NO and NO are also closely related, interconverting in the daytime in a time scale of a few minutes. The concentration of NO+NO (denoted NOx) controls the oxidative reaction chemistry as shown in the following reaction sequences, which describe the effect of hydrocarbon oxidation in atmospheres of high, low, and very low first, in the control of the sign and amount of ozone production with hydrocarbon oxidation (Crutzen, 1979):
The single most important criteria in the control of ozone production is the concentration of NOx. Ozone is of well-known significance as an atmospheric pollutant and also because of its role in the generation of other key species such as OH and HO (Crutzen 1979, Logan 1983). At the present time, boundary layer over many part of the continents, and most parts of the ocean, are currently in the low-NOx regime. Ozone, produced in continental regions where sufficient NOx and hydrocarbons are emitted in to the air, is destroyed in rural regions and over the ocean. To understand the impact of anthropogenic input into the atmosphere, it is vital that the concentrations of these gases be well measured and their role in continental and marine photochemistry and the impact of ozone generation and destruction over the vast regions of the marine atmosphere understood. As reported by J. Logan (1981), "The potential yield of ozone from oxidation of CO and methane could be as large as 8x10 molecules/cm/s if an adequate supply of NO were available. This source would suffice to double the concentration of tropospheric ozone in about 2 weeks."
The instrumentation built by AOML/OCD for the measurement of the most significant compounds is listed below.
|GAS||METHOD OF ANALYSIS||DETECTION LIMIT
|nitric oxide (NO)||chemiluminescence||5 ppt
|nitrogen dioxide (NO)||chemiluminescence||7 ppt
|sum of active N-oxides (NOy)||chemiluminescence||5 ppt
|peroxyacetyl nitrate (PAN)||gas chromatography||1 ppt
The instrumentation is capable of measuring the above mentioned compounds at the levels expected for the near-surface remote marine boundary layer troposphere.
In addition, a number of related chemical and meteorological measurements must be made in order to separate meteorological from chemical influences on the measured air concentration. Most significant are the measurement s of ozone (O) and carbon monoxide (CO). This instrumentation is also regularly used in conjunction with the N- oxides instrumentation, A meteorological data acquisition system (ADAS) has been built, which records temperature (wet and dry bulb), air speed and direction, and UV light intensity. A system of launching and receiving data from rawinsondes (weather balloons) is regularly employed.
The task is a component of NOAA's Radiatively-Important Trace Species (RITS) program. Additional experimental venues are being planned.
1993 North Atlantic Cruise
In 1993, AOML/OCD organized a cruise in the North Atlantic (Iceland to Miami). In the accompanying graphic, the concentration of nitrogen dioxide as measured aboard the R/V Malcolm Baldrige during the cruise is shown (Carsey, et al., 1994b). NO concentrations averaged 7.7 pptv (range 1 to 33 pptv). Rapid elevations of N-oxides (and other species) were observed at the onset of continental plumes on 6-Sept, 10-Sept, and 12-Sept. A complete description of the cruise data, including cruise information, sampling and analytical descriptions, and graphical and tabular data lists, is given in a data report (Carsey et al., 1995b). Chemical and aerosol results are currently being prepared for additional publications. In a related study, the concentration of PAN (peroxyacetyl nitrate), an important reservoir of nitrogen oxides, was found in the eastern North Atlantic to be a good indicator of continental (European) air masses with a distinctive diel cycle indicating active photochemistry underway in the air mass [Gallagher, et al., 1992].
1994 NO/NO/NOy Instrumentation
AOML/OCD co-organized and participated in an intercomparison of instrumentation for the measurement of nitrogen oxides in air (NO, NO, and NOy) at Harvard Forest, Mass. The results, distributed to all participants, indicated good agreement on most measurement parameters.
1995 Atlantic / Indian Ocean Cruise
AOML/OCD co-organized and participated in a research cruise in the South Atlantic and western Indian Ocean during 1995 on the NOAA ship MALCOLM BALDRIGE. The cruise track traversed five major wind and chemical regimes, North Atlantic northeasterly trade winds, S. Atlantic southeasterly trade winds, polar westerlies, S. Indian southeast trades, and Indian northeast monsoons. The cruise track was designed to obtain a broad view of the photochemical environment in the south and central Indian Ocean prior to monsoon development, as well as in the equatorial and south Atlantic Ocean regions while biomass burning is at a minimum. Along segments of this cruise track, measurements of nitrogen oxides, ozone, carbon dioxide, aerosols and other pertinent species were obtained, as well as associated meteorological and oceanographic data. The results have been recently published (Dickerson 1996, Rhoads, 1997).
1995 ACE-1 Cruise
AOML/OCD participated in the Aerosol Characterization Experiment (ACE-1) during the fall of 1995, on the NOAA ship DISCOVERER. The experiment included a transit cruise, from Seattle, WA, to Hobart, Tasmania, and the ACE-1 cruise, in the southwestern Pacific south and west of Tasmania. The experiment included other ships, aircraft, and ground station measurement (Cape Grim, Tasmania). During the cruise, AOML/OCD measured nitric oxide, nitrogen dioxide, and NOy. Some measurement results are shown here. the data has been transmitted to Codiac data distribution center. Results are currently being written up for publication.
