In Finnish conditions, mixing decreases preexisting particle concentration (CS) and RH as cleaner and drier air above the ABL is mixed to the boundary layer and thereby
newparticle formation would be more probable. However, our study indicates that en- trainment inhibits particle formation ( β<0 for w e in Eq. 10), despite the fact that it could be expected that the probability increases if entrainment velocity increases. This can be understood as the ABL grows fast also temperature is lower and RH is higher at the top of the ABL (the top of the ABL is located higher and therefore it is probably colder).
Gordon, H., Sengupta, K., Rap, A., Duplissy, J., Frege, C., Williamson, C., Heinritzi, M., Simon, M., Yan, C., Almeida, J., Tröstl, J., Nieminen, T., Ortega, I. K., Wagner, R., Dunne, E. M., Adamov, A., Amorim, A., Bernhammer, A.-K., Bianchi, F., Breitenlechner, M., Brilke, S., Chen, X., Craven, J. S., Dias, A., Ehrhart, S., Fischer, L., Flagan, R. C., Franchin, A., Fuchs, C., Guida, R., Hakala, J., Hoyle, C. R., Jokinen, T., Junninen, H., Kangasluoma, J., Kim, J., Kirkby, J., Krapf, M., Kürten, A., Laaksonen, A., Lehtipalo, K., Makhmutov, V., Mathot, S., Molteni, U., Monks, S. A., Onnela, A., Peräkylä, O., Piel, F., Petäjä, T., Praplan, A. P., Pringle, K. J., Richards, N. A. D., Ris- sanen, M. P., Rondo, L., Sarnela, N., Schobesberger, S., Scott, C. E., Seinfeld, J. H., Sharma, S., Sipilä, M., Steiner, G., Stozhkov, Y., Stratmann, F., Tomé, A., Virtanen, A., Vogel, A. L., Wagner, A. C., Wagner, P. E., Weingartner, E., Wimmer, D., Winkler, P. M., Ye, P., Zhang, X., Hansel, A., Dommen, J., Donahue, N. M., Worsnop, D. R., Baltensperger, U., Kulmala, M., Curtius, J., and Carslaw, K. S.: Reduced anthropogenic aerosol radiative forcing caused by biogenic newparticle formation, P. Natl. Acad. Sci. USA, 113, 12053–12058, 2016.
Received: 5 April 2007 – Published in Atmos. Chem. Phys. Discuss.: 30 May 2007 Revised: 29 August 2007 – Accepted: 14 September 2007 – Published: 20 September 2007
Abstract. The connection between newparticle formation and micro- and mesoscale meteorology was studied based on measurements at SMEAR II station in Southern Finland. We analyzed turbulent conditions described by sodar measure- ments and utilized these combined with surface layer mea- surements and a simple model to estimate the upper bound- ary layer conditions. Turbulence was significantly stronger on particle formation days and the organic vapor saturation ratio increase due to large eddies was stronger on event than nonevent days. We examined which variables could be the best indicators of newparticle formation and concluded that the formation probability depended on the condensation sink and temporal temperature change at the top of the atmo- spheric boundary layer. Humidity and heat flux may also be good indicators for particle formation.
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crease within a shorter time period. This indicates that observations of particle “bursts” are likely caused by hot spot-like emissions. Although emissions of alkyl iodides are su fficient for noticable newparticle formation by OIO in our clean scenarios, nucleation rates (both “real” and “apparent”) are significantly enhanced by additional fluxes of molecular iodine, even if I 2 mixing ratios range below 1 pmol mol −1 during day. Hence, 5
* Correspondence: firstname.lastname@example.org
Received: 4 July 2019; Accepted: 13 August 2019; Published: 26 August 2019
Abstract: Newparticle formation (NPF) was predicted to contribute to a major fraction of free tropospheric particle number and cloud condensation nuclei (CCN) concentrations by global models. At high altitudes, pre-existing particle concentrations are low, leading to limited condensational sinks for nucleation precursor gases, and temperatures are cooler compared to lower altitudes, whereas radiation is higher. These factors would all be in favor of nucleation to occur with an enhanced frequency at high altitudes. In the present work, long term data from six altitude stations (and four continents) at various altitudes (from 1465 to 5240 m a.s.l) were used to derive statistically relevant NPF features (frequency, formation rates, and growth rates) and seasonal variability. The combined information together with literature data showed that the frequencies of NPF events at the two Southern hemisphere (SH) stations are some of the highest reported thus far (64% and 67%, respectively). There are indications that NPF would be favored at a preferential altitude close to the interface of the free troposphere (FT) with the planetary boundary layer (PBL) and/or at the vicinity with clouds, which otherwise inhibit the occurrence of NPF. Particle formation rates are found to be lower at high altitudes than at low altitude sites, but a higher fraction of particles are formed via the charged pathway (mainly related to positive ions) compared to boundary layer (BL) sites. Low condensational sinks (CS) are not necessarily needed at high altitudes to promote the occurrence of NPF. For stations at altitudes higher than 1000 m a.s.l., higher CSs favor NPF and are thought to be associated with precursor gases needed to initiate nucleation and early growth.
