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APPENDIXES
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APPENDIX A
Current Tropospheric Chemistr y
Research In the Unitec! States
There are programs under way in the United States
and elsewhere that are already addressing certain
aspects of global tropospheric chemistry. In the United
States, these programs, active in several agencies are
formally coordinated through the Subcommittee on
Atmospheric Research of the Committee on Atmo-
spheres and Oceans, which is established under the Fed-
eral Coordinating Council for Sciences, Engineering,
and Technology. None of the current programs includes
all of the Global Tropospheric Chemistry Program ele-
ments recommended in this report, and all of them
together wig not, without significant augmentation,
achieve the goals of the recommended global program.
Relatively few of the existing programs have global
tropospheric chemistry issues as their focus. Most of the
larger programs are focused on urban or regional prob-
lems such as air pollution or acid rain. Nevertheless,
many of the research tasks encompassed by the existing
federal programs will contribute substantially to solving
tropospheric chemical problems encountered on the
global scale. A brief summary of the various programs
follows.
NSF's ATMOSPHERIC CHEMISTRY PROGRAM
The Atmospheric Chemistry Program of the Atmo-
spheric Sciences Division of the National Science Foun-
dation (NSF) supports a wide range of laboratory, field,
and modeling investigations of the troposphere, the
stratosphere, and planetary atmospheres. The ultimate
goal of understanding the complex interactions of hun-
dreds of chemical reactions with transport and radiation
phenomena is supported by studies of the pathways and
kinetics of molecular-level processes, of the global
cycling of chemical elements, and of new approaches to
the measurement of trace species, including free radi-
cals. Trace gases and aerosols are investigated in both
clean and polluted atmospheres.
The program lends support to advances in methodol-
ogies for the identification of individual aerosol particles
and to the study of the interaction of these particles with
their gaseous environment. The chemistry of the parti-
cle-size domain between molecular dimensions and fil-
terable particles receives added emphasis.
The Atmospheric Sciences Division of NSF, through
the University Corporation for Atmospheric Research,
supports the National Center for Atmospheric Research
(NCAR) to initiate, coordinate, and carry out atmo-
spheric research that requires long-term cooperative
efforts among scientists at NCAR and at universities
and government laboratories and to provide and
develop facilities and related services for the atmo-
spheric research community. Research within the
Atmospheric Chemistry and Aeronomy Division at
NCAR has recently focused on the role of CO, NO,
CH4, and nonmethane hydrocarbons in the tropo
171
OCR for page 172
172
- 1 ~
spheric O3 budget, on biospheric processes as they influ-
ence the atmosphere, on biomass burning as a source of
atmospheric trace gases, and on cloud chemistry and
. . . . .
ace precipitation anc its causes.
NASA's GLOBAL TROPOSPHERIC EXPERIMENT
A research effort named the Global Tropospheric
Experiment (GTE) has been initiated by the National
Aeronautics and Space Administration (NASA) to
study the chemistry of the global troposphere and its
interaction with the stratosphere. The first phase of the
project, aimed at developing and validating measure-
ment techniques for HxOy and NOx trace species in
tropospheric chemical cycles, is designed to lead to the
development and implementation of a cooperative
global tropospheric chemistry research program with
the goal of understanding the chemical cycles that con-
trol the composition of the global troposphere and its
charlges.
The immediate emphasis of the GTE is on the devel-
opment, testing, and evaluation of measurement tech-
niques that can achieve, under field conditions, the
extreme sensitivity required to determine accurately
atmospheric concentrations of key chemical species. A
later phase ofthe GTE will focus on widespread, system-
atic measurements supported by modeling and labora-
tory studies to understand the principal processes that
govern key chemical cycles in the troposphere.
The role of the global troposphere as the source and
sink for the stratosphere, the details of the troposphere-
stratosphere interchange, the processes that control
global tropospheric O3, and the atmospheric role in bio-
geochemical cycles are of particular interest to NASA,
as is the eventual development of an enhanced capability
to study the troposphere and its composition from space.
Instrument development in the initial phase of the
GTE will involve a three-step test and evaluation pro-
gram comprising a ground-based intercomparison, an
airborne intercomparison in the tropical troposphere
with particular attention to the boundary layer over the
ocean and over tropical forests, and an airborne inter-
comparison in the upper troposphere. This strategy will
systematically expose the measurement systems under
current development and evaluation to conditions that
will be encountered in later global tropospheric chemis-
try field experiments.
NOAA's GEOPHYSICAL MONITORING FOR
CLIMATIC CHANGE PROGRAM
The NOAA Air Resources Laboratory's Geophysical
Monitoring for Climatic Change (GMCC) program
operates four baseline observatories at which measure
APPENDIX A
meets are made of atmospheric trace constituents
important for climatic change. These observatories are
located in remote clean-air sites where the measured
values are representative of background concentrations
of trace gases and particles in the atmosphere. The
observatories are located at Barrow, Alaska; Hilo
(Mauna Loa), Hawaii; American Samoa; and South
Pole, Antarctica; and are also components of the WMO
Background Air Pollution Monitoring Network (BAP-
MoN) Program.
The objectives ofthe GMCC program are as follows:
I. To determine concentrations, their variations with
time and space, and properties of atmospheric trace
gases and aerosols that can potentially have an impact
on climate;
2. To understand the sources, sinks, transport, mod-
ification, and budgets ofthose trace constituents; and
3. To apply (in collaboration with others) those mea-
surement data to determine their effect on global
weather and climate. The GMCC monitoring effort at
the baseline observatories is primarily for long-term sur-
veillance of atmospheric trace species concentrations.
Additional flask sampling measurements of selected
atmospheric trace constituents are made near Niwot
Ridge, Colorado; at Boulder, Colorado; at a global net-
work of CO2 flask sampling stations; at a number oftotal
O3 monitoring stations located mainly in the contiguous
United States; and occasionally at other locations in
support of particular research objectives. GMCC
research primarily focuses on analyses of these data sets.
Programs for the measurement of O3 (surface, verti-
cal profiles, and total column), atmospheric aerosols,
halocarbons (Freons 1 1 and 12), N2O, water vapor, and
precipitation chemistry are currently under way by
NOAA at one or more of the GMCC program sites.
A primary objective for the GMCC program is to
make measurements of trace species in a monitoring
mode to document long-term trends. As such, most
programs are continuing, in contrast to expeditionary.
In the near future, programs will begin in the automa-
tion of Dobson spectrometers, and on the measurement
of radiatively active trace gases, and of gases and aero-
sols in the Arctic.
