Journal of Atmospheric Chemistry 29: 179–194, 1998.
c 1998 Kluwer Academic Publishers. Printed in the Netherlands.
179
Trace Gas Measurements Between Moscow and
Vladivostok Using the Trans-Siberian Railroad
P. J. CRUTZEN1 , N. F. ELANSKY2 , M. HAHN1 , G. S. GOLITSYN2 ,
C. A. M. BRENNINKMEIJER1, D. H. SCHARFFE1 , I. B. BELIKOV2 ,
M. MAISS1 , P. BERGAMASCHI1 , T. RÖCKMANN1 , A. M. GRISENKO3 and
V. M. SEVOSTYANOV3
1
Max Plank Institute for Chemistry, Atmospheric Chemistry Division, Mainz, Germany
Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia
3
Research Institute of Railroad Transport of Russia, Moscow, Russia
2
(Received: 17 March 1997; in final form: 23 July 1997)
Abstract. Using a laboratory wagon traveling along the Trans-Siberian railroad, O3 , NO, NO2 , CO,
CH4 , SF6 and black carbon aerosol have been measured during the summer of 1996. The expedition
from Niznij Novgorod (500 km east of Moscow) to Vladivostok (and back to Moscow) has shown
the great potential of the train method; here the first results are presented and discussed. A wealth of
boundary layer air data was obtained during the over 18000 km travel without serious contamination
problems from the electric train itself. The diurnal O3 cycle peaked generally below 50 nmole/mole,
showed the effects of changes in J (NO2 ), and often dropped to a few nmole/mole at night time
during inversions. Over the vast Siberian lowlands situated between the Ural mountains and the
river Yenisey, CH4 levels were consistently elevated at around 1.95 mole/mole, which we mainly
attribute to wetland emissions. Over eastern Siberia, however, CH4 levels were generally lower at
1.85 mole/mole. In contrast, over the west Siberian lowlands, CO levels were relatively low, often
reaching values of only 110 nmole/mole, whereas over eastern Siberia CO levels were higher. Very
high CO levels were detected over a 2000 km section east of Chita, along the river Amur, which
represented an enormous polluted air mass. 14 C analysis performed on several CO samples confirms
that the origin was biomass burning. SF6 , which was measured as a general conserved tracer, showed
an eastward attenuation from 4.0 to 3.9 pmole/mole, with peaks in a number of places due to local
Russian emissions.
Key words: tropospheric chemistry, ozone, Russia, trans-Siberian railroad, Siberia, carbon monoxide,
methane, nitrogen oxides, trace gases, atmospheric composition.
1. Introduction
Comparatively few measurements of atmospheric trace gases are available for the
vast continental area of Russia, of which Siberia (12:8 106 km2 ), situated east
of the Ural mountain range, constitutes a major part. However, there are many
good reasons for having a closer look at atmospheric composition and chemistry
in these regions. For instance, western Siberia’s abundant natural gas fields have
been implied repeatedly in the changes of global methane (e.g., Dlugokencky et
al., 1994). Indeed, escape of natural gas into the atmosphere during exploitation
and distribution under difficult conditions can be large, and losses of significance
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to the global budget are estimated by Andronova and Karol (1993) for exploitation
areas in the former Soviet countries. Besides these man made sources, the huge
Siberian tundra wetlands stretching from the Urals to the river Yenisey where the
Siberian highlands start, harbor an important, but inadequately quantified, natural
source of methane.
Because of the importance of methane both as a greenhouse gas and as major
player in atmospheric chemistry, further research is necessary, and several groups
already undertake measurements of methane in Russia (e.g., Tohjima et al., 1996;
Sugarawa et al., 1996; Nakayama, 1995; Inoue et al., 1995). The first questions
obviously are what CH4 concentrations and fluxes actually occur. Further, it would
be useful to be able to separate the CH4 contributions from wetlands from those
due to natural gas exploration, distribution and use. Using an aircraft Tohjima et
al. (1996) have surveyed CH4 at different levels over west Siberia and they find
significantly enhanced CH4 levels attributed to wetland emissions.
