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Jan Hovorka

Bio: Jan Hovorka is an academic researcher from Charles University in Prague. The author has contributed to research in topics: Aerosol & Particulates. The author has an hindex of 17, co-authored 43 publications receiving 769 citations.

Papers
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TL;DR: In this paper, the chemical and phase compositions of particles produced by laser ablation (266 nm Nd:YAG) of silicate NIST glasses and zircon were studied by SIMS and HR-TEM techniques.
Abstract: The chemical and phase compositions of particles produced by laser ablation (266 nm Nd:YAG) of silicate NIST glasses and zircon were studied by SIMS and HR-TEM techniques. The data suggest that the formation of phases of different mineralogy and/or chemical composition from the original sample at the ablation site can result in elemental fractionation (non-stoichiometric sampling) in material delivered to the ICP-MS for quantitative analysis. Evidence of the element fractionation is preserved in chemically zoned ejecta deposited around the ablation pit. The chemical composition and mineralogy of particles varies with particle size so that the efficiency of transport of particles also plays a role in elemental fractionation. During the first 250 pulses in a typical ablation experiment using a 266 nm laser, particle sizes are mainly <2.5 μm; thereafter they decrease to <0.3 μm. Pb and U are fractionated significantly during the ablation of both silicate glass and zircon. During the ablation of glass, both micron-sized, melt-derived, spherical particles, and nm-sized, condensate-derived particle clusters, are produced; the very smallest particles (<0.04 μm) have anomalously high Pb/U ratios. For zircon, both larger (0.2–0.5 μm) spherical particles and agglomerates of smaller (∼0.005 μm) particles produced by ablation are mixtures of amorphous and crystalline materials, probably zircon, baddeleyite (ZrO2) and SiO2. Evidence for thermal decomposition of zircon to baddeleyite and SiO2 is preserved in the wall of the ablation pit, and may lead to the commonly observed increase in Pb/U recorded during laser ablation ICP-MS analysis. It follows that a matrix-matched external calibration is essential for achieving highly precise and accurate laser (266 nm wavelength) ablation ICP-MS analysis of Pb and U in silicate samples.

128 citations

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TL;DR: In this paper, organic and elemental carbon (OC and EC) content in PM10 was studied at two sites in Prague, which were located in a suburb and in the downtown.

73 citations

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TL;DR: In this article, the authors evaluated the performance and the uncertainty of receptor models (RMs) in intercomparison exercises employing real-world and synthetic input datasets and concluded that RMs are capable of estimating the contribution of the major pollution source categories over a given time window with a level of accuracy that is in line with the needs of air quality management.

68 citations

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TL;DR: Positive Matrix Factorization-PMF was applied to hourly resolved elemental composition of fine and coarse aerosol particles to apportion their sources in the airshed of residential district, Ostrava-Radvanice and Bartovice in winter 2012, finding no statistical significant differences amongst the monitors.

58 citations

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TL;DR: The results indicate that water solubility could function as a limiting factor for bioaccessibility of inhaled particulate NPAHs and OPAhs, without considerable effect of surfactant lipids and proteins in the lung lining fluid.
Abstract: Among the nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) are some of the most hazardous substances to public health, mainly because of their carcinogenicity and oxidative potential. Despite these concerns, the concentrations and fate of NPAHs and OPAHs in the atmospheric environment are largely unknown. Ambient air concentrations of 18 NPAHs, 5 quinones, and 5 other OPAHs were determined at two urban and one regional background sites in central Europe. At one of the urban sites, the total (gas and particulate) concentrations of Σ10OPAHs were 10.0 ± 9.2 ng/m3 in winter and 3.5 ± 1.6 ng/m3 in summer. The gradient to the regional background site exceeded 1 order of magnitude. Σ18NPAH concentrations were typically 1 order of magnitude lower than OPAHs. Among OPAHs, 9-fluorenone and (9,10)-anthraquinone were the most abundant species, accompanied by benzanthrone in winter. (9,10)-Anthraquinone represented two-thirds of quinones. We found that a large fraction of the target substance particulate mass was carried by submicrometer particles. The derived inhalation bioaccessibility in the PM10 size fraction is found to be ≈5% of the total ambient concentration of OPAHs and up to ≈2% for NPAHs. For 9-fluorenone and (9,10)-anthraquinone, up to 86 and 18%, respectively, were found at the rural site. Our results indicate that water solubility could function as a limiting factor for bioaccessibility of inhaled particulate NPAHs and OPAHs, without considerable effect of surfactant lipids and proteins in the lung lining fluid.

