Ground-based measurements of ozone have been carried out at three stations in the German alps (47 deg N, 11 deg E, altitudes 740, 1776, and 2962 m a.s.l.) as well as at the coastal station Cape Point (34 deg S, 18 deg E). For the mountain sites (at 1776 and 2962 m), trend calculations based on monthly means have yielded O3 growth rates of 0.8 and 0.9 ppbv yr(exp -1), respectively, over the period 1978-91. Seasonally differentiated data sets have yielded higher rates for summer than for winter. The impact of near-ground photochemical O3 production on the observed O3 concentration is shown. No significant long-term O3 trend has been observed at 740 m (valley floor) as well as at the southern hemispheric station Cape Point. Evidence exists for a close relationship between the amplitude variations of the annual cycles of O3 and CO at Cape Point

Brunke, Ernst-Guenther

Scheel, Hans-Eckhart

Seiler, Wolfgang

Sladkovic, Rudolf

English

NASA Technical Reports Server

N95- 10593
MEASUREMENTS OF LOWER TROPOSPHERIC OZONE AT MID-LATITUDES OF
THE NORTHERN AND SOUTHERN HEMISPHERE
Hans-Eckhart Scheel l, Rudolf Sladkovic 1, Ernst-Ganther Brunke 2, Wolfgang Seiler l
I: Fraunhofer Institute for Atmospheric Environmental Research (IFU),
D-8100 Garmisch-Partenkirchen, Germany
2: APMA-EMATEK, Council for Scientific and Industrial Research,
Faure 7131, South Africa
ABSTRACT
Ground-based measurements of ozone have been
carried out at three stations in the German alps (47°N,
ll°E, altitudes 740, 1776 and 2962 m a.s.1.) as well as at
the coastal station Cape Point (34°S, 18°E). For the moun-
tain sites (at 1776 and 2962 m), trend calculations based on
monthly ineans have yielded 03 growth rates of 0.8 and 0.9
ppbv yr -', respectively, over the period 1978-91. Seasonal-
ly differentiated data sets have yielded higher rates for
summer than for winter. The impact of near-ground photo-
chemical 03 production on the observed 03 concentration is
shown. No significant long-term O trend has been
observed at 740 m (valley floor) as we_l as at the southern
hemispheric station Cape Point. Evidence exists for a close
relationship between the amplitude variations of the annual
cycles of 03 and CO at Cape Point.
1. INTRODUCTION
The existence of a long-term rising trend of lower
tropospheric ozone over large parts of the Northern Hemi-
sphere seems to be evident (Penkett, 1991 and references
therein). However, the observed growth rates differ
considerably among the different sites of observation (see
e.g. Low et al., 1992), which is at least partly due to
specific characteristics of the individual locations, such as
influences from local meteorology. It is assumed that
enhanced photochemical ozone production in the lower
troposphere is responsible for the increase in 0 3 observed
during the last decades (Logan, 1985). For the Southern
Hemisphere, long-term 03 records are only available from
a few sites. At none of these sites has a significant increase
in 03 been observed. For Antarctica even a decrease in 03
has been reported (Schnell et al., 1991).
We report here on in-situ measurements of ozone
performed at three neighboring stations in the German alps
(47°N, 11 °E) as well as at a coastal station in the south-
eastern part of Africa (34°S, 18°E). The alpine sites are lo-
cated at elevations of 740 m a.s.l. (station Garmisch, on the
floor of the valley), 1776 m a.s.l. (station Wank, ca. 1100
m above ground) and 2962 m a.s.l. (station Zugspitze, ca.
2200 m above ground). Details of the alpine sites and the
0 3 measurements have been described by Reiter et al.
(1987). Information on geographic location and instrumen-
tation of the coastal station Cape Point has been given by
Seiler et al. (1984) and Brunke et al. (1990).
2. NORTHERN HEMISPHERIC RESULTS
Figure 1 shows the monthly means of ozone for
Zugspitze together with trend estimates. The time series is
composed of seasonal variations, pronounced interannual
