Browsing by Subject "SIZE DISTRIBUTION"

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  • Yli-Juuti, Taina; Tikkanen, Olli-Pekka; Manninen, Hanna E.; Nieminen, Tuomo; Kulmala, Markku (2016)
    We analyzed nanoparticle growth during new-particle-formation events based on ten years of measurements carried out at a boreal forest site in Hyytiala, Finland, concentrating on the sub-3 nm particles and the role of sulfuric acid in their growth. Growth rates of 1.5-3 nm diameter particles were determined from ion spectrometer measurements and compared with parameterized sulfuric acid concentration and other atmospheric parameters. The calculated growth rates from sulfuric acid condensation were on average 7.4% of the observed growth rates and the two did not correlate. These suggest that neither sulfuric acid monomer condensation nor coagulation of small sulfuric acid clusters was the primary growth mechanism in these atmospheric conditions. Also no clear sign of organic condensation being the single main growth mechanism was seen. These observations are consistent with the hypothesis that several factors have comparative roles in the sub-3 nm growth.
  • Yao, Lei; Garmash, Olga; Bianchi, Federico; Zheng, Jun; Yan, Chao; Kontkanen, Jenni; Junninen, Heikki; Mazon, Stephany Buenrostro; Ehn, Mikael; Paasonen, Pauli; Sipilä, Mikko; Wang, Mingyi; Wang, Xinke; Xiao, Shan; Chen, Hangfei; Lu, Yiqun; Zhang, Bowen; Wang, Dongfang; Fu, Qingyan; Geng, Fuhai; Li, Li; Wang, Hongli; Qiao, Liping; Yang, Xin; Chen, Jianmin; Kerminen, Veli-Matti; Petäjä, Tuukka; Worsnop, Douglas R.; Kulmala, Markku; Wang, Lin (2018)
    Atmospheric new particle formation (NPF) is an important global phenomenon that is nevertheless sensitive to ambient conditions. According to both observation and theoretical arguments, NPF usually requires a relatively high sulfuric acid (H2SO4) concentration to promote the formation of new particles and a low preexisting aerosol loading to minimize the sink of new particles. We investigated NPF in Shanghai and were able to observe both precursor vapors (H2SO4) and initial clusters at a molecular level in a megacity. High NPF rates were observed to coincide with several familiar markers suggestive of H2SO4-dimethylamine (DMA)water (H2O) nucleation, including sulfuric acid dimers and H2SO4-DMA clusters. In a cluster kinetics simulation, the observed concentration of sulfuric acid was high enough to explain the particle growth to similar to 3 nanometers under the very high condensation sink, whereas the subsequent higher growth rate beyond this size is believed to result fromthe added contribution of condensing organic species. These findings will help in understanding urban NPF and its air quality and climate effects, as well as in formulating policies to mitigate secondary particle formation in China.
  • Gordon, Hamish; Kirkby, Jasper; Baltensperger, Urs; Bianchi, Federico; Breitenlechner, Martin; Curtius, Joachim; Dias, Antonio; Dommen, Josef; Donahue, Neil M.; Dunne, Eimear M.; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C.; Frege, Carla; Fuchs, Claudia; Hansel, Armin; Hoyle, Christopher R.; Kulmala, Markku; Kurten, Andreas; Lehtipalo, Katrianne; Makhmutov, Vladimir; Molteni, Ugo; Rissanen, Matti P.; Stozkhov, Yuri; Trostl, Jasmin; Tsagkogeorgas, Georgios; Wagner, Robert; Williamson, Christina; Wimmer, Daniela; Winkler, Paul M.; Yan, Chao; Carslaw, Ken S. (2017)
    New particle formation has been estimated to produce around half of cloud-forming particles in the present-day atmosphere, via gas-to-particle conversion. Here we assess the importance of new particle formation (NPF) for both the present-day and the preindustrial atmospheres. We use a global aerosol model with parametrizations of NPF from previously published CLOUD chamber experiments involving sulfuric acid, ammonia, organic molecules, and ions. We find that NPF produces around 67% of cloud condensation nuclei at 0.2% supersaturation (CCN0.2%) at the level of low clouds in the preindustrial atmosphere (estimated uncertainty range 45-84%) and 54% in the present day (estimated uncertainty range 38-66%). Concerning causes, we find that the importance of biogenic volatile organic compounds (BVOCs) in NPF and CCN formation is greater than previously thought. Removing BVOCs and hence all secondary organic aerosol from our model reduces low-cloud-level CCN concentrations at 0.2% supersaturation by 26% in the present-day atmosphere and 41% in the preindustrial. Around three quarters of this reduction is due to the tiny fraction of the oxidation products of BVOCs that have sufficiently low volatility to be involved in NPF and early growth. Furthermore, we estimate that 40% of preindustrial CCN0.2% are formed via ion-induced NPF, compared with 27% in the present day, although we caution that the ion-induced fraction of NPF involving BVOCs is poorly measured at present. Our model suggests that the effect of changes in cosmic ray intensity on CCN is small and unlikely to be comparable to the effect of large variations in natural primary aerosol emissions. Plain Language Summary New particle formation in the atmosphere is the process by which gas molecules collide