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Plume rise measurements at turbigo
Atmospheric Enuironmenr Vol. 16, No. 11, pp. 2565-2574, Printed in Great Britain.
lW4A98l/82/1l2565-10 0 1982 Pergamon
1982
PLUME RISE MEASUREMENTS
$03.00/O Press Ltd.
AT TURBIGO
D. ANFOSSI Instituto di Cosmo-Geofisica de1 CNR, Torino, Italy (First received 1 September 1981 and infinal form 29 December 1981) Abstract-The fourth C.E.C. campaign on remote sensing of air pollution, organized jointly by ENEL and the Commission of European Communities, was held at Turbigo (northern Italy) during September 1979. This paper presents analyses of plume measurements obtained during that campaign by the ENEL groundbased Lidar. The five stacks ofTurbigo Power Plant have different heights and emission parameters and their plumes usually combine, so a model for multiple sources developed by D. Anfossi et al. (1978, Atmospheric Enoironment 12, 1821-1826) was used to predict the plume rises. These predictions are compared with the observations. Measurements of uv and ur over the first 1000 m are compared with the curves derived from other observations in the PO Valley, using the no-lift balloon technique over the same range of downwind distance. Skewness and kurtosis distributions are shown, both along the vertical and the horizontal directions. In order to show the plume structure in more detail, we present two examples of Lidar-derived cross sections and the corresponding vertically and horizontally integrated concentration profiles.
NOMENCLATURE F
JC Hi
Hj 4nimH, A Hmin
d 9 s Ii
!i 0
P.
=P
L T.3 si,J (T
z)
VJ Pi,J
CERL ENEL ICGF IPS JRC UCL CNR CSI
1. INTRODUCTION
buoyancy parameter (m*s-‘) effective height of merged plume produced by N stacks (m) merging point height (m) stack heights (m) heights of lowest, highest stacks (m) maximum single plume rise from lowest stack H&m) exponent in Equation (2) variable containing all the parameters not directly related to buoyancy flux at source spacing between stacks (m) acceleration of gravity (m s-z) stability parameters (s-z) wind speed (ms-‘) entrainment constant sensible heat flux at ground level (calcn-2h-i) air density (gm-‘) specific heat at constant pressure (cal g- 1K- ‘) mixing height (m) ambient temperature (K) signal defined in Equation (1) range corrected center of gravity of Si,J signals (m) elevation angle of Jth Lidar shot distance, along the Jth shot, at which Si,J is measured (m) Central Electricty Research Laboratory, Leatherhead (UK) Italian Electricity Authority National Research Councfi, Istituto CosmoGeofisica. Torino (I) National. Research ‘Council, Istituto Plasma Spazio, Frascati (I) Joint Research Centre, Ispra (I) Universitt! Catholique de Louvain, Louvain-laNeuve (B) National Research Council (I) Consorzio per il Sistema Informatico, Torino (I).
During September 1979, the Commission of the European Communities (C.E.C.) and ENEL jointly organized an exercise on the remote sensing of air pollution around the Turbigo Power Plant. Detailed information on the Campaign, which was the fourth organized by C.E.C., its objectives and general results can be found in the Report of the Campaign Coordinators (Longhetto et al., 1981). Some reports (Anfossi et al., 1980; Cerutti et al., 1979; Laurent, 1979; Sandroni and De Groot, 1980; Van der Meulen and Bertels, 1980) have also been produced concerning the analyses of results obtained by various teams involved in the campaign. So only a few facts especially related to the present paper, need to be recalled here. The Turbigo Power Plant is located in the PO Valley (northern Italy) c. 35 km west from Milan. The full load capacity (1365 MW) is provided by six units, which are connected to five stacks (two units discharge to one chimney, see Table 1 and Fig. 1). Due to the presence of the Alps and Appennines surrounding the PO Valley, the low level wind climatology of the area is dominated by mountain and valley winds. At Turbigo, these winds have a quite regular
behaviour: a down-slope breeze flows from the N-NE Sector, and an up-slope breeze from the South. During the two daily periods of change of wind direction, the wind speed is very low ( < 1 m s- ‘). In such periods the air mass becomes stable, bringing about flow decoupling at different heights, and allowing widely sheared winds. The five plumes were tracked out to a distance of about 30 km of the stacks by the following instruments: three correlation spectrometers aboard mobile vans and one mobile differen-
2565
2566
D. ANFOSSI Table 1. Turbiao Power Plant soecifications. The two Ponente (P) stacks and the three Levante (L) stacks arc
separated by about 450&.
