5. The cases of southward transport and deposition of semivolatile organics (SVOs) from multiple sources in April.

            The prevailing weather conditions in April 1999 were changeable with frequent rainfall mainly over the central and to a lesser extent over the southern Balkan area. This may have increased wet deposition in the proximity of the emission sources. During this month, low pressure systems dominated the area, interrupted by a few transitory ridges of high pressure. As a result, periods of north-westerly flow, favouring  transport of air masses from former Yugoslavia to the south, were limited. On the 7th of April, a ridge of high pressure resulted to drier weather in the Balkans with winds blowing from northerly directions. These conditions lasted for not more than 1.5 days. Short-lived spell with northerly flow also occurred on 18-19 April 1999.

The combination of the information about the bombing with estimations about emissions from explosions found in the literature (Church, 1969) resulted to the following emission scenarios:

        April 4-7: Multiple sources scenario.

(a)    


April 4: One line source from 100 m to 500 m above ground level (AGL) over Belgrade (fuel storage), one over Novi Sad (oil refinery), one over Bogutovac (fuel storage) and one over Smederevo (petrochemical industry installations). The emission started at April 4, 2.00 UTC and lasted 12 hours.


Figure 8.1a: Time integrated concentrations calculated with HYSPLIT_4 modeling system for April 4. The stars indicate the geographic position of the sources. A line source is assumed at each location which stretches from 100 to 500 m AGL. The concentrations are given in relative units, corresponding to an emission rate of 1 unit of pollutant per hour.

 

 



(b) April 5: One line source from 100 m to 500 m above ground level (AGL) over Sombor (fuel storage), one over Novi Sad (power station)  and one over Nis (warehouse). The emission started at April 5, 1.00 UTC and lasted 12 hours.


 

Figure 8.1b: Time integrated concentrations calculated with HYSPLIT_4 modeling system for April 5. The stars indicate the geographic position of the sources. A line source is assumed at each location which stretches from 100 to 500 m AGL. The concentrations are given in relative units, corresponding to an emission rate of 1 unit of pollutant per hour.

 

(c)April 6: One line source from 100 m to 500 m above ground level (AGL) over Sombor (petrochemical industry warehouse), one over Novi Sad (bitumen storage & power station)  and one over Prizren (cement plant). The emission started at April 6, 1.00 UTC and lasted 12 hours.


Figure 8.1c: Time integrated concentrations calculated with HYSPLIT_4 modeling system for April 18-20. The stars indicate the geographic position of the sources. A line source is assumed at each location which stretches from 100 to 500 m AGL. The concentrations are given in relative units, corresponding to an emission rate of 1 unit of pollutant per hour.

 

 

 

(d) April 7: One line source from 100 m to 500 m above ground level (AGL) over Pristina (fuel storage), one over Novi Sad (industrial company) and one over Sombor (fuel storage). The emission started at April 7, 1.00 UTC and lasted 12 hours.

 


Figure 8.1d: Time integrated concentrations calculated with HYSPLIT_4 modeling system for April 18-20. The stars indicate the geographic position of the sources. A line source is assumed at each location which stretches from 100 to 500 m AGL. The concentrations are given in relative units, corresponding to an emission rate of 1 unit of pollutant per hour.

 


        April 1820: One line source from 100 m to 500 m AGL over Pristina and one over Kursumlija. The emission started at April 18, 21 UTC and lasted 12 hours.

 

 

Figure 8.2: Time integrated concentrations calculated with HYSPLIT_4 modeling system for April 18-20. The stars indicate the geographic position of the sources. A line source is assumed at each location which stretches from 100 to 500 m AGL. The concentrations are given in relative units, corresponding to an emission rate of 1 unit of pollutant per hour.

Time-integrated concentrations and depositions resulting from the aforementioned scenarios are shown in figures 8.1a-d and 8.2. It should be noted that other multiple sources (see Table I in Appendix) provided additional emissions which were not added in the calculations of these figures. As it is evident from figures 8.1a-d and 8.2, differences in the meteorological conditions resulted in distinctive differences in dispersion results between the two periods when there is evidence of transboundary transport over northern Greece (Rapsomanikis et al., 1999).

