The implementation of strict emission control measures in Beijing and surrounding regions during the 2015 China Victory Day Parade provided a valuable opportunity to investigate related air quality... Show moreThe implementation of strict emission control measures in Beijing and surrounding regions during the 2015 China Victory Day Parade provided a valuable opportunity to investigate related air quality improvements in a megacity. We measured NH3, NO2 and PM2.5 at multiple sites in and outside Beijing and summarized concentrations of PM2.5, PM10, NO2, SO2 and CO in 291 cities across China from a national urban air quality monitoring network between August and September 2015. Consistently significant reductions of 12-35% for NH3 and 33-59% for NO2 in different areas of Beijing during the emission control period (referred to as the Parade Blue period) were observed compared with measurements in the pre- and post-Parade Blue periods without emission controls. Average NH3 and NO2 concentrations at sites near traffic were strongly correlated and showed positive and significant responses to traffic reduction measures, suggesting that traffic is an important source of both NH3 and NOx in urban Beijing. Daily concentrations of PM2.5 and secondary inorganic aerosol (sulfate, ammonium and nitrate) at the urban and rural sites both decreased during the Parade Blue period. During (after) the emission control period, concentrations of PM2.5, PM10, NO2, SO2 and CO from the national city-monitoring network showed the largest decrease (increase) of 34-72% (50-214 %) in Beijing, a smaller decrease (a moderate increase) of 1-32% (16-44 %) in emission control regions outside Beijing and an increase (decrease) of 6-16% (2-7 %) in non-emission-control regions of China. Integrated analysis of modelling and monitoring results demonstrated that emission control measures made a major contribution to air quality improvement in Beijing compared with a minor contribution from favourable meteorological conditions during the Parade Blue period. These results show that controls of secondary aerosol precursors (NH3, SO2 and NOx) locally and regionally are key to curbing air pollution in Beijing and probably in other mega cities worldwide. Show less
The accurate representation of bidirectional ammonia (NH3) biosphere-atmosphere exchange is an important part of modern air quality models. However, the cuticular (or external leaf surface) pathway... Show moreThe accurate representation of bidirectional ammonia (NH3) biosphere-atmosphere exchange is an important part of modern air quality models. However, the cuticular (or external leaf surface) pathway, as well as other non-stomatal ecosystem surfaces, still pose a major challenge to translating our knowledge into models. Dynamic mechanistic models including complex leaf surface chemistry have been able to accurately reproduce measured bidirectional fluxes in the past, but their computational expense and challenging implementation into existing air quality models call for steady-state simplifications. Here we qualitatively compare two semi-empirical state-of-the-art parameterizations of a unidirectional non-stomatal resistance (R-w) model after Massad et al. (2010), and a quasi-bidirectional non-stomatal compensation-point (chi(w)) model after Wichink Kruit et al. (2010), with NH3 flux measurements from five European sites. In addition, we tested the feasibility of using backward-looking moving averages of air NH3 concentrations as a proxy for prior NH3 uptake and as a driver of an alternative parameterization of non-stomatal emission potentials (Gamma(w)) for bidirectional non-stomatal exchange models. Results indicate that the R-w-only model has a tendency to underestimate fluxes, while the chi(w) model mainly overestimates fluxes, although systematic underestimations can occur under certain conditions, depending on temperature and ambient NH3 concentrations at the site. The proposed Gamma(w) parameterization revealed a clear functional relationship be-tween backward-looking moving averages of air NH3 concentrations and non-stomatal emission potentials, but further reduction of uncertainty is needed for it to be useful across different sites. As an interim solution for improving flux predictions, we recommend reducing the minimum allowed R-w and the temperature response parameter in the unidirectional model and revisiting the temperature-dependent Gamma(w) parameterization of the bidirectional model. Show less
