摘要:

Ozone column amounts obtained by the total ozone mapping spectrometer (TOMS) in the southern polar region are analyzed during late austral winter and spring (days 240–300) for 1980–1991 using area‐mapping techniques and area‐weighted vortex averages. The vortex here is defined using the −50 PVU (1 PVU = 1.0 × 10−6K kg−1m2s−1) contour on the 500 K isentropic surface. The principal results are: (1) there is a distinct change after 1985 in the vortex‐averaged column ozone depletion rate during September and October, the period of maximum ozone loss, and (2) the vortex‐averaged column ozone in late August (day 240) has dropped by 70 Dobson units (DU) in a decade due to the loss in the dark and the dilution effect. The mean ozone depletion rate in the vortex between day 240 and the day of minimum vortex‐averaged ozone is about 1 DU d−1at the beginning of the decade, increasing to about 1.8 DU d−1by 1985, and then apparently saturating thereafter. The vortex‐average column ozone during September and October has declined at the rate of 11.3 DU yr−1(3.8%) from 1980 to 1987 (90 DU over 8 years) and at a smaller rate of 2 DU yr−1(0.9%) from 1987 to 1991 (10 DU over 5 years, excluding the anomalous year 1988). We interpret the year‐to‐year trend in the ozone depletion rate during the earlier part of the decade as due to the rise of anthropogenic chlorine in the atmosphere. The slower trend at the end of the decade indicates saturation of ozone depletion in the vortex interior, in that chlorine amounts in the mid‐1980s were already sufficiently high to deplete most of the ozone in air within the isolated regions of the lower‐stratospheric polar vortex. In subsequent years, increases in stratospheric chlorine may have enhanced wintertime chemical loss of ozone in the south polar vortex even before

ISSN:0148-0227    

DOI:10.1029/96JD00063

年代:1996

数据来源: WILEY

摘要:

Water vapor in the upper troposphere has a significant impact on the climate system. Difficulties in making accurate global measurements have led to uncertainty in understanding water vapor's coupling to the hydrologic cycle in the lower troposphere and its role in radiative energy balance. The Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite is able to retrieve water vapor concentration in the upper troposphere with good sensitivity and nearly global coverage. An analysis of these preliminary retrievals based on 3 years of observations shows the water vapor distribution to be similar to that measured by other techniques and to model results. The primary MLS water vapor measurements were made in the stratosphere, where this species acts as a conserved tracer under certain conditions. As is the case for the upper troposphere, most of the stratospheric discussion focuses on the time evolution of the zonal mean and zonally varying water vapor. Stratospheric results span a 19‐month period and tropospheric results a 36‐month period, both beginning in October of 1991. Comparisons with stratospheric model calculations show general agreement, with some differences in the amplitude and phase of long‐term variations. At certain times and places, the evolution of water vapor distributions in the lower stratosphere suggests the presence of meridional tran

ISSN:0148-0227    

DOI:10.1029/95JD03653

年代:1996

数据来源: WILEY

摘要:

Within the past year, two papers have been published which present updated profile ozone trends from the recently revised ground‐based Umkehr record [Miller et al., 1995] and the combined Nimbus 7 solar backscattered ultraviolet (SBUV) and NOAA 11 SBUV 2 satellite data record [Hollandsworth et al., 1995]. In this paper we compare the ozone trends and responses to the 11‐year solar cycle (represented by the F10.7 cm radio flux) derived from these two data sets for the period June 1977 to June 1991 (November 1978 to June 1991 for the satellite data). We consider data at northern midlatitudes (30°–50°N) at altitudes between 25 and 45 km derived from these two data sets. In particular, we investigate the effects of spatial sampling differences between the data sets on the derived signals. The trends derived from the two independent data sets are nearly identical at all levels except 35 km, where the Umkehr data indicate a somewhat more negative trend. The trend is approximately zero near 25 km but becomes more negative in the upper stratosphere, reaching nearly −7% per decade in the 40–45 km region. The upper stratospheric decreases are consistent with model results and are associated with the gas‐phase chemical effect of chlorofluorocarbons CFC's and other ozone‐destroying chemicals [World Meteorological Organization, 1995]. The ozone correlations in the two data sets with the F10.7 cm solar flux are similar, with near‐zero solar‐induced ozone variations in the 25–30 km region and statistically significant in‐phase variations at higher altitudes. Estimates of the solar cycle in the ozone time series at 40–45 km from a regression model indicate variations of about 4.5% from solar cycle maximum to minimum. Analysis of the satellite overpass data at the Umkehr station locations shows that the average of the data from the 11 Umkehr stations is a good approximation fo

