Allen S. Lefohn

Estimating historical anthropogenic global sulfur emission patterns for the period 1850-1990

Abstract It is important to establish a reliable regional emission inventory of sulfur as a function of time when assessing the possible effects of global change and acid rain. This study developed a database of annual estimates of national sulfur emissions from 1850 to 1990. A common methodology was applied across all years and countries allowing for global totals to be produced by adding estimates from all countries. The consistent approach facilitates the modification of the database and the observation of changes at national, regional, or global levels. The emission estimates were based on net production (i.e., production plus imports minus exports), sulfur content, and sulfur retention for each countrys production activities. Because the emission estimates were based on the above considerations, our database offers an opportunity to independently compare our results with those estimates based on individual country estimates. Fine temporal resolution clearly shows emission changes associated with specific historical events (e.g., wars, depressions, etc.) on a regional, national, or global basis. The spatial pattern of emissions shows that the US, the USSR, and China were the main sulfur emitters (i.e., approximately 50% of the total) in the world in 1990. The USSR and the US appear to have stabilized their sulfur emissions over the past 20 yr, and the recent increases in global sulfur emissions are linked to the rapid increases in emissions from China. Sulfur emissions have been reduced in some cases by switching from high- to low-sulfur coals. Flue gas desulfurization (FGD) has apparently made important contributions to emission reductions in only a few countries, such as Germany.

Spatial Variability of PM2.5 in Urban Areas in the United States

Abstract Data from the U.S. Environmental Protection Agencys Aerometric Information Retrieval System (now known as the Air Quality System) database for 1999 and 2000 have been used to characterize the spatial variability of concentrations of particulate matter with aerodynamic diameter ≤2.5 μg (PM2.5) in 27 urban areas across the United States. Different measures were used to quantify the degree of uniformity of PM2.5 concentrations in the urban areas characterized. It was observed that PM2.5 concentrations varied to differing degrees in the urban areas examined. Analyses of several urban areas in the Southeast indicated high correlations between site pairs and spatial uniformity in concentration fields. Considerable spatial variation was found in other regions, especially in the West. Even within urban areas in which all site pairs were highly correlated, a variable degree of heterogeneity in PM2.5 concentrations was found. Thus, even though concentrations at pairs of sites were highly correlated, their concentrations were not necessarily the same. These findings indicate that the potential for exposure misclassification errors in time-series epidemiologic studies exists.

A conceptual ozone dose-response model to develop a standard to protect vegetation.

Abstract The present air quality standard to protect vegetation from ozone is based on a measured concentration (i.e., exposure) rather than on plant uptake rates (or dose). Proposed exposure-based standards have led to concerns about the appropriateness of chamber studies. There has also been some debate about the importance of the diel phase difference between plant conductance and ozone concentration in assessing the potential for plant damage. In this paper, we use physical reasoning based on (i) plant defenses and (ii) general resistance concepts of dry deposition to derive a suggested general form of a dose-based standard. The dose-based standard is then related to the more traditional exposure-based standard. Although we develop the model in terms of plant injury, we also discuss how the model can be extended to include damage, which historically has been the focus of air quality standards. With this new dose-based approach, we clarify some of the issues concerning chambers and the interaction of the daily cycles of ozone concentration and plant stomatal conductance. We further demonstrate that (i) weighted fluxes can be used as a surrogate for plant defenses, (ii) injury or damage to vegetation is more likely to be correlated with a dose-based index that differentially weights ambient ozone concentration or plant uptake rates than one which does not, (iii) the potential for ozone injury or damage to plants can occur throughout the day, and (iv) when assessing the potential for plant damage, a differentially weighted flux-based standard is likely to be more precise and more discriminating than a cumulative ozone-based exposure index. Finally, because our basic premise relies on plant defensive mechanisms, we outline areas of research that are necessary before a dose-based standard can be implemented.

