Ozone and urban forests in Italy

Ozone levels along urban-to-rural gradients in three Italian cities (Milan, Florence, Bari) showed that average AOT40 values at rural and suburban sites were 2.6 times higher than those determined at urban sites. However, O₃ also exceeded the European criteria to protect forest health at urban sites, even when the standards for human health protection were met. For protecting street trees in Mediterranean cities, the objectives of measurement at urban sites should extend from the protection of human health to the protection of vegetation as well. A review of forest effects on O₃ pollution and of O₃ pollution on forest conditions in Italian cities showed that it was not possible to distinguish the effect of O₃ in the complex mixture of urban pollutants and stressors. A preliminary list of tree species for urban planning in the Mediterranean area shows the average tree capacity of O₃ removal and VOC emission.     

Ozone Regimes in or near Forests of the Western United States: Part 2. Factors Influencing Regional Patterns

Abstract

Ozone levels in or near forests of the western United States resulted from transport of ozone from urban areas, photochemical formation of ozone in nonurban areas from either natural or manmade precursors, and downward mixing of ozone from the tropospheric reservoir. Similarities in ozone exposure regimes were clearly associated with ozone characteristics, such as the shape of the diurnal curve in hourly ozone concentrations and the magnitudes of ozone levels. No single site characteristic dominated across the region. Eight classes of ozone regimes were identified: largeurban, medium-urban, small-urban, urban downwind-urban, urban-transport, rural, rural-remote, and remote. Sites in the western United States can be classified according to these classes. Of the sites included in the analysis, Olympic National Park, Colorado National Monument, Redwood National Park, Grand Canyon, and Crook County in Oregon showed the lowest impact from urban-generated ozone. The greatest impact of manmade ozone was found in forests of southern and central California, and to some extent in Rocky Mountain National Park and along the western slopes of the Cascades in Washington.

The eight groups of sites showing similar ozone exposure regimes as identified by Böhm et al.¹ corresponded closely with the eight classes of ozone regimes, indicating that regional similarities in ozone exposure regimes can be linked to ozone formation and transport processes despite a lack of geographic cohesion. Sixty-four percent of variance in ozone exposure regimes can be expressed in a twodimensional space called diurnal-curve space. Group membership is more cohesive in diurnal-curve than geographic space. Applications of diurnal-curve space include (1) a sensitive regional analysis of the nature and magnitudes of ozone exposure regimes in or near western forests; (2) a pro-active means for identifying sites with changing ozone exposure regimes; and (3) guidelines from which biologists can develop realistic experimental fumigation protocols. It is suggested that univariate statistics, such as 7-hour mean, 24-hour mean, SUM06, and SUM08, cannot identify up to 39% of the variance in ozone exposure regimes among sites in or near forests of the western United States.     

Ozone air pollution and foliar injury development on native plants of Switzerland

The objectives of this study were to examine the foliar sensitivity to ozone exposure of 12 tree, shrub, and herbaceous species native to southern Switzerland and determine the seasonal cumulative ozone exposures required to induce visible foliar injury. The study was conducted from the beginning of May through the end of August during 2000 and 2001 using an open-top chamber research facility located within the Lattecaldo Cantonal Forest Nursery in Canton Ticino, southern Switzerland (600 m asl). Plants were examined daily and dates of initial foliar injury were recorded in order to determine the cumulative AOT40 ppb h ozone exposure required to cause visible foliar injury. Plant responses to ozone varied significantly among species; 11 species exhibited visible symptoms typical of exposures to ambient ozone. The symptomatic species (from most to least sensitive) were Populus nigra, Viburnum lantana, Salix alba, Crataegus monogyna, Viburnum opulus, Tilia platyphyllos, Cornus alba, Prunus avium, Fraxinus excelsior, Ribes alpinum, and Tilia cordata; Clematis spp. did not show foliar symptoms. Of the 11 symptomatic species, five showed initial injury below the critical level AOT40 10 ppmh O3 in the 2001 season.     