and stick together to form atmospheric aerosol particles. Aerosols act as seeds for cloud droplets, so the concentration of aerosols in the atmosphere affects the properties of clouds. It is important to understand how aerosols affect clouds because they reflect a lot of incoming solar radiation away from Earth's surface, so changes in cloud properties can affect the climate. Before the Industrial Revolution, aerosol concentrations were significantly lower than they are today. In this article, we show using global model simulations that new particle formation was a more important mechanism for aerosol production than it is now. We also study the importance of gases emitted by vegetation, and of atmospheric ions made by radon gas or cosmic rays, in preindustrial aerosol formation. We find that the contribution of ions and vegetation to new particle formation was also greater in the preindustrial period than it is today. However, the effect on particle formation of variations in ion concentration due to changes in the intensity of cosmic rays reaching Earth was small.
  • Kivekäs, Niku; Carpman, Jimmie; Roldin, Pontus; Leppa, Johannes; O'Connor, Ewan; Kristensson, Adam; Asmi, Eija (2016)
    Field observations of new particle formation and the subsequent particle growth are typically only possible at a fixed measurement location, and hence do not follow the temporal evolution of an air parcel in a Lagrangian sense. Standard analysis for determining formation and growth rates requires that the time-dependent formation rate and growth rate of the particles are spatially invariant; air parcel advection means that the observed temporal evolution of the particle size distribution at a fixed measurement location may not represent the true evolution if there are spatial variations in the formation and growth rates. Here we present a zero-dimensional aerosol box model coupled with one-dimensional atmospheric flow to describe the impact of advection on the evolution of simulated new particle formation events. Wind speed, particle formation rates and growth rates are input parameters that can vary as a function of time and location, using wind speed to connect location to time. The output simulates measurements at a fixed location; formation and growth rates of the particle mode can then be calculated from the simulated observations at a stationary point for different scenarios and be compared with the 'true' input parameters. Hence, we can investigate how spatial variations in the formation and growth rates of new particles would appear in observations of particle number size distributions at a fixed measurement site. We show that the particle size distribution and growth rate at a fixed location is dependent on the formation and growth parameters upwind, even if local conditions do not vary. We also show that different input parameters used may result in very similar simulated measurements. Erroneous interpretation of observations in terms of particle formation and growth rates, and the time span and areal extent of new particle formation, is possible if the spatial effects are not accounted for.
  • Schirmer, T.; Abergel, A.; Verstraete, L.; Ysard, N.; Juvela, M.; Jones, A. P.; Habart, E. (2020)
    Context. Micro-physical processes on interstellar dust surfaces are tightly connected to dust properties (i.e. dust composition, size, and shape) and play a key role in numerous phenomena in the interstellar medium (ISM). The large disparity in physical conditions (i.e. density and gas temperature) in the ISM triggers an evolution of dust properties. The analysis of how dust evolves with the physical conditions is a stepping stone towards a more thorough understanding of interstellar dust.Aims. We highlight dust evolution in the Horsehead nebula photon-dominated region.Methods. We used Spitzer/IRAC (3.6, 4.5, 5.8 and 8 mu m) and Spitzer/MIPS (24 mu m) together with Herschel/PACS (70 and 160 mu m) and Herschel/SPIRE (250, 350 and 500 mu m) to map the spatial distribution of dust in the Horsehead nebula over the entire emission spectral range. We modelled dust emission and scattering using the THEMIS interstellar dust model together with the 3D radiative transfer code SOC.Results. We find that the nano-grain dust-to-gas ratio in the irradiated outer part of the Horsehead is 6-10 times lower than in the diffuse ISM. The minimum size of these grains is 2-2.25 times larger than in the diffuse ISM, and the power-law exponent of their size distribution is 1.1-1.4 times lower than in the diffuse ISM. In the denser part of the Horsehead nebula, it is necessary to use evolved grains (i.e. aggregates, with or without an ice mantle).Conclusions. It is not possible to explain the observations using grains from the diffuse medium. We therefore propose the following scenario to explain our results. In the outer part of the Horsehead nebula, all the nano-grain have not yet had time to re-form completely through photo-fragmentation of aggregates and the smallest of the nano-grain that are sensitive to the radiation field are photo-destroyed. In the inner part of the Horsehead nebula, grains most likely consist of multi-compositional mantled aggregates.
