Characterization of a high-resolution supercritical differential mobility analyzer at reduced flow rates

Classifying sub-3 nm particles effectively with relatively high penetration efficiencies and sizing resolutions is important for atmospheric new particle formation studies. A high-resolution supercritical differential mobility analyzer (half-mini DMA) was recently improved to classify aerosols at a sheath flow rate less than 100 L/min. In this study, we characterized the transfer functions, the penetration efficiencies, and the sizing resolution of the new half-mini DMA at the aerosol flow rate of 2.5-10 L/min and the sheath flow rate of 25-250 L/min using tetra-alkyl ammonium ions and tungsten oxide particles. The transfer functions of the new half-mini DMA at an aerosol flow rate lower than 5 L/min and a sheath flow rate lower than 150 L/min agree well with predictions using a theoretical diffusing transfer function. The penetration efficiencies can be approximated using an empirical formula. When classifying 1.48 nm molecular ions at an aerosol-to-sheath flow ratio of 5/50 L/min, the penetration efficiency, the sizing resolution, and the multiplicative broadening factor of the new half-mini DMA are 0.18, 6.8, and 1.11, respectively. Compared to other sub-3 nm DMAs applied in atmospheric measurements (e.g. the mini-cyDMA, the TSI DMA 3086, the TSI nanoDMA 3085, and the Grimm S-DMA), the new half-mini DMA characterized in this study is able to classify particles at higher aerosol and sheath flow rates, leading to a higher sizing resolution at the same aerosol-to-sheath flow ratio. Accordingly, the new half-mini DMA can reduce the uncertainties in atmospheric new particle formation measurement if coupled with an aerosol detector that could work at the corresponding high aerosol flow rate. (c) 2018 American Association for Aerosol ResearchPeer reviewe

New instrument for measuring atmospheric concentrations of non-OH oxidants of SO2

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Laboratory verification of a new high flow differential mobility particle sizer, and field measurements in Hyytiälä

Measurement of atmospheric sub-10 nm nanoparticle number concentrations has been of substantial interest recently, which, however, is subject to considerable uncertainty. We report a laboratory characterization of a high flow differential mobility particle sizer (HFDMPS), which is based on the Half-mini type differential mobility analyzer (DMA) and nano condensation nuclei counter (A11), and show the first results from atmospheric observations. The HFDMPS utilizes the state-of-the-art aerosol technology, and is optimized for sub-10 nm particle size distribution measurements by a moderate resolution DMA, optimized and characterized low-loss particle sampling line and minimal dilution in the detector. We present an exhaustive laboratory calibration to the HFDMPS and compare the measured size data to the Hyytiala long-term DMPS and Neutral cluster and ion spectrometer. The HFDMPS detects about two times higher 3-10 nm particle concentrations than the long-term DMPS, and the counting uncertainties are halved as compared to the long-term DMPS. The HFDMPS did not observe any sub-2.5 nm particles in Hyytiala, and the reason for that was shown to be the inability of diethylene glycol to condense on such small biogenic particles. Last, we discuss the general implications of our results to the sub-10 nm DMPS based measurements.Peer reviewe

On the time response determination of condensation particle counters

Condensation particle counter (CPC) technology has continued to evolve, with the introduction of several new instruments over the last several years. An important aspect in the characterization of these instruments is the measurement of their time response. Yet there is no standardly accepted approach for this measurement. Here we evaluate different classically used methods for determining CPC time response, and present the potential pitfalls associated with these approaches. Further, we introduce a new simple definition for the term response time, E, which is based on the first-order systems response, while providing a practical definition by corresponding to approximate to 95% change in concentration. We also present results for various commonly used CPCs, and for the Airmodus A11 nano Condensation Nucleus Counter (nCNC) system, the TSI 3777+3772 Nano Enhancer system, and Aerosol Dynamics Inc.'s (ADI) new versatile water condensation particle counter.Copyright (c) 2018 American Association for Aerosol ResearchPeer reviewe

Operation of the Airmodus A11 nano Condensation Nucleus Counter at various inlet pressures and various operation temperatures, and design of a new inlet system

Measuring sub-3 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 1-6 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 4.5 nm. Finally, our view of the guidelines for the optimal use of the Airmodus nCNC is provided.Peer reviewe

