Concentrations and biosphere–atmosphere fluxes of inorganic trace gases and associated ionic aerosol counterparts over the Amazon rainforest

Abstract

Abstract. 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 NH4+, Cl−, NO2-, NO3- and SO42- 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 NO3- 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 SO42- and NH4+, respectively. Deposition rates of NO3- and Cl− were higher at 7.1 and 7.8 mm s−1, respectively, reflecting their larger average size. The exchange of NH3 and HONO was bidirectional, with NH3 showing emission episodes in the afternoon and HONO in the early morning hours. This work provides a unique dataset to test and improve dry deposition schemes for these compounds for tropical rainforest, which have typically been developed by interpolation from conditions in temperate environments. A future campaign should focus on making similar measurements in the wet season in order to provide a complete view of the annual pattern of inorganic trace gas and coarse aerosol biosphere–atmosphere exchange over tropical rainforest.

Strong particle production and condensational growth in the upper troposphere sustained by biogenic VOCs from the canopy of the Amazon Basin

“…A5) showed a fair agreement with the observations in the free troposphere of the Central Amazon (Andreae & Andreae, 1988;Paralovo et al, 2019;Ramsay et al, 2020), which is an important prerequisite for an accurate simulation of the H2SO4-H2O binary nucleation in this model (Wexler et al, 1994). The modeled SO2 concentration in the PBL, especially near the ground surface, was higher than the observations (Ramsay et al, 2020), which could be related to several factors, 685 e.g. overestimated SO2 emission (Andreae, 2019) and/or inadequate scavenging (Hardacre et al, 2021), and requires further investigations.…”

“…The ACRIDICON-CHUVA (ACRIDICON stands for "Aerosol, Cloud, Precipitation, and Radiation The simulated SO2 concentration the location of the ATTO site (Fig. A5) showed a fair agreement with the observations in the free troposphere of the Central Amazon (Andreae & Andreae, 1988;Paralovo et al, 2019;Ramsay et al, 2020), which is an important prerequisite for an accurate simulation of the H2SO4-H2O binary nucleation in this model (Wexler et al, 1994). The modeled SO2 concentration in the PBL, especially near the ground surface, was higher than the observations (Ramsay et al, 2020), which could be related to several factors, 685 e.g.…”

Tropical and Boreal Forest – Atmosphere Interactions: A Review

“…Terrestrial ecosystems are linked to the atmosphere via vertical momentum fluxes, sensible and latent heat, and fluxes of atmospheric constituents (Ramsay et al, 2020(Ramsay et al, , 2021. The forest canopy is an essential feature of the biosphere-atmosphere interactions in tropical rainforests (Blundo et al, 2021).…”

Review of methods for assessing deposition of reactive nitrogen pollutants across complex terrain with focus on the UK

“…Dry deposition flux of N r can be estimated as the sum of dry deposition fluxes of NH 3 , nitric acid (HNO 3 ), nitrogen dioxide (NO 2 ) as well as aerosol components (NH 4 + and NO 3 − ) (recognising that there can be other significant N r chemical species in the atmosphere) with the concentrations of pollutants and micrometeorological measurements at multiple heights. 58 Although this approach has been used in challenging upland sites, 32 concentration gradients are particularly sensitive to measurement location in complex terrain, because each height effectively sees a different footprint which get small for the lowest height where the influence of local heterogeneity effects are largest. Hence when these approaches are used, spatial replication is ideally needed but is rarely done so that care needs to be taken in interpreting and generalising any results.…”