 

As mentioned before, aerosol samples were collected at Xanthi, Greece (41.15 oN, 25 oE), on a moving glass fiber filter band GF10 6 cm width with 1 m nominal porocity of a high volume sampler (Rapsomanikis et al, 1999). They were also collected by a PM2.5 m High Volume Dichotomous Virtual Impactor (HVDVI) (Solomon et al., 1983) on glass fiber 90 mm diameter GF/F filters with nominal porocity of 1 m. Parts of the filter band and parts of the HVDVI filters, constituting of 24h samples, were analysed using high resolution gas chromatography coupled with high resolution mass spectrometry by Scientific Analysis Laboratories Ltd (SAL), U.K. The background concentrations for the compounds of interest in the area was estimated from samples of filter band for days that air masses originated from the former Yugoslavia, before the onset of the conflict.

The following SVOs were quantitatively determined:

Dioxins and furans: 2,3,7,8-TCDD; 1,2,3,7,8-PeCDD; 1,2,3,6,7,8-HxCDD; 1,2,3,4,7,8-HxCDD; 1,2,3,7,8,9-HxCDD; 1,2,3,4,6,7,8-HpCDD; OCDD; 2,3,7,8-TCDF; 1,2,3,7,8-PeCDF; 2,3,4,7,8-PeCDF; 1,2,3,4,7,8-HxCDF; 1,2,3,6,7,8-HxCDF; 2,3,4,6,7,8-HxCDF; 1,2,3,7,8,9-HxCDF; 1,2,3,4,6,7,8-HpCDF; 1,2,3,4,7,8,9-HpCDF; OCDF.

PCBs: Tri-, tetra-, penta-, hexa- and hepta-chlorobiphenyls

PAHs: Napthalene, Acetapthylene, Acenaphthene, Fluorene, Phenanthene, Anthralene, Fluoranthene, Pyrene, Benzo(a)anthracene, Chrysene, Benzo(b/k)fluoranthene, Benzo(a)pyrene, Indeno(123-cd)pyrene, Benzo(ghi)perylene, Dibenzo(ah)anthracene.

 

Figure 9a: Time series of 24hr integrated aerosol samples for total dioxins, furans, PCB's and PAH's. For the dates that data are not depicted, concentrations were not detectable.

 

Figure 9a, adapted from Rapsomanikis et al. (1999), shows atmospheric concentrations of total dioxins, furans, PCBs and PAHs. As can be seen from the time series of SVOs in figure 9a, the two events can be clearly distinguished from background values. In the first episode concentrations of total dioxins, furans and PCBs increased ten fold, whilst concentrations of total PAHs increased twenty fold. The second episode is less prominent and increases were three fold for dioxins, furans and PAHs whilst no increase was observed for PCBs. The onset and end of these events is consistent with dispersion calculations depicted in figures 8.1a-d and 8.2.

 


Figure 9b: Time series of 24hr integrated aerosol samples for total phthalates. For the dates that data are not depicted, concentrations were not detectable.

 


Phthalates are used as plasticizers in a variety of plastics and are emitted in the atmosphere after burning of plastics in fires and / or municipal incinerators. Their toxicity and atmospheric concentrations are well documented with total concentrations ranging from 0.3 1.0 g/m3 (California EPA, 1994,Dugenest et al., 1999, Fredricson et al., 1999). Total values for the concentration of the following phthalates were determined in the atmosphere of Xanthi: Dimethyl phthalate, Di-n-butyl phthalate, Butyl benzyl phthalate, Bis (2 ethyl hexyl) phthalate Diethyl phthalate. Their time series in April is shown in figure 9b.

It should be emphasized that these events could not have been caused by pollution from nearby sources because of the unique combination of detected pollutant species as seen in figure 9a. Lack of similar measurements in the Balkans prevented any attempt to carry out a risk assessment analysis and a further validation of the model results.

Figure 10. Back trajectories at 850 hPa with end point in Xanthi, Greece, calculated with HYSPLIT_4 modeling system for April 7 and 8, respectively. The star indicates the geographic position of the source and the triangles the position of the air pollutants in 12hrs time intervals.

 

 

 

 

 

 

 

 

 

Figure 11. Back trajectories at 850 hPa with end point in Xanthi, Greece, calculated with HYSPLIT_4 modeling system for April 12 and 19, respectively. The star indicates the geographic position of the source and the triangles the position of the air pollutants in 12hrs time intervals.
In concluding this paragraph, we have calculated back-trajectories with starting level at 850 hPa (~1500 m height) calculated for the days of interest, with the Langrangian model HYSPLIT_4 (Draxler, 1997, Draxler, 1998). Such conditions were met for example with end point in Xanthi at 850 hPa (1500m height above sea level) on April 7, 8, 12, and 19 as seen in figures 10-11. These figures clearly show the origin of the air masses which moved southward carrying toxic gases which were measured at Xanthi..