Low O3 Levels Research Articles

Effect of Host Plant Ozone Stress on Colorado Potato Beetles

Effects of ozone (O3) stress of potato, Solanum tuberosum L., on fecundity, larval growth and survival of Colorado potato beetles, Leptinotarsa decemlineata (Say), were measured in greenhouse and field experiments. Chronic O3 exposure caused moderate to severe foliar injury on an O3-sensitive cultivar (‘Red Norland’) but caused only minor injury an O3-resistant cultivar (‘Superior’). Foliar injury caused by O3 was greater on old than on young leaves but feeding by adult beetles was greater on young leaves in all experiments. Foliar analyses of the five uppermost leaves (nodes 1–5) showed higher carbon (C) and higher nitrogen (N) concentration in Superior than in Norland. There were no significant O3 effects on C or N and no cultivar × O3 interactions. Egg production by newly emerged adult beetles feeding on plants exposed to high O3 levels was not significantly different from egg production on plants exposed to low O3 levels, regardless of cultivar O3 sensitivity. Feeding and energy conversion efficiency of neonates and survival of larvae to the adult stage were not significantly affected by the O3 treatment. Although present levels of tropospheric O3 are high enough to significantly affect yield of sensitive potato cultivars, our results indicate no significant effect of ambient O3 concentrations on Colorado potato beetle populations.

Chronic Ozone Exposure and Photosynthate Partitioning into Starch in Soybean Leaves,

Photosynthesis, photosynthate partitioning, and translocation are reportedly affected by ozone (O3), but the sensitivity of these processes in relation to other potential targets is not known. In this study, rates of net photosynthetic CO2 assimilation (Pn) and carbohydrate accumulation in fully expanded leaves in soybean canopies in the field were examined following season‐long exposure either to low‐O3 conditions (20–30 nL L−1 7‐h daily average, charcoal‐filtered air) or to chronic midlevel concentrations (50–60 nL L−1, ambient air plus supplemental O3). O3‐sensitive (cv. Forrest) and less sensitive (cv. Essex) lines of soybean were compared at two growth stages corresponding to altered sink demand (i.e., vegetative and early pod fill). Starch was a significant sink for photosynthate, accounting for ca. 29% of carbon assimilation at the vegetative growth stage and 35% at the later reproductive stage. Effects of O3 on Pn or the proportion of photosynthate partitioned into starch were not detected; differences on the order of 15% would have been significant. The lack of O3 effects on partitioning indicates that translocation of photosynthate from the leaf was probably not altered by O3 during the light in this study. Transient prior effects of O3 on partitioning are not excluded since average starch levels were reduced—whereas average sucrose levels were increased—in leaves of Forrest exposed to elevated O3. In contrast, leaf growth was affected by O3 under these conditions for both cultivars, but growth was affected in different ways. Leaf area was reduced significantly at both growth stages for cv. Forrest, whereas specific leaf mass was increased significantly in cv. Essex. These results indicate that low levels of O3 can affect leaf growth and development without producing long‐term effects on photosynthesis or partitioning of photosynthate.

Influence of stratosphere‐troposphere exchange on tropospheric ozone over the tropical Indian Ocean during the winter monsoon

Ozone (O3) and relative humidity (RH) soundings, launched over the Indian Ocean during the 1998 winter monsoon (February–March), were analyzed. In the marine boundary layer (MBL), O3 mixing ratios were relatively low (10–20 ppbv) except close to the Indian subcontinent (40–50 ppbv) where profiles were strongly influenced by pollution. Sometimes, relatively low O3 levels were observed in the upper troposphere. These were associated with deep convection in regions where MBL O3 levels were also low. In the midtroposphere (300–500 hPa), O3 maxima (60–90 ppbv) were often found with low RH. A remarkable new finding of this study is that in more than a third of the profiles, laminae with very high O3 mixing ratios (up to 120 ppbv) were observed just below the tropical tropopause (between 100 and 200 hPa). Back trajectory analyses showed that these layers originated in the vicinity of the subtropical jet stream (STJ). We hypothesize that stratosphere‐troposphere exchange (STE) near the subtropical jet by either shear‐induced differential advection or clear‐air turbulence (CAT) caused the midtropospheric maxima (STE followed by descent) and the upper tropospheric laminae. Another new finding is that stratospheric intrusions were not only found near the STJ but also deep within the tropics. Given the thickness of the midtroposphere intrusions (typically 3–5 km) and the very high O3 mixing ratios of the upper tropospheric laminae, it seems that STE plays an important role in the tropical tropospheric O3 budget, at least over the Indian Ocean during the winter monsoon.

