SOLA, 2008, Vol. 4, 117 120, doi:10.2151/sola.2008 030

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Spatiotemporal Variation in Tropospheric Column Ozone
over East Asia Observed by GOME and Ozonesondes
S. Hayashida1, N. Urita1*, K. Noguchi1, X. Liu2, 3, and K. Chance2
1
Faculty of Science, Nara Women’s University, Nara, Japan
2
Atomic and Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics, Cambridge,
Massachusetts, USA
3
Goddard Earth Sciences and Technology Center, University of Maryland, Baltimore, Maryland, USA

Abstract
We analyzed tropospheric column ozone (TCO)
observed by the GOME-1 (Global Ozone Monitoring
Experiment; European Space Agency, 1995) and ozonesondes to determine the spatiotemporal variation in
TCO over East Asia from 1996 to 2003. An enhanced
TCO belt (E-TCO belt) was observed at approximately
35°N throughout the year. The E-TCO belt moved
northward from winter to summer and southward fromsummer to winter, strongly suggesting connection withthe seasonal variation of meteorological conditions. The
large enhancement of TCO found over central China insummer suggests that there is significant outflow ofozone from that region. This study presents the firstsatellite-derived comprehensive picture of the TCO
spatiotemporal variation over East Asia, which has notbeen obtained from limited ground-based measurements.

1. Introduction
Tropospheric ozone plays important roles in controlling the chemical composition of the troposphere and influencing the energy budget of the Earth’s atmosphere.
According to a recent IPCC report (2007), radiative
forcing of tropospheric ozone is estimated to be thethird most important component among the greenhousegases. In Asia, recent increases in energy consumption
have led to a significant amount of emissions of ozone
precursors (Ohara et al. 2007). Therefore, monitoring of
spatiotemporal variation of tropospheric ozone over
Asia is now of a great concern.
Satellite measurements have the advantage of providing continuous monitoring of ozone over a wide
spatial range, thereby allowing the analysis of spatial
and temporal variations in ozone over large areas.
However, the separation of the relatively small tropospheric component (~10%) from the total column ozone
has been difficult. Liu et al. (2005, 2006) derived TCO
directly from Global Ozone Monitoring Experiment(GOME) ultraviolet measurements, adapting the spectroscopic technique proposed for GOME and SCIAMACHY
measurements (Chance et al. 1997). Noguchi et al. (2007)
validated the GOME-O3 data set by comparing it withozonesonde data in Japan. In this study, we apply the
GOME-O3 with ozonesonde data from four stations inJapan to determine the spatial distribution and temporal variation in TCO over East Asia.
Corresponding author: Sachiko Hayashida, Department ofInformation and Computer Sciences, Faculty of Science, Nara
Women’s University, Kitauoyanishi-machi, Nara-city 630-8263,
Japan. E-mail: sachiko@ics.nara-wu.ac.jp.
*Present affiliation: Mitsubishi Electric Limited, Itami, Japan.
©2008, the Meteorological Society of Japan.

2. Data analysis
We use version 2 of the GOME-derived TCO data set,
retrieved by Liu et al. (2005). The GOME-O3 version 2
data set is similar to the version 1 data set validated by
Noguchi et al. (2007), but has been extended from 2000
to June 2003 after degradation correction of the GOME
reflectance spectra, which results from filling voids ofthe coating of the scan mirror with contaminants (Liuet al. 2007). The spatial resolution of GOME-O3 isnormally 960 × 80 km2. We archived the swath data forevery orbit onto a 1° × 1° grid and averaged the data bymonths. Although GOME retrievals derive ozone profiles with 4 7 layers in the troposphere, the retrieved
vertical profiles are less reliable in the troposphere (Liuet al. 2005) relative to the integrated TCO. We use only
TCO in this study. Tropopause heights from the
National Centers for Environmental Prediction (NCEP)
reanalysis data were used to determine TCO. We use
GOME-O3 for the period from April 1996 to June 2003,
but excluded the period from July 1995 to March 1996.
The ozonesonde data are provided by the Japan
Meteorological Agency (JMA) for the four stations of
Sapporo (43.1°N, 141.3°E), Tsukuba (36.1°N, 140.1°E),
Kagoshima (31.6°N, 130.6°E), and Naha (26.2°N, 127.7°E). For consistency with the GOME data set, we also
apply the NCEP-based tropopause heights to the ozonesonde data when deriving TCO.