Abstract. The formation of secondary particles in the atmo- sphere accounts for more than half of global cloud conden- sation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the im- portance of ions for newparticle formation, but quantify- ing their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nanopar- ticle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of newparticle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chem- ical compositions involving monoterpenes, sulfuric acid, ni- trogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is nec- essary to stabilize newly formed clusters, i.e., in conditions in which neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.5 nm diameter. However, depending on particle growth rates and ion concen- trations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.5 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.5 nm. Ob- servations at Hyytiälä, Finland, showed lower ion concentra- tions and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrep- ancy.
total particles with the diameter 4–2000 nm (N 4−2000 ) are N 4−9 , and (iii) particles from 4 to 6 nm (N 4−6 ) are higher than those from 6 to 9 nm (N 6−9 ) (Young et al., 2007). Each
newparticle formation event is further classified as either a strong or weak event in the present study to better understand the condition in which newparticle formation is not active. For a strong event the conditions are (1) N 4−9 and N 4−2000 > 500 cm −3 and (2) a size distribution in which there are three modes present with peaks at <10, ∼20 and 60–200 nm (similar to Young et al., 2007) and in which the smallest mode has a
day, the optimal fitting parameters for Heidelberg data were n N36 =0.7 and ∆t N36 =1.7 h, the maximum correlation coe fficient being 0.67 (see Fig. 2b). For Hyyti¨al¨a data (see
Fig. 3b), the corresponding values were n N36 =2.4, ∆t N36 =1.3 h and R max =0.96. Clear positive correlation between N 3−6 and sulphuric acid was observed during all newparticle formation events at both locations. The mean value of the correlation coef- ficient between N 3−6 and sulphuric acid raised to the power n N36 is 0.75 (R in the range 0.57–0.90) for Heidelberg, and 0.82 (R in the range 0.54–0.97) for Hyyti ¨al ¨a. Compared
Leaitch, W.: Observations pertaining to the effect of chemical transformation in cloud on the anthropogenic aerosol size distribution, Aerosol Sci. Technol., 16, 157–173, 1996. 7480
Lee, S., Wilson, J., Baumgardner, D., Herman, R., Weinstock, E., Lafleur, B., Kok, G., Ander- son, B., Lawson, P., Baker, B., Strawa, A., Pittman, J., Reeves, J., and Bui, T.: Newparticle formation observed in the tropical/subtropical cirrus clouds, J. Geophys. Res., 109, D20209, 2004. 7485 , 7486
In the selected cases, the simulated concentrations of sul- phuric acid explained less than 10% of the nucleation mode growth, indicating that organic compounds are the main con- tributor to particle growth in this clean yet relatively sparsely vegetated subarctic environment. This observation is also in line with earlier analyses for more densely vegetated envi- ronments (Birmili et al., 2003; Boy et al., 2005). The crucial role of organics in newparticle growth offers a tentative hy- pothesis to the distinct features of new particles at the two sites: At the source station Pallas no particle formation at 7 nm is detected in case 1 and in case 2 the growth of formed particles is not as clear as at V¨arri¨o. Since the air mass in both cases reaches Pallas after travelling over land for only 9–10 h, the time for the organic vapours to accumulate in the air and to interact with the particles is relatively short. As a result, the growth rate of newly formed clusters remains low, they are effectively scavenged by pre-existing particles and may not reach the detection limit of the measurement instru- mentation.
Plain Language Summary Cloud properties are sensitive to the formation of new aerosol particles in the Arctic atmosphere, yet little is known about the chemistry and processes controlling this phenomenon. Here, based on comprehensive in situ measurements, we identify the very first steps of atmospheric newparticle formation, that is, formation of small clusters from compounds present in the gas phase, and candidates for the subsequent growth of these clusters to larger sizes, at two Arctic sites: one surrounded by open waters, the other one by sea ice. We show how environmental differences affect secondary aerosol formation via emissions and atmospheric chemistry of aerosol precursor gases. Our results provide previously unidentified insight into how future changes in the Polar environment could
rithm with a multi log normal distribution function (Hussein et al., 2005). In this work emphasis was on generating continuous time series of modal parameters, especially for the nucleation mode in terms of the mean diameter D p−nuc . A graph for each of the four selected event days based on measured particle size distributions without and with TD is shown in Fig. 5. As mentioned previously, on most of the B-event days the 20
The procedure developed in this paper sits somewhere between purely statistical and optimization approaches. The former was not selected on the basis that there is no evidence that ultrafiltration cakes con- form to any particular statistical configura- tion. The authors avoided using the latter approach because they are designed to seek a global optimum, not one solution amongst many. Moreover, optimization schemes present foreseeable difficulties with simulating large volumes. The pro- posed reconstruction approach uses an in- cremental particle-by-particle reconstruc- tion scheme of a cake slice, which corresponds to the volume captured by the TEM image. Adding particles one by one avoids having to specify the number of particles a priori and circumvents the diffi- cult choice of this unknown. At every itera- tion, i.e., every time a newparticle is added
Compared with traditional MCMC algorithms, PDMP is rejection-free, which means that there is no waste of proposal samples. Based on detailed balance condition, traditional MCMC algorithms are reversible. However, some theo- retic work and numerical experiments (, , , ) have shown that irre- versible Markov chain can outperform reversible MCMC with respect to mixing rate and asymptotic variance. PDMP is a typically irreversible Markov chain, which is of interest to investigate. Bouncy particle sampler (BPS) generates
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Another approach has been proposed by Daum’s et al. ,  that allows the reduction of the number of particles we need in order to get a tolerable level of errors in the ﬁltering problem. The main idea behind this method is the evolution in homotopy parameter λ (a "pseudotime") from prior to the target density. They introduced a particle ﬂow, in which particles are gradually transported without the necessity to randomly sample from any distribution. This approach as an optimal transport problem allows optimally move the set of particles according to Bayes’ rule. In other words, the particles are progressively transported according to their ﬂow. One can in this way reduce the number of needed samples, since the variance and bias of the estimator is lower and as a result reduce the computational burden in both the estimation and the prediction steps.
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Ruggeri, S.; Lefebvre, L. P.; Laurin, C.; Gendron, R.; Sammut, P.; Gauthier, M.