Reactive Nitrogen Compounds in the Arctic

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 90, NO. D6, PAGES 10,739-10,743, OCTOBER 20, 1985
Reactive Nitrogen Compounds in the Arctic
RUSSELL R. DICKERSON
Department of Meteorology, University of Maryland, College Park
Measurements of NO, NOx (NO + NO2), and NOy (NO. + 2N205 + NO3 + HONO + HO2NO2 +
PAN + R-ONOx) were made in March 1983 between 200 and 12,000 m altitude on several flights in the
Arctic and from Spitsbergen, Norway, to Cologne, West Germany. NO values were always below the
detection limit (10 ppt); NO, values (determined with a FeSO4 converter) were high, -600 ppt, in the
boundary layer and generally decreased sharply with altitude, although distinct strata of high NOr
were observed at altitudes up to 8000 m. NO s (measured with a 425øC Mo converter) showed altitude
profiles similar to NO, profiles with boundary layer values as high as 1500 ppt. Ratios of NO. to NOy
were 0.81 near the surface and 0.46 at 6400 m, probably owing to higher levels of PAN or other organic
compounds in the free troposphere. The possible global impact of high concentrations of reactive
nitrogen compounds in the Arctic is discussed.
INTRODUCTION
Reactive nitrogen compounds exert a profound effect on
the chemistry of the atmosphere. They contribute to the
acidity of precipitation and catalyze the photooxidation of
carbon monooxide and hydrocarbons to form ozone [Crut-
zen, 1973; Chameides and Walker, 1973]. Large amounts of
NOx (NO + NO2) are produced by combustion, but most of
this pollution remains in the planetary boundary layer (PBL)
because NOx is quickly removed by either dry deposition or
photochemical conversion to HNO3 followed by dry and wet
deposition [Logan, 1983; Fishman and Crutzen, 1978].
In the Arctic winter these removal mechanisms are largely
absent. Without solar UV radiation there is little photochem-
ical activity, and the absolute humidity is so low that
precipitation is virtually nonexistent. Crutzen and Gidel
[1983] predicted large concentrations of tropospheric NOy in
the Arctic winter. Reactive nitrogen compounds transported
Particulate nitrate, NO3-, is unlikely to contribute significantly
to the NOy levels reported here. If we assume that all
particles with a diameter less than 1.0 tam are collected by
to the Arctic in the winter are likely to remain in the
troposphere until spring unless they are transported to lower
latitudes. In this manner Arctic air, especially in the free
2
. , [,
troposphere, can act as a reservoir for odd nitrogen and
represent a globally important source of tropospheric NOx.
This article presents the first profiles of reactive nitrogen
compounds measured in the remote Arctic.
IO
21 MARCH 1983
EXPERIMENTAL
Details of the chemiluminescent NO instrument have been
presented elsewhere [Delany et al., 1982; Dickerson, 1984'
Dickerson et al., 1984] but will be summarized here. NO is 6
detected directly with a detection limit for a 20-s integration
time ofabout 10ppt (S'N = 1' 1 for +-2rrnoise). NOx (NO +
NO2) is detected after conversion to NO in a FeSO4 converter.
Known interferences include HONO and PAN; the latter
is converted with only about 10% efficiency. Nitrous oxide,
N20, has recently been tested in this laboratory and found to
4
be converted to NO with an efficiency of less than 5 x 10 -7.
Tests of organic nitrates and nitrites are currently being
conducted. NOy (NOx + 2xN205 + NO3 + HONO +
2
HO2NO2 + PAN + R-ONOx) is detected after conversion to
NO on a hot (425øC) Mo converter. R-ONOx represents
o
0 400 800 1200 1600 2000
organic N containing compounds other than PAN. In these
NOy (ppt)
Copyright 1985 by the American Geophysical Union.
Paper number 5D0387.
0148-0227/85/005D-0387502.00
10,739
experiments, nitric acid is assumed removed by the 1.5-mlong
stainless steel inlet tube [Goldan et al., 1983].
Uncertainty in NOy measurements depends on several
factors [Dickerson et al., 1984], including a background
signal from the converter. This effect was accounted for by
making measurements with zero air before and after the
flights, but it limits the precision of the measurements to 50
ppt. Inlet line losses of species such as N205, R-ONOx, and
HO2NO2 under widely varying temperature, pressure, and
humidity are unknown; thus the absolute accuracy of NOy
measurements cannot be stated with certainty but is probably
within a factor of 2. The values that follow can be
considered reasonable lower limits.
8
2
Fig. 1. Altitude profiles of NOy measured on March 21, 1983.
Graph drawn by connecting 30-s average values: (Profile 1) descent
(D), approximate location 85øN, 30øE; (profile 2) ascent (A), 87øN,
25øE; (profile 3) D, 79øN, 7øE. Dotted line on profile 3 indicates
interpolated data. Profile 1 dashed for clarity.

