A case study in the wintertime Vaal Triangle Air-Shed Priority Area on the utility of the nitrogen stable isotopic composition of aerosol nitrate to identify NOx sources

Authors

  • Katye E. Altieri Department of Oceanography, University of Cape Town https://orcid.org/0000-0002-6778-4079
  • Jessica Burger Department of Oceanography, University of Cape Town
  • Brigitte Language Unit for Environmental Sciences and Management, North-West University
  • Stuart J. Piketh Unit for Environmental Sciences and Management, North-West University

DOI:

https://doi.org/10.17159/caj/2022/32/1.12505

Keywords:

aerosol nitrate, stable isotopes, NOx sources, Highveld, Vaal Triangle

Abstract

In South Africa, the Highveld region and the Johannesburg-Pretoria megacity are known as global NOx (NOx = NO + NO2) “hotspots” identified by satellite-based instruments. The ultimate sink for atmospheric NOx is conversion to aerosol nitrate. However, measurements of aerosol nitrate concentrations do not provide information on which NOx sources served as nitrate precursors at that location. This complicates efforts to reduce concentrations of particulate matter (PM) in these air quality priority areas. Here, we measured the nitrogen stable isotopic composition of nitrate from daily wintertime collections of coarse mode PM2.5-10 (PM ≤ 10 and >2.5 µm in diameter) at three air quality monitoring stations located in the Vaal Triangle Air-Shed Priority Area (VTAPA). The overall aim of this case study was to evaluate the use of the distinct stable isotopic signatures of various NOx sources to identify their relative contribution to aerosol nitrate across the Highveld. The nitrogen isotopic ratios of aerosol nitrate were similar across the three sites, with greater day-to-day variability than site to site variability. Air mass history was the main driver of the variability in the nitrogen isotopic ratios of aerosol nitrate, with significantly higher isotopic ratios observed for air masses originating from the southwest. Using an isotope mixing model we determined that NOx from coal-burning is the dominant contributor to aerosol nitrate (66%), followed by biomass burning (16%), vehicles (12%), and soil emissions (6%).

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Author Biography

Katye E. Altieri, Department of Oceanography, University of Cape Town

Senior Researcher, Energy Research Centre

Group Leader, Energy Environment & Climate Change

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Published

2022-06-24

How to Cite

Altieri, K. E., Burger, J., Language, B., & Piketh, S. J. (2022). A case study in the wintertime Vaal Triangle Air-Shed Priority Area on the utility of the nitrogen stable isotopic composition of aerosol nitrate to identify NOx sources. Clean Air Journal, 32(1). https://doi.org/10.17159/caj/2022/32/1.12505

Issue

Section

Special Issue: Air Quality on the South African Highveld