C. PROJECT DESCRIPTION
Results from prior NSF support
R. Bales, PI.
The Bales group has had two recent grants covering air-snow interactions, specifically “SnowAtmosphere Transfer Function for Reversibly Deposited Chemical Species in West Antarctica” (OPP9526572; completed 8/00), and “Transfer function for photochemically produced species in Greenland
snow, firn and ice” (OPP-9813311; through 4/02). This research involved making measurements of
hydrogen peroxide (H2O2) and formaldehyde (HCHO) in the air, snow, firn and ice at Siple Dome and
South Pole in Antarctica, and Summit, Greenland. The aim was to better understand the air-snow transfer
of these species, and to interpret changes in concentrations of these species in ice cores. We found that
surface snow acts as an excellent proxy for atmospheric concentrations of H2O2. Atmosphere-to-snow
transfer of H2O2 at all three sites can be modeled by advection of surface air through the top few meters of
firn and diffusion of H2O2 into and out of snow grains in response to changing atmospheric concentrations
and snowpack temperatures. Firn continues to lose H2O2 to the atmosphere for at least 10-12 years (~3
m) after burial at current South Pole temperatures and accumulation rates. Losses occur over about 1-2
meters at Siple Dome owing to the warmer temperatures. HCHO is preserved in snow and firn at Siple
Dome, but concentrations are lower than for South Pole, reflecting the temperature difference between the
two sites. Measurements at Summit show that the top snow layers are an HCHO source. HCHO
concentrations in fresh snow are higher than those in equilibrium with atmospheric concentrations,
resulting in HCHO degassing in the days to weeks following snowfall. Measured bi-directional
summertime H2O2 fluxes from the snowpack at Summit in June 1996 reveal a daytime H2O2 release from
the surface snow reservoir and a partial re-deposition at night. The observations also provide the first
direct evidence of a strong net summertime H2O2 release from the snowpack, enhancing average
boundary layer H2O2 concentrations ~7-fold and the OH and HO2 concentrations by 70% and 50%,
respectively, relative to that estimated from photchemical modeling in the absence of the snowpack
source. Publications to result from this work include McConnell et al. [1997a, b; 1998, 2000, 2001], and
Hutterli et al. [1999; 2000, 2003], Dassau et al. [2003], and Jacobi et al. [2002, 2003].
Jochen Stutz, co-PI: has not received NSF funding
1
Introduction
Polar regions are among the most sensitive environments on our planet. Climate change and global
air pollution have already led to considerable impact in the Arctic. The thinning of sea ice [Rothrock et
al., 1999] and the decrease of its spatial extent [Parkinson et al., 1999] are indicators for change in the
global climate over the past century. Arctic haze and the accumulation of mercury in arctic fish and
mammals are examples of the impact of large-scale pollution transport to the arctic [MacDonald et al.,
2000]. Glaciers, firn, and snow in the Arctic also provide unique records of past climate and composition
of the atmosphere, and for example give insight into the past atmospheric oxidative capacity [Hutterli et
al., 2002; Hutterli et al., 2001]. These records are an essential tool to validate global climate and
chemistry models. The arctic is also believed to play an important role in the future development in our
climate. Feedback effects through the change of sea-ice extent and snowcover have the potential to further
amplify a temperature increase, such as the one already observed in the arctic [Serreze et al, 2000] over
the past 35 years.
It has recently become clear that the large snow-covered and sea-ice areas can influence the
atmospheric composition in the Arctic and Antarctica and, most likely, on larger scales [Honrath et al.,
2000a; Honrath et al., 2000b; Wagner, 1998]. The best-known examples are widespread ozone and
mercury depletion events caused by a large release of reactive halogens during polar spring [Barrie et al.,
1988]. The processing of nitrate absorbed on snow, releasing HONO and NO x has also been identified as
an important process that can significantly influence ozone chemistry and the oxidation power of the
atmosphere [Honrath et al., 2000b; Zhou et al., 2001]. Similarly the release of formaldehyde from the
1
1
snow will impact the levels of OH radicals in the atmosphere [Dassau et al., 2002; Sumner and Shepson,
1999; Sumner et al., 2002].
The sensitive response of the Arctic system to global changes in temperature and atmospheric
composition, as well as the potential climate feedback mechanisms motivates the performance of accurate
long-term measurements of atmospheric composition and the composition of snow and firn. The Summit
Greenland Environmental Observatory (GEOSummit), located at an elevation of 3100 m on the
Greenland ice sheet has been established and supported by NSF as a baseline observatory and is currently
the only high altitude research site in the Arctic with a large suite of continuous atmospheric
measurements. A number of core measurements are performed at GEOSummit, including meteorology,
continuous ground-level ozone, carbon cycle gases (flasks), energy balance, column ozone, snow
accumulation and snow chemistry (see www.geosummit.org for details). In addition a number of
intensive short-term experiments have been performed there [e.g. Bottenheim et al., 2002].
Here we propose to develop a new instrument to measure the concentrations of NO2, HONO,
HCHO, and halogen oxides in and above the remote artic boundary layer. The instrument will be based
on fully automated remote sensing measurements by multi-axis differential optical absorption
spectroscopy (MAX-DOAS) and will be built for a long-term or permanent unattended deployment at
GEOSummit. Details of the instrument and the proposed work plan are presented in section 3. First we
will review the scientific problems that motivate the development of the proposed instrument, followed
by a discussion of the objectives of our proposal.
1.1
Influence of air-snow exchange on ice core records, atmospheric composition and
global climate:
The fate of several greenhouse gases is strongly coupled to the oxidation power of the atmosphere
[Crutzen and Lelieveld, 2001; IPCC, 2001]. The chemistry influencing the current oxidation power, as
well as its past and future development is therefore highly significant. The atmospheric oxidation power is
dominated by the hydroxyl radical, OH. NO3 and halogens contribute to a lesser extent [Finlayson-Pitts
and Pitts, 2000]. OH reacts with methane and some CFC’s. Its levels therefore determine the tropospheric
residence time of these compounds, and thus indirectly influence global climate.
OH formation in remote areas is predominantly determined by ozone levels, which through
photolysis and reaction with water, produces OH directly. In addition, HCHO plays an important role
through the formation of HO2, which can be cycled to OH through reactions with O3, NO, and NO3.
Recent observations at Summit showed that HONO above snow is another important OH precursor in the
Arctic [Yang et al., 2002; Zhou et al., 2001].
Measurements at Summit show that both HCHO and HONO are formed in the snowpack [Dassau et
al., 2002; Zhou et al., 2001]. The air exchange between snow and firn and the atmosphere appears to be
the dominant release mechanism of these compounds. In the case of HONO, the photolysis of nitrate
(NO3-) in the snowpack has been identified as the chemical formation mechanism [Honrath et al., 2002].
