The Characterization of Ozone,Sulfur Dioxide,and Nitrogen Dioxide for Selected Monitoring Sites in the Federal Republic of Germany

Ambient ozone, sulfur dioxide, and nitrogen dioxide data collected at 11 rural gaseous air pollution monitoring stations located throughout the Federal Republic of Germany (FRG) were characterized to provide a basis for investigating the effect these air pollutants may have on forest decline. For any given year, with the exception of the Waldhof site, the ozone monitoring sites did not experience more than 50 occurrences of hourly mean concentrations equal to or above 0.10 ppm. In most cases, the number of occurrences equal to or above 0.10 ppm at the FRG ozone monitoring sites was below the number experienced at a rural forested site located at Whiteface Mountain, New York. Several of the FRG monitoring sites experienced a large number of occurrences of hourly mean ozone concentrations between 0.08 and 0.10 ppm. Hof, Selb, Arzberg, and Waldhof experienced several occurrences of elevated levels of sulfur dioxide concentrations. The nitrogen dioxide 24-h mean concentrations were low for all sites. Because the 24-h mean data may mask the occurrence of a few high concentration events, it is not known if any of the sites that monitored nitrogen dioxide experienced short-term elevated concentrations. To gain further insight into the possible effect of pollutant mixtures on vegetation, future efforts should involve characterizing the timing of multi-pollutant exposures.     

Spatial and Temporal Variability of Ozone Exposure in Forested Areas of the United States and Canada: 1978—1988

Ambient O₃ exposures have reduced growth rates of tree genotypes in some areas of the United States. For characterizing O₃ exposures in forested areas, data from primarily population-oriented sites have been used. It has been speculated that exposures calculated from population-oriented sites provide estimates greater than those that would actually be experienced in the majority of forested areas. Accordingly, we compared 1988 O₃ data from three remote forested sites with data from several population-oriented monitoring sites in and around the mid? and southern Appalachian Mountains. The number of hours ≥0.08 ppm was lower at the remote forested sites than at the nearby population-oriented locations. In addition, we characterized the temporal variability of O₃ exposures in forested regions of the United States and Canada for the period 1978-1988. We found that the years of highest O₃ exposure in the eastern United States during 1978-1988 were 1978, 1980, 1983, and 1988, with 1988 being the worst year in four of seven eastern forest regions. In 1988, the Whiteface Mountain summit site (1483 m) experienced approximately 10 percent more hourly average concentrations ≥0.08 ppm than in the second highest O₃ exposure year (i.e., 1979). Consistently throughout the 11-year period, the highest O₃ exposures at the Whiteface Mountain site occurred during the late evening and early morning hours, with the result that the longterm 7-h (0900-1559h) exposure index could not distinguish those years in which the highest exposures occurred from those in which the lowest occurred. Similar to the Whiteface Mountain site, two high-elevation Shenandoah National Park sites experienced their highest O₃ exposures in 1988. With the exception of 1986, the lower elevation site (Dickey Ridge) consistently experienced more frequent occurrences of hourly average concentrations ≥0.08 ppm than the higher elevation site (Big Meadows).     

The Characterization of Ozone and Sulfur Dioxide Air Quality Data for Assessing Possible Vegetation Effects

Since the 1960s, much effort has been devoted to collecting and formatting air quality data. This paper discusses 1) the availability of air quality data for assessing potential biological impacts associated with ozone and sulfur dioxide ambient exposures, 2) examples of how air quality data can be characterized for assessing vegetation effects, and 3) the limitations associated with some exposure parameters used for developing relevant vegetation doseresponse yield reduction models. Data are presented showing that some ozone monitoring sites not continuously affected by local urban sources experience consecutive hourly ozone exposures ≥0.10 ppm in the late evening and early morning hours. These sites experience their maximum ozone concentrations either in the spring or summer months. Sites influenced by local rural sources experience their maximum ozone concentrations during the summer months. It is suggested that further research be performed to identify whether the sensitivity of a target organism at the time of exposure, as well as the pollutant concentration and chemical form that enters into the target organism, is as important in defining effects as air pollutant exposure alone.     