Another major rationale to intensify atmospheric research in Siberia is the
important role of boreal (sub-arctic) forests (of which the Siberian forests form a
major component) in the global carbon dioxide budget, driving inter-annual and
perhaps important longer term carbon dioxide fluctuations (Ciais et al., 1995). The
vast forests and possibly the tundra as well, may also be large natural sources of
volatile organic carbon, which strongly influence chemistry of the boundary layer.
Furthermore, the forests also are of importance because of the occurrence of large
scale forest fires, by which major quantities of trace gases and aerosol are released
into the troposphere.
Little is known about O3 and NOx variations across Siberia. With an area of
12.8 million km2 and 32 million inhabitants most of Siberia may qualify as a
pristine region, where near to natural surface ozone levels should prevail. However,
there are also a number of industry and population centers with strong NOx , CO,
hydrocarbon and other trace gas emissions which affect O3 distribution.
Altogether we see a vast, important region, for which there are few observational
data. We thus have started to use for the first time the Trans-Siberian Railroad
between Moscow and Vladivostok for probing the chemistry of the boundary layer
atmosphere across the vast area of Russia, within the framework of project TROICA
(Trans-Siberian Observations on the Chemistry of the Atmosphere). Because the
Trans-Siberian railroad system is electrified contamination from locomotives is
largely excluded.
The railroad and its environs basically determine the quality and type of information one can obtain. Foremost measurement is limited to the boundary layer
where at nighttime trapping of contaminants can occur due to occurrence of inversions. Further, a wide variety of types of contamination occasionally can affect
the data. Even though the effects of the train itself are small, episodic variable
pollution from other trains using the railroad cannot be avoided. Then there are
of course the many cities, industries and populated areas traversed. Finally, for
certain sections, the railroad runs parallel to major connecting roads. No detailed
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181
data on their traffic density is available. A complete analysis of all these effects will
require much time. The present expedition, TROICA 2, followed a pilot study in
November–December 1995 under severe winter conditions (Crutzen et al., 1996).
We now describe this summer 1996 expedition and present and analyze some of
the features of the observations.
2. The Laboratory Railroad Wagon
The dedicated laboratory wagon (Research Institute of Railroad Transport of Russia), equipped with the instruments and housing 8 staff, was coupled directly to the
pulling locomotive of a passenger express train. Air intakes were mounted on the
side, 3 meter above the rail. The typical train speed was 80 km/hour, under which
conditions no contamination from wagons or locomotive was noticeable. Also,
no adverse effect from the downward venting locomotive engine cooling system,
which was used only during steep climbing, has been noted. Power was mainly
supplied by a main generator driven by the wheels of the wagon feeding into a
battery buffer. DC-AC inverters have been used to obtain the 230 V AC necessary
for most equipment. Due to some power supply problems, measurement with some
apparatus was interrupted occasionally. Also, some problems occurred due to earth
loops in the data acquisition system, which had to collect data from a range of
equipment.
3. Equipment
A brief overview of the equipment is given in Table I. The continuous analyzers
and automated gas chromatograph for CH4 were connected, together with the
GPS system, to PC based data loggers. For ozone, we used two analyzers in
parallel (Dasibi 1008 RS and RH). The overall error is estimated to be about
3 nmole/mole, and an internal calibration was used. NO and NO2 are more difficult
to measure and a standard photochemical analyzer was employed. The data near
and below 1 nmole/mole have a large error associated with them because of the
bad signal to noise ratio at the low end. Such data should thus mainly be seen as
qualitative indicators. For CH4 a Shimadzu 8A gas chromatograph with a flame
ionization detector was used. The reproducibility is within 1%, and the scale used
is made to match values for a cylinder calibrated by NOAA-CMDL in Boulder.
