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

Nitrous oxide emissions from a peatbog after 13 years of experimental nitrogen deposition

Nitrogen deposition was experimentally increased on a Scottish peatbog over a period of 13 years (2002–2015). Nitrogen was applied in three forms, NH3 gas, NH4Cl solution, and NaNO3 solution, at rates ranging from 8 (ambient) to 64 kg N ha−1 yr−1, and higher near the NH3 fumigation source. An automated system was used to apply the nitrogen, such that the deposition was realistic in terms of rates and high frequency of deposition events. We measured the response of nitrous oxide (N2O) flux to the increased nitrogen input. Prior expectations, based on the IPCC default emission factor, were that 1 % of the added nitrogen would be emitted as N2O. In the plots treated with NH4+ and NO3− solution, no response was seen, and there was a tendency for N2O fluxes to be reduced by additional nitrogen, though this was not significant. Areas subjected to high NH3 emitted more N2O than expected, up to 8.5 % of the added nitrogen. Differences in the response are related to the impact of the nitrogen treatments on the vegetation. In the NH4+ and NO3− treatments, all the additional nitrogen is effectively immobilised in the vegetation and top 10 cm of peat. In the NH3 treatment, much of the vegetation was killed off by high doses of NH3, and the nitrogen was presumably more available to denitrifying bacteria. The design of the wet and dry experimental treatments meant that they differed in statistical power, and we are less likely to detect an effect of the NH4+ and NO3− treatments, though they avoid issues of pseudo-replication

NH3 concentrations below the current critical level affect the epiphytic macrolichen communities – Evidence from a Northern European City

Acidophytic, oligotrophic lichens on tree trunks are widely considered to be the most sensitive biota to elevated con-centrations of atmospheric ammonia (NH3). We studied the relationships between measured NH3 concentrations and the composition of macrolichen communities on the acidic bark of Pinus sylvestris and Quercus robur and the base-rich bark of Acer platanoides and Ulmus glabra at ten roadside and ten non-roadside sites in Helsinki, Finland. NH3 and ni-trogen dioxide (NO2) concentrations were higher at the roadside than non-roadside sites indicating traffic as the main source of NH3 and nitrogen oxides (NOx). The diversity of oligotrophs on Quercus was lower at the roadside than non-roadside sites, while that of eutrophs was higher. The abundance and presence of oligotrophic acidophytes (e.g., Hypogymnia physodes) decreased with increasing NH3 concentration (2-year means = 0.15-1.03 mu g m-3) espe-cially on Q. robur, while those of eutrophic/nitrophilous species (e.g., Melanohalea exasperatula, Physcia tenella) in-creased. The abundance of some nitrophytes seemed to depend only on bark pH, i.e., their abundances were highest on Ulmus, which had the highest average bark pH. Overall, the results of lichen bioindicator studies may depend on tree species (bark pH) and lichen species used in calculating indices describing the air quality impact. Nevertheless, Quercus is recommended to be used to study the impact of NH3 alone and in combination with NOx on lichen commu-nities, because the responses of both oligotrophic acidophytes and eutrophic species can already be observed at NH3 concentrations below the current critical level.Peer reviewe

The import and export of organic nitrogen species at a Scottish ombrotrophic peatland

Dissolved organic nitrogen (DON) contributes significantly to the overall nitrogen budget, but is not routinely measured in precipitation or stream water. In order to investigate the contribution of DON to the deposition and export of N, precipitation, stream and soil water samples were collected from an ombrotrophic peatland and analysed for DON over a 2-year period. In wet-only deposition DON contributed up to 10 % of the total dissolved nitrogen (TDN) and was the most dominant fraction in soil water (99 %) and stream water (75 %). NH4 + was the most dominate form of N in precipitation, with NO3 - contributing the least to precipitation, soil water and stream water. Precipitation and stream DON were qualitatively analysed by a two-dimensional gas chromatograph coupled to a nitrogen chemiluminescence detector (GC × GC-NCD) after trapping onto C18 solid phase extraction (SPE) cartridges. Ten unique compounds were detected and five identified as pyrrole, benzonitrile, dodecylamine, N-nitrosodipropylamine and decylamine. Five compounds were present in both precipitation and stream samples: pyrrole, benzonitrile and three unidentified compounds. The SPE-extraction efficiency for DON was very low (11 %), but with improvements DON speciation could become a valuable tool to provide information on its sources and pathways and inform chemical transport models

The nitrogen, carbon and greenhouse gas budget of a grazed, cut and fertilised temperate grassland

