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The detailed mechanisms for excitation of all the night glow emissions remain very much in doubt. The green atomic oxygen line appears to be excited by a modification of the Chapman mechanism, although recent laboratory studies still show some inconsistent features. The red atomic oxygen line most likely results from the atomic exchange reaction between 0+ ions and either N2 or O2. However, comparison of laboratory measurements and airglow observations suggests these reactions have low pre-exponential factors. Recent laboratory measurements and Nicolet's estimate of the H-atom concentration at 85 km indicate that the reaction between H-atoms and ozone remains the most attractive process for excitation of the OH emission. It is shown that the mechanisms suggested by Krassovsky are not as likely as the H — O3 process.

The southern Ontario oxidant study (SONTOS) is one of the scientific responses to the problem of ozone exceedences in the Windsor/Quebec City corridor, the strip extending from Windsor in the extreme southwest of Ontario, along the north shores of Lake Erie and Lake Ontario and down the St Lawrence valley. This corridor includes the two major metropolitan areas of Toronto and Montreal and experiences more exceedences of the Canadian ozone guideline per year than any other part of the country. The overall objective of SONTOS is to elucidate the factors which lead to these high levels. The study design is based on intensive measurements made at a site to the NNW of Toronto, with supplementary measurements at other sites and on board an aircraft. This paper, and the seven which follow, describe and interpret the measurements made in the summer of 1992. Although this summer was noteworthy for generally very low ozone concentrations, a number of interesting observations have been made which have a bearing on the oxidant phenomenon in southern Ontario. In particular, this paper describes two specific events. In one, which occurred on 6 August 1992, the intensive measurement site experienced the impact of a polluted air mass, which had apparently travelled to the site from Toronto, by way of Lake Ontario. This case has been contrasted with an event in the last week of August, in which large-scale, organised southwesterly flow led to the conditions which more typically give rise to widespread ozone episodes in the province. Events similar to the 6 August episode occurred on several occasions during the study period, and underline the very important role of the Great Lakes in ozone transport and delivery in southern Ontario.

Five methods for the measurement of CH2O vapor were compared under remote tropospheric conditions. The techniques included an aqueous-scrubber enzyme fluorescence method (URIcoil), TDLAS (UNI), 2,4-dinitrophenylhydrazine (DNPH) impregnated-cartridges (BNL/WSUcart), an aqueous-scrubber DNPH method (BNL/WSUcoil), and an unpublished aqueous-scrubber immobilized-enzyme fluorescence method (NCARbound). This was part of the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) which was performed in four ∼30-day intensives. In MLOPEX 2a (fall 1991), the URIcoil technique indicated higher concentrations relative to the BNL/WSUcoil which were higher than UNI. The limited number of NCARbound measurements for MLOPEX 2a were greater than the other measurements and least reliable. During MLOPEX 2b (winter 1992), URIcoil, UNI, BNL/WSUcoil, and NCAR-bound gave comparable measurements of CH2O with the latter again being consistently higher than the first three methods and its performance and reliability was improved over MLOPEX 2a. URIcoil and BNL/WSUcoil were comparable in MLOPEX 2c (spring 1992) and 2d (summer 1992), whereas BNL/WSUcart was consistently higher than both for these intensives. The major source of difference between techniques was ascribed to variations in the analytical-procedural field blanks. Calibration differences were the most likely cause of URIcoil being higher than BNL/WSUcoil and BNL/WSUcoil being higher than UNI during MLOPEX 2a. Lower free troposphere median concentrations were between 100 and 150 ppt for all seasons and without a seasonal trend. These values were a factor of 2 to 3 lower than model estimates for this study site and were in keeping with earlier work.

