Imprints of anthropogenic air pollution sources on nitrate isotopes in precipitation in a tropical metropolitan area

• Published in: Atmospheric environment (1994) Vol. 288; p. 119300
• Main Authors: Passos, Ricardo G., Matiatos, Ioannis, Monteiro, Lucilena R., Almeida, Rafael S.S.P., Lopes, Nilva P., Carvalho Filho, Carlos A., Cota, Stela D.S.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-11-2022
• Subjects: Backward trajectory analysis; Geoprocessing; Stable isotopes; Tropics; Wet deposition; Backward trajectory analysis; Geoprocessing; Wet deposition; Stable isotopes; Tropics
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2022.119300

Identifying the origin of NOx emissions, their transformation into nitrate (NO3−) and its atmospheric deposition is important to better understand the impacts of air pollution on the environment and human health, on a local and regional scale. We measured nitrate isotopes (δ15N, δ18O of NO3−) in precipitation samples in a tropical station in Brazil in 2019–2020 and combined them with chemical, geospatial and meteorological data to trace NOx sources towards their wet deposition as NO3−. A total wet N deposition of ∼12 kg N/ha.year showed significant N air pollution, out of which the relative contribution of NO3−-N was ∼37% (4.6 kg NO3−-N/ha.year). The δ15N–NO3- values in precipitation ranged from −8.5 to +4.1‰, with a volume-weighted mean (VWM) value of −3.0 ± 2.7‰, whereas the δ18O–NO3- values ranged from +25.9 to +63.5‰ with a VWM value of +53.3 ± 7.3‰. The δ15N–NO3- results combined with air mass backward trajectory analysis and geospatial mapping revealed that the NOx emissions in Belo Horizonte originated from: vehicles and industries from the urban and industrialized areas, biomass burning related to wildfires, and ship emissions from the coastal areas. The temporal variation of δ15N, δ18O of NO3− values was attributed to NOx source variability and transformation processes. The use of integrated methods to evaluate the imprints of anthropogenic air pollution sources in Brazil will contribute to inform NOx source management strategies and improve air and water quality.
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•Urban and ship emissions were the main NOx sources in precipitation NO3-.•N emissions from wildfires in the Amazon area were identified in individual events.•The period of lockdown in Belo Horizonte resulted in reduced vehicle emissions.•High δ18O–NO3- in the cold period was partly due to formation via the N2O5 pathway.