Global distributions of atmospheric ammonia (NH3) measured with satellite instruments such as the Infrared Atmospheric Sounding Interferometer (IASI) contain valuable information on NH3... Show moreGlobal distributions of atmospheric ammonia (NH3) measured with satellite instruments such as the Infrared Atmospheric Sounding Interferometer (IASI) contain valuable information on NH3 concentrations and variability in regions not yet covered by ground-based instruments. Due to their large spatial coverage and (bi-)daily overpasses, the satellite observations have the potential to increase our knowledge of the distribution of NH3 emissions and associated seasonal cycles. However the observations remain poorly validated, with only a handful of available studies often using only surface measurements without any vertical information. In this study, we present the first validation of the IASI-NH3 product using ground-based Fourier transform infrared spectroscopy (FTIR) observations. Using a recently developed consistent retrieval strategy, NH3 concentration profiles have been retrieved using observations from nine Network for the Detection of Atmospheric Composition Change (NDACC) stations around the world between 2008 and 2015. We demonstrate the importance of strict spatiotemporal collocation criteria for the comparison. Large differences in the regression results are observed for changing intervals of spatial criteria, mostly due to terrain characteristics and the short lifetime of NH3 in the atmosphere. The seasonal variations of both datasets are consistent for most sites. Correlations are found to be high at sites in areas with considerable NH3 levels, whereas correlations are lower at sites with low atmospheric NH3 levels close to the detection limit of the IASI instrument. A combination of the observations from all sites (N-obs = 547) give a mean relative difference of -32.4 +/- (56.3) %, a correlation r of 0.8 with a slope of 0.73. These results give an improved estimate of the IASI-NH3 product performance compared to the previous upper-bound estimates (-50 to + 100 %). Show less
The 'Anthropocene' is now being used as a conceptual frame by different communities and in a variety of contexts to understand the evolving human environment relationship. However, as we argue in... Show moreThe 'Anthropocene' is now being used as a conceptual frame by different communities and in a variety of contexts to understand the evolving human environment relationship. However, as we argue in this paper, the notion of an Anthropos, or 'humanity', as global, unified 'geological force' threatens to mask the diversity and differences in the actual conditions and impacts of humankind, and does not do justice to the diversity of local and regional contexts. For this reason, we interpret in this article the notion of an Anthropocene in a more context-dependent, localized and social understanding. We do this through illustrating examples from four issue domains, selected for their variation in terms of spatial and temporal scale, systems of governance and functional interdependencies: nitrogen cycle distortion (in particular as it relates to food security); ocean acidification; urbanization; and wildfires. Based on this analysis, we systematically address the consequences of the lens of the Anthropocene for the governance of social-ecological systems, focusing on the multi-level, functional and sectoral organization of governance, and possible redefinitions of governance systems and policy domains. We conclude that the notion of the Anthropocene, once seen in light of social inequalities and regional differences, allows for novel analysis of issue-based problems in the context of a global understanding, in both academic and political terms. This makes it a useful concept to help leverage and (re-)focus our efforts in a more innovative and effective way to transition towards sustainability. (C) 2015 The Authors. Published by Elsevier Ltd. Show less
Erisman, J.W.; Eekeren, N. van; Wit, J. de; Koopmans, C.; Cuijpers, W.; Oerlemans, N.; Koks, B.J. 2016
Sustainable agriculture is an important component of many of the 17 Sustainable Development Goals agreed upon by the UN in 2015 (https://sustainabledevelopment.un.org/sdgs). However, the trend in... Show moreSustainable agriculture is an important component of many of the 17 Sustainable Development Goals agreed upon by the UN in 2015 (https://sustainabledevelopment.un.org/sdgs). However, the trend in agriculture is moving in the opposite, non-sustainable direction. Agriculture is one of the major drivers of biodiversity loss. Next to biodiversity loss due to habitat destruction by conversion of natural lands into agriculture, intensification of agriculture has led to a strong decline of specific farmland biodiversity. Furthermore, many agricultural landscapes face pollution by pesticides and fertilizers, and encounter depleted soils and erosion due to unsustainable farming practices. This is threatening not only biodiversity but also complete ecosystems and the ecosystem services on which agriculture itself depends. Moreover, the pressure of feeding an increasing number of people in combination with a change in diets towards more animal protein puts a lot of additional pressure on the current available agricultural lands and nature areas.We propose a holistic approach that contributes to the development and implementation of sustainable agricultural practices that both make use and support biodiversity and ecosystem services both in agricultural and in semi-natural areas. An agricultural system based on the full potential of (functional agro) biodiversity provides opportunities to create a resilient system in which both food production and nature can thrive. Show less