variabilty, and a long-term trend. The rates of increase were
highest during the period 1978-82. Thereafter the increase
in 03 was considerably slower. This is assumed to be at
least partly related to changes in meteorological conditions,
in particular to periods of enhanced cloudiness. The average
growth rate for the period 1978-91 amounts to 0.9 ppbv
yr -I. A time series of similar shape and comparable trend
has been obtained for the station Wank (growth rate 0.8
ppbv yr-l). Near the ground, at Garmisch, no trend is indi-
cated. Similar to Zugspitze (cf. Fig. 1) interannual varia-
tions with a period of 4 - 5 years are also present in the
time series of the two lower-laying stations. The ozone con-
centrations observed on the floor of the valley are the result
of source and sink relations that are strongly influenced by
local meteorology. This is evidenced by Figure 2, where the
average diurnal cycles for the individual stations are shown.
80
70
60
50
_ 4o
30
20
10
0
Zugspitze
78 80 82 84 88 8B 9D 92
TIME
Fig. 1. Monthly mean values of 03 at Zugspitze and 12-
month moving averages (thick curve) together with
trend estimates. The slope of the straight solid line
corresponds to an average growth rate (1978-91) of
0.92 ppbv yr -I. The non-linear regression function
(dotted line) indicates an increase in seasonal
amplitudes with growth rates of 1.2 and 0.7 ppbv
yr-" obtained for the summer maxima and winter
minima, respectively (slope of dashed lines).
II
https://ntrs.nasa.gov/search.jsp?R=19950004181 2020-06-16T11:48:32+00:00Z
In contrast to the valley, at the station Zugspitze local in-
fluence on the diurnal shape of ozone is only observed
during spring and summer. For most of the time, the 0 3
concentrations at this site can thus be regarded as represen-
tative of ozone levels characteristic of the lower free tropo-
sphere.
A temporal increase in the seasonal amplitudes is ex-
pected as a consequence of the seasonal dependence of
photochemical ozone production. In order to test whether
such an increase was reflected by the monthly means, a
non-linear regression function with a linear gain term for
the amplitudes was applied to the data. The resulting least
squares fit has indicated an increase in seasonal amplitudes
(peak-to-peak) of 4.6 ppbv over the whole time period.
Moreover, for Zugspitze the calculations have suggested an
average cycling time of 5.6 years for the interannual varia-
tions.
For a more detailed study of the impact of lower
tropospheric photochemical 03 production at the mountain
sites, trend estimates have been performed on seasonally
differentiated percentiles (5th, 25th, 50th (=median), 75th,
and 95th) using linear regression. Figure 3 summarizes the
results. Under conditions of enhanced photochemical 0 3
production, i.e. is for spring and summer, the high ozone
concentrations, as characterized by the 95th percentiles,
have been increasing at a rate which is nearly twice the rate
of the low concentrations. Accordingly, the rate of increase
estimated for high summer concentrations is considerably
greater than the rate determined for high winter concen-
trations (Fig. 3).
In Figure 4 the seasonal variations of 0 3 at Zug-
spitze are depicted. The maximum of the seasonal cycle is
observed in spring, which is in agreement with observations
reported from other European locations (cf. Logan, 1985).
For the first half of the measuring period, the seasonal
amplitude is smaller than for the second half. From a differ-
ent approach this confirms the above finding that the ampli-
tudes of the annual cycle have been increasing due to en-
hanced concentrations in spring and summer.
The strong impact of solar radiation and thus of
photochemistry on the ozone concentrations can be seen
from Figure 5. Daily maxima have been classified
according to the relative sunshine duration (RSD). Under
conditions of cloudy sky (RSD < 1% of the time), the
annual cycles at the mountain stations show similar levels.
60
4o
30-
o
o 20-
10-
