Ambient aromatic hydrocarbon measurements at Welgegund, South Africa

Jaars, Kerneels; Beukes, J. P.; Zyl, P. G. van; Venter, Andrew D.; Josipovic, Miroslav; Pienaar, Jacobus J.; Vakkari, Ville; Aaltonen, Hermanni; Laakso, H.; Kulmala, Markku; Tiitta, Petri; Guenther, Alex; Hellén, Heidi; Laakso, Lauri; Hakola, Hannele

doi:10.5194/acp-14-7075-2014

Cited by 50 publications

(49 citation statements)

References 67 publications

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“…At the measurement site there are continuous measurements of atmospheric aerosols, trace gases and meteorology (Booyens et al, 2015;Jaars et al, 2014;Laakso et al, 2013;Vakkari et al, 2014Vakkari et al, , 2015. In this paper, we present the data directly relevant to carbon cycle dynamics from September 2010 to August 2013.…”

Section: Instrumentationmentioning

confidence: 99%

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Räsänen¹,

Aurela²,

Vakkari³

et al. 2017

Biogeosciences

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Abstract. Tropical savannas and grasslands are estimated to contribute significantly to the total primary production of all terrestrial vegetation. Large parts of African savannas and grasslands are used for agriculture and cattle grazing, but the carbon flux data available from these areas are limited. This study explores carbon dioxide fluxes measured with the eddy covariance method for 3 years at a grazed savanna grassland in Welgegund, South Africa. The tree cover around the measurement site, grazed by cattle and sheep, was around 15 %. The night-time respiration was not significantly dependent on either soil moisture or soil temperature on a weekly temporal scale, whereas on an annual timescale higher respiration rates were observed when soil temperatures were higher. The carbon dioxide balances of the years 2010-2011, 2011-2012 and 2012-2013 were −85 ± 16, 67 ± 20 and 139 ± 13 gC m −2 yr −1 , respectively. The yearly variation was largely determined by the changes in the early wet season fluxes (September to November) and in the mid-growing season fluxes (December to January). Early rainfall enhanced the respiratory capacity of the ecosystem throughout the year, whereas during the mid-growing season high rainfall resulted in high carbon uptake.

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Section: Instrumentationmentioning

confidence: 99%

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Räsänen¹,

Aurela²,

Vakkari³

et al. 2017

Biogeosciences

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“…Laakso et al, 2008Laakso et al, , 2012Vakkari et al, 2011Vakkari et al, , 2013Venter et al, 2012;Jaars et al, 2014;Beukes et al, 2013). So far, regional modeling studies for southern Africa have mainly focused on the meteorology (e.g.…”

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confidence: 99%

The anthropogenic contribution to atmospheric black carbon concentrations in southern Africa: a WRF-Chem modeling study

et al. 2015

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Abstract. South Africa has one of the largest industrialized economies in Africa. Emissions of air pollutants are particularly high in the Johannesburg-Pretoria metropolitan area, the Mpumalanga Highveld and the Vaal Triangle, resulting in local air pollution. This study presents and evaluates a setup for conducting modeling experiments over southern Africa with the Weather Research and Forecasting model including chemistry and aerosols (WRF-Chem), and analyzes the contribution of anthropogenic emissions to the total black carbon (BC) concentrations from September to December 2010.The modeled BC concentrations are compared with measurements obtained at the Welgegund station situated ca. 100 km southwest of Johannesburg. An evaluation of WRF-Chem with observational data from ground-based measurement stations, radiosondes, and satellites shows that the meteorology is modeled mostly reasonably well, but precipitation amounts are widely overestimated and the onset of the wet season is modeled approximately 1 month too early in 2010. Modeled daily mean BC concentrations show a temporal correlation of 0.66 with measurements, but the total BC concentration is underestimated in the model by up to 50 %.Sensitivity studies with anthropogenic emissions of BC and co-emitted species turned off show that anthropogenic sources can contribute up to 100 % to BC concentrations in the industrialized and urban areas, and anthropogenic BC and co-emitted species together can contribute up to 60 % to PM 1 levels. Particularly the co-emitted species contribute significantly to the aerosol optical depth (AOD). Furthermore, in areas of large-scale biomass-burning atmospheric heating rates are increased through absorption by BC up to an altitude of about 600 hPa.

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“…The mono-aromatic groups also include the commonly measured benzene compounds and alkyl-substituted benzenes. In a study conducted by Jaars et al (2014) on volatile aromatic hydrocarbons measured at Welgegund, significantly higher aromatic hydrocarbon concentrations were observed in air masses that passed over anthropocentrically impacted regions. PAHs were also identified, although the relative ∑NRFs of PAHs detected were very low compared to the ∑NRFs of the other hydrocarbon species measured in this study.…”

Section: Hydrocarbonsmentioning

confidence: 96%

Size-resolved characterisation of organic compounds in atmospheric aerosols collected at Welgegund, South Africa

et al. 2015

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The organic fraction of atmospheric aerosols is 20 to 90 % of which only a small percentage has been chemically characterised. Two-dimensional gas chromatography with a time-of-flight mass spectrometer (GCxGC-TOFMS) is a powerful instrument used to chemically characterise organic compounds. Size-resolved characterisation and semi-quantification of ambient organic aerosol compounds were performed with a GCxGC-TOFMS for the first time in South Africa. Twenty-four-hour samples were collected for 1 year for three different size ranges. A combined total of 1056 different organic compounds could be tentatively characterised. The largest number of organic compounds tentatively identified was PM 2.5-1 (particles in the size range 1-2.5 μm), while this size fraction also had the highest total number of normalised response factors (∑NRF). On average, 52, 26, 6, 13 and 3 % of species tentatively identified were oxygenated species, hydrocarbons, halogenated compounds, Ncontaining compounds and S-containing compounds, respectively. Oxygenated compounds were the most abundant species. Alkane and mono-aromatic species were the largest number of hydrocarbons tentatively identified with the highest ∑NRFs. The largest number of oxygenated species tentatively characterised were carboxylic acids and esters, while ether compounds had the highest ∑NRFs. Most of the halogenated compounds tentatively identified were chlorinated species with the highest ∑NRFs in two size fractions. Iodate species had a significantly higher ∑NRF in the PM 2.5-1 size fraction. The largest number of N-containing J Atmos Chem species tentatively characterised with the highest ∑NRFs were amines. A small number of Scontaining compounds with low ∑NRFs were tentatively identified. The major sources of organic compounds measured at Welgegund were considered to be biomass burning and air masses moving over the anthropogenically impacted source regions.

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Ambient aromatic hydrocarbon measurements at Welgegund, South Africa

Cited by 50 publications

References 67 publications

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Carbon balance of a grazed savanna grassland ecosystem in South Africa

The anthropogenic contribution to atmospheric black carbon concentrations in southern Africa: a WRF-Chem modeling study

Size-resolved characterisation of organic compounds in atmospheric aerosols collected at Welgegund, South Africa

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