I.d 4
I--
0
5
w 4
t-
0
I
2
2.3 MARCH 198.3
i
i i i
400 800 1200 1600 2000
(0)
800 i i 1200 i i I io 0 i 2000
(o)
, I , ,
- 5,o ,L 4,0 ,-3.b ø.c '
i
200 400 600 800 I000
o , , , i , , , , , i i
0 200 400 600 800 I000 200 400 600 800 I000 200 4 O0 600 800 I000
(0) (0)
NOy (ppt)
i , ,
Fig. 2. Same as Figure 1 but for March 23, 1983. Profiles are as follows: (1) D, 77.5øN, 7øE; (2) A, 77øN, 3øE; (3) A,
78øN, 0øE; (4) A, 82øN, 0øE; (5) D, 84øN, 0øE; (6) A, 85øN, 0øE; (7) D, 84øN, 6øE; (8) A, 83øN, 9øE; (9) D, 81.5øN, 12.5øE;
(10) A, 80øN, 13øE; (11) D, 79øN, 11.5øE. Profile 5 has temperature plotted as well. Note that changes in NOv
concentration correspond to strata indicated by changes in lapse rate.
o
o o
o
I i i ß
i i i i i i I
200 400 600 8O0
' i i i ! i i i i
200 400 600 800
io00 200 400 600 800 iooo
(0) (0)
Iooo i 200 i i 4 )o i 60O i i 800 i i Iooo
(o) (o)
NOx--NOy - (ppt)
i i i i
i i i i i , , i
200 400 600 8O0
i
iooo
200 i i 400 i ' 6 ) 0 , 800 , , iOO0
Fig. 3. Altitude profiles for March 24, 1983. Heavy lines indicate NOv; light lines indicate NO,. Profiles are as
follows: (1) D, 80øN, 24øE; (2) A, 81øN, 27øE; (3) D, 82.5øN, 27øE; (4) D, 83øN, 24øE; (5) D, 83øN, 11øE; (6) A, 82øN,
10øE; (7) D, 80.5øN, 10øE; (8) A, 79øN, 10øE; (9) D, 78øN, 10øE; (10) A, 76.5øN, 10øE; (11) D, 75øN, 12øE; (12) A, 74øN,
12.5øE. Note increase in concentration between profiles 10 and 11 as aircraft passes through warm front into region of
circulation from eastern Europe.

::)6
90 85 80 75 70 60N
DICKERSON: BRIEF REPORT 10,741
o 12 I 24 MARCH 198.3
8
4
i i , i
0 0 400 800 1200 16)0 2000
NO x -- NOy --- (ppt)
Fig. 5. Same as Figure 3. Profiles are as follows: (12) A, 74øN,
12.5øE; (13) A, 72øN, 17øE; (14) D, 70øN, 19øE. Touchdown in
Troms½, Norway, followed profile 14.
15
?_4-25 MARCH 1983
0 I I ] I I[[ I I I f I I
0 I .0 Z.O $.0 4.0 5.0
NOx-- NOy (ppb)
30E Fig. 6. Observations recorded on descent and landing in Cologne,
Federal Republic of Germany (51øN, 7øE). Heavy lines are
lOW 0 IOE 20E
Fig. 4. Surface isobar analysis for 0600 UT, tviarch 24, 1983.
Between flying profiles 10 and 11 of Figure 3 the aircraft passed
NOy; light lines, NOx. The tropopause as indicated by temperature
and o7one concentration was located at about 9 km.
through the warm front shown; other fronts have been omitted in the
interest of clarity. Dashed line depicts flight path. Isobars drawn at
5-mbar intervals based on the Berliner Wetterkarte' Freien Univer-
Uncertainty in NOx measurements also depends on the
background signal, but this effect was generally much smallsitfit
Berlin.
er than for NOy. Air samples with dew points below -25øC
the backward facing sample inlet tube and that they are
converted by the molybdenum catalyst with 100% efficiency,
then the nitrate levels reported by Radke et al. [1984] would
contribute only about 60 ppt NOy in haze layers and 10 times
can significantly reduce the response time of the instrument
in the NOx mode, although the conversion efficiency is
apparently unaffected. At the low dew points encountered in
the upper troposphere of the Arctic the response time was of
the order of 2 min. The estimated absolute accuracy of NOx
less in clear air.
measurements above 50 ppt is -+40%.
I ! ! ! i i i ! !
A Hawker Siddeley 125 twin engine jet was leased by the
Max Planck Institute for Chemistry, Mainz, West Germany,
13
for the Arctic flights. Location, altitude, and temperature
were recorded by hand from the aircraft instruments.