We have attempted to describe how tunable diode laser absorption spectroscopy can be applied to measurements of clean and polluted air. Pb salt diodes emit in the infrared region where most gases of atmospheric interest have their strong absorptions, providing the basis for a universal system. The high monochromaticity of these diodes have made TDLAS the most specific method available for unequivocal identification of atmospheric species, a particularly useful property for complex mixtures in polluted air or in automobile stack emissions and for serving as a comparison standard for other, less definitive methods. The combination of modulation and long-path techniques have permitted sensitivities in the parts per trillion range, required for measurements in remote, clean air or for minor, but important constituents in complex mixtures. The rapid tuning rate of these diodes, permitting real-time measurements in the fractions of second range, has been exploited in measurements from fast-flying aircraft, for eddy correlation flux measurements and for studying transients in automobile exhaust. Interesting advances are being made in the use of TDLAS systems for making real-time isotope ratio measurements. Considerable improvements have been made in the operating temperatures and tuning ranges of commercially available diodes which have permitted the use of liquid N2 cryostats or Dewars. A miniature He cryostat cooling system has also been recently developed which weighs 7 kgm and requires only 75 watts of electrical energy. Commercial systems are now available which can fit in a standard instrument rack or small aircraft, and which can be operate automatically, without attendance for long periods of time. The price of these systems have also declined significantly. The main disadvantage of the TDLAS for atmospheric measurements is the limited number of species that can be measured by the same diode. This limitation can be mitigated to some extent by the use of multiplexing techniques which permit simultaneous operation of a number of diodes. The tuning range of modern laser diodes are continuously being extended and is now sufficient in many cases to encompass strong absorption lines from 4 or 5 gases. The high specificity of TDLAS depends on the molecule possessing resolved rotational-vibronic structure. Roughly speaking, this limits the method to molecules having less than 10 atoms or those having symmetrical structures. Extension to larger, asymmetric molecules has not yet been utilized although it is possible that fast scan techniques can be used to measure larger molecules which do not have completely resolved ro-vibrational spectra. Another limitation is that the best specificity and sensitivity is achieved when measurements are made at sub-atmospheric pressure. This necessitates the use of sampling cells which can introduce surface effects for reactive and unstable molecules. The pressure broadening of some molecules, such as N20, CH4, O3, HCI, NO, HNO3 and NH3, are however, sufficiently small that measurement at atmospheric pressure is possible with open paths. Increased interest is being shown in the application of laser diodes made of group III–V compounds to gas measurements. The attractive features of these diodes are that they operate at or near room temperature, while some are relatively inexpensive and of relatively high quality and power due to their wide-spread use in communication and consumer electronic industries. They operate in the near infrared region where absorption coefficients are some two three orders of magnitude lower than those in the fundamental, mid-infrared region. But high frequency modulation techniques can be used to regain some of the sensitivity so that, at present, detection limits approach 1–10% of the sensitivity achievable from the more complex and more expensive mid-infrared systems. In addition both the optical and electronic components are more readily available, less expensive, and much smaller which permits construction of relatively inexpensive, compact instruments. For a certain limited number of species, where ultra-high sensitivity is not required the NIR systems will provide advantages of size, simplicity and cost. For a more universal and sensitive system the Pb salt, mid-infrared diode systems will continue to provide a superior and highly specific measurement system. Improvements both in quality and performance of the Pb-salt diodes and in the hardware and software to operate the system will result in continuing improvements in sensitivity, reliability and performance of these systems as well as in cost reduction.

Spectroscopic methods afford a number of advantages for making atmospheric measurements. It is a passive technique which is capable of making real time, in situ measurements. Since each molecules has a characteristic spectrum it is possible to make simultaneous measurement of a number of species. In addition, unequivocal identification of the target species is possible if the instrument has sufficient spectral resolution. Detection limits as low as 1 part in 1013 have been reported as well as dynamic ranges as high as 108. Temporal resolution of fractions of a second can be achieved for “eddy correlation” flux measurements. – Fourier Transform Infrared Spectroscopy (FTIR) is, perhaps, the most universal method and is particularly useful in identifying new species in heavily polluted air. However, it lacks the sensitivity required for measurements of trace gases in clean air. Differential Optical Absorption Spectroscopy (DOAS) operates in the visible and the near UV which limits the number of measurable species. But it is capable of measuring highly reactive gases such as OH, NO3, and HONO. Tunable Diode Laser Absorption Spectroscopy (TDLAS) has very high spectral resolution, sensitivity and time response. Its main disadvantage is the need for a number of laser diodes to cover a wide spectral range. Laser Induced Fluorescence (LIF) is also capable of both high sensitivity and specificity. However, rather complex excitation sources have to be devised for each gas being investigated. Photoacoustic Absorption Spectroscopy (PAS) is, in principle very simple and capable of simultaneous measurements. In practice, however, it suffers from lack of resolution and serious interferences from CO2 and H2O.

A high resolution tunable diode laser absorption spectrometer (TDLAS) was used to measure the broadening effect of water vapor and other gases (dry air, nitrogen, oxygen, hydrogen and helium) on three methane lines in the v4 fundamental. The effects on methane eddy correlation flux measurements amount to a few percent for the least broadened line for expected H2O fluxes, to ≈10% for the most broadened line for higher H2O and lower CH4 fluxes likely to be encountered. The broadening coefficients of methane measured for air, N2, O2, and He are in good agreement with recently published values.

