On the accuracy of aerosol photoacoustic spectrometer calibrations using absorption by ozone

This is the final version of the article. Available from EGU via the DOI in this record.In recent years, photoacoustic spectroscopy has emerged as an invaluable tool for the accurate measurement of light absorption by atmospheric aerosol. Photoacoustic instruments require calibration, which can be achieved by measuring the photoacoustic signal generated by known quantities of gaseous ozone. Recent work has questioned the validity of this approach at short visible wavelengths (404 nm), indicating systematic calibration errors of the order of a factor of 2. We revisit this result and test the validity of the ozone calibration method using a suite of multipass photoacoustic cells operating at wavelengths 405, 514 and 658 nm. Using aerosolised nigrosin with mobility-selected diameters in the range 250-425 nm, we demonstrate excellent agreement between measured and modelled ensemble absorption cross sections at all wavelengths, thus demonstrating the validity of the ozone-based calibration method for aerosol photoacoustic spectroscopy at visible wavelengths.This work was funded by the Met Office. In addition, Nicholas W. Davies was supported by a NERC/Met Office Industrial Case studentship (ref 640052003). Michael I. Cotterell was supported by a Tom West Analytical Chemistry Trust Fund Fellowship. Michael I. Cotterell and Jim M. Haywood were supported by the CLARIFY-2017 Natural Environment Research Council funded proposal (NE/L013797/1)

Criteria for developing, assessing and selecting candidate EQ-5D bolt-ons.

PURPOSE: 'Bolt-on' dimensions are additional items added to multi-attribute utility instruments (MAUIs) such as EQ-5D that measure constructs not included in the core descriptive system. The use of bolt-ons has been proposed to improve the content validity and responsiveness of the descriptive system in certain settings and health conditions. EQ-5D bolt-ons serve a particular purpose and thus satisfy a certain set of criteria. The aim of this paper is to propose a set of criteria to guide the development, assessment and selection of candidate bolt-on descriptors. METHODS: Criteria were developed using an iterative approach. First, existing criteria were identified from the literature including those used to guide the development of MAUIs, the COSMIN checklist and reviews of existing bolt-ons. Second, processes used to develop bolt-ons based on qualitative and quantitative approaches were considered. The information from these two stages was formalised into draft development and selection criteria. These were reviewed by the project team and iteratively refined. RESULTS: Overall, 23 criteria for the development, assessment and selection of candidate bolt-ons were formulated. Development criteria focused on issues relating to i) structure, ii) language, and iii) consistency with the existing EQ-5D dimension structure. Assessment and selection criteria focused on face and content validity and classical psychometric indicators. CONCLUSION: The criteria generated can be used to guide the development of bolt-ons across different health areas. They can also be used to assess existing bolt-ons, and inform their inclusion in studies and patient groups where the EQ-5D may lack content validity

Impacts of hemispheric solar geoengineering on tropical cyclone frequency

Solar geoengineering refers to a range of proposed methods for counteracting global warming by artificially reducing sunlight at Earth’s surface. The most widely known SG proposal is stratospheric aerosol injection (SAI) which has impacts analogous to those from volcanic eruptions. Observations following major volcanic eruptions indicate that aerosol enhancements confined to a single hemisphere effectively modulate North Atlantic tropical cyclone (TC) activity in the following years. Here we investigate the effects of both single-hemisphere and global SAI scenarios on North Atlantic TC activity using the HadGEM2-ES general circulation model and various TC identification methods. We show that a robust result from all of the methods is that SAI applied to the southern hemisphere would enhance TC frequency relative to a global SAI application, and vice versa for SAI in the northern hemisphere. Our results reemphasize the perils of regional geoengineering and should motivate policymakers to regulate large-scale unilateral geoengineering deployments

Ubv CCD Standards Near 5C1 Radio Sources at Intermediate Galactic Latitude-I

We have been doing a photometric and astrometric sample survey programme on Schmidt plates in a few selected directions in the Galaxy with an aim to study galactic stellar populations. In order to calibrate Schmidt plates photometrically, it is necessary to have a number of photometric standards which cover the entire range of magnitudes to be studied on the plates. As Schmidt plates cover a wide area of the sky, the standards should also be spread over the surface of the plate so as to minimise geometrical effects present on the plate. This paper is first in a series of papers aimed at to provide photometric standards in the selected galactic directions to be studied. In this paper we present photometric magnitudes obtained through CCD observation in the galactic direction (l=170deg, b=45deg) centered at alpha(2000) = 9h 41m 20s and delta(2000) = +49deg 54' 20'' and covering an area of 14 sq degs. B and V magnitudes have been obtained for a total of 214 stars out of which for 73 stars U magnitudes also have been obtained. The magnitude range covered is 11<V<21 and 0.18<B-V<1.85.Comment: Postscript file, 13 pages, 1 figure (figure available on request), paper accepted for publication in the Bulletin of Astronomical Society of Indi

