Seasonal variation of aerosol water uptake and its impact on the direct radiative effect at Ny-Ålesund, Svalbard

© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 LicenseIn this study we investigated the impact of water uptake by aerosol particles in ambient atmosphere on their optical properties and their direct radiative effect (ADRE, W m-2) in the Arctic at Ny-Ålesund, Svalbard, during 2008. To achieve this, we combined three models, a hygroscopic growth model, a Mie model and a radiative transfer model, with an extensive set of observational data. We found that the seasonal variation of dry aerosol scattering coefficients showed minimum values during the summer season and the beginning of fall (July-August-September), when small particles (< 100 nm in diameter) dominate the aerosol number size distribution. The maximum scattering by dry particles was observed during the Arctic haze period (March-April-May) when the average size of the particles was larger. Considering the hygroscopic growth of aerosol particles in the ambient atmosphere had a significant impact on the aerosol scattering coefficients: the aerosol scattering coefficients were enhanced by on average a factor of 4.30 ± 2.26 (mean ± standard deviation), with lower values during the haze period (March-April-May) as compared to summer and fall. Hygroscopic growth of aerosol particles was found to cause 1.6 to 3.7 times more negative ADRE at the surface, with the smallest effect during the haze period (March-April-May) and the highest during late summer and beginning of fall (July-August-September).Peer reviewe

Dynamics of free-living ixodid ticks on a game ranch in the Central Province, Zambia

Free-living ixodid ticks were collected at monthly intervals from January to December 1996 by dragsampling the vegetation of Mtendere Game Ranch in the Chisamba District of the Central Province, Zambia. Ticks belonging to 11 species were recovered. Rhipicephalus appendiculatus was most abundant, comprising 90% of the total number collected. All life stages of this tick showed a definite seasonal pattern of activity. The adults were present mainly during the rainy season (February and March), the larvae during the cool and dry season (May to August), and the nymphs during the hot and dry season (August to October). Adults were most abundant in the wooded areas and nymphs in the open grasslands. Larvae of Amblyomma variegatum were only found from May to September, while larvae of Boophilus decoloratus were present throughout the year with peaks of abundance from January to February and again from August to November. Rhipicephalus evertsi evertsi larvae occurred throughout the year. Recent burning of the vegetation did not seem to affect the number of ticks collected. A possible burning regime to achieve a degree of tick control is discussed.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat X Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Measured and predicted aerosol light scattering enhancement factors at the high alpine site Jungfraujoch

Ambient relative humidity (RH) determines the water content of atmospheric aerosol particles and thus has an important influence on the amount of visible light scattered by particles. The RH dependence of the particle light scattering coefficient (&amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;) is therefore an important variable for climate forcing calculations. We used a humidification system for a nephelometer which allows for the measurement of &amp;sigma;&lt;sub&gt;sp&lt;/sub&gt; at a defined RH in the range of 20–95%. In this paper we present measurements of light scattering enhancement factors &lt;i&gt;f&lt;/i&gt;(RH)=&amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;(RH)/&amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;(dry) from a 1-month campaign (May 2008) at the high alpine site Jungfraujoch (3580 m a.s.l.), Switzerland. Measurements at the Jungfraujoch are representative for the lower free troposphere above Central Europe. For this aerosol type hardly any information about the &lt;i&gt;f&lt;/i&gt;(RH) is available so far. At this site, &lt;i&gt;f&lt;/i&gt;(RH=85%) varied between 1.2 and 3.3. Measured &lt;i&gt;f&lt;/i&gt;(RH) agreed well with &lt;i&gt;f&lt;/i&gt;(RH) calculated with Mie theory using measurements of the size distribution, chemical composition and hygroscopic diameter growth factors as input. Good &lt;i&gt;f&lt;/i&gt;(RH) predictions at RH&amp;lt;85% were also obtained with a simplified model, which uses the Ångström exponent of &amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;(dry) as input. RH influences further intensive optical aerosol properties. The backscatter fraction decreased by about 30% from 0.128 to 0.089, and the single scattering albedo increased on average by 0.05 at 85% RH compared to dry conditions. These changes in &amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;, backscatter fraction and single scattering albedo have a distinct impact on the radiative forcing of the Jungfraujoch aerosol

