Environmental Engineering Reference
In-Depth Information
c
wn
: mean aerosol concentration of all five sites of week
n
, c
wo
: mean aerosol
concentration of all five sites of week
o
, which is the week following week
n
.
Especially the winter 2006/2007 showed very high concentrations with maxima
values of up to 300 mg/m
3
. However, reasons causing such high concentrations are
complex, and will comprise temperatures, wind speed, wind directions and general
meteorological regional conditions. Those concentrations are higher than the con-
centrations during the previous winter and they are even higher as the concentrations
occurred during the dust storm seasons in spring. Thus, further investigations are
necessary to eluidate the various variations of PM
2.5
mass concentrations along the
year. Generally, the average PM
2.5
mass concentrations observed in Beijing exceed
those investigated in various cities of Europe
[17]
or in New York
[18]
but are still
in the range of PM
2.5
concentrations measured in Beijing in the years 1999 to 2003
[19-21]
. Thus, although many measures to reduce the aerosol concentration took
place during the last years, PM
2.5
mass concentration could not be reduced to
concentrations similar to that found in cities of Europe and the US. Most probably,
the economic development with all its consequences of enormous construction
activities or growing number of vehicles counteracts aerosol reducing measures.
The Meaning of Selected Metal Loads
for Aerosol Origin and Pollution
Concentrations of indicator elements within the aerosol can help to understand the
reasons for those variations in more detail. Indicator elements are chemical elements,
which mainly are associated to specific sources or source groups, such as anthro-
pogenic and geogenic sources. Such indicator elements are for example Pb and Ti.
Lead mainly indicates anthropogenic sources, such as combustion of petroleum
based fuel, where Pb is naturally abundant, and industrial metal processing activities.
Nevertheless, Pb also can occur in geogenic particles, but in most cases to a lesser
degree, compared to anthropogenic particles. Titanium indicates mainly geogenic
sources, although also used in some colors. Since humans nowadays almost use any
chemical element for some technical material, elements purely indicating geogenic
sources are hardly to be found
[22, 23]
.
However, in Beijing, Pb can be used as a good indicator for anthropogenic and
Ti for geogenic sources as shown in Fig.
3
. The ratio of Pb/Ti indicates periods
dominated by anthropogenic or geogenic sources of particles. A high TSP mass
concentration during autumn 2005 only shows a relative low ratio of Pb/Ti, indicat-
ing a predominance of geogenic particles whereas during winter 2005/2006 a high
ratio indicates the peak of the heating time. Again, in spring 2006, during the period
of dust storms, the ratio drops to its minimum within the period of observation
because of the predominating geogenic origin of the particles. For the rest of 2006,
Pb/Ti is more or less constantly increasing, indicating predominant anthropogenic
emissions as the cause for increasing TSP mass concentrations.
