6 research outputs found
Growth of sulphuric acid nanoparticles under wet and dry conditions
New particle formation, which greatly influences the number concentrations
and size distributions of an atmospheric aerosol, is often followed by a
rapid growth of freshly formed particles. The initial growth of newly
formed aerosol is the crucial process determining the fraction of nucleated
particles growing to cloud condensation nuclei sizes, which have a
significant influence on climate. In this study, we report the laboratory
observations of the growth of nanoparticles produced by nucleation of
H<sub>2</sub>SO<sub>4</sub> and water in a laminar flow tube at temperatures of 283, 293
and 303 K, under dry (a relative humidity of 1%) and wet conditions
(relative humidity of 30%) and residence times of 30, 45, 60 and 90 s.
The initial H<sub>2</sub>SO<sub>4</sub> concentration spans the range from 2 × 10<sup>8</sup>
to 1.4 × 10<sup>10</sup> molecule cm<sup>−3</sup> and the calculated
wall losses of H<sub>2</sub>SO<sub>4</sub> were assumed to be diffusion limited. The
detected particle number concentrations, measured by the Ultrafine
Condensation Particle Counter (UCPC) and Differential Mobility Particle
Sizer (DMPS), were found to depend strongly on the residence time.
Hygroscopic particle growth, presented by growth factors, was found to be in
good agreement with the previously reported studies. The experimental growth
rates ranged from 20 nm h<sup>−1</sup> to 890 nm h<sup>−1</sup> at relative humidity (RH) 1% and from
7 nm h<sup>−1</sup> to 980 nm h<sup>−1</sup> at RH 30% and were found to increase
significantly with the increasing concentration of H<sub>2</sub>SO<sub>4</sub>.
Increases in the nucleation temperature had a slight enhancing effect on the
growth rates under dry conditions. The influence of relative humidity on
growth was not consistent – at lower H<sub>2</sub>SO<sub>4</sub> concentrations, the
growth rates were higher under dry conditions while at H<sub>2</sub>SO<sub>4</sub>
concentrations greater than 1 × 10<sup>10</sup> molecule cm<sup>−3</sup>, the
growth rates were higher under wet conditions. The growth rates show only a
weak dependence on the residence time. The experimental observations were
compared with predictions made using a numerical model, which investigates
the growth of particles with three different extents of neutralization by
ammonia, NH<sub>3</sub>: (1) pure H<sub>2</sub>SO<sub>4</sub> – H<sub>2</sub>O particles; (2)
particles formed by ammonium bisulphate, (NH<sub>4</sub>)HSO<sub>4</sub>; (3) particles
formed by ammonium sulphate, (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>. The highest growth
rates were found for ammonium sulphate particles. Since the model accounting
for the initial H<sub>2</sub>SO<sub>4</sub> concentration predicted the experimental
growth rates correctly, our results suggest that the commonly presumed
diffusional wall losses of H<sub>2</sub>SO<sub>4</sub> in case of long-lasting
experiments are not so significant. We therefore assume that there are not
only losses of H<sub>2</sub>SO<sub>4</sub> on the wall, but also a flux of
H<sub>2</sub>SO<sub>4</sub> molecules from the wall into the flow tube, the effect being
more profound under dry conditions and at higher temperatures of the tube
wall. Based on a comparison with the atmospheric observations, our results
indicate that sulphuric acid alone cannot explain the growth rates of
particles formed in the atmosphere
\uab Les linguistiques du d\ue9tachement. Actes du Colloque International de Nancy (7-9 juin 2006) \ubb. Collection SCIENCES POUR LA COMMUNICATION, Peter Lang, Berne, 2009, N\ub0 87, p. 595.
Le num\ue9ro 87 de la collection SCIENCES POUR LA COMMUNICATION est consacr\ue9 \ue0 la publication des actes du Colloque International \uab Les linguistiques du d\ue9tachement \ubb qui s\u2019est tenu \ue0 Nancy les 7-9 juin 2006. Ce colloque, dont l\u2019organisation a \ue9t\ue9 assur\ue9e par l\u2019ATILF (Analyse et Traitement Informatique de la Langue Fran\ue7aise, CNRS et Nancy-Universit\ue9s) et par le laboratoire CRISCO (Centre de Recherches Inter-langues sur la Signification en Contexte, Universit\ue9 de Caen), avait le but de r\ue9unir tous les chercheurs s\u2019int\ue9ressant aux structures \uab \ue0 d\ue9tachement \ubb, c\u2019est-\ue0-dire aux phrases dites DISLOQU\uc9ES ou SEGMENT\uc9ES (dislocation \ue0 droite ou \ue0 gauche), mais aussi \ue0 l\u2019apposition et \ue0 d\u2019autres formes de discontinuit\ue9 syntaxique. S\u2019agissant de constructions qui se r\ue9alisent, avec de fortes ressemblances, dans l\u2019ensemble des syst\ue8mes linguistiques, les organisateurs ont veill\ue9 \ue0 ce que la plus grande vari\ue9t\ue9 de langues soit repr\ue9sent\ue9e, souhaitant aboutir, au-del\ue0 des difformit\ue9s th\ue9oriques et terminologiques, \ue0 une typologie des constructions \uab \ue0 d\ue9tachement \ubb. Les actes du colloque r\ue9pertorient donc tant les \ue9tudes portant sur l\u2019\ue9crit que celles sur l\u2019oral conversationnel, et pr\ue9sentent, en m\ueame temps, un \ue9chantillonnage repr\ue9sentatif des diff\ue9rents niveaux d\u2019analyse (syntaxique, s\ue9mantique, pragmatique, prosodique), du point de vue adopt\ue9 (synchronique ou diachronique) et des mod\ue8les th\ue9oriques de r\ue9f\ue9rence. En raison de leur grand nombre, les 41 contributions seront r\ue9parties ici par grandes aires th\ue9matiques ainsi que par niveau de saillance et/ou de repr\ue9sentativit\ue9 \ue0 l\u2019int\ue9rieur de chaque aire