252
R. Ferrara et al.
placed in such a position that the plume can be scanned at an angle of about 90°
to the wind direction. The flux is calculated from a vertical LIDAR scan by first
integrating the measured concentrations over the area of the vertical plane
mapped out by the scan. This integrated value is then multiplied by the wind
speed perpendicular to the plane at the height of the plume's center of gravity.
Flux measurements can be determined with a maximum accuracy of ± 20%.
4
Results and Discussion
On July 16 and 21, 1995 (T air = 30-36 0c), from 1l:00 to 18:00 h, the LIDAR
system was used to determine air mercury concentrations over the mine
complex. The measurements were made from different positions to catch the
plume at a more favorable angle with respect to the wind direction so as to obtain
the most reliable mercury flux value possible. A mean value of 66 glh was
obtained.
Since part of the flux could not be measured due to the presence of obstacles in
the zone scanned by the laser, it was estimated that the total mercury flux given
off by the abandoned mine structures was approximately 100 g/h. This high value
is comparable to the value measured for emissions from five geothermal power
plants (120 g/h) located 4 km from Abbadia San Salvatore (Ferrara et al. 1994),
and is much higher than the flux from all the roasted cinnabar spoil banks (a few
grams per hour) present on Mt. Amiata (Ferrara et aI., 1998).
Figure 2 shows an example of a horizontal section of the distribution of the air
mercury concentration determined with the LIDAR system over the mine
complex (07.16.95; time 17:30 h). Along the given measurement directions, mean
mercury concentrations were evaluated as presented in the circles for the
integration intervals marked along the lines. The length of the integration
intervals was selected depending on the concentration level of mercury. In
September 1990, Edner et aI. (1993), using the same technique over the same mine
complex (T air = 14°C), measured mercury levels ranging from 10 to 340 ngl
m 3 •
Attempts to measure the flux over the Abbadia mine structure with the LIDAR
technique in September 1994 (from the 19th to the 27th; T air = 10-30 °C) failed
due to lack of wind. Analogous determinations performed over the smaller mine
complex at Bagnore, also located in the Amiata district, showed emissions were
20 times higher in July than in September (Ferrara et aI., 1998). In line with this
finding, the mercury emission in the month of September from the Abbadia S.
Salvatore mining installation should be approximately 5 g/h. Even lower values
can be expected in the winter months, when temperatures average about 5 0c. In
fact, mercury emissions such as those from mine structures and roasted cinnabar
spoil banks are closely dependent on ambient temperature (Ferrara et al. 1997).
Although the LIDAR technique has shown itself to be particularly well suited
for determining mercury fluxes, it usually cannot be used, due to the presence of
R. Ferrara et al.
placed in such a position that the plume can be scanned at an angle of about 90°
to the wind direction. The flux is calculated from a vertical LIDAR scan by first
integrating the measured concentrations over the area of the vertical plane
mapped out by the scan. This integrated value is then multiplied by the wind
speed perpendicular to the plane at the height of the plume's center of gravity.
Flux measurements can be determined with a maximum accuracy of ± 20%.
4
Results and Discussion
On July 16 and 21, 1995 (T air = 30-36 0c), from 1l:00 to 18:00 h, the LIDAR
system was used to determine air mercury concentrations over the mine
complex. The measurements were made from different positions to catch the
plume at a more favorable angle with respect to the wind direction so as to obtain
the most reliable mercury flux value possible. A mean value of 66 glh was
obtained.
Since part of the flux could not be measured due to the presence of obstacles in
the zone scanned by the laser, it was estimated that the total mercury flux given
off by the abandoned mine structures was approximately 100 g/h. This high value
is comparable to the value measured for emissions from five geothermal power
plants (120 g/h) located 4 km from Abbadia San Salvatore (Ferrara et al. 1994),
and is much higher than the flux from all the roasted cinnabar spoil banks (a few
grams per hour) present on Mt. Amiata (Ferrara et aI., 1998).
Figure 2 shows an example of a horizontal section of the distribution of the air
mercury concentration determined with the LIDAR system over the mine
complex (07.16.95; time 17:30 h). Along the given measurement directions, mean
mercury concentrations were evaluated as presented in the circles for the
integration intervals marked along the lines. The length of the integration
intervals was selected depending on the concentration level of mercury. In
September 1990, Edner et aI. (1993), using the same technique over the same mine
complex (T air = 14°C), measured mercury levels ranging from 10 to 340 ngl
m 3 •
Attempts to measure the flux over the Abbadia mine structure with the LIDAR
technique in September 1994 (from the 19th to the 27th; T air = 10-30 °C) failed
due to lack of wind. Analogous determinations performed over the smaller mine
complex at Bagnore, also located in the Amiata district, showed emissions were
20 times higher in July than in September (Ferrara et aI., 1998). In line with this
finding, the mercury emission in the month of September from the Abbadia S.
Salvatore mining installation should be approximately 5 g/h. Even lower values
can be expected in the winter months, when temperatures average about 5 0c. In
fact, mercury emissions such as those from mine structures and roasted cinnabar
spoil banks are closely dependent on ambient temperature (Ferrara et al. 1997).
Although the LIDAR technique has shown itself to be particularly well suited
for determining mercury fluxes, it usually cannot be used, due to the presence of