  • Fanourgakis, George S.; Kanakidou, Maria; Nenes, Athanasios; Bauer, Susanne E.; Bergman, Tommi; Carslaw, Ken S.; Grini, Alf; Hamilton, Douglas S.; Johnson, Jill S.; Karydis, Vlassis A.; Kirkevag, Alf; Kodros, John K.; Lohmann, Ulrike; Luo, Gan; Makkonen, Risto; Matsui, Hitoshi; Neubauer, David; Pierce, Jeffrey R.; Schmale, Julia; Stier, Philip; Tsigaridis, Kostas; van Noije, Twan; Wang, Hailong; Watson-Parris, Duncan; Westervelt, Daniel M.; Yang, Yang; Yoshioka, Masaru; Daskalakis, Nikos; Decesari, Stefano; Gysel-Beer, Martin; Kalivitis, Nikos; Liu, Xiaohong; Mahowald, Natalie M.; Myriokefalitakis, Stelios; Schrodner, Roland; Sfakianaki, Maria; Tsimpidi, Alexandra P.; Wu, Mingxuan; Yu, Fangqun (2019)
    A total of 16 global chemistry transport models and general circulation models have participated in this study; 14 models have been evaluated with regard to their ability to reproduce the near-surface observed number concentration of aerosol particles and cloud condensation nuclei (CCN), as well as derived cloud droplet number concentration (CDNC). Model results for the period 2011-2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments and on the seasonal and short-term variability in the aerosol properties. There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of -24 % and -35 % for particles with dry diameters > 50 and > 120 nm, as well as -36 % and -34 % for CCN at supersaturations of 0.2 % and 1.0 %, respectively. However, they seem to behave differently for particles activating at very low supersaturations (<0.1 %) than at higher ones. A total of 15 models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N-3 (number concentration of particles with dry diameters larger than 3 nm) and up to about 1 for simulated CCN in the extra-polar regions. A global mean reduction of a factor of about 2 is found in the model diversity for CCN at a supersaturation of 0.2 % (CCN0.2) compared to that for N-3, maximizing over regions where new particle formation is important. An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter. Models capture the relative amplitude of the seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120 nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40 % during winter and 20 % in summer. In contrast to the large spread in simulated aerosol particle and CCN number concentrations, the CDNC derived from simulated CCN spectra is less diverse and in better agreement with CDNC estimates consistently derived from the observations (average NMB -13 % and -22 % for updraft velocities 0.3 and 0.6 m s(-1), respectively). In addition, simulated CDNC is in slightly better agreement with observationally derived values at lower than at higher updraft velocities (index of agreement 0.64 vs. 0.65). The reduced spread of CDNC compared to that of CCN is attributed to the sublinear response of CDNC to aerosol particle number variations and the negative correlation between the sensitivities of CDNC to aerosol particle number concentration (partial derivative N-d/partial derivative N-a) and to updraft velocity (partial derivative N-d/partial derivative w). Overall, we find that while CCN is controlled by both aerosol particle number and composition, CDNC is sensitive to CCN at low and moderate CCN concentrations and to the updraft velocity when CCN levels are high. Discrepancies are found in sensitivities partial derivative N-d/partial derivative N-a and partial derivative N-d/partial derivative w; models may be predisposed to be too "aerosol sensitive" or "aerosol insensitive" in aerosol-cloud-climate interaction studies, even if they may capture average droplet numbers well. This is a subtle but profound finding that only the sensitivities can clearly reveal and may explain intermodel biases on the aerosol indirect effect.