The advantages of tunable-diode-laser absorption spectrometry (TDLAS) for measuring trace atmospheric gases are universality, positive identification, good sensitivity, and rapid response time. A TDLAS system is described which is capable of making measurements aboard an aircraft. The instrument was employed during the Chemical Instrumentation Test and Evaluation (CITE) 2 program to measure NO2 on 11 flights and HNO3 on five flights. Detection limits were determined to be 25 parts per trillion by volume (pptv) for NO2 and 75 pptv for HNO3 with response times of 3 min. This was sufficient to permit measurements of NO2 in the free troposphere and HNO3 in the continental boundary layer a significant fraction of the time.

Results are reported on the performance of (1) denuder-tube/chemiluminescent, (2) nylon-filter/ion-chromatography, and (3) tunable-diode-laser/multipath-absorption HNO3 measurement instruments during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) program in summer 1986. The instrument designs, test protocols, and CITE 2 flights are described, and the results are presented in extensive graphs and discussed in detail. The data obtained with the three instruments are shown to be in very poor agreement at mixing ratios below 150 parts per trillion by volume (pptv), with significant discrepancies even at higher levels. Instrument (3) gave systematically higher values than (1) and (2). It is concluded that none of the instruments is accurate enough for reliable use at normal atmospheric HNO3 levels (around 100 pptv).

Results on NO2 instruments are reported from the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) program in summer 1986. The instruments tested were (1) a two-photon LIF system using a laser for NO2-NO photolysis, (2) a chemiluminescence (CL) detector using FeSO4 for NO2-NO conversion, (3) a CL detector using an arc lamp for NO2-NO photolysis, and (4) a tunable-laser-diode multipath-absorption system. The procedures for the CITE 2 ground-based and flight tests are described in detail, and the results are presented in extensive graphs. Instrument (2) was eliminated because the FeSO4 converted atmospheric PAN to NO, resulting in spuriously high NO2 values. The remaining instruments gave readings in 30-40-percent agreement at NO2 mixing ratios of 100-200 parts per trillion by volume (pptv). At ratios below 50 pptv, the correlation among the measurements was very poor, with a tendency for system (4) to give higher values than (1) or (3).

During August and September 1986, 11 aircraft flights were made over the eastern Pacific Ocean and continental United States. The suite of observations included simultaneous measurements of peroxyacetyl nitrate (PAN) and active nitrogen (NO{sub x} = NO + NO{sub 2}). At altitudes of 4.5-6.1 km in the middle free troposphere, PAN was usually 5-6 times NO{sub x} in maritime air masses and 2-4 times NO{sub x} in continental air masses. In air masses of tropical origin, or in the marine boundary layer, both PAN and NO{sub x} were typically less than 20-30 parts per trillion by volume, and the PAN to NO{sub x} ratio was less than one. The observations show that PAN can be a major component of the odd nitrogen budget in the middle free troposphere, and strongly reinforce earlier views that the abundance is mainly governed by long-range transport processes including formation during transport and continental boundary layer to free tropospheric exchange of PAN and its precursors. Unlike reservoir HNO{sub 3}, PAN can be transformed to active nitrogen and peroxy radicals by a variety of physical atmospheric processes that lead to air mass warming. Since NO{sub x} plays a critical role in determining photochemical O{sub 3} production,more » which in turn determines the oxidative power of the atmosphere, the observed large ratios of reservoir PAN to active NO{sub x} imply an important photochemical and dynamical role for PAN in the eastern Pacific remote free troposphere.« less

Results are reported from airborne measurements of NO, NO2, O3, and CO obtained in the free troposphere (FT) and boundary layer (BL) over the western U.S. and eastern Pacific during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) in summer 1986. The aircraft instrumentation and the CITE 2 flight protocols are described, and the results are presented in extensive tables and graphs. Over the ocean the median mixing ratios for NO and NO2 were found to be 4.0 and 10.4 parts per trillion by volume (pptv), respectively, in the BL and 12.4 and 18.0 pptv in the FT; the corresponding values over land were 34.5 and 75.0 pptv in the BL and 13.0 and 36.0 pptv in the FT. in continental air masses. NO(x) is shown to be positively correlated with O3 and CO and negatively correlated with dewpoint over the ocean, whereas over land NO(x) was positively correlated with O3, CO, and dewpoint.