.,.,w
Winter
Autumn
Time of cycle: 0:00 - 24:00 [CET]
Fig. 2. Average diurnal cycle of 03 (1986-88) at the
stations Garmisch, Wank, and zugspitze for the dif-
ferent seasons.
12
10
& 8
_ 6
_ 2
°
o -2
5 -6
_ -8
0
t_ -10
-12
- 14
JAN F _ APR MAY JUN JUL AUG S P OCT NOV DEC
MONTH
Fig. 4. Average seasonal variations (calculated from the dif-
ference between monthly mean value and 12-month
moving average) of 0 3 at Zugspitze for different
time periods (79-90; 79-85 and 86-90).
2.4
2.2
2
SPRING
SUMMER
.._ 1.4
c_
it:::
_ o4
0.2
0
-.- 0.2
WINTER []
1-
|i
H II
|I
* L! !
1R
Ilfl ° u
AUTUMN
_[
-o., .4 I go I "_'_ I _' I ='o I _,'_ g I go I _'_ I g I _'o I _'_ I
2_ 7_ Max. 2_ 7_ Mox. 2_ 7_ Mox. 2_ 7_ Mox.
[3er centilcs: El. 25, 50(medien), 75. 95 _ / E_
ZUg_pitz_ Wonk (7;or rni_ c h
Fig. 3. Ozone trend (1978-90) at the mountain sites (Zugspitze, Wank) as a function of season and statis-
tical parameters. For Garmisch (floor of the valley) none of the rates shown by the bars is statis-
tically significant.
12
Peak ozone levels in the valley (at Garmisch) are lower by
about 12 ppbv. In contrast, under conditions of intense solar
radiation (RSD > 80 %), the peak of the distribution for
Garmisch even surpasses the one for Zugspitze, which re-
flects a significant contribution from locally produced
ozone. For RSD > 80 %, however, highest 03 concen-
trations are observed at Wank, i.e. at an elevation of about
1000 m above ground. This supports the finding from
model calculations (lVlcKeen et al., 1989) that optimum
conditions for photochemical ozone production can be ex-
pected around this altitude.
3
80
70
60
50
4O
30
2O
10
0
RSD <1 X
: RSD >80
Ga,RMtSC H
WANK ZUGSPITZE
MONTH OF YEAR
WANK
ZUGSPn'ZE
Fig. 5. Average annual distributions of dally Oa maxima
(.1978-91)'for low and high relative sunshine dura-
tion (RSD < 1% and > 80 %).
3. SOUTHERN HEMISPHERIC RESULTS
The time series of 03 at Cape Point as given by the
monthly means (Oct. 82 - Dec 91) is shown in Figure 6.
The shape is characterized by both seasonal cycling and
great interannual variability. Maximum 03 concentrations
occur in austral winter (July) and minima in summer (Janu-
ary). The annual means of 03 center around 21 ppbv with
average seasonal amplitudes of about _+7 ppbv. So far, the
monthly means do not indicate any long-term trend of 03 at
Cape Point. This is confirmed when the monthly means for
the individual seasons are considered separately. However,
in view of the strong interannual variabilty and the severe
data gaps, the results obtained so far should be regarded as
preliminary.
In Figure 7 the average annual cycle of ozone is
shown. As is generally assumed for these southern latitudes,
the cycle of surface ozone is mainly controlled by two types
of processes, i.e. stratosphere/troposphere exchange (Liu et
al., t980) as well as photochemical ozone destruction
(Fishman et al., 1979). The latter process, which is closely
related to the annual cycle of solar UV radiation (Fig.7), is
assumed to lead to the 0 3 minima observed around January.
In contrast to the rather symmetric shape of the UV cycle,
the ozone distribution with its maximum in July shows a
slight shoulder between August and November.
The ozone distribution thus suggests that additional
processes might contribute to its shape. One such process
could possibly be biomass burning. This seems to be im-
plicated by the following findings: Firstly, carbon mon-
oxide, which has been measured at Cape Point since 1978
(Seiler et al., 1984; Brunke et al., 1990), shows an annual
distribution with a maximum around September/October
(Fig. 7). The CO maximum thus coincides with the shoul-
der observed in the 03 distribution during austral spring.
After various interpretations have been put forward to
explain the annual cycle of CO (Khalil and Rasmussen,
1984; Seiler et al., 1984; Fraser et al., 1986), recent publi-
cations have largely attributed the occurrence of the CO
maximum to biomass burning (Heintzenberg and Bigg,