  • Pirjola, L.; Rönkkö, T.; Saukko, E.; Parviainen, H.; Malinen, A.; Alanen, J.; Saveljeff, H. (2017)
    Exhaust emissions emitted by a non-road mobile machine were studied chasing a tractor in real-world conditions and repeating the same transient tests with a similar engine on an engine dynamometer where additionally, non-road steady state tests were carried out. The engines were equipped with an oxidation catalyst (DOC) and a selective catalytic reduction (SCR)system, and they were fuelled by fossil diesel fuel with ultra-low sulphur content and hydrotreated vegetable oil (HVO). By substituting diesel fuel with HVO the on-road emissions of nitrogen oxides (NOx) reduced 20% and particle number 44%, the emission factors being EFNOx =1.62 +/- 0.04 g/kWh and EFN = (28.2 +/- 7.8) x 10(13) #/kWh. Similar trend was observed for NOx at laboratory although the emissions were somewhat smaller than on-road. In contrast to real-world, in the laboratory experiment the EFN was only 2% smaller with HVO than with diesel, and these emission factors were almost one order of magnitude smaller than observed on-road. The number size distribution and volatility measurements showed that in real-world experiments small nucleation mode particles were formed during uphill and during downhill in engine braking conditions. These were not observed at laboratory. However, nucleation mode particles were observed in the laboratory experiments at high load steady driving conditions. At steady state tests the emissions strongly depended on engine load and engine speed with both fuels. (C) 2017 Elsevier Ltd. All rights reserved.
  • Molgaard, Bjarke; Viitanen, Anna-Kaisa; Kangas, Anneli; Huhtiniemi, Marika; Larsen, Soren Thor; Vanhala, Esa; Hussein, Tareq; Boor, Brandon E.; Hämeri, Kaarle; Koivisto, Antti Joonas (2015)
    Due to the health risk related to occupational air pollution exposure, we assessed concentrations and identified sources of particles and volatile organic compounds (VOCs) in a handcraft workshop producing fishing lures. The work processes in the site included polyurethane molding, spray painting, lacquering, and gluing. We measured total VOC (TVOC) concentrations and particle size distributions at three locations representing the various phases of the manufacturing and assembly process. The mean working-hour TVOC concentrations in three locations studied were 41, 37, and 24 ppm according to photo-ionization detector measurements. The mean working-hour particle number concentration varied between locations from 3000 to 36,000 cm(-3). Analysis of temporal and spatial variations of TVOC concentrations revealed that there were at least four substantial VOC sources: spray gluing, mold-release agent spraying, continuous evaporation from various lacquer and paint containers, and either spray painting or lacquering (probably both). The mold-release agent spray was indirectly also a major source of ultrafine particles. The workers' exposure can be reduced by improving the local exhaust ventilation at the known sources and by increasing the ventilation rate in the area with the continuous source.
  • Kalivitis, Nikos; Kerminen, Veli-Matti; Kouvarakis, Giorgos; Stavroulas, Iasonas; Tzitzikalaki, Evaggelia; Kalkavouras, Panayiotis; Daskalakis, Nikos; Myriokefalitakis, Stelios; Bougiatioti, Aikaterini; Manninen, Hanna E.; Roldin, Pontus; Petäjä, Tuukka; Boy, Michael; Kulmala, Markku; Kanakidou, Maria; Mihalopoulos, Nikolaos (2019)
    Atmospheric new particle formation (NPF) is a common phenomenon all over the world. In this study we present the longest time series of NPF records in the eastern Mediterranean region by analyzing 10 years of aerosol number size distribution data obtained with a mobility particle sizer. The measurements were performed at the Finokalia environmental research station on Crete, Greece, during the period June 2008-June 2018. We found that NPF took place on 27% of the available days, undefined days were 23% and non-event days 50 %. NPF is more frequent in April and May probably due to the terrestrial biogenic activity and is less frequent in August. Throughout the period under study, nucleation was observed also during the night. Nucleation mode particles had the highest concentration in winter and early spring, mainly because of the minimum sinks, and their average contribution to the total particle number concentration was 8 %. Nucleation mode particle concentrations were low outside periods of active NPF and growth, so there are hardly any other local sources of sub-25 nm particles. Additional atmospheric ion size distribution data simultaneously collected for more than 2 years were also analyzed. Classification of NPF events based on ion spectrometer measurements differed from the corresponding classification based on a mobility spectrometer, possibly indicating a different representation of local and regional NPF events between these two measurement data sets. We used the MALTE-Box model for simulating a case study of NPF in the eastern Mediterranean region. Monoterpenes contributing to NPF can explain a large fraction of the observed NPF events according to our model simulations. However the adjusted parameterization resulting from our sensitivity tests was significantly different from the initial one that had been determined for the boreal environment.