Biochemical changes in needles of Pinus radiata D. Don trees in relationship to long-term ozone exposure indices

Ambient concentrations of ozone in Europe are high enough to cause negative effects on vegetation. Therefore, many efforts have been made to determine exposure indices and critical levels for protection of vegetation. In this context, the choice of a suitable attribute to determine the pollutant effect is of paramount importance. Until now, much of the work has been done with attributes such as biomass or growth. In the present work correlation factors have been established between biochemical parameters (peroxidase activity, ascorbate and sulfhydryl contents) of Pinus radiata trees and exposure indices of ozone. Our results show that peroxidase cannot be used as an indicator of effects of long-term exposure to ozone but still remains as an excellent indicator of short-term ozone fluctuations in the field. Ascorbate may act as an intermediate indicator responding to both short fluctuations and long-term exposures to ozone. Finally, sulfhydryl may be used as a long-term indicator in relation to the AOT (average over threshold) exposure index. Our results also point to the fact that Pinus radiata may be affected by ozone at AOT values lower than 10 ppm.h as already observed with other tree species.     

The use of kriging to estimate monthly ozone exposure parameters for the Southeastern United States

This paper explores the feasibility of (1) using kriging to predict the monthly mean of daily 7-h mean (0900-1559) O3 concentrations, (2) using kriging to estimate the per cent of hourly mean O3 concentrations equal to or greater than 0.07 ppm (137 microg m(-3)) for a specific month, and (3) developing a quantitative relationship between the monthly mean of the daily 7-h (0900-1559) average O3 concentration and the monthly number of hourly concentrations > or = 0.08p ppm (157 microg m(-3)). We found that kriging can be used to estimate the (1) monthly mean of daily 7-h mean O3 concentrations and (2) the percentage of hourly concentrations for a given month > or = 0.07 ppm when sufficient spatial coverage was available. However, the per cent > or = 0.07 ppm parameter exhibited much greater relative variability than the monthly 7-h exposure index. A strong statistical association was found between the monthly number of occurrences > or = 0.08 ppm and monthly 7-h mean concentrations above 0.05 ppm (98 microg m(-3)). Because of the variability that cumulative indices, such as the monthly percentage of hourly concentrations > or = 0.07 ppm , exhibit from site to site, it appears that whether kriging techniques or mathematical regressions are used to estimate the number of elevated O3 hourly concentrations above selected thresholds, large uncertainties associated with the predicted values will exist. These large uncertainties will make it difficult to accurately estimate vegetation effects caused by ambient levels of O3. However, if a generalized quantitative relationship between repeated occurrences of hourly mean concentrations > or = 0.07 ppm or > or = 0.08 and vegetation effects can be developed, it may be possible, using kriged monthly values accompanied with confidence intervals, to identify those areas where vegetation may be at risk. However, before it will be possible to implement such an approach, researchers will have to better quantify the relationship between realistic O3 exposures and vegetation effects.     

Ground-Level Ozone in Eastern Canada: Seasonal Variations,Trends, and Occurrences of High Concentrations

Over the past few years, concern has increased in Canada over the health and environmental impacts of elevated concentrations of ground-level ozone. During the summer the most populated regions of Canada frequently record ozone concentrations that exceed the one-hour average maximum acceptable air quality objective of 32 parts per billion (ppb). In 1988 the Canadian Council of Ministers of the Environment agreed to develop a federal/provincial management plan to control nitrogen oxide and volatile organic compound emissions to reduce ozone concentrations in all affected regions of the country. In addition to the proposed interim control measures, the plan recommended that studies be undertaken to acquire the information necessary to develop sound control strategies. This report represents one of those studies and provides a summary of ground-level ozone measurements for eastern Canada for the 1980 to 1991 period with an emphasis on seasonal variations, trends, and occurrences of high concentrations.

Southwestern Ontario experiences the highest maximum hourly ozone concentrations and the greatest frequency of hours greater than the 82 ppb acceptable objective. Urban sites have the highest frequencies of ozone concentration measurements in the < 10 ppb range, while rural and remote sites show peaks in frequency distribution in the 20 to 30 ppb range. Trend analysis of summertime (May to September) average daily maximum ozone concentration showed no consistent pattern for eastern Canadian sites during 1980 to 1991. Sites in Montreal showed statistically insignificant downward trends while sites in Toronto showed small but statistically significant upward trends. These ozone-increasing trends are associated with reductions in nitric oxide concentrations. At all sites there was large year-to-year variability in peak ozone levels and in the frequency of hours with ozone concentrations above the maximum acceptable objective.     

Rural Ozone Across the Eastern United States: Analysis of CASTNet Data, 1988–1995

ABSTRACT

A predominantly rural ozone monitoring network was operated under the auspices of the Clean Air Status and Trends Network (CASTNet) from 1988 until 1995. Ozone data from sites in the eastern United States are presented and several indices are used to describe the spatial and temporal distribution of ozone concentration and exposure. These indices are SUM06, W126, the 8-hour rolling average (MAX_8hr>80), and the current National Ambient Air Quality Standards (NAAQS) for ozone. Ozone indices were selected to illustrate the spatial and temporal distribution of ozone, and the sensitivity of this distribution to different representations of concentration or exposure.

