On the sources of uncertainty in the sub-3 nm particle concentration measurement

The number of experiments characterizing sub-3 nm aerosol particle dynamics has increased significantly over the recent years. In these experiments, it is essential to know/determine size resolved particle number concentrations accurately. Despite particle concentration measurement being relatively simple experiment, it can contain large uncertainties from various sources in the sub-3 nm size range. In this study we aim to identify and examine some of these sources. We simulated four different condensation particle counters (CPCs) (TSI 3777, ADI vWCPC, Airmodus A11 and an ideal CPC with d50 (lowest detection threshold) of 1.5 nm) and one differential mobility analyzer (DMA) (TSI nano DMA) and study the resulting uncertainties when using them to measure three different particle size distributions. First, we show that Poisson counting uncertainty root N represents the standard deviation, sigma, of the number of counted particles in all CPC and DMPS counting experiments. Second, the state-of-the-art DMA-CPC particle sizing system is examined with respect to counting statistics. Third, the performance of the instruments is assumed to be well-known, and instrumental non-idealities and the inversion routine are assessed. Fourth,+/- 0.5 nm offset is inserted to the CPC d50, and its effect on the measured particle concentration is examined. Our results highlight the importance of knowing the CPC d50 accurately to narrow down the particle concentration uncertainty. Furthermore, the results show that the current DMA-CPC measurements are subject to considerable counting uncertainty in low particle concentration environments. Based on the analysis we summarize suggestions for further research and instrumental development for more accurate sub-3 nm particle concentration measurements in the future.Peer reviewe

First measurements of the number size distribution of 1-2nm aerosol particles released from manufacturing processes in a cleanroom environment

This study was conducted to observe a potential formation and/or release of aerosol particles related to manufacturing processes inside a cleanroom. We introduce a novel technique to monitor airborne sub 2nm particles in the cleanroom and present results from a measurement campaign during which the total particle number concentration (>1nm and >7 nm) and the size resolved concentration in the 1 to 2nm size range were measured. Measurements were carried out in locations where atomic layer deposition (ALD), sputtering, and lithography processes were conducted, with a wide variety of starting materials. During our campaign in the clean room, we observed several time periods when the particle number concentration was 10(5) cm(-3) in the sub 2nm size range and 10(4) cm(-3) in the size class larger than 7nm in one of the sampling locations. The highest concentrations were related to the maintenance processes of the manufacturing machines, which were conducted regularly in that specific location. Our measurements show that around 500cm(-3) sub 2nm particles or clusters were in practice always present in this specific cleanroom, while the concentration of particles larger than 2nm was less than 2cm(-3). During active processes, the concentrations of sub 2nm particles could rise to over 10(5) cm(-3) due to an active new particle formation. The new particle formation was most likely induced by a combination of the supersaturated vapors, released from the machines, and the very low existing condensation sink, leading to pretty high formation rates J(1.4 nm) = (9 4) cm(-3) s(-1) and growth rates of particles (GR(1.1-1.3 nm) = (6 +/- 3) nm/h and GR(1.3-1.8 nm) = (14 +/- 3) nm/h).Copyright (c) 2017 American Association for Aerosol ResearchPeer reviewe

Production of neutral molecular clusters by controlled neutralization of mobility standards

Measuring aerosols and molecular clusters below the 3 nm size limit is essential to increase our understanding of new particle formation. Instruments for the detection of sub-3 nm aerosols and clusters exist and need to be carefully calibrated and characterized. So far calibrations and laboratory tests have been carried out using mainly electrically charged aerosols, as they are easier to handle experimentally. However, the charging state of the cluster is an important variable to take into account. Furthermore, instrument characterization performed with charged aerosols could be biased, preventing a correct interpretation of data when electrically neutral sub-3 nm aerosols are involved. This article presents the first steps to generate electrically neutral molecular clusters as standards for calibration. We show two methods: One based on the neutralization of well-known molecular clusters (mobility standards) by ions generated in a switchable aerosol neutralizer. The second is based on the controlled neutralization of mobility standards with mobility standards of opposite polarity in a recombination cell. We highlight the challenges of these two techniques and, where possible, point out solutions. In addition, we give an outlook on the next steps toward generating well-defined neutral molecular clusters with a known chemical composition and concentration.Peer reviewe

Combining instrument inversions for sub-10 nm aerosol number size-distribution measurements