For CO a modified Thermo Environmental 48S instrument was used which was
calibrated every day using a gas mixing system. After each 23 minute measurement
interval, zero signal was recorded for 7 minutes. Because this analyzer required
a considerable recovery time after a power interruption, there are some voids in
the CO record. The error obtained is estimated to be approximately 10%. Black
carbon aerosol was measured using an aethalometer developed at the Institute
of Atmospheric Physics, based on the common principle of light absorption. Its
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Table I. Overview of equipment
Apparatus
Parameter measured
Resolution
UV photometer
Photochemical
Gas chromatograph fid
Gas filter correlation
Aethalometer
68 aluminum cans 5 bar
18 steel cans 5 bar
15 alum. cylinders 50 bar
Global positioning system
Meteorological
Radiation
Data acquisition (IAP)
O3
NO and NO2
CH4
CO
Black carbon aerosol
CH4 , SF6
CH4 , CO and SF6
CH4 , CO and 13 C, 18 O, 14 CO, SF6
Coordinates, altitude
T, rel. hum., solar radiation
Global, J (NO2 )
Pentium and 386 (Intel) PC
2 km
2 km
10 m
5 km
5 km
3 km
4 km
80 km
200 m
performance is well characterized by comparisons with other instruments. The
error is 10%.
Air samples were collected by means of a diaphragm pump and a high pressure
oil-free compressor in three types of containers. Many low cost aluminum cans
were used as a back-up for obtaining concentration data for CH4 . Unfortunately,
the quality was not sufficient for additional analysis apart from SF6 , for which
excellent results were been obtained. The (fewer) large samples collected allow
for isotopic analysis of CO and CH4 which can give useful information about the
causes of concentration increases.
The SF6 analyses were carried out at the Institut für Umweltphysik (University
of Heidelberg). Analytical system and absolute calibration are the same as used
and described by Maiss et al. (1996), showing an analytical precision of 0.5%
for SF6 .
Solar radiation measurement included integral solar flux, and J (NO2 ). Because
it was not possible to measure the upward J (NO2 ) flux on the train it was estimated
from the downward flux using results from separate experiments. For a range of
zenith angels, the upward flux was 5 to 8% of the downward flux. Because of
some calibration inconsistencies the data conservatively are estimated to have an
uncertainty of 15%.
Of importance is the time resolution of the various analyzers, and the degree of
integration used for interpreting the data in relation to the temporal environmental
fluctuations which in turn depend on the actual train speed (Table I). Fast sampling,
at 2 minute intervals, is possible with the CH4 gas chromatograph, where the
sampling loop space velocity corresponds to a reaction time of a second. The other
extremes are the large samples used for isotopic analysis for CH4 and CO, which
integrate over about 1 hour.
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4. The Trans-Siberian Railroad
The Transsib (finished in 1916) leads from Moscow to Vladivostok over a distance
of 9313 km (Figure 1). Its first 1500 km towards the Ural mountain range traverse the
European part of Russia, which is the most densely populated and industrialized
part of the country. However, returning to Moscow, the Transsib took the more
northerly route via Kirov, thus circumventing the more densely populated area due
east of Moscow. Overall this area is relatively flat. The Ural mountain range, which
is a system of shallow (highest peak 1885 m) N–S trending parallel ridges forms
the natural boundary with west Siberia, which consists of a vast swampy forested
plain, bordered in the south by Kazakhstan. At 4100 km, near Krasnojarsk, the
mid-Siberian highlands start where the railroad takes a southern track, traveling
south of Lake Baikal, to subsequently cross several mountain ridges, upon which
it runs roughly parallel to the river Amur, part of which forms the border with
China, to Khabarovsk, where it sharply turns south for the remaining 500 km to
Vladivostok at the Sea of Japan.
The population of Siberia is chiefly concentrated in the narrow southern belt
along the railroad, and by no means should the train data be seen as representative
for the enormous area of Siberia. However, even though human settlement concentrates along the railroad, the sheer vastness of the continent means that many
sections of the railroad runs through pristine areas. Frequently, the Transsib runs
over many hundreds of kilometers through terrain without any settlements or roads.
5. The Expedition
Equipment was installed and tested at Niznij Novgorod (500 km east of Moscow),
where the journey started on 25 July. Automated measurement started near Sverdlovsk after some initial delay due to technical problems. Routine exchange of
the electric locomotives occurred every 300 to 400 km, amounting to about 60
locomotive changes during the near 17 600 km covered. Approximately a total of
200 stops at railroad stations were made. The wagon arrived in Vladivostok on
2 August, and departed for the return journey on 6 August. The total duration
of the day and night travel was 330 hours. For most of the section Khabarovsk–
Vladivostok diesel locomotives have been used, excluding measurements. Both
legs of the trip were along the same track, except for the section Sverdlovsk to
Omsk, which ran via Kurgan and Petropavlovsk traveling east and more northerly
via Tyumen returning west.
