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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  26 May 2020

26 May 2020

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This preprint is currently under review for the journal ACP.

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

Y. Sim Tang1, Chris R. Flechard2, Ulrich Dämmgen3, Sonja Vidic4, Vesna Djuricic4, Marta Mitosinkova5, Hilde T. Uggerud6, Maria J. Sanz7,8,9, Ivan Simmons1, Ulrike Dragosits1, Eiko Nemitz1, Marsailidh Twigg1, Netty van Dijk1, Yannick Fauvel2, Francisco Sanz-Sanchez7, Martin Ferm10, Cinzia Perrino11, Maria Catrambone11, David Leaver1, Christine F. Braban1, J. Neil Cape1, Mathew R. Heal12, and Mark A. Sutton1 Y. Sim Tang et al.
  • 1UK Centre for Ecology & Hydrology (UKCEH), Bush Estate, Penicuik, Midlothian EH26 0QB, UK
  • 2French National Research Institute forAgriculture, Food and Environment (INRAE), UMR 1069 SAS, 65 rue de St-Brieuc, 35042 Rennes Cedex, France
  • 3von Thunen Institut (vTI), Bundesallee 50, 38116 Braunschweig, Germany
  • 4Meteorological and Hydrological Service of Croatia (MHSC), Research and Development Division, Gric 3, 10000 Zagreb, Croatia
  • 5Slovak Hydrometeorological Institute (SHMU), Departmentof Air Quality, Jeseniova 17, 833 15 Bratislava, Slovak Republic
  • 6Norwegian Institute for Air Research (NILU), P.O. Box 100, N-2027 Kjeller, Norway
  • 7The Mediterranean Center for Environmental Studies (CEAM), Parque Tecnológico, C/Charles H. Darwin 14, 46980 Paterna (Valencia), Spain
  • 8Basque Centre for Climate Change, Sede Building 1, Scientific Campus of the University of the Basque Country, 48940, Leioa, Bizkaia, Spain
  • 9Ikerbasque, Basque Science Foundation, María Díaz Haroko Kalea, 3, 48013 Bilbo, Bizkaia, Spain
  • 10IVL Swedish Environmental Research Institute, P.O. Box 5302, S-400 14, Gothenburg, Sweden
  • 11C.N.R. Institute of Atmospheric Pollution Research, via Salaria Km. 29, 300–00015, Monterotondo st, Rome, Italy
  • 12School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, UK

Abstract. 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 analyzed. Speciated measurements were made with a low-volume denuder and filter pack method (DELTA®) as part of the EU NitroEurope (NEU) integrated project. Altogether, there were 64 sites in 20 countries (2006–2010), coordinated between 7 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 4 main ecosystem types (crops, grassland, forests and semi-natural). 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 NO3- were at cropland sites in intensively managed agricultural areas (e.g. Borgo Cioffi in Italy), and smallest 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 were 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 were 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.

Y. Sim Tang et al.

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Y. Sim Tang et al.

Y. Sim Tang et al.


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Short summary
Continuous, concurrent monthly measurement of reactive gases (NH3, HNO3, SO2, HCl) and aerosols (NH4+, NO3-, SO42-, Cl-, Na+) at 64 rural sites across 20 European countries over a 4 year period showed dominance of NH3 and NH4NO3 in the atmospheric composition. Differences in spatial and temporal concentrations between European regions and 4 major ecosystem types were observed are discussed, driven by variations in emissions, chemical interactions, meteorology and gas : aerosol phase partitioning.
Continuous, concurrent monthly measurement of reactive gases (NH3, HNO3, SO2, HCl) and aerosols...