NSF's SEAREX PROGRAM
The Ocean Science Division of NSF has been spon-
soring a coordinated research effort investigating the
atmospheric transport of material from continental
regions to the ocean. The Sea-Air Exchange
(SEAREX) program was initiated in 1977 and directly
involves 11 universities and laboratories from the
United States, France, and England, and cooperative
OCR for page 173
APPENDIX A
ancillary programs with investigators from New
Zealand, Australia, Japan, and the People's Republic of
China. The SEAREX program has concentrated its
efforts on investigating air-sea exchange in the westerly
and trade wind regimes of the North and South Pacific
Ocean. The objectives of SEAREX are as follows:
1. The measurement of the rate of exchange of
selected trace elements and organic compounds across
the sea-air interface,
2. The investigation of the mechanisms of exchange
of these substances, and
3. The identification of the sources for these sub-
stances in the marine atmosphere.
Chemical substances being investigated in SEAREX
include selected heavy metals (e.g., Pb, Cd, Hg, Zn, Se,
Fe, Mn, V, and Cr), soil dust, sea salt, halogens, 2~0Pb
and typo, sulfate, nitrate, phosphate, particulate
organic carbon, and such organic species as PCB, DDT,
HCB, aliphatic hydrocarbons, phthalate plasticizers,
fatty acids, fatty and polycyclic alcohols, and low-molec-
ular-weight ketones and aldehydes. Extensive field pro-
grams have been carried out at Enewetak Atoll, Mar-
shall Islands in 1979, at American Samoa at the NOAA
GMCC station site in 1981, and in northern New
Zealand in 1983. A final SEAREX field program is
planned from an oceanographic research vessel located
at about 40 ° N. 1 70 °W in 1986.
THE NATIONAL ACID PRECIPITATION
ASSESSMENT PROGRAM
The Acid Precipitation Act of 1980 established the
Interagency Task Force on Acid Precipitation to develop
and implement a comprehensive locational Acid Precipi-
tation Assessment Program. The act required the task
force to produce a national plan for a 10-year research
program. The purpose of the National Acid Precipita-
tion Assessment Program is to increase understanding
of the causes and effects of acid precipitation. The
national program includes research, monitoring, and
assessment activities that emphasize the timely develop-
ment of a firmer scientific basis for decision making.
The National Acid Precipitation Assessment Program is
co-chaired by the Environmental Protection Agency
(EPA), NOAA, and the Department of Agriculture, and
it includes a major involvement by the national labora-
tories of the Department of Energy (DOE).
Research is proposed in the National Plan in nine
categories. Each of the research tasks described focuses
on a specific area and generally involves the coordinated
participation of several agencies.
Focusing on research needs and tasks relevant to
atmospheric sciences in general and atmospheric chem
173
istry in particular, the plan pursues the following
. .
O Electives:
1. Identify the natural emissions that can influence
precipitation chemistry and develop an experimental
data base that sufficiently characterizes the source
strengths of these species.
2. Quantify pollutant emissions of interest from
man-made sources with supporting energy-use, eco-
nomic, and technical data for appropriate sources and
regions for certain time periods.
3. Develop and maintain quality-assured emission
models and methods to support other task groups assess-
ing control strategies for acid deposition.
4. Conduct special research projects into economic,
energy-use, technological, and other factors that affect
pollutant emissions from major man-made sources.
5. Determine the important aspects of meteorologi-
cal transport of acidic substances and their precursors on
spatial scales ranging from local to global.
6. Determine the important overall physical and
chemical pathways and specific reaction processes regu-
lating the formation of acid substances in the atmo-
sphere through laboratory and field measurements and
theoretical interpretation.
7. Determine the relative importance of wet and dry
removal processes for acid substances and their precur-
sors within the atmosphere.
8. Develop state-of-the-science modeling frame-
works using advanced products resulting from the
atmospheric processes research program. The models
will serve as the media for integrating the full spectrum
of phenomenological research in acid deposition and as
the primary assessment tools in identifying future con-
trol strategies for mitigation.
9. Develop a comprehensive data base for evaluation
and verification of acidic deposition models and associ-
ated process component modules.
10. Determine the spatial and temporal variations in
the composition of atmospheric deposition within the
United States for a period measured in decades through
a National Trends Network.
The time schedules contained in this federal plan call for
preliminary assessment of the research results by 1985-
1986 and a more complete assessment by 1988-1989.
OTHER RELATED PROGRAMS
In addition to the above programs that have regional-
to global-scale tropospheric chemistry as their major
thrust, several mission agencies support work that is
applicable to the research goals of a global tropospheric
chemistry program.
The DOE has supported for many years a program
OCR for page 174
174
designed to yield understanding of the relationship
between energy production activities and effects on the
atmosphere, and, from work of its predecessor agencies,
to study the impact of nuclear explosions in the atmo-
sphere. Chemistry program elements involve labora-
tory and field studies of the mechanisms and kinetics of
the production and transformation of emissions related
to use of energy. A major research area is the study ofthe
physics and chemistry ofthose processes that control the
removal from and reinsertion into the atmosphere of
gases and aerosols. Recent emphasis has also been
placed on problems related to emerging energy technol-
ogies. Since 1978, the DOE has been engaged in a major
effort to analyze the causes and climatic consequences of
CO2 buildup in the atmosphere, an activity that
requires measurement of fluxes and involves study of
the carbon cycle as a whole in the biosphere, including
the atmosphere.
1
APPENDIX A
The EPA, as the regulatory agency with responsibility
for establishing and enforcing environmental standards
within the limits of various statutory authorities, con-
ducts a major atmospheric research and monitoring
program. A major fraction of this activity is directed
toward understanding and characterizing problems
within urban and regional air sheds with focus on crite-
ria pollutants, hazardous pollutants, long-range trans-
port, transformations, particles, vehicular emissions,
and large-scale and long-term effects of air pollution on
the biosphere. An analysis ofthis program is beyond the
scope ofthis report, but the program has produced, and
continues to produce, results of immediate application
to global tropospheric chemistry investigations. Partic-
ularly notable examples are the studies of the long-range
transport and fate of atmospheric pollutants and the
extensive transport and fate models designed for appli-
cations on scales up to the regional.
OCR for page 175
APPENDIX B
Remote Sensor Technology
The following overview will provide a perspective of
the ultimate role of spaceborne remote sensor tech-
niques in providing global measurements to improve
understanding of the processes involved in the chemis-
tr.y, dynamics, arid transport phenomena in the global
troposphere. To provide this perspective, this overview
will highlight two spaceborne sensors that are currently
providing measurements from space, provide a survey
of potential instrument techniques that can provide key
measurements important to tropospheric science, and
project some technological developments that need to be
implemented to realize the hill potential of remote sen-
sor techniques from space. Ultimately, remote sensor
techniques should be utilized from orbiting satellites for
long-duration missions to exploit the potential to mea-
sure and detect long-term trends related to changes in
the global balance of the troposphere due to anthropo-
genic and nonanthropogenic processes.) However, the
path to developing research instruments for long-dura-
tion satellites should capitalize on other airborne and
spaceborne platforms, including high-flying aircraft,
the opportunity to iterate a variety of measurements
with evolving mathematical models of the troposphere,
and provide the instrument scientific community with
the opportunity to develop and evaluate advanced sen-
sor technology to optimize the measurement base
required to validate the mathematical models devel-
oped.
