ISSN:0148-0227    

DOI:10.1029/JD090iD07p12807

年代:1985

数据来源: WILEY

摘要:

The Wallops Island Instrument Intercomparison Workshop represented the first comprehensive intercomparison of techniques to measure ambient, free‐tropospheric levels of carbon monoxide, nitric oxide, and hydroxyl. The workshop was conducted as part of the National Aeronautics and Space Administration's Global Tropospheric Experiment. A summary of workshop operations and the results from the “exchange of standards” portion of the workshop are presented. The intercomparison results from the ambient measurement portions of the workshop are discussed in other papers in this issue of the jo

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12808

年代:1985

数据来源: WILEY

摘要:

A modified laser‐induced fluorescence (LIF) technique for measuring tropospheric levels of OH is discussed. Although this system is still of the single‐photon laser‐induced fluorescence type (SP‐LIF), it has undergone major design changes. These changes have overcome several of the major problems encountered in first generation SP‐LIF sensors. Two of the more important of these are (1) the generation of high artificial levels of OH from the laser photolysis of atmospheric O3and (2) the degradation in detection sensitivity resulting from temporal fluctuations in the nonresonant fluorescence background. In the 2‐λ LIF approach, two nearly identical laser systems are employed such that both “on” line OH signal monitoring and “off” line background levels are measured almost simultaneously (e.g., within 500 μs). This approach, in effect, freezes the atmosphere for purposes of comparing “on” versus “off” line signal measurements. Concerning the problem of laser‐generated OH, two approaches have been explored: the use of very short laser pulses and the use of reduced laser energies. The OH field measuring system reported on in this work used only the reduced energy scheme. Numerous tests have shown that the 2‐λ SP‐LIF system displays no measurable detection bias and, under typical operating conditions, displays shot‐noise‐limited extraction of weak signals. In addition, this in situ sampling system has lent itself to direct in‐flight OH calibrations. Tests also have been developed that quantitatively establish the magnitude of the O3/H2O/OH interference signal (which in nearly all cases was ≤20% of the total OH signal). Finally, the question of OH losses in the sampling manifold has been addressed, and the evidence strongly suggests that this loss is negligibly small. Null experiments, laboratory and in‐flight calibration exercises, and O3/H2O interference tests, as well as ground‐based OH measurements, are reported on. Collectively, these results indicate that the 2‐λ LIF OH system can provide reliable OH measurements down to the fundamental limits of its sensitivity, e.g., typically 1×106molecules/cm3for a 30‐min integration time at mid free‐tropospheric altitudes. The detection limit of this system at ground level as well as at mid‐latitudes should be adequate to address many interesting questions in tropospheric chemistry; however, further improvements will be required for routine high

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12819

年代:1985

数据来源: WILEY

摘要:

This paper describes an airborne lidar instrument for detecting OH, using the technique of laser‐induced fluorescence. The detection limit is determined mainly by the shot noise of the solar background. For daytime measurements at 6100 m (20,000‐ft) a detection limit of about 1×106OH/cm3was obtained with a 2‐hour acquisition time under favorable cond

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12835

年代:1985

数据来源: WILEY

摘要:

Results from an intercomparison of techniques to measure tropospheric levels of nitric oxide (NO) are discussed. The intercomparison was part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and was conducted at Wallops Island, Virginia, in July 1983. Instruments intercompared included a laser‐induced fluorescence system and two chemiluminescence instruments. The intercomparisons were performed with ambient air at NO mixing ratios ranging from 10 to 60 pptv and NO‐enriched ambient air at mixing ratios from 20 to 170 pptv. All instruments sampled from a common manifold. The techniques exhibited a high degree of correlation among themselves and with changes in the NO mixing ratio. Agreement among the three techniques was placed at approximately ±30%. Within this level of agreement, no artifacts or species interferences were identi

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12843

年代:1985

数据来源: WILEY

摘要:

In July of 1983, ambient measurements of nitric oxide (NO) were obtained at Wallops Island, Virginia, during the NASA GTE/CITE ground‐based instrument intercomparison field study. The instrument, which was designed for measurements in the remote troposphere from an aircraft platform, is briefly described. Ten days of ambient air observations showed broadly uniform diurnal behavior, although considerable variability was encountered. Two distinct synoptic meteorological conditions resulted in markedly different levels of nitric oxide abundance. When the local winds were from the north to west sectors, which placed the sampling site within 130 to 300 km of large urban centers, the midday mixing ratios were typically in the range of 200–300 pptv. In contrast, when the air mass sustained a 1‐ or 2‐day period over the Atlantic Ocean, the mixing ratios were substantially lower and in the 50–60 p

