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

Exploring the potential of nano-Köhler theory to describe the growth of atmospheric molecular clusters by organic vapors using cluster kinetics simulations

Atmospheric new particle formation (NPF) occurs by the formation of nanometer-sized molecular clusters and their subsequent growth to larger particles. NPF involving sulfuric acid, bases and oxidized organic compounds is an important source of atmospheric aerosol particles. One of the mechanisms suggested to depict this process is nano-Köhler theory, which describes the activation of inorganic molecular clusters to growth by a soluble organic vapor. In this work, we studied the capability of nano-Köhler theory to describe the initial growth of atmospheric molecular clusters by simulating the dynamics of a cluster population in the presence of a sulfuric acid–base mixture and an organic compound. We observed nano-Köhler-type activation in our simulations when the saturation ratio of the organic vapor and the ratio between organic and inorganic vapor concentrations were in a suitable range. However, nano-Köhler theory was unable to predict the exact size at which the activation occurred in the simulations. In some conditions, apparent cluster growth rate (GR) started to increase close to the activation size determined from the simulations. Nevertheless, because the behavior of GR is also affected by other dynamic processes, GR alone cannot be used to deduce the cluster growth mechanism.</p

Simple proxies for estimating the concentrations of monoterpenes and their oxidation products at a boreal forest site

The oxidation products of monoterpenes likely have a crucial role in the formation and growth of aerosol particles in boreal forests. However, the continuous measurements of monoterpene concentrations are usually not available on decadal timescales, and the direct measurements of the concentrations of monoterpene oxidation product have so far been scarce. In this study we developed proxies for the concentrations of monoterpenes and their oxidation products at a boreal forest site in Hyytiala, southern Finland. For deriving the proxies we used the monoterpene concentration measured with a proton transfer reaction mass spectrometer (PTR-MS) during 2006-2013. Our proxies for the monoterpene concentration take into account the temperature-controlled emissions from the forest ecosystem, the dilution caused by the mixing within the boundary layer and different oxidation processes. All the versions of our proxies captured the seasonal variation of the monoterpene concentration, the typical proxy-to-measurements ratios being between 0.8 and 1.3 in summer and between 0.6 and 2.6 in winter. In addition, the proxies were able to describe the diurnal variation of the monoterpene concentration rather well, especially in summer months. By utilizing one of the proxies, we calculated the concentration of oxidation products of monoterpenes by considering their production in the oxidation and their loss due to condensation on aerosol particles. The concentration of oxidation products was found to have a clear seasonal cycle, with a maximum in summer and a minimum in winter. The concentration of oxidation products was lowest in the morning or around noon and highest in the evening. In the future, our proxies for the monoterpene concentration and their oxidation products can be used, for example, in the analysis of new particle formation and growth in boreal environments.Peer reviewe

CyberParks Songs and Stories - Enriching Public Spaces with Localized Culture Heritage Material such as Digitized Songs and Stories.

This chapter offers theoretical considerations and reflections on technological solutions that contribute to digitally supported documentation, access and reuse of localised heritage content in public spaces. It addresses immaterial cultural heritage, including informal stories that could emerge and be communicated by drawing hyperlinks between digitised assets, such as songs, images, drawings, texts and more, and not yet documented metadata, as well as augmenting interaction opportunities with interactive elements that relate to multiple media stored in databases and archives across Europe. The aim is to enable cultural heritage to be experienced in novel ways, supported by the proliferation of smartphones and ubiquitous Internet access together with new technical means for user profiling, personalisation, localisation, context-awareness and gamification. The chapter considers cyberparks as digitally enhanced public spaces for accessing and analyzing European cultural heritage and for enriching the interpretation of the past, along with theoretical ramifications and technological limitations. It identifies the capacities of a proposed digital environment together with design guidelines for interaction with cultural heritage assets in public spaces. The chapter concludes with describing a taxonomy of digital content that can be used in order to enhance association and occupation conditions of public spaces, and with discussing technological challenges associated with enriching public spaces with localized cultural heritage material

On Model Selection, Bayesian Networks, and the Fisher Information Integral

We study BIC-like model selection criteria and in particular, their refinements that include a constant term involving the Fisher information matrix. We perform numerical simulations that enable increasingly accurate approximation of this constant in the case of Bayesian networks. We observe that for complex Bayesian network models, the constant term is a negative number with a very large absolute value that dominates the other terms for small and moderate sample sizes. For networks with a fixed number of parameters, d, the leading term in the complexity penalty, which is proportional to d, is the same. However, as we show, the constant term can vary significantly depending on the network structure even if the number of parameters is fixed. Based on our experiments, we conjecture that the distribution of the nodes’ outdegree is a key factor. Furthermore, we demonstrate that the constant term can have a dramatic effect on model selection performance for small sample sizes.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

Growth of atmospheric clusters involving cluster-cluster collisions : comparison of different growth rate methods

We simulated the time evolution of atmospheric cluster concentrations in a one-component system where not only do clusters grow by condensation of monomers, but cluster-cluster collisions also significantly contribute to the growth of the clusters. Our aim was to investigate the consistency of the growth rates of sub-3aEuro-nm clusters determined with different methods and the validity of the common approach to use them to estimate particle formation rates. We compared the growth rate corresponding to particle fluxes (FGR), the growth rate derived from the appearance times of clusters (AGR), and the growth rate calculated based on irreversible vapor condensation (CGR). We found that the relation between the different growth rates depends strongly on the external conditions and the properties of the model substance. The difference between the different growth rates was typically highest at the smallest, sub-2aEuro-nm sizes. FGR was generally lower than AGR and CGR; at the smallest sizes the difference was often very large, while at sizes larger than 2aEuro-nm the growth rates were closer to each other. AGR and CGR were in most cases close to each other at all sizes. The difference between the growth rates was generally lower in conditions where cluster concentrations were high, and evaporation and other losses were thus less significant. Furthermore, our results show that the conventional method used to determine particle formation rates from growth rates may give estimates far from the true values. Thus, care must be taken not only in how the growth rate is determined but also in how it is applied.Peer reviewe

Measurement report: Atmospheric new particle formation at a peri-urban site in Lille, northern France

Formation of ultrafine particles (UFPs) in the urban atmosphere is expected to be less favored than in the rural atmosphere due to the high existing particle surface area acting as a sink for newly formed particles. Despite large condensation sink (CS) values, previous comparative studies between rural and urban sites reported higher frequency of new particle formation (NPF) events over urban sites in comparison to background sites as well as higher particle formation and growth rates attributed to the higher concentration of condensable species. The present study aims at a better understanding the environmental factors favoring, or disfavoring, atmospheric NPF over Lille, a large city in the north of France, and to analyze their impact on particle number concentration using a 4-year long-term dataset. The results highlight a strong seasonal variation of NPF occurrences with a maximum frequency observed during spring (27 events) and summer (53 events). It was found that high temperature (T&gt;295 K), low relative humidity (RH &lt;45 %), and high solar radiation are ideal to observe NPF events over Lille. Relatively high CS values (i.e., ∼2×10-2 s−1) are reported during event days suggesting that high CS does not inhibit the occurrence of NPF over the ATmospheric Observations in LiLLE (ATOLL) station. Moreover, the particle growth rate was positively correlated with temperatures most probably due to higher emission of precursors. Finally, the nucleation strength factor (NSF) was calculated to highlight the impact of those NPF events on particle number concentrations. NSF reached a maximum of four in summer, evidencing a huge contribution of NPF events to particle number concentration at this time of the year.</p