PRESENT SPACEBORNE SENSOR
MEASUREMENTS
Three classes of remote sensors have demonstrated
unique capabilities in meeting some ofthe measurement
needs in the global troposphere. The first class includes
imaging spectroradiometers currently being used in
Earth Observation Satellite Systems for meteorological
and earth resource measurements. These sensors have
recently shown the ability to detect regions of elevated
haze layers and aerosol loading in the troposphere. A
second class of instruments includes passive remote sen
sors that measure spectral emission or absorption of
the Space Shuttle, and possibly spaceborne pallets or atmospheric molecules with external sources of radia
free flyers of shorter duration missions. This approach lion. Vertical distributions of molecular species, pres
sure, and temperature can be inferred through the use of
inversion algorithms. A third class of instruments
includes active remote sensors in which lasers ire the
ultraviolet, visible, and infrared portion ofthe spectrum
are used in a similar mode as an active radar system.
will provide the atmospheric science community with
Report of the NASA Working Group on Tropospheric Program
Plaurling.~. H. Seinfeld. NASA RP 1062. 1981.
175
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176
Through a combination of scattering by aerosols and
molecules in the atmosphere and selective absorption by
atmospheric molecules, these sensors can provide
range-resolved measurements of tropospheric mole-
cules and aerosol loading.
HAZY AIR MASSES
(Jurrent research objectives and approaches for spec-
troradiometer systems encompass the following ele-
ments. Overall, the current objective is to evaluate capa-
bilities of existing satellite and aircraft systems in
. . . . . . . ~
conjunction Wlt n exlstmg image processing systems tor
monitoring air pollution episodes
· Outline the extent of the pollution area as seen on
the visible imagery.
· Attempt to measure the threshold quantitatively
over land as well as water.
· Note the condition, if any, under which the area is
seen on the infrared imagery.
· Track the motion of the pollution area by noting the
motion of its "center of gravity" or the motion of any
discrete edge or feature.
· Compare any apparent motion with wind informa-
tion obtained from conventional meteorological
sources.
· Delineate the radiance values associated with indi-
vidual pixels within the area and draw isopleths of
selected radiances.
· Measure the variation of the radiance, i.e., the
change of the isopleth values, as `` function of the time of
day.
· Make a correction for wind-related changes in the
apparent density of the haze to obtain the variation in
radiance related primarily to the solar zenith angle.
· Follow up university efforts to calibrate the SMS/
GOES satellite visible sensors, and continue this effort
by comparing the radiances as seen by the GOES sen-
sors over a region of uniform brightness, with radiances
expected from that surface through a normal haze-free
atmosphere, as predicted by the Fraser model. In this
model, the solar relationship to the surface is included.
· Adjust the radiances measured by the SMS/GOES
sensors according to the calibration, and with the
adjusted values, calculate the optical depth and mass
loading at various locations of the smog area by using
the Fraser model.
~.
· (correlate any computed smog density with various
APPENDIX B
. . .
height of inversionlayers, relative humidity, and ground
visibility. The ground-based smog measurements are
optical thickness and particulate count.
· Attempt to generate atleast two sets of correlations,
one based on the model-calculated mass loading, and
another based on the basic SMS/GOES radiances.
Under the modeling phase of the study, the approach
involves an investigation of the scattered sunlight radi
ance. The radiance of the sunlight scattered toward a
satellite is being computed for models of the air pollution
for two purposes: (1) To determine the response of the
radiance to the important physical parameters; (2) To
estimate the accuracy with which air pollution parame
ters such as aerosol optical thickness, sulfate mass, and
visibility can be derived from satellite observations. The
important variable parameters for study in specifying
the model are the bidirectional reflectivity ofthe ground,
the aerosol optical thickness, the relative humidity and
amount of water vapor, the composition of the aerosols,
and their size distribution.
The computed radiation characteristics will be com
pared with experimental results. Even more impor
tantly, the aerosol parameters derived from satellite
observations will be verified with experimental results.
A large body of good experimental data on the physical
and chemical characteristics of dense air pollution was
obtained during the Persistent Elevated Pollution Epi
sodes (PEPE/NEROS) Field Measurement Program
during the summer of 1980. The basic program does not
provide for measurements of the aerosol optical thick
ness, which is the most important aerosol parameter
that will be derived from satellite observations. Solar
transmission observations at about 12 stations obtained
during the PEPE/NEROS experiment will be utilized.
The transmission observations will be analyzed to
derive values of the aerosol optical thickness.
The satellite observations expected during the PEPE/
NEROS experiment include the visible and infrared
spin and scan radiometer (VISSR) on GOES. In addi
- lion, more precise radiometer data will be used from the
coastal zone color scanner (CZCS) on Nimbus 7.
MEASUREMENT OF AIR POLLUTION FROM
SATELLITES (MAPS)
An earth-orbiting experiment flown on the Space
Shuttle can provide scientists with data to accurately
map changes within the earth's atmosphere. The exper
meteoro~og~ca~ parameters, as weft as with various iment, Measurement of Air Pollution from Satellites
ground-based measurements. The most interesting (MAPS),charted concentrations ofCO gas around the
meteorological parameters for initial investigation world over a range oflatitudes extending from30°Sto
appear to be wind at various levels, the existence and 38°N during the second Space Shuttle flight. The per
OCR for page 177
APPENDIX B
formance of MAPS on this flight proved the system to be
a faster, more efficient method of mapping trace gases in
the earth's atmosphere than chromatograph devices.
MAPS used a gas filter radiometer to obtain mea-
surements of the CO mixing ratio in the middle tropo-
sphere and stratosphere. The radiometer method is sim-
pler and much less expensive than previous gas
chromatograph devices. The experiment produced con-
centration maps of CO.
Early analysis of MAPS data concentrated on mea-
surements performed during orbital Pass 15 on Novem-
ber 13, 1981 . This orbital pass of the Shuttle began over
Central America, continued east over the Mediterra-
nean Sea, turned southeast over the Persian Gulf, the
Arabian Sea, and extended to the southern tip of India.
The concentration of CO within this extended area
ranged from 70 ppb over the eastern Atlantic Ocean and
140 ppb in the Mediterranean area. These measure-
ments were performed in less than 20 min from the
vantage point of the Shuttle. Similar measurements
from aircraft platforms would have required observa-
tions over many hours.
Analysis of experiment data so far indicates signifi-
cant concentrations of middle troposphere CO mixing
with both north-south and east-west variation over the
North Atlantic and the Mediterranean Sea and the
Middle East. Accuracy of the measurement has been
determined to be within 15 percent with a repeatability
of about 5 percent from orbit to orbit. CO gas is pro-
duced by natural processes (e.g., oxidation of CH4 in
wetland areas and forest fires) and man's activities (e.g.,
slash-and-burn agriculture and automobile emissions).
