摘要:

Kumar and Monteith's (1981) model for the remote sensing of crop growth has been used to estimate continental net primary productivity (NPP) as well as its seasonal and spatial variations. The model assumes a decomposition of NPP into independent parameters such as incident solar radiation (S0), radiation absorption efficiency by canopies (ƒ), and conversion efficiency of absorbed radiation into organic dry matter (e). The precision on some of the input parameters has been improved, compared to previous uses of this model at a global scale: remote sensing data used to derive ƒ have been calibrated, corrected of some atmospheric effects, and filtered;ehas been considered as biome‐dependent and derived from literature data. The resulting global NPP (approximatively 60 GtCper year) is within the range of values given in the literature. However, mean NPP estimates per biome do not agree with the literature (in particular, the estimation for tropical rain forests NPP is much lower and for cultivations much higher than field estimates), which results in zonal and seasonal variations of continental NPP giving more weight to the temperate northern hemisphere than to the equatorial z

ISSN:0148-0227    

DOI:10.1029/93JD03221

年代:1994

数据来源: WILEY

摘要:

This paper discusses potentially potent new atmospheric sources and sinks of nitrous oxide (N2O), which is an important species by virtue of its being the dominant source of odd nitrogen (NOx) in the stratosphere and also a greenhouse gas. It is suggested that some of the excited nascent ozone from O, O2recombination may form N2O via its reaction with N2. It is also conceivable that other metastable states of O3accessible by optical pumping from the ground state might also be a potential source of N2O in the natural atmosphere. Additional atmospheric sources of N2O include reactions of excited NO3(Ā2E'), NO2(Ā2B1,2B2) and OH(A) with N2, and of N2(A3∑) with O2. Highly vibrationally excited O2†(ν>12) could be an important new sink of N2O in the stratosphere. This new N2O sink might also be a new NOxsource in the stratosphere, depending on what fraction of the reactions of O2†(high ν) with N2O produces NO and NO2. At the lower altitudes, where O2†(ν>12) density would become too small to matter, reactions of NO2with N2O might be a potential N2O sink. The new sources need not conflict with the observed vertical profile of N2O, because: (1) the new O2†(high ν) sink could ensure the observed decrease of N2O mixing ratios in the upper atmosphere, and (2) the sources in the troposphere would be indistinguishable from the surface sources due to strong mixing and N2O long photochemical lifetime in this region. While some of these new sources and sinks are based on direct experimental data, others are based on new theoretical analysis of relevant experiments. Even so it is encouraging that the new sources could help us in removing the source deficit in the current N2O budget. So long as a prospect exists that NOxmight be produced in reactions of O2†(high ν) with N2O, it is constructive to speculate that the “new” N2O chemistry might have an effects on our current perceptions of NOxcatalyzed stratospheric ozone depletion. If an important new source of NOxhas been missed then an equally potent sink of NOxhas also been missed, and it is possible that the inclusion of the latter into the current assessment models might affect our current perception of the atmospheric environmental effects of man

ISSN:0148-0227    

DOI:10.1029/93JD01911

年代:1994

数据来源: WILEY

摘要:

Distributions of organic hydroperoxides (ROOH), hydrogen peroxide (H2O2), other trace gases, and meteorological parameters were measured from an aircraft over the northeastern United States in August and September 1988. The data set consists of 13 flight missions on 14 days with 177 vertical profiles at altitudes between 100 and 3500 m. The mixing ratio of ROOH varied from below the detection limit of 0.1 parts per billion by volume (ppbv) up to 3.14 ppbv, with generally higher average values in the free troposphere (FT) than in the planetary boundary layer (PBL). The average ratio of ROOH to the H2O2mixing ratios was about 50%. The ROOH mixing ratio was strongly correlated with H2O2, indicating similar production and loss mechanisms for ROOH and H2O2. The observed lower variability of the ROOH mixing ratios in comparison with that of H2O2is probably due to a longer atmospheric residence time of ROOH. Combined with the lower ROOH mixing ratios, this longer residence time indicates that the production and loss processes of ROOH are slower than those of H2O2. An ROOH formation rate of 56±8 parts per trillion by volume ROOH/h% H2O was determined from the difference of ROOH mixing ratios between afternoon and morning flights on September 16. This formation rate is about twice as large as the rate predicted by a simple photochemical box model with methane chemistry, indicating that organic hydroperoxides other than CH3OOH may also be formed. The estimations of HO2and RO2concentrations in the free troposphere from H2O2, ROOH, and O3formation rates were consistent

ISSN:0148-0227    

DOI:10.1029/93JD03222

年代:1994

数据来源: WILEY

摘要:

A technique is developed to determine the amount of ozone and other products, such as nitric acid and peroxyacetylnitrate (PAN), generated by the individual organic components of a complex atmospheric organic/NOxmixture. The technique is applied to the SAPRC 90 photochemical mechanism to study the individual contributions of carbonyls, aromatics, alkanes, alkenes, and carbon monoxide to ozone, nitric acid, PAN, and free radical production at varying organic to NOxratios typical of atmospheric conditions.