ISSN:0148-0227    

DOI:10.1029/96JD00229

年代:1996

数据来源: WILEY

摘要:

Ozone concentrations obtained with the technique of solar occultation from the Solar Maximum Mission (SMM)/Ultraviolet Spectrometer and Polarimeter (UVSP) and Earth Radiation Budget Satellite (ERBS)/Stratospheric Aerosol and Gas Experiment II (SAGE II) satellite‐borne instruments are compared in the latitude regions of 5° to 15° north and south for the lower mesosphere (53–68 km) for 1985–1989, the period when both instruments were operational. The estimated trends are all positive signifying increasing ozone. At 55 km in the northern region they are 0.60(±0.47)%/year for SAGE II and 2.56(±0.61)%/year for SMM/UVSP during the 1985–1989 period. At 60 km the trends are 0.38(±1.06)%/year for SAGE II and 1.63(±0.56)%/year for SMM/UVSP. Corresponding numbers at 55 km in the southern region are 1.23(±0.82)%/year for SAGE II and 2.38(±0.62)%/year for SMM/UVSP. At 60 km the trends are 1.34(±1.01)%/year for SAGE II and 2.14(±0.56)%/year for SMM/UVSP. At 65 km, where only SMM/UVSP data are used, estimated trends are 0.92(±0.74)%/year in the northern region and 2.59(±0.92)%/year in the southern region. Theory predicts that the increase in solar radiation between 1985 and 1989 should enhance ozone by 1.5%. If temperature feedback is included in the model, then ozone is predicted to decrease. These figures are smaller than the observed 5 to 10% increase. A long‐term temperature decrease will also contribute

ISSN:0148-0227    

DOI:10.1029/95JD02705

年代:1996

数据来源: WILEY

摘要:

We report simultaneous measurements of the stratospheric concentration profiles of OH, HO2, H2O2, H2O, O3, HNO3, NO2, N2O, HCl, HOCl, and ClO during a midlatitude balloon flight in 1989. Measurements were made over almost an entire diurnal cycle by the Smithsonian Astrophysical Observatory Far‐Infrared Spectrometer (FIRS‐2) and the Jet Propulsion Laboratory Balloon Microwave Limb Sounder (BMLS). We analyze these measurements using a photochemical model constrained by observations of long‐lived gases. Measured HOxspecies (OH and HO2) and H2O2show fair agreement with theory throughout the diurnal cycle. Measurements of HNO3are higher than theory near the concentration peak, while the levels of NO2are consistent with the model at most altitudes. Measurements of ClO and HOCl are less than predicted concentrations, suggesting a source of HCl in addition to the reaction of Cl with CH4. Possibilities for such a source include a minor HCl + O2product channel for the reaction of ClO with OH and a minor HCl + O3channel for the reaction of ClO wit

ISSN:0148-0227    

DOI:10.1029/96JD00064

年代:1996

数据来源: WILEY

摘要:

Volume mixing ratio profiles of fluorine source gases (CF2Cl2, CFCl3, CF2ClCFCl2, CHF2Cl, CF4, and SF6) and reservoir gases (COF2and HF) have been derived from a series of high‐resolution infrared solar spectra recorded by the Jet Propulsion Laboratory MkIV interferometer during a September 1993 balloon flight from Fort Sumner, New Mexico (34°N, 104°W). The total fluorine budget over the 5‐ to 38‐km altitude range has been evaluated by adding these individual measured profiles to modeled predictions for the unmeasured gas COFCl (considered to be at most 6% of the total fluorine budget). The results indicate a steady decrease of total fluorine, with increasing altitude, from a tropospheric value of about 1.82 parts per billion by volume (ppbv) to 1.48 ppbv at 38 km. The latter value, made up entirely of the reservoir species, is commensurate with tropospheric concentrations of fluorine reported in the late 1980s and with time‐dependent two‐dimensional model predictions (1.45 ppbv). Therefore the “age” of the stratospheric air mass estimated from the MkIV fluorine budget is 4–5 years, in agreement with model simulations (≈6 years) and recent