The release of HONO and NOx from the snowpack not only directly influences OH levels, but is also an
important mechanism for the recycling of NOx [Finlayson-Pitts and Pitts, 2000]. The release may thus
have an important impact on the global NOx budget. Although HCHO is believed to be formed
photochemically within the snowpack [Sumner and Shepson, 1999], the mechanism is currently unclear.
The complex chemistry of ozone and OH is also strongly dependent on the levels of nitrogen oxides,
which propagate the cycling of OH and HO2 as well as provide a chain termination step through the OH +
NO2 reaction (although the latter may not be as important since the HNO3 deposited into the snow will be
released again as HONO, forming OH again).
The importance of atmospheric chemistry and the oxidation power for the global climate has led to
the search of records for these properties in the past. Ice core records for a variety of reactive atmospheric
species of photochemical interest have been developed (e.g. [Fuhrer et al., 1996; Sigg et al., 1992;
Staffelbach et al., 1991, Wolff et al., 1995]). CO, NOx (using NO3- as proxy), CH4, HCHO and H2O2 have
2
2
all been investigated in ice Table 1: Previous observations of NO2 ,HONO and HCHO at GEOSummit.
cores as a means for assessing Also shown are levels of halogen oxides in various environments
changes in the state of the
Mixing ratios
reference
atmosphere, and all are HCHO
50 – 1500 ppt [Dassau et al., 2002; Jacobi et al.,
photochemically linked. Ice
2002; Sumner and Shepson, 1999]
core data are used to constrain
HONO
2 – 20 ppt
[Dibb et al., 2002]
models of past atmospheric
NO2
20 -75 ppt
[Dibb et al., 2002]
photochemistry, and assess
BrO
Arctic
0
–
30
ppt
[Foster et al., 2001; Tuckermann et
changes in the oxidation
al., 1997]
capacity of the atmosphere
[Fitzenberger et al., 2000;
[Staffelbach et al., 1991]. BrO Free trop. 1 – 2 ppt
McElroy et al., 1999]
Except for CH4, they are all
BrO
Salt
0
–
200
ppt
[Hebestreit et al., 1999; Stutz et al.,
also impacted by postLakes
2002]
depositional physical and
IO
0
–
6
ppt
[Alicke et al., 1999; Allan et al.,
chemical processes in the
2000]
snowpack/firn, in ways that
are, as yet, poorly understood.
Although considerable progress has been made (cf. [Hutterli et al., 1999; 2003]), the air-snow transfer
function for a some important reactive species has yet to be reliably defined.
There have now been several measurement campaigns conducted at Summit and at Alert, Nunavut,
during which NO2, HONO and HCHO were measured [Dassau et al., 2002; De Serves, 1994; Hutterli et
al., 1999; Sumner and Shepson, 1999; Zhou et al., 2001]. Typical ranges of mixing ratios observed at
Summit are summarized in Table 1. The values were measured during short periods of time, mostly
during summer. To improve our understanding of the seasonal behavior, and to improve the quantification
for long-term snow and ice records, measurements over extended periods of time are required. However,
the techniques thus far employed are work-intensive and cumbersome, and thus not suitable for
automated long-term operations. There is therefore a need to develop new analytical methods that can fill
this gap.
1.2
Halogen Oxides and their influence on polar and global ozone and mercury levels
The discovery of boundary layer ozone depletion events in the Arcitc [Barrie et al., 1988] has
triggered an increased interest in atmospheric chemistry in Arctic regions. It is widely accepted today that
the rapid destruction of ozone proceeds through catalytic processes involving reactive halogen species, in
particular Br and BrO [Hausmann and Platt, 1994; Oltmans et al., 1989]. Reactive halogens have also
recently been linked to the depletion of gaseous mercury and an increase of Hg deposition through
oxidation reactions that are still poorly understood [Schroeder et al., 1998]. BrO has been observed over
vast areas in the Arctic and Antarctica from satellites [Richter et al., 1998; Wagner and Platt, 1998], over
salt lakes [Hebestreit et al., 1999; Stutz et al., 2002], and also in the marine boundary layer [Leser et al.,
2003b], showing that the release of bromine is a widespread phenomenon. Observations also indicate that
low levels of BrO may be present in the free troposphere [Fitzenberger et al., 2000; McElroy et al.,
1999]. Evidence of the presence of reactive chlorine and reactive iodine has also been reported [Alicke et
al., 1999; Allan et al., 2000]. It is believed that bromine is released from salt deposits on sea ice or near
salt lakes, as well as on salt aerosol, by an explosion-like autocatalytic mechanism [Vogt et al., 1996].
Reactive iodine compounds (IO, OIO, etc.) are believed to originate from the photolysis of iodo-organic
compounds emitted by algae in the ocean [Carpenter et al., 1999]. Table 1 gives an overview of some of
the reported concentrations of halogen measurements in the atmosphere.
Reactive halogens can influence the ozone budget, and thus the oxidation power of the atmosphere,
on a global level, even at fairly low concentrations. A number of local observations have shown that Cl
and Br levels can be high enough to influence the oxidation power of the troposphere [Foster et al.,
2001]. In particular, in the arctic high levels of bromine can lead to a considerable oxidation of HCHO
3
3
and alkenes. No information on globally averaged background bromine or iodine levels is currently
available. Low reactive halogen levels, in particular bromine and iodine, in the free troposphere could,
however, have significant impact on the global ozone budget [McElroy et al., 1999]. Model calculations
have shown that bromine concentrations in the range of 107 molec. cm-3 can severely increase the
chemical loss rates of ozone. It is, however, unclear if such high background levels of reactive halogens
are indeed present on a global scale and during all seasons. Most global chemistry and climate models
today do not consider halogen chemistry in the free troposphere and may thus not describe the full extent
of ozone chemistry. The significance of halogens for mercury chemistry has been shown in the Arctic
[Schroeder et al., 1998]. As in the case of ozone, it is not clear what the impact of elevated halogen levels
on mercury is on larger scales. There is thus a need to quantify the presence of reactive halogens over
longer time periods to assess whether the observations in the free troposphere by [Fitzenberger et al.,
2000; McElroy et al., 1999] are representative for larger temporal and spatial scales.
1.3
Monitoring future changes in Arctic and global pollution.
One of the most important tasks of air quality research is to monitor a) how future global
industrialization, urbanization, and other human activities will alter regional and global atmospheric
composition and chemistry over the next century, and b) how this will affect atmospheric radiative
forcing [Molina et al., 2001]. Remote areas, such as the Arctic and Antarctica, offer the possibility to
study the response of background levels of various pollutants or their proxies to global changes in
emissions. These arguments have lead to the establishment of various monitoring networks around the
world (e.g. Global Atmospheric Watch). Most of these networks are concentrating on long-lived trace
gases and ozone. Pollutants such as NOx or VOC’s are often not included in the suite of measurements.