The Northern Wetlands Study (NOWES) was undertaken to better define the role of northern wetlands and particularly of the large continuous wetland of the Hudson Bay lowland. CO 2 , CH 4 , N 2 O, O 3 , and nonmethane hydrocarbons (NMHC) between the surface and the atmosphere were measured across a 140-km transect, representing approximately 5000 years of peatland evolution. This transect was located in the southern portion of the Hudson Bay lowland. A second study of surface exchange was conducted in the subarctic region of the northern Hudson Bay lowland. Regional flux surveys were conducted by aircraft between the two study areas. An integral part of the study was to determine the size of the source/sink of various gases and to compare the flux estimates made by several different techniques

Absolute rate constants are reported for the deactivation of O(1D) by five trace atmospheric constituents for the temperature range 200–350 K. O(1D) atoms produced by photolyzing ozone with a frequency quadrupled pulse from a Nd‐YAG laser are monitored directly by means of the O(1D) →O(3P) emission at 630 nm. All the gases studied here are thought to deactivate O(1D) primarily through reactive channels. Their rate constants exhibit no detectable temperature dependence. The rate constants are (in units of 10−10 cm3/molecule⋅s) N2O: 1.1,±0.2, H2: 0.99±0.3, HCl: 1.4±0.4, NH3: 2.5±0.5, CH4: 1.4±0.4. The present results and those of our previous studies are compared with rate constants obtained using the time‐resolved attenuation of resonance absorption technique.

Absolute rate constants and their temperature dependencies for the deactivation of O(1D) by five important atmospheric gases are reported. O(1D) atoms are produced by photolysis of ozone at 266 nm and the atoms are directly observed in time resolved decay of the O(1D) →O(3P) radiation at 630 nm. Gases which only quench O(1D) (O2, N2, and CO2) are observed to have a small negative temperature dependence while O3 and H2O, which also have a reactive channel, display no temperature dependence. Arrhenius expressions for the reactions measured are (A in units of 10−10 cm3/molecule⋅ s, E in cal/mole) O2(T=104–354 K) 0.29 exp(134/RT), N2(T=104–354 K) 0.20 exp(214/RT), CO2(T=139–200 K) 1.2 and (T=200–354 K) 0.68 exp(233/RT). The rate constants for O3 and H2O are 2.4×10−10 and 2.3×10−10 cm3/molecule⋅ s over ranges of 103–393 K and 253–353 K, respectively. The results are compared with other energy dependent measurements and with the theories reported in the literature.

The rate constant k1 for the quenching of O(1D) atoms by N2O relative to the rate constant k2 for the quenching by N2 was determined by measuring the amount of NO produced as a function of the amount of N2 added to constant flows of N2O in helium flowed through the photolysis cell. The high sensitivity of the chemiluminescence technique for NO measurement permitted very low conversions to be used. The ratio k1/k2 was found to be 4.0 at 23±2 °C and 2.9 at −96±2 °C. The accuracy of these ratios is believed to be better than ±10%. The fraction k1a/k1 of the reaction which produces NO (with rate constant k1a) was determined by measuring the NO produced from the photolysis of N2O—helium mixtures in a flow system and the rate of pressure increases when the same mixture was photolysed in the cell under static conditions. The ratio k1a/k1 was found to be 0.62 both at 23 ± 2 °C and at −96 ± 2 °C, with an uncertainty of ±15%. The branching fraction was found to be independent of the partial pressure of helium in contrast with other reports of a “hot atom” effect. The significance of these rate constant ratios to stratospheric chemistry is discussed.

The relative rate constants for the reaction channels were determined using chemical‐ionization mass spectrometry to measure the products of Reaction (1). O(1D2) atoms were produced by the photodissociation of N2O at wavelengths greater than 1950 A. The measurements were carried out in mixtures of N2O with helium added to remove the excess kinetic energy carried by the O(1D2). We find the ratio k1a/k1b is sensitive to the presence of helium increasing from a value of 0.68 in pure N2O to a value of 0.80 with [He]/[N2O]?10. In addition, at 300 K we find that (1a) and (1b) consititute the only significant channels for the reaction with (k1c+k1d+k1e)/(k1a+k1b ) ?0.038. The ratio k1a/k1b is found to decrease slowly with increasing temperature over the range 170–434 K. These data can be fitted by the expression k1a/k1b= (0.72±0.11) +(21.6±7.0)/T.

Rate constants for proton-transfer reactions of the type XH/sup +/ + HCN(CH/sub 3/CN) ..-->.. H/sub 2/CN/sup +/(CH/sub 3/CNH/sup +/) + X where X = H/sub 2/, N/sub 2/, CO, H/sub 2/O, and CO/sub 2/ and of the type HCN(CH/sub 3/CN) + X/sup -/ ..-->.. CN/sup -/(CH/sub 2/CN/sup -/) + XH where X = H, D, OH, SH, NH/sub 2/, C/sub 2/H, and CH/sub 3/O have been measured at 297 +- 2K using the flowing afterglow technique. These reactions for which the measured rate constants span a range from 0.15 to 1.5 X 10/sup -8/cm/sup 3/ molecule/sup -1/s/sup -1/ represent some of the fastest ion-molecule reactions observed to date. The rate constants are compared with the predictions of Langevin, average-dipole-orientation and locked-dipole theories of ion-molecule collisions. The average-dipole-orientation theory provides the most realistic collision rates for these reactions although these appear to be underestimated by approx.10 to approx.40%. The observed dependence of the efficiency for proton transfer on exothermicity indicates that the assumption of unit reaction probability resident in such comparisons may break down at low exothermicities.