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12853

年代:1985

数据来源: WILEY

摘要:

This paper reports on a new two‐photon laser‐induced fluorescence (TP‐LIF) sensor capable of making routine measurements at the few parts per trillion volume level. This direct spectroscopic detection method has been demonstrated to be a reliable instrument while performing both on the ground and in the air. As currently designed it is unique in being “signal” rather than “signal‐to‐noise” limited. The latter characteristic enables the TP‐LIF sensor to make atmospheric measurements of NO under environmental conditions that might normally be considered unsuitable for a laser technique. These include clouds, rain, and, in general, high‐atmospheric‐aerosol loading conditions. Of special interest is the insensitivity of the TP‐LIF NO instrument to changes in pressure while operating in the troposphere. This characteristic has enabled this sensor to be used to record real‐time altitude profiles of NO. Future improvements should make possible two measurement opportunities: (1) NO flux measurements via the airborne eddy‐correlation method and (2) nitrogen isotopic distribution measurements (e.g., N15O16versus N14O16) as a means of iden

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12861

年代:1985

数据来源: WILEY

摘要:

The NASA Goddard Space Flight Center/Wallops Flight Facility nitric oxide detector used in the July 1983 GTE/CITE 1 instrument intercomparison is a chemiluminescence system which, at that time, had a detection limit of about 2 pptv (S/N= 1) for 60‐s integrations. A substantial amount of NO concentration data was taken with this system at Wallops Island, Virginia, a site that should be typical of numerous nonurban coastal areas of the eastern United States and for which little other data are available. Midday concentrations under conditions of northwest winds averaged about 200 pptv, a value low enough to imply lower NOxamounts than are generally thought to exist in the eastern United States. During a 2‐day period when the sampled air had spent 1–2 days over the Atlantic Ocean, average NO concentrations of 70 and 33 pptv were observed. Measurements at night indicated an average NO concentration of 16 pptv under wind conditions making contamination of the sampled air by local anthropogenic sources unl

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12875

年代:1985

数据来源: WILEY

摘要:

Results from an intercomparison of techniques to measure tropospheric levels of carbon monoxide (CO) are discussed. The intercomparison was conducted as part of the National Aeronautics and Space Administration's Global Tropospheric Experiment (GTE) and was held at Wallops Island, Virginia, in July 1983. Instruments intercompared included a laser differential absorption method and three grab sample/gas chromatograph methods. The intercomparison consisted of simultaneous measurements of ambient levels of CO and controlled injections of CO from a common manifold. Results from the techniques exhibited a high degree of correlation among themselves and with changes in the CO mixing ratio. The results suggested a level of agreement among the techniques of about 15%. However, a day‐to‐day bias between the techniques was observed, which resulted in differences between techniques as large as

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12881

年代:1985

数据来源: WILEY

摘要:

We have performed over 900 measurements of atmospheric dimethyl sulfide (DMS) in five different marine locations: the equatorial Pacific; Cape Grim, Tasmania; the Bahamas; the North Atlantic; and the Sargasso Sea. At all locations, DMS concentrations were usually in the range of 100–400 ng S m−3, with similar average concentrations of approximately 150 ng S m−3(107 parts per thousand by volume). Highest concentrations occurred during, but were not limited to, periods of sustained high winds and overcast skies, presumably owing to faster exchange from surface seawater and less photochemical activity in the atmosphere. Lowest values occurred during airflow from continental regions, which provides higher levels of oxidants and free radicals to react with DMS. Averaged over time, the concentrations in clean marine air reached a maximum at night and a minimum in the afternoon, when concentrations were about one third lower than during the nighttime maximum. The observed concentrations of DMS in the marine atmosphere and their diurnal variability agree well with model simulations involving OH and NO3oxidation of DMS and are consistent with a global sea‐to‐air DMS flux of about 40±20 Tg S yr−1. DMS may represent a major sink for NO3in the marine

ISSN:0148-0227    

DOI:10.1029/JD090iD07p12891

年代:1985

数据来源: WILEY