摘要:

Methane (CH4) emissions were measured from the Nashua, New Hampshire municipal landfill using static enclosure and atmospheric tracer methods. The spatial variability of emissions was also examined using geostatistical methods. One hundred and thirty nine enclosure measurements were performed on a regular grid pattern over the emitting surface of the landfill resulting in an estimate of whole landfill emissions of 15,800 L CH4min−1. Omnidirectional variograms displayed spatial correlation among CH4fluxes below a separation distance of 7 m. Eleven tracer tests, using sulfur hexafluoride (SF6) as a tracer gas, resulted in a mean emissions estimate of 17,750 L CH4min−1. The favorable agreement between the emission estimates was further refined using the observed relationship between atmospheric pressure and CH4flux. This resulted in a pressure‐corrected tracer flux estimate of whole landfill emissions of 16,740 L CH4

ISSN:0148-0227    

DOI:10.1029/96JD00864

年代:1996

数据来源: WILEY

摘要:

Field, laboratory, and computer modeling methods were utilized to quantitatively assess the capability of aerobic microorganisms to oxidize landfill‐derived methane (CH4) in cover soils. The investigated municipal landfill, located in Nashua, New Hampshire, was operating without gas controls of any type at the time of sample collection. Soil samples from locations of CH4flux to the atmosphere were returned to the laboratory and subjected to incubation experiments to quantify the response of oxidation in these soils to temperature, soil moisture, in situ CH4mixing ratio, soil depth, and oxygen. The mathematical representations of the observed oxidation reponses were combined with measured and predicted soil characteristics in a computer model to predict the rate of CH4oxidation in the soils at the locations of the measured fluxes described byCzepiel et al.[this issue]. The estimated whole landfill oxidation rate at the time of the flux measurements in October 1994 was 20%. Local air temperature and precipitation data were then used in conjunction with an existing soil climate model to estimate an annual whole landfill oxidation rate in 1994 of 10

ISSN:0148-0227    

DOI:10.1029/96JD00222

年代:1996

数据来源: WILEY

摘要:

During a recent flight experiment, contrails were produced from fuels with normal and very high sulfur content. A color effect was observed [Schumann et al., 1996]. When observed with the Sun in the back, the low‐sulfur contrail appeared grey with weak contrast against the cloud deck underneath, whereas the high‐sulfur contrail appeared slightly brown with higher contrast. In order to give an explanation, we compute the optical properties of the soot‐containing droplets in the contrails and perform a simple radiative transfer computation. We find that the degree of activation of the soot particles is the basic parameter for the explanation of color and contrast of the contrails. It determines the size and number concentration of the droplets, which both in turn determine the optical properties of the contrail as a whole. For the visual appearance of the relatively optically thin contrails (τ ≲ 1.2) the soot volume fraction in the droplets plays only a mi

ISSN:0148-0227    

DOI:10.1029/96JD01169

年代:1996

数据来源: WILEY

摘要:

A subgrid‐scale plume model has been developed for a better treatment of dynamics of the emissions from concentrated emission sources in air quality models. The model is based on the Gaussian model description of the dispersion of NOxemissions from the power plants. Detailed inorganic and, if desired, organic atmospheric chemistry is included in the model. The plume model has been interfaced with the Urban and Regional Multiscale (URM) model and has been used to quantify the impact of subgrid‐scale plume modeling on evolution of ozone and other species in the Northeast. Various simulations were performed in the northeastern United States where there are a large number of power plants over the domain. First, a case was chosen where only one large point source was followed using the subgrid plume model to better identify the local impacts of subgrid treatment. Two simulations were performed for this case; the first included a detailed inorganic chemistry in the plume, whereas the second included only simple NO‐NO2‐O3chemistry. A second case was chosen where all point sources emitting more than 25 tons NOxper day were followed independently using the plume model to study the regionwide impact on predicted ozone. In addition to the two plume treatments used in the test above, a third was added that followed the plume chemistry using a full organic plus inorganic mechanism. In this case, the limited‐NOx, detailed inorganic and detailed inorganic plus organic chemistry, are compared with the base case where the power plant emissions were injected directly into the airshed grid. Using the subgrid‐scale plume model for large point sources had significant local impacts on predicted ozone concentrations, but regionwide impact was very small (less than 2%). Results from the simulation with the detailed organic chemistry found little difference than the detailed inorganic chemistry, though significant local differences were found between those and the simplified NOxchemistry or the calculation without the subgrid‐sc