We know in the case of NOx that human influence has lead to an increase of global tropospheric levels
over the last few centuries. This change has contributed to a doubling of global ozone levels, and thus
contributed to global climate change [IPCC, 2001].
Highly accurate measurements of trace gases such as NO2 and HCHO over long time periods in
remote areas can contribute significantly to the understanding of the state of our atmosphere and its future
changes. While the technology to measure NO2, and HCHO exists, it is often expensive and requires
operation by trained personnel. In addition, the acquisition of these instruments as well as their
maintenance is, in many cases, quite expensive. Finally, most technologies today require regular (often
daily) calibrations, which makes these techniques prone to uncertainties in their long-term accuracy.
An additional motivation for the monitoring of global air pollution is the validation of current and
future satellite instruments. Measurements from satellites have revolutionized our ability to study the
global distribution and transformation of pollutants. Global measurements of NO2, HCHO, and BrO, for
example, give unique insights into the distribution, chemistry, and sources of these trace gases. The
performance of these new satellite instruments, however, depends crucially on the validation of the space
borne instruments by ground measurements. There is thus a need for ground-based methods that allow the
measurement of trace gas concentrations and columns from the ground over the lifetime of the satellite
experiments. Both, the need of long-term monitoring of HCHO, NO2, and BrO, as well as validation of
satellites in remote areas, contribute to the motivation of this proposal.
2
Rationale and Objectives
Our predictive capability for the future state of the atmosphere relies in part on our ability to quantify
air-snow-ice interactions, understand chemical processes that influence the oxidation capacity, and
monitor pollutant levels in remote locations. Motivated by the fact that the Arctic is an environment
sensitive to future changes in global climate and composition, there is growing scientific interest in
maintaining baseline monitoring stations, such as GEOSummit. A number of previous short-term
observations at GEOSummit and other locations in the arctic have shown that there is a need for
continuous measurement of NO2, HONO, HCHO, and reactive halogens in the Arctic. In each of these
studies the analytical methods involved a flow injection analysis type methodology, using aqueous phase
4
4
chemistry and fluorimetry for detection. These methods are not at all amenable to a harsh environment
such as Summit, exhibit frequent down time, have a relatively slow response, and are subject to potential
interferences. They also require regular on-site attention/maintenance. In the case of HCHO and NO2,
we find that, due to their relatively short photochemical lifetime in daylight, there is a strong diel cycle,
and fast measurements are necessary to capture and understand their behavior. For NO 2, the
measurements have typically been conducted using photolytic conversion to NO (followed by O3
chemiluminescence determination of the NO). However, this method is subject to interferences, e.g.
HONO, which in the near snowpack air at Summit can be significant. Conversion efficiencies can also be
variable, leading to added analytical uncertainty. In addition, most of the analytical techniques are not
easy to operate over long periods of time and an automatic operation is challenging.
Motivated by the lack of long-term observations and an analytical technique suitable for automatic
operation in the Arctic, we propose here to develop an instrument to monitor NO2, HONO, HCHO and
the halogen oxides BrO, and IO in remote areas in the Arctic. This instrument will be deployed at
GEOSummit and will serve as a first version for instruments that have the potential to become a standard
system for other remote polar locations. Design criteria of the instrument are sensitive and specific
measurement of these trace gases, long-term stability, and a fully automated and inexpensive operation.
The instrument will be constructed to contribute to the study of the following scientific questions
listed and discussed below:
How does the air-snow exchange of formaldehyde impact atmospheric chemistry? How does release from
and uptake into the snow-pack influence HCHO levels in firn and in ice cores?
Interest in HCHO chemistry in the arctic is motivated by two separate aspects. First, HCHO is a
precursor to OH radicals, which largely dominate the oxidation power of our atmosphere. Processes such
as the proposed photolytic formation of HCHO in the snowpack, followed by a release into the
troposphere, can have an impact on Arctic radical levels. Since this process seems to occur on other
snow-covered surfaces, it may also be important outside of polar regions. However, we currently have no
good quantification of this mechanism, in particular with respect to its seasonal dependence. It is also
highly desirable to measure vertical profiles of HCHO to distinguish between the release of HCHO from
the snow-pack and its gas-phase formation.
HCHO is also an important proxy for the past oxidation power of the atmosphere in ice core and firn
records. Recent success in establishing the transfer function for HCHO allows for more quantitative
interpretations of ice cores [Hutterli et al., 1999; 2002]. However, two remaining critical needs are to
evaluate the transfer function using year-round atmospheric measurements, and to relate ground-level
measurements with those in the free troposphere. Up to now we have relied on modeling for these values.
Our incomplete knowledge in both cases is partially due to the lack of specific, fast, and reliable
long-term measurement capabilities. No continuous record over an entire year or longer exists. One of the
main tasks of the MAX-DOAS instrument we propose to develop here is to perform measurements of the
tropospheric concentration of HCHO over a time scale of one to several years. The instrument will also
measure HCHO vertical profiles, which are of particular interest to relate ground level and free
tropospheric concentrations.
How does the formation and release of HONO and NOx influence Artic air chemistry and the NO3- levels
in firn and ice? How do these processes impact the global NOx budget?
HONO and NOx formation and release from the snowpack can impact OH radical levels through the
photolysis of HONO and the reaction of OH with NO2. In addition, the chemistry of nitrogen oxides is
strongly linked to ozone formation. The various chemical mechanisms lead to a significant influence of
HONO and NOx levels on the oxidation power of the Arctic troposphere. The release of NOx and HONO
from the snowpack also is a process that reverses the removal of NOx from the atmosphere through its
conversion to HNO3 and the deposition of NO3-. Such a reversal can have an impact on the NOx budget on
larger scales.
5
5
NO3- in ice cores is also used as a proxy for NOx. The interpretation of these records requires a better
understanding of the air-snow exchange mechanisms, as well as the processes forming HONO and NOx in
the firn. In contrast to HCHO, the air-snow transfer function for nitrogen species is not as clear.
Conceptually, post-depositional loss of NO3- involves the same physical processes as for HCHO [Bales,
1995]; however, photochemical reactions in the near-surface snow recycle NOx to the atmosphere,
complicating the interpretation of air-snow concentration relationships. Year-round atmospheric
measurements will enable extending our current spring/summer understanding of these processes to the
remainder of the year. It has been shown that a year-round understanding of air-snow transfer processes is
needed to interpret the seasonally varying concentrations in ice cores [Bales and Wolff, 1996].
