The Influence of Meteorology and Air Transport on CO2 Atmospheric Distribution over South Africa

This paper demonstrates the role of meteorology and air transport in influencing the South African atmospheric CO2 distribution. CO2 data from December 2004 to December 2009 acquired by the Tropospheric Emission Spectrometer (TES) instrument onboard the Aura satellite were used to establish the CO2 vertical distribution at selected regions in South Africa. The Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) atmospheric model backward trajectories were used to determine the long-range air transport impacting on South African CO2 atmospheric distribution and to detect the source areas of air masses impacting on South Africa’s atmosphere. The study found that long-range air transport can result in the accumulation or dilution of atmospheric CO2 at various sites in South Africa, depending on the source region and type of air flow. The long-range air transport from different source regions at the upper air level between the 700 and 500 hPa stable layers and the layer above 500 hPa strengthens the inhomogeneity in the vertical distribution of CO2, which is caused by the decoupling effect of the upper air stable layers. This long-range air transport also involves intercontinental air transport.

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Chemical composition, main sources and temporal variability of PM<sub>1</sub> aerosols in southern African grassland

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-15517-2013 ◽

2013 ◽

Vol 13 (6) ◽

pp. 15517-15566 ◽

Cited By ~ 2

Author(s):

P. Tiitta ◽

V. Vakkari ◽

M. Josipovic ◽

P. Croteau ◽

J. P. Beukes ◽

...

Keyword(s):

South Africa ◽

Chemical Composition ◽

Source Region ◽

Organic Aerosols ◽

Organic Aerosol ◽

Dry Season ◽

Wet Season ◽

Air Mass ◽

Air Masses ◽

Source Regions

Abstract. 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 emissions, 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 utilized 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 characterize 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 and peaked when air mass passed over the highly populated and industrialized region (iHV). The significance of aerosol acidity on the evolution of OOA was also discussed.

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Chemical composition, main sources and temporal variability of PM<sub>1</sub> aerosols in southern African grassland

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-1909-2014 ◽

2014 ◽

Vol 14 (4) ◽

pp. 1909-1927 ◽

Cited By ~ 58

Author(s):

P. Tiitta ◽

V. Vakkari ◽

P. Croteau ◽

J. P. Beukes ◽

P. G. van Zyl ◽

...

Keyword(s):

South Africa ◽

Chemical Composition ◽

Source Region ◽

Organic Aerosols ◽

Organic Aerosol ◽

Dry Season ◽

Wet Season ◽

Air Masses ◽

Source Regions ◽

Combustion Sources

Abstract. 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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Ambient aromatic hydrocarbon measurements at Welgegund, South Africa

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-4189-2014 ◽

2014 ◽

Vol 14 (4) ◽

pp. 4189-4227

Author(s):

K. Jaars ◽

J. P. Beukes ◽

P. G. van Zyl ◽

A. D. Venter ◽

M. Josipovic ◽

...

Keyword(s):