Evaluating biases in filter-based aerosol absorption measurements using photoacoustic spectroscopy

This is the final version. Available from Copernicus Publications via the DOI in this record.Biases in absorption coefficients measured using a filter-based absorption photometer (Tricolor Absorption Photometer, or TAP) at wavelengths of 467, 528 and 652 nm are evaluated by comparing to measurements made using photoacoustic spectroscopy (PAS). We report comparisons for ambient sampling covering a range of aerosol types including urban, fresh biomass burning and aged biomass burning. Data are also used to evaluate the performance of three different TAP correction schemes. We found that photoacoustic and filter-based measurements were well correlated, but filter-based measurements generally overestimated absorption by up to 45 %. Biases varied with wavelength and depended on the correction scheme applied. Optimal agreement to PAS data was achieved by processing the filterbased measurements using the recently developed correction scheme of Müller et al. (2014), which consistently reduced biases to 0 %–18% at all wavelengths. The biases were found to be a function of the ratio of organic aerosol mass to light-absorbing carbon mass, although applying the Müller et al. (2014) correction scheme to filter-based absorption measurements reduced the biases and the strength of this correlation significantly. Filter-based absorption measurement biases led to aerosol single-scattering albedos that were biased low by values in the range 0.00–0.07 and absorption Ångström exponents (AAEs) that were in error by (0.03–0.54). The discrepancy between the filter-based and PAS absorption measurements is lower than reported in some earlier studies and points to a strong dependence of filterbased measurement accuracy on aerosol source type.Natural Environment Research CouncilNatural Environment Research Council/Met OfficeResearch Council of Norway (ACBC and NetBC grants)Royal Society of Chemistry (Analytical Chemistry Trust Fund, Tom West Fellowship

Gluon-induced W-boson pair production at the LHC

Pair production of W bosons constitutes an important background to Higgs boson and new physics searches at the Large Hadron Collider LHC. We have calculated the loop-induced gluon-fusion process gg -> W*W* -> leptons, including intermediate light and heavy quarks and allowing for arbitrary invariant masses of the W bosons. While formally of next-to-next-to-leading order, the gg -> W*W* -> leptons process is enhanced by the large gluon flux at the LHC and by experimental Higgs search cuts, and increases the next-to-leading order WW background estimate for Higgs searches by about 30%. We have extended our previous calculation to include the contribution from the intermediate top-bottom massive quark loop and the Higgs signal process. We provide updated results for cross sections and differential distributions and study the interference between the different gluon scattering contributions. We describe important analytical and numerical aspects of our calculation and present the public GG2WW event generator.Comment: 20 pages, 4 figure

Metallicities of Planet Hosting Stars: A Sample of Giants and Subgiants

This work presents a homogeneous derivation of atmospheric parameters and iron abundances for a sample of giant and subgiant stars which host giant planets, as well as a control sample of subgiant stars not known to host giant planets. The analysis is done using the same technique as for our previous analysis of a large sample of planet-hosting and control sample dwarf stars. A comparison between the distributions of [Fe/H] in planet-hosting main-sequence stars, subgiants, and giants within these samples finds that the main-sequence stars and subgiants have the same mean metallicity of \simeq +0.11 dex, while the giant sample is typically more metal poor, having an average metallicity of = -0.06 dex. The fact that the subgiants have the same average metallicities as the dwarfs indicates that significant accretion of solid metal-rich material onto the planet-hosting stars has not taken place, as such material would be diluted in the evolution from dwarf to subgiant. The lower metallicity found for the planet-hosting giant stars in comparison with the planet-hosting dwarfs and subgiants is interpreted as being related to the underlying stellar mass, with giants having larger masses and thus, on average larger-mass protoplanetary disks. In core accretion models of planet formation, larger disk masses can contain the critical amount of metals necessary to form giant planets even at lower metallicities.Comment: 38 pages, 7 figures, 4 tables, accepted for publication in Ap