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A stochastistic, Weibull probability model was developed and verified to simulate the underlying frequency distributions of hourly ozone (O3) concentrations (exposure dynamics) using the single, weekly mean values obtained from a passive (sodium nitrite absorbent)sampler. The simulation was based on the data derived from a co-located continuous monitor. Although at the moment the model output may be considered as being specific to the elevation and location of the study site, the results were extremely good. This effort for the approximation of the O3 exposure dynamics can be extended to other sites with similar data sets and in developing a generalized understanding of the stochastic O3 exposure/plant response relationships, conferring measurable benefits to the future use of passive O3 samplers, in the absence of continuous monitoring. [ABSTRACT FROM AUTHOR]

Field surveys for symptoms of foliar injury in a regional airshed that is influenced by a number of point sources of SOx, NOx and hydrocarbons, combined with foliar and soil sulfur analyses, confirmed earlier results that Saskatoon serviceberry (Amelanchier alnifolia Nutt.) cv. Smokey can be used as a biological indicator of chronic sulfur dioxide exposures, in the presence of other phytotoxic air pollutants such as ozone. [ABSTRACT FROM AUTHOR]

A stochastic, three-parameter, Weibull frequency distribution, probability generator was tested by using theoretical data. Subsequently, it was applied to replace missing values of hourly atmospheric concentrations of trace gases that were continuously monitored at three study sites, for 2 years. The results were highly accurate and realistic. The cumulative means and the medians calculated by the Weibull method were intermediate between corresponding values calculated by uniform substitution of missing values with `zero' or with half of the minimum detection limit of the appropriate measurement instrument used. Furthermore, the Weibull method allowed the replacement of as many as100 missing values on either side of a measured data sub-set, without altering the overall characteristics of the true frequency distribution of the entire data set. [ABSTRACT FROM AUTHOR]

During some past two decades there has been a growing interest amongair pollution/vegetation effects-scientists to use passive sampling systems for quantifying ambient, gaseous air pollutant concentrations, particularly in remote and wilderness areas. On the positive side, excluding the laboratory analysis costs, passive samplers are inexpensive, easy to use and do not require electricity to operate. Therefore, they are very attractive for use in regional-scale air quality assessments. Passive samplers allow the quantification of cumulative airpollutant exposures, as total or average pollutant concentrations over a sampling duration. Such systems function either by chemical absorption or by physical adsorption of the gaseous pollutant of interestonto the sampling medium. Selection of a passive sampler must be based on its known or tested characteristics of specificity and linearity of response to the chemical constituent being collected. In addition, the effects of wind velocity, radiation, temperature and relative humidity must be addressed in the context of absorbent/adsorbent performance and sampling rate. Because of all these considerations, passive samplers may provide under- or overestimations of the cumulative exposures, compared to the corresponding data from co-located continuous monitors or active samplers, although such statistical variance can be minimized by taking necessary precautions. On the negative side,cumulative exposures cannot identify short-term (

Saskatoon serviceberry or Saskatoon (Amelanchier alnifolia Nutt. cv.Smoky) seedlings were planted at five study sites within a 35,000 km2 airshed, that is influenced by a number of isolated stationary sources of sulfur dioxide (SO2), oxides of nitrogenand hydrocarbons, among others. The locations of the five sites werebased on the results of a meteorological dry deposition model for the oxides of sulfur and nitrogen. Visible foliar injury responses of Saskatoon were used as a biological indicator of SO2 exposures, through monthly field surveys. During late July 1998, unifacial,interveinal chlorosis was observed on some 12% of the seedlings at one study site. By September, the chlorosis had become more severe (necrosis) on some 70% of the plants at that site. Site specific ambientSO2 levels were relatively low (maximum 5-min concentration of 52.8 ppb). Similar data were unavailable for all, but one othersite. Therefore, foliar total S and SO42--S concentrations were analyzed in September at four of the five study sites. Previously soil SO42--S at these sites had been analyzed. There were spatial variabilities among these parameters. Based on the overall examination of these data, it is concluded that the observed visible injury symptoms were due to chronic SO2 exposures, exacerbated by the presence of ozone (O3). Independent of this literature based speculation, visible foliar injury responses of Saskatoon can be used as a biological indicator foracute or chronic ambient SO2 exposures, in the presence of other phytotoxic air pollutants. [ABSTRACT FROM AUTHOR]

Clear quantitative differences (particularly with NH4+ and NO3-) were observed in the chemical composition of rain collected by an in situ, refrigerated event sampler versus using a non-refrigerated, composite, weekly sampling protocol, at a site in the upper Midwestern USA. There was a non-linear, parabolic relationship between pH and SO42- or NO3- concentrations. Such relationships could be stratified by the occurrences of three different classes of rainfall chemistry, governed by three different types of branching air trajectories preceding them. These overall processes were influenced by source-receptor issues. A Fourier modulated, three-way parabolic splineregression model was used to explain the non-linear relationships between H+ and SO42- or NO3-. This model performed much better (R2: 0.008--0.61) than the linear (R2: 0.008--0.31) and non-modulatedthree-way parabolic spline (R2: 0.22--0.36) regression analyses. Overall, the study allowed an integration of rainfall chemistry with synoptic meteorology and numerical modelling. (c) 1998 Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