Cm)
I
(MY)
1P
l.
2P
N
.
11 .
21
lL
50 m
Fig. 1. Relative positions of the chimneys.
tial Lidar measured the gas plumes; three ground based
Lidars, one Lidar installed on a jet aircraft and a fieldmill electrometer mounted on a mobile van, measured the aerosol plumes. The present paper deals with the measurements made by the ENEL Lidar operated by a joint ENELjCNR team.
2. METHOD The ENEL Lidar (manufactured by Impuls Physik) has a monostatic configuration with 100 MW peak power and 20 ns duration. It is based on a Q-switched ruby laser operating at a wavelength of 6943 A. Returned signals are displayed on a oscilloscope (in the intensity vs time configuration) and recorded by a Polaroid camera.
All the echoes recorded during the campaign were read by a digitizer and stored on tape (Anfossi et al., 1980). The tape was then read and processed by a computer to produce geometrical parameters of each cross-section, plume azimuth, height and position of the centre of gravity of backscattering aerosols, and higher order moments (standard deviation, skewness and kurtosis in the vertical and cross-wind horizontal directions). If the angle between Lidar shots and plume trajectory differed by more than _t 30 degrees from the normal to the plume trajectory, these moments were not calculated, since they would not have been meaningful. To investigate the structure of the plumes, we computed both vertically and horizontally integrated concentration profiles and Lidar-derived plume cross sections. All the computations are based on rangecorrected backscattered signals. Let the signal Sr,J be the ratio between received and transmitted power as a function of the distance pi,J (along the shot line), ~JJthe elevation angle of the Jth shot and i indicate the distances (on the Jth shot) at which Si,J are measured. We have: N
M
CJfIi
'i,.lPt.l
1
1
for the coordinateyof the centre of gravity of received echoes in the cross-wind direction. Similar expressions may be easily derived from the other computed quantities (see Hoff and Froude, 1979).
3. PLUME RISE
Almost all the measured cross-sections related to merged plumes (coming either from the two Ponente stacks or from the three Levante stacks: see Table 1).So to compute the rise of plumes we used the multiple
Plume rise measurements
sources rise model developed by Anfossi et al. (1978), that is: (2) where
1+
AHmin- Max - Hmd (iv-1)d
1*
(3)
To choose the values of a to be used in (2) and of AH,i, to be used in (3) we used the scheme reported in Table 2, which is consistent with previous measurements of the rise of single plumes in the PO Valley (Bacci et al., 1974; Anfossi et al., 1976; Sandroni er al., 1981). Figures (2) and (3) show a comparison between calculated plume heights (Equations (2) and (3) and Table 2) and the measured heights z Figure 2 refers to neutral and unstable conditions while Fig. 3 refers to the stable cases. Both drawings include a few single stack plumes; the rises of these were computed by means of appropriate equations of Table 2. Both figures show some agreement, at least on the average, between observation and theory, but a large scatter. We also report the following. (i) Light and sheared winds prevailed throughout the exercise. This greatly limited the precision of the comparison, since it is often very difficult to choose a value for the wind speed ii. We considered the “best” choice of wind speed to be the average over the Iayer occupied by the plume of pi-bal wind measurements made by ENEL and JRC teams near the Power
2567
at Turbigo
Station. In some cases data from pi-bals operated further away by other teams (such as IPS) were also included. (ii) Subdivision of cases into stable or neutral cases was based on the temperature profiles. These were observed by many teams: ICGF, UCL, CERL and JRC. In Fig. 3 we denote by 0 and Cl the night-time cases for the Ponente or Levante stacks, respectively. All other symbols refer to morning conditions before the destruction of the nocturnal inversion. (iii) Almost all the data of relevance to the comparison, i.e. power plant parameters, wind and stability, were measured with a minimum temporal resolution of I/2 h. This helps to explain the large scatter in the two diagrams, *use in principle the greater the rate of variation of a parameter the smaller should be the sampling time. The effect of such a sampling rate can be seen, e.g. in Fig. 3 where a set of successive calculation (for the night period) gave almost identical values of H,k (2: 220m) while the measured values HM varied from 140 to 370m. (iv) The few cases which refers to single plumes exhibit differences between computed and measured data as large as those which occurred for merged plumes (see Figs 2 and 3). (v) The distance x at which the final phase of rise begins was calculated as follows (see also Table 2): x = 3x* for neutral conditions, x = 2%
for stable
4s for
convectively
unstable conditions. This last formula (Weil and Hoult, 1973) is obtained
Table 2. Summary of the plume rise models for a single plume which were used to calculate AH,i, in Equation (3)
‘Ilki
PYASE
D. ANFOSSI
2568 %ean (m) 900_
100
300
500
700
900
H Calc (ml
Fig. 2. Neutral and unstable cases. Comparison between computed and measured plume heights: o Ponente and A Levante plumes in the transitional phase; l Ponente and I Levante plumes in the unstable final phase; qLevante plumes in the neutral final phase; A single Levante plume.
