Surface-atmosphere exchange of inorganic water-soluble gases and associated ions in bulk aerosol above agricultural grassland pre- and post- fertilisation

Robbie Ramsay, C.F. Di Marco, Mathew R. Heal, Marsailidh M. Twigg, Nicolas Cowan, Matthew R. Jones, Sarah R. Leeson, W. J. Bloss, L. J. Kramer, L. R. Crilley, Matthias Sorgel, M. O. Andreae, E. Nemitz

Research output: Contribution to journalArticlepeer-review


The increasing use of intensive agricultural practices can lead to damaging consequences for the atmosphere through enhanced emissions of air pollutants. However, there are few direct measurements of the surface-atmosphere exchange of trace gases and water–soluble aerosols over agricultural grassland, particularly of reactive nitrogen compounds. In this study, we present measurements of the concentrations, fluxes and deposition velocities of the trace gases HCl, HONO, HNO3, SO2 and NH3, and their associated water-soluble aerosol counterparts Cl-, NO2-, NO3-, SO42-, NH4+ as determined hourly for one month in May–June 2016 over agricultural grassland near Edinburgh, UK, pre- and post- fertilisation. Measurements were made using the Gradient of Aerosols and Gases Online Registration (GRAEGOR) wet–chemical two–point gradient instrument. Emissions of NH3 peaked at 1460 ng m-2 s-1 three hours after fertilisation, with an emission of HONO peaking at 4.92 ng m-2 s-1 occurring five hours after fertilisation. Apparent emissions of NO3- aerosol were observed after fertilisation which, coupled with a divergence of HNO3 deposition velocity (Vd) from its theoretical maximum value, suggested the reaction of emitted NH3 with atmospheric HNO3 to form ammonium nitrate aerosol. The use of the conservative exchange fluxes of tot-NH4+ and tot-NO3- indicated net emission of tot-NO3-, implying a ground source of HNO3 after fertilisation. Daytime concentrations of HONO remained above the detection limit (30 ng m-3) throughout the campaign, suggesting a daytime source for HONO at the site. Whilst the mean Vd of NH4+ was with 0.93 mm/s in the range expected for the accumulation mode, the larger average Vd for Cl- (3.65 mm/s), NO3- (1.97 mm/s), SO42- (1.89 mm/s) reflected the contribution of a super-micron fraction and decreased with increasing PM2.5/PM10 ratio (a proxy measurement for aerosol size), providing evidence – although limited by the use of a proxy for aerosol size – of a size-dependence of aerosol deposition velocity for aerosol chemical compounds, which has been suggested from process orientated models of aerosol deposition.
Original languageEnglish
Article numberacp-18-16953-2018
Pages (from-to)16953-16978
Number of pages26
JournalAtmospheric Chemistry and Physics
Early online date11 Jul 2018
Publication statusPublished - 30 Nov 2018


  • surface-atmosphere exchange
  • acid gases
  • water-soluble ions
  • HNO3
  • HONO
  • nitrous acid
  • nitrate aerosol
  • chloride aerosol

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