  • Wimmer, Daniela; Mazon, Stephany Buenrostro; Manninen, Hanna Elina; Kangasluoma, Juha; Franchin, Alessandro; Nieminen, Tuomo; Backman, John; Wang, Jian; Kuang, Chongai; Krejci, Radovan; Brito, Joel; Morais, Fernando Goncalves; Martin, Scot Turnbull; Artaxo, Paulo; Kulmala, Markku; Kerminen, Veli-Matti; Petäjä, Tuukka (2018)
    We investigated atmospheric new particle formation (NPF) in the Amazon rainforest using direct measurement methods. To our knowledge this is the first direct observation of NPF events in the Amazon region. However, previous observations elsewhere in Brazil showed the occurrence of nucleation-mode particles. Our measurements covered two field sites and both the wet and dry season. We measured the variability of air ion concentrations (0.8-12 nm) with an ion spectrometer between September 2011 and January 2014 at a rainforest site (T0t). Between February and October 2014, the same measurements were performed at a grassland pasture site (T3) as part of the GoAmazon 2014/5 experiment, with two intensive operating periods (IOP1 and IOP2 during the wet and the dry season, respectively). The GoAmazon 2014/5 experiment was designed to study the influence of anthropogenic emissions on the changing climate in the Amazon region. The experiment included basic aerosol and trace gas measurements at the ground, remote sensing instrumentation, and two aircraft-based measurements. The results presented in this work are from measurements performed at ground level at both sites. The site inside the rainforest (T0t) is located 60 km NNW of Manaus and influenced by pollution about once per week. The pasture (T3) site is located 70 km downwind from Manaus and influenced by the Manaus pollution plume typically once per day or every second day, especially in the afternoon. No NPF events were observed inside the rainforest (site T0t) at ground level during the measurement period. However, rain-induced ion and particle bursts (hereafter, "rain events") occurred frequently (643 of 1031 days) at both sites during the wet and dry season, being most frequent during the wet season. During the rain events, the ion concentrations in three size ranges (0.8-2, 2-4, and 4-12 nm) increased up to about 10(4)-10(5) cm(-3). This effect was most pronounced in the intermediate and large size ranges, for which the background ion concentrations were about 10-15 cm(-3) compared with 700 cm(-3) for the cluster ion background. We observed eight NPF events at the pasture site during the wet season. We calculated the growth rates and formation rates of neutral particles and ions for the size ranges 2-3 and 3-7 nm using the ion spectrometer data. The observed median growth rates were 0.8 and 1.6 nm h(-1) for 2-3 nm sized ions and particles, respectively, with larger growth rates (13.3 and 7.9 nm h(-1)) in the 3-7 nm size range. The measured nucleation rates were of the order of 0.2 cm(-3) s(-1) for particles and 4-9 x 10(-3) cm(-3) s(-1) for ions. There was no clear difference in the sulfuric acid concentrations between the NPF event days and nonevent days (similar to 9 x 10(5) cm(-3)). The two major differences between the NPF days and nonevent days were a factor of 1.8 lower condensation sink on NPF event days (1.8 x 10(-3) s(-1)) compared to nonevents (3.2 x 10(-3) s(-1)) and different air mass origins. To our knowledge, this is the first time that results from ground-based sub-3 nm aerosol particle measurements have been obtained from the Amazon rainforest.
  • Baranizadeh, Elham; Murphy, Benjamin N.; Julin, Jan; Falahat, Saeed; Reddington, Carly L.; Arola, Antti; Ahlm, Lars; Mikkonen, Santtu; Fountoukis, Christos; Patoulias, David; Minikin, Andreas; Hamburger, Thomas; Laaksonen, Ari; Pandis, Spyros N.; Vehkamäki, Hanna; Lehtinen, Kari E. J.; Riipinen, Ilona (2016)
    The particle formation scheme within PMCAMx-UF, a three-dimensional chemical transport model, was updated with particle formation rates for the ternary H2SO4-NH3-H2O pathway simulated by the Atmospheric Cluster Dynamics Code (ACDC) using quantum chemical input data. The model was applied over Europe for May 2008, during which the EUCAARI-LONGREX (European Aerosol Cloud Climate and Air Quality Interactions-Long-Range Experiment) campaign was carried out, providing aircraft vertical profiles of aerosol number concentrations. The updated model reproduces the observed number concentrations of particles larger than 4 nm within 1 order of magnitude throughout the atmospheric column. This agreement is encouraging considering the fact that no semi-empirical fitting was needed to obtain realistic particle formation rates. The cloud adjustment scheme for modifying the photolysis rate profiles within PMCAMx-UF was also updated with the TUV (Tropospheric Ultraviolet and Visible) radiative-transfer model. Results show that, although the effect of the new cloud adjustment scheme on total number concentrations is small, enhanced new-particle formation is predicted near cloudy regions. This is due to the enhanced radiation above and in the vicinity of the clouds, which in turn leads to higher production of sulfuric acid. The sensitivity of the results to including emissions from natural sources is also discussed.