by taking x equal to the downwind distance at which the vertical plume velocity becomes equal to the standard deviation ov of the vertical wind component. According to Tennekes (1970) I”. (vi) In spite of the large scatter, no systematic trend is apparent: values of H, - H, were 5 m in stable conditions and = 0.5 m in neutral conditions. Nor does a classification into Ponente (lower) and Levante (taller) stack data reveal any trend. (vii) Values of the correlation coefficient between measured and calculated heights were 0.74 in stable conditions and 0.85 in neutral conditions. (viii) We consider therefore that this multiple source model predicted the plume heights at Turbigo with a good average accuracy but with a large scatter.
4. PLUME STATISTICS
By using expressions obviously similar to (I), we computed higher order moments of the distribution of
backscattering aerosols along the cross-wind and vertical directions. Figures 4 and 5 show the measured standard deviations by and bz, as functions of downwind distance x, for neutral and stable conditions, respectively. They are compared to the curves previously obtained by our group in the PO Valley by means of the no-lift balloon technique (Santomauro et al., 1978). In Fig. 4 we show the A and D curves in order to cover the whole range from unstable to neutral conditions, while in Fig. 5 we show only the E curve. From both drawings it can be seen that there is satisfactory agreement as far as the cY curves are concerned, whereas the 0, curves areconsistently lower than the measurements. This agrees with previous observations, by airborne SO2 sampling, of the plume of Turbigo Power Plant at 2750m downwind (Sandroni et al., 1981). In that paper, the excess of u, was attributed to the presence of plumes which merged but were not completely mixed. The present series of measurements seems to support that hypothesis, especially, for the stable case. However the present Lidar measurements were restricted to the first 1000 m from the stacks. Thus
Piume rise m~surements at Turbigo Ii
Meas
I
2569
n
Iml
I_
I_
I_
1-y
I100
300
500
700
"Ctik Iml
Fig. 3. Stable cases. As in Fig. 2 except: o Ponente and n Levante plumes in the transitional phase; I Levante plumes in the final stage; o Ponente and Cl Levante plumes in the final stage during night-time; A single Levante plume.
another factor too could have contributed to enlarge our oz values, for it is well known (Pasquill, 1976; Hamilton, 1978 quoted by Hoff and Froude, 1979) that in the first km downwind of the stack, the growth of the plume is principally due to self-induced turbulence caused by the buoyant plume, while the atmospheric turbulence is relatively ineffective. Figure 6 shows the computed frequency distributions of skewness and kurtosis along the Y (crosswind) and 2 (vertical) directions. Data were classified,
as before, into stable and neutral situations. Since the statistics are poor, it can only be said generally that all the cross-sections are far from Gaussian and that there is no evidence here of any substantially different behaviour in neutral and in stable conditions. We remark from Fig. 6(a) that the aerosol distribution was asymmetric, in that, viewing the crosssection from the stacks, most of aerosols were on the right side. This result is likely to be associated with directional shear.
2570
D.
ANFOSSI
OY
(4
Cm)
tm)
103
103
5.102
5.102
102
102
5.10
5.10
A
D
10
10
D
i
-r
50
102
5~lOZ
103
X(m)
*
,
z
so
lo2
5
,
/
JO2
103
X(m)
Fig. 4. Measured values of ug and 0, in the neutral cases: o Ponente plumes; Akevante plumes; A and D curves refer to no-lift balloon measurements in the PO Valley (Santomauro et al., 1978).
rc / /
a
5
Cm
(cl)
102
Io3_r
5.10;
.102--
/IbA
10:
0
A tA
b0
A
lo*__
A
A
A
5.10
E
5 .10..-
10
/
10 -E I
50
I
102
1
I
5.102
103
x(m)
50
I
102
Fig. 5. As Fig. 4 in stable cases: o Ponente early morning; l Ponente night-time; Nevante no-lift balloon measurements in the PO Valley.