Nitrogen (N) cycle dynamics and N deposition play an important role in determining the terrestrial biosphere's carbon (C) balance. We assess global and biome-specific N deposition effects on C... Show moreNitrogen (N) cycle dynamics and N deposition play an important role in determining the terrestrial biosphere's carbon (C) balance. We assess global and biome-specific N deposition effects on C sequestration rates with the dynamic global vegetation model LPJ-GUESS. Modeled CN interactions are evaluated by comparing predictions of the C and CN version of the model with direct observations of C fluxes from 68 forest FLUXNET sites. N limitation on C uptake reduced overestimation of gross primary productivity for boreal evergreen needleleaf forests from 56% to 18%, presenting the greatest improvement among forest types. Relative N deposition effects on C sequestration (dC/dN) in boreal, temperate, and tropical sites ranged from 17 to 26kgCkgN(-1) when modeled at site scale and were reduced to 12-22kgCkgN(-1) at global scale. We find that 19% of the recent (1990-2007) and 24% of the historical global C sink (1900-2006) was driven by N deposition effects. While boreal forests exhibit highest dC/dN, their N deposition-induced C sink was relatively low and is suspected to stay low in the future as no major changes in N deposition rates are expected in the boreal zone. N deposition induced a greater C sink in temperate and tropical forests, while predicted C fluxes and N-induced C sink response in tropical forests were associated with greatest uncertainties. Future work should be directed at improving the ability of LPJ-GUESS and other process-based ecosystem models to reproduce C cycle dynamics in the tropics, facilitated by more benchmarking data sets. Furthermore, efforts should aim to improve understanding and model representations of N availability (e.g., N fixation and organic N uptake), N limitation, P cycle dynamics, and effects of anthropogenic land use and land cover changes. Show less
Seitzinger, S.P.; Gaffney, O.; Brasseur, G.; Broadgate, W.; Ciais, P.; Claussen, M.; ... ; Uematsu, M. 2015
The maturing of Earth system science as a discipline has underpinned the development of concepts such as the Anthropocene and planetary boundaries. The International Geosphere-Biosphere Programme's... Show moreThe maturing of Earth system science as a discipline has underpinned the development of concepts such as the Anthropocene and planetary boundaries. The International Geosphere-Biosphere Programme's (IGBP) scientific and institutional history is deeply intertwined with the development of the concept of the Earth as a system as well as the discipline of Earth system science. Here we frame the broader programme of IGBP through its core projects and programme-level activities and illustrate this co-evolution. We identify and discuss three phases in the programme's history. In its first phase beginning in 1986, IGBP focused on building international networks and global databases that were key to understanding Earth system component processes. In the early 2000s IGBP's first major synthesis and associated activities promoted a more integrated view of the Earth system informed by greater emphasis on interdisciplinarity. Human actions were seen as an integral part of the Earth system and the concept of the Anthropocene came to the fore. In recent years IGBP has increased focus on sustainability and multifaceted engagement with policy processes. IGBP closed at the end of 2015 after three decades of coordinating international research on global change. The programme's longevity points to its capacity to adapt its scientific and institutional structures to changing scientific and societal realities. Its history may offer lessons for the emerging Future Earth initiative as it seeks to rally international collaborative research around sustainability and solutions. (C) 2016 The Authors. Published by Elsevier Ltd. Show less