Stratospheric air samples have been obtained at 17.7, 22.3, and 26.2 km using balloon borne sampling spheres launched from Laramie, Wyo. These samples have been analyzed for CFCl3, CF2Cl2 and N2O, using electron capture detector gas chromatography. The concentrations of all three constituents are compared with theoretical models and found to be in excellent agreement. The dissociation products of N2O, CFCl3, and CF2Cl2 (NO and chlorine atoms) catalytically destroy ozone in the stratosphere. A knowledge of the concentrations of these species in the stratosphere is therefore essential to an understanding of the ozone balance.

Nitric oxide mixing ratios have been measured under high sun conditions in the stratosphere over the altitude range 17–30.5 km during four balloon flights launched from New Mexico. Experimental evidence is also presented to confirm that no serious sampling errors were encountered either from contamination of the sampled air or from removal of nitric oxide in the inlet to the instrument.

Measurements of formaldehyde, HCHO, using tunable diode laser abssrption spectroscopy (TDLAS) are reported for four sites in North America. The TDLAS apparatus and its application to these measurements is described. Detection limits of ca. 0.25 ppbv were obtained with a three-minute time resolution. Two distinct types of diurnal behaviour were observed: in the absence of local pollution sources the HCHO diurnal variation was weak and HCHO is not lost during the night. We conclude that the lifetime of HCHO with respect to dry deposition was greater than 50 h at the least-polluted site. At sites downwind of pollution sources, the HCHO peaks near noon and declines in the afternoon. At the least-polluted location, the most probable value for HCHO was 0.25–0.5 ppbv, while hourly averaged values up to 12 ppbv were observed at the other locations.

A highly sensitive, lightweight, portable instrument has been developed for continuous monitoring of N02 in air. It operates by detecting the chemiluminescence produced when N02 encounters a surface wetted with a specially formulated solution containing luminol. Unlike other chemiluminescent instruments it measures N02 directly and does not require prior conversion of N02 to NO. It does not respond to H202, NO, HNO3, NH3, CO, C02, S02 or organic nitrates. The only interferences encountered to date are from 03 and PAN with the response to 03 being less than 0.2% of its response to N02. The response time of the instrument is less than 1 s and its sensitivity is better than 5 pptv. The instrument shows a negative temperature dependence of about 2% °C−1 which is compensated electronically. Measurements have been made with the instrument during a number of field missions in polluted urban and relatively clean rural air. The relative influences of photochemistry and transport from local sources has been observed. Simultaneous measurements made with this instrument and the unequivocal tunable diode laser absorption spectroscopy method have shown excellent agreement.

Atmospheric models designed to predict the effect on the ozone budget of the injection of nitric oxide into the stratosphere by high-flying aircraft require a knowledge of the NO concentration in the unperturbed atmosphere. Moreover, a monitoring program will require a base line against which to measure the magnitude of any future stratospheric pollution. A number of measurements have recently been reported, not only on NO, but also on NO2, and HNO3 which are interconverted by stratospheric photochemistry. All the methods but two employ "remote-sensing" optical absorption or emission techniques. Infrared solar absorption using long optical paths at twilight has proven to be very sensitive in detecting trace atmospheric constituents but quantitative interpretation appears to be very difficult. Chemiluminescence and direct "particle" sampling have provided insitu measurements.The spread in the reported values of mixing ratios is very large for NO2, appreciable, but smaller for NO, and smallest for HNO3. Insufficient data are available to assess how much of this spread is due to measurement errors and how much is due to natural variability in the mixing ratios. Intercomparisons of the measurements for different nitrogen compounds are made by consideration of the principal chemical reactions governing their relative concentrations. Discrepancies exist which should diminish as more accurate chemical rate data and synoptic stratospheric measurements become available.

The photodissociation coefficient of NO2, J NO 2, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J NO 2 measured were 10.5±0.3 and 10.3±0.3×10-3 s-1 at 24 and 32 km respectively. The decrease in J NO 2 at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J NO 2 using a simplified isotropic multiple scattering computer routine.

