Observation of nighttime new particle formation over the French Landes forest.

Improving the understanding of processes related to atmospheric particle sources is essential to better assess future climate. Especially, how biogenic volatile organic compounds (BVOCs) are involved in new particle formation (NPF) is still unclear, highlighting the need for field studies in sites that have not yet been explored. Weakly anthropised, mostly composed of maritime pines (known as strong monoterpene emitters), vast and under the influence of sea spray inputs, the Landes forest (located in the southwestern part of France) is a suitable ecosystem to explore these questions. The aim of the present work was to investigate for the first time NPF in the Landes forest, and to identify the conditions for NPF. During a field campaign conducted in July 2015, clear NPF was observed during nighttime, at a high frequency rate (37.5%), whereas only two daytime episodes were observed. Growth rates during NPF events were in the range 9.0-15.7nmh-1, and nucleation rates (J10) in the range 0.8-8 particles cm3s-1, typically in the range of reported values from rural sites. Nocturnal NPF started at sunset, lagging the reductions of temperature and ozone concentration as well as the increase of relative humidity, atmospheric stability and monoterpene concentration. We established that NPF occurred during more stratified atmosphere episodes, reflecting that NPF is more influenced by local processes at the Landes forest site (Bilos). Concentration of the sum of monoterpenes, here mainly α- and ß-pinene, was observed to be maximal during NPF episodes. On the contrary, ozone concentration was lower, which may indicate a larger consumption during nights where NPF episodes occur. Results strongly suggest the contribution of BVOC oxidation to nocturnal NPF, in both nucleation and the growth stages.

Effects of avocado and soya bean lipidic non-saponifiables on the components of skin connective tissue after topical application in the hairless rat: biophysical and biomechanical determination.

Synopsis The non-saponifiable lipidic fractions of avocado and soya bean applied percutaneously to hairless rats for 15 days had been shown to produce biochemical modifications of dermal connective tissue components: increases of soluble collagen and of the ratio soluble collagen/insoluble collagen. In this present study, we tried to show whether these biochemical modifications could be confirmed by biophysical analytical methods and could affect the biochemical properties of the skin. The experiments were carried out on three groups of rats treated by application to the dorsal skin, either with 0.9% NaCl (control), or sweet almond oil (vehicle), or with a mixture of 2/3 soya bean and 1/3 avocado in solution at 5% of sweet almond oil (treated group). After 15 days treatment, the rats were killed and the skin of the treated area dissected. X-ray diffraction diagrams were recorded by varying the position of previously dried samples in controlled conditions. Results indicated that the vehicle decreased the orientation degree of collagen fibres, acting on their reticulation. The addition of the non-saponifiable fraction did not significantly add to the vehicle effect. The study of thermostability of the cutaneous collagen by differential scanning calorimetry showed that non-saponifiables increased the slope of the rise of temperature of denaturation. The quantity of heat absorbed during the denaturation (enthalpy variation) reached around 0.04 J mg(-1) of collagen in the control groups and did not exceed 0.03 J mg(-1) of collagen in the treated ones. Taken in conjunction with previous work it is probable that the non-saponifiables increase the proportion of soluble collagen. The elasticity of whole skin, determined by a static method using an Instron exten-siometer was significantly modified by treatment with non-saponifiables. They produced a decrease of the elasticity module. These results correspond to a decrease of collagen reticulation degree.

Biochemical effects of unsaponifiable lipidic components of avocado and soya bean administered percutaneously on the connective tissue components of hairless rat skin.

Synopsis The unsaponifiable lipidic fractions of avocado and soya bean were administered percutaneously, on the dorsal skin of hairless rats for 15 days, in a 5% sweet almond oil solution. This treatment produced a modification of dermal connective tissue components. The biochemical analysis showed an increase of soluble proteins, especially of salt soluble collagen together with a decrease of proteins insoluble in neutral buffer. The ratio, soluble proteins:insoluble proteins, increases as well as the ratio soluble collagen: insoluble collagen. These modifications can be considered as a result of the activation of connective tissue metabolism. The above results are in agreement with those obtained when the unsaponifiables were administered per os to rats.