We present a retrieval method for ammonia (NH3) total columns from ground-based Fourier transform infrared (FTIR) observations. Observations from Bremen (53.10 degrees N, 8.85 degrees E), Lauder ... Show moreWe present a retrieval method for ammonia (NH3) total columns from ground-based Fourier transform infrared (FTIR) observations. Observations from Bremen (53.10 degrees N, 8.85 degrees E), Lauder (45.04 degrees S, 169.68 degrees E), Reunion (20.9 degrees S, 55.50 degrees E) and Jungfraujoch (46.55 degrees N, 7.98 degrees E) were used to illustrate the capabilities of the method. NH3 mean total columns ranging 3 orders of magnitude were obtained, with higher values at Bremen (mean of 13 : 47 x 10(15) molecules cm(-2)) and lower values at Jungfraujoch (mean of 0 : 18 x 10(15) molecules cm(-2)). In conditions with high surface concentrations of ammonia, as in Bremen, it is possible to retrieve information on the vertical gradient, as two layers can be distinguished. The retrieval there is most sensitive to ammonia in the planetary boundary layer, where the trace gas concentration is highest. For conditions with low concentrations, only the total column can be retrieved. Combining the systematic and random errors we have a mean total error of 26% for all spectra measured at Bremen (number of spectra (N) = 554), 30% for all spectra from Lauder (N = 2412), 25% for spectra from Reunion (N = 1262) and 34% for spectra measured at Jungfraujoch (N = 2702). The error is dominated by the systematic uncertainties in the spectroscopy parameters. Station-specific seasonal cycles were found to be consistent with known seasonal cycles of the dominant ammonia sources in the station surroundings. The developed retrieval methodology from FTIR instruments provides a new way of obtaining highly time-resolved measurements of ammonia burdens. FTIR-NH3 observations will be useful for understanding the dynamics of ammonia concentrations in the atmosphere and for satellite and model validation. It will also provide additional information to constrain the global ammonia budget. Show less
Damme, M. van; Erisman, J.W.; Clarisse, L.; Dammers, E.; Whitburn, S.; Clerbaux, C.; ... ; Coheur, P.F. 2015
We exploit 6 years of measurements from the Infrared Atmospheric Sounding Interferometer (IASI)/MetOp-A instrument to identify seasonal patterns and interannual variability of atmospheric NH3. This... Show moreWe exploit 6 years of measurements from the Infrared Atmospheric Sounding Interferometer (IASI)/MetOp-A instrument to identify seasonal patterns and interannual variability of atmospheric NH3. This is achieved by analyzing the time evolution of the monthly mean NH3 columns in 12 subcontinental areas around the world, simultaneously considering measurements from IASI morning and evening overpasses. For most regions, IASI has a sufficient sensitivity throughout the years to capture the seasonal patterns of NH3 columns, and we show that each region is characterized by a well-marked and distinctive cycle, with maxima mainly related to underlying emission processes. The largest column abundances and seasonal amplitudes throughout the years are found in southwestern Asia, with maxima twice as large as what is observed in southeastern China. The relation between emission sources and retrieved NH3 columns is emphasized at a smaller regional scale by inferring a climatology of the month of maximum columns. Show less
Erisman, J.W.; Dammers, E.; Van Damme, M.; Soudzilovskaia, N.A.; Schaap, M.; Banzhaf, M. 2015
An overview of the achievements and the current state of knowledge on reactive nitrogen in Europe, focusing on deposition, critical load exceedances, and modeled and measured trends.
Grinsven, H.J.M. van; Erisman, J.W.; Vries, W. de; Westhoek, H. 2015
Most global strategies for future food security focus on sustainable intensification of production of food and involve increased use of nitrogen fertilizer and manure. The external costs of current... Show moreMost global strategies for future food security focus on sustainable intensification of production of food and involve increased use of nitrogen fertilizer and manure. The external costs of current high nitrogen (N) losses from agriculture in the European Union, are 0.3-1.9% of gross domestic product (GDP) in 2008. We explore the potential of sustainable extensification for agriculture in the EU and The Netherlands by analysing cases and scenario studies focusing on reducing N inputs and livestock densities. Benefits of extensification are higher local biodiversity and less environmental pollution and therefore less external costs for society. Extensification also has risks such as a reduction of yields and therewith a decrease of the GDP and farm income and a smaller contribution to the global food production, and potentially an i0ncrease of global demand for land. We demonstrate favourable examples of extensification. Reducing the N fertilization rate for winter wheat in Northwest Europe to 25-30% below current N recommendations accounts for the external N cost, but requires action to compensate for a reduction in crop yield by 10-20%. Dutch dairy and pig farmers changing