South Africa ◽

Aromatic Hydrocarbon ◽

Human Health ◽

Aromatic Hydrocarbons ◽

Night Time ◽

Air Mass ◽

Air Masses ◽

Igneous Complex ◽

Source Regions ◽

Bushveld Igneous Complex

Abstract. Aromatic hydrocarbons are associated with direct adverse human health effects and can have negative impacts on ecosystems due to their toxicity, as well as indirect negative effects through the formation of tropospheric ozone and secondary organic aerosol that affect human health, crop production and regional climate. Measurements were conducted at the Welgegund measurement station (South Africa) that is considered to be a regionally representative background site. However, the site is occasionally impacted by plumes from major anthropogenic source regions in the interior of South Africa, which include the western Bushveld Igneous Complex (e.g. platinum, base metal and ferrochrome smelters), the eastern Bushveld Igneous Complex (platinum and ferrochrome smelters), the Johannesburg–Pretoria metropolitan conurbation (>10 million people), the Vaal Triangle (e.g. petrochemical and pyrometallurgical industries), the Mpumalanga Highveld (e.g. coal-fired power plants and petrochemical industry) and also a region of anti-cyclonic recirculation of air mass over the interior of South Africa. The aromatic hydrocarbon measurements were conducted with an automated sampler on Tenax-TA and Carbopack-B adsorbent tubes with heated inlet for one year. Samples were collected twice a week for two hours during daytime and two hours during night-time. A thermal desorption unit, connected to a gas chromatograph and a mass selective detector was used for sample preparation and analysis. Results indicated that the monthly median total aromatic hydrocarbon concentrations ranged between 0.01 to 3.1 ppb. Benzene levels did not exceed local air quality standards. Toluene was the most abundant species, with an annual median concentration of 0.63 ppb. No statistically significant differences in the concentrations measured during daytime and night-time were found and no distinct seasonal patterns were observed. Air mass back trajectory analysis proved that the lack of seasonal cycles could be attributed to patterns determining the origin of the air masses sampled. Aromatic hydrocarbon concentrations were in general significantly higher in air masses that passed over anthropocentrically impacted regions. Interspecies correlations and ratios gave some indications of the possible sources for the different aromatic hydrocarbons in the source regions defined in the paper. The highest contribution of aromatic hydrocarbon concentrations to ozone formation potential was also observed in plumes passing over anthropocentrically impacted regions.

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Identifying source regions of air masses sampled at the tropical high-altitude site of Chacaltaya using WRF-FLEXPART and cluster analysis

10.5194/acp-2021-126 ◽

2021 ◽

Author(s):

Diego Aliaga ◽

Victoria A. Sinclair ◽

Marcos Andrade ◽

Paulo Artaxo ◽

Samara Carbone ◽

...

Keyword(s):

Boundary Layer ◽

High Altitude ◽

Long Range ◽

Diurnal Cycle ◽

Observation Time ◽

Particle Nucleation ◽

Free Troposphere ◽

Air Mass ◽

Air Masses ◽

Source Regions

Abstract. Observations of aerosol and trace gases in the remote troposphere are vital to quantify background concentrations and identify long term trends in atmospheric composition on large spatial scales. Measurements made at high altitude are often used to study free tropospheric air however such high-altitude sites can be influenced by boundary layer air masses. Thus, accurate information on air mass origin and transport pathways to high altitude sites is required. Here we present a new method, based on the source-receptor relationship (SRR) obtained from backwards WRF-FLEXPART simulations and a k-means clustering approach, to identify source regions of air masses arriving at measurement sites. Our method is tailored to areas of complex terrain and to stations influenced by both local and long-range sources. We have applied this method to the Chacaltaya (CHC) GAW station (5240 m a.s.l.,16.35° S, 68.13° W) for the 6-month duration of the “Southern hemisphere high altitude experiment on particle nucleation and growth” (SALTENA) to identify where sampled air masses originate and to quantify the influence of the boundary layer and the free troposphere. A key aspect of our method is that it is probabilistic and for each observation time, more than one air mass (cluster) can influence the station and the percentage influence of each air mass can be quantified. This is in contrast to binary methods, which label each observation time as influenced either by boundary layer or free troposphere air masses. We find that on average, 9% of the air sampled at CHC, at any given observation time, has been in contact with the surface within 4 days prior to arriving at CHC, 24% of the air was located below 1.5 km above ground level and consequently, 76% of the measured air masses at CHC represent free tropospheric air. However, pure free-tropospheric influences are rare and often samples are concurrently influenced by both boundary-layer and free-tropospheric air masses. A clear diurnal cycle is present with very few air masses that have been in contact with the surface being detected at night. The 6-month analysis also shows that the most dominant air mass (cluster) originates in the Amazon and is responsible for 29% of the sampled air. Furthermore, short-range clusters (origins within 100 km of CHC) have high temporal frequency modulated by local meteorology driven by the diurnal cycle whereas the mid- and long-range clusters’ (>200 km) variability occurs on timescales governed by synoptic-scale dynamics. To verify the reliability of our method, in-situ sulfate observations from CHC are combined with the SRR clusters to correctly identify the (pre-known) source of the sulfate: the Sabancaya volcano located 400 km northwest from the station.