1
5.102
I
103
X(nJ
early morning; E curve refer to the
Plume rise measurements at Turbigo
2571
D. ANFOW
HORIZONTAL
VERTICAL
i\
,I, 00
Y (ml
Fig. 8. Integrated
densities
corresponding
to the cross-section
in Fig. 7.
+450
v
-410
CrosswInd
Fig. 9. As Fig. 7, but for merged
drawn
Levante
Plumes;
dtstance
17.20h,
(m)
13 September,
z=
650m,
x = 1115m.
Plume rise m~surements
2573
at Turbigo IO
HORIZONTAL
00
4.
z
-150
Cl50
Fig. 10. Integrated densities corresponding to the cross-section drawn in Fig. 9.
5. PLUME STRUCTURE
Plume cross-sections were computed from the recorded range corrected backscattered signals Sil (see Figs 7 and 9). Missing plume densities (Lidar shots are fired at discrete elevation angles) were obtained by interpolation. Figures 8 and 10 show the corresponding vertical and horizontal cross-plume integrated densities, respectively. These indicate the profiles of vertical and horizontal aerosol concentraion and represent what could be seen by two mobile integrating instruments viewing the plume from beneath or laterally, respectively. It is apparent from almost all such plume crosssections, (including those in Figs 7 and 9) that, after merging, plumes neither ~in~in their ~divid~lity nor mix completely in such a way as to produce a new single plume. In other words the merging and entrainment processes produce a complicated distribution, with several maxima and minima of concentration inside the merged plume. On the other hand the integrated concentrations (including those of Figs 8 and 10) are less irregular. Acknowledgements-This work was partly supported by Finalizzato “Progetto Promozione della Qualita dell’Ambiente, CNR”. We wish to thank all the teams
participating in the Turbigo Campaign and, in particular, those provided us with the meteorological data. The skilful work of Mr. S. Viarengo who operated the Lidar, and of Dr. A. Coilo (C.S.I. Piemonte), who performed the cross-section inte~~tions is also greatly appreciated.
REFERENCES Anfossi D., Bacci P., Giraud C., Longhetto A. and Piano A. (1976) Meteorological surveys at La Spezia site. In Atmospheric Pollution (Edited by Benarie M.), pp. 531-540. Elsevier, Amsterdam. Anfossi D., Bonino C., Bossa F. and Richiardone R. (1978) Plume rise from multiple sources: a new model. Atmospheric Environment iZ, 1821-1826.
Anfossi D.. Bacci P.. Elisei G.. Lonnhetto A. and Viarenao S. (1980) Lidar measurement .md
2574
D. ANFOSSI
Laurent D. (1979) Teledetection des panaches par la mesure du champ Clectrique terrestre sur le site de Turbigo Iors de la 4-tme campagne CCE. Int. Rep. ELF AQUITANE DL/PP/No 3240, Lacq. Longhetto A., Guillot P., Anfossi D., Bacci P., Eli& G., Frego G., Sandroni S. and Varey R. (1981) Final report on the remote Sensing exercise at Turbigo, September 1979. Rapport0 Interno ENEL/DSR/CRTN, Milan. Pasquill F. (1976) Atmospheric dispersion parameters in gaussian plume modeling. Part II. Possible requirements for change in the Turner Workbook Values, U.S.E.P.A. Report 600/4-76-030b, Research Triangle Park, U.S.A. Sandroni S. and De Groot M. (1980) Intercomparison of sulphur dioxide remote sensors at the 1979 european Turbigo. Atmospheric community campaign at Environment 14, 1131-1333.
Sandroni S., Bacci P. and Anfossi D. (1981) Aircraft observations of plumes emitted from elevated sources. Atmospheric Environmenr 15, 95-100. Santomauro L., Bacci P., Longhetto A., Anfossi D. and Richaiardone R. (1978) Experimental evaluation of diffusion parameters at local scale by means of no-lift balloons. J. appl. Met. 17, 1441-1449. Tennekes H. (1970) Free convection in the turbulent Ekman layer of the atmosphere. J. ammosSot. 27, 1027-1034. Van der Meulen A. and Bartels C. (1980) Vierde EEG teledetectie campagne van gasvormige luchtverontreininging te Turbigo (It), 1979. Int. Rep. RIV-Memo FL/l980/12/20 Bilthoven. Weil J. C. and Hoult D. P. (1973)A correlation ofground level concentrations of sulfur dioxide downwind of the Keystone stacks. Atmospheric Environment 7, 707-721.
lW4A98l/82/1l2565-10 0 1982 Pergamon
1982
PLUME RISE MEASUREMENTS
$03.00/O Press Ltd.