Man's contribution to the global atmospheric budget of
CO has grown significantly during this century, result-
ing in a large asymmetry between the CO concentration
in the northern and southern hemispheres.
The major atmospheric sink for CO is a complex
sequence of photochemical reactions that oxidize CO
molecules into CO2. One ofthe initial steps in this oxida-
tion process is the combination of CO with the hydroxyl
radical OH. OH plays a major role in a variety of other
atmospheric processes, notably reactions involving
SO2, nitrogen oxides, and chlorofluoromethanes.
CO oxidation can potentially divert OH from reac-
tions with these other gaseous species and alter the over-
al1 chemical balance within the earth's atmosphere.
NASA plans to refly MAPS on the seventh Shuttle
mission, scheduled for summer 1984, to study seasonal
variations in the total abundance and regional distribu-
tion of CO within the earth's atmosphere.
Although the second Shuttle flight was abbreviated,
the experiment collected data for about 42 hr. and the
investigators were able to corroborate the sampled areas
177
with the instrument readings taken with underflying
aircraft and with other surface information.
Reduction of MAPS data is continuing at the present
time, and the first global map of CO concentrations at
low-latitudes to midlatitudes is now available.
FUTURE INSTRUMENT TECHNIQUES
Passive Remote Sensors
In general, remote sensors for atmospheric applica-
tions can be developed to measure changes in the three
basic properties of electromagnetic waves including
energy (absorption or emission), wavelength (frequency
shifts), and polarization. Passive spectroscopic remote
sensors, summarized in this section, correspond to the
class of sensors that measures one of these properties
(absorption or emission) with an external source of radi-
ation. For tropospheric measurements from space or
aircraft observing platforms, the downward-viewing
modes (nadir) provide the widest vertical and horizontal
coverage. Solar occultation measurements from space
and airborne platforms have been used extensively in
stratospheric applications, but due to the extent of global
cloud cover, geographical coverage of the troposphere is
severely limited in this operational mode. External
sources of radiation for nadir-viewing experiments
include upwelling thermal radiance of the earth-atmo-
sphere system, reflected radiation from the surface ofthe
earth, and scattered radiation from molecules and aero-
sols in the atmosphere. Compared to detection of direct
solar radiation through the atmosphere, as in strato-
spheric solar occultation measurements, these sources of
radiation are relatively weak and require more sensitive
detection instruments. However, in addressing some of
the tropospheric scientific questions, sensors developed
for stratospheric observations in solar occultation can be
used from ground-based platforms to provide some ver-
tical layering of tropospheric constituents, which are
important in establishing global concentrations of well-
mixed gases, or those gases showing seasonal and tem-
poral variability. In addition, with improvements in sen-
sitivity and instrument optimization to a 300°K source
and broader spectral response functions, many sensors
developed for stratospheric applications should become
viable tropospheric sounders from space platforms.
Before addressing the question of the available pas-
sive remote sensing techniques, some basic properties of
atmospheric radiation should be considered for the vari-
ous external sources of radiation. In viewing the upwell-
ing thermal radiance of the earth-atmosphere system,
passive instruments detect radiation that is a composite
of energy transmitted through the atmosphere, that is
OCR for page 178
178
absorbed and reemitted by atmospheric molecules at all
altitudes between the source and the sensor. The ther-
mal emission of this radiation is primarily governed by
the temperature lapse rate of the lower atmosphere,
which ranges from approximately 300 °K near the
ground to 220°K in the lower stratosphere. Since the
Planck function of a blackbody radiator peaks at
approximately 10 ,um for a 300°K blackbody, the
desired wavelength region varies from 4.5 to 15.0 ,um.
Also, in this wavelength range, contributions to atmo-
spheric radiance from scattered solar radiation are small
and can be considered of a second order. Because of the
pressure broadening of the spectroscopic absorption or
emission lines, the energy received in the wings of the
atmospheric emission lines reflects the presence of mole-
cules at high pressures (i.e., lower altitudes), while
energy received near line centers is representative of
molecules at lower pressures (i.e., higher altitudes).
This gives rise to the possibility that by selectively mea-
suring radiation at various spectral regions from line
center, one could, in principle, generate vertical profiles
of gas concentrations. This is analogous to the inference
of temperature profiles by remote sensing methods
using thermal infrared wavelengths where wavelengths
in various parts ofthe emission line of a uniformly mixed
gas (e.g., CO2 and N2O) are used to obtain altitude
discrimination. In order to invert radiances detected at
the top of the atmosphere to concentration profiles,
inversion algorithms must be developed that take into
account emission of the earth-atmosphere system, gov-
erned by the temperature lapse rate. In inverting the
radiance to obtain useful concentration accuracies, tem-
perature profiles must be simultaneously measured with
the radiance to a desired accuracy of approximately +
2°K. For measurements of minor trace gases in the
troposphere, thermal emissions are weak due to a com-
bination of low concentrations and low reservoir tem-
peratures. Also, the temperature lapse rate and the rela-
tively low-pressure gradient in the atmosphere limit the
degree of vertical discrimination possible, independent
of the spectral resolving power of the instrument beyond
a resolution of approximately 0.01 cm- ~ . Furthermore,
radiances emitted and absorbed near the ground (within
the first 3 km) are faced with the limitation of a small
temperature gradient between the earth and the layer of
atmosphere near the earth, thus making fine discrimi-
nation of layers near the ground difficult.
In the free troposphere, however, broad layers of the
atmosphere can be identified when simulating the inver-
sion of the earth-atmosphere radiance in the thermal
infrared, and weighted averages of gas concentrations at
specific altitudes can be obtained. Therefore, these tech-
niques provide the synoptic coverage and spatial resolu-
tion required to study the global transport of minor trace
gases such as CO (refer to previous section). Such obser
APPENDIX B
vations are required to address those scientific questions
related to global budgets and distributions of gas con-
centrations and to the relative changes that occur over
time of some ofthe well-mixed gases such as CH4, N2O,
and CO2, especially in the free troposphere.
The other two external sources of radiation that can
be used in tropospheric sounding of atmospheric trace
gases include reflected radiation from the earth's surface
and scattered radiation from the earth's atmosphere. In
the latter mode, scattered radiation from aerosols and
molecules is predominant in the ultraviolet and visible
portion of the spectrum and can be used to infer inte-
grated molecular concentrations through direct absorp-
tion by atmospheric spectra. In the ultraviolet and visi-
ble portion of the spectrum, the dependence of line
width on pressure has a smaller functional dependence
than in the infrared, and vertical layering of the atmo-
sphere using this physical process is more difficult to
infer than in the thermal infrared. However, inversion
of radiance data in the ultraviolet and visible is less
sensitive than the thermal infrared to the knowledge of
atmospheric temperature profiles. Relevant tropo-
spheric molecules in this spectral region include 03,
SO2, and NO2.