Trains approaching from the opposite direction form an intermittent source
of contamination. Between Novosibirsk and Krasnoyarsk their average frequency
peaked at 5 hour,1 and dropped to 2 hour,1 in eastern Siberia. Most of this traffic
is local, and fortunately uses the electric overhead power. The distance between
trains running in the same direction ranged between 30 and 75 km. Overall little
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Figure 1. Map of Russia between Moscow and Vladivostok, with the Transsib. The interruptions in the track drawn here are 500 km markers. For traveling east to Vladivostok (9313.06),
the general wind direction is plotted above, for traveling west back to Moscow, below the track.
Continuous measurements started at 2000 km east of Moscow. Between Sverdlovsk (1833) and
Omsk (2733), traveling east, the southerly route via Kurgan (2193) and Petropavlovsk (2459)
has been taken. Traveling west, the route went north via Tyumen (2161) through a remote area.
Between Kurgan, via Petropavlovsk, and Omsk, the Transsib runs parallel to the M 51 until
Novosibirsk (3359), where it follows the M 53 and M 55 until beyond Ulan Ude (5673), past
Lake Baikal. Between Moscow and Sverdlovsk (TW), and between Ulan Ude and Khabarovsk
(8549), only smaller roads follow the Transsib, or no roads at all. Between Khabarovsk and
Vladivostok, the Transsib runs parallel with the M 60. The new names for the cities Sverdlovsk
and Kirov are Ekaterinburg and Vjatka respectively.
City names and distances from Moscow: Ya, Yaroslavl, 292; Ni, Niznij Novgorod, 500; Ki,
Kirov, 973; Pm, Perm, 1452; Sv, Sverdlovsk, 1833; Ty, Tyumen, 2161; Ku, Kurgan, 2193;
Pe, Petropavlovsk, 2459; Om, Omsk, 2733; No, Novosibirsk, 3359; Kr, Krasnojarsk, 4122;
Ka, Kansk, 4369; Tu, Tulun, 4819; Ir, Irkutsk, 5208; Ul, Ulan Ude, 5673; Ch, Chita, 6222;
Ur, Urusha, 7234; Be, Belogorsk, 7890; Kh, Khabarovsk, 8549; Vl, Vladivostok, 9313.
contamination is expected from other trains in summer (coal heating may be used
in winter).
The concentrations of the various trace gases as a rule depend strongly on
the meteorological conditions, synoptical situation and orography. It is however
beyond the scope of this paper to present a detailed analysis for the 2 weeks of
measurement, during which many weather system were encountered. Therefore, in
the discussion of the data below, we will give only meteorological and synoptical
information for the most important features of the measurements.
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6. Discussion of the Data
The most important measurement results are shown in Figure 2. We first discuss
and analyze the chemically very active species O 3 and NOx , followed by CO and
CH4 , and finally SF6 . Considering the vast distance covered, including rural and
industrial areas, O3 values are relatively consistent, with daytime maxima between
30 and 50 nmole/mole. Variability is dominated by the diurnal cycle, with generally
a steep rise with increasing insolation, and a slower, variable drop-off during the
night. In several instances, near 5 nmole/mole minima are observed, often towards
the end of the night; e.g., traveling east (TE) at 3900TE, 5200TE, 6600TE, 7800TE,
and traveling west (TW) at 4600TW, 5800TW, and 6900TW. The main cause of
these deep minima is not the reaction with NO from traffic or cities and industry.
Considering the low night time temperatures, and the NOx values being mostly
in the low nmole/mole range, deposition under inversion conditions has played a
major role. At 2000–4000 km from Moscow, traveling east (TE) and traveling west
(TW) the diurnal O3 cycle is weak and depressed night-time values are absent.
At the same time, at least TW, nighttime temperatures were rather high, e.g., at
3000TW. There may have been only a weak or no inversion. At 2600–3300TW O3
values actually do not decline at all during night. In this case, no appreciable NO
and NO2 , was present and the air was very clean, with only CH4 being elevated.