Diurnal evolution of negative atmospheric ions above the boreal forest : from ground level to the free troposphere

At SMEAR II research station in Hyytiala, located in the Finnish boreal forest, the process of new particle formation and the role of ions has been investigated for almost 20 years near the ground and at canopy level. However, above SMEAR II, the vertical distribution and diurnal variation of these different atmospheric ions are poorly characterized. In this study, we assess the atmospheric ion composition in the stable boundary layer, residual layer, mixing layer, and free troposphere, and the evolution of these atmospheric ions due to photochemistry and turbulent mixing through the day. To measure the vertical profile of atmospheric ions, we developed a tailored set-up for online mass spectrometric measurements, capable of being deployed in a Cessna 172 with minimal modifications. Simultaneously, instruments dedicated to aerosol properties made measurements in a second Cessna. We conducted a total of 16 measurement flights in May 2017, during the spring, which is the most active new particle formation season. A flight day typically consisted of three distinct flights through the day (dawn, morning, and afternoon) to observe the diurnal variation and at different altitudes (from 100 to 3200 m above ground), to capture the boundary layer development from the stable boundary layer, residual layer to mixing layer, and the free troposphere. Our observations showed that the ion composition is distinctly different in each layer and depends on the air mass origin and time of the day. Before sunrise, the layers are separated from each other and have their own ion chemistry. We observed that the ions present within the stable layer are of the same composition as the ions measured at the canopy level. During daytime when the mixing layer evolved and the compounds are vertically mixed, we observed that highly oxidized organic molecules are distributed to the top of the boundary layer. The ion composition in the residual layer varies with each day, showing similarities with either the stable boundary layer or the free troposphere. Finally, within the free troposphere, we detected a variety of carboxylic acids and ions that are likely containing halogens, originating from the Arctic Sea.Peer reviewe

Comprehensive global genome dynamics of Chlamydia trachomatis show ancient diversification followed by contemporary mixing and recent lineage expansion.

Chlamydia trachomatis is the world's most prevalent bacterial sexually transmitted infection and leading infectious cause of blindness, yet it is one of the least understood human pathogens, in part due to the difficulties of in vitro culturing and the lack of available tools for genetic manipulation. Genome sequencing has reinvigorated this field, shedding light on the contemporary history of this pathogen. Here, we analyze 563 full genomes, 455 of which are novel, to show that the history of the species comprises two phases, and conclude that the currently circulating lineages are the result of evolution in different genomic ecotypes. Temporal analysis indicates these lineages have recently expanded in the space of thousands of years, rather than the millions of years as previously thought, a finding that dramatically changes our understanding of this pathogen's history. Finally, at a time when almost every pathogen is becoming increasingly resistant to antimicrobials, we show that there is no evidence of circulating genomic resistance in C. trachomatis

