摘要:

An efficient three‐dimensional spectral model is used to investigate the tropospheric and stratospheric circulation, chemistry, and photochemistry of the long‐lived atmospheric species CFCl3, CF2Cl2, CH3CCl3, CCl4, and N2O. The model uses precalculated three‐dimensional spectral fields of vorticity, vertical velocity, temperature, and ozone concentration and current estimates of the magnitudes and distributions of industrial and natural sources of the various species. Explicit calculations of instantaneous photodissociation rates for each species are carried out, and reactions with atmospheric OH and O(1D) and dissolution in the ocean are also included in the model where relevant. Available measurements of the horizontal, vertical, and temporal distribution of the modeled atmospheric species generally compare favorably with our calculations. However, there are some disagreements, particularly between the observed and calculated surface distributions of CH3CCl3and the vertical distributions of CCl4, which are critically discussed. Assuming that their destruction is dominated by photodissociation and reaction with O(1D), the calculated present‐day global atmospheric lifetimes of CFCl3, CF2Cl2, CCl4, and N2O are 73, 210, 48, and 182 years, respectively. Decreasing the O2absorption cross sections in the Schumann‐Runge continuum (2000–2200 Å) by 40% results in a decrease of the CFCl3lifetime to 44 years. The calculated atmospheric lifetime of CH3CCl3due to photodissociation and reaction with OH and O(1D) is 12 years, but this result depends on the prescribed seasonally dependent zonally invariant OH distribution used

ISSN:0148-0227    

DOI:10.1029/JD091iD03p03985

年代:1986

数据来源: WILEY

摘要:

The present paper describes a probable budget for acetonitrile and discusses the release of this gas through biomass burning and human activity. The different loss processes in the middle atmosphere are mainly due to the reaction with hydroxyl radicals and atomic oxygen. It is shown that the destruction of CH3CN by scavenging due to precipitation is probably not more efficient than the direct gas phase reactions. Losses due to ion chemistry are very difficult to estimate at present but are probably of secondary importance, except locally, where formation of multi‐ion complexes is significant. A one‐dimensional calculation shows that the vertical profiles of CH3CN, deduced from ion mass spectrometry data, can be reproduced satisfactorily if an annual global emission ranging from 1.5 × 1010g to 5 × 1011g is adopted, depending on the values of the reaction rate constants and eddy diffusion coefficient. The global atmospheric lifetime of CH3CN is estimated to be about 0.5 to 1.4 years. Finally, the calculated acetonitrile profiles are introduced in an ion model to calculate the abundances of the major positive stratospheric ions. The results are consistent with present observa

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04003

年代:1986

数据来源: WILEY

摘要:

A set of results about the positive ion composition of the stratosphere, consisting of some recently obtained as well as some previously reported data, is presented and analyzed. It is compared with model calculations described in a companion paper. A review of the abundances of proton hydrates and nonproton hydrates shows that the latter most probably result from the presence of acetonitrile (CH3CN) in the atmosphere. The vertical mixing ratio profile of this gas deduced from positive ion composition measurements is in good agreement with a model based on the assumption that acetonitrile is released at the earth's surface and subsequently destroyed in the atmosphere by chemical reactions (mainly with hydroxyl radicals). The results of an analysis of the possible isotopic mass peaks of mass 96 (H+(CH3)(H2O)3) is not in contradiction with this conclusion.

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04017

年代:1986

数据来源: WILEY

摘要:

The behavior of ions in the D and E regions is shown to exhibit large latitudinal and seasonal variations. These are due to the meridional transport of neutral species (NO, O, H2O), which interact with ion chemistry, to temperature variations, and to differences in the solar input and in high‐energy particle precipitation. This paper presents a two‐dimensional model of the ion composition in the D and E regions, which shows that the lower ionosphere is clearly dynamically controlled. The importance of the latitudinal and seasonal dependence of the nitric oxide concentration is pointed out. The model also shows that noticeable changes in the meridional distribution of ions should be attributed to the variability in the solar irradiance and in the strength of particle precipitation in relation to the 11‐year solar

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04025

年代:1986

数据来源: WILEY

摘要:

Sensitivity studies related to the effects of line cutoff, spectral resolution, and temperature and pressure interpolations in radiative transfer have been performed so that a data set of absorption coefficients for water vapor, CO2, and O3may be created efficiently. Results show that computations of absorption coefficients are affected only slightly by cutting a line off at a wave number 190 times the Lorentz half width from the center, or, equivalently, cutting off 0.33% of the line intensity from the wings. To achieve a relative cooling rate error smaller than 2%, it is sufficient to precompute the absorption coefficient at three temperatures (210, 250, and 290 K) and 19 pressures with Δ(log10p) = 0.2. The absorption coefficient at other conditions can be interpolated linearly with pressure and exponentially with a quadratic in temperature. For the spectral resolution the absorption coefficients can be adequately computed at 0.01, 0.002, 0.005, and 0.025 cm−1intervals in the thermal water vapor, the CO2and O3bands, and the solar water vapor bands, respectively, which limits the error to only a few percent in the cooling and heating rates. Using the precomputed absorption coefficients, repeated monochromatic calculations of atmospheric heating/cooling rates for radiation model developments and for comparison with less detailed calculations are no longer difficu