CASTNet is unique in that a uniform set of site selection criteria and uniform procedures, including traceability to a single primary standard, provide a high degree of comparability across sites. Sites were selected to avoid undue influence from point sources, area sources, or local activities. The sites reflect a wide range of land use and terrain types including agricultural and forested, in flat, rolling, and complex terrain from the eastern seaboard across the Appalachian Mountains to the Midwest.

Results indicate that ozone concentrations varied greatly in time and space across the eastern United States. Sites in the upper northeast, upper midwest, and southern periphery subregions experienced relatively low ozone during the years of record compared to sites in the northeast, midwest, and south central subregions. Ozone exposures at an individual rural site are dependent on many factors, including terrain, meteorology, and distance from sources of precursors. Relative to the current (as of 1996) NAAQS, only a handful of CASTNet sites near major urban areas report exceedances. In contrast, the majority of CASTNet sites might exceed the proposed new primary standard for ozone.

Sites at high elevation (>900m) in the east exhibit relatively high exposure statistics (e.g., SUM06 and W126), but no exceedance of the current ozone standard from 1988 through 1995. Terrain effects explain some of the variability within subregions and are an important consideration in the design of monitoring networks for ozone and possibly other pollutants.     

Factors determining the robustness of AOT40 and other ozone exposure indices

The robustness problem is considered for mathematical indices that describe the adverse effects of vegetation exposure to ozone. It is shown that some of them may demonstrate infinitely high sensitivity of the exposure estimate to small variations of ozone concentrations or internal parameters of specific functional. In particular, for the accumulated exposure over a threshold of 40 ppb (AOT40) index such conditions are not extraordinary, but rather describe quite often situations in remote areas in Northern Europe. Taking into account inevitable uncertainties in both calculated and observed ozone concentrations, a high sensitivity of ozone impact indices results in an instability of the exposure estimates and creates problems in their use. Theoretical consideration of the problem enabled to formulate the necessary and sufficient conditions for the limited sensitivity of a time-integrating index. An example of a modified AOT formulation fulfilling the obtained criteria and hence not experiencing the sensitivity problem is considered.     

Surface ozone in Yosemite National Park

During the summers of 2003 and 2005, surface ozone concentrations were measured with portable ozone monitors at multiple locations in and around Yosemite National Park. The goal of these measurements was to obtain a comprehensive survey of ozone within Yosemite, which will help modelers predict and interpolate ozone concentrations in remote locations and complex terrain. The data from the portable monitors were combined with concurrent and historical data from two long-term monitoring stations located within the park (Turtleback Dome and Merced River) and previous investigations with passive samplers. The results indicate that most sites in Yosemite experience roughly similar ozone concentrations during well-mixed daytime periods, but dissimilar concentrations at night. Locations that are well exposed to the free troposphere during evening hours tend to experience higher (and more variable) nocturnal ozone concentrations, resulting in smaller diurnal variations and higher overall ozone exposures. Locations that are poorly exposed to the free troposphere during nocturnal periods tend to experience very low evening ozone, yielding larger diurnal variations and smaller overall exposures. Ozone concentrations are typically highest for the western and southern portions of the park and lower for the eastern and northern regions, with substantial spatial and temporal variability. Back-trajectory analyses suggest that air with high ozone concentrations at Yosemite often originates in the San Francisco Bay Area and progresses through the Central California Valley before entering the park.     

Fatty acids and ultrastructure of ozone-exposed Aleppo pine (Pinus halepensis Mill.) needles

Fifteen or 18-month-old Aleppo pine seedlings were fumigated with different concentrations and doses of ozone over a period of 2-16 days in controlled-environmental growth chambers. The total fatty acid content and ultrastructure of the current year needles were subsequently analysed. In acute, high concentration exposures, significant reductions in the levels of linolenic acid were detected. Increases in myristic or palmitic acid were common in needles exposed to lower concentrations of ozone. Ultrastructural studies revealed reductions in chloroplast size and a darkening of stroma at low ozone exposures while at high concentrations disruption of the chloroplast membranes was also identified.     