  • Belz, Regina G.; Sinkkonen, Aki (2021)
    BACKGROUND Low toxin doses that do not affect mean responses in plant populations can still change the growth of subpopulations. Studies covering vegetative stages ascribed fast-growing plants higher thresholds for growth stimulation and inhibition, compared with the rest of the population. We hypothesized that such selective effects also play a role after reproduction; that is, the offspring of glyphosate-treated tolerant, fast-growing phenotypes is more tolerant than the offspring of untreated plants. An experimental, high-density barley population was exposed to a range of glyphosate concentrations in the greenhouse, and reproduction and final growth were analyzed for selective effects. Therefore, F0, F1 treated and F1 non-treated offspring were re-exposed to glyphosate. RESULTS Low doses of glyphosate inhibited the growth and reproduction of slow-growing plants at concentrations that did not change the population mean. Concentrations that inhibited average-sized plants hormetically increased the biomass and seed yield of fast-growing plants. Compared with F0 and F1 non-treated offspring, F1-treated offspring from hormetically stimulated fast-growing plants were more glyphosate tolerant. Hence, a pesticide can shape the reproductive pattern of a plant population and alter offspring tolerance at concentrations that have no effect on average yield. CONCLUSIONS Toxin levels that do not change the population mean still alter the reproductive output of individuals. Sensitive phenotypes suffer, whereas the reproduction of tolerant phenotypes is boosted compared with toxin-free conditions. Because glyphosate is one of the leading herbicides in the world, tolerant phenotypes may benefit from current agricultural practices. If these results apply to other toxicants, low toxin doses may increase the fitness of tolerant phenotypes in a way not previously anticipated.
  • Hussein, Tareq; Boor, Brandon E.; dos Santos, Vanessa N.; Kangasluoma, Juha; Petäjä, Tuukka; Lihavainen, Heikki (2017)
    Air pollution research and reports have been limited in the Middle East, especially in Jordan with respect to aerosol particle number concentrations. In this study, we utilized a simple "mobile setup" to measure, for the first time, the spatial variation of aerosol concentrations in Eastern Mediterranean. The mobile setup consisted of portable aerosol instruments to measure particle number concentrations (cut off sizes 0.01, 0.02, 0.3, 0.5, 1, 2.5, 5, and 10 mu m), particle mass concentrations (PM1, PM2.5, and PM10), and black carbon concentration all situated on the back seat of a sedan car. The car was driven with open windows to ensure sufficient cabin air ventilation for reliable outdoor aerosol sampling. Although the measurement campaign was two days long, but it provided preliminary information about aerosols concentrations over a large spatial scale that covered more than three quarters of Jordan. We should keep in mind that the presented concentrations reflect on road conditions. The submicron particle concentrations were the highest in the urban locations (e.g., Amman and Zarqa) and inside cities with heavy duty vehicles activities (e.g., Azraq). The highest micron particle concentrations were observed in the southern part of the country and in places close to the desert area (e.g., Wadi Rum and Wadi Araba). The average submicron concentration was 4.9 x 10(3)-120 x 10(3) cm-3 (5.7-86.7 mu g m(-3)) whereas the average micron particle concentration was 1-11 cm(-3) (8-150 mu g m(-3), assume rho(p) = 1 g cm(-3)). The main road passing through Jafr in the eastern part of Jordan exhibited submicron concentration as low as 800 cm(-3). The PM10 concentration consisted of about 40-75% as PM1. The black carbon (BC) concentration variation was in good agreement with the PM1 as well as the submicron particle number concentration.
  • Wehner, B.; Werner, F.; Ditas, F.; Shaw, R. A.; Kulmala, M.; Siebert, H. (2015)
    During the CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArba-dos) campaign, the interaction between aerosol particles and cloud microphysical properties was investigated in detail, which also includes the influence of clouds on the aerosol formation. During two intensive campaigns in 2010 and 2011, helicopter-borne measurement flights were performed to investigate the thermodynamic, turbulent, microphysical, and radiative properties of trade-wind cumuli over Barbados. During these flights, 91 cases with increased aerosol particle number concentrations near clouds were detected. The majority of these cases are also correlated with enhanced irradiance in the ultraviolet (UV) spectral wavelength range. This enhancement reaches values up to a factor of 3.3 greater compared to background values. Thus, cloud boundaries provide a perfect environment for the production of precursor gases for new particle formation. Another feature of cloud edges is an increased turbulence, which may also enhance nucleation and particle growth. The observed events have a mean length of 100 m, corresponding to a lifetime of less than 300 s. This implies that particles with diameters of at least 7 nm grew several nanometers per minute, which corresponds to the upper end of values in the literature (Kulmala et al., 2004). Such high values cannot be explained by sulfuric acid alone; thus extremely low volatility organic compounds (ELVOCs) are probably involved here.