It is probable that O3 was relatively constant due to vertical exchange under these
clean air conditions. In general the diurnal O3 variations appear to correlate with
temperature, with low night time temperature minima nearly always coinciding
with low O3 . The diurnal cycle in O3 is strongly connected to (a) a nighttime ozone
destruction at the surface during the establishment of boundary layer inversion, and
(b) a daytime downward flux of O3 rich air from the free troposphere. The latter is
indicated by the fact that high O3 concentrations of the order of 35 to 50 nmole/mole
were measured both during low and high J (NO2 ) conditions. However, peak values
reaching up to 50 nmole/mole appear to be sufficient to consider the possibility
of photochemical ozone formation in an atmosphere which receives substantial
emissions of hydrocarbons from vegetation, as well as possibly significant amounts
of NO from fossil fuel and biomass burning. Additional measurements of NOx and
hydrocarbons planned for future expeditions are needed to clarify the potential
importance of photochemical ozone formation.
In eastern Siberia remarkably high night time O3 values have been observed.
At 7300TE, O3 actually increased in the dark from 20 to 35 nmole/mole. At 7100–
7500TW nighttime values were constantly high. This time however, in both cases,
extremely high CO values with modest NOx levels are observed. Further below we
will analyze this large event in more detail.
NO and NO2 variations are dominated by extreme spatial variability, which is
to be expected with industry and transportation as major sources. Insofar these
sources are extended, certain correlations may be observed. Especially for NO and
CO, road traffic was at times a source of contamination. The effects of roads will
be difficult to quantify and strongly depends on meteorological conditions.
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Figure 2a.
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Figure 2b.
Figure 2. Measurement data for O3 , J (NO2 ), NOx , CO, CH4 , SF6 , the temperature and
humidity. For both CO and CH4 the discrete analyses are shown with the continuous curve.
The scale for CH4 has been offset by 1.7 mole/mole. For methane and CO the data have been
clipped to provide more vertical resolution. Interruptions in the continuous records occurred
during several occasions as shown. For SF 6 the 3.87 pmole/mole limit corresponds to latitudes
south of 30 , while 3.98 to 4.03 pmole/mole to the latitude band of 40 to 60 . For those parts
of the record where doubt existed about possible contamination problems, the data have been
disregarded.
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The section 2200–3200 shows an interesting effect. While TE NOx was present,
TW it was absent. TE the train followed the southerly route between Sverdlovsk
(1833) and Omsk, via Kurgan (2192) where it is joined by the motorway M51,
through Petropavlovsk (2459) and Omsk (2733) up to Novosibirsk (3360). In
contrast TW, NOx is low over the entire distance. From Omsk back to Sverdlovsk
this can be explained because the northerly route via Tyumen through a thinly
populated area was taken. However, for the easterly section Novosibirsk to Omsk,
where the M51 runs closely parallel over a substantial part, one would expect NOx
to be high in both directions. The most likely reason for the absence of NOx TW is
that this section was traversed during night with little road traffic. Thus, as we can
see from the other parameters, e.g., CO, this area is very clean and has no other
potential sources for NOx than the M51 during daytime. The above shows some
of the complexity of the train data, which can be deconvoluted, in particular when
correlations between species are used, and more trips have been made.
7. CO and CH4
CO and CH4 are important gases, especially for background tropospheric chemistry.
Both have been measured in situ in a continuous mode, whilst whole air samples
were taken as well. The agreement between the two data sets is good. For 6300–
8300TW the data based on the grab samples are a substitute for the missing
continuous data.
For CO the total concentration range is large, even disregarding short high
spikes. CO abundances are consistently at their lowest level over west Siberia near
110 nmole/mole. Such low levels were even encountered TE at about 1000 km
from Moscow. The route back to Moscow followed the northern track, via Perm
(1450) and Kirov (970). This area is more sparsely populated then the southerly
section via Kazan and Niznij Novgorod, explaining the rather low CO levels. For
comparison, in remote N.H. areas like e.g., Spitsbergen, values in late summer
drop to about 90 nmole/mole (unpublished results). This means that we probably
have seen rather clean boundary layer air over large distances. The low CO values
actually are an additional check on the usefulness of the train as a platform for air
chemical observations, because CO sources are abundant, and generally show up
clearly.
