Environmental Engineering Reference
In-Depth Information
special regards are spent to soot and sulphate containing particles
[2-6]
. However,
also metals are considered to contribute to the negative health impacts of particles
[7-13]
. Epidemiological studies often refer to the general mass concentrations of
particles because of the complexity of the specific toxicities of relevant substances
in atmospheric particles, which are for large parts still not known
[6, 14]
. Since the
total PM
2.5
mass concentration and the concentrations of metals in PM
2.5
are impor-
tant to assess the air quality of megacities, this study aims to investigate exemplarily
their spatial distributions over two years in Beijing.
Methods
Samples of PM
2.5
were taken at five stations established along a 50 km long transect
running through Beijing from North-West to South-East. The specific locations are
presented in
[15]
. PM
2.5
was taken during day and night time, from 7 a.m. to 7 p.m.
and 7 p.m. to 7 a.m., respectively. Each sampling interval lasted for 1 week. For
sampling, mini-volume samplers were used pumping 200 L air per hour. Samples
were collected on quartz fiber filters of 50 mm in diameter. Gravimetric analysis
was performed after at least 48 h equilibration with a microbalance (Sartorius MP2)
for five times.
Chemical Analyses
For the analysis of trace metals, one quarter of the filters were digested in Teflon
vessels with concentrated HNO
3
(Merck, subboiled), concentrated HF (Merck, p.a)
and concentrated HClO
4
(Merck, p.a). Determination of elements was performed
with HR-ICP-MS (Axiom). Quality control was performed by additional analysis
of reference material SRM 1648 (urban particulate matter) acquired from NIST
(National Institute of Standards, USA). Results of standard material are within
±10% of the certified values for element concentrations.
Results and Discussion
Average PM
2.5
mass concentrations at all five stations are presented for each meteo-
rological season in Fig.
1
. It is obvious that the lowest PM
2.5
mass concentration
occurred during summer time, although this concentration is still far above the
newly introduced PM
2.5
threshold value of 15 mg/m
3
in the US. Nevertheless, with
respect to the Olympic Games taking place in Beijing in August 2008, it is at least
good information. Up to more than 120 mg/m
3
PM
2.5
mass concentration was
observed during other seasons, especially during winter time.