In viewing reflected solar radiation from the earth's
surface, one should restrict observations to approxi-
mately the 1.0- to 3.5- ,um region, since in this range the
radiance at the top of the atmosphere is primarily due to
reflected solar radiation, and absorption can be used as
the physical process to infer molecular concentrations.
Some vertical layering of molecular concentrations can
be achieved through pressure broadening ofthe molecu-
lar absorption lines in the atmosphere, and integrated
measurements to the ground are possible. The accuracy
of the retrieved concentrations has a smaller functional
dependence on the temperature profile than in the
upwelling thermal infrared region. In the intermediate
spectral band (i.e., 3.5 to 4.5 ,um), the radiance at the
top of the atmosphere is composed of comparable values
of the upwelling thermal radiance and reflected solar
radiation. Although interesting absorption and emis-
sion lines of major atmospheric molecules lie in this
region, inversion of the radiance measurement to
molecular concentrations is complicated by the com-
plexity ofthe radiative transfer equation, which makes it
difficult to quantitatively invert radiances to obtain
molecular concentrations.
A summary of the current passive remote sensors
developed under the NASA remote sensing program
has been reviewed by Levine and Allario2 and will not be
discussed further.
2"The global troposphere: biogeochemical cycles, chemistry,
and remote sensing." J. S. Levine and F. Allario. Environmental
Monitoring and Assessment 1: 263-306. ~ 982.
OCR for page 179
APPENDIX B
Active Remote Sensors
The use of laser techniques for measuring range-
resolved concentrations of aerosols, molecular constitu-
ents, and meteorological parameters in the stratosphere
and troposphere has represented a major research activ-
ity in the NASA research and applications programs
over the last decade. In considering some of the funda-
mental limitations in using external sources of radiation
for measuring tropospheric molecules, it should be obvi-
ous that the use of powerful and tunable, monochroma-
tic sources in the ultraviolet, visible, and infrared por-
tions ofthe spectrum has the potential to remove some of
the limitations of passive remote sensing imposed by the
physical processes of the atmosphere. For example, in
probing the troposphere from the top of the atmosphere
in the nadir mode, the laser beam has the potential to
probe down to the surface of the atmosphere, and
through the process of molecular absorption and range
gating (to be discussed later), the vertical distribution of
molecular concentrations, aerosols, and meteorological
parameters can, in principle, be obtained to a spatial
resolution of c 0.1 km. The ability to meet these mea-
surement needs is dependent on the energy of the laser
and the magnitude of the differential absorption cross
section of the species to be measured. In general, the
ability of lidar systems to obtain individual measure-
ment parameters to a given accuracy depends on the
magnitude of optical scattering coefficients and molecu-
lar absorption cross sections, if one assumes sufficient
flexibility in system parameters, such as telescope size,
detector quantum efficiency, and energy of the laser
transmitter.
Research in the NASA program has evolved from
initial studies with h~xed-wavelength lasers to measure
optical backscatter from aerosols, to the use of tunable
and narrow bandwidth lidar systems for remote mea-
surements of atmospheric gases and aerosols in the
troposphere. Investigations have been conducted by
using Raman scattering techniques for remote measure-
ments of water vapor and SO2, but this technique was
found to be limited to high gas concentrations, short
ranges, and nighttime operation as a result of the small
Rarnan scattering coefficients. The differential absorp-
tion lidar (DIAL) technique can overcome some of these
limitations because absorption cross sections can be 6 to
8 orders of magnitude larger than the Raman cross sec-
tions. This technique has recently been demonstrated as
viable for detecting O3 and aerosol layering in the tropo-
sphere from an aircraft platform. In general, successful
demonstrations of the feasibility of DIAL techniques
have evolved as the technology of the tunable laser
sources has improved in energy output, spectral purity,
and amplitude and frequency stability. DIAL tech-
niques, to date, have been applied from fixed and
~. . .
179
mobile ground stations to detect aerosols and SO2 emit-
ted by stack plumes and to measure the vertical distribu-
tion of tropospheric aerosols, 03, and water vapor from
aircraft platforms.
The principle of the DIAL techniques is discussed
below. In general, the DIAL technique depends on the
existence of a molecular feature (absorption line) that is
specific to a gas molecule, whose spectroscopic charac-
teristics are well known in the atmosphere (i.e., line
intensity, line position, and line broadening as a func-
tion of pressure), and which is relatively free of spectro-
scopic interference from other molecules in the atmo-
sphere. In order to detect the molecular feature, the
wavelength of the laser is tuned to overlap the absorp-
tion feature, preferably at the center ofthe line. A second
laser wavelength is required whose wavelength is
removed from the molecular feature but sufficiently
close by in wavelength to detect the same atmospheric
scattering properties of the atmosphere at the two wave-
lengths. The two laser wavelengths are pulsed and can
be fired simultaneously or within a time spacing that
essentially freezes atmospheric dynamics during the
measurement period (i.e., c 100 ns). The two laser
pulses are backscattered to the receiver telescope by
atmospheric aerosols and molecules, so that the return
signal represents a time history of the atmospheric scat-
tering and absorption properties of the atmosphere for
each laser pulse. This time history is related to a spatial
profile of the atmospheric scattering and absorption
properties of the atmosphere, through the equation
(cAt)12 = AR, where At represents a time gating interval
that can be selectable in time to correspond to a range
gate interval, AR. In the date processing mode, the ratio
of return signals at the "on" wavelength, Pon, to the
"off' wavelength, Poff' iS measured and, through the
lidar equation, can be related to the molecular concen-
tration of the gas in the atmosphere as a function of
range from the transmitting telescope. Another useful
mode for a DIAL experiment is to employ a continuous
wave (COO) laser that uses reflection from the ground to
return the two laser wavelengths back to the receiving
telescope. In the infrared, where pressure broadening of
atmospheric spectral lines as a function of altitude is
larger than in the ultraviolet and visible portion of the
spectrum, one can selectively probe various segments of
the absorption line by tuning the wavelength of the
transmitting laser from the central peak into the wings to
obtain vertical layering of the selected tropospheric mol-
ecule. Conceptually, this is similar to the passive solar
reflected technique discussed earlier. In this case, how-
ever, the source of radiation is monochromatic, allowing
a single absorption line to be probed. Furthermore, the
radiative transfer equation for the transmitted and
reflected signals through the atmosphere can be
described by straightforward atmospheric processes.
OCR for page 180
180
A summary of the current active remote sensors
developed under the NASA remote sensing program is
given by Levine and Allario3 and will not be discussed
further here.
FUTURE THRUSTS
A Workshop on Passive Remote Sensors for perform-
ing tropospheric measurements was conducted in Vir-
ginia Beach, Virginia, July 20-23, 1981. The purpose of
this workshop was to define the long-range role of pas-
sive remote sensors in tropospheric research and to iden-
tify the technology advances necessary to implement
that prescribed role. Recommendations and conclu-
sions from the two panels of the workshop attendees are
given below. Details leading to these conclusions are
given in NASA CP 22374 and are abstracted below.