Major peaks of CO stretching over up to 100 km unambiguously coincide with
large cities. Perm (1452), Omsk (2733), Novosibirsk (3359), Krasnojarsk (4121),
Tulun (4819), Ulan-Ude (5673), and Chita (6221) giving excellent examples, with
usually high NO2 and black carbon concentrations as well. Between 3300 (Novosibirsk) and 6000 km, CO values appears to be higher traveling in both directions.
East of Novosibirsk where the Transsib enters the Siberian highlands, frequent
sections occur where the Transsib and the major route (M53 and from Irkutsk
onwards the M55) wind together through many valleys. Lower CO levels emerge
again between Ulan Ude (5673) and Chita (6221). Beyond Chita the Transsib
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189
runs lonely through remote mountain areas roughly parallel at a distance of 100 to
200 km from the river Amur. Just here at maximum remoteness, at 7200 to 8000 km
from Moscow, we intercepted in both directions a colossal CO increase (TE over
1.4 mole/mole was recorded, off-scale in Figure 2). Over a distance of at least
1000 km, CO levels of over 300 nmole/mole prevailed. This represents an enormous amount of CO, which was TE accompanied by elevated black carbon. From
the train a haze was visible and at night a strong absorption of moonlight through
the smoke was observed; during daytime TW J (NO2 ) were very low. Concurrent
with the elevated CO values, also CH4 was enhanced, which is clearly visible for
TE, when the highest CO values occurred.
Backtrajectory analysis shows that TE, up to Urusha, large scale air movement
was from the west, and turned northerly soon after that, coinciding with the strong
increase in CO concentration. Also while passing through Belogorsk, air masses
moved in from northern Siberia, however after passing further south through the
Chinese border area. This situation lasted until Khabarovsk had been reached.
Returning west, the air masses had not moved from the area, and again high CO
values were recorded. The Transsib section under discussion up to Svobodnyj
(7830), with major wood industry, actually runs through extensive forests which
form a southward extension of the taiga forests which extend across the Amur into
China. It is highly likely that large scale forest fires have occurred.
Isotopic analysis can provide information about the sources and sinks of the
trace gases CO2 , CH4 and CO. For this purpose 16 large air samples have been
collected. Although the detailed interpretation will be published elsewhere (Bergamaschi et al., 1997), we show the use 14 CO measurements in the case of this
large event. Figure 3 gives the abundance of 14 CO in molecules per cm3 STP as a
function of the accompanying CO concentration for 10 air samples. Two of these
samples taken at 7472 TE and 7825 TE while crossing the region with extreme
CO values, show increased 14 CO abundance closely correlated with increased CO
values. This correlation implies that the excess CO contains a certain amount of
14 C, which points to the biogenic origin of the excess CO. Normal 14 CO levels in
the mid latitude northern hemisphere reach about 12 molecules per cm3 in summer
(Brenninkmeijer et al., 1992). From the linear regression in Figure 3 we can calculate that the specific activity of the excess CO corresponds to 37 14 CO molecules
per 1000 nmole/mole increase in CO. This in turn corresponds to a 14 C/12 C ratio
of 1:48 10,12 , which matches the specific 14 C activity of contemporary organic
material. Therefore it is concluded that the excess CO is derived from forest burning. Although mainly due to 14 C input from the atmospheric nuclear test explosions
the specific activity of contemporary organic material may show some variation
related to the exact timing of the carbon fixation by the particular biomass, we
can confidently estimate that at least about 90% of the excess CO is from biomass
burning.
