Air sparging in an aquifer below a less permeable horizontal layer is modeled using a two-phase flow approach. Supported by numerical simulations, we show that a steady state situation is reached. For an analysis of the steady state, we distinguish three different flow regimes, which occur between the well screen and the unsaturated zone. Just below the interface that separates the high and the low permeable layers a regime with almost hydrostatic capillary pressures develops. We use this observation to derive an ordinary differential equation for the pressure at the interface, which leads to an approximation of the air flow pattern just below and within the low permeable layer. The approximation provides an estimate for the radius of influence as a function of the physical parameters. The agreement between the analytical approximation and the numerical steady state results is almost perfect when heterogeneity is increased. With a few modifications the analysis applies also to a dense non-aqueous phase liquid (DNAPL) spill above a less permeable layer.

Comparison with an illustrative numerical simulation shows that the analytical approximation provides a good estimate of the radial spreading of the DNAPL flow on top of and within the low permeable layer. DOI: Abstract Trace metals are ubiquitous in urban ambient air, with mass concentrations in the range of a few μg/m3 down to less than 100 pg/m3. To measure such low concentrations represents a challenge for chemical and physical analysis. alen paralda tower hepa air purifierIn this study, ambient aerosol was collected in Zürich (Switzerland) in 1-h intervals and three size fractions (aerodynamic diameters 0.1−1 μm, 1−2.5 μm, and 2.5−10 μm), using a three-stage rotating drum impactor (RDI). honeywell whisper quiet air purifier hfd-123-hdThe samples were analyzed by energy-dispersive Synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) to obtain size-segregated hourly elemental aerosol mass concentrations for Cr, Mn, Fe, Cu, Zn, Br, and Pb, along with S, Cl, and Ca under the selected experimental conditions. rainbow rainmate air freshener purifier

The high sensitivity of SR-XRF allowed for detection limits of <50 pg/m3 for most of the above elements, with a net analysis time of only 15 s per sample. The data obtained with this technique illustrate that there is a considerable gain of relevant information when time resolution for measurements is increased from 1 day to 1 h. The individual size fractions of a specific element may show significantly different short-term patterns. Citing ArticlesRelated ContentCitation data is made available by participants in CrossRef's Cited-by LinkingFor a more comprehensive list of citations to this article, users are encouraged to perform a search in SciFinder. Sampling and Online Analysis of Alkalis in Thermal Process Gases with a Novel Surface Ionization Detector , , , and 2011 AbstractPDF w/ LinksIdentifying Sources of Uncertainty from the Inter-Species Covariance of Measurement Errors and 2011 AbstractPDF w/ LinksSize segregation behavior of heavy metals in superfine pulverized coal using synchrotron radiation-induced X-ray fluorescence , , , , , 2016 High time-resolved elemental components in fine and coarse particles in the Pearl River Delta region of Southern China: Dynamic variations and effects of meteorology , , , , , , , , , , 2016 Semi-continuous sampling of health relevant atmospheric particle subfractions for chemical speciation using a rotating drum impactor in series with sequential filter sampler

, , , , , , , , 2016 Inter-annual variability of wintertime PM2.5 chemical composition in Xi'an, China: Evidences of changing source emissions , , , , , , , 2016 Present role of PIXE in atmospheric aerosol research 2015 Feasibility study of ED-XRF analysis of atmospheric particulate matter samples collected with high time resolution , , , , , , 2015 Direct on-strip analysis of size- and time-resolved aerosol impactor samples using laser induced fluorescence spectra excited at 263 and 351 nm , , , , 2014 Quantitative analysis of elements (C, N, O, Al, Si and Fe) in polyamide with wavelength dispersive X-ray fluorescence spectrometry , , , 2013 Nondestructive characterization of the contaminated biodegradable fraction of municipal solid waste using synchrotron radiation-induced micro-X-ray fluorescence , , , 2013 A review of methods for long term in situ characterization of aerosol dust , , 2012 6Fine and coarse PM composition and sources in rural and urban sites in Switzerland: Local or regional pollution?

, , , 2012 Dimensional characterization of selected elements in airborne PM10 samples using μ-SRXRF : Dimensional characterization of PM10 samples using μ-SRXRF , , , , , 2012ED-XRF set-up for size-segregated aerosol samples analysis , , , , , , , , , 2011 Size-fractionated characterization and quantification of nanoparticle release rates from a consumer spray product containing engineered nanoparticles , , , , , , , , 2010 Deposition Uniformity and Particle Size Distribution of Ambient Aerosol Collected with a Rotating Drum Impactor , , , , , , , , 2009 Characterization of atmospheric aerosols using Synchroton radiation total reflection X-ray fluorescence and Fe K-edge total reflection X-ray fluorescence-X-ray absorption near-edge structure☆U , F , C , P , J , G , G 2008 X-ray fluorescence spectrometry for high throughput analysis of atmospheric aerosol samples: The benefits of synchrotron X-raysN , P , C , M , A , G , K , D , C , M 2008 Atomic spectrometry update. Environmental analysis , , , , , 2007 A new technique for the deposition of standard solutions in total reflection X-ray fluorescence spectrometry (TXRF) using pico-droplets generated by inkjet printers and its applicability for aerosol analysis with SR-TXRF☆U , S , M , G , C , S , P , C , G , G 2006 Application of the focused ion beam technique in aerosol science: detailed investigation of selected, airborne particles , 2006 Atomic spectrometry update?