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Atmospheric mercury in the Southern Hemisphere – Part 2: Source apportionment analysis at Cape Point station, South Africa

10.5194/acp-2020-63 ◽

2020 ◽

Cited By ~ 2

Author(s):

Johannes Bieser ◽

Hélène Angot ◽

Franz Slemr ◽

Lynwill Martin

Keyword(s):

South Africa ◽

Southern Hemisphere ◽

Source Region ◽

Global Scale ◽

Atmospheric Mercury ◽

Air Masses ◽

Sources And Sinks ◽

Relative Contribution ◽

Range Transport ◽

Significant Step

Abstract. Mercury (Hg) contamination is ubiquitous. In order to assess its emissions, transport, atmospheric reactivity, and deposition pathways, Hg monitoring stations have been implemented on a global scale over the past 10–20 years. Despite this significant step forward, the monitoring efforts have been insufficient to fulfill our understanding of Hg cycling in the Southern Hemisphere. While oceans make up 80 % of the Southern Hemisphere's surface area, little is known about the effects of oceans on Hg cycling in this region. For instance, in the context of growing interest in effectiveness evaluation of Hg mitigation policies, the relative contribution of anthropogenic and legacy emissions to present-day atmospheric Hg levels is unclear. This paper constitutes Part 2 of the study describing a decade of atmospheric Hg concentrations at Cape Point, South Africa, i.e. the first long-term (> 10 years) observations in the Southern Hemisphere. Building on the trend analysis reported in Part 1, here we combine atmospheric Hg data with a trajectory model to investigate sources and sinks of Hg at Cape Point. We find that the continent is the major sink and the Ocean, especially warm regions, is the major source for Hg. Further, we find that mercury concentrations and trends from long range transport are independent of the source region (e.g. South America, Antarctica) and thus indistinguishable. Therefor, by filtering out air masses from source and sink regions we are able to create a dataset representing a southern hemispheric background Hg concentrations. Based on this dataset we were able to show that the inter-annual variability of Hg concentrations is not driven by changes in atmospheric circulation but rather due to changes in global emissions (gold mining and biomass burning).

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Southern African Air Transport After Apartheid

The Journal of Modern African Studies ◽

10.1017/s0022278x00010752 ◽

1992 ◽

Vol 30 (2) ◽

pp. 341-348 ◽

Cited By ~ 11

Author(s):

Gordon H. Pirie

Keyword(s):

United States ◽

South Africa ◽

South African ◽

United States Of America ◽

The United States ◽

Air Transport ◽

African Countries ◽

Similar Action ◽

Black African ◽

The 1960S

Aviation in Southern Africa was subject throughout the 1980s to increasingly intense political pressures. As ever, the cause was protests about apartheid. The severe blow that black African countries dealt to South African Airways (S.A.A.), the Republic's state-owned national airline, in the 1960s by withdrawing overflying rights was magnified by similar action from a wider spectrum of non-African governments. In the mid-1980s, Australia and the United States of America, for example, revoked S.A.A.'s landing rights, and forbad airlines registered in their countries from flying to South Africa. Other carriers, such as Air Canada, closed their offices and then terminated representation in South Africa.

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Ambient aromatic hydrocarbon measurements at Welgegund, South Africa

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-7075-2014 ◽

2014 ◽

Vol 14 (13) ◽

pp. 7075-7089 ◽

Cited By ~ 36

Author(s):

K. Jaars ◽

J. P. Beukes ◽

P. G. van Zyl ◽

A. D. Venter ◽

M. Josipovic ◽

...