1999 Indian Ocean Experiment
The equatorial Indian Ocean during the
northeast winter monsoon season is a unique natural laboratory to study how
air pollution affects climate processes over the ocean.
It may be the only place in the world where an intense source of
continental aerosols, anthropogenic trace species and their reaction products
(e.g., sulfates and ozone) from the northern hemisphere is directly connected
to the pristine air of the southern hemisphere by a cross equatorial monsoonal
flow into the intertropical convergence zone (ITCZ). Asia and the Indian subcontinent, which together have a
population of over 2 billion people, emit large quantities of pollutants that
can be carried to the Indian Ocean during the northern hemisphere winter by
monsoon winds from the northeast. The
Indian Ocean Experiment (INDOEX) was designed to investigate how these
pollutants are transported through the atmosphere and how they affect the
atmospheric composition and solar radiation processes over the ocean.
Approximately 150 scientists conducted
field experiment in INDOEX 21-Feb through 2-April-1999. Measurements were made from four aircraft (the U.S. C-130,
the Geophysica (http://ape.iroe.fi.cnr.it),
the French Mystere, and the Dutch Citation); an Indian research vessel (Sagar
Kanya); a U.S. research vessel (NOAA R/V Ron Brown); and several ground
stations: Kaashidhoo Climate Observatory, Maldives (http://www-indoex.ucsd.edu/KCO.html),
Mauritius Universit, Pune, India, Trivandrum, India, Mt. Abu, India, and
Tromelin Island, Reunion. Information
was also obtained from operational and research satellites, 4-D high-resolution
analyzed fields, and global climate models.
The Ron Brown’s cruise track included time both south and north of the
ITCZ, as well as intercomparison experiments with ground stations and aircraft
where possible. Early
findings of the presence of a dense pollution haze layer derived from distant
continental sources suggest that the pollution events observed in INDOEX may be
symptomatic of large-scale pollution transport that may be occurring in other
regions of the earth. The project
has received considerable press coverage here (N.Y.Times Nat’l., 10-June-1999,
p. A23) and abroad (Times of India, 24-June-1999).
Preliminary results show that air pollutants dramatically impact this region. A dense brownish pollution haze extending from the ocean surface to 1 to 3 km altitude was found (see photo). The haze layer covered much of the research area almost constantly during the 6-week intensive experiment. The affected area includes most of the northern Indian Ocean including the Arabian Sea, much of the Bay of Bengal, and the equatorial Indian Ocean to about 5 degrees south of the equator. The haze is caused by high concentrations of sub-micron aerosols composed of soot, sulfates, nitrates, organic particles, fly ash and mineral dust. The haze layer also contains relatively high concentrations of gases including carbon monoxide, various organic compounds, and sulfur dioxide. Visibility over the open ocean was often under 10 km, a range that is typically found near polluted source regions of the United States and Europe. The aerosols reduce the solar radiation absorbed by the ocean surface by as much as 10%. Cloud formation is also affected because water vapor condenses on the pollution particles.
Information on the INDOEX project can be
found at http://www-indoex.ucsd.edu. AOML-derived
references to date: T. P. Carsey,
"Shipboard measurements of active nitrogen gases during INDOEX."
Presented at the 1999 Fall Meeting of the American Geophysical Union, San
Francisco, California, December, 1999. B.
G. Doddridge, W. T. Luke, C. A. Piety, R. R. Dickerson, A. M. Thompson, J. C.
Witte, J. E. Johnson, T. S. Bates, P. K. Quinn, T. P. Carsey, "Trace gas
and aerosols over the Atlantic during the ACE-Aerosols Cruise."
Presented at the 1999 Fall Meeting of the American Geophysical Union, San
Francisco, California, December, 1999. T.
P. Carsey, D. D. Churchill, M. L. Farmer, C. J. Fischer, A. A. Pszenny, V. B.
Ross, E. S. Saltzman, M. Springer-Young, and B. Bonsang. Nitrogen Oxides and
Ozone Production in the North Atlantic Marine Boundary Layer.
J. Geophys. Res. 102, 10653-10665, 1997.
Tropical North Pacific (Marine Inorganic Halgens) Experiment, 1999
A significant observation from the pre-INDOEX cruise in 1995 was large diel variation (~32%) of ozone concentration. Simulation of these results was attempted with MOCCA, a photochemical box model with detailed aerosol chemistry (Sander and Crutzen, 1996). The model was constrained with photolysis rates, humidity, aerosol concentrations, NO, CO, and O3 specified by shipboard observations and ozonesonde data. Conventional homogeneous chemistry, wherein ozone photolysis to O(1D) and HOx dominates ozone destruction chemistry (as described above) was able to account for only about one third of the observed diel variation. Inclusion of bromine (Br) chemistry (Sander and Crutzen, 1996; Vogt et al., 1996) provided an additional photochemical ozone sink and improved the simulation considerably. These results suggested that bromine plays an important role in photochemistry in parts of the marine boundary layer and imply that the marine atmosphere may represent a stronger natural ozone sink than previously assumed. In addition, chlorine may also be released from moist seasalt aerosols in forms that can be easily photolyzed to yield Cl atoms (Keene et al., 1990). The Cl atom is an extremely powerful oxidant. It reacts with methane about 10 times faster than does OH, with dimethylsulfide about 20 times faster, and with some nonmethane hydrocarbons as much as 200 times faster. Thus, Cl chemistry may have a significant impact on the lifetimes of several trace gases that play key roles in atmospheric chemistry and climate (Keene et al., 1993).