Resolving aerosol dynamical processes in the sub-10 nm range is crucial for our understanding of the contribution of new particle formation to the global cloud condensation nuclei budget or air pollution. Accurate measurements of the particle size distribution in this size-range are challenging due to high diffusional losses and low charging and/or detection efficiencies. Several instruments have been developed in recent years in order to access the sub-10 nm particle size distribution; however, no single instrument can provide high counting statistics, low systematic uncertainties and high size-resolution at the same time. Here we compare several data inversion approaches that allow combining data from different sizing instruments during the inversion and provide python/Julia packages for free usage of the methods. We find that Tikhonov regularization using the L-curve method for optimal regularization parameter estimation gives very reliable results over a wide range of tested data sets and clearly improves standard inversion approaches. Kalman Filtering or regularization using a Poisson likelihood can be powerful tools, especially for well-defined chamber experiments or data from mobility spectrometers only, respectively. Nullspace optimization and non-linear iterative regression are clearly inferior compared to the aforementioned methods. We show that with regularization we can reconstruct the size-distribution measured by up to 4 different mobility particle size spectrometer systems and several particle counters for datasets from Hyytiala and Helsinki, Finland, revealing the sub-10 nm aerosol dynamics in more detail compared to a single instrument assessment.Peer reviewe

Characterization of three new condensation particle counters for sub-3 nm particle detection during the Helsinki CPC workshop : the ADI versatile water CPC, TSI 3777 nano enhancer and boosted TSI 3010

In this study we characterized the performance of three new particle counters able to detect particles smaller than 3 nm during the Helsinki condensation particle counter (CPC) workshop in summer 2016: the Aerosol Dynamics Inc. (ADI; Berkeley, USA) versatile water condensation particle counter (vWCPC), TSI 3777 nano enhancer (TSI Inc., Shoreview, USA) and modified and boosted TSI 3010-type CPC from Universite Blaise Pascal called a B3010. The performance of all CPCs was first measured with charged tungsten oxide test particles at temperature settings which resulted in supersaturation low enough to not detect any ions produced by a radioactive source. Due to similar measured detection efficiencies, additional comparison between the 3777 and vWCPC were conducted using electrically neutral tungsten oxide test particles and with positively charged tetradodecylammonium bromide. Furthermore, the detection efficiencies of the 3777 and vWCPC were measured with boosted temperature settings yielding supersaturation which was at the onset of homogeneous nucleation for the 3777 or confined within the range of liquid water for the ADI vWCPC. Finally, CPC-specific tests were conducted to probe the response of the 3777 to various inlet flow relative humidities, of the B3010 to various inlet flow rates and of the vWCPC to various particle concentrations. For the 3777 and vWCPC the measured 50% detection diameters (d50s) were in the range of 1.3-2.4 nm for the tungsten oxide particles, depending on the particle charging state and CPC temperature settings, between 2.5 and 3.3 nm for the organic test aerosol, and in the range of 3.2-3.4 nm for tungsten oxide for the B3010.Peer reviewe

Activation of sub-3 nm organic particles in the particle size magnifier using humid and dry conditions

The accurate measurement of aerosol particles and clusters smaller than 3 nm in diameter is crucial for the understanding of new particle formation processes. The particle counters used for measuring these particles are typically calibrated with metal or salt particles under dry conditions, which does not always represent the field conditions where these instruments are later used. In this study, we calibrated the All nano Condensation Nucleus Counter (nCNC), consisting of the PSM (Particle Size Magnifier) and a laminar flow butanol based CPC (Condensational Particle Counter), with well-defined biogenic oxidation products from beta-caryophyllene oxidation and compared it to a calibration with tungsten oxide under the same conditions. The organic particles were detected less efficiently than the inorganic ones. This resulted in a higher cut-off size for beta-caryophyllene oxidation products than for tungsten oxide. At the same PSM settings, the cut-off size for tungsten oxide was 1.2 nm and for beta-caryophyllene oxidation products 1.9 nm. However, repeating the calibration of the biogenic particles at 13% relative humidity at 31 degrees C, increased their detection efficiency in the PSM, increasing the cut-off diameter to 1.6 nm. Additionally, we present a comparison of the ion concentrations measured with the PSM and the NAIS (Neutral Cluster and Air Ion Spectrometer) during new particle formation experiments in the CLOUD (Cosmics Leaving Outdoors Droplets) chamber. In these experiments, we produced particles from different organic precursors, such as alpha-pinene, beta-caryophyllene and isoprene, as well as iodine. This way, we could determine the shift in cut-off diameter of the PSM for several different atmospherically relevant chemical compounds and compare it to the laboratory calibrations. We saw a diameter shift for the organic precursors of +0.3 nm in the PSM compared to the NAIS. These two approaches agreed well with each other and show that it is important to know the chemical composition of the measured particles to determine the exact size distribution using a supersaturation scanning method.Peer reviewe

Observed coupling between air mass history, secondary growth of nucleation mode particles and aerosol pollution levels in Beijing