Intensively managed grazed grasslands in temperate climates are globally important environments for the exchange of the greenhouse gases (GHGs) carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). We assessed the N and C budget of a mostly grazed and occasionally cut and fertilised grassland in SE Scotland by measuring or modelling all relevant imports and exports to the field as well as changes in soil C and N stocks over time. The N budget was dominated by import from inorganic and organic fertilisers (21.9 g N m−2 a−1) and losses from leaching (5.3 g N m−2 a−1), N2 emissions (2.9 g N m−2 a−1), and NOx and NH3 volatilisation (3.9 g N m−2 a−1), while N2O emission was only 0.6 g N m−2 a−1. The efficiency of N use by animal products (meat and wool) averaged 9.9 % of total N input over only-grazed years (2004–2010). On average over 9 years (2002–2010), the balance of N fluxes suggested that 6.0 ± 5.9 g N m−2 a−1 (mean ± confidence interval at p > 0.95) were stored in the soil. The largest component of the C budget was the net ecosystem exchange of CO2 (NEE), at an average uptake rate of 218 ± 155 g C m−2 a−1 over the 9 years. This sink strength was offset by carbon export from the field mainly as grass offtake for silage (48.9 g C m−2 a−1) and leaching (16.4 g C m−2 a−1). The other export terms, CH4 emissions from the soil, manure applications and enteric fermentation, were negligible and only contributed to 0.02–4.2 % of the total C losses. Only a small fraction of C was incorporated into the body of the grazing animals. Inclusion of these C losses in the budget resulted in a C sink strength of 163 ± 140 g C m−2 a−1. By contrast, soil stock measurements taken in May 2004 and May 2011 indicated that the grassland sequestered N in the 0–60 cm soil layer at 4.51 ± 2.64 g N m−2 a−1 and lost C at a rate of 29.08 ± 38.19 g C m−2 a−1. Potential reasons for the discrepancy between these estimates are probably an underestimation of C losses, especially from leaching fluxes as well as from animal respiration. The average greenhouse gas (GHG) balance of the grassland was −366 ± 601 g CO2 eq. m−2 yr−1 and was strongly affected by CH4 and N2O emissions. The GHG sink strength of the NEE was reduced by 54 % by CH4 and N2O emissions. Estimated enteric fermentation from ruminating sheep proved to be an important CH4 source, exceeding the contribution of N2O to the GHG budget in some years

Fungal colonization patterns and enzymatic activities of peatland ericaceous plants following long-term nutrient addition

Northern peatlands are often dominated by ericaceous shrub species which rely on ericoid mycorrhizal fungi (ERM) for access to organic sources of nutrients, such as nitrogen (N) and phosphorus (P), and host abundant dark septate endophytes (DSE). Relationships between hosts and fungal symbionts may change during deposition of anthropogenic N and P. We studied the long-term effects of N and P addition on two ericaceous shrubs, Calluna vulgaris and Erica tetralix, at Whim Bog, Scotland by analyzing fungal colonization of roots, enzymatic activity, and fungal species composition. Unexpectedly, the frequency of typical ERM intracellular colonization did not change while the occurrence of ERM hyphae tended to increase and DSE hyphae to decrease. Our findings indicate that altered nutrient limitations shift root associated fungal colonization patterns as well as affecting ericaceous root enzyme activity and thereby decomposition potential. Reduction of recalcitrant fungal biomass in melanized DSE may have implications for peatland C sequestration under nutrient addition.Peer reviewe

Response of a peat bog vegetation community to long-term experimental addition of nitrogen

1. We report results from a long‐term experiment in which additional nitrogen has been deposited on a peat bog in central Scotland for over 14 years, in three different forms: as ammonia (NH3) gas, as ammonium (NH4+) solution, or as nitrate (NO3-) solution. The automated experiment was designed to apply nitrogen in such a way that mimics real‐world nitrogen deposition. Background nitrogen deposition at the site was 0.8 g N m−2 year−1). 2. Observations of cover for 46 species were made. We analysed the change in six common species in relation to nitrogen dose and form. The responses differed among species and nitrogen forms, but five out of the six species declined, and NH3 produced the biggest change in cover per unit of nitrogen addition. The exception was the graminoid sedge Eriophorum vaginatum, which increased dramatically in the NH3 treatment. Multivariate analyses identified responses to nitrogen dose across treatments which were consistent with the univariate results. 3. We surmised that the larger experimental response to nitrogen observed in the NH3 treatment (cf. the NH4+ and NO3- treatments) was because of the higher nitrogen concentrations at the vegetation surface produced by dry deposition. NH4+ and NO3- were sprayed in solution, but much of this will enter the peat porewater, and be further diluted. Because NH3 deposits directly to the leaf, it stays contained within the small volume of water on and in the leaf, producing a high internal concentration of nitrogen ions. 4. Synthesis: Consistent trends with nitrogen were discernible across species. All species showed a decline with NH3 treatment, except for Eriophorum vaginatum which increased. In the absence of phosphorous and potassium (PK), all species declined with NH4+ and NO3-, except for Calluna vulgaris and Hypnum jutlandicum. The effect of PK was not consistent across species. Per unit of nitrogen deposited, NH3 generally had a larger impact on vegetation composition than NH4+ or NO3-. However, the actual deposition rate of NH3 on UK peat bogs is lower than the other forms. In the case of the most common species of the peat‐forming genus Sphagnum, we estimate that NH4+ deposition has the largest impact, followed by NO3- and NH3