ISSN:0148-0227    

DOI:10.1029/96JD00227

年代:1996

数据来源: WILEY

摘要:

The absorption cross sections for HCFC‐123 (CF3CHCl2) and HCFC‐142b (CH3CF2Cl) have been measured in the gas and liquid phases over the temperature range of about 220–330 K. The liquid phase results were converted into effective gas phase cross sections using a wavelength shift procedure, thereby extending the gas phase cross sections to longer wavelengths. The results are compared with other available data and lend increased confidence in atmospheric lifetime calculations for these important industrial alternatives to the fully halogenated chlorofluoroca

ISSN:0148-0227    

DOI:10.1029/96JD00226

年代:1996

数据来源: WILEY

摘要:

Uptake of BrONO2onto submicron sulfuric acid aerosol was studied in a cylindrical flow reactor coupled to a chemical ionization mass spectrometer. On aerosol particles of ∼0.1 μm radius, the reaction of BrONO2with H2O to produce HOBr and HNO3is very efficient, with the reaction probability γ ≈ 0.8 for H2SO4‐content ≤ 70 wt%. The equilibrium constant for the gas phase process, BrONO2+ H2O ⇄ HOBr + HNO3, was measured and the heats of formation of the bromine compounds were deduced. The conversion of HOBr back into BrONO2via reaction with HNO3can be neglected in the stratosphere. The heterogeneous hydrolysis of BrONO2, followed by photolysis of the HOBr product, is a major source of HOxin the lower stratosphere. The role of bromine as an activator of chlorine is als

ISSN:0148-0227    

DOI:10.1029/96JD00347

年代:1996

数据来源: WILEY

摘要:

We present data to show that at least some of the observed polar stratospheric cloud (PSC) particles sampled by the ER 2 on January 20, 1989, during the Airborne Arctic Stratospheric Expedition (AASE 1) were composed of a water‐rich HNO3/H2O solid phase. The PSC water content derived from the ER 2 data on this day is larger than that of nitric acid trihydrate (NAT), nitric acid dihydrate (NAD) or an aqueous ternary solution of H2SO4/HNO3/H2O. Here, we suggest that these particles were composed of a water‐rich metastable HNO3/H2O solid phase and refer to such clouds as Type 1c PSCs, which are different from Type 1a (crystalline NAT or NAD particles) or Type 1b (aqueous ternary solution droplets) PSCs. Type 1c PSCs could either be crystalline (a higher hydrate of HNO3and H2O) or amorphous, and the data analysis presented here cannot distinguish between these different solid phases. The observed PSC on this day could have been a mixture of water‐rich HNO3‐containing solid particles with liquid ternary droplets and/or NAT (NAD) aerosols. However, a mixture of cloud particles composed of ternary solution droplets and NAT (NAD) aerosols is inconsistent with the data. A surface adsorption/reaction process occurring on frozen sulfate surfaces is suggested as a formation mechanism for Type 1c PSCs in the stratosphere. A possible mechanism for the formation of large HNO3‐containing aerosols (NAT or NAD) starting with Type 1c PSCs is

ISSN:0148-0227    

DOI:10.1029/96JD00062

年代:1996

数据来源: WILEY

摘要:

A numerical method to solve chemical equilibrium equations and a method of coupling the equilibrium calculations to nonequilibrium growth and evaporation are discussed. The equilibrium program solves any number of equations for gas, aqueous, ionic, and solid equilibrium concentrations over large spatial grids and particle size grids. It also simultaneously computes electrolyte mean mixed activity coefficients and aerosol liquid water content. Mean mixed activity coefficient calculations require mean binary activity coefficient information. Temperature‐dependent mean binary activity coefficient polynomials were constructed using mean binary activity coefficient data at 298 K, apparent molal enthalpy data, and apparent molal heat capacity data. The equilibrium solver is mole and charge conserving, requires iteration, but always converges. Solutions to the equilibrium equations are used for two purposes. The first is to estimate surface vapor pressures over particles containing a solution and/or a solid phase. Such vapor pressures are then applied in gas‐aerosol transfer equations. The second is to estimate intraparticle composition and size immediately after gas‐aerosol tra

ISSN:0148-0227    

DOI:10.1029/96JD00348

年代:1996

数据来源: WILEY