The data set of N and S compound measurements from WATOX-85 has been examined in detail to assess that data quality and suitability for use in addressing the goals of the Western Atlantic Ocean Experiment. Accuracy estimates for particulate SO42− and NO3−, SO2 and HNO3 have been made on the basis of the investigators' estimates and the results of intercomparisons. Intercomparisons of ground-based particulate SO42− and all filter SO2 and HNO3 measurements show them to be consistent with the 20% accuracies quoted by the investigators. Ground-based particulate NO3− and aircraft particulate SO42− show inconsistencies such that the accuracies can be no better than 28% and the aircraft particulate NO3 has an accuracy of no better than 60%.

The flowing afterglow and selected ion flow tube techniques are applied in a room temperature study of the kinetics of proton‐transfer reactions of the type XH++Y?YH++X for X or Y=He, H2, O2, Kr, O, N2, Xe, CO2, CH4, CD4, N2O, OH, and CO, and for the deuteration of O2 by D3+. Equilibrium constants are determined and changes in thermodynamic state properties (ΔG°, ΔH°, ΔS°) are derived for the reactions with X/Y=H2/O2, O2/Kr, H2/Kr, H2/N2, O/N2, N2/Xe, Xe/CO2, CO2/CH4, CH4/N2O, and N2O/CO. Proton affinities are reported for O2, H2, Kr, O, N2, Xe, CO2, CH4, N2O, and CO, together with the heats of formation of their protonated species. Also a correlation is presented between the kinetic and thermodynamic results obtained in this study.

This paper reports new surface and aircraft measurements of sulphur and nitrogen species made during WATOX-85 at Lewes, Delaware and Bermuda. Concentrations of most species measured in this portion of the western Atlantic Ocean atmosphere were higher than those found in remote marine environments, showing clearly the influence of anthropogenic emissions from North America. The experiment was designed such that measurements were made following cold frontal passages in conditions of strong, dry westerly flow, to ensure that measurements at Bermuda were in air masses that had earlier crossed the east coast in the region of Lewes. Boundary-layer SO 2 concentrations decreased by a factor of 20 between the east coast and Bermuda, while sulphate was the same at both locations. First-order decay distances for SO 2 and total S were 340 and 620 km, respectively, under these conditions. The decay distance for total S is substantially shorter than previously determined, indicating that SO 2 in particular is removed in near-coastal environments more quickly than previously supposed. Boundary-layer NO x and HNO 3 concentrations decreased by close to an order of magnitude between the east coast and Bermuda, whereas for NO 3 − the decrease was a factor of two. Corresponding first-order decay distances of NO ' x and total N were 500 and 550km, respectively.

The photodissociation coefficient, J NO2 of NO2 in the atmosphere was calculated at 235 and 298 K using the measured temperature dependences of the absorption cross-sections and quantum yields. These calculations gave a ratio J NO2(298 K)/J NO2(235 K)=1.155±0.010 which is only weakly dependent on altitude, surface albedo and solar zenith angle.

Regulations to limit the use of trichloroethylene as a degreasing solvent have led to an increased use of the more photochemically inert solvent methyl chloroform as a substitute. Model calculations show that about 15 percent of the methyl chloroform released into the atmosphere will reach the stratosphere. Time scenarios based on past production figures and reasonable projections for future release rates lead to a steady-state ozone depletion due to this solvent about 20 percent as large as those resulting from the continuous release of chlorofluoromethanes at 1973 rates.

The possibility of significant losses of chlorofluoromethanes and their photochemical products in the troposphere or stratosphere has been examined. A number of laboratory measurements have been carried out involving possible ambient positive and negative ions and CFCL3, CF2Cl2 and HCl. No reactions between ions expected to have significant concentrations and these species have been observed. It appears that the reactions which might have been important are in fact endothermic. This is a result of normal atmospheric chemistry leading to very stable ions on a very short time scale. We conclude that ionmolecule reactions do not play a significant role in restricting the lifetime of CFCl3 or CF2Cl2 in the atmosphere or in removing the reactive products Cl, HCl, and ClO.

A number of N2O profiles obtained in the troposphere and stratosphere at five latitudes are reported. The variability in the reported stratosphere N20 mixing ratios is substantial and indicates a strong dependence on both stratospheric transport and photochemistry. A profile obtained at Panama indicates a relatively large transport of N2O into the stratosphere at low latitudes. This profile represents the first one obtained in the tropics. From the observed data, area-averaged, global vertical eddy diffusion coefficients were derived that were found to be a factor of 1.5 to 3 times larger than those derived by Hunten from data obtained at locations not including the tropics. The derived eddy diffusion profile is heavily weighted by one single profile in the tropics and more observations are needed to substantiate this finding. The estimated flux of N20 into the stratosphere was equal to 15×1012 g(N) per year and the total stratospheric production of NOx was estimated to be 1.6×1012 g(N) per year....

Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time-resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) at 298 K are reported for N2, O2, CO2, O3, H2, D2, CH4, HCl, NH3, H2O, N2O, and Ne. The results obtained are compared with previous relative and absolute measurements reported in the literature.

An enhanced “greenhouse effect” due to an increase in atmospheric CO 2 is expected to produce significant climatic changes. If the combustion of fossil fuels is the only anthropogenic source of atmospheric CO 2 , measurements show that 54% resides in the atmosphere. The largest reservoir for the remaining 46% is the oceans. Known oceanic processes can account for 35% and the major uncertainty appears to be the role played by the intermediate waters. If, however, deforestation is as large a source of additional atmospheric CO 2 as some have suggested, carbon balance cannot be obtained with presently identified removal processes. Various computer models have been used to calculate the effects of increasing atmospheric CO 2 . These include energy balance, radiative-convective and general circulation models (GCM's). Many feedback mechanisms must be considered including water vapour, clouds, oceans and the cryosphere. Although representing a considerable advance over other models, GCM's still require many approximations, of which the treatment of oceans and clouds are the most questionable. These models predict, for the scenario of the doubling of atmospheric CO 2 , an increase in global surface temperature of about 3°C with larger increases, up to 10° at higher latitudes. Significant changes in evaporation and precipitation patterns are also indicated.

An instrument, specifically designed for measurements from a balloon platform in the stratosphere, has been used to obtain ground-level values of the atmospheric photodissociation coefficient of nitrogen dioxide, JNO2.A typical clear-sky value is 8.0×10-3 s-1 when the solar zenith angle is 40°. Measurements were made as a function of solar zenith angle and correlated with a calibrated Eppley UV radiometer. It is shown that JNO2may be expressed as a simple function of the radiometer output so that estimates of JNO2can be made using just an upward looking radiometer to an accuracy of about 20%. The measurements are also found to be in good agreement with calculations of JNO2using a simplified isotropic multiple scattering computer routine.

Measurements of NO and NOx' (as measured by a chemiluminescent analyzer equipped with a FeSO4 converter) were made from an aircraft off the east coast of North America in January and February 1986. These measurements show the mixing ratios of the nitrogen oxides to be higher than encountered in remote continental or marine environments. Both the free troposphere and boundary layer mixing ratio distributions are skewed to ward high mixing ratios and are best described by a gamma probability distribution. The mean mixing ratios observed were 2.9 parts per billion by volume (ppbv) in the boundary layer and 0.55 ppbv in the free troposphere for NOx', and 0.56 ppbv in the boundary layer and 0.18 in the free troposphere for NO.

The reactions of O3 with CH3ONO and C2H5ONO were studied using infrared absorption spectroscopy in a static reactor at temperatures between 298 and 352K. Both reactions followed simple second-order kinetics forming the corresponding nitrate: The rate coefficients are given by .

Methods of production and detection of reactive species of oxygen and nitrogen are discussed briefly. Kinetic data for reactions of these species which have aeronomic interest are reviewed. New data, obtained during the past 4 years are critically compared, and recommendations made for "best" values where possible. An attempt is also made to delineate important areas where additional work is needed to meet the demands of atmospheric modelling.

A mass spectrometric study was made of oxygen activated by microwave and by a-c. glow discharge. Appearance potential curves for normal oxygen at masses 16 and 32 indicated the occurrence of multiple electron impact processes. The change in the curves when the oxygen was activated could be interpreted by assuming the presence of O-atoms in the 3P ground state, and O2 molecules in the 1Δg excited state. No evidence was obtained for the presence of ozone up to pressures of 2 mm. Hg. The recombination coefficient of O-atoms on pyrex was found to be 1.1 × 10−4. Only one oxygen atom in 21 was ionized before recombining in the mass spectrometer ion source. The rate constant for the reaction of O-atoms with N2O is less than 1 × 10−8 cm.3 mole−1 sec.−1, and several orders of magnitude less than this for the reaction O(3P) + N2O → 2NO. The reaction of O-atoms with NO2 was much faster than with NO, but no evidence was found for the formation of NO3.

The spectral distribution of the chemiluminescent reactions O+NO→NO2+hv has been determined over the wavelength region 3875–14 000 A. The absolute rate constant was determined by a method of chemical actinometry which required only relative intensity measurements and which is virtually free from geometry errors. The rate constant over this spectral region was found to be 6.4×10—17 cm3 molecule—1 sec—1 within an accuracy of 30%. This reaction can be used as a standard from which the rate constants for other chemiluminescent reactions can be readily obtained without requiring detector calibration or geometry corrections.

