Environmental Engineering Reference
In-Depth Information
Fig. 7
Annual course for the ratio nitrate/sulphate from TSP samples at site 4 with additional
meteorological data
The ratio is lowest in summer time when most rain occurs in Beijing. In this time, as
mentioned above, the secondary formation of sulphate is high due to the high humidity
and strong solar radiation. The temperature plays an indirect role to that effect and
the long cold winters account for a long heating period in Beijing (usually from
mid-November to mid-March
[9]
).
Fluoride and chloride concentrations were very low in PM
2.5
samples and therefore
not detectable with IC (detections limits: 0.2 and 0.4 mg/L, respectively) in many
samples. In TSP samples, the mean annual concentrations were 0.8 ± 0.6 µg/m
3
for
fluoride and 3.3 ± 3.9 µg/m
3
for chloride.
The annual courses for selected cations in TSP samples are presented in Fig.
8
.
Calcium was the most abundant water-soluble cation with an annual mean concen-
tration of about 13.4 ± 5.0 µg/m?. Usually, Ca can be seen as a geogenic element.
In Beijing, however, Ca is also closely connected to construction activities. As a
consequence of the fast growing city and lots of building activities for the Olympic
Games in August 2008, there is a high density of construction sites in Beijing.
Ca-rich particles in Beijing aerosols have been related to dust from construction
sites
[10]
. Ca has also been used as an indicator element for construction dust in
Beijing
[9]
. In contrast to the coarse particles, PM
2.5
samples showed lower Ca
concentrations which partly could not be detected by IC. For fine particles, ammonium
was the most important cation.
The percentage of measured water-soluble cations with respect to total dust
concentrations of the according element varies between 35% and 72%. Total element
concentrations were measured with ICP-MS after total digestion of one quarter of
the filter.
Finally, the comparison between water-soluble anions and cations suggested a
strong correlation between ammonium and sulphate (r = 0.77, n = 53) whereas