Effects of relative humidity on aerosol light scattering in the Arctic

Aerosol particles experience hygroscopic growth in the ambient atmosphere. Their optical properties – especially the aerosol light scattering – are therefore strongly dependent on the ambient relative humidity (RH). In-situ light scattering measurements of long-term observations are usually performed under dry conditions (RH&amp;gt;30–40%). The knowledge of this RH effect is of eminent importance for climate forcing calculations or for the comparison of remote sensing with in-situ measurements. This study combines measurements and model calculations to describe the RH effect on aerosol light scattering for the first time for aerosol particles present in summer and fall in the high Arctic. For this purpose, a field campaign was carried out from July to October 2008 at the Zeppelin station in Ny-Ålesund, Svalbard. The aerosol light scattering coefficient &amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;(&amp;lambda;) was measured at three distinct wavelengths (λ=450, 550, and 700 nm) at dry and at various, predefined RH conditions between 20% and 95% with a recently developed humidified nephelometer (WetNeph) and with a second nephelometer measuring at dry conditions with an average RH&amp;lt;10% (DryNeph). In addition, the aerosol size distribution and the aerosol absorption coefficient were measured. The scattering enhancement factor &lt;i&gt;f&lt;/i&gt;(RH, &amp;lambda;) is the key parameter to describe the RH effect on &amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;(&amp;lambda;) and is defined as the RH dependent &amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;(RH, &amp;lambda;) divided by the corresponding dry &amp;sigma;&lt;sub&gt;sp&lt;/sub&gt;(RH&lt;sub&gt;dry&lt;/sub&gt;, &amp;lambda;). During our campaign the average &lt;i&gt;f&lt;/i&gt;(RH=85%, λ=550 nm) was 3.24&amp;plusmn;0.63 (mean &amp;plusmn; standard deviation), and no clear wavelength dependence of &lt;i&gt;f&lt;/i&gt;(RH, &amp;lambda;) was observed. This means that the ambient scattering coefficients at RH=85% were on average about three times higher than the dry measured in-situ scattering coefficients. The RH dependency of the recorded &lt;i&gt;f&lt;/i&gt;(RH, &amp;lambda;) can be well described by an empirical one-parameter equation. We used a simplified method to retrieve an apparent hygroscopic growth factor &lt;i&gt;g&lt;/i&gt;(RH), defined as the aerosol particle diameter at a certain RH divided by the dry diameter, using the WetNeph, the DryNeph, the aerosol size distribution measurements and Mie theory. With this approach we found, on average, &lt;i&gt;g&lt;/i&gt;(RH=85%) values to be 1.61&amp;plusmn;0.12 (mean&amp;plusmn;standard deviation). No clear seasonal shift of &lt;i&gt;f&lt;/i&gt;(RH, &amp;lambda;) was observed during the 3-month period, while aerosol properties (size and chemical composition) clearly changed with time. While the beginning of the campaign was mainly characterized by smaller and less hygroscopic particles, the end was dominated by larger and more hygroscopic particles. This suggests that compensating effects of hygroscopicity and size determined the temporal stability of &lt;i&gt;f&lt;/i&gt;(RH, &amp;lambda;). During sea salt influenced periods, distinct deliquescence transitions were observed. At the end we present a method on how to transfer the dry in-situ measured aerosol scattering coefficients to ambient values for the aerosol measured during summer and fall at this location

The Phylogeography of Rabies in Grenada, West Indies, and Implications for Control

In Grenada, West Indies, rabies is endemic, and is thought to be maintained in a wildlife host, the small Indian mongoose (Herpestes auropunctatus) with occasional spillover into other hosts. Therefore, the present study was undertaken to improve understanding of rabies epidemiology in Grenada and to inform rabies control policy. Mongooses were trapped island-wide between April 2011 and March 2013 and examined for the presence of Rabies virus (RABV) antigen using the direct fluorescent antibody test (dFAT) and PCR, and for serum neutralizing antibodies (SNA) using the fluorescent antibody virus neutralization test (FAVN). An additional cohort of brain samples from clinical rabies suspects submitted between April 2011 and March 2014 were also investigated for the presence of virus. Two of the 171 (1.7%) live-trapped mongooses were RABV positive by FAT and PCR, and 20 (11.7%) had SNAs. Rabies was diagnosed in 31 of the submitted animals with suspicious clinical signs: 16 mongooses, 12 dogs, 2 cats and 1 goat. Our investigation has revealed that rabies infection spread from the northeast to the southwest of Grenada within the study period. Phylogenetic analysis revealed that the viruses from Grenada formed a monophyletic clade within the cosmopolitan lineage with a common ancestor predicted to have occurred recently (6–23 years ago), and are distinct from those found in Cuba and Puerto Rico, where mongoose rabies is also endemic. These data suggest that it is likely that this specific strain of RABV was imported from European regions rather than the Americas. These data contribute essential information for any potential rabies control program in Grenada and demonstrate the importance of a sound evidence base for planning interventions

Aspects of Nucleon Compton Scattering

We consider the spin-averaged nucleon forward Compton scattering amplitude in heavy baryon chiral perturbation theory including all terms to order ${\cal O} (q^4)$. The chiral prediction for the spin-averaged forward Compton scattering amplitude is in good agreement with the data for photon energies $\omega \le 110$ MeV. We also evaluate the nucleon electric and magnetic Compton polarizabilities to this order and discuss the uncertainties of the various counter terms entering the chiral expansion of these quantities.Comment: 17 pp, TeX, 7 figures available from the authors, preprint CRN-93/5

Comparison of ambient aerosol extinction coefficients obtained from in-situ, MAX-DOAS and LIDAR measurements at Cabauw

Peer reviewe

Ground-based and airborne in-situ measurements of the Eyjafjallajökull volcanic aerosol plume in Switzerland in spring 2010