The Characterization of Ozone Data for Sites Located in Forested Areas of the Eastern United States

Six years (1978-1983) of ozone monitoring data from sites located within six forested areas were examined. Areas that experienced the lowest to the highest ozone exposures were located in (1) northern New England/New York and upper Great Lakes, (2) New York/Pennsylvania/Maryland, (3) southeastern/southern, and (4) New Jersey pinelands. In general, higher ozone concentrations were observed in 1978, 1980 and 1983 as compared to the other three years examined. Ozone concentrations varied considerably within the areas. Recommendations for additional ozone monitoring sites are made. A concentrated effort should be made to examine ozone monitoring data from subsequent years (1984, 1985, and 1986) to explore whether the 6-year period 1978 through 1983 is representative of the annual variability of ozone concentrations over eastern forested areas. To better understand the relationship between ozone exposure and possible forest effects, we recommend that the temporal distributions of elevated ozone concentrations over a growing season be examined. The occurrence of elevated ozone levels during specific growth periods during a season may be an important aspect that biologists may wish to explore.     

The characterization of ozone concentrations at a select set of high-elevation sites in the eastern United States

Hourly averaged data for ozone collected in 1986 and 1987 were analyzed and characterized for a select set of high-elevation sites in the eastern United States. Pressure-corrected adjustments may be necessary when comparing ozone concentrations measured at two different elevations. When unadjusted concentrations (i.e. in units of parts per million) were used, the Whiteface Mountain sites showed what appeared to be an ozone elevational gradient. A gradient was not observed for the two MCCP Shenandoah National Park sites (SH1 and SH2). When adjusted ozone values (i.e. in units of micrograms per cubic meter) were used, the elevational gradient reported for Whiteface Mountain was no longer observed. When unadjusted concentrations were used, in most cases the high-elevation sites appeared to be receiving greater ozone exposure than the nearby, lower elevation sites. When adjusted ozone values were used, a consistent conclusion was not evident. On a regional basis for the period May through September 1987, when unadjusted concentrations were used, the high-elevation sites in the South appeared to experience higher cumulative ozone exposures than sites in the North. When adjusted ozone values were used, the geographic gradient was not strong. Assuming that target sensitivity remains nearly constant as elevation changes, adjusted concentrations should be taken into consideration when evaluating the relationship between ozone exposures at high-elevation sites and biological effects.     

Consideration of Air Quality Standards for Vegetation With Respect to Ozone

Present evidence suggests that ozone is the most damaging of all air pollutants affecting vegetation. It is the principal oxidant in the photochemical smog complex. Concentrations of ozone have exceeded 0.5 part per million (ppm) in the Los Angeles area. One-tenth of this level for 8 hours is known to injure very sensitive tobacco varieties. Many plant species are visibly affected after a few hours exposure at concentrations much lower than 0.5 ppm. There is also some evidence that ozone reduces plant growth. Many factors must be taken into account when considering standards to protect vegetation from ozone damage. These include ozone concentration and methods of measurement, time of exposure, possible additive effects of other pollutants, sensitivity of plant species, their economic value, and the extent of injury which can be tolerated. The response of a species to the pollutant is conditioned by genetic factors and environmental conditions. Lack of specific routine methods for measuring ozone in ambient air is a handicap. California and Colorado established standards for oxidants at 0.15 and 0.10 ppm, respectively, for 1 hour. How these standards relate to the ozone dosage causing acute and chronic injury to various plant species is discussed.     

A theoretical investigation of the pressure and temperature dependence of atmospheric ozone deposition to trees

Methods for describing the exposure patterns of forests to atmospheric ozone concentrations are compared with special emphasis on the situation at high altitudes, such as the Appalachian Mountains of the eastern USA. Limitations to the use of ozone concentration as mass per unit volume are discussed and a correction for temperature and pressure changes is derived. If identical ozone mass concentrations were measured at two sites separated by 2000 m elevation, the ozone flux at the lower site would exceed the flux at the higher site by 4-8% due to temperature and pressure effects on both air volume and ozone deposition velocity. It is recommended that ozone exposures be described in terms of 'flux-corrected' mass concentrations or volumetric mixing ratios when ambient ozone data from sites at different altitudes are to be compared.     

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 0₃, 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 0₃ standard may not be appropriate for protecting vegetation and human health from 0₃ 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 0₃ 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 0₃ 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.     

Important Considerations for Establishing a Secondary Ozone Standard to Protect Vegetation

Air quality standards are established to prevent or minimize the risk of adverse effects from air pollution to human health, vegetation, and materials. In order to develop standards which provide an adequate measure of protection to vegetation, it is necessary to define, in as precise terms as possible, the relationship between ambient air quality and the potential for adverse effects on 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 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.     

