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