AT TURBIGO
D. ANFOSSI Instituto di Cosmo-Geofisica de1 CNR, Torino, Italy (First received 1 September 1981 and infinal form 29 December 1981) Abstract-The fourth C.E.C. campaign on remote sensing of air pollution, organized jointly by ENEL and the Commission of European Communities, was held at Turbigo (northern Italy) during September 1979. This paper presents analyses of plume measurements obtained during that campaign by the ENEL groundbased Lidar. The five stacks ofTurbigo Power Plant have different heights and emission parameters and their plumes usually combine, so a model for multiple sources developed by D. Anfossi et al. (1978, Atmospheric Enoironment 12, 1821-1826) was used to predict the plume rises. These predictions are compared with the observations. Measurements of uv and ur over the first 1000 m are compared with the curves derived from other observations in the PO Valley, using the no-lift balloon technique over the same range of downwind distance. Skewness and kurtosis distributions are shown, both along the vertical and the horizontal directions. In order to show the plume structure in more detail, we present two examples of Lidar-derived cross sections and the corresponding vertically and horizontally integrated concentration profiles.
NOMENCLATURE F
JC Hi
Hj 4nimH, A Hmin
d 9 s Ii
!i 0
P.
=P
L T.3 si,J (T
z)
VJ Pi,J
CERL ENEL ICGF IPS JRC UCL CNR CSI
1. INTRODUCTION
buoyancy parameter (m*s-‘) effective height of merged plume produced by N stacks (m) merging point height (m) stack heights (m) heights of lowest, highest stacks (m) maximum single plume rise from lowest stack H&m) exponent in Equation (2) variable containing all the parameters not directly related to buoyancy flux at source spacing between stacks (m) acceleration of gravity (m s-z) stability parameters (s-z) wind speed (ms-‘) entrainment constant sensible heat flux at ground level (calcn-2h-i) air density (gm-‘) specific heat at constant pressure (cal g- 1K- ‘) mixing height (m) ambient temperature (K) signal defined in Equation (1) range corrected center of gravity of Si,J signals (m) elevation angle of Jth Lidar shot distance, along the Jth shot, at which Si,J is measured (m) Central Electricty Research Laboratory, Leatherhead (UK) Italian Electricity Authority National Research Councfi, Istituto CosmoGeofisica. Torino (I) National. Research ‘Council, Istituto Plasma Spazio, Frascati (I) Joint Research Centre, Ispra (I) Universitt! Catholique de Louvain, Louvain-laNeuve (B) National Research Council (I) Consorzio per il Sistema Informatico, Torino (I).
During September 1979, the Commission of the European Communities (C.E.C.) and ENEL jointly organized an exercise on the remote sensing of air pollution around the Turbigo Power Plant. Detailed information on the Campaign, which was the fourth organized by C.E.C., its objectives and general results can be found in the Report of the Campaign Coordinators (Longhetto et al., 1981). Some reports (Anfossi et al., 1980; Cerutti et al., 1979; Laurent, 1979; Sandroni and De Groot, 1980; Van der Meulen and Bertels, 1980) have also been produced concerning the analyses of results obtained by various teams involved in the campaign. So only a few facts especially related to the present paper, need to be recalled here. The Turbigo Power Plant is located in the PO Valley (northern Italy) c. 35 km west from Milan. The full load capacity (1365 MW) is provided by six units, which are connected to five stacks (two units discharge to one chimney, see Table 1 and Fig. 1). Due to the presence of the Alps and Appennines surrounding the PO Valley, the low level wind climatology of the area is dominated by mountain and valley winds. At Turbigo, these winds have a quite regular
behaviour: a down-slope breeze flows from the N-NE Sector, and an up-slope breeze from the South. During the two daily periods of change of wind direction, the wind speed is very low ( < 1 m s- ‘). In such periods the air mass becomes stable, bringing about flow decoupling at different heights, and allowing widely sheared winds. The five plumes were tracked out to a distance of about 30 km of the stacks by the following instruments: three correlation spectrometers aboard mobile vans and one mobile differen-
2565
2566
D. ANFOSSI Table 1. Turbiao Power Plant soecifications. The two Ponente (P) stacks and the three Levante (L) stacks arc
separated by about 450&.