RECOMMENDATIONS AND CONCLUSIONS
Sensor Systems Panel Recommendations
Following are the conclusions and recommendations
from a systems point of view for passive remote sensing
oftropospheric constituents:
1. Passive remote systems exhibit promise and
should be developed for two-layer measurement of some
of the more abundant tropospheric species (e.g., O3,
CO, CH4, CO2, HNO3, H2O, and NO).
2. A measurement scenario consisting of a combina-
tion of nadir viewing and solar occultation should be
considered for measurement of gases such as O3 and
HNO3. Measurement of these gases in the troposphere
presents a unique challenge in that well over 90 percent
of the total burden of the gas resides in the stratosphere.
3. For multilayer (i.e., more than two) measure-
ments of a wide range of species, a nadir-viewing instru-
ment capable of obtaining continuous spectra in the 3- to
15- Em spectral region with a spectral resolution of less
than 0.1 cm- ~ is desired.
4. Gas filter radiometer instruments (e.g., MAPS
and HALOE) should be developed concurrently with a
scanning instrument (see previous recommendation).
Such systems may provide near-term two-layer tropo-
spheric measurements of gases such as CO and CH4
with only modest improvements in system perfor-
mance. For gases such as O3 and NO, major problems
may be encountered with the gas cell technology and
resolving more than one atmospheric layer.
Child.
4Tropospher?c Passive Remote Sensing. L. S. Keafer, Ir. (ed.~.
NASA CP 2237.
APPENDIX B
5. Further development of aerosol retrieval
algorithms is required for obtaining aerosol thickness
and size distributions on a global scale. Although the
technology currently exists for obtaining aerosol infor-
mation over water, additional channels extending from
the visible to near infrared would be desirable for future
measurements.
6. The prospect and the possibility of initiating a
feasibility study to determine if polarization measure-
ments of scattered solar radiation can yield the refractive
index (i.e., composition) of aerosols should be reas-
sessed.
7. Existing spectrally scanning radiometers (e.g.,
interferometers) and/or gas filter systems should be
employed from balloon and Shuttle platforms to study
the effects-of instrument noise and background fluctua-
tions on inversion techniques. Short-term nadir-view-
ing Shuttle missions should be coordinated with existing
solar occultation missions to study the feasibility of uti-
lizing simultaneous occultation and nadir-viewing data.
8. Feasibility studies for both gas filter and spectrally
scanning instruments should be initiated to study (a) the
extent to which nadir-viewing systems can obtain pro-
f~les oftwo ormorelayers within the troposphere, (b) the
accuracy requirements on molecular line parameters,
meteorological parameters (i.e., temperature and pres-
sure), radiance data, and background effects, and (c) the
extent to which solar scattering can be used to obtain
lower-level tropospheric data.
Sensing Technology Panel Recommendations
The technology needs presented earlier are restated
in Table B. 1 as critical needs and are recommended as
technology development thrusts for elements of several
passive sensing techniques for tropospheric research. In
one sense, this table indicates the needs once a system is
chosen. In a larger sense, the technology requirements
and their apparent difficulty and cost should be a critical
part of the instrument evaluation studies. Certain tech-
nology thrusts, however, are needed regardless of the
sensing system choice. Examples from Table B. 1 are as
follows: (~) detector arrays, (2) cryogenic cooling (of
sensors and optics), (3) sophisticated optical elements,
and (4) data processing as an integral part of the sensor.
Although not explicit in Table B.1, calibration tech-
niques and equipment should be added to the list of
needed technology thrusts. In response to the continu-
ing need for more sensitive and accurate measurements
over the full globe for long periods of time, producing
great volumes of data, the workshop participants felt
that the application of technology advances in these five
areas would yield the greatest benefit in passive remote
sensing of the troposphere.
OCR for page 181
APPENDIX B
TABLE B. 1 Technology Thrusts
Sensor
Technology Needs
Gas filter radiometry
All types
Broadband spectrometry
All types
Grating type
Interferometer
Narrow-band spectrometry
Laser heterodyne type
Fabry-Perot
Gas filter test cells
Linear, high dynamic range
detectors
Highly uniform optical elements
Onboard smart processing
Cryogenics/cooling
103 element arrays
Large gratings
Mitigation of background
fluctuations
Multiaperture, multiband
interferometer
In-flight alignment verification
Tunable lasers and heterodyne
arrays
Improved coatings at long
wavelengths
SUMMARY
In the current state of development of remote sensors,
two sensor systems are being used from spaceborne plat-
forms, and several active and passive systems have pro-
gressed to the stage where they are being used or pro-
posed in field measurement programs from airborne
and ground-based platforms to measure gaseous species
(e.g., CO, 03, SO2, H2O, NH3, and NO2), tropo-
spheric aerosols, mixing heights, and optical extinction
coefficients. Future developments of remote sensing sys-
tems are aimed toward extending this capability to other
molecular species with improved sensitivity and vertical
resolution.
Passive remote sensors are categorized generically
into four categories: (1) gas filter correlation techniques,
(2) interferometry, (3) infrared heterodyne radiometry,
and (4) spectroradiometers. Technological improve-
ments in the sensitivity of passive remote sensors should
expand the number of instruments within each generic
class as potential payloads for airborne and space plat-
forms. Despite the potential improvements in the sensi-
tivity of passive remote sensors through technological
improvements in systems and detector technology, sev-
eral fundamental limitations in passive sensors will
restrict the use of these instruments for some of the
scientific experiments envisioned in tropospheric
research. Passive sensors in the thermal infrared have
difficulty measuring molecules in the biosphere and are
limited to measuring in broad vertical layers in the mid
181
die and upper troposphere. The relatively long integra-
tion times required to measure low-concentration spe-
cies will restrict the horizontal resolution of the
measurement to broad geographic areas and will proba-
bly require the use of geostationary satellite platforms to
investigate regional areas, such as the northeastern U.S.
corridor. Instruments using earth-scattered sunlight are
capable of measuring total integrated burdens of molec-
ular species, but have inherently limited temporal and
geographic coverage. Despite these limitations, passive
remote sensors do exhibit several attractive characteris-
tics for global measurements. Their systems and tech-
nology are the most advanced for satellite missions. Pas-
sive instruments using upwelling thermal radiance have
potential for measuring a large number of interesting
tropospheric molecules simultaneously and should be
effective in studying the chemistry of selected chemical
systems. Passive instruments using earth-scattered sun-
light have the capability of measuring the total burden of
several major tropospheric gases. A satellite mission
incorporating both types of instruments should be inves-
tigated in light of the scientific requirements for an early
dedicated satellite for the lower atmosphere.