Formation and Transport of the Madrid Ozone Plume

Abstract

The main results of an experimental study focusing on the formation and transport of photochemical pollution in the Madrid air basin are presented. This southern European, heavily populated urban area is located on an elevated plateau at a height of 700 m, near a mountain range with maximum heights of around 2,400 m. Daily and seasonal cycles of ozone were documented during a one-year survey at three semi-rural sites located 30 km away from the urban center. Maximum hourly values of up to 140 ppb were measured, and the ozone generated within the urban plume on polluted days (when values exceeded 90 ppb) has been estimated at around 40-50 ppb.A meteorological characterization of these smoggy days pointed out the influence of thermally induced local wind flows on the concentration daily cycles at the measuring sites, denoting a preferred advection of the urban plume. Moreover, during intensive summer field campaigns, the use of meteorological and ozone sondes, as well as an instrumented aircraft, revealed some features about the horizontal and vertical distribution of the polluted air masses, as well as their evolution within the planetary boundary layer. Ozone plumes have been detected up to 100 km away from the city, usually mixed in a layer that reaches a height of 1,000-1,500 m in the afternoon. On some occasions, ozone-enriched layers have been detected as high as 4,000 m during morning hours, suggesting possible tropospheric injection induced by topographydriven flows or convective mesoscale systems that are usually present in the center of the Iberian Peninsula in the summer.     

Ozone exposure thresholds and foliar injury on forest plants in Switzerland

Canton Ticino in southern Switzerland is exposed to some of the highest concentrations of tropospheric ozone in Europe. During recent field surveys in Canton Ticino, foliar symptoms identical to those caused by ozone have been documented on native tree and shrub species. In Europe, the critical ozone level for forest trees has been defined at an AOT40 of 10 ppm.h O3 (10 ppm.h accumulated exposure of ozone over a threshold of 40 ppb) during daylight hours over a six-month growing season. The objective of this study was to determine the amount of ambient ozone required to induce visible foliar symptoms on various forest plant species in southern Switzerland. Species were grown within eight open-top chambers and four open plots at the Vivaio Lattecaldo Cantonal Forest Nursery in Ticino, Switzerland. Species differed significantly in terms of the ppb.h exposures needed to cause visible symptoms. The most to least symptomatic species grown within open-plots in this study rank as Prunus serotina, Salix viminalis, Vibrnum lantana, Rhamnus cathartica, Betula pendula, Rumex obtusifolius, Sambucus racemosa, Morus nigra, Prunus avium, Fraxinus excelsior, Rhamnus frangula, Alnus viridis, Fagus sylvatica and Acer pseudoplatanus. Similar rankings were obtained in the non-filtered chamber plots. The ranking of species sensitivity closely follows AOT values for the occurrence of initial symptoms and symptom progression across the remainder of the exposure season. Species that first showed evidence of foliar injury also demonstrated the most sensitivity throughout the growing season, with symptoms rapidly advancing over ca. 25-30% of the total plant leaf surfaces by the end of the observation period. Conversely, those species that developed symptoms later in the season had far less total injury to plant foliage by the end of the observation period (1.5 to < 5% total leaf area injured). The current European ambient ozone standard may be insufficient to protect native plant species from visible foliar injury, and many more native species may be sensitive to ozone-induced foliar injury than are currently known.     

The Chemical and Meteorological Conditions Associated with High and Low Ozone Concentrations in Southeastern Michigan and Nearby Areas of Ontario

This analysis represents the first characterization of the photochemistry and transport of ozone in the Detroit metropolitan area and provides a basis for comparing data for Detroit to that for other cities. The characterization is based on a comprehensive set of meteorological and chemical measurements obtained at a site in the urban core of Detroit during the summer of 1981, together with measurements of O₃, nitrogen oxides (NO _X ), and nonmethane organic compounds (NMOC) from rural, suburban, and urban areas in southeastern Michigan and adjacent areas of Ontario.

For the quartile (23 days) with highest ozone maxima (97-180 ppb), the maxima occurred 10-70 km north-northeast of the city on days that were warm and hazy with light southsouthwest winds. On such days there was a marked accumulation of ozone precursors (NMOC and NO_X) in the early morning, as well as a rapid chemical removal of NO _X (NO _X half-life of ～5 h) from morning to midday. The timing of the daily ozone increase across the study region suggests that local photochemical generation in a moving plume was responsible for more than half of the ozone measured downwind. However, there was also evidence that ozone transported into Detroit as part of the regional background was a significant part of the O₃ maxima on high ozone days. The average contributions of photochemistry and transport for the 23 days with the highest ozone maxima were estimated to be 57 ppb and 47 ppb, respectively.     