EFFECT OF SURFACE OZONE EXPOSURES ON VEGETATION GROWN IN THE SOUTHERN APPALACHIAN MOUNTAINS: IDENTIFICATION OF POSSIBLE AREAS OF CONCERN

Abstract The results described in this paper are derived from an analysis, for the 8-yr period 1983–1990, that combined experimental exposure-response effects data for deciduous and coniferous seedlings and/or trees with characterized 03 ambient exposure data for a local area and soil moisture to identify areas that may be at risk in the Southern Appalachian Mountains. Results from seedling and tree experiments operated in open-top chambers were used to characterize 0 3 exposure regimes that resulted in growth loss under controlled conditions. Available 0 3 monitoring data were characterized for the states of Alabama, Georgia, South Carolina, North Carolina, West Virginia, Tennessee, Kentucky, and Virginia, using the W126 biologically based cumulative exposure index. As a part of the analysis, both the occurrences of hourly average 03 concentrations ⩾ 0.10 ppm and the soil moisture conditions in the geographic area were considered. Combining exposure information with moisture availability and experimental exposure-response data, the extreme northern and southern portions of the Southern Appalachian area were identified as having the greatest potential for possible vegetation effects. The study was based mostly on results from individual tree seedlings grown in chambers and pots and additional research is needed to identify what differences in effects might be observed if exposures were similar to those experienced in forests. Furthermore, we recommend future investigations to verify the location and presence of specific vegetation species and amounts and whether actual growth losses occurred in those areas of concern that have been identified in this study.

An Evaluation of the Kriging Method to Predict 7-h Seasonal Mean Ozone Concentrations for Estimating Crop Losses

Using kriging, a statistical technique, the National Crop Loss Assessment Network (NCLAN) program estimated growing season 5-month (May-September) ambient 7-h mean O3 concentrations for each of the major crop growing areas of the United States for 1978-1982. The O3 estimates were used to predict economic benefits anticipated by lowering O3 levels in the United States. This paper reviews NCLAN’s use of kriging to estimate 7-h seasonal mean O3 concentrations for crop growing regions. Although the original kriging program used by NCLAN incorrectly calculated the diagonal elements of the kriging equations, this omission did not result in significant errors in the predicted estimates. Most of the data used in estimating the 7-h seasonal values were obtained from urban areas; the use of these data tended to underestimate the 7-h seasonal O3 concentrations in rural areas. It is recommended that only O3 data that are representative of agricultural areas and have been collected under accepted quality assurance pro...

Ozone Descriptors for an Air Quality Standard to Protect Vegetation

Exposure of plants to ozone (O3) causes injury and reduced growth. Describing the form and function of the O3 exposure in relation to plant response is important in the regulatory process. Research has shown that plants show greater response to O3 as concentration increases. The duration of the O3 exposure is also important in the ability of vegetation to maintain O3 repair mechanisms. The O3 entering the leaf is important in plant response, thus O3 fluxes are more important than ambient concentrations. However, at this time an air quality standard useful for the regulatory process should be based on ambient O3 exposures. The selection of O3 exposure descriptors should incorporate factors pertinent to plant response. Research suggests that exposure descriptors which give greater weight to peak concentrations, and those which account for cumulative exposure, show the closest relationship to plant response. Ozone exposure summaries using concentration averages do not adequately relate plant response with am...

Establishing relevant ozone standards to protect vegetation and human health: exposure/dose-response considerations.

For assessing the efficacy of a specific form of the National Ambient Air Quality Standard for O3, those exposure patterns that result in vegetation and human health effects must be identified. For vegetation, it has been found that the higher hourly average concentrations should be weighted more than the lower concentrations. Controlled human exposure work supports the suggestion that concentration may be more important than exposure duration and ventilation rates. It has been indicated in the literature that the current form of the federal O3 standard may not be appropriate for protecting vegetation and human health from O3 exposures. The proposed use of the cumulative index alone as a form of the standard may not provide sufficient protection to vegetation. An extended-period average index, such as a daily maximum 8-hour average concentration, may not be appropriate to protect human health because of the reduced ability to observe differences among hourly O3 concentrations exhibited within exposure regimes. For both vegetation and human health effects research, additional experimentation is required to identify differences in responses that occur when ambient-type exposure regimes are applied. Any standard promulgated to protect vegetation and human health from O3 exposures should consider combining cumulative exposure indices with other parameters so that those unique exposures that have the potential for eliciting an adverse effect can be adequately described.

