Gordana Pehnec, Vladimira Vađić, Mirjana Čačković, Silva Žužul

Gordana Pehnec, Vladimira Vađić, Mirjana Čačković, Silva Žužul

Abstract No. 40
ABSTRACT
Ozone (O3) is a secondary pollutant formed through
photochemical reactions of nitrogen oxides and volatile
organic compounds. As a strong oxidant, it may cause
harmful health effects and damage plants and a variety of
materials. O3 concentrations have been measured
continuously in Zagreb, Croatia from 1999. This paper
presents the results of O3 measurements at three urban
locations (north, centre, and south) with different traffic
density for the period 1999-2008. The aim was to find
variations and trends in ozone concentrations. The
measuring method used in this work is based on active
sampling of ozone in the absorption solution of sodium
nitrite. Nitrite ion reacts with ozone and forms a nitrate,
which is then determined by ion chromatography. Over
the whole measuring period, average annual O3
concentrations in Zagreb ranged between 20 μg m-3 and
40 μg m-3 in the north, between 19 μg m-3 and 3 μg m-3 in
the city centre, and between 7 μg m-3 and 35 μg m-3 in
the south. Over the spring and summer months, daily
averages occasionally exceeded the Croatian limit value
of 110 μg m-3. The highest daily value of 196 μg m-3 was
measured in the city centre. In general, over the ten years
of measurement ozone concentrations increased in the
south, while in the north and in the centre they showed a
slow decrease or no changes in annual averages and in
the annual number of days with exceeded limit values.
TRENDS OF OZONE CONCENTRATIONS IN THE AIR OF
ZAGREB, CROATIA
Gordana Pehnec, Vladimira Vađić, Mirjana Čačković, Silva Žužul
Institute for Medical Research and Occupational Health, Ksaverska c. 2, 10000 Zagreb, Croatia
Table 1. Summary statistics of 24-hour averages of ozone mass concentrations
(μg m-3) in Zagreb for the period March 1999 – December 2008
Measuring
site
North
Centre
METHODOLOGY
South
19 99
20 00
20 01
20 02
20 03
20 04
20 05
20 06
20 07
20 08
1999-2008
19 99
20 00
20 01
20 02
20 03
20 04
20 05
20 06
20 07
20 08
1999-2008
19 99
20 00
20 01
20 02
20 03
20 04
20 05
20 06
20 07
20 08
1999-2008
N
25 0
26 4
28 3
22 4
31 5
35 9
36 4
34 4
34 8
34 9
3 10 0
24 6
30 5
33 9
34 1
35 4
35 6
35 7
35 8
34 3
36 0
3 35 9
306.0
311.0
359.0
360.0
347.0
354.0
364.0
336.0
341.0
343.0
3421.0
C50
Cmax
STD
18.1
24.8
20.4
28.8
25.8
25.6
29.7
23.2
29.6
26.3
25.8
13.8
26.0
15.8
26.4
20.0
15.4
16.4
17.3
21.5
24.1
19.1
37.8
3.7
3.9
24.7
13.0
17.8
23.1
25.5
27.3
33.1
19.9
64.8
126.3
110.0
159.9
88.5
80.1
167.8
93.5
66.2
116.1
167.8
121.8
193.9
196.3
180.4
163.4
136.2
103.2
84.5
95.4
87.7
196.3
103.6
113.6
46.0
97.5
82.5
83.7
158.9
117.8
115.7
122.8
158.9
1 5. 0
2 4. 8
2 1. 0
2 8. 2
1 5. 0
1 3. 9
2 1. 2
1 4. 3
1 1. 2
1 6. 3
1 8. 6
1 9. 0
2 5. 3
2 9. 8
2 8. 5
2 5. 3
1 8. 6
1 6. 5
1 3. 0
1 6. 4
1 7. 4
2 2. 1
1 3. 5
1 3. 2
7.8
2 3. 0
1 5. 3
1 8. 8
2 3. 9
1 7. 9
2 1. 5
2 5. 9
2 2. 0
40
N>110
30
0
2
1
7
0
0
4
0
0
1
15
1
4
8
4
8
2
0
0
0
0
27
0
1
0
0
0
0
2
1
2
4
10
N – number of samples
C50 – median
Cmax – maximum
STD – standard deviation
N>110 – number of days with the concentration higher than 110 μg m-3
20
y = 0.12x + 28.93
r = 0.084
10
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Centre
40
30
20
y = -0.33x + 27.42
r = 0.200
10
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
South
40
30
20
y = 1.92x + 15.35
r = 0.490
10
0
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Figure 1. Trends of ozone concentrations at three
measuring sites in Zagreb
CONCLUSIONS
14
12
10
8
6
4
2
0
N >110
Active sampling was done by sucking the air in glass
bubblers filled with absorption solution containing
NaNO2. Samples were collected from 1 March 1999 to 31
December 2008 at three sites in Zagreb:
- North - residential part of the town with modest
traffic
- Centre - densely populated area with dense traffic
(old town)
- South - densely populated residential part of the town
(new town with district heating)
Samples were taken every 24 hours in the north. In the
centre and the south they were taken every 24 hours on
workdays and every 72 hours on weekends. Ozone
concentration was determined from the amount of
nitrate ion formed in the reaction of nitrite ion with
ozone. The nitrate ion was analyzed by ion
chromatography. The detection limit of the method was
0.019 mg L-1 for the nitrate ion, which corresponds to
ozone concentration of 0.5 μg m-3 in air sampled over 24
hours.
Year
North
Spring
Summer
Autumn
Winter
North
Centre
South
Figure 2. Seasonal differences in the number of days with ozone
concentrations higher than 110 μg m-3 (N>110) for the whole
period March 1999-December 2008
Over the ten years of measurement ozone concentrations increased in
the south, while in the north and in the centre they showed a slow
decrease or no changes in annual averages and in the annual number of
days with exceeded limit values. Over the spring and summer months,
daily averages occasionally exceeded the Croatian limit of 110 μg m-3. The
highest daily value of 196 μg m-3 was measured in the city centre in
August 2001. This site also had the highest number of days with
concentrations above the limit. Ozone concentrations in Zagreb show
seasonal variations similar to those described in the literature. They are
the highest when sunlight is the most intense, that is, in June, July, and
August. The increasing trend in the south may be explained by increasing
traffic density in the centre of town and by the northerly winds that carry
NO2 and other ozone precursors to the south.