The observed mixing ratio of CH4 generally exceeds 1.8 mole/mole, which is
close to the summer minimum observed at Yakutsk (129 E, 64 N) (Maksyutov
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Figure 3. The number of 14 CO molecules plotted against the CO mixing ratio for 10 CO
samples. The background 14 CO level at this time of the year is around 12 molecules per
cm3 STP. Only CO of biogenic origin can raise this number. The regression slope is 0.0375
molecules/cm3 per nmole/mole,1 .
et al., 1995). Minimum CH4 levels, indicative of clean air conditions, have been
observed in east Siberia only. As expected, conditions suitable for background
observations only occurred during daytime. Elevated CH4 levels have three main
characteristics. Very pronounced are the many spikes that occur in the record, corresponding to localized increases of tens of percent. These spikes are superimposed on
a clearly varying background level. Furthermore, this background level appears to
be very similar for the travel in both directions; a clear correlation is present. These
large general changes and their persistence point to extensive, important source
areas. Second, the spikes are more frequent during night time, which undoubtedly
is related to the inversion conditions mentioned before. Third, CH4 levels appear to
be distinctly higher up to approximately 5000 km from Moscow with the highest
average levels occurring between 2000 and 4000 km, corresponding to Sverdlovsk
to Krasnojarsk at either side of the West Siberian lowlands. We also see some
elevated CH4 values between approximately 7000 and 8000 km, which however is
linked to the massive biomass burning feature discussed above. Below we will first
focus on the observations in West Siberia.
The 2 source types that can be responsible for the large scale CH 4 increase in
West Siberia are natural gas and biogenic methane from wetlands. Natural gas can
leak from pipelines, pumping stations and wells, and would as such constitute distinct localized sources. Its emissions may be characterized by concurrent increases
of related hydrocarbons, or by isotopic composition.
Of special interest is the section TW from Krasnojarsk (4222), via Novosibirsk
(3359), Omsk (2733) and Tyumen (2161) to Sverdlovsk (1833). Back-trajectory
calculations show that whilst near Krasnoyarsk air movement was still from the
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191
south west, upon approaching Novosibirsk, the air flow turned south, thus first
passing over the west Siberian wetlands. For the remainder of the trip, this situation persisted. Between Tyumen and Novosibirsk, very clean conditions prevailed,
as witnessed by low NOx , low and constant CO, and low black carbon. The lack
of an O3 minimum indicates the absence of an inversion, contributing to the occurrence of clean air conditions. Indeed there appears to be no systematic day-night
difference for CO and CH4 . In view of the absence of inversion, the high CH4 levels
observed have great significance, indicating a large and extensive CH4 source. The
most probable source is CH4 from wetlands. The very low CO levels indicate that
combustion processes are not associated with the increased CH4 levels. For comparison, for 4200–4800TW we see in contrast an example of many CH4 spikes,
however, this time with concomitant CO and NOx spikes, indicating industrial
sources.
Further east, from Novosibirsk to Krasnoyarsk indicators for pollution like
NOx , CO, black carbon and also SF6 do increase, with the direct influence of
Novosibirsk also clearly recognizable. However, CH4 now appears to be somewhat
lower compared to the previous section Tyumen to Novosibirsk. The reason for
this decrease is most probably the change in topography, as the railroad leaves the
plains and enters a hilly landscape. Also, the distance to the wetlands increases east
from Novosibirsk.
However, the important section Sverdlovsk (1833) to Novosibirsk (3359) also
has to be considered TE. As pointed out before, in this direction the track went
further south via Kurgan and Petropavlovsk, at some further distance of the actual
lowlands. Nevertheless there are many lakes along this route as well. As discussed,
this particular route up to Omsk crosses a more populated area, and runs very
close to the M51. For the section Kurgan to Omsk which was traveled during
the night, NOx appears to be elevated, although CO values are barely elevated.
Concurrently, the CH4 level increases and many spikes occur, in particular from
100 km past Kurgan onwards, where the M51 runs very close to the road. The
occurrence of spikes suggests local sources, which could in first instance indicate
natural gas leaks, because traffic as such would be a small source only. Apart from
this, CH4 from nearby lakes, ponds and marshes may also play a role; however, the
coincidence with the proximity of the road raises doubts whether natural emissions
are the main cause. Further east, from Omsk to Novosibirsk high CH4 levels occur
at 3300 TE. This time there is an unambiguous correlation with NOx and CO and
pollution clearly contributes to the high values, approaching Novosibirsk.