The field program was conducted at a shorefront sampling station on the windward side of Oahu, Hawaii, now maintained by Prof. Barry Huebert and his group of the University of Hawaii. AOML-OCD measured ozone and nitrogen oxides (NO, NO2, NOy) during the experiment. Data from the experiment is still being evaluated. A preliminary analysis; however, a preliminary presentation of the diel variation in ozone concentration is shown in the figure; these data were consistent with other gas-phase measurements obtained during the experiment.
Carsey, T. P., and M. L. Farmer, 1992. Active nitrogen gases in the North Atlantic boundary layer during ASTEX. Presented at the Fall 1992 meeting of the American Geophysical Union, December 7, 1992 (Eos 73, 84, 1992).
Carsey, T. P., M. L. Farmer, C. J. Fischer, A. Mendez, A. A. Pszenny, V. Ross III, P.-Y. Whung, M. Springer-Young, and M. P. Zetwo, 1994a. Atmospheric Chemistry Measurements from the 1992 ASTEX/MAGE Cruise, 30-May-1992 through 21-July 1992, Cruise Number 91-126. NOAA Data Report ERL AOML-26.
Carsey, T. P., M. L. Farmer, V. Ross III, M. Springer-Young, and M. Zetwo. 1994b. Significant Trace Species in the Boundary Layer of the North Atlantic During September, 1993. Presented at the Fall, 1994 AGU meeting in San Francisco, CA, 5 Dec 1994 (Eos 75, 95, 1994).
Carsey, T. P., D. D. Churchill, M. L. Farmer, C. J. Fischer, A. A. Pszenny, V. B Ross, E. S. Saltzman, M Springer-Young, and B. Bonsang, 1995a. Nitrogen oxides and ozone production in the North Atlantic Marine Boundary Layer. J. Geophys. Res. (in review).
Carsey, T. P., M. L. Farmer, C. J. Fischer, A. Mendez, V. B. Ross, and M. Springer-Young, 1995b. Atmospheric Chemistry Measurements during Leg 4 (RITS) of the 1993 North Atlantic Cruise. NOAA Data Report (in press).
Crutzen, P., 1979. The Role of NO and NO2 in the Chemistry of the Troposphere and Stratosphere. Ann. Rev. Earth Planet. Sci. 7, 443-472.
Gallagher, M. S., T. P. Carsey, and M. L. Farmer, 1990. Peroxyacetyl nitrate in the North Atlantic. Global Biogeochem. Cyc. 4, 297- 308.
Huebert, B. J., A. Pszenny, and B. Blomquist, 1994. The ASTEX/MAGE experiment. J. Geophys. Res. (submitted).
Logan, J, M. L. Prather, S. C. Wofsy, and M. B. McElroy, 1981. Tropospheric Chemistry: A Global Perspective. J. Geophys. Res. 86, 7210-7254.
Logan, J, 1983. Nitrogen Oxides in the Troposphere: Global and Regional Budgets. J. Geophys. Res. 88, 10785-10807.
McFarland, M., D. Kley, J. W. Drummond, A. L. Schmeltekopf and R. H. Winkler, 1979. Nitric Oxide Measurements in the Equatorial Pacific Region. Geophys. Res. Lett. 6, 605-607.
Pszenny, A. A., T. P. Carsey, P. Y. Whung, M. P. Zetwo, M. L. Farmer, and C. J. Fischer, 1994. Measurements of various chemical concentrations in the marine boundary layer during the 1992 ASTEX/MAGE experiment. Presented at the 1994 AGU Spring Meeting, May 25, 1994 (Eos 75, 89, 1994).
Torres, A. L., and A. M. Thompson, 1993. Nitric Oxide in the Equatorial Pacific Boundary Layer: SAGA 3 Measurements. J. Geophys. Res. 98, 16949-19954.
R. Dickerson, P. Kelley, K. Rhodes, T. Carsey, M. Farmer,and P. Crutzen. "Measurement of reactive nitrogen compounds over the Indian Ocean." Presented at the meeting of the American Chemical Society, New Orleans, LA March, 1996 (Chem. Eng. News 74, 84, 1996.)
K. Rhoads, P. Kelley, R. Dickerson, T. Carsey, M. Farmer, D. Savoie, and J. Prospero, "Composition of the troposphere over the Indian Ocean during the monsoonal transition," J. Geophys. Res. 102, 18981-18995, 1997.