to less intensive production maintain or even improve farm income by price premiums on their products, and/or by savings on external inputs. A scenario reducing the Dutch pig and poultry sector by 50%, the dairy sector by 20% and synthetic N fertilizer use by 40% lowers annual N pollution costs by 0.2-2.2 billion euro (40%). This benefit compensates for the loss of GDP in the primary sector but not in the supply and processing chain. A 2030 scenario for the EU27 reducing consumption and production of animal products by 50% (demitarean diet) reduces N pollution by 10% and benefits human health. This diet allows the EU27 to become a food exporter, while reducing land demand outside Europe in 2030 by more than 100 million hectares (2%), which more than compensates increased land demand when changing to organic farming. We conclude that in Europe extensification of agriculture is sustainable when combined with adjusted diets and externalization of environmental costs to food prices. Show less
Damme, M. van; Clarisse, L.; Dammers, E.; Liu, X.; Nowak, J.B.; Clerbaux, C.; ... ; Coheur, P.F. 2015
Limited availability of ammonia (NH3) observations is currently a barrier for effective monitoring of the nitrogen cycle. It prevents a full understanding of the atmospheric processes in which this... Show moreLimited availability of ammonia (NH3) observations is currently a barrier for effective monitoring of the nitrogen cycle. It prevents a full understanding of the atmospheric processes in which this trace gas is involved and therefore impedes determining its related budgets. Since the end of 2007, the Infrared Atmospheric Sounding Interferometer (IASI) satellite has been observing NH3 from space at a high spatio-temporal resolution. This valuable data set, already used by models, still needs validation. We present here a first attempt to validate IASI-NH3 measurements using existing independent ground-based and airborne data sets. The yearly distributions reveal similar patterns between ground-based and space-borne observations and highlight the scarcity of local NH3 measurements as well as their spatial heterogeneity and lack of representativity. By comparison with monthly resolved data sets in Europe, China and Africa, we show that IASI-NH3 observations are in fair agreement, but they are characterized by a smaller variation in concentrations. The use of hourly and airborne data sets to compare with IASI individual observations allows investigations of the impact of averaging as well as the representativity of independent observations for the satellite footprint. The importance of considering the latter and the added value of densely located airborne measurements at various altitudes to validate IASI-NH3 columns are discussed. Perspectives and guidelines for future validation work on NH3 satellite observations are presented. Show less
The global nitrogen (N) cycle at the beginning of the 21st century has been shown to be strongly influenced by the inputs of reactive nitrogen (N-r) from human activities, including combustion... Show moreThe global nitrogen (N) cycle at the beginning of the 21st century has been shown to be strongly influenced by the inputs of reactive nitrogen (N-r) from human activities, including combustion-related NOx, industrial and agricultural N fixation, estimated to be 220 TgNyr(-1) in 2010, which is approximately equal to the sum of biological N fixation in unmanaged terrestrial and marine ecosystems. According to current projections, changes in climate and land use during the 21st century will increase both biological and anthropogenic fixation, bringing the total to approximately 600 TgNyr(-1) by around 2100. The fraction contributed directly by human activities is unlikely to increase substantially if increases in nitrogen use efficiency in agriculture are achieved and control measures on combustion-related emissions implemented.Some N-cycling processes emerge as particularly sensitive to climate change. One of the largest responses to climate in the processing of Nr is the emission to the atmosphere of NH3, which is estimated to increase from 65 TgNyr(-1) in 2008 to 93 TgNyr(-1) in 2100 assuming a change in global surface temperature of 5 degrees C in the absence of increased anthropogenic activity. With changes in emissions in response to increased demand for animal products the combined effect would be to increase NH3 emissions to 135 TgNyr(-1). Another major change is the effect of climate changes on aerosol composition and specifically the increased sublimation of NH4NO3 close to the ground to form HNO3 and NH3 in a warmer climate, which deposit more rapidly to terrestrial surfaces than aerosols. Inorganic aerosols over the polluted regions especially in Europe and North America were dominated by (NH4)(2)SO4 in the 1970s to 1980s, and large reductions in