ISSN:0148-0227    

DOI:10.1029/96JD01372

年代:1996

数据来源: WILEY

摘要:

Our high precision database of the global distribution of SF6in the troposphere [Maiss et al., 1996] is used in a two‐dimensional atmospheric transport model (2D‐HD model) to study the behavior of this new tracer in comparison to the classical global atmospheric transport tracer krypton 85. The 2D‐HD model grid has been derived from the three‐dimensional Hamburg TM2 model with the same resolution in the vertical and meridional direction and was designed to run on any standard personal computer. The same vertical convection scheme and wind fields as in the TM2 model, reduced to two dimensions, were used in the calculations. In addition, the horizontal diffusion parameter of the model was adjusted by matching the model‐estimated mean meridional85Kr distribution with observations over the Atlantic Ocean. To simulate global tropospheric SF6concentrations, an almost linearly increasing SF6source strength has been applied since 1970. The latitudinal distribution of the SF6source was assumed to be similar to the global electrical power production. Excellent agreement between SF6model results and observations is achieved with the85Kr‐tuned 2D‐HD transport model with respect to the global meridional concentration distribution, and particularly in middle to high northern latitudes. In the southern hemisphere at the German Antarctic station Neumayer, a significant seasonal cycle of SF6has been observed which is reproduced by the model, however, with a smaller amplitude. This finding may point to possible shortcomings of the model's transport scheme when simulating the seasonality of stratosphere‐troposphere exchange in high sou

ISSN:0148-0227    

DOI:10.1029/96JD01058

年代:1996

数据来源: WILEY

摘要:

We estimate the average transport time from the tropical tropopause to various regions of the northern hemisphere lower stratosphere (stratospheric age) using simultaneous mixing ratio measurements of CFC‐115 and CO2measured by the Whole Air Sampler (WAS) during Airborne Arctic Stratospheric Expedition II (AASE II). Our inferred ages are consistent with those presented in previous studies. We discuss sources of uncertainties that affect age estimates in general, as well as specific uncertainties arising from inferring ages using CO2and CFC‐115 abundances. We infer inorganic chlorine (Cly) and bromine (Bry) at various lower stratospheric locations using the WAS organic chlorine and bromine measurements in combination with modeled tropospheric halocarbon trends and with our estimated ages. Inferred Clyand Bryabundances generally increase with increasing latitude and altitude. For our analyzed locations inside the polar vortex, we estimate a maximum Clyabundance of about 2.7 parts per billion by volume (ppbv) and a maximum Bryabundance of about 13.7 parts per trillion by volume (pptv). The locations of these maxima correspond to an average N2O mixing ratio of about 100 ppbv, and to a fractional dissociation of organic chlorine and bromine of 0.85 and 0.90, respectively. Finally, we discuss the expected future limitations of using CFC‐115 to estimate stratospheric age due to the production limitations prescribed by the amendments and adjustments to the Montreal Pro

ISSN:0148-0227    

DOI:10.1029/96JD01167

年代:1996

数据来源: WILEY

摘要:

The role of the horizontal dynamical mixing on the ozone destruction by chlorine in the polar stratosphere is investigated. We use a one‐dimensional high‐resolution model to represent the microstructure of chemical species distribution on which the effective reactivity depends. The chemical model is idealized by only considering two species, ozone and chlorine (assumed to be under the active form ClO). Ozone destruction is proportional to the square of chlorine content. We compare the effects of a chaotic type of mixing, represented as a Bernoulli map over the unit interval, with purely diffusive mixing, which is used in most parameterizations of turbulence. The comparison is done for various values of the chemical reactivity constant. Owing to the nonlinearity of the chemical reaction, reactivity decreases with mixing if the chemical constant is small, while it increases with mixing for large values of the chemical constant. In any situation, large discrepancies in the ozone destruction are observed between chaotic and diffusive mixing, indicating the need for a better representation of the mixing processes in studies of stratospheric chemis

ISSN:0148-0227    

DOI:10.1029/96JD00856

年代:1996

数据来源: WILEY

摘要:

Although the new (1992) ozone profile retrieval algorithm for Umkehr measurements provides much better agreement with ozone sounding results than the old (1964) algorithm, considerable discrepancies remain with respect to ozone trends at different levels in the atmosphere. These discrepancies have been found by the comparison of long‐term trends obtained from the Umkehr measurements at Arosa and the ozone balloon soundings at Payerne (Switzerland). It is investigated here whether these obvious discrepancies can be removed by using time‐dependent a priori profiles. This procedure is successful only in the lowest part of the atmosphere, below about 19 km. To further explore this problem, synthetic Umkehr observations are calculated from the ozonesonde profiles. Trends are calculated for both the synthetic and actual Umkehr observations. The difference pattern between these Umkehr observation trends is compared with the difference in ozone profile retrieval trends from the synthetic and actual observations. The distinctive difference patterns strongly indicate an inherent disagreement between the Umkehr observations and the ozonesonde profiles. The application of corrections for stratospheric aerosol effects to the Umkehr profiles reduces, but does not eliminate, a discrepancy above 32 km. It is concluded that the discrepancies are due to the constant mixing ratio assumption used in computing the residual ozone above balloon burst level and to the fair‐weather bias of Umkehr observations (there are Umkehr observations at Arosa on fewer than 20% of the sonde observation days at Payerne). This sampling difference influences the results for the lower stratosphere. The study furthermore indicates that the ozone trends derived from Umkehr measurements for altitudes above about 32 km are robust for time‐dependent changes in the a priori profiles at lower altitudes. Based on the results of this study, we conclude with revised recommendations as to which atmospheric layers should be used for Umkehr trend

ISSN:0148-0227    

DOI:10.1029/95JD03794

年代:1996

数据来源: WILEY

摘要:

The production and loss of stratospheric OH involve relatively fast reactions that are in near‐photochemical equilibrium. In this study, we compare OH measured by our balloon‐borne far infrared limb observing spectrometer with that predicted from a simple model that uses water and ozone fields obtained from instruments on the upper atmosphere research satellite. This comparison is made for latitudes near 34°N over a full diurnal cycle for five balloon flights that span a period of over 2 years. The ratio of measurement to the photochemical model at 40 km is 0.95, with an uncertainty of 0.08 (at a 90% confidence level) due to the measurement. Comparison at other altitudes and as a function of the diurnal cycle also shows excellent agree

ISSN:0148-0227    

DOI:10.1029/96JD01168

年代:1996

数据来源: WILEY

摘要:

Monthly means of UV erythemal dose at ground level from the Robertson‐Berger (RB) sunburn meter (1976–1992) and the UV‐Biometer model 501 MED meter (1993–1994) located at Belsk (21°E, 52°N), Poland, are examined. The monthly means are calculated from all‐sky daily means of UV erythemal dose. Ancillary measurements of column ozone (by Dobson spectrophotometer), sunshine duration (by Campbell‐Stokes heliograph), and total (sun and sky) radiation (by a pyranometer) are considered to explain variations in the UV data. A multiple regression model is proposed to study trends in the UV data. The model accounts for the UV erythemal dose changes induced by total ozone, sunshine duration (surrogate for cloud cover variations), or total solar radiation (surrogate for combined cloud cover and atmospheric turbidity impact on the UV radiation), trends due to instrument drift, step changes in the data, and serial correlations. A strong relationship between monthly all‐sky UV erythemal dose changes and total ozone (and total solar radiation) is found. Calculations show that an erythemal radiative amplification factor (RAF) due to ozone under all skies is close to its clear‐sky value (about 1). However, the model gives evidence that the RAF due to ozone is smaller for cloudier (and/or more turbid) atmospheres than long‐term reference. Total solar radiation change of 1% is associated with a change of 0.7% in the UV erythemal dose. Modeled trends in the Belsk's UV data, inferred from the model using ozone and total solar radiation as the UV forcing factors, are 2.3% ± 0.4% (1σ) per decade in the period 1976–1994. The large increase in the UV erythemal dose, of the order of 4% per decade due to ozone depletion (−3.2% per decade), is partially compensated by a decreasing tendency (−2.8% per decade) in total solar radiation. The model estimates the trend in the UV data of the order of 0.1% per decade (not statistically significant) due to superposition of the instrument drift and long‐term effects related to other UV influencing factors (no

ISSN:0148-0227    

DOI:10.1029/96JD00217

年代:1996

数据来源: WILEY