Keyword(s):

South Africa ◽

Aromatic Hydrocarbon ◽

Human Health ◽

Aromatic Hydrocarbons ◽

Night Time ◽

Air Mass ◽

Air Masses ◽

Igneous Complex ◽

Source Regions ◽

Bushveld Igneous Complex

Abstract. Aromatic hydrocarbons are associated with direct adverse human health effects and can have negative impacts on ecosystems due to their toxicity, as well as indirect negative effects through the formation of tropospheric ozone and secondary organic aerosol, which affect human health, crop production and regional climate. Measurements of aromatic hydrocarbons were conducted at the Welgegund measurement station (South Africa), which is considered to be a regionally representative background site. However, the site is occasionally impacted by plumes from major anthropogenic source regions in the interior of South Africa, which include the western Bushveld Igneous Complex (e.g. platinum, base metal and ferrochrome smelters), the eastern Bushveld Igneous Complex (platinum and ferrochrome smelters), the Johannesburg–Pretoria metropolitan conurbation (> 10 million people), the Vaal Triangle (e.g. petrochemical and pyrometallurgical industries), the Mpumalanga Highveld (e.g. coal-fired power plants and petrochemical industry) and also a region of anticyclonic recirculation of air mass over the interior of South Africa. The aromatic hydrocarbon measurements were conducted with an automated sampler on Tenax-TA and Carbopack-B adsorbent tubes with heated inlet for 1 year. Samples were collected twice a week for 2 h during daytime and 2 h during night-time. A thermal desorption unit, connected to a gas chromatograph and a mass selective detector was used for sample preparation and analysis. Results indicated that the monthly median (mean) total aromatic hydrocarbon concentrations ranged between 0.01 (0.011) and 3.1 (3.2) ppb. Benzene levels did not exceed the local air quality standard limit, i.e. annual mean of 1.6 ppb. Toluene was the most abundant compound, with an annual median (mean) concentration of 0.63 (0.89) ppb. No statistically significant differences in the concentrations measured during daytime and night-time were found, and no distinct seasonal patterns were observed. Air mass back trajectory analysis indicated that the lack of seasonal cycles could be attributed to patterns determining the origin of the air masses sampled. Aromatic hydrocarbon concentrations were in general significantly higher in air masses that passed over anthropogenically impacted regions. Inter-compound correlations and ratios gave some indications of the possible sources of the different aromatic hydrocarbons in the source regions defined in the paper. The highest contribution of aromatic hydrocarbon concentrations to ozone formation potential was also observed in plumes passing over anthropogenically impacted regions.

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Effect of regional precursor emission controls on long-range ozone transport – Part 1: short-term changes in ozone air quality

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-7033-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 7033-7077

Author(s):

J. J. West ◽

V. Naik ◽

L. W. Horowitz ◽

A. M. Fiore

Keyword(s):

Air Quality ◽

Long Range ◽

Surface Ozone ◽

Source Region ◽

Lower Troposphere ◽

Ozone Production ◽

Nox Emissions ◽

Short Term ◽

Source Regions ◽

Ozone Transport

Abstract. Observations and models demonstrate that ozone and its precursors can be transported between continents and across oceans. We model the influences of 10% reductions in anthropogenic nitrogen oxide (NOx) emissions from each of nine world regions on surface ozone air quality in that region and all other regions. In doing so, we quantify the relative importance of long-range transport between all source-receptor pairs, for direct short-term ozone changes. We find that for population-weighted concentrations during the three-month "ozone-season", the strongest inter-regional influences are from Europe to the Former Soviet Union, East Asia to Southeast Asia, and Europe to Africa. The largest influences per unit of NOx reduced, however, are seen for source regions in the tropics and Southern Hemisphere, which we attribute mainly to greater sensitivity to changes in NOx in the lower troposphere, and secondarily to increased vertical convection to the free troposphere in tropical regions, allowing pollutants to be transported further. Results show, for example, that NOx reductions in North America are ~20% as effective per unit NOx in reducing ozone in Europe during summer, as NOx reductions from Europe itself. Reducing anthropogenic emissions of non-methane volatile organic compounds (NMVOCs) and carbon monoxide (CO) by 10% in selected regions, can have as large an impact on long-range ozone transport as NOx reductions, depending on the source region. We find that for many source-receptor pairs, the season of greatest long-range influence does not coincide with the season when ozone is highest in the receptor region. Reducing NOx emissions in most source regions causes a larger decrease in export of ozone from the source region than in ozone production outside of the source region.