As in the case of HCHO, the database of HONO and NOx measurements in the arctic is limited to
short field experiments. In addition, the wet-chemical methods employed in the past may show cross
sensitivities with other trace gases, imposing a systematic error on the results. Long-term trace gas
measurements that would allow a better quantification of the various processes are currently unavailable.
The proposed MAX-DOAS instrument will thus contribute to a better understanding of the air-snow
chemistry of HONO and NOx in the arctic by providing long-term measurements of the concentrations
and vertical profiles of HONO and NO2 at GEOSummit.
At what levels are halogen oxides present in the atmosphere, in particular in the free troposphere? How
do these levels impact the global ozone budget and thus our climate? How do halogens impact the global
mercury budget?
Halogen oxides can impact tropospheric ozone and mercury levels, as is obvious in sudden polar
ozone depletion events. The observation of halogens such as bromine and iodine at other locations implies
that these reactive halogens could be present on a global scale at higher levels than thus far assumed. It is
unlikely that halogens are directly formed at GEOSummit. However, the remote high altitude location
allows access to the free remote troposphere. As several reports have indicated, bromine could be present
at levels that are sufficient to significantly influence free tropospheric ozone concentrations. The
monitoring of halogens in the free troposphere over an extended period of time is thus important to
answer whether halogen-catalyzed ozone loss is indeed important in the free troposphere. Since halogens
are also suspected to convert Hg(0) into more soluble Hg(II), the observations will also shed new light on
the fate of mercury.
The MAX-DOAS technique has been used successfully to measure halogen oxides such as BrO in
the past [Hönninger and Platt, 2002]. However, current instruments do not have the detection limits
necessary to make measurements of the low levels of halogens expected in the free troposphere. It is thus
part of this project to further improve the technique and to design the next generation of MAX-DOAS
systems that has improved capabilities of measuring low concentrations of halogen oxides.
How will changes in anthropogenic emissions of NOx and VOC’s change the composition of the remote
troposphere? How will this influence the oxidation power of the atmosphere and global climate?
Only by establishing a monitoring network of fully automated and highly sensitive instruments will
we be able to assess how the development of future emission and the effectiveness of abatement strategies
are reflected in remote areas and in the global atmosphere. Trace gases that influence the oxidation power
of the atmosphere and the chemistry of ozone are of particular significance, since they also influence
various greenhouse gases such as methane and ozone. NO2 and HCHO (as a proxy for the oxidation of
VOC’s) are such gases for which there are currently no simple fully automated long-term monitoring
methods for remote areas. We thus propose to develop technology and methods that can be used for
monitoring in remote areas and for augmenting the current baseline monitoring stations, both in polar
regions and other locations.
Motivated by these scientific questions, the objective of this proposal is to develop a next-generation
MAX-DOAS instrument to measure a variety of trace gases in the remote Arctic atmosphere. Specifically
we propose to:
6
6





Design and construct a Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS)
instrument that meets the following criteria:
o Detection limits of HONO, NO2, and HCHO of 10, 10, and 40 ppt respectively, and detection
limits in the sub-ppt range for BrO and IO.
o Long-term stability without regular calibrations.
o Unattended automatic operation.
o Capability to measure vertical profiles, or at least to distinguish boundary layer and free
tropospheric concentrations.
Develop software that allows automatic operation, self check of instrument, and remote control.
Develop software that allows the near real-time analysis of spectra in the field.
Validate the instrument in field campaigns at GEOSummit to assess its detection limits.
Deploy instrument at GEOSummit and operate for a period of at least 3 years to:
o Prove the concept and the reliability,
o Contribute to answering the scientific questions posed above.
We intend to link this effort with the objectives and activities of other arctic programs such as
SEARCH (Study of Environmental Arctic Change). One of the four main objectives of SEARCH
(http://psc.apl.washington.edu/search/) is “Long term observations to detect and monitor the
environmental changes”. While not a part of SEARCH, our instrument will compliment the sea-level
observations that are proposed under SEARCH. The instrument will also contribute to answering the
scientific questions identified by a NSF-OPP sponsored Arctic community workshop in November 2002
[Shepson et al., 2003]. Data from the proposed instrument will be made available to the scientific
community through the same means as are core measurements at GEOSummit. That is, following
processing the data will be posted on the internet, and later made available through a permanent archive.
The online data will also be used in educational efforts, both for the general public and in the classroom
environment.
3
Research Plan
The following section lays out the research approach and the proposed instrument. Before giving a
more detailed description of the technical specification of the proposed MAX-DOAS instrument, the
basic principles of the MAX-DOAS technique are reviewed.
3.1
The principle of Multi-axis DOAS
DOAS is a well-established remote-sensing technique to measure the integrated absorption of trace
gases along a light path in the atmosphere (e.g., [Geyer et al., 1999; Platt, 1994; Solomon et al., 1987;
Stutz and Platt, 1997]). Concentrations can be derived by applying the Beer-Lambert law to narrow band
absorbers. DOAS is an absolute spectroscopic method and calibration of the instruments is not necessary
[Platt, 1994]. It is one of the most specific and sensitive techniques for NO2, HCHO, HONO, and various
halogen oxides [Finlayson-Pitts and Pitts, 2000]. In the past few years a new DOAS measurement
technique that collects scattered sunlight sequentially or simultaneously at various viewing elevation
angles has evolved [Hönninger et al., 2003]. This multi-axis DOAS (MAX-DOAS) technique is an
advancement of zenith- and off-axis measurements successfully used to study stratospheric chemistry
(e.g., Solomon et al., 1987]. The spectral analysis of the absorption spectra yields the integrated
concentration over the light path through the atmosphere, which is often called the slant column density S.
As illustrated in Figure 1, S depends on the solar zenith angle  and the telescope’s viewing angle . The
slant column can be converted into the vertical column density V, by a conversion factor called air mass
factor A.
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7
3.1.1 Determination of the trace gas levels in the lower
troposphere.
z
trace gas profile
c(z)

A
SH
The principle of MAX-DOAS is based on the fact that the
scattering process
most probable scattering process for solar light occurs below
the tropopause [Hönninger et al., 2003] (Figure 1). The slant
S
column SH of an absorber in the stratosphere or upper
MAX DOAS

troposphere depends on the solar zenith angle  SH = VH / cos
 (Figure 1A). In contrast, the slant column SL of an absorber
in the lower troposphere depends mostly on the viewing angle
trace gas profile
z

B
S
: SL = VL / sin  (Figure 1B). A measured total slant column S
c(z)
can be expressed as linear combination of SL and SH:
S() = VL / sin  + VH / cos .