Pan-European rural monitoring network shows dominance of NH3 gas and NH4NO3 aerosol in inorganic atmospheric pollution load

A comprehensive European dataset on monthly atmospheric NH3, acid gases (HNO3, SO2, HCl), and aerosols (NH4+, NO3-, SO42-, Cl−, Na+, Ca2+, Mg2+) is presented and analysed. Speciated measurements were made with a low-volume denuder and filter pack method (DEnuder for Long-Term Atmospheric sampling, DELTA®) as part of the EU NitroEurope (NEU) integrated project. Altogether, there were 64 sites in 20 countries (2006–2010), coordinated between seven European laboratories. Bulk wet-deposition measurements were carried out at 16 co-located sites (2008–2010). Inter-comparisons of chemical analysis and DELTA® measurements allowed an assessment of comparability between laboratories. The form and concentrations of the different gas and aerosol components measured varied between individual sites and grouped sites according to country, European regions, and four main ecosystem types (crops, grassland, forests, and semi-natural). The smallest concentrations (with the exception of SO42- and Na+) were in northern Europe (Scandinavia), with broad elevations of all components across other regions. SO2 concentrations were highest in central and eastern Europe, with larger SO2 emissions, but particulate SO42- concentrations were more homogeneous between regions. Gas-phase NH3 was the most abundant single measured component at the majority of sites, with the largest variability in concentrations across the network. The largest concentrations of NH3, NH4+ and NO-3 were at cropland sites in intensively managed agricultural areas (e.g. Borgo Cioffi in Italy), and the smallest were at remote semi-natural and forest sites (e.g. Lompolojänkkä, Finland), highlighting the potential for NH3 to drive the formation of both NH4+ and NO3- aerosol. In the aerosol phase, NH4+ was highly correlated with both NO3- and SO42-, with a near-1:1 relationship between the equivalent concentrations of NH4+ and sum(NO3- + SO42-) of which around 60 % was as NH4NO3. Distinct seasonality was also observed in the data, influenced by changes in emissions, chemical interactions, and the influence of meteorology on partitioning between the main inorganic gases and aerosol species. Springtime maxima in NH3 were attributed to the main period of manure spreading, while the peak in summer and trough in winter were linked to the influence of temperature and rainfall on emissions, deposition, and gas–aerosol-phase equilibrium. Seasonality in SO2 was mainly driven by emissions (combustion), with concentrations peaking in winter, except in southern Europe, where the peak occurred in summer. Particulate SO42− showed large peaks in concentrations in summer in southern and eastern Europe, contrasting with much smaller peaks occurring in early spring in other regions. The peaks in particulate SO42- coincided with peaks in NH3 concentrations, attributed to the formation of the stable (NH4)2SO4. HNO3 concentrations were more complex, related to traffic and industrial emissions, photochemistry, and HNO3:NH4NO3 partitioning. While HNO3 concentrations were seen to peak in the summer in eastern and southern Europe (increased photochemistry), the absence of a spring peak in HNO3 in all regions may be explained by the depletion of HNO3 through reaction with surplus NH3 to form the semi-volatile aerosol NH4NO3. Cooler, wetter conditions in early spring favour the formation and persistence of NH4NO3 in the aerosol phase, consistent with the higher springtime concentrations of NH4+ and NO3−. The seasonal profile of NO3- was mirrored by NH4+, illustrating the influence of gas–aerosol partitioning of NH4NO3 in the seasonality of these components. Gas-phase NH3 and aerosol NH4NO3 were the dominant species in the total inorganic gas and aerosol species measured in the NEU network. With the current and projected trends in SO2, NOx , and NH3 emissions, concentrations of NH3 and NH4NO3 can be expected to continue to dominate the inorganic pollution load over the next decades, especially NH3, which is linked to substantial exceedances of ecological thresholds across Europe. The shift from (NH4)2SO4 to an atmosphere more abundant in NH4NO3 is expected to maintain a larger fraction of reactive N in the gas phase by partitioning to NH3 and HNO3 in warm weather, while NH4NO3 continues to contribute to exceedances of air quality limits for PM2.5

MetNH3 Whim Bog Intercomparison Off-line ammonia metrology intercomparison

There is no regular quality assurance programme for ammonia passive samplers despite widespread use of these samplers across Europe and the rest of the world. In order to improve standards and begin to embed quality assurance in the measurement of ambient ammonia using passive samplers, within the EMRP MetNH3 project a passive sampler intercomparison was planned to enable side-by side exposure of the samplers to varying levels of ammonia in the field. From this experiment and in parallel the NPL CATFAC experiment (also within MetNH3), sufficient information and protocols could be developed. The method and infrastructure developed will then be available for future studies

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