emissions of SO2 have removed most of the SO42- from the atmosphere in these regions. Inorganic aerosols from anthropogenic emissions are now dominated by NH4NO3, a volatile aerosol which contributes substantially to PM10 and human health effects globally as well as eutrophication and climate effects. The volatility of NH4NO3 and rapid dry deposition of the vapour phase dissociation products, HNO3 and NH3, is estimated to be reducing the transport distances, deposition footprints and inter-country exchange of N-r in these regions.There have been important policy initiatives on components of the global N cycle. These have been regional or country-based and have delivered substantial reductions of inputs of Nr to sensitive soils, waters and the atmosphere. To date there have been no attempts to develop a global strategy to regulate human inputs to the nitrogen cycle. However, considering the magnitude of global Nr use, potential future increases, and the very large leakage of Nr in many forms to soils, waters and the atmosphere, international action is required. Current legislation will not deliver the scale of reductions globally for recovery from the effects of Nr deposition on sensitive ecosystems, or a decline in N2O emissions to the global atmosphere. Such changes would require substantial improvements in nitrogen use efficiency across the global economy combined with optimization of transport and food consumption patterns. This would allow reductions in Nr use, inputs to the atmosphere and deposition to sensitive ecosystems. Such changes would offer substantial economic and environmental co-benefits which could help motivate the necessary actions. Show less
Particle deposition velocities (11-3000 nm diameter) measured above grassland by eddy covariance during the EU GRAMINAE experiment in June 2000 averaged 0.24 and 0.03 mm s(-1) to long (0.75 m) and... Show moreParticle deposition velocities (11-3000 nm diameter) measured above grassland by eddy covariance during the EU GRAMINAE experiment in June 2000 averaged 0.24 and 0.03 mm s(-1) to long (0.75 m) and short (0.07 m) grass, respectively. After fertilisation with 108 kg N ha(-1) as calcium ammonium nitrate, sustained apparent upward fluxes of particles were observed. Analysis of concentrations and fluxes of potential precursor gases, including NH3, HNO3, HCl and selected VOCs, shows that condensation of HNO3 and NH3 on the surface of existing particles is responsible for this effect. A novel approach is developed to derive particle growth rates at the field scale, from a combination of measurements of vertical fluxes and particle size-distributions. For the first 9 days after fertilization, growth rates of 11 nm particles of 7.04 nm hr(-1) and 1.68 nm hr(-1) were derived for day and night-time conditions, respectively. This implies total NH4NO3 production rates of 1.11 and 0.44 mu g m(-3) h(1), respectively. The effect translates into a small error in measured ammonia fluxes (0.06% day, 0.56% night) and a large error in NH4+ and NO3- aerosol fluxes of 3.6% and 10%, respectively. By converting rapidly exchanged NH3 and HNO3 into slowly depositing NH4NO3, the reaction modifies the total N budget, though this effect is small (<1% for the 10 days following fertilization), as NH3 emission dominates the net flux. It is estimated that 3.8% of the fertilizer N was volatilised as NH3, of which 0.05% re-condensed to form NH4NO3 particles within the lowest 2 in of the surface layer. This surface induced process would at least scale up to a global NH4NO3 formation of ca. 0.21 kt N yr(-1) from NH4NO3 fertilisers and potentially 45 kt N yr(-1) from NH3 emissions in general. Show less
The exchange of Ammonia (NH3) between grassland and the atmosphere was determined using Relaxed Eddy Accumulation (REA) measurements. The use of REA is of special interest for NH3, since the... Show moreThe exchange of Ammonia (NH3) between grassland and the atmosphere was determined using Relaxed Eddy Accumulation (REA) measurements. The use of REA is of special interest for NH3, since the determination of fluxes at one height permits multiple systems to be deployed to quantify vertical flux divergence (either due to effects of chemical production or advection). During the Braunschweig integrated experiment four different continuous-sampling REA systems were operated during a period of about 10 days and were compared against a reference provided by independent application of the Aerodynamic Gradient Method (AGM). The experiment covered episodes before and after both cutting and fertilizing and provided a wide range of fluxes -60-3600 ng NH3 m(-2) s(-1) for testing the REA systems. The REA systems showed moderate to good correlation with the AGM estimates, with r(2) values for the linear regressions between 0.3 and 0.82. For the period immediately after