Association of ground-state oxygen and hydrogen atoms at pressures of 0.4–4.0 torr and 300°K results in chemiluminescence. The emission corresponds to the transition OH(A2σ+)→OH(X2Π). The (0,0) band is the most intense but the (0,1)(1,0) and (1,1) bands were also observed. The (0,0) band intensity was found to follow the kinetic relation I=K[O][H], where K decreases with pressure. The kinetics are consistent with a two-body excitation followed by collisional quenching.Since the (A2σ+) state does not correlate with ground-state atoms it must be excited by preassociation. Evidence for such a curve crossing near the heat of association is obtained from the vibrational intensity ratios and from the rotational energy distribution.

The kinetics of the reactions of H atoms with H2S and with COS were measured at 298deg;K in a flow system using mass-spectrometric detection. The rate constants were found to be 3.8 × 10−13 and 2.2 × 10−14 cm3 part−1 sec−1, respectively, with an estimated accuracy of 25%. At high flow rates of H2S, 0.5 molecules of H2S are consumed per H atom originally present. At all flow rates of COS, H2S is a major product, CO production equals COS consumption, and 0.5 molecules of COS are consumed per H atom. The results are consistent with the reaction HS + HS H2S + S being the dominant process for thiyl radicals, and evidence is presented to indicate that its reaction rate is close to collisional frequency.

In the reaction between NO and O-atoms, the concentration of NO remains essentially unaltered. The reaction can therefore be considered as a NO-catalyzed recombination of O-atoms. Its rate can be conveniently studied by following the disappearance of O-atoms by an isothermal calorimetric technique. The reaction was found to be third order, first order in the concentrations of O, NO, and M, where M is some third body. The third-order rate constant was found to be 1.85 × 1016 cc2 mole−2 sec−1 when M = O2, A, or He and 2.0 × 1016 cc2 mole−2 sec−1 when M = CO2 The rate constant was found to have a slight negative temperature coefficient which corresponded to a negative Arrhenius activation energy of about 0.2 kcal/mole. A detailed mechanism for the reaction has been proposed.

— The only detectable emission from discharged oxygen was a band system at 7619 A. However, when a film of mercuric oxide was interposed between the discharge and the observation position, the intensity of this band was greatly enhanced and additional bands were observed at 6340, 7030 and at 12,700 A, in agreement with the findings of Bader and Ogryzlo. A linear relationship, however, was found between the intensities at 6340 and at 12,700 A, instead of the quadratic dependence reported by these authors. A rapid reaction was found to occur between O3, and O2>(1Σ+g) molecules but the reappearance of the 7619 A, emission after all the O3 had been reacted indicates a production process of O2(1Σ+g) molecules, probably from O2(1Δg). The value of the rate constant for the reaction 02(1Σ+g) + O32O2+ O is approximately 6times10-13 cm3/molecule per sec. The rate constant for the comparable reaction with O2(1Δg) molecules is probably lower than this by a factor of at leat 4.

The conductance of NaCl and KCl in 50‐mole percent methanol‐water mixtures has been measured at concentrations from 0.0005 to 0.01 N. The data can be represented within experimental error by the Onsager‐Shedlovsky equation, the limiting conductances being 66.62 and 75.10, respectively. The limiting conductances of chloride ion, obtained from these values, and the limiting transference numbers reported in the accompanying paper, satisfy the rule of independent ionic mobilities, but at finite concentrations the chloride ion conductance is less for the potassium salt than for the sodium. The decrease in limiting ion conductances as compared with those in water is greater than can be accounted for by viscosity alone. The results are also in disagreement with the Bjerrum theory of ion pair formation if the mean ionic diameter, determined thermodynamically, is significant in transport processes.

A pulsed, flowing afterglow has been utilized to measure rate constants at room temperature for the following reactions involving NO: N2++NO→NO++N2,k1≈5(+1,−3)×10−10cm3/sec,N++NO→NO++N,k2=8(+1,−4)×10−10cm3/sec,O2++NO→NO++O2,k3≈8(+2,−5)×10−10cm3/sec,O++NO→NO++O,k4≤2.4×10−11cm3/sec. In addition the following related reactions have been measured: N++O2↗NO++O↘N+O2+,k5≈1(+0.1,−0.6)×10−9cm3/sec,N2++O2→O2++N2,k6≈1(+0.2,−0.6)×10−10cm3/sec,O2++N→NO++O,k7≈1.8(+0.2,−0.9)×10−10cm3/sec. Some additional information concerning the end products of N++O2 is offered.