3. Enhanced TCO belt observed with GOME
The global maps of GOME monthly mean TCO in
Fig. 4 of Liu et al. (2006) depict an enhanced TCO belt
(hereafter, E-TCO belt) in the mid-latitude Northern
Hemisphere (NH), which is particularly evident insummer. Figure 1 shows the GOME TCO maps over East
Asia in June and December 1997. Over the area along
the Pacific Rim, the E-TCO belt moves northward fromwinter to summer and southward from summer towinter.
We define the latitude of the belt (Lb) as the latitude
where the TCO obtains its maximum value along a longitude. The Lb values between longitudes 125 140°E do
not depend significantly on longitude within the area
analyzed here. Thus, we consider the Lb value at 130°E
to be the representative value for the analyzed area.
Figure 2a presents the time-latitude cross-section of
TCO along 130°E, with Lb values indicated by dots.
Clear seasonal variation in the TCO can be seen in thebelt, with a summer maximum and winter minimum.
The latitude of the E-TCO belt (Lb ) is low (~27°N) in
winter and shifts higher (~45°N) in summer.
Figure 2b illustrates the time series of the maximum
TCO along 130°E (red), as well as Lb values (blue). The
time series of Lb clearly shows that the E-TCO beltreaches its northernmost latitude (Lb at ~40°N) in118

Hayashida et al., Tropospheric Ozone over East Asia

Fig. 1. Maps of GOME monthly mean tropospheric column ozone (TCO) over East Asia in (a) June and (b) December 1997.

August, whereas the maximum TCO is greatest in June.
Year-to-year variability can also be seen in the amplitude of the seasonal variation in Lb and maximum TCO.

4. Comparison of seasonal variation in
GOME- and ozonesonde-observed TCO
The lower panels of Fig. 2 show time series of ozonesonde-observed TCO at the four stations in Japan (blacklines), which are located between 26.2° and 43.1°N (theirlatitudes are indicated by dotted lines in Fig. 2a). For
comparison, GOME-derived TCO values at the same gridwith the ozonesonde station are plotted (blue lines). As
already reported by Noguchi et al. (2007), the ozonesonde-observed TCO values indicate good correlation
with GOME-derived TCO values. The time series of
GOME-derived TCO at 130°E and at the latitude of eachozonesonde station are also shown by red lines. Good
consistency of red and black lines suggest that ozonesonde-observed TCO values can be interpreted as crosssections of the spatiotemporal picture of the GOMEderived TCO along the dotted lines indicated in Fig. 2a.
Sapporo is located north of the peak latitude of the
E-TCO belt throughout the year. Thus, the TCO peak of
the belt is not detected at Sapporo. The seasonal variation at Sapporo shows a broad peak in June/July, withthe maximum value less than the E-TCO maximum.
Tsukuba is located approximately in the middle of theenhanced TCO belt in June; thus, the phase of theseasonal variation at Tsukuba is almost consistent withthat of TCO-maximum, but with larger amplitude.
Although pollution from nearby Tokyo may occasionally perturb the tropospheric ozone at Tsukuba (Logan
1999), the seasonal variation shown in Fig. 2d is generally as expected at the latitude of Tsukuba. Kagoshima
is located at approximately the southern edge of the
major part of the E-TCO belt, and the peak season isearlier than in Tsukuba and Sapporo. The southernmost
station of Naha shows a pattern well known for the
lower latitudes of East Asia, namely a spring maximum
and summer minimum (e.g., Liu et al. 2002). The E-TCO
belt is situated far north of Naha throughout the year,
and the maximum value of the E-TCO belt is notobserved there (Figs. 2a,f).

5. Discussion
The retrieval algorithm for TCO uses climatologicalozone profiles to initialize and regularize the retrievals(Liu et al. 2006). The retrieved data are similar to apriori data, meaning that the a priori data intrinsically
include the seasonal variation in the tropospheric ozone.
However, the a priori data are not dependent on longitude and are set to be constant for the years analyzed;
therefore, we can consider the spatiotemporal patternof TCO (Fig. 1) to be its real variation. We have also
analyzed the seasonal variation in TCO derived from a
combination of Ozone Monitoring Instrument (OMI) andMicrowave Limb Sounder (MLS) data (Ziemke et al.
2006). The technique for deriving tropospheric ozone
was based on the tropospheric ozone residual (TOR)
method. This analysis confirmed that the features of
TCO seasonal variation in 2004 and 2005 are similar to
those shown in Fig. 2a (figure not shown). The consistency of the two satellite-based data sets and the similarity of the TCO seasonal variation in GOME-O3 andozonesonde data (Fig. 2) demonstrate the reliability ofthe pattern of TCO seasonal variation shown in Fig. 2a.
Previous studies have investigated the seasonalvariation in TCO at the four stations in Japan as a combination of transport effects and chemical production/
loss processes. Our analysis presented the first satellitederived comprehensive picture of the TCO spatiotemporal variation over East Asia as indicated in Fig. 2athat has never been obtained before. The time series ofthe ozonesonde-TCO at each station can be interpreted
as a cross section of the spatiotemporal picture of the
GOME-derived TCO (Fig. 2a). In other words, thefeatures of seasonal variation in TCO differ at eachstation based on a combination of the temporal evolution of ozone concentration and the latitudinal shift ofthe E-TCO belt.
The enhancement of TCO could be attributed to thefollowing three effects: ozone intrusion from the stratosphere; outflow from polluted regions, especially China;
and the effect of biomass burning in Southeast Asia
(e.g., Liu et al. 2002, Sudo and Akimoto 2007). We havecarefully examined TCO values in the lee of central
China where the NO2 concentration is very high (Richteret al. 2005), and found strong enhancement of TCO near
the coastline of and over the Yellow Sea, and around
Tsushima Island in particular. The ozone enhancement
is very likely connected to ozone production in the