(1)
scattering process
By performing measurements at a small  and 
S
at constant  one can derive the tropospheric slant column by
MAX DOAS

SL* = S(S(, which can then be converted to VL
with the tropospheric air-mass factor determined by 1/sin  or
a radiative transfer model. This subtraction is done Figure 1: Setup of a MAX-DOAS
system. The slant column density of an
spectroscopically by dividing the low elevation spectrum ()
absorber in the lowest km of the
by the zenith spectrum (). This division also removes
atmosphere
changes
with
the
the strong solar Fraunhofer absorptions in the low elevation
telescope’s
viewing
angle.
spectrum, which is an essential step for DOAS with solar light.
This method was recently successfully employed to measure BrO and the thickness of the tropospheric
BrO layer in the Arctic [Hönninger and Platt, 2002]. Leser et al., [2003], have estimated the total
uncertainty of the simple geometric considerations to ~20%. The accuracy can be considerably improved
by employing detailed radiative transfer calculations as will be explained below.
L
H
L
3.1.2 Derivation of vertical trace gas profiles in the lower troposphere
The MAX-DOAS measurements, in combination with radiative transfer calculations, also offer the
exciting possibility to derive vertical concentration profiles, by taking advantage of the long light path at
low elevation angles. Radiative transfer calculations show that as  decreases the lower parts of the
atmosphere contribute more and more to the slant column S. To derive trace gas profiles one divides the
lower troposphere (we assume that the stratospheric/upper tropospheric slant column SH is already
subtracted from S, see above) into n layers of height di. The ith layer contains the absorbing trace gas, for
example NO2, at a concentration ci. To weigh the contribution of the ith layer to the slant column SL,k at a
given viewing angle k, we introduce the so-called box air mass factor Ai,k [Friedeburg, 2003]. SL,k is
determined by:
n
S L , k   ci  d i  Ai , k
(2)
i 1
To derive the concentrations ci in each of the n layers it is sufficient to measure at n different viewing
angles k (k = 1, …, n). In addition, the box air mass factors Ai,k have to be calculated by a radiative
transfer model for each viewing angle and altitude. It is then possible to solve the linear equation system 2
given by the n observations of SL,k and determine the vertical concentration profile if the Ai,k are
sufficiently dependent on elevation angles and height intervals, as it is the case for low altitudes.
8
8
0.2 atm. spectrum
3.1.3 Stratospheric trace gas columns
0.0
o
=1
-0.2
HCHO
-3
1x1020
o
0
=3
-3
-1x1015
o
-3
=5
NO
2x10
2
0
o
=10
10
-3
-2x10
HCHO airmass factor
Simultaneous to tropospheric columns MAX-DOAS also
provides stratospheric trace gas columns by using the solar
zenith angle dependence (see equation 2). This method has
been used for many years to study stratospheric chemistry
[Solomon et al., 1987]. While the scientific objective of this
proposal centers around tropospheric trace gases, the
stratospheric observations, for example of O3, offer an exciting
possibility to introduce real-time measurements from the Arctic
into the classroom, for example when discussing stratospheric
ozone chemistry.
-4
3x10
05
-4
-3x10
o
=90
HCHO + residual
NO2 + residual
residual
0 325
30
40 330
50
60335 70 340
80
solar
zenith
angle
Wavelength (nm)
90
Figure2:3:HCHO
AMF measurement
for HCHO in Los
the
Figure
lowest on
500m
above
GEOSummit.
Angeles
11/16/03
17:20UT
at =3
The lowest
viewing
and
SZA = elevation
61. The
SCDangle
of
has
the
highest
AMF.
The
SZA
16
-2
(2.5  0.2)  10 cm is equivalent to
dependence
1052
 84 pptis weak.
of HCHO for a
boundary layer height of 400 m
3.1.4 Radiative transfer modeling
By employing radiative transfer models to derive the air
mass factors, the interpretation of the MAX-DOAS
measurements can be considerably improved over the simple
approach in equation 1. We currently use a detailed MonteCarlo radiative transfer model (TRACI = Trace Gas Radiative
Monte Carlo Implementation), developed by [Friedeburg, 2003; Hönninger et al., 2003]. The model
calculates radiative transfer in the atmosphere in full spherical geometry and three dimensions. Multiple
Rayleigh and Mie scattering, as well as the Earth’s albedo, are taken into account. Equation 2 illustrates
that, if the concentrations ci are known, the accuracy of the radiative transfer calculations can be verified.
The natural choice to perform this verification is by using the visible absorptions of O2 and O4, which, in
the case of O4 is simultaneously measured with NO2 by MAX-DOAS. This validation is an important
aspect of MAX-DOAS and we will come back to it in section 3.2.3.
3.1.5 Preliminary results
To investigate the feasibility of NO2 and HCHO measurements by MAX-DOAS, our group at UCLA
has recently developed an instrument for exploratory studies of various aspects of this new method. The
UCLA MAX-DOAS consists of two motorized mirrors, which can automatically collect scattered
sunlight from any point in the sky, and a spectrometer-photodiode array detector (PDA) unit for spectral
analysis. Figure 2 shows an example for HCHO measurement in Los Angeles at an elevation angle of 3
compared to a zenith measurement. The HCHO absorption is clearly larger than the unexplained residual
of the analysis. NO2 can also be identified. Important for the extrapolation of these results to the proposed
instrument is the smallest detectable absorption structure, which is typically as large or somewhat smaller
than the peak-to-peak size of the residual. In our test measurements the smallest detectable differential
optical density was ~410-4. This number can be lowered to 10-4 by increasing the amount of collected
light, as has been shown for BrO long-path DOAS measurements in Salt Lake City [Stutz et al., 2002].
3.2
Proposed instrument design
The requirements of a long-term operation in the harsh Arctic environment, as well as the low tracegas mixing ratios in remote polar locations, such as Summit, Greenland, determine the design of the
instrument proposed here. In addition, the measurement of vertical profiles enters the design
considerations. Based on our exploratory measurements we propose to develop a MAX-DOAS system
that measures at four fixed low-elevation angles and sequentially at  = 90 using a CCD based
spectrograph-detector system.
3.2.1 Choice of wavelength range and viewing geometry
To obtain the best detection limits for the different trace gases, wavelength regions around the
strongest absorption bands (Table 2) have to be chosen. The wavelength range to be covered thus extends
from 300 – 470 nm for the targeted trace gases. Another important parameter for a MAX-DOAS
9
9
HCHO airmass factor
instrument is the choice of the viewing geometry, i.e. the
o
=1
number of telescopes and their elevation angles. To avoid
20
problems that result from sequential elevation scanning we
o
=3
intend to use four telescopes each aiming at a different
15
o
=5
elevation. Preliminary radiative transfer calculations for
o
10 =10
GEOSummit for HCHO in the lowest 500 m of the atmosphere
(Figure 3) show air mass factors of up to 22 at low viewing
o
5 =90
elevation angles of  = 1 compared to AMF = 3 at  = 90. It
should be noted here that the 90 AMF is 3, and not 1 as one
0
30
40
50
60
70
80
90
may expert, due to the high ground albedo of snow and the
solar zenith angle
resulting multiple scattering. The NO2 air mass factors (not
shown) are even higher and reach 35 for  = 1. To achieve the Figure 3: AMF for HCHO in the
desired detection limits for boundary layer trace gases we lowest 500m above GEOSummit.
