摘要:

We have determined the deposition rates of210Pb and137Cs from the atmosphere to the landscape of the eastern and mid‐western United States by measuring their inventories in core samples of undisturbed soils. The mean inventories in lowland sites are 27.7 dpm cm−2for210Pb and 21.8 dpm cm−2for137Cs as of January 1984. The mean annual concentration of210Pb in surface air at the 9 sites of the SURE network decreases smoothly from about 0.060 dpm m−3near the Mississippi River to about 0.030 near the Atlantic coast. The ratio of deposition rate to surface air concentration is 0.62 ± 0.03 cm s−1for210Pb and 1.36 ± 0.08 cm s−1for137Cs. Using the activity vs. altitude profiles of Moore, et al. [1973], for210Pb and the fission product nuclide,90Sr, we calculate tropospheric aerosol mean residence times for210Pb and137Cs, of 4.8 and 5.5 days, respectively. This near equality precludes a rapid decrease of the aerosol scavenging rate constant in the mid‐troposphere. The137Cs/210Pb ratios in soils from elevations above 1000 m in the Appalachian Mountains are lower than those in adjacent lowland soils, indicating the preferential removal of aerosols from the lower layer of the troposphere, presumably by cloud droplet impaction or by seede

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14355

年代:1986

数据来源: WILEY

摘要:

The rainout‐determined lifetimes of highly soluble particulate and gaseous atmospheric compounds are investigated using general circulation model simulations in which removal is explicitly calculated in terms of the local, model‐produced precipitation rates. Our calculations indicate that because of the episodic and asymmetric nature of rainout, species' lifetimes depend not only on the amount of precipitation but also on the characteristics of the precipitation regime (such as duration and frequency of the precipitation events) and on the direction of the tracer main flow (determined by the species' average mixing ratio gradient). For this reason, averaged rainout lifetimes of tracers flowing downward from the stratosphere are found to differ substantially from those of tracers of surface origin flowing upward or tracers of a more ubiquitous tropospheric source. These results imply that the use of a first‐order parameterization to simulate rainout in a photochemical model that does not explicitly calculate precipitation can be inadequate in representing this process. A computationally efficient parameterization that includes the effects of intermittence and asymmetry of rainout is proposed, and it is shown how this parameterization can be used to estimate rainout‐determined tropospheric residence times from observational data sets. A review of published estimates of submicron aerosol tropospheric residence times based on observations shows that these are consistent with our model

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14367

年代:1986

数据来源: WILEY

摘要:

An attempt is made to estimate Lagrangian time scales connected with clouds in the atmosphere. Three‐dimensional wind and relative humidity obtained from the First GARP Global Experiment (FGGE) data set are used to compute three‐dimensional trajectories with accompanying clouds. From the meteorological history of the trajectories, estimates are made of the average time from the release of a trajectory until the first cloud passage and the average time between first and second cloud passage. Geographical and seasonal variations of these parameters are calculated and discussed. Since the “clouds” parameterized from the FGGE data are limited to those connected with the large‐scale flow in the atmosphere, a substantial bias in our estimates is introduced. This implies that the estimates are more representative for major cloud systems, often connected with precipitation, than for clouds i

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14377

年代:1986

数据来源: WILEY

摘要:

Chemical processes involving sulfur and nitrogen species in clouds and precipitation have been incorporated into a diagnostic, two‐dimensional numerical model for narrow cold‐frontal rainbands (NCFR). The chemical species include sulfur dioxide, sulfate, ammonium, nitric acid, hydrogen peroxide, and peroxyacetyl nitrate. The model is initialized through specification of the airflow field, a temperature‐humidity sounding, and initial profiles of the various chemical species. Outputs of the model (discussed in detail in Part 2) (Hegg et al., this issue) are the steady state, two‐dimensional fields of the mass mixing ratio of various chemical species (e.g., cloud water sulfate or nitrate, precipitation sulfate, or nitrate). In view of similarities between NCFR and moderately strong convective systems, this model should also be useful in diagnostic studies of the sulfur and nitrogen chemistry of a variety of convective clouds and

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14385

年代:1986

数据来源: WILEY

摘要:

The kinematic, diagnostic model of the physics and chemistry of narrow cold‐frontal rainbands (described by Rutledge et al. (this issue)) is used to explore chemical interactions within convective precipitation systems. Cloud microphysical and dynamical processes are found to be comparable with chemical processes in affecting chemical deposition. In‐cloud sulfate production contributes up to ∼50% to wet sulfate deposition. Hydrogen peroxide appears to be the primary oxidant for the production of sulfate in clouds, but the sulfate production is not a linear function of H2O2concentration, and different sulfate production mechanisms can dominate at different heights in a cloud system. The model predicts that the relationships between sulfur input and sulfate deposition, and nitrogen input and nitrate deposition in narrow cold‐frontal rainbands, are, in general, nonlinear. Under certain conditions, the model shows that chemical species, particularly SO2, can be redistributed over significant heights by convective cloud systems. The model predicts concentrations of chemical species in precipitation that are similar to the limited field observations that are av

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14403

年代:1986

数据来源: WILEY

摘要:

Reaction mechanisms are formulated for the atmospheric photooxidation of the organosulfur compounds, dimethyl sulfide, CH3SCH3, methanethiol, CH3SH, and diethyl sulfide, C2H5SC2H5. Predictions of the mechanisms are compared with available data on laboratory photooxidations of these three species to identify critical uncertainties in chemical pathways and reaction rate constants. The sensitivity of product yields to these uncertainties is investigated.