Ozone reactions with indoor materials during building disinfection

There is scant information related to heterogeneous indoor chemistry at ozone concentrations necessary for the effective disinfection of buildings, i.e., hundreds to thousands of ppm. In the present study, 24 materials were exposed for 16 h to ozone concentrations of 1000–1200 ppm in the inlet streams of test chambers. Initial ozone deposition velocities were similar to those reported in the published literature for much lower ozone concentrations, but decayed rapidly as reaction sites on material surfaces were consumed. For every material, deposition velocities converged to a relatively constant, and typically low, value after approximately 11 h. The four materials with the highest sustained deposition velocities were ceiling tile, office partition, medium density fiberboard and gypsum wallboard backing. Analysis of ozone reaction probabilities indicated that throughout each experiment, and particularly after several hours of disinfection, surface reaction resistance dominated the overall resistance to ozone deposition for nearly all materials. Total building disinfection by-products (all carbonyls) were quantified per unit area of each material for the experimental period. Paper, office partition, and medium density fiberboard each released greater than 38 mg m⁻² of by-products.     

Reproducibility of the Pulmonary Function Response of Older Men and Women to a 2-Hour Ozone Exposure.

To test the reproducibility of the pulmonary function response to ozone exposure in older individuals, eight men and eight women, average age 62.8 years, participated in three 2-hour exposures to 0.45 ppm ozone at 23.3 C and 62.5 percent relative humidity. The first and second exposures were separated by an average time of 17.2 days, and 27.3 days separated the second and third exposures. Subjects alternated riding a bicycle ergometer for 20 minutes at an average minute ventilation of 26 liters BTPS (body temperature pressure, saturated), with 20-minute rest periods. Forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV-1), and forced expiratory flow between 25 and 75% of FVC (FEF 25- 75%) were measured pre and post exposure. The reproducibility of individual pre-post changes were assessed by calculation of the best linear fit and correlation coefficients between exposures. For FVC and FEV-1, the slopes were significantly different from 1, and correlation coefficients not significantly different from zero, implying that older individuals may not respond consistently to similar ozone exposures.     

Ozone pollution and ozone biomonitoring in European cities. Part I: Ozone concentrations and cumulative exposure indices at urban and suburban sites

In the frame of a European research project on air quality in urban agglomerations, data on ozone concentrations from 23 automated urban and suburban monitoring stations in 11 cities from seven countries were analysed and evaluated. Daily and summer mean and maximum concentrations were computed based on hourly mean values, and cumulative ozone exposure indices (Accumulated exposure Over a Threshold of 40 ppb (AOT40), AOT20) were calculated. The diurnal profiles showed a characteristic pattern in most city centres, with minimum values in the early morning hours, a strong rise during the morning, peak concentrations in the afternoon, and a decline during the night. The widest amplitudes between minimum and maximum values were found in central and southern European cities such as Düsseldorf, Verona, Klagenfurt, Lyon or Barcelona. In the northern European cities of Edinburgh and Copenhagen, by contrast, maximum values were lower and diurnal variation was much smaller. Based on ozone concentrations as well as on cumulative exposure indices, a clear north–south gradient in ozone pollution, with increasing levels from northern and northwestern sites to central and southern European sites, was observed. Only the Spanish cities did not fit this pattern; there, ozone levels were again lower than in central European cities, probably due to the direct influence of strong car traffic emissions. In general, ozone concentrations and cumulative exposure were significantly higher at suburban sites than at urban and traffic-exposed sites. When applying the newly established European Union (EU) Directive on ozone pollution in ambient air, it was demonstrated that the target value for the protection of human health was regularly surpassed at urban as well as suburban sites, particularly in cities in Austria, France, northern Italy and southern Germany. European target values and long-term objectives for the protection of vegetation expressed as AOT40 were also exceeded at many monitoring sites.     

Ozone in the urban southeastern United States

Ozone measurements (daily maximum values) from the Aerometric Information Retrieval System database are analyzed for selected sites, during 1980 to 1988, in southeastern USA. Frequency distributions, for most sites during most years, show a typical bell-shaped curve with the higher frequency around the yearly daily maximum ozone mean of about 100 to about 110 microg m(-3) (50-55 ppbv). Abnormal years in ozone concentration may skew the distribution as the mean shifts. A correlation of daily maximum ozone concentrations above 140 microg m(-3) (70 ppbv) between sites shows a division between the sites in the northern protion of the region and those in the southern portion of the region. Variations in ozone levels are well correlated over distances of several hundred kilometers, suggesting that high values are associated with synoptic scale episodes. An ozone exposure analysis also shows higher ozone exposures (250-300 ppm days) in the northerly sites as compared to the southerly sites (150-170 ppm days).