of Helsinki | Lehtipalo K.,University of Helsinki | Lehtipalo K.,Airmodus Ltd. | And 8 more authors.
Aerosol Science and Technology | Year: 2013

To calibrate a newly developed condensation particle counter, samples of known chemical composition are needed as the chemistry plays a role in the activation process. For that, we have built a calibration setup and produced ammonium sulfate, sodium chloride, tungsten oxide, silver, alkyl halide, and ionic liquid clusters down to 1 nm in mobility diameter in positive and negative mode. The chemical composition of most negatively charged clusters was solved using high-resolution mass spectrometer and we identified about 70% of the total signal of the mass spectrometer. For the Airmodus Particle Size Magnifier, which was the instrument to be calibrated, we measured cutoff diameters of 1.1, 1.3, 1.4, 1.6, and 1.6-1.8 nm for negative sodium chloride, ammonium sulfate, tungsten oxide, silver, and positive organics, respectively. From the alkyl halide and ionic liquid experiments, we concluded that the composition plays a bigger role than the charge state of the cluster in the activation process. We also showed that relative humidity of the sample flow can change the detection efficiency of the Particle Size Magnifier, which adds some uncertainties to the measured number concentrations. © 2013 American Association for Aerosol Research.


Kangasluoma J.,University of Helsinki | Franchin A.,University of Helsinki | Duplissy J.,University of Helsinki | Ahonen L.,University of Helsinki | And 9 more authors.
Atmospheric Measurement Techniques | Year: 2016

Measuring sub-3g nm particles outside of controlled laboratory conditions is a challenging task, as many of the instruments are operated at their limits and are subject to changing ambient conditions. In this study, we advance the current understanding of the operation of the Airmodus A11 nano Condensation Nucleus Counter (nCNC), which consists of an A10 Particle Size Magnifier (PSM) and an A20 Condensation Particle Counter (CPC). The effect of the inlet line pressure on the measured particle concentration was measured, and two separate regions inside the A10, where supersaturation of working fluid can take place, were identified. The possibility of varying the lower cut-off diameter of the nCNC was investigated; by scanning the growth tube temperature, the range of the lower cut-off was extended from 1-2.5 to 1-6g nm. Here we present a new inlet system, which allows automated measurement of the background concentration of homogeneously nucleated droplets, minimizes the diffusion losses in the sampling line and is equipped with an electrostatic filter to remove ions smaller than approximately 4.5g nm. Finally, our view of the guidelines for the optimal use of the Airmodus nCNC is provided. © 2016 Author(s).


Kangasluoma J.,University of Helsinki | Junninen H.,University of Helsinki | Lehtipalo K.,University of Helsinki | Lehtipalo K.,Airmodus Ltd. | And 8 more authors.
AIP Conference Proceedings | Year: 2013

We studied the chemical composition of commonly used condensation particle counter calibration ions with a mass spectrometer and found that in our calibration setup the negatively charged ammonium sulphate, sodium chloride and tungsten oxide are the least contaminated whereas silver on both positive and negative and the three mentioned earlier in positive mode are contaminated with organics. We report cut-off diameters for Airmodus Particle Size Magnifier (PSM) 1.1, 1.3, 1.4, 1.6 and 1.6-1.8 nm for negative sodium chloride, ammonium sulphate, tungsten oxide, silver and positive organics, respectively. To study the effect of sample relative humidity on detection efficiency of the PSM we used different humidities in the differential mobility analyzer sheath flow and found that with increasing relative humidity also the detection efficiency of the PSM increases. © 2013 AIP Publishing LLC.


