Meteorological measurements at Auchencorth Moss from 1995 to 2016

The Auchencorth Moss atmospheric observatory has being measuring meteorological parameters since 1995. The site was originally set‐up to measure the deposition of sulphur dioxide at a site that represented the vegetation and climate typical of NW Europe, in relatively clean background air. It is one of the longest running flux monitoring sites in the region, over semi‐natural vegetation, providing infrastructure and support for many measurement campaigns and continuous monitoring of air pollutants and greenhouse gases. The meteorological sensors that are used, data processing and quality reviewing procedures are described for a set of core measurements up to 2016. These core measurements are essential for the interpretation of the other atmospheric variables

Long-term measurements of NH3 and SO2 fluxes at three contrasting grasslands by time averaged gradients (TAG)

The Time Averaged Gradient (TAG) approach was applied to measure long-term dry net exchange fluxes of NH3 and SO2 to three contrasting temperate grasslands in the UK. The measurements were made at: Auchencorth Moss, an acid peatland site with little grazing; Plynlimon, an upland grassland on mixed soil and significant sheep grazing; Easter Bush, an intensively managed permanent grassland with N fertilisation, used for silage and cattle and sheep grazing. A data series of five years, from 1999 to 2003, for SO2 and a data series of two years, from 2001 to 2003 for NH3 was obtained at Auchencorth Moss. The measurements provided a characterisation of the chemical climate, meteorology, turbulent characteristics, as well as deposition-emission fluxes at the field site. At Plynlimon, fluxes of SO2 and NH3 were measured from June 2000 to September 2003. A refined TAG system was implemented to improve estimates of gradients and reduce uncertainty on the fluxes, and was applied at Easter Bush measuring NH3 fluxes from autumn 2001 to spring 2003, and at Auchencorth Moss from autumn 2004 to date. The TAG systems provided long-term series of average net fluxes of SO2 at -7.04 ng m-2 s-1 and -3.4 ng m-2 s-1 at Plynlimon and Auchencorth Moss, respectively. The data do not permit accurate description of short term fluxes, but provide long term estimates of S dry deposition for comparison between sites. For ammonia the dry deposition fluxes were on average -7.6, -5.98, and -12.2 ng m-2 s-1 for Auchencorth Moss, Plynlimon and Easter Bush respectively, indicating differences in NH3 concentrations and exchange processes. Several discrepancies in NH3 flux between sites reflect the interaction of temperature, rain and different grassland managing regimes

Ammonia concentrations at a site in Southern Scotland from 2 yr of continuous measurements

Atmospheric ammonia (NH3) concentrations were measured using a continuous-flow annular denuder over a period of 2 yr at a rural site near Edinburgh, Scotland. Meteorological parameters as well as sulphur dioxide (SO2) concentrations were also recorded. The overall arithmetic mean NH3 concentration was 1.4 μg m−3. Although an annual cycle with largest NH3 concentrations in summer was apparent for seasonal geometric mean concentrations, arithmetic mean concentrations were largest in the spring and autumn, indicating the increased importance of occasional high concentration events in these seasons. The NH3 concentrations were influenced by local sources as well as by background concentrations, dependent on wind direction, whereas SO2 geometric standard deviations indicated more distant sources. The daily cycle of NH3 and SO2 concentrations was dependent on wind speed (u). At u 1 m s−1 this cycle was less pronounced for both gases and NH3 concentrations were largest around 1800 hours. These opposite diurnal cycles may be explained by the interaction of boundary layer mixing with local sources for NH3 and remote sources for SO2. Comparing the ammonia data with critical levels and critical loads shows that the critical level is not exceeded at this site over any averaging time. In contrast, the N critical load would probably be exceeded for moorland vegetation near this site, showing that the contribution of atmospheric NH3 to nitrogen deposition in the long term is a more significant issue than exceedance of critical levels

Measurements of Ozone Deposition to Vegetation Quantifying the Flux, the Stomatal and Non-Stomatal Components

Ozone deposition to vegetation represents the major sink for boundary layer ozone and yet the underlying mechanism of reaction and uptake at the surface is poorly understood. While overall rates of O3 deposition are known, the fractions of the flux absorbed by stomata and deposited to non-stomatal surfaces in the field have been poorly quantified. This paper reports 4 years of continuous fluxes by micrometeorological methods to moorland vegetation in southern Scotland. The flux has been partitioned between stomatal and non-stomatal fluxes and shows over a seasonal scale that the non-stomatal deposition (50 kg O3 ha– y–1) dominates the overall flux (77 kg O3 ha–1 y–1) and represents 70% of the total deposition. The surface resistance for non-stomatal O3 deposition (rns) decreases with temperature from 400 s m–1 at 0°C to 200 s m–1 at 15°C in dry conditions and is consistent with thermal decomposition of ozone at the surface with an apparent activation energy of about 36 kJ mole–1. The 4 years of continuous flux measurements show that stomatal conductance, when O3 concentrations are 80 µg m–3, is substantially smaller than for smaller O3 concentrations, although whether this is a response to VPD or O3 remains unclea

Advances in micrometeorological methods for the measurement and interpretation of gas and particle nitrogen fluxes

The application of micrometeorology for flux measurements of nitrogen species between terrestrial ecosystems and the atmosphere and some of their main limitations are reviewed. New methods which are gaining rapid acceptance such as relaxed eddy accumulation are also described. A new development to provide long term average fluxes by time averaged gradients is shown to yield long-term average NH3 fluxes over moorland within 10% of values obtained using continuous wet denuder methods and at less than 10% of the cost. The use of mass balance methods to quantify fluxes at the plot, landscape and regional scale are described, and show that in suitable conditions and for some countries, methods to check national inventories of radiatively active gases are now available

Measurements of ozone deposition to a potato canopy

Potatoes are an important staple crop, grown in many parts of the world. Although ozone deposition to many vegetation types has been measured in the field, no data have been reported for potatoes. Such measurements, including the latent-heat flux, were made over a fully grown potato field in central Scotland during the summer of 2006, covering a 4-week period just after rainfall and then dry, sunny weather. The magnitude of the flux was typical of many canopies showing the expected diurnal cycles. Although the bulk-canopy stomatal conductance declined as the field dried out (~300 mmol-O3 m-2 s-1 to ~70 mmol-O3 m-2 s-1), the total ozone flux did not follow the same trend, indicating that non-stomatal deposition was significant. Over a dry surface non-stomatal resistance (Rns) was 270-450 s m-1, while over a wet surface Rns was ~50% smaller and both decreased with increasing surface temperature and friction velocity. From the variation with relative humidity (RH) it is suggested that three processes occur on leaf surfaces: on a very dry surface ozone is removed by thermal decomposition, possibly enhanced by photolytic reactions in the daytime and so Rns decreases as temperature increases; at 50-70% RH a thin film of liquid blocks the "dry" process and resistance increases; above 60-70% RH sufficient surface water is present for aqueous reactions to remove ozone and resistance decreases