Cm)
I
(MY)
1P
l.
2P
N
.
11 .
21
lL
50 m
Fig. 1. Relative positions of the chimneys.
tial Lidar measured the gas plumes; three ground based
Lidars, one Lidar installed on a jet aircraft and a fieldmill electrometer mounted on a mobile van, measured the aerosol plumes. The present paper deals with the measurements made by the ENEL Lidar operated by a joint ENELjCNR team.
2. METHOD The ENEL Lidar (manufactured by Impuls Physik) has a monostatic configuration with 100 MW peak power and 20 ns duration. It is based on a Q-switched ruby laser operating at a wavelength of 6943 A. Returned signals are displayed on a oscilloscope (in the intensity vs time configuration) and recorded by a Polaroid camera.
All the echoes recorded during the campaign were read by a digitizer and stored on tape (Anfossi et al., 1980). The tape was then read and processed by a computer to produce geometrical parameters of each cross-section, plume azimuth, height and position of the centre of gravity of backscattering aerosols, and higher order moments (standard deviation, skewness and kurtosis in the vertical and cross-wind horizontal directions). If the angle between Lidar shots and plume trajectory differed by more than _t 30 degrees from the normal to the plume trajectory, these moments were not calculated, since they would not have been meaningful. To investigate the structure of the plumes, we computed both vertically and horizontally integrated concentration profiles and Lidar-derived plume cross sections. All the computations are based on rangecorrected backscattered signals. Let the signal Sr,J be the ratio between received and transmitted power as a function of the distance pi,J (along the shot line), ~JJthe elevation angle of the Jth shot and i indicate the distances (on the Jth shot) at which Si,J are measured. We have: N
M
CJfIi
'i,.lPt.l
1
1
for the coordinateyof the centre of gravity of received echoes in the cross-wind direction. Similar expressions may be easily derived from the other computed quantities (see Hoff and Froude, 1979).
3. PLUME RISE
Almost all the measured cross-sections related to merged plumes (coming either from the two Ponente stacks or from the three Levante stacks: see Table 1).So to compute the rise of plumes we used the multiple
Plume rise measurements
sources rise model developed by Anfossi et al. (1978), that is: (2) where
1+
AHmin- Max - Hmd (iv-1)d
1*
(3)
To choose the values of a to be used in (2) and of AH,i, to be used in (3) we used the scheme reported in Table 2, which is consistent with previous measurements of the rise of single plumes in the PO Valley (Bacci et al., 1974; Anfossi et al., 1976; Sandroni er al., 1981). Figures (2) and (3) show a comparison between calculated plume heights (Equations (2) and (3) and Table 2) and the measured heights z Figure 2 refers to neutral and unstable conditions while Fig. 3 refers to the stable cases. Both drawings include a few single stack plumes; the rises of these were computed by means of appropriate equations of Table 2. Both figures show some agreement, at least on the average, between observation and theory, but a large scatter. We also report the following. (i) Light and sheared winds prevailed throughout the exercise. This greatly limited the precision of the comparison, since it is often very difficult to choose a value for the wind speed ii. We considered the “best” choice of wind speed to be the average over the Iayer occupied by the plume of pi-bal wind measurements made by ENEL and JRC teams near the Power
2567
at Turbigo
Station. In some cases data from pi-bals operated further away by other teams (such as IPS) were also included. (ii) Subdivision of cases into stable or neutral cases was based on the temperature profiles. These were observed by many teams: ICGF, UCL, CERL and JRC. In Fig. 3 we denote by 0 and Cl the night-time cases for the Ponente or Levante stacks, respectively. All other symbols refer to morning conditions before the destruction of the nocturnal inversion. (iii) Almost all the data of relevance to the comparison, i.e. power plant parameters, wind and stability, were measured with a minimum temporal resolution of I/2 h. This helps to explain the large scatter in the two diagrams, *use in principle the greater the rate of variation of a parameter the smaller should be the sampling time. The effect of such a sampling rate can be seen, e.g. in Fig. 3 where a set of successive calculation (for the night period) gave almost identical values of H,k (2: 220m) while the measured values HM varied from 140 to 370m. (iv) The few cases which refers to single plumes exhibit differences between computed and measured data as large as those which occurred for merged plumes (see Figs 2 and 3). (v) The distance x at which the final phase of rise begins was calculated as follows (see also Table 2): x = 3x* for neutral conditions, x = 2%
for stable
4s for
convectively
unstable conditions. This last formula (Weil and Hoult, 1973) is obtained
Table 2. Summary of the plume rise models for a single plume which were used to calculate AH,i, in Equation (3)
‘Ilki
PYASE
D. ANFOSSI
2568 %ean (m) 900_
100
300
500
700
900
H Calc (ml
Fig. 2. Neutral and unstable cases. Comparison between computed and measured plume heights: o Ponente and A Levante plumes in the transitional phase; l Ponente and I Levante plumes in the unstable final phase; qLevante plumes in the neutral final phase; A single Levante plume.