Considerable effort has been expended by NASA and
other organizations during the past decade to develop
active remote sensing techniques using lasers. The
active remote sensing systems in the NASA Air Quality
Program can be classified into fixed and tunable wave-
length systems. The former is important primarily in
measurements of tropospheric and stratospheric aero-
sols, aerosol extinction, and measurements of inversion
layer heights. Tunable wavelength lidar systems cur-
rently have the highest potential for measuring a variety
of trace gases in the troposphere simultaneously, with
vertical range extending to the ground and with vertical
resolution approaching 1 krn. Active remote sensors
under development, however, have high potential to
meet some of the major scientific requirements for mea-
surements in the troposphere from an airborne plat-
form, including vertical resolution of approximately 1
km for major species, vertical range extending to the
ground, day/night operation, true column-content
measurements, and inherent high spectral resolution
and tunability to measure tropospheric species simulta-
neously and uniquely in a background of interfering
gases. For applications to space platforms, however,
major technological developments must be made in the
sources themselves, including high power and effi-
ciency, improved collimation and spectral purity, wider
tunability, and higher frequency and amplitude stabil-
ity. In order to perform many of the scientific investiga-
tions of the troposphere, it will be necessary to develop
appropriate sources for active remote sensing systems.
Further, existing instruments must be tested under
OCR for page 182
182
flight conditions not only to demonstrate their opera-
tional reliability and sensitivities, but also to provide
data that can be interpreted and analyzed under condi-
tions as dose to an actual mission as possible. The time
scale for utilization of laser systems and research satellite
investigations is currently difficult to estimate because of
APPENDIX ~
the rapidly emerging technology of laser systems.
Therefore, in generating scientific requirements for sat-
ellite missions, the science requirements must be tem-
pered somewhat by the status of laser technology, and, in
some cases, priorities for missions must be dictated by
availability of laser technology.
l
OCR for page 183
APPENDIX ~
Element Cycle Matrices
A matrix approach was used in an effort to systemati-
cally, but simply, indicate what is currently known about
the primary species involved in the sulfur, carbon, halo-
gen, nitrogen, and trace element cycles, as well as the
importance of the species in each cycle to an overall
understanding of that cycle. Individual species were
rated to indicate current knowledge and their impor-
tance in each cycle relative to their major sources,
removal and transformation processes, and tropo-
spheric distribution. In the "knowledge" category, rat-
ings range from one (very low, or no, knowledge) to four
(high knowledge level almost all is known that it is
necessary to know). In the "importance" category, rat-
ings range from one (the factor is very important in
understanding the complete element cycle) to four (the
factor has little or no importance in understanding the
element cycle).
The combination of the "knowledge" and "impor
tance factors tor each component of each matrix leads
to an "urgency" factor for that component. An urgency
factor of A indicates a very important component of an
element cycle about which very little is known. Low
"urgency" factors (e.g., B or C) flag areas that require
research emphasis in each element cycle. A "D"
urgency factor indicates a relatively unimportant com-
ponent of a cycle about which quite alot is known. These
areas would require relatively little research emphasis in
that cycle.
Two matrices are presented for each element cycle in
the following tables (Tables C . 1 through C. 5~. The first
is the "knowledge" and "importance" matrix. Both the
"knowledge" and "importance" ratings are indicated
in each matrix element, with the "importance" rating
in parentheses. The second matrix indicates the
"urgency" factor ratings for each cycle.
183
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184
TABLE C.1 Sulfur Cycle
APPENDIX C
H2S so2
DMS COS
Sulfate Other
Knowledge and (Importanceja
Source
Anthropogenic 4~2) 4~1) 2 (2) 2 (2) 3 (l) 2 (2)
Biological ~ (2) l (l) 1 (2) 1 (2) 2 (1) ~ (2)
Other natural 1~3) l (2) ~ (3) l (3) ~ (2) 1~3)
Stratospheric l (2) l (3)
Removal
Wet (land) 2 (2) 3 (l) 1 (2) l (2) 3 (1) 3 (2)
Wet~ocean) 1~2) 1~1) l (2) l (2) l (l) l (2)
Dry~land) 2 (3) 2 (1) l (2) l (2) 2 (1) 1 (2)
Dry (ocean) l (2) 2 (l) l (2) l (2) l (l) l (2)
Transformation
Homogeneous aq.phase 2(3) 2(2) '(3) 1(3) 3(2) 1(3)
Homogeneous gas phase 2(3) 2(1) 2(2) 2(2) - 1(2)
Heterogeneous 2(2) 2(1) 1(2) 1(2) 3(1) 1(2)
Distribution 2 (2) 2 (2) 1(2) 1(2) 2 (2) 2 (3)
Urgency Factor6
Source
Anthropogenic C B B B B B
Biological A A A A A A
Other natural B A B B A B
Stratospheric - - - - A B
Removal
Wet(land) B B A A B C
Wet (ocean) A A A A A A
Dry (land) B A A A A A
Dry (ocean) A A A A A A
Transformation
Homogeneous aq.phase C B B B C B
Homogeneous gas phase B A B B A
Heterogeneous B A A A B A
Distribution B B A A B C
Interaction with other HrO' C C C C C
cycles N N H. Oy H.~Oy N
H;Oy H.rO' Aerosol H~O
Aerosol
aKnowledge: 1 = low, 4 = high; Importance: 1 = high, 4 = low.
6Urgency factor: A = extremely urgent for that cycle, B = considerably urgent, C = moderately urgent, D = of little urgency.
OCR for page 185
APPENDIX C
TABLE C.2 Carbon Cycle
185
Gas Phase
Methane and
· Organ~c Compounas
Carbonaceous Its React~on
Aerosol Products C2-Cs c5
Knowledge and (Importance)
Anthropoge ic 2(3) 2(3) 2(3) 2(,3)
Biolog c 1 ( ) ( ) ( ) ~
Other natural - - (2) (2
Stratospheric - - _
Wet (1 md) 1 (2) - 1 (2) 1 (2)
Transformation 1(2) 1(2) ~ (2)
Homogeneous aq.phase - 2 1 1(1) 2(1)
Homogeneous gas phase 1 1 ( ) 1 (1) 1 (1)
Heterogeneous ( )
Distributlon 1(1) 3(1) 1(1) 1(1)
Urger~cy Factorb
Source C
Anthropogenic C C A A
Biological A _ A A
Other natural
Stratospheric
Removal
Wet (land) A _ BA BA
Wet(ocean) A A
Dry(land) A _ B B
Dry (ocean) B
Transformation
Homogeneous aq.phase - A A A
Homogeneous gas phase - _ A A
Heterogeneous A B A A
~Distribtution ith th S H'`Oy HxOy H~Oy
cycles N N N N
C C Aerosol
Aerosol
aKnowledge: 1 = low, 4 = high; Importance: 1 = high, 4 = low.
bUrgency factor: A = extremely urgent for that cycle, B = considerably urgent, C = moderately urgent, D = of little urgency.
