SILVER ANNIVERSARY International Conference on Heavy Metals in the Environment, 6-10 August, 2000; Ann Arbor, Michigan

 

 

An estimation OF trace METAL EMISSIONS IN VILNIUS CITY

 

Darius Valiulis, Kęstutis Kvietkus*, Darius Čeburnis and Jonas Šakalys

 

Atmospheric Pollution Research Laboratory, Institute of Physics, Goštauto 12, 2600 Vilnius, Lithuania, kvietkus@ktl.mii.lt

 

Abstract

 

Daily air samples of heavy metals (HM) were collected at heights of 10 m, 55 m and 170 m in Vilnius TV tower, during October 26 - December 20, 1999.  Sampling period was divided between day (8 AM – 21 PM) and night (22 PM – 7 AM) time. The aerosols were separated into fine and coarse fraction with a virtual impactor (cut-off diameter - 2.5 μm). Concentration gradients were determined for all metals in both fractions (Ba, Pb, V, Sb, Zn) with the exception of vanadium on fine particles. Heavy metals emission rates from Vilnius city were calculated using vertical gradients of HM concentrations and meteorological measurement data.

 

INTRODUCTION

 

Historically the rate of heavy metals emission has been low because of the low volatility of most metals (except mercury). However, with the advent of high-temperature processes (smelting and fossil fuel combustion), the rate of emission for some metals has substantially increased. With increased emissions have come increased metal concentrations in the atmosphere and in atmospheric deposition (Blank et al., 1998).

As in many cities worldwide, the concentrations of air pollutants in the Vilnius city sometimes exceed the limit values. The only safe way to avoid air pollution episodes is obviously the reduction of pollutant emissions. However, it is established that serious pollution episodes in the urban environment are not generally caused by the sudden increase in the emission of pollutants, but as a result from a short-term unfavorable meteorological conditions (Zickus and Kvietkus, 1998).

The composition and size of the particles vary upon their origin. The ones that are formed from combustion are small, while the natural ones are quite large (Williams et al., 1998).

The main goal of the present work was the investigation of heavy metals emissions using vertical profile measurement data in Vilnius city.

 

MATERIALS AND METHODS

 

 Daily air samples of heavy metals were taken at heights of 10 m, 55 m and 170 m in Vilnius TV tower, situated in a western part of the city, during October 26 - December 20, 1999. Sampling period was divided between day (8 AM – 21 PM) and night (22 PM – 7 AM) time. Aerosols were collected into fine (<2.5 μm) and coarse (>2.5 μm) fractions using virtual impactor (Ulevičius et al., 1999). Aerosol samples were collected with low volume samplers (1 m3 / h) on Whatman 40 filters. After collection filters were extracted in 0.2 M HNO3 using ultrasonic bath for 1 hour. Preparation parameters were selected after pilot investigation (Čeburnis et. al., 1999). Concentrations of HM were determined in fine and coarse aerosol fractions using an atomic absorption spectrophotometer Zeeman/3030. Elements under consideration were Barium (Ba), Lead (Pb), Antimony (Sb), Vanadium (V) and Zinc (Zn).

 

 

RESULTS AND DISCUSSIONS

 

Vertical concentration profiles were obtained for all studied heavy metals as presented in Figure 1. The concentration gradients were negative for all elements with an exception of vanadium on fine particles, during day and night time. The gradient of vanadium concentration on fine particles during day time was positive near the ground. The concentration of vanadium was increasing up to the 55 m height. Referring to the main source of vanadium being stack emissions from the fossil fuel combustion, the vanadium concentration profile on fine particles corresponds well that assumption. However, concentration profiles of  all other elements points to the conclusion that  the main source of all other elements, including vanadium on coarse particles, is  the surface. The profile of lead concentrations on fine and coarse particles (Figure 1) is the typical one, very similar ones were obtained for other elements.

 

 

 

 

The concentration gradients of the elements were calculated at 10 m height using vertical profiles (Table 1). As it was mentioned above the concentration gradients on fine and coarse aerosols, during day and night time were negative for all elements with the exception of V on fine particles.

 

 

Table 1. Vertical concentration gradients (ng/m4) of heavy metals in Vilnius city.

 

Element

day-fine

night-fine

day-coarse

night-coarse

Pb

-.0776

-.0751

-.0191

-.0301

V

.00597

-.0162

-.0073

-.0152

Ba

-.0191

-.0249

-.0215

-.0313

Zn

-.154

-.243

-.085

-.115

Sb

-.0223

-.0142

-.0183

-.013

 

 

 

Heavy metals emissions from the surface of Vilnius city were calculated using following equation:

,

 

where K is the coefficient of turbulent diffusion; dc/dz is the concentration gradient.

 

Coefficient of turbulent diffusion was calculated using data of Vilnius air quality meteorological mast. Than emission of heavy metals were calculated and presented  in Table 2.

 

Table 2. Emissions of heavy metals (ng/m2s) in Vilnius city.

 

Element

day-fine

night-fine

day-coarse

night-coarse

Pb

0.0388

0.0150

0.0096

0.0060

Ba

0.0096

0.0050

0.0108

0.0063

Zn

0.0770

0.0486

0.0425

0.0230

Sb

0.0112

0.0028

0.0092

0.0026

 

 

As it might be supposed the emission of elements during the nighttime were lower. It is clear that emission intensity is very much related with human activity in Vilnius city and most probably originated from a transport traffic. On the other hand the absolute emission values are too low to have significant influence on regional trace metal concentration background.

 

CONCLUSIONS

 

The trace metal concentration gradients on  fine and coarse aerosols during day and night time were negative for all elements with the exception of vanadium on fine particles. This corresponds well to the main source of vanadium being stack emissions from fossil fuel combustion. Heavy metals emissions, calculated for the city of Vilnius, are approximately twice higher during daytime than that during the nighttime.

The obtained results are characteristic for late fall – winter season and probably do not reflect the annual values.

References

 

1.      Žičkus M. and Kvietkus K. (1998), Proceedings of the Sixth International Conference on Air Pollution, AIR POLLUTION VI, September 18-21, 1998, Comp. Mech. Publication, 515-523.

2.      Blank P., Friedrich R., John C., Obermeier A. and Wickert B. (1998), Proceedings of  the EUROTRAC Symposium 1998. Editors: P.M. Borrel and P. Borrel.  2000, WIT press, Southampton, 737-740.

3.      Williams P.I., Gallagher M.W., Choularton T.W., Coe H. and Bower K.N. (1998),  Proceedings of  the EUROTRAC Symposium 2000. Editors: P.M. Borrel and P. Borrel.  2000, WIT press, Southampton, 822-825.

4.      Ulevičius V., Juozaitis A. and Šopauskienė, D. (1999), Environmental Physics, 20, (2), 20-27, Vilnius, Lithuania.

5.      Čeburnis D., Valiulis D. and Šakalys J. (1999),  Environmental Physics, 21 (1), 31-36, Vilnius, Lithuania.