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Local and regional modelling of NH3 surface exchange is required to quantify nitrogen deposition to, and emissions from, the biosphere. However, measurements and model parameterisations for many remote ecosystems – such as tropical rainforest – remain sparse. Using 1 month of hourly measurements of NH3 fluxes and meteorological parameters over a remote Amazon rainforest site (Amazon Tall Tower Observatory, ATTO), six model parameterisations based on a bidirectional, single-layer canopy compensation point resistance model were developed to simulate observations of NH3 surface exchange. Canopy resistance was linked to either relative humidity at the canopy level (RHz′0), vapour pressure deficit, or a parameter value based on leaf wetness measurements. The ratio of apoplastic NH+4 to H+ concentration, Γs, during this campaign was inferred to be 38.5 ± 15.8. The parameterisation that reproduced the observed net exchange of NH3 most accurately was the model that used a cuticular resistance (Rw) parameterisation based on leaf wetness measurements and a value of Γs=50 (Pearson correlation r=0.71). Conversely, the model that performed the worst at replicating measured NH3 fluxes used an Rw value modelled using RHz′0 and the inferred value of Γs=38.5 (r=0.45). The results indicate that a single-layer canopy compensation point model is appropriate for simulating NH3 fluxes from tropical rainforest during the Amazonian dry season and confirmed that a direct measurement of (a non-binary) leaf wetness parameter improves the ability to estimate Rw. Current inferential methods for determining Γs were noted as having difficulties in the humid conditions present at a rainforest site.

The Amazon rainforest presents a unique, natural laboratory for the study of surface–atmosphere interactions. Its alternation between a near-pristine marine-influenced atmosphere during the wet season and a vulnerable system affected by periodic intrusions of anthropogenic pollution during the dry season provides an opportunity to investigate some fundamental aspects of boundary-layer chemical processes. This study presents the first simultaneous hourly measurements of concentrations, fluxes, and deposition velocities of the inorganic trace gases NH3, HCl, HONO, HNO3, and SO2 as well as their water-soluble aerosol counterparts NH+4, Cl−, NO−2, NO−3 and SO2−4 over the Amazon. Species concentrations were measured in the dry season (from 6 October to 5 November 2017), at the Amazon Tall Tower Observatory (ATTO) in Brazil, using a two-point gradient wet-chemistry instrument (GRadient of AErosols and Gases Online Registration, GRAEGOR) sampling at 42 and 60 m. Fluxes and deposition velocities were derived from the concentration gradients using a modified form of the aerodynamic gradient method corrected for measurement within the roughness sub-layer. Findings from this campaign include observations of elevated concentrations of NH3 and SO2 partially driven by long-range transport (LRT) episodes of pollution and the substantial influence of coarse Cl− and NO−3 particulate on overall aerosol mass burdens. From the flux measurements, the dry season budget of total reactive nitrogen dry deposition at the ATTO site was estimated as −2.9 kg N ha−1a−1. HNO3 and HCl were deposited continuously at a rate close to the aerodynamic limit. SO2 was deposited with an average daytime surface resistance (Rc) of 28 s m−1, whilst aerosol components showed average surface deposition velocities of 2.8 and 2.7 mm s−1 for SO2−4 and NH+4, respectively. Deposition rates of NO−3 and Cl− were higher at 7.1 and 7.8 mm s−1, respectively, reflecting their larger average size. The exchange of NH3 and

The Amazon rainforest presents a unique, natural laboratory for the study of surface–atmosphere interactions. Its alternation between a near-pristine marine-influenced atmosphere during the wet season and a vulnerable system affected by periodic intrusions of anthropogenic pollution during the dry season provides an opportunity to investigate some fundamental aspects of boundary-layer chemical processes. This study presents the first simultaneous hourly measurements of concentrations, fluxes, and deposition velocities of the inorganic trace gases NH3, HCl, HONO, HNO3, and SO2 as well as their water-soluble aerosol counterparts NH+4, Cl−, NO−2, NO−3 and SO2−4 over the Amazon. Species concentrations were measured in the dry season (from 6 October to 5 November 2017), at the Amazon Tall Tower Observatory (ATTO) in Brazil, using a two-point gradient wet-chemistry instrument (GRadient of AErosols and Gases Online Registration, GRAEGOR) sampling at 42 and 60 m. Fluxes and deposition velocities were derived from the concentration gradients using a modified form of the aerodynamic gradient method corrected for measurement within the roughness sub-layer. Findings from this campaign include observations of elevated concentrations of NH3 and SO2 partially driven by long-range transport (LRT) episodes of pollution and the substantial influence of coarse Cl− and NO−3 particulate on overall aerosol mass burdens. From the flux measurements, the dry season budget of total reactive nitrogen dry deposition at the ATTO site was estimated as −2.9 kg N ha−1a−1. HNO3 and HCl were deposited continuously at a rate close to the aerodynamic limit. SO2 was deposited with an average daytime surface resistance (Rc) of 28 s m−1, whilst aerosol components showed average surface deposition velocities of 2.8 and 2.7 mm s−1 for SO2−4 and NH+4, respectively. Deposition rates of NO−3 and Cl− were higher at 7.1 and 7.8 mm s−1, respectively, reflecting their larger average size. The exchange of NH3 and