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Fig. 2. (a) Time-latitude cross-section of tropospheric column ozone (TCO) along 130°E. Black dots indicate the latitude of the
maximum TCO (Lb). Dotted lines correspond to the latitudes of the four ozonesonde stations. (b) Time series of maximum TCO(red), and the latitude of the E-TCO belt (Lb: blue). (c) (f): (black) Time series of TCO based on ozonesonde observations at four
stations in Japan: (c) Sapporo (43.1°N, 141.3°E), (d) Tsukuba (36.1°N, 140.1°E), (e) Kagoshima (31.6°N, 130.6°E), and (f) Naha (26.2°N, 127.7°E).(red) Time series of GOME-O3 at 130°E and at the latitude of an ozonesonde station. (blue) Time series of GOMEO3 at the same grid with the ozonesonde station. For Kagoshima the two time series of GOME-O3 are identical. Shaded periods
refer to El Ni
no episodes.

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Hayashida et al., Tropospheric Ozone over East Asia

polluted air from China or the Korean Peninsula. Somemodel studies utilized tagged ozone experiments and determined that the monsoonal flow transports Asianozone towards the northeast in summer in the lower andmiddle troposphere (e.g., Liu et al. 2002). Zhu et al.
(2004) also reported connection of surface ozone over
Waliguan station (on the northeastern edge of the
Tibetan Plateau) with the monsoon wind system. On theother hand, interannual variability in TCO at low
latitude (~20°N) is correlated with the phase of El Ni
noyear (shaded period in Fig. 2), suggesting the effect of
biomass burning (Fishman et al. 2005).
Naja and Akimoto (2004) investigated the long-term
trends in tropospheric ozone using ozonesonde data collected from four stations in Japan (Naha andKagoshima, in particular), but they did not find any
specific trend in TCO after the 1990s. We confirmed
their results by applying a similar approach. However,this study suggests that Naha is not a suitable station to
detect the effect of air pollution from China because
Naha is located far south of the E-TCO belt. Data from
Kagoshima are much more appropriate for suchresearch purposes. However, the approach based on
backward trajectory calculations would be insufficient
to reveal the ozone trend over East Asia, because theTCO data at the Japanese stations are not always representative over the region through the year. As shown in
Fig. 1, the enhancement of TCO depends on latitude, sothat some stations may fail to detect the air mass withhigh ozone in some period in a year. Besides, the mostenhanced TCO near Oki and Tsushima Islands (Fig. 1a)is not detected by any ozonesonde measurement. This
study suggests that additional ozonesonde measurements at or around Oki Island or Tsushima Island,
where the maximum TCO was detected, are desirable tomonitor tropospheric ozone over East Asia. It is alsosuggested that we need a comprehensive data set that
includes ground-based and satellite-based measurements to determine the long-term trend of TCO.

6. Summary
We compared GOME- and ozonesonde-TCO at Naha,
Kagoshima, Tsukuba, and Sapporo stations in Japan todetermine the spatial distribution of and temporal variation in TCO over East Asia. We focused on data from1996 to 2003 and investigated the seasonal variation in
TCO.
Our analysis shows an enhanced TCO belt at approximately 30°N that moves northward from winter tosummer and southward from summer to winter, corresponding to the seasonal variation of meteorologicalcondition. The E-TCO belt reaches its northernmost
latitude (~40°N) in August, whereas the TCO reaches amaximum in June, when photochemical production ismost vigorous. The seasonal variation in TCO derived
from ozonesonde measurements is consistent with the
behavior of the GOME TCO at the same latitude. Our examination of the outflow of ozone from central China
confirms the significant enhancement of TCO over that
region. Additional ozonesonde measurements at or
around Oki Island or Tsushima Island, where themaximum TCO is found, are desirable to monitor
tropospheric ozone, especially as related to air pollution
from China and the Korean Peninsula.

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Manuscript received 17 July 2008, accepted 6 October 2008
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