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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
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Research article
13 Apr 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Drivers for spatial, temporal and long-term trends in atmospheric ammonia and ammonium in the UK
Yuk S. Tang1, Christine F. Braban1, Ulrike Dragosits1, Anthony J. Dore1, Ivan Simmons1, Netty van Dijk1, Janet Poskitt2, Gloria Dos Santos Pereira2, Patrick O. Keenan2, Christopher Conolly3, Keith Vincent3, Rognvald I. Smith1, Mathew R. Heal4, and Mark A. Sutton1 1CEH, Bush Estate, Penicuik, Midlothian EH26 0QB
2CEH, Lancaster Environment Centre, Bailrigg, Lancaster LA1 4AP
3Ricardo Energy & Environment, Gemini Building, Fermi Avenue, Harwell, Oxon OX11 0QR
4School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ
Abstract. A unique long-term dataset from the UK National Ammonia Monitoring Network (NAMN) is used here to assess spatial, seasonal and long-term variability in atmospheric ammonia (NH3: 1998–2014) and particulate ammonium (NH4+: 1999–2014) across the UK. Extensive spatial heterogeneity in NH3 concentrations is observed, with lowest annual mean concentrations at remote sites (< 0.2 μg m−3) and highest in the areas with intensive agriculture (up to 22 μg m−3), while NH4+ concentrations show less spatial variability (e.g. range of 0.14 to 1.8 μg m−3 annual mean in 2005). Temporally, NH3 concentrations are influenced by environmental conditions and local emission sources. In particular, peak NH3 concentrations are observed in summer at background sites (defined by 5 km grid average NH3 emissions < 1 kg N ha−1 y−1) and in areas dominated by sheep farming, driven by increased volatilization of NH3 in warmer summer temperatures. In areas where cattle, pig and poultry farming is dominant, the largest NH3 concentrations are in spring and autumn, matching periods of manure application to fields. By contrast, peak concentrations of NH4+ aerosol occur in spring, associated with long-range transboundary sources. An estimated decrease in NH3 emissions by 16 % between 1998 and 2014 was reported by the UK National Atmospheric Emissions Inventory. Annually averaged NH3 data from NAMN sites operational over the same period (n = 59) show an indicative downward trend, although the reduction in NH3 concentrations is smaller and non-significant (−6.3 % (Mann–Kendall, MK); −3.1 % (linear regression, LR)). In areas dominated by pig and poultry farming, a significant reduction in NH3 concentrations between 1998 and 2014 (−22 % (MK); −21 % (LR): annually averaged NH3) is consistent with, but not as large as the decrease in estimated NH3 emissions from this sector over the same period (−39 %). By contrast, in cattle-dominated areas there is a slight upward trend (non-significant) in NH3 concentrations (+12 %, (MK); +3.6 % (LR): annually averaged NH3), despite the estimated decline in NH3 emissions from this sector since 1998 (−11 %). At background and sheep dominated sites, NH3 concentrations increased over the monitoring period. These increases (non-significant) at background (+17 % (MK); +13 % (LR): annually averaged data) and sheep dominated sites (+15 % (MK); +19 % (LR): annually averaged data) would be consistent with the concomitant reduction in SO2 emissions over the same period, leading to a longer atmospheric lifetime of NH3, thereby increasing NH3 concentrations in remote areas. The observations for NH3 concentrations not decreasing as fast as estimated emission trends are consistent with a larger downward trend in annual particulate NH4+ concentrations (1999–2014: −47 % (MK); −49 % (LR), p < 0.01, n = 23), associated with a slower formation of particulate NH4+ in the atmosphere from gas-phase NH3.

Citation: Tang, Y. S., Braban, C. F., Dragosits, U., Dore, A. J., Simmons, I., van Dijk, N., Poskitt, J., Dos Santos Pereira, G., Keenan, P. O., Conolly, C., Vincent, K., Smith, R. I., Heal, M. R., and Sutton, M. A.: Drivers for spatial, temporal and long-term trends in atmospheric ammonia and ammonium in the UK, Atmos. Chem. Phys. Discuss.,, in review, 2017.
Yuk S. Tang et al.
Yuk S. Tang et al.
Yuk S. Tang et al.


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Short summary
A unique long-term dataset of NH3 and NH4+ data from the NAMN is used to assess spatial, seasonal and long-term variability across the UK. NH3 is spatially variable, with distinct temporal profiles according to source types. NH4+ is spatially smoother, with peak concentrations in spring from long-range transport. Decrease in NH3 is smaller than emissions, but NH4+ decreased faster than NH3, due to a shift from stable (NH4)2SO4 to semi-volatile NH4NO3, increasing the atmospheric lifetime of NH3.
A unique long-term dataset of NH3 and NH4+ data from the NAMN is used to assess spatial,...