This dataset contains information about meteorological conditions and ammonia concentration and deposition rates resulting from an experimental setup. An NH3 enhancement experiment along with a full suite of multi-height meteorological measurements was established in a tropical forest in central Sri Lanka. Under suitable wind conditions measured at the meteorological tower, NH3 is released towards two monitoring transects. Along the downwind monitoring transects, NH3 concentrations in the air are measured using monthly passive samplers. Deposition rates are modelled using a bi-directional resistance model based on measured NH3 concentrations in the air, micrometeorology and plant physiology. Additionally, NH3 concentrations were measured at high temporal resolution at a fixed downwind distance from the source to achieve the target enhancement concentrations. The work was supported by UKRI GCRF South Asian Nitrogen Hub (Grant NE/S009019/1). Full details about this dataset can be found at https://doi.org/10.5285/998c2b2b-7470-42b0-81e7-409b91752377

This dataset contains information about meteorological conditions, ammonia concentration and deposition rates resulting from an experimental ammonia (NH3) enhancement setup in a tropical forest in central Sri Lanka. The experiment is designed for controlled enhancement of ambient NH3 concentration within the study plot under natural field conditions so that effects of NH3 on tropical vegetation can be studied. This will help identify tolerance thresholds of vegetation to NH3 as an air pollutant and determine critical levels that can be incorporated into regional environmental policy. Meteorological measurements were recorded at multiple heights on a meteorological tower. Under suitable wind conditions, NH3 was released towards two vegetation monitoring transects replicating pollution from a point source, and NH3 concentrations in the air were measured using monthly passive samplers. Continuous meteorological data, NH3 release, and NH3 concentration data are provided in 15-minute intervals and this dataset relates to measurements taken in 2023 – 2024. Deposition rates were modelled using a bi-directional resistance model on a monthly timescale based on measured NH3 concentrations in the air, micrometeorology and plant physiology. This dataset provides an extension of the 2022 dataset to enable longer term analysis of NH3 deposition and its effects in a tropical forest. The work was supported by UKRI GCRF South Asian Nitrogen Hub (Grant NE/S009019/1). Full details about this dataset can be found at https://doi.org/10.5285/449e746d-6291-4653-a3e0-b18f897abc3e

[This dataset is embargoed until April 1, 2026]. The dataset contains field measurements of atmospheric ammonia under forest canopies in the Himalayas in India, Pakistan, Nepal and Bhutan and in a tropical forest in Sri Lanka between 2022 and 2024. Monthly mean atmospheric ammonia concentrations are provided from 33 sites across the five countries. This dataset provides the first ever empirical measurements of ammonia from South Asian forests and can be used to estimate ecological impact, inform policy decisions, validate atmospheric chemistry transport models and satellite data and design future air quality and ecological monitoring in the region. The ammonia concentration data was collected monthly by deploying passive citric acid-coated samplers at the study locations. Full details about this dataset can be found at https://doi.org/10.5285/9c4aee69-3693-4f18-97c8-ff740045f3de