Ozone distribution and phytotoxic potential in mixed conifer forests of the San Bernardino Mountains, southern California

In the San Bernardino Mountains of southern California, ozone (O(3)) concentrations have been elevated since the 1950s with peaks reaching 600ppb and summer seasonal averages >100ppb in the 1970s. During that period increased mortality of ponderosa and Jeffrey pines occurred. Between the late 1970s and late1990s, O(3) concentrations decreased with peaks approximately 180ppb and approximately 60ppb seasonal averages. However, since the late 1990s concentrations have not changed. Monitoring during summers of 2002-2006 showed that O(3) concentrations (2-week averages) for individual years were much higher in western sites (58-69ppb) than eastern sites (44-50ppb). Potential O(3) phytotoxicity measured as various exposure indices was very high, reaching SUM00 - 173.5ppmh, SUM60 - 112.7ppmh, W126 - 98.3ppmh, and AOT40 - 75ppmh, representing the highest values reported for mountain areas in North America and Europe.     

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).     

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.     

Distribution of ozone and other air pollutants in forests of the Carpathian Mountains in central Europe.

Ozone (O3) concentrations were monitored during the 1997-1999 growing seasons in 32 forest sites of the Carpathian Mountains. At all sites (elevation between 450 and 1320 m) concentrations of O3, nitrogen dioxide (NO2), and sulfur dioxide (SO2) were measured with passive samplers. In addition, in two western Carpathian locations, Vychodna and Gubalówka, ozone was continuously monitored with ultraviolet (UV) absorption monitors. Highest average hourly O3 concentrations in the Vychodna and Guba?ówka sites reached 160 and 200 microg/m3 (82 and 102 ppb), respectively (except for the AOT40 values, ozone concentrations are presented as microg/m3; and at 25 degrees C and 760 mm Hg, 1 microg O3/m3 = 0.51 ppb O3). These sites showed drastically different patterns of diurnal 03 distribution, one with clearly defined peaks in the afternoon and lowest values in the morning, the other with flat patterns during the entire 24-h period. On two elevational transects, no effect of elevation on O3 levels was seen on the first one, while on the other a significant increase of O3 levels with elevation occurred. Concentrations of O3 determined with passive samplers were significantly different between individual monitoring years, monitoring periods, and geographic location of the monitoring sites. Results of passive sampler monitoring showed that high O3 concentrations could be expected in many parts of the Carpathian range, especially in its western part, but also in the eastern and southern ranges. More than four-fold denser network of monitoring sites is required for reliable estimates of O3 distribution in forests over the entire Carpathian range (140 points). Potential phytotoxic effects of O3 on forest trees and understory vegetation are expected on almost the entire territory of the Carpathian Mountains. This assumption is based on estimates of the AOT40 indices for forest trees and natural vegetation. Concentrations of NO2 and SO2 in the entire Carpathian range were typical for this part of Europe and below the expected levels of phytotoxicity.     

Differences in growth, leaf senescence and injury, and stomatal density in birch (Betula pendula Roth.) in relation to ambient levels of ozone in Finland

The differences in growth, leaf senescence, visible ozone injuries and stomatal density between one coastal site (natural ozone) and two inland sites (natural and elevated ozone) in Finland were determined for saplings of Betula pendula clones grown under open-field conditions during two growing seasons. Responses in growth, leaf senescence, visible injuries, and stomatal density were determined in relation to cumulative ozone exposure accumulated over the thresholds of 30, 40 and 50 ppb (10(9)) during the exposure period. In addition, the effects of the different ozone exposures on ultrastructure of chloroplasts were studied. Increasing ozone exposure resulted in reduced shoot dry weight, stimulated (first year) or reduced (second year) height growth, accelerated autumn yellowing of leaves, increased stomatal density, visible symptoms and chloroplast injuries, and increased number and size of plastoglobuli. Newly expanded mature leaves in midsummer were more sensitive to ozone episodes than younger developing leaves in the early growing season. In most parameters, the best correlation was achieved with the exposure index AOT30. Ozone risk for birch is highest in the southern coastal area of Finland, where background ozone concentrations are higher than in inland sites.     