Ozone, sulfur dioxide, and nitrogen dioxide trends at rural sites located in the united states

Abstract We have investigated the existence of trends for ozone, sulfur dioxide, and nitrogen dioxide at rural sites in the U.S. For the ozone analysis, at 54 of the 77 sites (70%) for the 10-year analysis (1979–1988) and at 118 of 147 sites (80%), with at least 4 years of data for the 5-year analysis (1984–1988), there was no indication of trends, either positive or negative. For the 10-year analysis, ozone sites in the Southern and Midwest forestry regions showed more positive than negative signiicant slope estimates. For the 5-year analysis, similar results were obtained, except that the mid-Atlantic region also experienced more positive than negative significant slope estimates. In most of the agricultural regions, there were not many significant trends in either the 10- or 5-year analysis. However, for the agricultural Appalachian region, 50% and 34% of the trends, respectively, were significant and there were more positive than negative significant ozone trends for both the 10- and 5-year periods. For sulfur dioxide, there was an indication of trends at 37 of 64 sites (58%) for the 10-year analysis (1978–1987). For the 5-year analysis (1983–1987), with at least 4 years of data, there was no indication of trends at 115 of 137 sites (84%). For sites in some regions of the U.S., there is an indication that sulfur dioxide concentrations have declined for both the 5- and 10-year periods, but the rate of decline on an aggregate basis has slowed in the 5-year period. There is a strong indication that the sulfur dioxide level decreased at many sites in the Midwest forestry and the Corn belt agricultural regions for the 10-year period. In the Southern forestry and Appalachian agricultural regions, many sites showed a decrease in the index for the 10-year, but not the 5-year, period. The lack of monitoring data for nitrogen dioxide made any conclusion extremely tenuous.

NCLAN results and their application to the standard-setting process : protecting vegetation from surface ozone exposures

The current form of the standard is not appropriate for protecting vegetation from O3 exposures. As an alternative to the current form of the standard, it has been suggested in the literature that a maximum cumulative 3-month SUM06 O3 exposure index be used as the form of a secondary standard to protect agricultural crops. However, applying this index may result in inconsistent protection for vegetation. It appears that cumulative indices will have to be combined with other parameters to accurately quantify the occurrence of high hourly average concentrations. This paper describes the characterization of the hourly O3 exposures in selected National Crop Loss Assessment Network (NCLAN) experiments and discusses the application of the results to the standard-setting process. Our results indicated that, in most cases, the NCLAN experimental data we analyzed appeared to support the observation that the repeated occurrences of hourly average O3 concentrations of 0.10 ppm and higher result in adverse effects on vegetation. For the NCLAN experiments, the characterized distributions reflected the ability of the high hourly average concentrations to affect crop yield reduction. Prior to suggesting a new form of the secondary standard, it will be important to carefully characterize the specific regimes responsible for affecting vegetation and identify the important components of those regimes responsible for the effects. By applying this approach, it should be possible to limit the occurrence of inconsistent results when applying a new form of the secondary standard.

Important Considerations for Establishing a Secondary Ozone Standard to Protect Vegetation

Based on recent evidence published in the literature, as well as retrospective studies using data from the National Crop Loss Assessment Network (NCLAN), cumulative indices can be used to describe exposures of ozone for predicting agricultural crop effects. However, the mathematical form of the standard that may be proposed to protect crops does not necessarily have to be of the same form as that used in the statistical or process oriented mathematical models that relate ambient ozone exposures with vegetation effects. This paper discusses the limitations associated with applying a simple statistic that may take the place of a more biologically meaningful exposure parameter. While the NCLAN data have been helpful in identifying identifying indices that may be appropriate for establishing exposure-response relationships, the limitations associated with the NCLAN protocol need to be considered when attempting to apply these relationships in the establishment of a secondary national ambient air quality standard. The Weibull model derived from NCLAN experiments must demonstrate its generality and universal applicability. Furthermore, its predictive power must be tested using independent sets of field data.