OCR for page 186
186
APPENDIX C
TABLE C.3 Trace Element Cycles
Hg Se As B P Pb
-
Knowledge and (Importanceja
Source
Anthropogenic 3 (1) 3 (1) 3 (1) 2 (2) 3 (2) 4 (1)
Biological 2 (1) 2 (1) 2 (2) 2 (1) 1 (2) 1 (2)
Other natural 2 (2) 1 (2) 2 (2) 2 (1) 2 (2) 2 (2)
Stratospheric - -
Removal
Wet (land) 2 (1) 2 (1) 2 (1) 2 (1) 3 (1) 3 (1J
Wet (ocean) 2 (1) 1 (1) 2 (1) 2 (1) 2 (1) 3 (1)
Dry (land) 1 (3) 1 (2) 1 (2) 1 (4) 2 (2) 2 (3)
Dry (ocean) 1 (2) 1 (3) 1 (3) 1 (3) 2 (2) 2 (4)
Transformation
Homogeneous aq. phase 1 (3) 2 (3) 2 (3) 2 (2) 2 (4) 1 (4)
Homogeneous gas phase 2 (1) 1 (3) 1 (3) 1 (2) 1 (4) 1 (4)
Heterogeneous 1~2) 1~1) 1~1) 1~2) 1~4) 1~3)
Distribution 2 (1) 1 (1) 2 (1) 1 (1) 2 (1) 3 (1)
IJraent:v Factorb
, · 4~, · , _ ,
Source
Anthropogenic B B B B C B
Biological A A B A B B
Other natural B A B A B B
Stratospheric
Removal
Wet (land) A A A A B B
Wet (ocean) - A A A A A B
Dry (land) B A A B B C
Dry (ocean) A B B B B C
Transformation
Homogeneous aq. phase B C C B C B
Homogeneous gas phase A B B A B B
Heterogeneous A A A A B B
Distribution A A A A A B
Interactions with HxO' HxO' HxO' HxO
other cycles C C C
aKnowledge: 1 = low, 4 = high; Importance: 1 = high, 4 = low.
bUrgency factor: A = extremely urgent for that cycle, B = considerably urgent, C
= moderately urgent, D = of little urgency.
OCR for page 187
APPENDIX C
TABLE C.4 Halogen Cycles
187
Fo F.; F- Clo Cli Cl- BrO
Bri Br- Io Ii I
Knowledge and (Importancef
Source
Anthropogenic 3~2) 2~2) 2~2) 3~1) 3~2) 3~2) 2~1) 2~2) 2~2) 2~2) 2~2) 2~2)
Biological 2~2) 1~3) 2~2) 2~1) 1~3) 2~2) 1~1) 1~3) 2~2) 2~1) 1~3) 2~2)
Other natural 3~3) 3~3) 2~3) 3~3) 3~3) 1~3) 2~3) 2~3) 2~3) 2~3) 2~3)
Stratospheric 3~4) 4~4) 4~4) 3~4) 3~4) 3~4) 2~4) 2~4) 2~4) 2~4) 2~4) 2~4)
Removal
Wet (land) 3~2) 2~2) 3~2) 2~2) 3~2) 3~2) 2~2) 2~2) 2~2) 2~2) 2~2) 2~2)
Wet (ocean) 2~2) 2~2) 2~2) 2~2) 3~2) 3~2) 2~2) 2~2) 3~2) 2~2) 2~2) 2~2)
Dry (land) 2~3) 3~3) 3~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3)
Dry~ocean) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3) 2~3)
Transformation
Homogeneous aq. phase 2~2) 3~2) 2~2) 3~2) - 2~2) 2~2) - 2~2) 2~2)
Homogeneous gas phase 2~2) 2~2) - 2~2) 3~2) 2~1) 2~2) 2~1) 2~2)
Heterogeneous 1~2) 1~2) 2~2) 2(1) - 1(2) 1(1) 1(2) 2(1)
Distribution 3(2) 2(2) 2(2) 3(2) 2(2) 3(2) 1(2) 1(2) 1(2) 2(2) 1(2) 1(2)
Urgency Factor6
Source
Anthropogenic
Biological
Other natural
Stratospheric
Removal
Wet (land)
Wet (ocean)
Dry (land)
Dry (ocean)
Transformation
Homogeneous aq. phase
Homogeneous gas phase
Heterogeneous
Distribution
Interactions with
other cycles
C B B
B B B
C C
D D D
B
C
C
B C
B B
C C
C C
B C B
B B - B
A A - B
C B B C
Aerosol
B C C
A B B
C C C
D D D
B C C
B C C
C C C
C C C
C
C
A
B
S
N
HxOy
Aerosol
A B B
A B B
B C C
C C C
B
B
C
C
B C
B B
C C
C C
B B B
A B B
C C C
C C C
B B B
B B B
C C C
C C C
B B B B
A B - A B
A A A A
B A
A A A
HxOy
Aerosol
HxOy
Aerosol
aKnowledge: 1 = low, 4 = high; Importance: 1 = high, 4 = low.
6Urgency factor: A = extremely urgent for that cycle, B = considerably urgent, C = moderately urgent, D = of little urgency.
NOTES: XO = organic gaseous compounds; X; = inorganic gaseous compounds; X~ = halides in droplets and aerosols; I- includes IO3 .
OCR for page 188
188
TABLE C.5 Nitrogen Cycle
APPENDIX C
Odd
Nitrogen
Species NH3/NH4 HCN N~O
Knowledge and (Importancef
Source
Anthropogenic 2(2) 3(3) 1(2) 2(1)
Biological 1(1) 1(1) 1(3) 2(1)
Other natural 2(4) 2(3) - 2(3)
Stratospheric 3(3) 3(4) 1(3) 3(4)
Removal
Wet(land) 2(~) 2(1) 2(2) 2(4)
Wet(ocean) 1(1) 1(1) 2(2) 2(4)
Dry(land) I (~) 1 (1) 2 (3) 3 (4)
Dry(ocean) 1(1) 1(~) 2(3) 3(4)
Transformation
Homogeneous aq.phase 2(2) 2(3) 2(2)
Homogeneous gas phase 3(1) 2(2) - 2(2) 4(2)
Heterogeneous 2(2) 2(3) 2(2)
Distribution 2(1) 1(1) 2(3) 4(2)
Urgency Facto7i
Source
Anthropogenic B C A A
Biological A A B A
Other natural C C B C
Stratospheric . C D B D
Removal
Wet(land) A A B C
Wet(ocean) A A B C
Dry(land) A A C D
Dry(ocean) A A C D
Transformation
Homogeneous aq.phase B C B
Homogeneous gas phase B B B C
Heterogeneous B C B
Distribution A A C C
Interactions with H `O' S H':Oy
other cycles S Aerosol
C
Aerosol
aKnowledge: 1 = low, 4 = high; Importance: 1 = high, 4 = low.
bUrgency factor: A = extremely urgent for that cycle, B = considerably urgent, C
= moderately urgent, D = of little urgency.
Representative terms from entire chapter:
passive remote