1990; Fishman et al., 1991, and reference therein). Second-
ly, Fishman et al. (1991), who studied upper tropospheric
ozone from satellite data, have shown that ozone which
originates from biomass burning also displays annual
cycling with increasing concentrations from July to Novem-
ber. According to the results presented by Fishman et al.
(1991), the rise of integrated 03 in the troposphere over
Cape Point partly parallels the shape of the CO distribution
observed at ground-level, but is not in phase with the sur-
face ozone observed at Cape Point (maximum in July). We
thus speculate that the seasonal increase in ozone in the
upper troposphere, which originates from biomass burning,
does put its mark on the distribution of surface 03 at Cape
Point during the months August to November.
5O
2"
8
'_0
3D
2D
10
0 i i i i i J i i i i L
82 83 _,4 B5 B6 87 _]8 8g 90 g 1
YEAR
Fig. 6. Monthly means of 03 as obtained for Cape Point
(34°S, 18°E) between Oct. 82 and Dec. 91.
Periods of data loss, which are due to instrumental
failures, have been interpolated by values from the
average annual cycle (dotted line).
30 70
25
2O
8
10
• ', C0
,,' ' 65
dAN FEB MAR APR MAY dUN JUL AUG SEP OCT NOV DEC
MONTH
60
55 ,::x
o
5O
,I-5
¢0
Fig. 7. Average annual cycles of 03 (1983-91), UV radia-
tion (1989-91) and CO (1979-91) at Cape Point.
13
At Cape Point, the annual peak-to-peal{ anaplitudes
of 0 3 and CO (Fig. 8) show a close relationsnip tcorrela-
t.ion coefficient of 0.9). This result has not yet been ana-
lyzed in detail; nonetheless it seems to support the view of
either partly common sources or partly common transport
mechanisms for 0 3 and CO. Interestingly, the highest
amplitudes were observed for E1-Nifio years, when among
others the tropical meteorology and thus transportproy.___.ses
are strongly affected. Such a possible impact of EI-N_fio
events on trace gas levels observed at Cape Point seems to
merit further attention when more data are available.
4O 2O
o.
_.20
E
.<
I
0
o 10
83 84 85 85 87 88 89 90 91
YEAR
P"_ COE_ 03
10 -_
E
I
5 _
Fig. 8. Comparison between the annual peak-to-peak ampli-
tudes of 03 and CO at Cape Point. The data yield a
correlation coefficient of 0.9.
Logan, J.A., 1985: Tropospheric ozone: Seasonal behavior,
trends, and anthropogenic influence. I, Geophys.
Res. 90, 10463-10882.
Low, P.S., P.M. Kelly, and T.D. Davies, 1992: Variations
in surface ozone over Europe. Geophys. Res. Lett.
19, 1117-1120.
McKeen, S., D. Kley, and A. Volz, 1989: The historical
trend of tropospheric ozone over Western Europe:
A model perspective. In "Ozone in the Atmo-
sphere', R.D. Bojkov, P. Fabian (eds.), pp. 552-
556.
Penkett, S.A., 1991: Changing ozone - Evidence for a
perturbed atmosphere. Environ. Sci. Technol. 25,
631-635.
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troposphere, simultaneously recorded at
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Hofmann, E.G. Dutton, T. Deshler, W.T. Sturges,
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Harris, 1991: Decrease of summer tropospheric
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REFERENCES
Brunke, E.-G., H.E. Scheel, and W. Seller, 1990: Trends
of tropospheric CO, N20 and CH4as observed at
Cape Point, South Africa. Atmos. t:nviron. 24A,
585-595.
Fishman, J., S. Solomon, and P.J. Crutzen, 1979:
Observational and theoretical evidence in support of
a significant in-situ photochemical source of
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Fishman, J, K. Fakhruzzaman, B. Cros, and D. Nganga,
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Southern Hemisphere deduced from satellite
analyses. _ 252, 1693-1696.
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monoxide and methychloroform in the Southern
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Measurements of lower tropospheric ozone at mid-latitudes of the Northern and Southern Hemisphere

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