Wimmer D.,Goethe University Frankfurt | Wimmer D.,University of Helsinki | Lehtipalo K.,University of Helsinki | Lehtipalo K.,Airmodus Ltd. | And 17 more authors.
Atmospheric Chemistry and Physics | Year: 2015

Over the last few years, several condensation particle counters (CPCs) capable of measuring in the sub-3 nm size range have been developed. Here we study the performance of CPCs based on diethylene glycol (DEG) at different temperatures during Cosmics Leaving OUtdoor Droplets (CLOUD) measurements at CERN. The data shown here are the first set of verification measurements for sub-3 nm CPCs under upper tropospheric temperatures using atmospherically relevant aerosol particles. To put the results in perspective we calibrated the DEG-CPC at room temperature, resulting in a cut-off diameter of 1.4 nm. All diameters refer to mobility equivalent diameters in this paper. At upper tropospheric temperatures ranging from 246.15 K to 207.15 K, we found cut-off sizes relative to a particle size magnifier in the range of 2.5 to 2.8 nm. Due to low number concentration after size classification, the cut-off diameters have a high uncertainty (±0.3 nm) associated with them. Operating two laminar flow DEG-CPCs with different cut-off sizes together with other aerosol instruments, we looked at the growth rates of aerosol population in the CLOUD chamber for particles smaller than 10 nm at different temperatures. A more consistent picture emerged when we normalized the growth rates to a fixed gas-phase sulfuric acid concentration. All of the instruments detected larger growth rates at lower temperatures, and the observed growth rates decreased as a function of temperature, showing a similar trend for all instruments. The theoretical calculations had a similar but much smaller temperature dependency. © Author(s) 2015.


Schobesberger S.,University of Helsinki | Vaananen R.,University of Helsinki | Leino K.,University of Helsinki | Virkkula A.,University of Helsinki | And 12 more authors.
Boreal Environment Research | Year: 2013

We conducted airborne observations of aerosol physical properties over the southern Finland boreal forest environment. The aim was to investigate the lower tropospheric aerosol (up to 4-km altitude) over an area of 250 by 200 km, in particular during new particle formation (NPF) events, and to address the spatial variability of aerosol number concentration and number size distribution. The regional NPF events, detected both airborne and at the ground, with air masses originating from the Arctic or northern Atlantic Ocean were studied throughout the boundary layer and throughout the area covered. Three suitable case studies are presented in more detail. In two of these studies, the concentrations of nucleation mode particles (3-10 nm in diameter) were found considerably higher (up to a factor of 30) in the upper parts of the planetary boundary layer compared to ground-based measurements during the nucleation events. The observed vertical variation can be connected to boundary layer dynamics and interactions between the boundary layer and the lower free troposphere, likely yielding high concentrations of newly formed aerosol particles. Our results suggest that nucleation does not necessarily occur close to the surface. In one presented case we found evidence of NPF occurring in a limited area above cloud, in the complete absence of a regional NPF event. © 2013.


Rose C.,CNRS Laboratory of Physics and Meteorology | Sellegri K.,CNRS Laboratory of Physics and Meteorology | Asmi E.,Finnish Meteorological Institute | Hervo M.,CNRS Laboratory of Physics and Meteorology | And 9 more authors.
Atmospheric Chemistry and Physics | Year: 2015

The formation of new aerosol particles in the atmosphere is a key process influencing the aerosol number concentration as well as the climate, in particular at high altitude, where the newly formed particles directly influence cloud formation. However, free tropospheric new particle formation (NPF) is poorly documented due to logistic limitations and complex atmospheric dynamics around high-altitude stations that make the observation of this day-time process challenging. Recent improvements in measurement techniques make now possible the detection of neutral clusters down to ∼ 1 nm sizes, which opens new horizons in our understanding of the nucleation process. Indeed, only the charged fraction of clusters has been reported in the upper troposphere up to now. Here we report day-time concentrations of charged and neutral clusters (1 to 2.5 nm mobility diameter) recorded at the interface between the boundary layer (BL) and the FT as well as in the FT at the altitude site of Puy de Dôme (1465 m a.s.l.), central France, between 10 and 29 February 2012. Our findings demonstrate that in the FT, and especially at the interface between the BL and the FT, the formation of 1.5 nm neutral clusters significantly exceeds the one of ionic clusters during NPF events, clearly indicating that they dominate in the nucleation process. We also observe that the total cluster concentration significantly increases during NPF events compared to the other days, which was not clearly observed for the charged cluster population in the past. During the studied period, the nucleation process does not seem to be sulfuric acid-limited and could be promoted by the transport of pollutants to the upper troposphere, coupled with low temperatures. © 2015 Author(s).

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