Ambient aromatic hydrocarbon measurements at Welgegund, South Africa
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Date
2014Author
Jaars, K.
Beukes, J.P.
Van Zyl, P.G.
Venter, A.D.
Josipovic, M.
Pienaar, J.J.
Tiitta, P.
Laakso, L.
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Show full item recordAbstract
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
URI
http://hdl.handle.net/10394/15865https://doi.org/10.5194/acp-14-7075-2014
https://www.atmos-chem-phys.net/14/7075/2014/