Ground-level ozone in the Pearl River Delta region: Analysis of data from a recently established regional air quality monitoring network

The ambient air quality monitoring data of 2006 and 2007 from a recently established Pearl River Delta (PRD) regional air quality monitoring network are analyzed to investigate the characteristics of ground-level ozone in the region. Four sites covering urban, suburban, rural and coastal areas are selected as representatives for detailed analysis in this paper. The results show that there are distinct seasonal and diurnal cycles in ground-level ozone across the PRD region. Low ozone concentrations are generally observed in summer, while high O₃ levels are typically found in autumn. The O₃ diurnal variations in the urban areas are larger than those at the rural sites. The O₃ concentrations showed no statistically significant difference between weekend and weekdays in contrast to the findings in many other urban areas in the world. The average ozone concentrations are lower in urban areas compared to the sites outside urban centers. Back trajectories are used to show the major air-mass transport patterns and to examine the changes in ozone from the respective upwind sites to a site in the center of the PRD (Wanqingsha). The results show higher average ozone concentrations at the upwind sites in the continental and coastal air masses, but higher 1 h-max O₃ concentrations (by 8–16 ppbv) at the center PRD site under each of air-mass category, suggesting that the ozone pollution in the PRD region exhibits both regional and super-regional characteristics.     

Seasonal ozone behavior along an elevation gradient in the Colorado Front Range Mountains

Ambient surface ozone was monitored for one year at a series of seven sites along an elevation gradient from 1600 m to 3500 m above sea level (ASL) in Boulder County, Colorado. Spatial variability of ozone, quantified as the root mean squared deviation of hourly ozone per kilometer horizontal separation, decreased with elevation and distance from local sources, validating the assumption that (except at the City of Boulder (BO) site) the results of the study are representative of the Colorado Front Range. The northern hemisphere (NH) tropospheric spring ozone peak was clearly apparent in late April and early May and affected ozone at all elevations. Ozone consistently increased with elevation during winter, with a mean monthly rate of 1.5 ppbv per 100 m elevation. In summer, this monotonic increase in ozone with elevation was not observed; instead mean monthly ozone increased in two steps, by ～15 ppbv between 1610 m and 1940 m ASL and by ～10 ppbv between 3350 m and 3530 m ASL to a maximum of 60 ppbv. The amplitude of the diurnal ozone cycle decreased with increasing elevation. Average summertime diurnal swings in ozone concentration had a magnitude of 29 ppbv at 1610 m ASL, and 7–16 ppbv at the mid-elevation sites. In winter a diurnal cycle was observed only at the BO site, ozone concentrations at the remaining six locations changed on a multi-day timescale, indicating regional background behavior as the primary factor for wintertime ozone. Even the highest elevation site was influenced by transported urban air pollution in summer, indicated by the average 5 ppbv diurnal increase in ozone. Ozone exposure at the mid- to high-elevation sites in many instances approached and exceeded the 8-h National Ambient Air Quality Standard of 75 ppbv. The elevated ozone levels along this transect were interpreted to be caused by the confounding effects of the high elevation of these sites, increased ozone in long-range transported air, and anthropogenic ozone production in air transported from the nearby urban and suburban areas east of the Colorado Front Range Mountains.     

Estimates of ozone AOT40 from passive sampling in forest sites in South-Western Europe

Weekly-fortnightly ozone (O3) concentrations measured by passive sampling at 81 forest monitoring plots in France, Italy, Spain and Switzerland over the period 2000-2002 were used to estimate the cumulative exposure index AOT40. The estimation method is based on a deterministic model which describes the O3 daily profile as a function of relative altitude (the difference between the altitude of the site and the lowest altitude within a 5 km radius) and the time of the day. Estimated AOT40 values (AOT40(e)) were evaluated against co-located automatic measurement stations and with 14 independent automatic stations located throughout Italy whose weekly mean O3 values were used to simulate passive samplers. AOT40 can be predicted by modelling passive sampling data (R2: 0.90; P<0.0001, SE of estimates: 3271 ppb h), although considerable deviations can occur for individual sites. Estimated AOT40 shows a distinct, significant latitudinal and altitudinal gradient. Taking the 3-year average as a whole, exceedance of critical level of 5000 ppb h occurs at 77-100% of the monitored sites, respectively.     

Preliminary background ozone concentrations in the mountain and coastal areas of Bulgaria

Urban and non-urban rural ozone (O3) concentrations are high in Bulgaria and often exceed the European AOT40 ecosystem as well as the AOT60 human health standards. This paper presents preliminary estimates to establish background, non-urban O3 concentrations for the southern region of Bulgaria. Ozone concentrations from three distinctly different sites are presented: a mountain site influenced by mountain-valley wind flow; a coastal site influenced by sea-breeze wind flow; and a 1700-m mountain peak site without 'local' wind flow characteristics. The latter offers the best estimate of 46-50 ppb for a background O3 level. The highest non-urban hourly value, 118 ppb, was measured at the mountain-valley site.     

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.     