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Quantifying the contribution of long-range transport to Particulate Matter (PM) mass loadings at a suburban site in the North-Western Indo Gangetic Plain (IGP)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-11409-2015 ◽

2015 ◽

Vol 15 (8) ◽

pp. 11409-11464 ◽

Cited By ~ 2

Author(s):

H. Pawar ◽

S. Garg ◽

V. Kumar ◽

H. Sachan ◽

R. Arya ◽

...

Keyword(s):

Air Quality ◽

Long Range ◽

Source Region ◽

Ambient Air ◽

Quality Standard ◽

Long Range Transport ◽

Ambient Air Quality ◽

Air Masses ◽

Range Transport ◽

Ambient Air Quality Standard

Abstract. Many sites in the densely populated Indo Gangetic Plain (IGP) frequently exceed the national ambient air quality standard (NAAQS) of 100 μg m−3 for 24 h average PM10 and 60 μg m−3 for 24 h average PM2.5 mass loadings, exposing residents to hazardous levels of PM throughout the year. We quantify the contribution of long range transport to elevated PM levels and the number of exceedance events through a back trajectory climatology analysis of air masses arriving at the IISER Mohali Atmospheric Chemistry facility (30.667° N, 76.729° E; 310 m a.m.s.l.) for the period August 2011–June 2013. Air masses arriving at the receptor site were classified into 6 clusters, which represent synoptic scale air mass transport patterns and the average PM mass loadings and number of exceedance events associated with each air mass type were quantified for each season. Long range transport from the west leads to significant enhancements in the average coarse mode PM mass loadings during all seasons. The contribution of long range transport from the west and south west (Source region: Arabia, Thar desert, Middle East and Afghanistan) to coarse mode PM varied between 9 and 57% of the total PM10−2.5 mass. Local pollution episodes (wind speed < 1 m s−1) contributed to enhanced coarse mode PM only during winter season. South easterly air masses (Source region: Eastern IGP) were associated with significantly lower coarse mode PM mass loadings during all seasons. For fine mode PM too, transport from the west usually leads to increased mass loadings during all seasons. Local pollution episodes contributed to enhanced PM2.5 mass loadings during winter and summer season. South easterly air masses were associated with significantly lower PM2.5 mass loadings during all seasons. Using simultaneously measured gas phase tracers we demonstrate that most PM2.5 originated from combustion sources. The fraction of days in each season during which the PM mass loadings exceeded the national ambient air quality standard was controlled by long range transport to a much lesser degree. For the local cluster, which represents regional air masses (Source region: NW-IGP), the fraction of days during which the national ambient air quality standard (NAAQS) of 60 μg m−3 for 24 h average PM2.5 was exceeded, varied between 22% of the days associated with this synoptic scale transport during monsoon season and 85% of the days associated with this synoptic scale transport during winter season; the fraction of days during which the national ambient air quality standard (NAAQS) of 100 μg m−3 for the 24 h average PM10 was exceeded, varied between 37% during monsoon season and 84% during winter season. Long range transport was responsible for both, bringing air masses with a significantly lower fraction of exceedance days from the Eastern IGP and air masses with a moderate increase in the fraction of exceedance days from the West (Source region: Arabia, Thar desert, Middle East and Afghanistan). In order to bring PM mass loadings in compliance with the national ambient air quality standard (NAAQS) and reduce the number of exceedance days, mitigation of regional pollution sources in the NW-IGP needs to be given highest priority.

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