摘要:

The nonlinear coupling of atmospheric trace constituents can, at least in principle, cause concentrations to oscillate with time. This is demonstrated for a simplified scheme encompassing only the tropospheric gas phase chemistry of CO, O3, HOx, and NOx. Oscillating concentrations with a common period of about 33 days were found for all chemical compounds under the forcing by time independent sources for CO and NO. Linear stability analysis shows that the periodic solution is locally stable. The periodicity is found for a large domain of NO and CO source strengths. The presence of methane destroys the oscillation. This finding limits the applicability for problems of the real atmosphere. The source strengths of NO and CO necessary to produce undamped oscillations in the model are much larger than the corresponding globally averaged source strengths. In the polluted boundary layer, however, the source strengths of NO and CO could very well be encountered. Evaluation of the Lyapunov exponents and of the dependence on the initial conditions indicates that the periodic solution is attained independent of the initial conditions, usually within a few days. Thus even if the meteorological and source strength conditions do not persist for the time of a whole period, parts of it may still be observable.

ISSN:0148-0227    

DOI:10.1029/96JD00339

年代:1996

数据来源: WILEY

摘要:

In this study we compare the results of model simulations of CFC‐11 in the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM2) with two different published emission distributions. We find that for predicted CFC‐11 concentrations at the Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment (ALE/GAGE) observation sites there is very little difference resulting from the two distributions. However, the difference is apparent in major transport events such as pollution events. This has important implications for assessment of regional emissions from a sparse network like ALE/GAGE using inverse methods. It also implies that differences between modeled and observed CFC‐11 concentrations are due predominantly to model transport errors not model emission e

ISSN:0148-0227    

DOI:10.1029/96JD00865

年代:1996

数据来源: WILEY

摘要:

The observed rate of increase in atmospheric CH4declined gradually during the late 1980s [Steele et al., 1992] and then fell dramatically by ∼4 to 7 parts per billion by volume (ppbv) yr−1from 1991 to 1992 [Dlugokencky et al., 1994a]. Post‐1993 the CH4growth rate has recovered to pre‐1991 levels. In this study, we assess the sensitivity of the CH4growth rate to changes in CH4emissions from the coal and gas industries over the last 15 years using a global two‐dimensional (2‐D) model of the atmosphere. Emissions are estimated from available production data, and in the case of natural gas, a spectrum of leakage rates is assumed. Changes in the former Soviet Union (FSU) have been assessed separately from the rest of the world (ROW). Prior to 1989, increased coal and natural gas production led to an increase in the CH4growth rate (i.e., opposite to that which was observed). During the period 1989 to 1993 the modelled CH4growth rate decreased by ∼1–2 ppbv yr−2at northern mid‐latitudes (assuming constant gas leakage rates), showing that declining emissions, primarily in the form of natural gas from the FSU, may have contributed to the general reduction in the CH4growth rate from 1989 to 1991. However, this does not explain the large reduction which was observed between 1991 and 1992. A model run with FSU gas leakage rates decreasing by 1% yr−1from 5% in 1990 to 2% in 1993 shows a decrease in the CH4growth rate of ∼9–12 ppbv yr−1(or ∼3–5 ppbv yr−2) over this period. This is similar in magnitude to the observed decline over the same period. This sensitivity study illustrates the large potential for significantly lowering the growth rate of atmospheric CH4by reducing fossil fuel emissions from coal and, in particular, by reducing the leakage rat

ISSN:0148-0227    

DOI:10.1029/95JD03795

年代:1996

数据来源: WILEY

摘要:

Wetlands are one of the most important sources of atmospheric methane (CH4), but the strength of this source is still highly uncertain. To improve estimates of CH4emission at the regional and global scales and predict future variation requires a process‐based model integrating the controls of climatic and edaphic factors and complex biological processes over CH4flux rates. This study used a methane emission model based on the hypothesis that plant primary production and soil organic matter decomposition act to control the supply of substrate needed by methanogens; the rate of substrate supply and environmental factors, in turn, control the rate of CH4production, and the balance between CH4production and methanotrophic oxidation determines the rate of CH4emission into the atmosphere. Coupled to data sets for climate, vegetation, soil, and wetland distribution, the model was used to calculate spatial and seasonal distributions of CH4emissions at a resolution of 1° latitude × 1° longitude. The calculated net primary production (NPP) of wetlands ranged from 45 g C m−2yr−1for northern bogs to 820 g C m−2yr−1for tropical swamps. CH4emission rates from individual gridcells ranged from 0.0 to 661 mg CH4m−2d−1, with a mean of 40 mg CH4m−2d−1for northern wetland, 150 mg CH4m−2d−1for temperate wetland, and 199 mg CH4m−2d−1for tropical wetland. Total CH4emission was 92 Tg yr−1. Sensitivity analysis showed that the response of CH4emission to climate change depends upon the combined effects of soil carbon storage, rate of decomposition, soil moistu