Pienitehoinen korkeajännitelähde aerosolimittauksiin

Tässä insinöörityössä suunniteltiin ja rakennettiin pienitehoinen säädettävä 10 kV:n tarkkuusjännitelähde, erityisesti DMA:han (Differential Mobility Analyzer) perustuvien aerosolimittausten tarpeisiin. Työssä panostettiin lähteen laajaan säätöalueeseen sekä tarkkuuteen erityisesti pienillä jännitteillä. Jännitelähteen käyttötarkoitus on halutun sähkökentän luominen DMA:n sisälle. Työssä suunniteltiin jännitelähde, joka helpottaa aerosolimittauksia, sen laajan säätöalueen, tarkkuuden sekä helpon käytettävyyden avulla. Aikaisemmin käytettyjen jännitelähteiden suurimmat ongelmat ovat niiden alimman tuotetun jännitteen rajallisuudessa ja stabiiliudessa. Lisäksi aikaisemmin käytössä olleita jännitelähteitä voidaan ohjata ainoastaan analogisilla signaaleilla, jotka ovat herkkiä häiriölle, ja tarvitsevat tietokoneeseen kytkettäessä erillisen ohjauskortin. Suunniteltu jännitelähde voidaan liittää tietokoneeseen sarjaportin kautta. Lisäksi usean jännitelähteen ohjaaminen samasta sarjaportista on mahdollista laitteita ketjuttamalla. Työssä tutkittiin ja ratkottiin erilaisia mittaustarkkuuteen vaikuttavia ilmiöitä, kuten vastusten epälineaarisuus jännitteen ja lämpötilan suhteen. Rakennettu laite sisältää kaksi hakkuriastetta ja operaatiovahvistimeen perustuvan lineaarisen shunttiregulaattorin. Laitteessa tuotetaan ja mitataan tasajännitesignaaleja, joiden tarkkuus on muutamia kymmeniä mikrovoltteja. Insinöörityön tuloksena syntyi tarkka korkeajännitelähde, josta voidaan rakentaa useampia kappaleita. Rakennetun jännitelähteen virhe asetusjännitteestä on pienempi kuin 2 promillea yli 100 V:n jännitteillä sekä pienempi kuin 200 mV alle 100 V:n jännitteillä.In this thesis a 10 kV low-power high voltage supply for DMA (Differential Mobility Analyzer) based aerosol measurements was designed and constructed. The main focus was to achieve a wide output voltage range and precision with a single device. The main function of the device is to produce the desired voltage to the electrodes inside the DMA. The goal was to produce a high voltage supply that fits better to its task than the currently used ones. Previously used supplies lack precision in low voltages, so two voltage supplies are required to generate voltages in the whole range required. Also the lack of direct digital method of controlling the output voltage is an issue. Analog signals are sensitive to error and cannot be directly generated from a computer. An additional control device is required to generate analog signals. The constructed high voltage supply can be controlled digitally through a serial port and multiple devices can be connected to the same port by chaining the devices. One of the main challenges in the thesis was the resistor nonlinearity against high voltage and temperature. Other big challenges were generation and measurement of low voltage signals of a couple of μV. The device consists of two switching mode stages and a linear shunt regulator based on low offset operational amplifier. Switching mode stages are driven by microcontroller with pulse width modulation signals. As a result of the thesis, a reproducible precision high voltage supply was created. The constructed device output voltage error is less than 2 ‰ from setpoint on voltages above 100 V and less than 200 mV on voltages below 100 V

The Pokémon GO Experience: A Location-Based Augmented Reality Mobile Game Goes Mainstream

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Data inversion methods to determine sub-3 nm aerosol size distributions using the particle size magnifier

Measuring particle size distribution accurately down to approximately 1 nm is needed for studying atmospheric new particle formation. The scanning particle size magnifier (PSM) using diethylene glycol as a working fluid has been used for measuring sub-3 nm atmospheric aerosol. A proper inversion method is required to recover the particle size distribution from PSM raw data. Similarly to other aerosol spectrometers and classifiers, PSM inversion can be deduced from a problem described by the Fredholm integral equation of the first kind. We tested the performance of the stepwise method, the kernel function method (Lehtipalo et al., 2014), the H&A linear inversion method (Hagen and Alofs, 1983), and the expectation-maximization (EM) algorithm. The stepwise method and the kernel function method were used in previous studies on PSM. The H&A method and the expectation-maximization algorithm were used in data inversion for the electrical mobility spectrometers and the diffusion batteries, respectively (Maher and Laird, 1985). In addition, Monte Carlo simulation and laboratory experiments were used to test the accuracy and precision of the particle size distributions recovered using four inversion methods. When all of the detected particles are larger than 3 nm, the stepwise method may report false sub-3 nm particle concentrations because an infinite resolution is assumed while the kernel function method and the H&A method occasionally report false sub-3 nm particles because of the unstable least squares method. The accuracy and precision of the recovered particle size distribution using the EM algorithm are the best among the tested four inversion methods. Compared to the kernel function method, the H&A method reduces the uncertainty while keeping a similar computational expense. The measuring uncertainties in the present scanning mode may contribute to the uncertainties of the recovered particle size distributions. We suggest using the EM algorithm to retrieve the particle size distributions using the particle number concentrations recorded by the PSM. Considering the relatively high computation expenses of the EM algorithm, the H&A method is recommended for preliminary data analysis. We also gave practical suggestions on PSM operation based on the inversion analysis.Peer reviewe