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04047

年代:1986

数据来源: WILEY

摘要:

Infrared profiles and strength measurements have been obtained at a spectral resolution of 1.6 cm−1for the absorption bands of CF2Cl2(fluorocarbon 12) from 800 to 1200 cm−1at 296 and 200 K. A slight temperature dependence of the band strength seems to be observed for the ν3+ ν9combination band and for the (ν3+ ν9) ν6and (ν1) ν8band systems. The low‐temperature band profiles become narrower and the Q branches stronger than they are at room temperature. In particular, for the ν6band, which is important for atmospheric sensing, the absorption coefficient shows an enhancement of 30% between 296 and 200 K at the peaks of the Q branch. These room temperature and low‐temperature data may be useful for greenhou

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04056

年代:1986

数据来源: WILEY

摘要:

An experiment is described which investigated the relationship between marine aerosol particles and satellite‐detected radiance. The experiment resulted in a near‐simultaneous set of visible and near‐infrared satellite images and aircraft aerosol particle and state variable measurements. These data demonstrated that satellite‐detected radiance at red‐visible and near‐infrared wavelengths is positively correlated with aerosol optical depth. Further, the data show that relative humidity changes account for variations in aerosol particle size which in turn lead to variations in satellite‐detected upwelling radiance. Therefore it appears possible to use satellite imagery to investigate variations of marine boundary layer aerosol particles and rela

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04063

年代:1986

数据来源: WILEY

摘要:

Perturbations to the visible radiation by the El Chichón aerosol layers in the stratosphere have been observed using in situ time‐lapse photography of the earth horizon from a balloon gondola. The measurements were performed on May 18, 1982, from Laredo, Texas (27.3°N, 99.5°W), during a sounding performed with optical particle counters that measured aerosol size distributions in six different size ranges. The results of the microdensitometry of the photographic film agree well with the corresponding quantities determined from the optical counter data by applying Mie theory for spherical particles. The optical thickness of the stratosphere from a height of about 18.8 km to the top of the atmosphere, averaged over visible wavelengths, was found to be on the order of 0.18. At a height close to the maximum reached by the balloon (27 km) the residual optical thickness due to aerosol particles was found to be on the order of 0.7 × 10−3. The isodensity contours in the stratosphere described the main pattern of the intensity distributions of multiply scattered sunlight in the vicinity of the earth horizon. This pattern, observed at relatively high solar elevation, indicated that both the upward and downward intensities, besides depending on the particle characteristics and on their vertical distribution, also depend on variations of the general distribution in the underlying cloud c

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04073

年代:1986

数据来源: WILEY

摘要:

Nightly dew samples were collected on Allegheny Mountain in southwest Pennsylvania in August 1983. The dew was found to be acidic, with meanpH∼4.0. Free H+comprised>80% of the total acidity, and the composition approximated an H2SO4/HNO3mixture with average SO42−/NO3−mol ratio ∼1.3. The chemistry of the dew resembled that of rain at Allegheny, though the dew was generally more dilute. Atmospheric HNO3(g) was chiefly responsible for the dew NO3−. SO2was the source of ∼80% of the dew SO42−. The allocation of dew H+among atmospheric precursors was HNO3∼30%, SO2≥ 60%, aerosol H+≤ 10%. The most acidic dews were associated with wind from the west. Average deposition velocities (stated in centimeters per second) to dew were HNO3, 0.24; NO2,<0.02; SO2, ∼0.04; aerosol SO42−, ∼0.02; aerosol NH4+, 0.024; and aerosol species, 0.02–1. Comparison of the HNO3deposition velocity with ten‐fold higher summer daytime values reveals a pronounced diurnal variation. The 0.24 cm/s value for HNO3may represent a maximum for any gas or submicron aerosol species whenever the atmosphere is strongly stable. Not all of the S(IV) in dew had been converted to SO42−by morning; thus the rate of oxidation must have been on a time scale of hours at nighttime ambient temperatures. In contrast, S(IV) in rain and fog samples was not evident. Deposition fluxes and cumulative deposition totals involving dew, rain, and settled fog water were compared. Rain proved by far the most important for deposition of all

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04083

年代:1986

数据来源: WILEY

摘要:

Acetylene (C2H2) is an important hydrocarbon species which is present in trace quantities in the troposphere and lower stratosphere. Potential loss processes for atmospheric C2H2include reactions with OH, Cl, O, and Br as well as photodissociation. Rate data for the first three reactions are available in the literature, but the latter reaction has not been the subject of any previous studies. We have measured the rate constant for the reaction at four temperatures over the range 210–393 K and at pressures between 15 and 100 torr Ar. The technique employed was flash photolysis combined with time‐resolved detection of atomic bromine via Br resonance radiation. The reaction was shown to be independent of total pressure (Ar) and temperature over the indicated ranges. The average of all experiments gives the valuek= (4.0 ± 0.8) × 10−15cm3s−1, where the error is 2 standard deviations. The result is compared with previous data from our laboratory for reactions of H, Cl, OH, and NH2with C2H2. Loss rates for atmospheric C2H2have been calculated as a function of altitude for reactions with OH, Cl,

ISSN:0148-0227    

DOI:10.1029/JD091iD03p04097

年代:1986

数据来源: WILEY