ISSN:0148-0227    

DOI:10.1029/93JD03400

年代:1994

数据来源: WILEY

摘要:

The globally averaged net downward annual fluxes of reactive nitrogen (NOy) and O3from the stratosphere are estimated using observed correlations of N2O with NOyand O3. The linearity of the observed correlations in the lower stratosphere allows the downward fluxes of NOyand O3to be related to the upward flux of N2O. The upward flux N2O can be calculated from a mass balance and stratospheric photochemistry. In this way, the complicated photochemistry and transport of NOyand O3can be bounded by a much simpler calculation involving N2O. The estimated NOynet flux of 0.45 Tg (N) yr−1(range 0.23–0.73) is slightly less than previous estimates, but within the range of uncertainty. Precipitation of NOyfrom the Antarctic winter stratosphere may be a significant fraction of the annual global flux out of the lower stratosphere. The global budget for stratospheric NOyshows that an N2O lifetime greater than 160 years is inconsistent with extensive mass flow through the Antarctic winter vortex. The estimated O3flux of 3.5×1010molecules cm−2s−1(range 1.5–6.8) agrees well with previous estimates using completely independent

ISSN:0148-0227    

DOI:10.1029/93JD03558

年代:1994

数据来源: WILEY

摘要:

Five years of measurements of PAN and O3at a rural site in eastern Canada are reported. The measurements were made year‐round and only interrupted due to instrumental failures. The data are analyzed by advanced statistical methods to determine temporal trends, both for PAN and O3individually and with respect to their covariance. Since the data are clearly lognormally distributed, this analysis is performed on the logarithmic transform of the data. PAN shows a statistically significant long‐term trend but O3does not. It is argued that this trend may be the result of a change in the overall hydrocarbon composition of the air, since no trend in NOxemissions appears to have taken place over the same time period in eastern North America. Strong seasonal trends in PAN and O3are found that are similar in overall pattern but differ in detail. The similarity in shape leads to a significant covariance between PAN and O3. The differences in detail can be interpreted as indicative of well‐known atmospheric processes, such as the impact of stratospheric folding occurrences leading to additional O3with respect to PAN in the spring and reduced photochemical activity and lower temperatures in the winter months, which results in a decoupling of the covariance between O3and PAN. On a day‐to‐day basis the covariance between PAN and O3is strong due to the fact that it is essentially determined by meteorological variation. Episodes of alternatively clean and polluted air are observed, each lasting circa 3 days. Seasonal trends in the diurnal patterns are also evident for both compounds: diurnal variation in the summer is considerable but becomes negligible in the winter. PAN displays a larger diurnal variation than O3in the summer, which can be explained by their relative dry deposition v

ISSN:0148-0227    

DOI:10.1029/93JD02716

年代:1994

数据来源: WILEY

摘要:

Aircraft measurements of atmospheric aerosol particles were performed in the free troposphere up to 5.0 km altitude over the North Pacific Ocean in August 1983 and 1984. Particles were analyzed for a single‐particle base with the regent thin‐film technique in conjunction with a transmission electron microscope. The calcium thin‐film method was used for the specific determination of the molecular form of sulfate particles. Nitrate and sulfate in particles was identified by the nitron and barium chloride thin‐film method, respectively. Ammonium was examined by the thin‐film method of sodium tetraphenyl boron. Collected aerosols were related to the origin of air parcels. Sulfuric acid particles in submicron size range formed by the photochemical oxidation of sulfur‐bearing gases and subsequent gas‐to‐particle conversion are the basic aerosols in the unpolluted free marine troposphere. They contain a small amount of NH4+and more acidic than NH4HSO4. The chemical composition of the predominant aerosol changed drastically according to the origin of air parcels. Sulfuric acid aerosols were predominant in the air parcels originating from the midlatitude maritime atmosphere. On the other hand, for air parcels that have passed over the continent within several days, sulfate aerosols neutralized fully by ammonia are predominant. The extension of the continental air mass supplies ammoniated sulfate aerosols to remote marine atmosphere about 1200 km from land. Mineral dust particles are transported from Asian continent over the northwestern Pacific Ocean via the free troposphere. Nitrate was heterogeneously formed on the mineral dust particles and they were present in the air parcels passed over mainland of Japan, whereas few nitrate particles were found in the midlatitude marine atmosphere. Ammoniated sulfate particles, nitrate‐containing particles, and mineral dust particles are the tracers of the con