The lowest elevation viewing angle
propose to have one telescope with  = 1. An additional
has the highest AMF. The SZA
sequentially measured telescope will be aimed at the zenith dependence is weak.
( = 90) to provide a Fraunhofer reference spectrum and to
remove the stratospheric contribution to the slant column. To determine vertical trace gas profiles
additional viewing elevations have to be added. The box air mass factors for a solar zenith angle of 75 at
Summit are shown in Figure 4. The box air mass factors change for each viewing angle and height, which
makes the solution of equation 2 possible. At ~5000 m above the top of Greenland the box air mass
factors becomes equal for all elevation angles. MAX-DOAS is thus insensitive to trace gases above this
altitude. However, the total columns can still be determined (see 3.1.3). Based on these preliminary
results we currently favor 4 viewing angles:  = 1, 3, 5, 10 and an additional 90 reference
measurement. As part of this project we propose to perform more calculations to optimize this choice.
This choice is a compromise between vertical resolution and measurement frequency. We anticipate a
measurement frequency of less than 20 minutes for solar zenith angle smaller than 80. To maintain low
noise levels, the integration times will be longer for larger solar zenith angle.
3.2.2 Instrument Setup
HCHO box airmass factor
Figure 5 shows a schematic of the proposed instrument. It consists of three main components:
Spectrograph-detector combination, telescope and quartz-fiber transfer optics, and a controlling computer
with corresponding software. The following section will specify the individual components:
Spectrograph detector combination. We propose to use a combination of an imaging spectrograph with a
two-dimensional charged-coupled-device detector (CCD). A fiber bundle that is arranged in four
vertically separated arrays (Figure 5) will be projected on
the CCD, thus simultaneously measuring four viewing
60
directions. We propose to purchase a 300 mm focal length
elevation angle
o
50
f/4 Czerny-Turner type spectrometer (ACTON Spectra Pro
1
o
300i) that allows the imaging of the fiber array onto the
3
40
o
CCD detector. A number of adaptations have to be made
5
o
30
to this spectrograph. A thermal stabilization to  0.2 K
10
o
improves the long-term stability. Additional baffles in the
90
20
spectrograph reduce stray light, which is essential for
10
accurate measurements below 350 nm, and is thus part of
the development process. The spectrometer will be
0
equipped with two UV-blazed gratings of 1200 g/mm and
0
1
2
3
4
5
6
altitude [km] (agl)
300 g/mm. The first offers a better spectral resolution
(~0.35 nm) and analysis statistics, but only covers ~70 nm, Figure 4: HCHO box airmass factors show
thus requiring sequential measurements of HCHO and a clear dependence of elevation angle and
NO2. The second grating covers 240 nm at a lower altitude below 5 km altitude
10
10
quartz fiber slit
resolution of ~1 nm, and measures the entire wavelength for all trace gases. The suitability of both
gratings will be determined during the test measurements, after which a decision for the final setup will be
made.
We chose a 2048  512 pixel thermoelectrically cooled UV enhanced back-illuminated CCD array
(Princeton Instrument Spec-10: 2KBUV). The array is 6.9 mm high, allowing a high light throughput
(compared to a PDA which is only 2.5 mm high). The quantum efficiency is above 50% for the desired
wavelength range, and the detector noise (~3 e- rms) is far superior to the older PDA’s and much better
than for most other available CCD detectors. The detector can be cooled down to -70C, reducing the
dark current to negligible values. The CCD chip is permanently sealed in a vacuum chamber, eliminating
the necessity of evacuating the detector on a regular basis. Both spectrograph and CCD detector only
require power (~300W) to operate, and are maintenance free.
The combination of imaging spectrometer – CCD detector offers many advantages over other
spectrometer/detector combinations for our application. There are however, a number of challenges that
need to be overcome to achieve the low residual structure and thus detection limits required in our
application. The dispersion and instrument function (spectral resolution) is not adequately uniform
perpendicular to the dispersion direction (along the slit direction) and the sensitivity of the CCD pixels
varies over the array by 0.1 - 1%. The consequence of these two effects is that spectra measured at
different vertical locations on the CCD detector, i.e. spectra 1 and 3 in Figure 5, are different. A zenith
light spectrum measured on CCD position 3 (Figure 5) cannot be used as a Fraunhofer reference for a low
elevation spectrum measured at position 1 (Figure 5). A division of the two spectra will not entirely
remove the Fraunhofer bands, due to different instrument functions (resolutions). In addition, the pixel
sensitivity variation may introduce additional structures, even if the latter is corrected by other methods,
such as the measurement of a white light source. Consequently, steps have to be taken to ensure that a
Fraunhofer spectrum ( = 90) is measured for each position of the CCD (see next section).
Telescope and quartz-fiber transfer optics. We propose to build a 4-telescope system for the
elevation angles  = 1, 3, 5, and 10, each with a lens and an field of view of ~0.3. The light from
these telescopes will be transferred by fiber transfer optics to the spectrograph, where 45 fibers
( 200m) will be arranged in four 1.2 mm high slits (Figure 5). The fibers also serve as depolarizers.
Zenith-viewing reference spectra for all four low elevations will be measured in-between low elevation
measurements. We want to stress
again that the measurement of
rotational axis
A
zenith.
B
Fraunhofer reference spectra with the
quartz prisms
telesc.
mounted on
fibers
fiber bundles
same instrument function and pixel
4
1
axis
sensitivity is absolutely essential to
3
2
reach low detection limits. This
2
3
requirement
outweighs
the
1
4
disadvantage of making low-elevation
telescopes
and zenith measurements sequentially.
with fiber
low elev.
stepper motor
bundle
telesc.
translational stage
In the unlikely case that temporal
1
change in stratospheric trace gas
levels indeed pose a problem, we will
2
3
change viewing direction more
electronics
4
frequently and average the respective
CCD detector
spectra. We propose to develop a new
1
spectrograph
approach to measure Fraunhofer
PC
2
references by using of a fiber
3
4
multiplexer (see below) that can also
wavelength
be used in future MAX-DOAS
applications with 2D-CCD detectors. Figure 5: Schematics of the proposed MAX-DOAS instrument.