A firm conclusion regarding the cause of the substantially elevated CH4 levels
cannot be given on basis of the limited analysis. TW, further north and closer to
the wetland areas, CH4 values are very high, even during daytime in the absence
of inversions, and emissions from wetlands are the likely cause. TE, further south
at some greater distance form the main wetlands, it seems that the proximity of the
M51 renders the interpretation, without additional data difficult if not impossible.
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The isotope data together with a detailed treatment to be published elsewhere
(Bergamaschi et al., 1997) should allow a more definite conclusion.
8. SF6
Finally, we discuss the measurements of air samples for SF6 , which is a powerful
tracer for large scale air movements. Interesting features can be derived from the
continental longitudinal set of SF6 mixing ratios shown in Figure 2, the first ones
to be measured. The general level is consistent with observations made at the same
time at four background monitoring stations north of 28 N (Izaña, Kasprowy,
Fraserdale, Alert; Ingeborg Levin, private communication). The mean meridional
surface distribution of SF6 peaks between 40 and 60 N (Levin and Hesshaimer,
1996) which coincides with the latitude range of the present study. The expected corresponding concentration range derived from other continental background
measurements are marked in Figure 2. The TROICA results match this higher
concentration range only locally.
In general a gradual eastward decline can be seen, corresponding with an eastward decrease of sources in agreement with the urban/industrial gradient. Results
for the easternmost 3000 km of both tracks compare well, although the large scale
air mass transport was dominated once by northern and the other time by southern
directions. Thus, far east from Europe, one of the world’s main SF6 source regions,
no clear latitudinal gradient was discernable. Sections of elevated concentration
values TW, around 1000 km (from Perm to Kirov with northern winds) and around
3500 km (from Krasnoyarsk to Novosibirsk, with low southwestern winds) can
only be explained by local sources in the nearby industrialized regions. Trajectory
analyses show why these patterns are not found during the forward track. They
further allow to identify all results above 4.05 pmole/mole as due to local pollution since in these cases air masses have passed areas of intensive mechanical
engineering and power, steel and aluminum production.
9. Conclusions
The Trans-Siberian Railroad can be used successfully to measure a range of trace
gases over a poorly documented, but vast and important area. In particular the
fact that such a large area can be covered relatively rapidly (and at modest cost)
renders the idea of using trains in remote regions for air monitoring attractive. Up
to date fixed monitoring stations play a dominant role in obtaining observational
data for atmospheric and biogeochemistry on a large scale (NOAA-CMDL and
Global Atmosphere Watch, (Brenninkmeijer, 1996)). Notwithstanding it is clear
that at least for Siberia, the railroad concept has a good potential, and it is not
difficult to think of additional regions where it may be a useful concept. Regular
measurement using trains will also provide opportunities for monitoring regional
air pollution. Contamination from the electric locomotive is absent, yet necessarily
TRACE GAS MEASUREMENTS BETWEEN MOSCOW AND VLADIVOSTOK
193
railroad systems tend to concur with human activities, and thus localized pollution
sources. Therefore detailed analysis, and observations during different seasons
and different meteorological conditions will be necessary. However, in the present
case, for many sections, often over vast distances, local pollution was absent and
we obtained useful novel data on background chemical composition.
Although this limited analysis cannot yield far-reaching conclusions, high CH4
levels have been observed over west Siberia, tentatively linked to the extensive
wetlands. In contrast, CH4 levels were low over eastern Siberia where however
large CO increases were encountered in the remote area north of the Amur river.
By using isotope analysis, this CO could be unambiguously identified as resulting
from biomass burning. Throughout the years a wealth of data can be gathered, the
analysis of which, using meteorological data, would allow a detailed picture to be
constructed of source regions, transport and interaction of trace gases. Particularly
the contributions from fixed local sources could be filtered out and mapped, and
would thus give useful information in its own right.
Acknowledgements
This TROICA 2 expedition and the joint research has been supported financially
by the Volkswagen Foundation. We are grateful to A. S. Elokhov, D. Skripkin, and
S. N. Elansky for partaking in the expedition. B. G. Doddridge kindly advised on
methods to improve the CO analyzer. We also thank Volker Walz and in particular
Ingeborg Levin, Institute for Environmental Physics, University of Heidelberg for
cooperation in SF6 analysis.
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