fertilization, the REA systems showed average fluxes 20% to 70% lower than the reference. At periods with low fluxes REA and AGM can agree within a few %. Overall, the results show that the continuous REA technique can now be used to measure NH3 surface exchange fluxes. While REA requires greater analytical precision in NH3 measurement than the AGM, a key advantage of REA is that reference sampling periods can be introduced to remove bias between sampling inlets. However, while the data here indicate differences consistent with advection effects, significant improvements in sampling precision are essential to allow robust determination of flux divergence in future studies. Wet chemical techniques will be developed further since they use the adsorptive and reactive properties of NH3 that impedes development of cheaper optical systems. Show less
A major international experiment on ammonia (NH3) biosphere-atmosphere exchange was conducted over intensively managed grassland at Braunschweig, Germany. The experimental strategy was developed to... Show moreA major international experiment on ammonia (NH3) biosphere-atmosphere exchange was conducted over intensively managed grassland at Braunschweig, Germany. The experimental strategy was developed to allow an integrated analysis of different features of NH3 exchange including: a) quantification of nearby emissions and advection effects, b) estimation of net NH3 fluxes with the canopy by a range of micrometeorological measurements, c) analysis of the sources and sinks of NH3 within the plant canopy, including soils and bioassay measurements, d) comparison of the effects of grassland management options on NH3 fluxes and e) assessment of the interactions of NH3 fluxes with aerosol exchange processes. Additional technical objectives included the inter-comparison of different estimates of sensible and latent heat fluxes, as well as continuous-gradient and Relaxed Eddy Accumulation (REA) systems for NH3 fluxes.The prior analysis established the spatial and temporal design of the experiment, allowing significant synergy between these objectives. The measurements were made at 7 measurement locations, thereby quantifying horizontal and vertical profiles, and covered three phases: a) tall grass canopy prior to cutting (7 days), b) short grass after cutting (7 days) and c) re-growing sward following fertilization with ammonium nitrate (10 days). The sequential management treatments allowed comparison of sources-sinks, advection and aerosol interactions under a wide range of NH3 fluxes.This paper describes the experimental strategy and reports the grassland management history, soils, environmental conditions and air chemistry during the experiment, finally summarizing how the results are coordinated in the accompanying series of papers. Show less
Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel... Show moreImproved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA) were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: emissions increased after grass cutting (-50 to 700 ng m(-2) s(-1) NH3) and after N-fertilization (0 to 3800 ng m(-2) s(-1)) compared with before the cut (-60 to 40 ng m(-2) s(-1)).Effects of advection and air chemistry were investigated using horizontal NH3 profiles, acid gas and particle flux measurements. Inverse modelling of NH3 emission from an experimental farm agreed closely with inventory estimates, while advection errors were used to correct measured grassland fluxes. Advection effects were caused both by the farm and by emissions from the field, with an inverse dispersion-deposition model providing a reliable new approach to estimate net NH3 fluxes. Effects of aerosol chemistry on net NH3 fluxes were small, while the measurements allowed NH3-induced particle growth rates to be calculated and aerosol fluxes to be corrected.Bioassays estimated the emission potential I" = [NH4+]/[H+] for different plant pools, with the apoplast having the smallest values (30-1000). The main within-canopy sources of NH3 emission appeared to be leaf litter and the soil surface, with I" up to 3 million and 300 000, respectively. Cuvette and within-canopy analyses confirmed the role of leaf litter NH3 emission, which, prior to cutting, was mostly recaptured within the canopy.Measured ammonia fluxes were compared with three models: an ecosystem model (PaSim), a soil vegetation atmosphere transfer model (SURFATM-NH3) and a dynamic leaf chemistry model (DCC model). The different models each reproduced the main temporal dynamics in the flux, highlighting the importance of canopy temperature dynamics (Surfatm-NH3), interactions with ecosystem nitrogen cycling (PaSim) and the role of leaf surface chemistry (DCC model). Overall, net above-canopy fluxes were mostly determined by stomatal and cuticular uptake (before the cut), leaf litter emissions (after the cut) and fertilizer and litter emissions (after fertilization). The dynamics of ammonia emission from leaf litter are identified as a priority for future research. Show less