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14417

年代:1986

数据来源: WILEY

摘要:

Cloud chamber experiments were conducted to measure the rate of conversion of gaseous SO2to aqueous sulfate under conditions of warm‐cloud formation. The rate of SO2conversion in cloudy air with 140 ppb ozone was approximately 1000 times faster than conversion in clouds without ozone. The rates of SO2oxidation observed in these experiments with simulated clouds (pH 4.5–5.5) and ozone concentrations in the range of 25–430 ppb are consistent with previously published kinetics for SO2in bulk‐water experiments with much higher concentrations o

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14439

年代:1986

数据来源: WILEY

摘要:

Two climate models, a one‐dimensional radiative‐convective model and a seasonal statistical‐dynamical model, have been used to obtain a qualitative understanding of climate forcing mechanisms and feedback processes associated with the climatic impact of carbonaceous Arctic aerosols. The models are consistent in suggesting that such aerosols should produce surface warming in Arctic regions, but the manner in which this is accomplished is a bit unusual. Since the aerosols appear in a region and season for which the atmosphere exhibits strong static stability, aerosol‐induced changes in the surface radiation budget would be expected to govern the change in surface climate. Although the direct impact of the aerosol is to reduce absorbed solar radiation at the surface, this effect is minimized by the high surface albedos, which in turn, due to the large surface reflection, enhance aerosol solar absorption. This aerosol‐induced atmospheric heating then results in increased infrared emission from the atmosphere to the surface that more than compensates for the reduced surface solar absorption, thus producing surface warming. The seasonal statistical‐dynamical model further exhibits interesting cryospheric feedback processes, while suggesting springtime Arctic warming that is roughly consistent in timing with observed trends in high latitude temperatures, an effect some have attributed to CO2‐in

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14445

年代:1986

数据来源: WILEY

摘要:

Three independent examples are discussed which suggest that photochemical ozone production in the troposphere can be observed in the tropics from an analysis of total ozone data. The first finding shows that the seasonal cycle of total columnar ozone is dominated by the seasonal cycle of tropospheric ozone, even though tropospheric ozone accounts for only 5–15% of the total ozone. Second, a case study is presented which shows that enhanced total ozone observed over the Amazon Basin can be associated with the presence of biomass burning. In situ measurements have confirmed that biomass burning does result in the production of photochemically generated ozone, analogous to the formation of “smog” near industrialized areas. Third, an analysis of the distribution of carbon monoxide obtained from a space shuttle platform is strongly correlated with the concurrent distribution of total ozone between 5°S and 10°N. Because all of the sources of carbon monoxide are located in the troposphere, this finding likewise suggests that the gradients of total ozone at low latitudes must also reflect processes occurring in the trop

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14451

年代:1986

数据来源: WILEY

摘要:

HCOOH and CH3COOH are important chemical constituents of cloud water and precipitation, but sources for these compounds in the atmosphere are at present unknown. The question of source identification was addressed through the analysis of 465 samples of precipitation collected at 14 continental and marine locations around the world. Continental precipitation during growing seasons contained, relative to marine precipitation and to continental precipitation during nongrowing seasons, higher absolute concentrations of organic acids and higher ratios of HCOOT(HCOOHaq+ HCOO−) to CH3COOT(CH3COOHaq+ CH3COO−). The concentrations of HCOOTand CH3COOTin precipitation at most locations were also highly correlated. These results support the hypothesis that organic acidity in precipitation may originate with two major sources, volatile vegetative constituents over continents and a second weaker source in both continental and marine regions. Relative to the similar ratios of HCOOTto CH3COOTin the aqueous phase, differences in precipitationpH resulted in large regional differences in calculated equilibrium vapor phase concentrations. The mechanism(s) by which proportionate concentrations of HCOOTand CH3COOTare maintained in the aqueous phase remains an open question. Comparisons between precipitation in impacted and remote regions indicate that although possibly important near large population and industrial centers, anthropogenic emissions are probably not major sources for organic acids in precipitation over broad geographic regi

ISSN:0148-0227    

DOI:10.1029/JD091iD13p14466

年代:1986

数据来源: WILEY