Atmospheric aerosols have significant effects on the climate and on human health. New particle formation (NPF) is globally an important source of aerosols but its relevance especially towards aerosol mass loadings in highly polluted regions is still controversial. In addition, uncertainties remain regarding the processes leading to severe pollution episodes, concerning e.g. the role of atmospheric transport. In this study, we utilize air mass history analysis in combination with different fields related to the intensity of anthropogenic emissions in order to calculate air mass exposure to anthropogenic emissions (AME) prior to their arrival at Beijing, China. The AME is used as a semi-quantitative metric for describing the effect of air mass history on the potential for aerosol formation. We show that NPF events occur in clean air masses, described by low AME. However, increasing AME seems to be required for substantial growth of nucleation mode (diameter < 30 nm) particles, originating either from NPF or direct emissions, into larger mass-relevant sizes. This finding assists in establishing and understanding the connection between small nucleation mode particles, secondary aerosol formation and the development of pollution episodes. We further use the AME, in combination with basic meteorological variables, for developing a simple and easy-to-apply regression model to predict aerosol volume and mass concentrations. Since the model directly only accounts for changes in meteorological conditions, it can also be used to estimate the influence of emission changes on pollution levels. We apply the developed model to briefly investigate the effects of the COVID-19 lockdown on PM2.5 concentrations in Beijing. While no clear influence directly attributable to the lockdown measures is found, the results are in line with other studies utilizing more widely applied approaches.Peer reviewe

Ion-induced sulfuric acid-ammonia nucleation drives particle formation in coastal Antarctica

Formation of new aerosol particles from trace gases is a major source of cloud condensation nuclei (CCN) in the global atmosphere, with potentially large effects on cloud optical properties and Earth's radiative balance. Controlled laboratory experiments have resolved, in detail, the different nucleation pathways likely responsible for atmospheric new particle formation, yet very little is known from field studies about the molecular steps and compounds involved in different regions of the atmosphere. The scarcity of primary particle sources makes secondary aerosol formation particularly important in the Antarctic atmosphere. Here, we report on the observation of ion-induced nucleation of sulfuric acid and ammonia-a process experimentally investigated by the CERN CLOUD experiment-as a major source of secondary aerosol particles over coastal Antarctica. We further show that measured high sulfuric acid concentrations, exceeding 10(7) molecules cm(-3), are sufficient to explain the observed new particle growth rates. Our findings show that ion-induced nucleation is the dominant particle formation mechanism, implying that galactic cosmic radiation plays a key role in new particle formation in the pristine Antarctic atmosphere.Peer reviewe

From Extractivism to Global Extractivism : The Evolution of an Organizing Concept

All the named authors were members of the Helsinki Research Working Group on Global Extractivisms and Alternatives, who jointly constructed this article. Equal authorship by all authors is recognised.Research on extractivism has rapidly proliferated, expanding into new empirical and conceptual spaces. We examine the origins, evolution, and conceptual expansion of the concept. Extractivism is useful to analyze resource extraction practices around the world. ‘Global Extractivism’ is a new conceptual tool for assessing global phenomena. We situate extractivism within an ensemble of concepts, and explore its relation to development, the state, and value. Extractivism as an organizing concept addresses many fields of research. Extractivism forms a complex of self-reinforcing practices, mentalities, and power differentials underwriting and rationalizing socio-ecologically destructive modes of organizing life-through subjugation, depletion, and non-reciprocity.Peer reviewe

Variation of size-segregated particle number concentrations in wintertime Beijing

The spatial and temporal variability of the number size distribution of aerosol particles is an indicator of the dynamic behavior of Beijing's atmospheric pollution cocktail. This variation reflects the strength of different primary and secondary sources, such as traffic and new particle formation, as well as the main processes affecting the particle population. In this paper, we report size-segregated particle number concentrations observed at a newly developed Beijing station during the winter of 2018. Our measurements covered particle number size distributions over the diameter range of 1.5 nm-1 mu m (cluster mode, nucleation mode, Aitken mode and accumulation mode), thus being descriptive of a major fraction of the processes taking place in the atmosphere of Beijing. Here we focus on explaining the concentration variations in the observed particle modes, by relating them to the potential aerosol sources and sinks, and on understanding the connections between these modes. We considered haze days and new particle formation event days separately. Our results show that during the new particle formation (NPF) event days increases in cluster mode particle number concentration were observed, whereas during the haze days high concentrations of accumulation mode particles were present. There was a tight connection between the cluster mode and nucleation mode on both NPF event and haze days. In addition, we correlated the particle number concentrations in different modes with concentrations of trace gases and other parameters measured at our station. Our results show that the particle number concentration in all the modes correlated with NOx, which reflects the contribution of traffic to the whole submicron size range. We also estimated the contribution of ion-induced nucleation in Beijing, and we found this contribution to be negligible.Peer reviewe