Because the fiber multiplexer uses The fiber multiplexer is shown in A, the telescope multiplexer in B.
11
11
technology which has not been demonstrated for this application, a backup approach that requires a larger
telescope assembly and is more sensitive to environmental conditions, will also be considered.
Fiber multiplexer (Figure 5A). A fifth zenith-viewing telescope is added to the four low elevation
telescopes. A fiber bundle, with 4  600m fibers, transfers the zenith light to the multiplexer. The fibers
are arranged linearly at the multiplexer. The slightly different viewing geometry for the four fibers in the
zenith telescope does not cause problems since the 90 air mass factor is insensitive to small angular
variations. The fibers from the four low-elevation telescopes and from a Hg reference lamp (not shown in
Figure 5A) will be arranged at the multiplexer with the same geometry parallel to each other. Opposite, an
identical arranged fiber bundle will be mounted on a high accuracy computer controlled translation stage
(Thorlabs VX25D, linear accuracy < 0.02 m) to align the spectrograph bundle with one of the three
other bundles. The detailed construction and testing of this new multiplexer will be one of the first tasks
of this proposal. We anticipate that with today’s manufacturing accuracies the transmission loss in the
multiplexer of less than 20% can be achieved. The advantage of the fiber multiplexer is an entirely
passive telescope assembly, which is fairly small, insensitive to low temperatures, and can be easily
mounted outside. The only moving part, the translational stage, can be mounted in a thermally stable
environment. This advantage justifies the effort to develop this new device.
Telescope Multiplexer (Figure 5B). While we are certain that the multiplexer is technically feasible,
it is a new development and unforeseen problems can occur. As alternative setup we propose a
multiplexer in the telescope. This setup involves moving four quartz-prisms in front of the four telescopes
with one stepper motor. However, because stepper motors need to be protected against the environment,
an additional housing around the telescope is required, increasing the size of the telescope assembly. In
addition, the Hg reference lamp (not shown in Figure 5B) will also have to be mounted in the telescope.
Mounting the telescope assembly would thus be more difficult, and the longevity and long-term operation
can pose a challenge.
Computer and software. The instrument will be controlled by a standard personal computer that
controls the acquisition and storage of the 2D spectra, the grating and the multiplexer. We also plan to
connect a small camera to the computer to take pictures of the meteorological condition and to aid in the
interpretation of the data. We will adapt existing software [Gomer et al., 1996; Stutz and Platt, 1996] for
these tasks. In addition, the ability to remotely check and control the instrument at GEOSummit will be
developed. Because the instrument will produce ~90 Mbyte of raw data per hour, we plan to develop
software to convert the 2D spectra online into four spectra (one for each elevation angle). After the
conversion, only ~300 kByte of data per hour will be sent to our lab, while the raw data can be backed up
on a less regular schedule. It is important to obtain data continuously to ensure that the instrument is
operational.
3.2.3 Analysis software development
The underlying mathematical methods to analyze skylight DOAS spectra are well known [Stutz and
Platt, 1996]. However, our experience has shown that the analysis routines need to be adapted to any new
type of instrument. Current DOAS software still requires a large amount of manual operation. As part of
this proposal we will thus develop software that is able to automatically perform the spectral analysis of
the spectra, giving the slant column densities for each viewing elevation, together with the respective
statistical errors as a result. Ultimately this software will be combined with the acquisition program to
deliver slant column densities online directly after the acquisition of the spectra, reducing the time delay
between measurement and data availability.
An important task, and probably the main challenge for MAX-DOAS are the radiative transfer
calculations. Radiative codes for this purpose are available [Hönninger et al., 2003]. The true challenge is
not the code, but rather the often-unknown input data, i.e. aerosol optical properties, vertical aerosol
distribution, and the presence of fog, clouds and snow. Without additional measurements of these
properties, the radiative transfer calculations are inherently uncertain. However, MAX-DOAS offers the
ability to validate the radiative transfer calculations by using the absorptions of O4 and O2. Today the
12
12
validation of the radiative Table 2: Wavelength regions and anticipated detection limits
transfer
calculations
is
AMF
AMF
det. lim.
det. lim.
’

usually achieved manually,
boundary
free
boundary
free trop. 3
[nm]
[10-19
and an adaptation of the
layer1
trop.2
layer 3
[ppt]
cm2]
calculations to the observed
[ppt]1
O4 and O2 columns is rarely HCHO 320
1.5
21.3
7.0
33
50
performed. This approach is NO2
440
3
37.9
5.8
9.5
25
4.5
21.3
7.0
11
18
too work-intensive for a HONO 350
345
125
21.3
7.0
0.4
0.6
long-term monitoring. We BrO
440
250
37.9
5.8
0.1
0.3
will
therefore
develop IO
1
calculated
for
the
lowest
500
m
above
GEOSummit
for
SZA
=
75
software that allows the
observed O4 (and if needed 2 calculated for the 1000 - 5000 m above GEOSummit for SZA = 75 and  = 10
O2) levels to be fed into the 3 based on the AMF difference between  = 1/10 and  = 90
radiative
transfer
calculations with the goal of optimizing the accuracy of the air mass factors and box air mass factors. In
addition, we plan to use additional information, such as meteorological data and relative intensities. Two
approaches appear to be feasible. A look-up table approach, which will be based on a large number of
radiative transfer calculations for different conditions at GEOSummit, will be relatively fast, but is
restricted to one location. Alternatively, we want to investigate whether current radiative transfer codes
can be accelerated to make online calculations possible. Ultimately the goal is to have a program that can
decide, based on available data, what the best input data for the radiative transfer calculations. These
programs need to be extensively tested against the data.
The final code that we propose to develop is the deconvolution process for the vertical trace gas
profiles. The mathematical methods for solving equation 2 are available [Hoenninger et al., 2003]. The
challenge is, however, to integrate the radiative transfer calculations into the calculations and the
determination of the statistical errors for every trace gas profile, considering both the uncertainty of the
slant columns [Stutz and Platt, 1996] and of the Box air mass factors. We anticipate that by the fourth
year of the project all software components can be combined, and that the MAX-DOAS instrument will
automatically calculate trace gas columns. We however, propose storing raw data and performing
periodic offline tests of the accuracy of the instrument.