55 citations


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TL;DR: The basic evidence on the health effects of particulate matter is summarized and an in-depth analysis is provided to address the implications for policy-makers so that more stringent strategies can be implemented to reduce air pollution and its health effects.

1,920 citations

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TL;DR: In this paper, a protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16-32?m.
Abstract: A protocol was established for simultaneous measurements of zircon U-Pb ages and trace elements by LA-ICP-MS at spot sizes of 16–32 ?m. This was accomplished by introducing N2 into ICP to increase the sensitivity. The obtained U-Pb ages for zircon standards GJ-1, TEMORA and SK10-2 are consistent with the preferred values within about 1% uncertainty (2 σ ) by simple external calibration against zircon standard 91500. Different data reduction softwares could yield different uncertainties for calculation of U-Pb ages. The commercially available program GLITTER4.4 could apply an improper uncertainty calculation strategy, but it may yield artificial high precisions for single analyses. Our trace element analyses indicate that Si is not an ideal internal standard for zircon when calibrated against the NIST glasses. Calibration against the NIST glasses using Si as an internal standard, a systematic deviation of 10%–30% was found for most trace elements including Zr. However, the trace element compositions of zircon can be accurately measured by calibration against multiple reference materials with natural compositions (e.g., BCR-2G, BHVO-2G and BIR-1G), or calibration against NIST SRM 610 and using Zr as an internal standard. Analyses of two pieces of GJ-1 demonstrate that it is relatively homogenous for most trace elements (except for Ti).

1,227 citations

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TL;DR: In this paper, the authors proposed a data reduction approach to correct the effects of downhole elemental fractionation by first observing the elemental response and then applying an appropriate (and often unique) model to the data.
Abstract: Elemental fractionation effects during analysis are the most significant impediment to obtaining precise and accurate U-Pb ages by laser ablation ICPMS. Several methods have been proposed to minimize the degree of downhole fractionation, typically by rastering or limiting acquisition to relatively short intervals of time, but these compromise minimum target size or the temporal resolution of data. Alternatively, other methods have been developed which attempt to correct for the effects of downhole elemental fractionation. A common feature of all these techniques, however, is that they impose an expected model of elemental fractionation behavior; thus, any variance in actual fractionation response between laboratories, mineral types, or matrix types cannot be easily accommodated. Here we investigate an alternate approach that aims to reverse the problem by first observing the elemental fractionation response and then applying an appropriate (and often unique) model to the data. This approach has the versatility to treat data from any laboratory, regardless of the expression of downhole fractionation under any given set of analytical conditions. We demonstrate that the use of more complex models of elemental fractionation such as exponential curves and smoothed cubic splines can efficiently correct complex fractionation trends, allowing detection of spatial heterogeneities, while simultaneously maintaining data quality. We present a data reduction module for use with the lolite software package that implements this methodology and which may provide the means for simpler interlaboratory comparisons and, perhaps most importantly, enable the rapid reduction of large quantities of data with maximum feedback to the user at each stage. Copyright 2010 by the American Geophysical Union.

914 citations

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TL;DR: For the first time, mass spectra of intact proteins were obtained using laser desorption without adding a matrix in this study, demonstrating the applicability of ELDI to the analysis of proteins and synthetic organic compounds.
Abstract: A new method of electrospray-assisted laser desorption/ionization (ELDI) mass spectrometry, which combines laser desorption with post-ionization by electrospray, was applied to rapid analysis of solid materials under ambient conditions. Analytes were desorbed from solid metallic and insulating substrata using a pulsed nitrogen laser. Post-ionization produced high-quality mass spectra characteristic of electrospray, including protein multiple charging. For the first time, mass spectra of intact proteins were obtained using laser desorption without adding a matrix. Bovine cytochrome c and an illicit drug containing methaqualone were chosen in this study to demonstrate the applicability of ELDI to the analysis of proteins and synthetic organic compounds.

482 citations

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TL;DR: A review of the published literature on source apportionment of ambient particulate matter (PM) in Europe using receptor models (RMs) was conducted by as discussed by the authors, where consistent records were identified for source contribution estimates of PM mass concentrations for 272 records and of organic carbon (OC) in PM for 60 records.

481 citations