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 as well as their associated water-soluble aerosol counterparts Cl−, NO2−, NO3−, SO42− and NH4+ as determined hourly for 1 month in May–June 2016 over agricultural grassland near Edinburgh, UK, pre- and postfertilisation. Measurements were made using the Gradient of Aerosols and Gases Online Registrator (GRAEGOR) wet-chemistry two-point gradient instrument. Emissions of NH3 peaked at 1460ng m−2 s−1 3h after fertilisation, with an emission of HONO peaking at 4.92ng m−2 s−1 occurring 5h 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 (30ng m−3) throughout the campaign, suggesting a daytime source for HONO at the site. Whilst the mean Vd of NH4+ was 0.93mm s−1 in the range expected for the accumulation mode, the larger average Vd for Cl− (3.65mm s−1), NO3− (1.97mm s−1) and SO42− (1.89mm s−1) 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 aer

The interaction between biosphere and atmosphere in the cycling of gas and aerosol species is of key importance in considering overall emission and deposition rates of nutrients and pollutants. Understanding of the biosphereatmosphere processes that govern these cycles is critical to modelling global concentrations of atmospheric aerosols and trace gases, which in turn is vital to developing predictions for future climate, air quality and trans‐boundary air pollution. However, to understand these processes, more measurements over a variety of different ecosystems are required, preferably measurements which are taken in real time, which are of high temporal resolution and record a variety of species simultaneously and at potentially low background concentrations. In particular, very little is known about the role of biosphere‐atmosphere exchange in the nutrient cycling in and above tropical rain forests. While aerosol concentrations can provide information on the regional transport of compounds, fluxes allow an insight into the chemical process in the forest. In this work, the concentrations and fluxes of water‐soluble aerosol species NH4 +, Cl‐, NO2 ‐, NO3 ‐ and SO4 2‐ in total suspended particulate (TSP) and their precursor gases NH3, HCl, HNO2, HNO3 and SO2 were measured using a Gradient of Aerosols and Gases Online Registrator (GRAEGOR) above a tropical rainforest site located at the Amazon Tall Tower Observatory (ATTO) in Amazonia, Brazil. Measurements were taken during the dry season from the 4 October to 10 November 2017. From the measured concentration‐gradients and ancillary meteorological measurements, fluxes for each species were derived using the hybrid Aerodynamic Gradient Method and the Modified Bowen Ratio Method. Deposition velocities for each species were calculated and compared to theoretical deposition velocities, and interpreted in relation to measurements of leaf wetness at the canopy level. The average concentrations for aerosol species at each

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 as well as their associated water-soluble aerosol counterparts Cl−, NO2−, NO3−, SO42− and NH4+ as determined hourly for 1 month in May–June 2016 over agricultural grassland near Edinburgh, UK, pre- and postfertilisation. Measurements were made using the Gradient of Aerosols and Gases Online Registrator (GRAEGOR) wet-chemistry two-point gradient instrument. Emissions of NH3 peaked at 1460ng m−2 s−1 3h after fertilisation, with an emission of HONO peaking at 4.92ng m−2 s−1 occurring 5h 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 (30ng m−3) throughout the campaign, suggesting a daytime source for HONO at the site. Whilst the mean Vd of NH4+ was 0.93mm s−1 in the range expected for the accumulation mode, the larger average Vd for Cl− (3.65mm s−1), NO3− (1.97mm s−1) and SO42− (1.89mm s−1) 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 aer

The interaction between biosphere and atmosphere in the cycling of gas and aerosol species is of key importance in considering overall emission and deposition rates of nutrients and pollutants. Understanding of the biosphereatmosphere processes that govern these cycles is critical to modelling global concentrations of atmospheric aerosols and trace gases, which in turn is vital to developing predictions for future climate, air quality and trans‐boundary air pollution. However, to understand these processes, more measurements over a variety of different ecosystems are required, preferably measurements which are taken in real time, which are of high temporal resolution and record a variety of species simultaneously and at potentially low background concentrations. In particular, very little is known about the role of biosphere‐atmosphere exchange in the nutrient cycling in and above tropical rain forests. While aerosol concentrations can provide information on the regional transport of compounds, fluxes allow an insight into the chemical process in the forest. In this work, the concentrations and fluxes of water‐soluble aerosol species NH4 +, Cl‐, NO2 ‐, NO3 ‐ and SO4 2‐ in total suspended particulate (TSP) and their precursor gases NH3, HCl, HNO2, HNO3 and SO2 were measured using a Gradient of Aerosols and Gases Online Registrator (GRAEGOR) above a tropical rainforest site located at the Amazon Tall Tower Observatory (ATTO) in Amazonia, Brazil. Measurements were taken during the dry season from the 4 October to 10 November 2017. From the measured concentration‐gradients and ancillary meteorological measurements, fluxes for each species were derived using the hybrid Aerodynamic Gradient Method and the Modified Bowen Ratio Method. Deposition velocities for each species were calculated and compared to theoretical deposition velocities, and interpreted in relation to measurements of leaf wetness at the canopy level. The average concentrations for aerosol species at each