  • Schobesberger, S.; Franchin, A.; Bianchi, F.; Rondo, L.; Duplissy, J.; Kuerten, A.; Ortega Colomer, Ismael Kenneth; Metzger, A.; Schnitzhofer, R.; Almeida, J.; Amorim, A.; Dommen, J.; Dunne, E. M.; Ehn, M.; Gagne, S.; Ickes, L.; Junninen, H.; Hansel, A.; Kerminen, V-M; Kirkby, J.; Kupc, A.; Laaksonen, A.; Lehtipalo, K.; Mathot, S.; Onnela, A.; Petaja, T.; Riccobono, F.; Santos, F. D.; Sipila, M.; Tome, A.; Tsagkogeorgas, G.; Viisanen, Y.; Wagner, P. E.; Wimmer, D.; Curtius, J.; Donahue, N. M.; Baltensperger, U.; Kulmala, M.; Worsnop, D. R. (2015)
  • Franco, Eugenia; Gyllenberg, Mats; Diekmann, Odo (2021)
    Despite their relevance in mathematical biology, there are, as yet, few general results about the asymptotic behaviour of measure valued solutions of renewal equations on the basis of assumptions concerning the kernel. We characterise, via their kernels, a class of renewal equations whose measure-valued solution can be expressed in terms of the solution of a scalar renewal equation. The asymptotic behaviour of the solution of the scalar renewal equation, is studied via Feller’s classical renewal theorem and, from it, the large time behaviour of the solution of the original renewal equation is derived.
  • Bannister, Michele T.; Alexandersen, Mike; Benecchi, Susan D.; Chen, Ying-Tung; Delsanti, Audrey; Fraser, Wesley C.; Gladman, Brett J.; Granvik, Mikael; Grundy, Will M.; Guilbert-Lepoutre, Aurelie; Gwyn, Stephen D. J.; Ip, Wing-Huen; Jakubik, Marian; Jones, R. Lynne; Kaib, Nathan; Kavelaars, J. J.; Lacerda, Pedro; Lawler, Samantha; Lehner, Matthew J.; Lin, Hsing Wen; Lykawka, Patryk Sofia; Marsset, Michael; Murray-Clay, Ruth; Noll, Keith S.; Parker, Alex; Petit, Jean-Marc; Pike, Rosemary E.; Rousselot, Philippe; Schwamb, Megan E.; Shankman, Cory; Veres, Peter; Vernazza, Pierre; Volk, Kathryn; Wang, Shiang-Yu; Weryk, Robert (2016)
    We report the discovery and orbit of a new dwarf planet candidate, 2015 RR245, by the Outer Solar System Origins Survey (OSSOS). The orbit of 2015 RR245 is eccentric (e = 0.586), with a semimajor axis near 82 au, yielding a perihelion distance of 34 au. 2015 RR245 has g - r = 0.59 +/- 0.11 and absolute magnitude H-r = 3.6 +/- 0.1; for an assumed albedo of p(V) = 12%, the object has a diameter of similar to 670. km. Based on astrometric measurements from OSSOS and Pan-STARRS1, we find that 2015 RR245 is securely trapped on ten-megayear timescales in the 9: 2 mean-motion resonance with Neptune. It is the first trans-Neptunian object (TNO) identified in this resonance. On hundred-megayear. timescales, particles in 2015 RR245-like orbits depart and sometimes return to the resonance, indicating that 2015 RR245 likely forms part of the long-lived metastable population of distant TNOs that drift between resonance sticking and actively scattering via gravitational encounters with Neptune. The discovery of a 9: 2 TNO stresses the role of resonances in the long-term evolution of objects in the scattering disk. and reinforces the view that distant resonances are heavily populated in the current solar system. This object further motivates detailed modeling of the transient sticking population.
