Roy W. Dixon

The effect of riming on the ion concentrations of winter precipitation: 1. A quantitative analysis of field measurements

Although riming has been demonstrated to influence precipitation chemistry, its relative importance as a mechanism for the transfer of trace species into snow is not well known. To overcome the qualitative measure of riming in past studies, the mass fraction of snow originating from accreted cloud droplets (rimed mass fraction) is estimated indirectly in this study from replicas of collected snow crystals and flakes. The rimed mass fraction is then compared with the concentrations of various ionic trace species in collected snow and cloud water samples at a prealpine site in Switzerland from 10 case studies. The ratio of the precipitation to the cloud water concentration for a given ion, which indicates the transfer efficiency of the species from clouds to snow, was found to be correlated weakly to the rimed mass fraction for all sample periods investigated. However, much of the variability in the relationship came from sampling periods when the precipitation intensity was low. The relative importance of riming and other scavenging processes was estimated from the sample set, although this estimate is complicated by differences in concentration between cloud droplets collected by snow and those sampled at the site and by case to case variability. Under conditions of higher precipitation intensities, riming appears to be the dominant transfer mechanism for the incorporation of the major ionic species into snow.

Scientific goals and experiments of the project “winter precipitation at Mount Rigi”: An overview

Wet deposition plays an important role as a mechanism for cleansing of the polluted troposphere. Fluxes of pollutants from the atmosphere to earths surface can affect soil and aquatic ecosystems. The investigation of the pollutant incorporation into wet deposition is therefore of considerable interest for environmental research.The project “Winter precipitation at Mount Rigi” addresses the processes determining the chemical composition of wet deposition through an integrated approach considering atmospheric physical and chemical processes and their complex interactions. The investigated topics include: aerosol and gas scavenging, atmospheric chemistry (cloud water chemistry), cloud physics and dynamics. The design of the experiment, using three ground based measuring stations at the northwestern slope of the mountain, and the conceptual ideas using case study investigations are discussed.

Additional mass transport considerations in the formation of hydroxyalkylsulfonates

Abstract The formation rates of hydroxyalkylsulfonates in cloud droplets was examined with consideration of aldehyde mass transport to droplets and hydration rates of aldehydes in cloud droplets. Detailed calculations were performed for hydroxymethanesulfonate formation in cloud droplets. It was found that mass transport of formaldehyde into droplets can occur rapidly enough so that methylene glycol dehydration is not the rate limiting step as it is, under certain conditions, in a closed system.

Development of a novel ion-pairing UPLC method with cation-exchange solid-phase extraction for determination of free timolol in human plasma

A novel UPLC-UV method was developed for analysis of timolol in human plasma using a simple, fast, and cost effective ion-exchange SPE procedure, followed by separation on a C18 UPLC column with a mobile phase consisting of acetonitrile, phosphate buffer, and sodium 1-octane sulfonate as an ion pairing agent. The method was fully validated according to US-FDA guidelines, and was found to be sufficiently accurate and precise for analysis of timolol in human plasma for clinical pharmacokinetic studies. The application of ion-exchange SPE cartridges for purification of timolol in plasma produced excellent percent recoveries and good sample clean-up, while the ion-pairing separation described here allowed quantitation of timolol without interference from endogenous sample components. The method lower limit of detection was 1.7 ng/mL and the lower limit of quantitation was 5.0 ng/mL, allowing for analysis of therapeutic concentrations of timolol in plasma.

Solar-powered aerosol samplers for use with PIXE analysis

Abstract Monitoring of airborne pollutants in pristine areas is often hampered by the lack of electrical power and by difficult site access. Increased concern about effects of acid deposition in remote areas has necessitated development of appropriate sampling and analytical techniques. PIXE analysis of aerosol particles requires small amounts of material; hence samples collected by low flowrate, solar-powered pumps may still be adequate to achieve useful analytical sensitivities. We report on the application of two aerosol samplers, modified for solar-powered, unattended operation, at a 3000 m elevation site in the Sequoia National Park. PIXE detection limits for samples from a solar-powered stacked filter unit (SFU) sampler are compared to a standard SFU. Time-resolved sampling was performed using a single rotating impaction stage sampler (SPASI). Samples were analyzed by PIXE in 8-h increments. Higher concentration pollutants, such as S and K, were observed in these samples. Reduced sampling sensitivity for the SPASI unit (and remote location) precluded observation of lower concentration pollutant metals such as Ni and Pb. These metals were regularly above detection limits in the time-integrated (7 d) SFU samples. The usefulness of time-resolved sampling was shown by relating S and K variations to meteorology and aerosol transport.