The volcanic aerosol plume resulting from the Eyjafjallajökull eruption in Iceland in April and May 2010 was detected in clear layers above Switzerland during two periods (17–19 April 2010 and 16–19 May 2010). In-situ measurements of the airborne volcanic plume were performed both within ground-based monitoring networks and with a research aircraft up to an altitude of 6000 m a.s.l. The wide range of aerosol and gas phase parameters studied at the high altitude research station Jungfraujoch (3580 m a.s.l.) allowed for an in-depth characterization of the detected volcanic aerosol. Both the data from the Jungfraujoch and the aircraft vertical profiles showed a consistent volcanic ash mode in the aerosol volume size distribution with a mean optical diameter around 3 ± 0.3 &amp;mu;m. These particles were found to have an average chemical composition very similar to the trachyandesite-like composition of rock samples collected near the volcano. Furthermore, chemical processing of volcanic sulfur dioxide into sulfate clearly contributed to the accumulation mode of the aerosol at the Jungfraujoch. The combination of these in-situ data and plume dispersion modeling results showed that a significant portion of the first volcanic aerosol plume reaching Switzerland on 17 April 2010 did not reach the Jungfraujoch directly, but was first dispersed and diluted in the planetary boundary layer. The maximum PM&lt;sub&gt;10&lt;/sub&gt; mass concentrations at the Jungfraujoch reached 30 &amp;mu;gm&lt;sup&gt;&amp;minus;3&lt;/sup&gt; and 70 &amp;mu;gm&lt;sup&gt;&amp;minus;3&lt;/sup&gt; (for 10-min mean values) duri ng the April and May episode, respectively. Even low-altitude monitoring stations registered up to 45 &amp;mu;gm&lt;sup&gt;&amp;minus;3&lt;/sup&gt; of volcanic ash related PM&lt;sub&gt;10&lt;/sub&gt; (Basel, Northwestern Switzerland, 18/19 April 2010). The flights with the research aircraft on 17 April 2010 showed one order of magnitude higher number concentrations over the northern Swiss plateau compared to the Jungfraujoch, and a mass concentration of 320 (200–520) &amp;mu;gm&lt;sup&gt;&amp;minus;3&lt;/sup&gt; on 18 May 2010 over the northwestern Swiss plateau. The presented data significantly contributed to the time-critical assessment of the local ash layer properties during the initial eruption phase. Furthermore, dispersion models benefited from the detailed information on the volcanic aerosol size distribution and its chemical composition

Intercomparison of stratospheric chemistry models under polar vortex conditions

Several stratospheric chemistry modules from box, 2-D or 3-D models, have been intercompared. The intercomparison was focused on the ozone loss and associated reactive species under the conditions found in the cold, wintertime Arctic and Antarctic vortices. Comparisons of both gas phase and heterogeneous chemistry modules show excellent agreement between the models under constrained conditions for photolysis and the microphysics of polar stratospheric clouds. While the mean integral ozone loss ranges from 4-80% for different 30-50 days long air parcel trajectories, the mean scatter of model results around these values is only about +/-1.5%. In a case study, where the models employed their standard photolysis and microphysical schemes, the variation around the mean percentage ozone loss increases to about +/-7%. This increased scatter of model results is mainly due to the different treatment of the PSC microphysics and heterogeneous chemistry in the models, whereby the most unrealistic assumptions about PSC processes consequently lead to the least representative ozone chemistry. Furthermore, for this case study the model results for the ozone mixing ratios at different altitudes were compared with a measured ozone profile to investigate the extent to which models reproduce the stratospheric ozone losses. It was found that mainly in the height range of strong ozone depletion all models underestimate the ozone loss by about a factor of two. This finding corroborates earlier studies and implies a general deficiency in our understanding of the stratospheric ozone loss chemistry rather than a specific problem related to a particular model simulation

Extending the allelic spectrum at noncoding risk loci of orofacial clefting

Genome-wide association studies (GWAS) have generated unprecedented insights into the genetic etiology of orofacial clefting (OFC). The moderate effect sizes of associated noncoding risk variants and limited access to disease-relevant tissue represent considerable challenges for biological interpretation of genetic findings. As rare variants with stronger effect sizes are likely to also contribute to OFC, an alternative approach to delineate pathogenic mechanisms is to identify private mutations and/or an increased burden of rare variants in associated regions. This report describes a framework for targeted resequencing at selected noncoding risk loci contributing to nonsyndromic cleft lip with/without cleft palate (nsCL/P), the most frequent OFC subtype. Based on GWAS data, we selected three risk loci and identified candidate regulatory regions (CRRs) through the integration of credible SNP information, epigenetic data from relevant cells/tissues, and conservation scores. The CRRs (total 57 kb) were resequenced in a multiethnic study population (1061 patients; 1591 controls), using single-molecule molecular inversion probe technology. Combining evidence from in silico variant annotation, pedigree- and burden analyses, we identified 16 likely deleterious rare variants that represent new candidates for functional studies in nsCL/P. Our framework is scalable and represents a promising approach to the investigation of additional congenital malformations with multifactorial etiology