by taking x equal to the downwind distance at which the vertical plume velocity becomes equal to the standard deviation ov of the vertical wind component. According to Tennekes (1970) I”. (vi) In spite of the large scatter, no systematic trend is apparent: values of H, - H, were 5 m in stable conditions and = 0.5 m in neutral conditions. Nor does a classification into Ponente (lower) and Levante (taller) stack data reveal any trend. (vii) Values of the correlation coefficient between measured and calculated heights were 0.74 in stable conditions and 0.85 in neutral conditions. (viii) We consider therefore that this multiple source model predicted the plume heights at Turbigo with a good average accuracy but with a large scatter.
4. PLUME STATISTICS
By using expressions obviously similar to (I), we computed higher order moments of the distribution of
backscattering aerosols along the cross-wind and vertical directions. Figures 4 and 5 show the measured standard deviations by and bz, as functions of downwind distance x, for neutral and stable conditions, respectively. They are compared to the curves previously obtained by our group in the PO Valley by means of the no-lift balloon technique (Santomauro et al., 1978). In Fig. 4 we show the A and D curves in order to cover the whole range from unstable to neutral conditions, while in Fig. 5 we show only the E curve. From both drawings it can be seen that there is satisfactory agreement as far as the cY curves are concerned, whereas the 0, curves areconsistently lower than the measurements. This agrees with previous observations, by airborne SO2 sampling, of the plume of Turbigo Power Plant at 2750m downwind (Sandroni et al., 1981). In that paper, the excess of u, was attributed to the presence of plumes which merged but were not completely mixed. The present series of measurements seems to support that hypothesis, especially, for the stable case. However the present Lidar measurements were restricted to the first 1000 m from the stacks. Thus
Piume rise m~surements at Turbigo Ii
Meas
I
2569
n
Iml
I_
I_
I_
1-y
I100
300
500
700
"Ctik Iml
Fig. 3. Stable cases. As in Fig. 2 except: o Ponente and n Levante plumes in the transitional phase; I Levante plumes in the final stage; o Ponente and Cl Levante plumes in the final stage during night-time; A single Levante plume.
another factor too could have contributed to enlarge our oz values, for it is well known (Pasquill, 1976; Hamilton, 1978 quoted by Hoff and Froude, 1979) that in the first km downwind of the stack, the growth of the plume is principally due to self-induced turbulence caused by the buoyant plume, while the atmospheric turbulence is relatively ineffective. Figure 6 shows the computed frequency distributions of skewness and kurtosis along the Y (crosswind) and 2 (vertical) directions. Data were classified,
as before, into stable and neutral situations. Since the statistics are poor, it can only be said generally that all the cross-sections are far from Gaussian and that there is no evidence here of any substantially different behaviour in neutral and in stable conditions. We remark from Fig. 6(a) that the aerosol distribution was asymmetric, in that, viewing the crosssection from the stacks, most of aerosols were on the right side. This result is likely to be associated with directional shear.
2570
D.
ANFOSSI
OY
(4
Cm)
tm)
103
103
5.102
5.102
102
102
5.10
5.10
A
D
10
10
D
i
-r
50
102
5~lOZ
103
X(m)
*
,
z
so
lo2
5
,
/
JO2
103
X(m)
Fig. 4. Measured values of ug and 0, in the neutral cases: o Ponente plumes; Akevante plumes; A and D curves refer to no-lift balloon measurements in the PO Valley (Santomauro et al., 1978).
rc / /
a
5
Cm
(cl)
102
Io3_r
5.10;
.102--
/IbA
10:
0
A tA
b0
A
lo*__
A
A
A
5.10
E
5 .10..-
10
/
10 -E I
50
I
102
1
I
5.102
103
x(m)
50
I
102
Fig. 5. As Fig. 4 in stable cases: o Ponente early morning; l Ponente night-time; Nevante no-lift balloon measurements in the PO Valley.