  • Cook, Nathaniel V.; Ragozzine, Darin; Granvik, Mikael; Stephens, Denise C. (2016)
    During the planet formation process, billions of comets are created and ejected into interstellar space. The detection and characterization of such interstellar comets (ICs) (also known as extra-solar planetesimals or extra-solar comets) would give us in situ information about the efficiency and properties of planet formation throughout the galaxy. However, no ICs have ever been detected, despite the fact that their hyperbolic orbits would make them readily identifiable as unrelated to the solar system. Moro-Martin et al. have made a detailed and reasonable estimate of the properties of the IC population. We extend their estimates of detectability with a numerical model that allows us to consider "close" ICs, e.g., those that come within the orbit of Jupiter. We include several constraints on a "detectable" object that allow for realistic estimates of the frequency of detections expected from the Large Synoptic Survey Telescope (LSST) and other surveys. The influence of several of the assumed model parameters on the frequency of detections is explored in detail. Based on the expectation from Moro-Martin et al., we expect that LSST will detect 0.001-10 ICs during its nominal 10 year lifetime, with most of the uncertainty from the unknown number density of small (nuclei of similar to 0.1-1 km) ICs. Both asteroid and comet cases are considered, where the latter includes various empirical prescriptions of brightening. Using simulated LSST-like astrometric data, we study the problem of orbit determination for these bodies, finding that LSST could identify their orbits as hyperbolic and determine an ephemeris sufficiently accurate for follow-up in about 4-7 days. We give the hyperbolic orbital parameters of the most detectable ICs. Taking the results into consideration, we give recommendations to future searches for ICs.
  • Sihto, Sanna-Liisa; Mikkilä, Jyri; Vanhanen, Joonas; Ehn, Mikael; Liao, Li; Lehtipalo, Katrianne; Aalto, Pasi; Duplissy, Jonathan; Petäjä, Tuukka; Kerminen, Veli-Matti; Boy, Michael; Kulmala, Markku (2011)
    As a part of EUCAARI activities, the annual cycle of cloud condensation nuclei (CCN) concentrations and critical diameter for cloud droplet activation as a function of supersaturation were measured using a CCN counter and a HTDMA (hygroscopicity tandem differential mobility analyzer) at SMEAR II station, Hyytiälä, Finland. The critical diameters for CCN activation were estimated from (i) the measured CCN concentration and particle size distribution data, and (ii) the hygroscopic growth factors by applying κ-Köhler theory, in both cases assuming an internally mixed aerosol. The critical diameters derived by these two methods were in good agreement with each other. The effect of new particle formation on the diurnal variation of CCN concentration and critical diameters was studied. New particle formation was observed to increase the CCN concentrations by 70–110%, depending on the supersaturation level. The average value for the κ-parameter determined from hygroscopicity measurements was κ = 0.18 and it predicted well the CCN activation in boreal forest conditions in Hyytiälä. The derived critical diameters and κ-parameter confirm earlier findings with other methods, that aerosol particles at CCN sizes in Hyytiälä are mostly organic, but contain also more hygrosopic, probably inorganic salts like ammonium sulphate, making the particles more CCN active than pure secondary organic aerosol.
  • Wu, Hao; Li, Zhanqing; Li, Hanqing; Luo, Kun; Wang, Yuying; Yan, Peng; Hu, Fei; Zhang, Fang; Sun, Yele; Shang, Dongjie; Liang, Chunsheng; Zhang, Dongmei; Wei, Jing; Wu, Tong; Jin, Xiaoai; Fan, Xinxin; Cribb, Maureen; Fischer, Marc L.; Kulmala, Markku; Petäjä, Tuukka (2021)
    A new mechanism of new particle formation (NPF) is investigated using comprehensive measurements of aerosol physicochemical quantities and meteorological variables made in three continents, including Beijing, China; the Southern Great Plains site in the USA; and SMEAR II Station in Hyytiala, Finland. Despite the considerably different emissions of chemical species among the sites, a common relationship was found between the characteristics of NPF and the stability intensity. The stability parameter (zeta = Z/L, where Z is the height above ground and L is the Monin-Obukhov length) is found to play an important role; it drops significantly before NPF as the atmosphere becomes more unstable, which may serve as an indicator of nucleation bursts. As the atmosphere becomes unstable, the NPF duration is closely related to the tendency for turbulence development, which influences the evolution of the condensation sink. Presumably, the unstable atmosphere may dilute pre-existing particles, effectively reducing the condensation sink, especially at coarse mode to foster nucleation. This new mechanism is confirmed by model simulations using a molecular dynamic model that mimics the impact of turbulence development on nucleation by inducing and intensifying homogeneous nucleation events.