In 2015 the European Joint Research Center (JRC) for air quality in Ispra, Italy, carried out an intercomparison for the determination of PM10 and PM2.5 in ambient air. Five laboratories also analyzed the content of heavy metals (arsenic, cadmium, lead and nickel) in PM10 from filter samples collected during the intercomparison. Thus, all steps from sampling in the field to instrumental quantification of heavy metals in the laboratory could be statistically analyzed. The different techniques of sampling and sample work-up had no significant influence on the analysis results. However, the method of instrumental analysis strongly influenced them: The results of laboratories using the Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) coincided well in most cases. For laboratories using the Energy Dispersed X-Ray Fluorescence (ED-XRF) technique the uncertainty of the results strongly depended on the metal concentration. For cadmium the concentrations generally were too low for analysis by ED-XRF, for arsenic, lead and nickel the relative uncertainties decreased exponentially with increasing concentrations. The relation between metal concentration and the relative uncertainty of analysis results could be described as power functions. Analysis of lead and nickel by ED-XRF is well possible in the range of the EU limit and target values for these metals.
We identify stellar structures in the PHANGS sample of 74 nearby galaxies and construct morphological masks of sub-galactic environments based on Spitzer 3.6 mu m images. At the simplest level, we distinguish five environments: centres, bars, spiral arms, interarm regions, and discs without strong spirals. Slightly more sophisticated masks include rings and lenses, which are publicly released but not explicitly used in this paper. We examine trends with environment in the molecular gas content, star formation rate, and depletion time using PHANGS-ALMA CO(2-1) intensity maps and tracers of star formation. The interarm regions and discs without strong spirals clearly dominate in area, whereas molecular gas and star formation are quite evenly distributed among the five basic environments. We reproduce the molecular Kennicutt-Schmidt relation with a slope compatible with unity within the uncertainties and without significant slope differences among environments. In contrast to what has been suggested by early studies, we find that bars are not always deserts devoid of gas and star formation, but instead they show large diversity. Similarly, spiral arms do not account for most of the gas and star formation in disc galaxies, and they do not have shorter depletion times than the interarm regions. Spiral arms accumulate gas and star formation, without systematically boosting the star formation efficiency. Centres harbour remarkably high surface densities and on average shorter depletion times than other environments. Centres of barred galaxies show higher surface densities and wider distributions compared to the outer disc; yet, depletion times are similar to unbarred galaxies, suggesting highly intermittent periods of star formation when bars episodically drive gas inflow, without enhancing the central star formation efficiency permanently. In conclusion, we provide quantitative evidence that stellar structures in galaxies strongly affect the organisation of molecular gas and star formation, but their impact on star formation efficiency is more subtle. ; Instituto de Salud Carlos III Spanish Government PID2019-106027GA-C44 European Research Council (ERC) 694343 National Science Foundation (NSF) National Research Foundation of Korea 1615105 1615109 1653300 National Aeronautics and Space Administration (NASA) under ADAP grants NNX16AF48G NNX17AF39G German Research Foundation (DFG) SFB 881 138713538 Heidelberg Cluster of Excellence "STRUCTURES" in the framework of Germany's Excellence Strategy EXC-2181/1 390900948 European Research Council via the ERC Synergy Grant "ECOGAL" 855130 SKA South Africa 694343 721463 726384/Empire Academy of Finland 297738 German Research Foundation (DFG) KR4801/1-1 KR4598/2-1 KR4801/2-1 BI1546/3-1 European Research Council (ERC) 714907 National Science Foundation (NSF) 1903946 Spanish Government AYA2016-79006-P Spanish Government European Commission PID2019-108765GB-I00 Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU INP IN2P3 French Atomic Energy Commission Centre National D'etudes Spatiales Programme National 'Physique et Chimie du Milieu Interstellaire' (PCMI) of CNRS/INSU INC/INP - CEA Natural Sciences and Engineering Research Council of Canada (NSERC) RGPIN-2017-03987 Spanish funding grant (MINECO/FEDER) AYA2016-79006-P Spanish funding grant (MCIU/AEI/FEDER) PGC2018-094671-B-I00 Spanish funding grant (MICINN) PID2019-108765GB-I00 German Research Foundation (DFG) 138713538 - SFB 881 ; Versión sometida a revisión - Preprint