A white clover model system (consisting of O3-sensitive [NC-S] and tolerant [NC-R] clones) offers an opportunity to establish cause (temporally dynamic O3 exposures) and effect (temporally variable, chronic plant biomass responses) relationships under chamberless, ambient conditions on a regional scale. However, our understanding of the performance of the system (ambient O3 exposures and the responses of NC-S:NC-R) requires improvement. For example, there are residual carry-over effects in the biomass responses of NC-S:NC-R between successive harvests in a given growth season. However, there were no clear increasing or decreasing trends in these ratios from harvest to harvest during a given growth season. Based on observed differential, perhaps random variations in the biomass responses of NC-S:NC-R, one may conclude that growth regulating factors other than the ambient O3 were responsible for the observed variability. This is supported by the results of the linear regressionanalysis between the O3 exposure potentials (O3 flux) and the biomass responses of NC-S:NC-R. Future research must include not only site specific measurements of ambient O3 concentrations and the biomass responses of NC-S and NC-R, but also hourly horizontal windspeeds, air temperature, global radiation and relative humidity, to derive more realistic and reliable numerical relationships of cause (O3 fluxes) and effect (NC-S:NC-R biomass). The resulting predictive models need to be of time-series in their nature to account for the stochasticity of the underlying relationships. [ABSTRACT FROM AUTHOR]

The status of computer simulation models from around the world for evaluating the possible ecological, environmental, and societal consequences of global change is presented in this paper. In addition, a brief synopsis of the state of the science of these impacts is included. Issues considered include future changes in climate and patterns ofland use for societal needs. Models discussed relate to vegetation (e.g. crop), soil, bio-geochemistry, water, and wildlife responses to conventional, forecasted changes in temperature and precipitation. Also described are models of these responses, alone and interactively, to increased CO2, other air pollutants and UV-B radiation,as the state of the science allows. Further, models of land-use change are included. Additionally, global multiple sector models of environment, natural resources, human population dynamics, economics, energy, and political relations are reviewed for integrated impact assessment. To the extent available, information on computer software and hardware requirements is presented for the various models. The paper concludes with comments about using these technologies as they relate to ecological risk assessment for policy decision analysis. Such an effort is hampered by considerable uncertainties with the output of existing models, because of the uncertainties associated with input data and the definitions of their dose-response relationships. The concluding suggestions point the direction for new developments in modeling and analyses that are needed for the 21st century. [ABSTRACT FROM AUTHOR]

Statistical analysis was performed using selected sets of combined data from the US National Crop Loss Assessment Network and the European Open-Top Chambers Programme to examine the relationships between the occurrences of hourly ambient ozone (O3) concentrations and adverse crop yield responses. The results suggest that the frequency of occurrences of relatively low hourly O3 concentrations (~ < 35 ppb) are not as important as moderate to higher concentrations in eliciting negative crop biomass responses. They also suggestthat daily peak (highest) hourly O3 values (~ > 90 ppb) may not be as critical, most likely because they frequently do not occur during time periods when conditions that promote atmospheric conductivity (O3 deposition) and plant uptake (O3 absorption) are in coherence. [ABSTRACT FROM AUTHOR]

Atmospheric photochemical processes resulting in the production of tropospheric ozone (O3) and other oxidants are described. The spatial and temporal variabilities in the occurrence of surface level oxidants and their relationships to air pollution meteorology arediscussed. Models of photooxidant formation are reviewed in the context of control strategies and comparisons are provided of the air concentrations of O3 at select geographic locations around the world. This overall oxidant (O3) climatology is coupled to human health and ecological effects. The discussion of the effectsincludes both acute and chronic responses, mechanisms of action, human epidemiological and plant population studies and briefly, efforts to establish cause-effect relationships through numerical modeling. Ashort synopsis is provided of the interactive effects of O3 with other abiotic and biotic factors. The overall emphasis of thepaper is on identifying the current uncertainties and gaps in our understanding of the state of the science and some suggestions as to how they may be addressed. [ABSTRACT FROM AUTHOR]

There is an ongoing debate as to which components of the ambient ozone (O3) exposure dynamics best explain adverse crop yield responses. A key issue is regarding the importance of peak versus mid-range hourly ambient O3 concentrations. While in this paper the importance of peak atmospheric O3 concentrations isnot discounted, if they occur at a time when plants are conducive for uptake, the corresponding importance of more frequently occurring mid-range O3 concentrations is described. The probability of co-occurrence of high O3 concentrations and O3 uptake limiting factors is provided using coherent data sets of O3 concentration, air temperature, air humidity, mean horizontal wind velocity and global radiation measured at representative US and German air quality monitoring sites. Using the PLant-ATmosphere INteraction (PLATIN) model, the significance of the aforementioned meteorological parameters on ozone uptake is examined. In addition, the limitations of describing the O3 exposure for plants underambient, chamberless conditions by SUM06, AOT40 or W126 exposure indices are discussed. [ABSTRACT FROM AUTHOR]