Measurements of sulphur dioxide in rural air: data quality issues

Discrepancies between long-term average SO2 concentrations measured by UV-Fluorescence monitors in the AURN and DELTA denuders from AGA-Net are caused by inadequate performance of UV-F monitors at low concentrations. The hourly data are essential for measuring possible exceedances of limit values – for which the AURN was established – and there is no suggestion that they are no longer fit for that purpose. However, as operated at present they should not be used to provide data for assessing long-term average concentrations. The DELTA denuders in AGA-Net were specifically designed for that purpose, and provide the data needed to assess rural (and suburban) concentrations for model evaluation across the UK

Effects of Ground Level Ozone on Vegetation

All the experiments conducted in this project use ozone exposures that either are already currently occurring or are expected to occur over UK uplands this century, if predictions of increasing „background‟ ozone exposure are correct. Uplands are particularly vulnerable to such increases, because they are windy and wet – conditions which favour ozone uptake by vegetation. Consequently, the observations on ozone effects on upland plant species are likely to occur in the foreseeable future, if they are not already happening. The novel field ozone exposure system at Keenley Fell (Northumberland) has been operating since spring 2007. Seasonal average increases in ozone exposure at 10 m from the release point were very small in 2007, increasing to around 5 ppb above ambient in 2008 and 2009. The effects of the ozone treatments on this conservation-managed grassland should be seen in the context of this very modest increase in annual mean exposure. Average deposition velocity for ozone at Keenley Fell was between 1 mm/s (night) and 5 mm/s (mid-day), varying with weather conditions. These flux data will assist with the modelling of ozone deposition to upland grasslands. Limited flux measurements for CO2 showed uptake during the day and release at night, as expected, and will contribute to modelling interactions between ozone and carbon fluxes under these conditions. The ozone treatments at Keenley Fell had no effect on total above-ground production in any of the three years. However, there was a cumulative decrease in forb biomass, with an associated change in forb species composition, over the three years. This was accompanied by an increase in grass biomass. These effects of ozone are antagonistic to the objectives of the conservation management at this site. The biomass and flowering of a small number of individual forb species were significantly reduced by ozone exposure at Keenley Fell. Importantly, these species included the hemi-parasite Rhinanthus minor which is frequently used to enhance species diversity in this type of conservation management. Hence, the observed effects of ozone on species composition may partly have been caused through its adverse effects on Rhinanthus . Data compiled from several experiments show adverse effects of ozone on semi-natural plant species at concentrations as low as 30 ppb, with 12 of the species studied showing effects at concentrations below 50 ppbv. Effects on roots were greater than on shoots, with potentially significant implications for overwintering, drought tolerance and carbon sequestration

Variations on Birkhoff's theorem

The relation between the expanding universe and local vacuum solutions, such as that for the Solar System, is crucially mediated by Birkhoff's theorem. Here we consider how that relation works, and give generalizations of Birkhoff's theorem when there are geometric and matter and perturbations. The issue of to what degree dark matter might influence the solar system emerges as a significant question.Comment: Conference proceeding for ERE 2012, submitted to GRG for ERE2012 special issue, based on arXiv:1005.1809, arXiv:1101.4520 and arXiv:1202.024

The Tin Gee-Gee

https://digitalcommons.library.umaine.edu/mmb-vp/6657/thumbnail.jp

Measurement of dry deposition to bulk precipitation collectors using a novel flushing sampler

Bulk precipitation samplers, which are continuously open, also sample gases and particles deposited on the funnel surface. Wet-only samplers, which open only during precipitation, avoid this problem, but can be bulky (leading to disruption of air flow and droplet collection) and need electrical power. We describe here a simple battery-powered modification to a standard bulk sampler that allows the separate measurement of deposition to the funnel surface and wet deposition by washing the funnel surface when precipitation is detected. Comparison of this design with a standard bulk sampler over 3 months at a site in eastern Scotland showed that dry deposition to the funnel surface contributed around 20% of sulphate, 20-30% of nitrate and 20-40% of ammonium ions. There was also a significant loss of ammonium and nitrate in the modified sampler, presumably in the tubing, even though a biocide had been added to the sample bottles. This observation has implications for bulk samplers of similar design, with a sample bottle at ground level. Deposition of sea salts and calcium was greater to the flushing collectors than to the bulk collectors, implying that regular cleaning of funnel surfaces with 10% methanol solution subtly alters the capture efficiency for larger particles