RESULTS AND DISCUSSION
High concentrations of reactive nitrogen compounds were
frequently encountered on the flights in the Arctic. As
shown in Figures 1-3, the lower 1.0 km of the atmosphere
typically contained about 700 ppt N Oy, most of which was
NOx. This is several times higher than has been found in
other remote locations in the northern hemisphere [e.g.,
Kelly et al., 1980; Helas and Warneck, 1981; Bollinger et al.,
1984]. Distinct strata of high concentrations of both NOx and
NOy existed in the free troposphere at altitudes up to 8 km.
High levels of reactive nitrogen compounds were accompanied
by high levels of CO, H2, and CO2 (W. Seiler, private
communication, 1983), making combustion the primary can-
didate for a source.
NO was always below the detection limit of the instrument,
-- 10 ppt. This may seem surprising in view of the high
NO2 levels encountered, but the intensity of UV radiation
was always very low. On the equinox at 80øN the sun is
never more than 10 ø above the horizon. The frequency of
NO2 photolysis at this zenith angle is difficult to measure or
calculate [Dickerson et al., 1982; Parrish et al., 1983] but is
surely very slow. In addition, the ratio of NO2 to NO is often

10,742 DICKERSON: BRIEF REPORT
much higher than is predicted by a simple NO-NO2-O3 On descent into Cologne (Figure 6) the highest NO v and
photostationary state [Kelly et al., 1980]. Such low NO NO concentrations of the entire project were encountered.
levels then are reasonable.
These could be the result of air traffic in the vicinity of the
Pollutants in the Arctic air exist in strata not because they airport or convective transport of polluted PBL air. Towerare
released locally at distinct altitudes but because they are ing cumulus and snow showers were reported in Cologne
transported there in well-defined air strata. Figure 2 shows a
temperature profile recorded in parallel with NOy concentra-
(Berliner Wetterkarte, March, 24 and 25, 1983).
tions. At least five distinct air strata are apparent from the
varying lapse rates. An extremely stable layer in the first few
CONCLUSIONS
hundred meters existed, followed by an isothermal layer up High concentrations of reactive nitrogen compounds have
to about 1.2 km, designated as the PBL. Above this altitude been predicted to exist in the Arctic winter. The measurethe
air becomes less stable, and the concentration of NOy ments reported here confirm these predictions and suggest
drops off. Between 2.6 and 4.3 km there was an air mass with that the Arctic troposphere may act as a reservoir for NO
a uniform lapse rate containing high pollutant levels; above and that this NOx may be transported to the remote regions
4.3 km the temperature decreases rather quickly with alti- where it can increase global ozone production from tropostude,
and the new air mass was markedly cleaner. The phereic photochemistry. Pollutants existed in the boundary
results of this study testify that polluted layers are common layer and in distinct layers at higher elevations. These strata
in the Arctic, at least in the early spring when solar heating is are the result of air mass transport at distinct altitudes up to
very low.
about 8 km. Movement of air masses along lines of constant
On 13 profiles both NOx and NOy were measured at the
bottom (---0.2 km) and top (--6.4 km) of the flight pattern.
potential temperature could account for these high strata.
The ratio of NOx to NOy decreases significantly with alti-
This affords the opportunity to compare NOx to NOy ratios tude. Photochemical calculations suggest that this NOy is not
in the PBL to ratios in the free troposphere. The results were composed of N205 but more likely PAN, HO2NO2 or some
0.81 +- 0.2 (-+ 1 standard deviation) in the PBL and 0.46 +_ 0.2 R-ONO. Although the observations and calculations reportin
the free troposphere. Recalling that HNO3 was probably ed here give a strong indication that the chemistry of the
efficiently removed by the stainless steel inlet system, these Arctic troposphere can significantly affect global atmospherratios
argue in favor of high concentrations of some other ic chemistry, the data are far too sparse in temporal and
reactive nitrogen compounds in the free troposphere. N205, spatial scale to draw any general conclusions about mean or
PAN, R-ONO, and HO2NO2 are likely candidates.
It is possible to calculate the amount of N205 expected to
be present in these measurements by assuming steady state,
seasonal pollution levels; further investigation is called for.
that NO2, NO3, and N205 are the only species detected, and Acknowledgments. The author wishes to thank R. Schnell and
that together they compose NOy. The strong temperature B. Ottar for helping to organize the Arctic research expeditions and
Conti-Flug GmbH, Cologne, for their helpful cooperation on the
dependence of N205 dissociation and the difficulty in calcuflights.
Assistance from P. Crutzen, L. Nunnermacker, W. Seller,
lating accurate NO3 photolysis rates make the results very and F. Slemr is also acknowledged. This work was supported in part
uncertain, but if they are correct, then N205 contributed less by NSF grant ATM-83-05843 and the Max Planck Institute for
than $% to the total odd nitrogen observed at 6.4 km. Details
of the steady state calculation are available from the author.
PAN has been measured in the range of hundreds of ppt in
Chemistry in Mainz, West Germany.
the free troposphere [Singh and Salas, 1983] and may well
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(Received February 18, 1985;
revised March 26, 1985;
accepted March 29, 1985.)