3.3
Anticipated performance and validation efforts
The anticipated detection limits (Table 2) were calculated using the minimum detectable optical
densities of 10-4 that we determined based on past DOAS applications, and the AMF and differential
absorption cross sections listen in Table 2. The HCHO detection limits of ~30 ppt are sufficient to
monitor this compound and to derive its vertical profile. Similarly, the detection limits for the halogen
oxides are sufficient to determine whether they are present at mixing ratios above 0.5 ppt in the free
troposphere. For NO2 and HONO, the detection limits are sufficient for most monitoring purposes and to
distinguish lower from free tropospheric levels. However, it would be highly desirable to further improve
the detection limits for these two compounds to derive vertical profiles. As part of this proposal we will
therefore investigate if the residual structure of the instrument can be further reduced. If an improvement
cannot be achieved through optimization of the instrument, we will average concentrations to reduce the
error. To confirm the performance of the instrument we intend to compare it to other available techniques.
While the schedule for field experiments in the coming years is not yet fixed, we anticipate that short field
campaigns will be performed at GEOSummit during the second half of our project. We will participate in
these efforts to test and validate the MAX-DOAS.
13
13
3.4
Project plan
Year
1
Goal
 Radiative transfer calculations to determine final design of telescope
 Choice and purchase of detector and spectrometer
 Design and construction of telescope and fiber assembly
 Characterization and optimization of spectrograph/detector
 First test measurements in Los Angeles
 Presentation of concept and instrument at AGU conference
2
 Tests and optimization of telescope at clean air site
 Development of software for automatic operation
 Construction of hardware for deployment in Greenland
 Deployment to GEOSummit in Summer 2006
 Publication of construction details and test measurement results
3
 Offline analysis of first Greenland measurements
 Development of online analysis software
 Improvement of radiative transfer software
 Validation of instrument in intensive field experiments
 Publication and presentation of initial results
4
 Continued offline analysis of data
 Installation and testing of online analysis software in Greenland
 Display of online data on GEOSummit web-page
 Validation through participation on intensive field experiments
 Interpretation of measurement results
 Publication and presentation of results
5
 Quality checks of online analysis and instrument behavior
 Interpretation of measurement results
 Publication and presentation of results
We plan to present our progress and results at national meetings, for example the AGU or AMS
meetings. A number of publications in peer-reviewed journals will be written starting the second year of
the project.
3.5
Project Management
R. Bales is currently the PI on the GEOSummit year-round measurement program (OPP-0336450),
which involves deployment of instruments and measurements for a number of scientists. He also carries
out science coordination for GEOSummit (OPP-9910303). As PI on the current proposal, he will integrate
the DOAS instruments to be developed by Co-PI J. Stutz into the ongoing measurement program. Both
UCLA and UC Merced will be involved in deployment and evaluation of the instrument, with its longterm operation falling under the core-measurement project. Both Bales and Stutz plan to use data from the
instrument, both for studies of atmospheric photochemistry and for understanding the snow-atmosphere
transfer for reactive species. A number of other scientists working in the Arctic are also interested in
using data from the instrument (see attached letters from J. Dibb and P. Shepson).
4
Impact and benefits to society and education
The change of the earth’s climate and changes in the atmospheric composition on a global scale are
among the most serious environmental challenges of the future. The potential impacts for life on our
planet are of great concern, and the development of strategies to mitigate global climate change is thus a
priority for today’s societies. However, our current understanding of the climate system is, in many
aspects, insufficient to make prediction of future development, for example by using 3D models. A
14
14
number of climate changes have manifested in the Arctic, where significant feedback mechanisms are
suspected to act. It is one of the most important tasks of arctic research to quantify these feedbacks,
requiring a detailed understanding of the atmospheric composition, atmosphere-snowpack interactions,
and the linkage with other environmental variables.
Our proposal aims to contribute to an improved understanding of the role of the Arctic in the climate
system by introducing a new experimental method that may be used for regional and global monitoring
networks, as well as be used in the investigation of various arctic processes that are potentially important.
The new instrument at GEOSummit will contribute to detecting, understanding and modeling Arctic
change. These efforts are supported by a number of community initiatives, including: i) the World
Meteorological Organization’s (WMO’s) Global Atmospheric Watch (GAW); ii) SEARCH (A Study of
Environmental Arctic Change), which is a science initiative with multi-agency support in the U.S.; and
iii) Air-Ice Chemical Interactions (AICI), a proposed successor to the IGBP-IGAC (International Global
Atmospheric Chemistry Program) Polar Air and Snow Chemistry (PASC) activity; and other proposed
initiatives. Our project will provide unique continuous baseline measurements of important reactive trace
gases at GEOSummit, which serve a number of scientists and individual research projects. Long-term,
core measurements are part of the nations and international communities science infrastructure; this
proposal provides for a improvement in that infrastructure. The international science community has
chosen Summit for multidisciplinary, multi-investigator studies, significant infrastructure is in place, and
a number of Arctic researchers are collaborating there. The current project builds on the ongoing
atmospheric measurement program and the intermittent measurements that have been conducted over the
past decade.
There are at least three main broader impacts of this project that reflect the suggestions of the ACOPP
(Advisory
Committee
for
NSF’s
Office
of
Polar
Programs)
(see
http://www.nsf.gov/od/opp/opp_advisory/oaccrit2.htm). First and foremost, improved observational
capabilities through the development of next-generation instruments enhances infrastructure for research
and education. Not only the measurements, but also the continued operation of the instrument, provides
critical research infrastructure for understanding and predicting Arctic change. The measurements in this
proposal are of interest for scientists working in the area of Arctic atmospheric chemistry (see attached
letters).
Second, as a future part of the GEOSummit monitoring capabilities, the new instrument contributes
to the dissemination of scientific understanding of the Arctic system. We will put considerable effort into
making data and information widely available in near real time. This has thus far not been attempted for
DOAS instruments, and it is therefore a focus of this project to develop the software that allows real-time
analysis of DOAS observations. We anticipate that in the last years of the project the measurement results
will be posted with very little delay on the GEOSummit web-page. In addition, the construction details of
the instrument and the scientific results from its operation will be made available to the community and
published in peer reviewed journals.
Third, education of the global community is an objective of the long-term measurements, using
www-available data and educational materials. As part of GEOSummit, we will encourage educationresearch linkages. For example, the PI has hosted K-12 teachers under NSF.s TEA (Teachers
Experiencing Antarctica and the Arctic) program, as other scientists working at GEOSummit. Both
graduate and undergraduate students will also be benefit from the data and technology provided by this
proposal. J. Stutz, for example, teaches a large general education class for non-science undergraduate
students at UCLA (AS2: Air Pollution). The use of real data will enhance the classroom experience for
the students and expose them to state of the art research measurements. R. Bales is also very active in K12 education, serving as the lead PI for hydrology under the international GLOBE (Global Learning and
Observations to Benefit the Environment) program (globe.hwr.arizona.edu), which has trained over
20,000 teachers in 12,000 schools to integrate environmental measurements and learning into their
curricula. Through those connections with teachers and schools, he will take advantage of opportunities
to disseminate the information developed under this proposal to them.
15
15