References

ACP

Atmospheric Chemistry and Physics

ACP

Atmos. Chem. Phys.

1680-7324

Copernicus Publications

Göttingen, Germany

10.5194/acp-14-1909-2014

Chemical composition, main sources and temporal variability of PM1 aerosols in southern African grassland

Tiitta

https://orcid.org/0000-0003-4694-3648

² ⁶ ¹ Vakkari

³ ⁵ Croteau

⁴ Beukes

J. P.

² van Zyl

P. G.

² Josipovic

² Venter

A. D.

² Jaars

² Pienaar

J. J.

² Ng

N. L.

https://orcid.org/0000-0001-8460-4765

⁷ Canagaratna

M. R.

⁴ Jayne

J. T.

⁴ Kerminen

V.-M.

https://orcid.org/0000-0002-0706-669X

³ Kokkola

⁵ Kulmala

³ Laaksonen

⁵ ⁶ Worsnop

D. R.

³ ⁴ ⁶ Laakso

² ⁵

Department of Environmental Science, Univ. of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland

School of Physical and Chemical Sciences, North-West University, Potchefstroom 2520, South Africa

Department of Physics, Univ. of Helsinki, P.O. Box 64, 00014 Helsinki, Finland

Aerodyne Research, Inc., Billerica, MA 08121, USA

Finnish Meteorological Institute, Erik Palménin aukio 1, 00101 Helsinki, Finland

Department of Applied Physics, Univ. of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland

School of Chemical and Biomolecular Engineering and School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332-0100, USA

18 02 2014

14 4 1909 1927

2014

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

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The full text article is available as a PDF file from https://acp.copernicus.org/articles/14/1909/2014/acp-14-1909-2014.pdf

Southern Africa is a significant source region of atmospheric pollution, yet long-term data on pollutant concentrations and properties from this region are rather limited. A recently established atmospheric measurement station in South Africa, Welgegund, is strategically situated to capture regional background concentrations, as well as emissions from the major source regions in the interior of South Africa. We measured non-refractive submicron aerosols (NR-PM1) and black carbon over a one year period in Welgegund, and investigated the seasonal and diurnal patterns of aerosol concentration levels, chemical composition, acidity and oxidation level. Based on air mass back trajectories, four distinct source regions were determined for NR-PM1. Supporting data utilised in our analysis included particle number size distributions, aerosol absorption, trace gas concentrations, meteorological variables and the flux of carbon dioxide. The dominant submicron aerosol constituent during the dry season was organic aerosol, reflecting high contribution from savannah fires and other combustion sources. Organic aerosol concentrations were lower during the wet season, presumably due to wet deposition as well as reduced emissions from combustion sources. Sulfate concentrations were usually high and exceeded organic aerosol concentrations when air-masses were transported over regions containing major point sources. Sulfate and nitrate concentrations peaked when air masses passed over the industrial Highveld (iHV) area. In contrast, concentrations were much lower when air masses passed over the cleaner background (BG) areas. Air masses associated with the anti-cyclonic recirculation (ACBIC) source region contained largely aged OA. Positive Matrix Factorization (PMF) analysis of aerosol mass spectra was used to characterise the organic aerosol (OA) properties. The factors identified were oxidized organic aerosols (OOA) and biomass burning organic aerosols (BBOA) in the dry season and low-volatile (LV-OOA) and semi-volatile (SV-OOA) organic aerosols in the wet season. The results highlight the importance of primary BBOA in the dry season, which represented 33% of the total OA. Aerosol acidity and its potential impact on the evolution of OOA are also discussed.

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