Ternary nucleation of H_2SO_4, NH_3 and H_2O

A classical theory of the ternary homogeneous nucleation of sulfuric acid—ammonia—water is presented. For NH3 mixing ratios exceeding 1 ppt, the presence of ammonia enhances the binary (sulfuric acid—water) nucleation rate by several orders of magnitude. However, the limiting component for ternary nucleation—as for binary nucleation—is sulfuric acid. The sulfuric acid concentration needed for significant ternary nucleation is several orders of magnitude below that required in binary case

Modification of the 4 MeV electron beam from a linear accelerator for irradiation of small superficial skin tumors

Uniform dose distribution with steep lateral gradient within depth range of 0–0.5 cm is crucial to be able to treat small skin lesions. The standard nominal 4 MeV electron beam from Elekta Versa HD linear accelerator was modified with degrading filter to remove the lateral scatter from treatment head and minimize the penumbra. The energy degrading method was verified based on dosimetric properties and output factors (OFs)with comparison of four types of measurement methods. The properties of degraded 4 MeV electron beam and developed electron applicators seem optimal for treating small targets near the skin surface. © 2019 The AuthorsNon peer reviewe

Cluster activation theory as an explanation of the linear dependence between formation rate of 3nm particles and sulphuric acid concentration

International audienceAccording to atmospheric observations new particle formation seems to be a function of sulphuric acid concentration to the power from one to two. The nucleation theorem then predicts that the critical cluster contains one to two sulphuric acid molecules. However, existing nucleation theories predicts that the power is more (or equal) than 2. Here we present an activation theory, which can explain the observed slope. In cluster activation the clusters containing one sulphuric acid molecule will activate for further growth due to heterogeneous nucleation, heterogeneous chemical reactions including polymerization or activation of soluble clusters. In the activation process organic vapours are typically needed as condensing agents

Why formation rate of 3 nm particles depends linearly on sulphuric acid concentration?

International audienceAccording to atmospheric observations new particle formation seems to be a function of sulphuric acid concentration to the power from one to two. The nucleation theorem then predicts that the critical cluster contains one to two sulphuric acid molecules. However, existing nucleation theories predicts that the power is more (or equal) than 2. Here we present an activation theory, which can explain the observed slope. In cluster activation the clusters containing one sulphuric acid molecule will activate for further growth due to heterogeneous nucleation, heterogeneous chemical reactions including polymerization or activation of soluble clusters. In the activation process organic vapours are typically needed as condensing agents

Institute for Atmospheric and Earth System Research (INAR) : Showcases for making science diplomacy

Science diplomacy can be defined as "the use of scientific collaborations between countries to address joint problems and to build constructive international partnerships for delivering effective scientific advice for policy making". During the last 10 years, the Institute for Atmospheric and Earth System Research (INAR) has been active in finding ways to solve global Grand Challenges, particularly climate change and poor air quality in polluted megacities, and at the same time, better bridge research to international climate policy and science diplomacy processes. INAR has introduced Pan-Eurasian Experiment programme running since the year 2012 (www.atm.helsinki.fi/peex) to better address the scientific challenge to understand Atmosphere - Earth Surface - Biosphere interactions and feedbacks in the Northern Eurasian context. INAR has also launched a measurement concept called the Global Network of Stations Measuring Earth Surface and Atmosphere Interactions (GlobalSMEAR) and has hosted the European Centre of the International Eurasian Academy of Sciences since 2015. Most recently, INAR has coordinated the Arena for the gap analysis of the existing Arctic Science Co-Operations (AASCO), 2020-2021, to promote research with a holistic and integrated approach in understanding feedbacks and interactions globally and locally at the Arctic and outside the Arctic environments.Non peer reviewe

Relation of air mass history to nucleation events in Po Valley, Italy, using back trajectories analysis

International audienceIn this paper, we study the transport of air masses to San Pietro Capofiume (SPC) in Po Valley, Italy, by means of back trajectories analysis. Our main aim is to investigate whether air masses originate over different regions on nucleation event days and on nonevent days, during three years when nucleation events have been continuously recorded at SPC. The results indicate that nucleation events occur frequently in air masses arriving from Central Europe, whereas event frequency is much lower in the air transported from southern directions and from the Atlantic Ocean. We also analyzed the behaviour of meteorological parameters during 96 h transport to SPC, and found that, on average, event trajectories undergo stronger subsidence during the last 12 h before the arrival at SPC than nonevent trajectories. This causes a reversal in the temperature and relative humidity (RH) differences between event and nonevent trajectories: between 96 and 12 h back time, temperature is lower and RH is higher for event than nonevent trajectories and between 12 and 0 h vice versa. Boundary layer mixing is stronger along the event trajectories compared to nonevent trajectories. The absolute humidity (AH) is similar for the event and nonevent trajectories between about 96 h and about 60 h back time, but after that, the event trajectories AH becomes lower due to stronger rain. We also studied transport of SO2 to SPC, and conclude that although sources in Po Valley most probably dominate the measured concentrations, certain Central and Eastern European sources also make a substantial contribution

Waterfalls as sources of small charged aerosol particles

In this study, we measured the mobility distributions of cluster and intermediate ions with an ion spectrometer near a waterfall. We observed that the concentration of negative 1.5–10 nm ions was one-hundred fold higher than a reference point 100 m away from the waterfall. Also, the concentration of positive intermediate ions was found to be higher than that at the reference point by a factor of ten. This difference was observed only at the smallest sizes; above 10 nm the difference was insignificant

Commentary on cloud modelling and the mass accommodation coefficient of water

International audienceThe mass accommodation coefficient of water is a quantity for which different experimental techniques have yielded conflicting values in the range 0.04-1. From the viewpoint of cloud modelling, this is an unfortunate situation, since the value of the mass accommodation coefficient affects the model results, e.g. the number concentration of activated cloud droplets. In this commentary we note that in cloud modelling, the primary quantity of interest is the droplet growth rate rather than the mass accommodation coefficient, and that experimental investigations of droplet growth rates provide more direct verification of cloud models than do measurements of the mass accommodation coefficient. Furthermore, we argue that the droplet growth rates calculated in cloud model studies are consistent with experimental results obtained so far only if a mass accommodation coefficient of unity is applied

Carbon dioxide fluxes and carbon balance of an agricultural grassland in southern Finland

A significant proportion of the global carbon emissions to the atmosphere originate from agriculture. Therefore, continuous long-term monitoring of CO2 fluxes is essential to understand the carbon dynamics and balances of different agricultural sites. Here we present results from a new eddy covariance flux measurement site located in southern Finland. We measured CO2 and H2O fluxes at this agricultural grassland site for 2 years, from May 2018 to May 2020. In particular the first summer experienced prolonged dry periods, which affected the CO2 fluxes, and substantially larger fluxes were observed in the second summer. During the dry summer, leaf area index (LAI) was notably lower than in the second summer. Water use efficiency increased with LAI in a similar manner in both years, but photosynthetic capacity per leaf area was lower during the dry summer. The annual carbon balance was calculated based on the CO2 fluxes and management measures, which included input of carbon as organic fertilizers and output as yield. The carbon balance of the field was -57 +/- 10 and -86 +/- 12 g C m(-2) yr(-1) in the first and second study years, respectively.Peer reviewe