The chemistry of sulfur and nitrogen species in a fog system A multiphase approach

Concentration and phase distribution of sulfur and nitrogen species during a particular fog episode in the Po Valley are experimentally described in this paper. Chemical measurements were carried out simultaneously at different heights within the fog layer, up to 50 m. Microphysical and meteorological parameters necessary for the description of the fog multiphase system were also concurrently measured as a function of height. The fog cycle (formation, evolution, dissipation) is described in terms of the total acidity of a unit volume of air containing gas species, interstitial aerosol particles and fog droplets. The fog system was not closed and input of acidic and basic components was observed during fog evolution. The driving force which determines the acidity of the fog multiphase atmospheric system was found to be the presence of NH 3 and its partitioning among the different phases. A strong decrease of fog water pH (from 5.6 down to 2.8) was observed during fog evolution and was attributed to a HNO 3 input to the system. These acidic and basic inputs are described in terms of a titration/back-titration process of the fog system. The SO 2 oxidation process in fog water was found to be of minor importance in determining the SO 4 = concentration within the fog system, due to both low SO 2 concentration and limited oxidant availability during the experiment. DOI: 10.1034/j.1600-0889.1992.t01-4-00005.

Activation properties of ambient aerosol in the Netherlands

A cloud chamber has been used to study the cloud activation of ambient aerosol in The Netherlands. The large dimensions and throughput of the chamber allowed unperturbed collection of aerosol and droplets with cascade impactors and on-line measurements with cloud monitors (FSSP) inside the facility. The study provided maxima for the number of man-made aerosol acting as cloud nuclei in marine clouds in The Netherlands. Emphasis was given to the investigation of cloud formation in marine air, since sensitivity studies had shown that such clouds are most effectively influenced by the (extra) anthropogenic aerosol particles. For this reason the supersaturations in the study were low (on average 0.12\%), similar to those in actual marine stratus. The effect of the anthropogenic aerosols on cloud formation was determined by comparing the number of droplets formed in `'clean'' arctic marine air to the number of droplets formed in `'polluted'' marine air (air which had travelled over the U.K.). Air masses with the total aerosol number concentration of the order of 100 cm(-3) were considered as `'clean'' marine air. Air masses with higher aerosol concentrations were divided into `'moderately'' and `'heavily'' polluted with total aerosol concentrations of the order of 1000 and 10,000 cm(-3), respectively. In the clean marine air all potential cloud nuclei (particles lar er than the threshold size of the smallest reference particles that were activated al given supersaturation) were activated and the number of cloud droplets formed was on average 45 cm(-3). In the moderately polluted air 72\% of potential cloud nuclei were activated and the average droplet number was 190 cm(-3). The difference in the actual cloud droplet number and the number of potential cloud nuclei could be explained by the presence of water-insoluble particles which do not activate. In the heavily polluted air the average droplet concentration was around 320 cm(-3) which is, on average, 24\% of the number of potential cloud nuclei. Copyright (C) 1996 Elsevier Science Lt

Advanced Real-Time Process Analytics for Multistep Synthesis in Continuous Flow

In multistep continuous flow chemistry, studying complex reaction mixtures in real time is a significant challenge, but provides an opportunity to enhance reaction understanding and control. We report the integration of four orthogonal Process Analytical Technology tools (NMR, UV/vis, IR and UHPLC) in the multistep synthesis of an Active Pharmaceutical Ingredient, mesalazine. This synthetic route makes optimal use of flow processing for nitration, high temperature hydrolysis and hydrogenation steps, as well as three inline separations. Advanced data analysis models were developed (indirect hard modelling, deep learning and partial least squares regression), to quantify the desired products, intermediates and impurities in real time, at multiple points along the synthetic pathway. The capabilities of the system have been demonstrated by operating both steady state and dynamic experiments and represents a significant step forward in data-driven continuous flow synthesis

Microphysics of clouds: Model vs measurements

International audienc