Deposition of atmospheric ammonia (NH3) to semi-natural ecosystems leads to serious adverse effects, such as acidification and eutrophication. A step in quantifying such effects is the measurement... Show moreDeposition of atmospheric ammonia (NH3) to semi-natural ecosystems leads to serious adverse effects, such as acidification and eutrophication. A step in quantifying such effects is the measurement of NH3 fluxes over semi-natural and agricultural land. However, measurement of NH3 fluxes over vegetation in the vicinity of strong NH3 sources is challenging, since NH3 emissions are highly heterogeneous. Indeed, under such conditions, local advection errors may alter the measured fluxes. In this study, local advection errors (Delta F-z,F-adv) were estimated over a 14 ha grassland field, which was successively cut and fertilised, as part of the GRAMINAE integrated Braunschweig experiment. The magnitude of Delta F-z,F-adv was determined up to 810 m downwind from farm buildings emitting between 6.2 and 9.9 kg NH3 day(-1). The GRAMINAE experiment provided a unique opportunity to compare two methods of estimating Delta F-z,F-adv: one inference method based on measurements of horizontal concentration gradients, and one based on inverse dispersion modelling with a two-dimensional model.Two sources of local advection were clearly identified: the farm NH3 emissions leading to positive Delta F-z,F-adv ('bias towards emissions') and field NH3 emissions, which led to a negative Delta F-z,F-adv ('bias towards deposition'). The local advection flux from the farm was in the range 0 to 27 ng NH3 m(-2) s(-1) at 610 m from the farm, whereas Delta F-z,F-adv due to field emission was proportional to the local flux, and ranged between -209 and 13 ng NH3 m(-2) s(-1). The local advection flux Delta F-z,F-adv was either positive or negative depending on the magnitude of these two contributions. The modelled and inferred advection errors agreed well. The inferred advection errors, relative to the vertical flux at 1 m height, were 52% on average, before the field was cut, and less than 2.1% when the field was fertilised. The variability of the advection errors in response to changes in micrometeorological conditions is also studied. The limits of the 2-D modelling approach are discussed. Show less
Burkhardt, J.; Flechard, C.R.; Gresens, F.; Mattsson, M.; Jongejan, P.A.C.; Erisman, J.W.; ... ; Sutton, M.A. 2009
Ammonia exchange fluxes between grassland and the atmosphere were modelled on the basis of stomatal compensation points and leaf surface chemistry, and compared with measured fluxes during the... Show moreAmmonia exchange fluxes between grassland and the atmosphere were modelled on the basis of stomatal compensation points and leaf surface chemistry, and compared with measured fluxes during the GRAMINAE intensive measurement campaign in spring 2000 near Braunschweig, Germany. Leaf wetness and dew chemistry in grassland were measured together with ammonia fluxes and apoplastic NH4+ and H+ concentration, and the data were used to apply, validate and further develop an existing model of leaf surface chemistry and ammonia exchange. Foliar leaf wetness which is known to affect ammonia fluxes may be persistent after the end of rainfall, or sustained by recondensation of water vapour originating from the ground or leaf transpiration, so measured leaf wetness values were included in the model. pH and ammonium concentrations of dew samples collected from grass were compared to modelled values.The measurement period was divided into three phases: a relatively wet phase followed by a dry phase in the first week before the grass was cut, and a second drier week after the cut. While the first two phases were mainly characterised by ammonia deposition and occasional short emission events, regular events of strong ammonia emissions were observed during the post-cut period. A single-layer resistance model including dynamic cuticular and stomatal exchange could describe the fluxes well before the cut, but after the cut the stomatal compensation points needed to numerically match measured fluxes were much higher than the ones measured by bioassays, suggesting another source of ammonia fluxes. Considerably better agreement both in the direction and the size range of fluxes were obtained when a second layer was introduced into the model, to account for the large additional ammonia source inherent in the leaf litter at the bottom of the grass canopy. Therefore, this was found to be a useful extension of the mechanistic dynamic chemistry model by keeping the advantage of requiring relatively little site-specific information. Show less