ISSN:0148-0227    

DOI:10.1029/96JD00219

年代:1996

数据来源: WILEY

摘要:

Measurements of the18O/16O isotopic ratio of atmospheric carbon dioxide made by the University of Colorado, Boulder on flask samples provided by the Climate Monitoring and Diagnostics Laboratory of the National Oceanic and Atmospheric Administration appear to have been contaminated by oxygen isotope exchange between CO2and water inside the glass flasks. The18O/16O ratios measured for samples from high‐humidity sites collected during 1990–1993 show considerable scatter and are believed not to represent the true oxygen isotopic composition of atmospheric CO2. Laboratory experiments have demonstrated that oxygen isotope exchange occurs between CO2and water condensed on the flask walls. Complete isotopic equilibrium is not observed, even for storage times greater than 1 month; the extent of exchange differs for individual flasks. The experiments show that air samples to be stored in glass flasks must be dried to a dew point of 2°C or lower before storage to eliminate artifacts associated with oxygen exch

ISSN:0148-0227    

DOI:10.1029/96JD00053

年代:1996

数据来源: WILEY

摘要:

This study compares Nimbus 7 total ozone mapping spectrometer (TOMS) total column ozone with ozone data from two different satellite instruments measuring vertical profiles of ozone in the stratosphere. The first instrument is the microwave limb sounder (MLS) onboard the upper atmosphere research satellite (UARS) and the second is the solar backscattered ultraviolet (SBUV2) nadir sounder aboard NOAA 11. Previous studies have shown that TOMS data exhibit a zonal wave maximum (amplitudes ∼20–30 Dobson units) in total column ozone in the tropical South Atlantic region near 0° longitude. This wave structure occurs in all seasons but maximizes around August–October in association with intense biomass burning in South America and southern Africa. Results of this investigation show that MLS stratospheric column ozone integrated between 1 to 68‐hPa shows no such feature. Horizontal structures of 1 to 68‐hPa MLS column ozone are found to be incoherent with TOMS and SBUV2 total column data in the tropics in all seasons. This study provides the first evidence from a UARS data set that the southern tropical wave 1 peak in TOMS may have relatively small dependence on stratospheric ozone. Combined MLS, TOMS, SBUV2, and ozonesonde station data show that zonal asymmetries observed in total column ozone in the tropics originate primarily from tropospheric effects (dynamics coupled with biomass burning). Outside of the tropics, zonal patterns in total ozone originate mostly from stratospheric dynamics. Wave signatures in TOMS, SBUV2, and MLS column ozone all show generally coherent horizontal structures in middle and high latitudes, especially during seasons of large planetary wave events such as in the southern hemisphere during southern win

ISSN:0148-0227    

DOI:10.1029/96JD01057

年代:1996

数据来源: WILEY

摘要:

Measurements of the land surface exchange of nitrous acid over grass and sugar beet surfaces reveal both upward and downward fluxes with flux reversal occurring at an ambient concentration of nitrogen dioxide of about 10 ppb. This confirms earlier preliminary findings and strengthens the hypothesis that substantial production of nitrous acid can occur on land surfaces from reaction of nitrogen dioxide and water vapor. Detailed measurements of nitrous acid have been made in central urban, suburban, and rural environments. These measurements, in conjunction with a simple box model, indicate that the atmospheric concentrations of nitrous acid are explicable in terms of a small number of basic processes in which the most important are the surface production of nitrous acid from nitrogen dioxide, atmospheric production from the NO‐OH reaction and loss of nitrous acid by photolysis and dry deposition. In the suburban atmosphere, concentrations of nitrous acid are strongly correlated with nitrogen dioxide. In the rural atmosphere a different behavior is seen, with much higher nitrous acid to nitrogen dioxide ratios occurring in more polluted air with nitrogen dioxide concentrations in excess of 10 ppb. At lower nitrogen dioxide concentrations, net deposition of nitrous acid at the ground leads to very low concentrations in advected air. The model study indicates that during daytime in the suburban atmosphere, production of HONO from the NO‐OH reaction can compete with photolysis giving a HONO concentration of a few tenths of a part per billion. At the highest observed daytime concentrations of HONO, production of OH radical from its photolysis can proceed at a rate more than 10 times faster than from photolysis of oz

ISSN:0148-0227    

DOI:10.1029/96JD00341

年代:1996

数据来源: WILEY

摘要:

Experiments to determine the concentration of photochemically available Fe in ambient aerosol samples were carried out using a novel photochemical extraction procedure. Ambient aerosol samples, which were collected on Teflon filters, were suspended in an aqueous solution within a photochemical reactor and irradiated. Under these conditions, which were favorable to the photochemical weathering of aerosol particles, the relative amount of Fe(II)aqto Fetotalwas shown to increase. The extent and rate of Fe(II)aqphotoproduction was used to characterize the Fe in aerosol samples collected from Whiteface Mountain, New York, Pasadena, California, San Nicholas Island, California, and Yosemite National Park, California. Photochemically available Fe concentrations found ranged from<4 ng m−3(0.07 nmole m−3) to 308 ng m−3(5.52 nmole m−3), Fetotalconcentrations ranged from 10 ng m−3(0.18 nmole m−3) to 3400 ng m−3(61 nmole m−3), and the percentage of photochemically available Fe to Fetotalranged from 2.8% to 100%. Aerosol samples were also collected during biomass burning events in southern California; these samples showed insignificant changes in the photochemically available Fe (compared to nonbiomass burning samples) in conjunction with large increases of Fetotal. Calculations based on these experiments also provide further evidence that redox reactions of Fe in cloudwater could be an important in situ source of oxidants (OH, HO2/O2−). The estimated oxidant production rate in cloudwater based on these experiments is between 0 and 60 nM s−1, with an average value of 16 nM s−1. This estimated in situ oxidant production rate due to Fe chemistry is approximately equal to previous estimates of the oxidant flux to cloudwat

ISSN:0148-0227    

DOI:10.1029/96JD00857

年代:1996

数据来源: WILEY

摘要:

During late spring of 1991, airborne measurements in the smoke plume from the Kuwait oil fires indicated that SO2was removed from the gas phase at rates of ∼6 to 8% h−1and that NOxwas removed at rates of ∼7 to 23% h−1. Photochemical calculations indicate that homogeneous chemical reactions were responsible for only a small fraction of this removal. Also, indirect evidence suggests that heterogeneous removal of SO2on black carbon (or soot) and salt aerosols produced by the fires was relatively slow. The highest rates of SO2and NOxremoval were associated with high concentrations of atmospheric soil dust. This was likely due to heterogeneous oxidation of the SO2and NOxon the surfaces of soil dust particles. The removal of SO2and NOxon soil dust was probably accelerated by the alkaline nature of the dust. Heterogeneous reactions on soil dust particles proceeded more rapidly in regions of dispersed smoke than in the core of the plume; this was probably due to the depletion of the available surface area of the soil dust in regions of dense smoke. On the basis of smoke samples collected during the experiment we estimate that the quasi‐second‐order reaction rate for SO2is (9 ± 4) × 10−8(μg soil dust m−3)−1s−1. For a soil dust concentration of 200 μg m−3this implies a removal rate for SO

ISSN:0148-0227    

DOI:10.1029/96JD00978

年代:1996

数据来源: WILEY

摘要:

A Lagrangian radiation fog model is applied to a fog event at Summit, Greenland. The model simulates the formation and dissipation of fog. Included in the model are detailed gas and aqueous phase chemistry, and deposition of chemical species with fog droplets. Model predictions of the gas phase concentrations of H2O2, HCOOH, SO2, and HNO3as well as the fog fluxes of S(VI), N(V), H2O2, and water are compared with measurements. The predicted fluxes of S(VI), N(V), H2O2, and fog water generally agree with measured values. Model results show that heterogeneous SO2oxidation contributes to approximately 40% of the flux of S(VI) for the modeled fog event, with the other 60% coming from preexisting sulfate aerosol. The deposition of N(V) with fog includes contributions from HNO3and NO2initially present in the air mass. HNO3directly partitions into the aqueous phase to create N(V), and NO2forms N(V) through reaction with OH and the nighttime chemistry set of reactions which involves N2O5and water vapor. PAN contributes to N(V) by gas phase decomposition to NO2, and also by direct aqueous phase decomposition. The quantitative contributions from each path are uncertain since direct measurements of PAN and NO2are not available for the fog event. The relative contributions are discussed based on realistic ranges of atmospheric concentrations. Model results suggest that in addition to the aqueous phase partitioning of the initial HNO3present in the air mass, the gas phase decomposition of PAN and subsequent reactions of NO2with OH as well as nighttime nitrate chemistry may play significant roles in depositing N(V) with fog. If a quasi‐liquid layer exists on snow crystals, it is possible that the reactions taking place in fog droplets also occur to some extent in clouds as well as at the snow surfac

ISSN:0148-0227    

DOI:10.1029/96JD00340

年代:1996

数据来源: WILEY