ISSN:0148-0227    

DOI:10.1029/93JD03191

年代:1994

数据来源: WILEY

摘要:

We constructed an atmospheric sampling system for Hg vapor that utilizes a single vacuum pump connected via a manifold to six separate mass flow controllers (MFC). The manifold system reduces the size and power requirements for collection of replicate samples, is ideally suited for use on meteorological towers, and achieves the precise control of air‐sampling volumes required for computing air/surface exchange rates from concentration gradients of Hg vapor. In testing our air sampling systems, we found consistent calibration errors between the manufacturer's calibrations and a standard bubble flow meter. Errors as high as 30% decreased systematically with increasing flow rate to values of 3–5% at near‐maximum flow. The relative error patterns established between adjacent MFC units in each system were found to be relatively stable over time. Using gold‐coated sand amalgamation traps for Hg vapor and the flow correction factors computed from our calibrations, we routinely achieve precision for replicate measurements of Hg vapor in background air of 0.5–2% (expressed as relative standard errors of mean concentrations of 1.5–3.5 ng/m3). Application of the flow correction factors measurably decreases the level of bias between mean concentrations of Hg vapor measured with adjacent sampling systems and is necessary to reduce uncertainty associated with quantifying gradients in atmospheric con

ISSN:0148-0227    

DOI:10.1029/93JD02657

年代:1994

数据来源: WILEY

摘要:

A multiscale air quality model has been developed to follow accurately and efficiently the long‐range transport of pollutants emitted from urban areas. The model employs a two‐dimensional finite element scheme to follow the horizontal transport. The multiscale capability is obtained by using local finite element refinements. The model is applied to a 3‐day intensive measuring period (August 27–29, 1987) over southern California. Uniform and nonuniform grid systems are employed in the simulations. Uniform grid systems used resolutions of 5×5 km2, 10×10 km2, and 20×20 km2, horizontally. Two nonuniform grid systems are used. The first combines the 5×5 km2grid over urban Los Angeles with the 10×10 km2grid over the rest of the domain, while the second uses the 5×5 km2grid followed by the 10×10 km2grid and 20×20 km2grid over the ocean and sparsely populated areas. Uniform coarsening of the grid impacted the urban areas by diluting NOxemissions, leading to higher levels of urban ozone predictions. The impact on regional areas was complex. The ozone being transported downwind was not followed as accurately as on the fine grid and the regional levels usually decreased. On the other hand, the artificial dilution of NOxemissions had the adverse effect of increasing regional ozone levels. Therefore grid coarsening sometimes leads to what appears to be satisfactory levels of regional ozone for the wrong reason. By using fine grids over the source areas, more satisfactory predictions of both urban and regional ozone levels were obtained. This is also computationally more efficient than using uniform fine grids over th

ISSN:0148-0227    

DOI:10.1029/93JD03197

年代:1994

数据来源: WILEY

摘要:

The lower boundary of a spectral mechanistic model is prescribed with 100 hPa geopotentials, and its performance during a November 1989 through March 1990 integration is compared with National Meteorological Center observations. Although the stratopause temperatures quickly become biased near the pole in both hemispheres, the model develops a residual mean circulation which shows significant descent over the winter pole and ascent in the tropics and over the summer pole at pressures less than 10 hPa. The daily correspondence of observed to modeled features in the upper stratosphere and mesosphere degrades after one month. However, the long‐term variability qualitatively follows the observations. The results of off‐line transport experiments are also described. A passive tracer is instantaneously injected into the flow over the poles and evolves in a manner which is consistent with the residual mean circulation. It demonstrates a significant cross‐equatorial flux in the mesosphere near solstice, and air which originates in the southern hemisphere polar mesosphere can be found descending deep into the northern polar stratosphere at the end of the integration. Nitrous oxide is also transported, and its ability to act as a dynamical tracer is evaluated by comparison to the evolution of the passive t

ISSN:0148-0227    

DOI:10.1029/93JD03578

年代:1994

数据来源: WILEY