1
5.102
I
103
X(nJ
early morning; E curve refer to the
Plume rise measurements at Turbigo
2571
D. ANFOW
HORIZONTAL
VERTICAL
i\
,I, 00
Y (ml
Fig. 8. Integrated
densities
corresponding
to the cross-section
in Fig. 7.
+450
v
-410
CrosswInd
Fig. 9. As Fig. 7, but for merged
drawn
Levante
Plumes;
dtstance
17.20h,
(m)
13 September,
z=
650m,
x = 1115m.
Plume rise m~surements
2573
at Turbigo IO
HORIZONTAL
00
4.
z
-150
Cl50
Fig. 10. Integrated densities corresponding to the cross-section drawn in Fig. 9.
5. PLUME STRUCTURE
Plume cross-sections were computed from the recorded range corrected backscattered signals Sil (see Figs 7 and 9). Missing plume densities (Lidar shots are fired at discrete elevation angles) were obtained by interpolation. Figures 8 and 10 show the corresponding vertical and horizontal cross-plume integrated densities, respectively. These indicate the profiles of vertical and horizontal aerosol concentraion and represent what could be seen by two mobile integrating instruments viewing the plume from beneath or laterally, respectively. It is apparent from almost all such plume crosssections, (including those in Figs 7 and 9) that, after merging, plumes neither ~in~in their ~divid~lity nor mix completely in such a way as to produce a new single plume. In other words the merging and entrainment processes produce a complicated distribution, with several maxima and minima of concentration inside the merged plume. On the other hand the integrated concentrations (including those of Figs 8 and 10) are less irregular. Acknowledgements-This work was partly supported by Finalizzato “Progetto Promozione della Qualita dell’Ambiente, CNR”. We wish to thank all the teams
participating in the Turbigo Campaign and, in particular, those provided us with the meteorological data. The skilful work of Mr. S. Viarengo who operated the Lidar, and of Dr. A. Coilo (C.S.I. Piemonte), who performed the cross-section inte~~tions is also greatly appreciated.
REFERENCES Anfossi D., Bacci P., Giraud C., Longhetto A. and Piano A. (1976) Meteorological surveys at La Spezia site. In Atmospheric Pollution (Edited by Benarie M.), pp. 531-540. Elsevier, Amsterdam. Anfossi D., Bonino C., Bossa F. and Richiardone R. (1978) Plume rise from multiple sources: a new model. Atmospheric Environment iZ, 1821-1826.
Anfossi D.. Bacci P.. Elisei G.. Lonnhetto A. and Viarenao S. (1980) Lidar measurement .md
2574
D. ANFOSSI
Laurent D. (1979) Teledetection des panaches par la mesure du champ Clectrique terrestre sur le site de Turbigo Iors de la 4-tme campagne CCE. Int. Rep. ELF AQUITANE DL/PP/No 3240, Lacq. Longhetto A., Guillot P., Anfossi D., Bacci P., Eli& G., Frego G., Sandroni S. and Varey R. (1981) Final report on the remote Sensing exercise at Turbigo, September 1979. Rapport0 Interno ENEL/DSR/CRTN, Milan. Pasquill F. (1976) Atmospheric dispersion parameters in gaussian plume modeling. Part II. Possible requirements for change in the Turner Workbook Values, U.S.E.P.A. Report 600/4-76-030b, Research Triangle Park, U.S.A. Sandroni S. and De Groot M. (1980) Intercomparison of sulphur dioxide remote sensors at the 1979 european Turbigo. Atmospheric community campaign at Environment 14, 1131-1333.
Sandroni S., Bacci P. and Anfossi D. (1981) Aircraft observations of plumes emitted from elevated sources. Atmospheric Environmenr 15, 95-100. Santomauro L., Bacci P., Longhetto A., Anfossi D. and Richaiardone R. (1978) Experimental evaluation of diffusion parameters at local scale by means of no-lift balloons. J. appl. Met. 17, 1441-1449. Tennekes H. (1970) Free convection in the turbulent Ekman layer of the atmosphere. J. ammosSot. 27, 1027-1034. Van der Meulen A. and Bartels C. (1980) Vierde EEG teledetectie campagne van gasvormige luchtverontreininging te Turbigo (It), 1979. Int. Rep. RIV-Memo FL/l980/12/20 Bilthoven. Weil J. C. and Hoult D. P. (1973)A correlation ofground level concentrations of sulfur dioxide downwind of the Keystone stacks. Atmospheric Environment 7, 707-721.