Ozone exposure

Increased tropospheric ozone concentrations cause damage to both human health and the environment. To assess the exposure of forest areas and selected tree species to ozone, it is necessary to calculate the ozone exposure distribution. The present article describes the application of an ozone interpolation model to the calculation of the ozone exposure distribution in combination with forest inventory data. The exposure of forest regions to ozone was assessed by means of an AOT40 map (accumulated ozone exposure over a threshold of 40 ppb). The calculation was performed by hourly running of the model during the summer term and accumulation of the patterns that exceeded 40 ppb. The exposure of the primary Austrian tree species to ozone can be assessed due to the spatial relation of ozone exposure and tree species patterns. This spatial relation also allows the verification of assumptions concerning ozone-related tree damage.     

Ozone and forests in South-Western Europe--What have we learned?

Monitoring of forest condition and ozone (O3) at 83 sites in France, Italy, Luxenbourg, Spain and Switzerland resulted in a number of findings in relation to the knowledge of O3 exposure (concentration and cumulative AOT40), feasibility of the assessment of stomatal O3 flux and relationships between O3 and crown defoliation of beech and visible symptoms on native vegetation. However, the project provides evidence of issues to be addressed within the current monitoring system (data quality, validation sites and response indicators) and indications as to how the monitoring of O3 risk in the context of an effect-oriented monitoring program can be improved.     

Vertical Ozone Profile in the Lower Troposphere over Chicago

ABSTRACT

A 15-year (1981-95) climatology for the diurnal maximum ozone concentration (DMOC) was developed using 1-hr average ozone concentrations in the Baltimore-Washington area, which was made up of four regions: Baltimore, Washington, non-urban Maryland, and non-urban northern Virginia. The DMOC time series for each of these regions were divided into four terms representing different behavioral time scales: the long-term mean; the mean in-tra-annual perturbation; the interannual perturbation; and the synoptic perturbation. The urban regions had smaller values of the long-term mean ozone, but the annual range was larger. The values of the interannual perturbation were largest in the summer, when ozone production is significant, and smallest in the late winter and early spring. The interannual perturbation in the summer in the four regions consistently had positive departures in 1983, 1988, and 1991, and it had negative departures in 1981, 1984, 1985, 1989, 1990, and 1992. Summers with large positive interannual departures experienced a large number of ozone exceedances (i.e., relative to the 1-hr National Ambient Air Quality Standard of 125 parts per billion [ppb]), and summers with large negative departures experienced few or no exceedances. About 50% of the exceedances had concentrations ranging in value from 125-135 ppb, and about 75% had concentrations from 125-145 ppb.     

Study on the formation and transport of ozone in relation to the air quality management and vegetation protection in Tenerife (Canary Islands)

An experimental study on the formation and transport of ozone in ambient air was performed in Tenerife (Canary Islands) in order to investigate the processes affecting ozone levels and air quality. The special features of Tenerife (prevalence of the trade wind pattern (NE), orography and the specific location of the local ozone sources) permit to quantify the role of the ‘long-range transport from northern latitudes' versus the ‘formation and transport of ozone downwind of the main urban areas' of Tenerife. Levels of O₃, NO₂ and O_X were monitored in different types of environments to achieve this purpose. The results showed that: (1) upwind of the urban areas ozone is mainly transported from the ocean by trade winds, (2) local ozone titration (by NO) and ozone replenishment from the ocean are the main causes of ozone variations in urban and suburban areas, and (3) photochemical ozone production occurs downwind of the urban areas. Photochemical production causes daylight O₃ and O_X levels downwind of urban areas to be frequently (60% and 35% days/year, respectively) higher than upwind of the urban sites (O₃ and O_X excess frequently in the range 5–20 ppbv). Due to the above processes, different daily ozone cycles occur in short distances (<30 km), with maximum O₃ levels during daylight or night depending on the site. Ozone phytotoxicity was assessed by calculating the AOT40 index upwind and downwind of the main urban areas. The critical value for the 5-day-AOT40 index was simultaneously exceeded at the two sites (few times/year) during long-range transport events. During the additional exceedances of the critical value downwind of the urban area, relatively high 5-day-AOT40 values were recorded upwind of the urban site. Thus, long-range transport from northern latitudes may produce relatively high 5-days-AOT40 levels in the oceanic boundary layer. These results are important for the protection of the large number of endemic plants in the Canaries. The conceptual model discussed in this study may be qualitatively applied to other islands which possess features similar to those of Tenerife.