OZONE ADAPTATION IN MICE AND ITS ASSOCIATION WITH ASCORBIC ACID IN THE LUNG

We have previously shown that ozone (O3) adaptation occurred in rats after daily exposure to an "urban-type" concentration. The adaptation was positively associated with an excess of ascorbic acid (AA) in bronchoalveolar lavage fluid (BALF), suggesting that AA may play a role in the adaptation mechanism. This relationship was not seen at higher and more toxic exposures. The present work exposed mice to low and high levels of O3 to see if the adaptation?AA relationship is common among rodent species. Male CD-1 mice were studied during repeated 6-h/day exposures to 0.0 or 0.25 ppm O3 for 10 days and 10 days of recovery in air (experiment 1) and to 0.0, 0.5, or 1.0 ppm O3 for 5 days (experiment 2). Approximately 20 h after each daily exposure, groups of mice were randomly selected from each concentration type and examined for patterns of response. They were anesthetized (urethane, ip), intubated, and the lungs were lavaged with 37°C saline. BALF was assayed for cells, cell differential, protein, albumin, lactate dehydrogenase, lysozymes, N

Analysis of the CEPEX ozone data using a 3D chemistry-meteorology model

The ozone (O3) data collected during the Central Equatorial Pacific Experiment (CEPEX) are analysed with the aid of the 3D global photochemistry model MATCH-MPIC (Model of Atmospheric Transport and Chemistry-Max-Planck-Institute for Chemistry version). This study focuses on using MATCH-MPIC to address three specific questions: (1) are the individual CEPEX O3 soundings, in particular the extremely low O3 levels occasionally observed in the upper troposphere (UT), reproducible by a state-of-the-art global photochemical model driven with analysed meteorological data from the same time period as the measurements (March 1993): (2) are the CEPEX O3 data likely to be representative of the mean state of the regional atmosphere, or do they instead indicate the degree of variability in this region of the atmosphere; and (3) what causes the UT O3 minima? It is found that MATCH-MPIC is not able to reproduce the soundings obtained during CEPEX on an individual basis; however, the model does reproduce some of the key features present in the observations, such as UT minima and mid-tropospheric maxima similar to those observed during CEPEX. the UT O3 minima computed by the model are mainly due to convective pumping of low-O3 marine boundary-layer air, as is demonstrated by comparison with the results of a run in which convective transport of O3 is suppressed. the UT O3 minima simulated by MATCH-MPIC (with O3 between 5 and 10 nmol mol-1) are less intense than those observed (with O3 < 5 nmol mol-1), even at relatively high model spatial and temporal resolution, and with a convection scheme that would be expected to readily produce UT O3 minima via intense pumping of low-O3 marine boundary-layer air directly into the UT convective outflow regions. This may indicate that additional photochemical loss processes are involved, either in situ in the UT or, in particular, near the surface in the convective inflow regions. where the model tends to overestimate the observed O3 levels. In addition, although a significant temporal variability for O3 in this region is computed, it is still less than indicated by the observations in the UT. This high degree of variability implies that individual O3 soundings will often differ considerably from the mean over a longer period. For instance, 20-50% less O3 in the UT during the CEPEX period is computed with MATCH-MPIC than the average for March. Thus, the CEPEX expedition was perhaps fortunate in encountering extreme conditions which produced extensive UT O3 minima. which have helped to demonstrate one end of the large degree of variability of O3 in the tropical troposphere.

Analysis of the CEPEX ozone data using a 3D chemistry‐meteorology model

AbstractThe ozone (O3) data collected during the Central Equatorial Pacific Experiment (CEPEX) are analysed with the aid of the 3D global photochemistry model MATCH‐MPIC (Model of Atmospheric Transport and Chemistry‐Max‐Planck‐Institute for Chemistry version). This study focuses on using MATCH‐MPIC to address three specific questions: (1) are the individual CEPEX O3 soundings, in particular the extremely low O3 levels occasionally observed in the upper troposphere (UT), reproducible by a state‐of‐the‐art global photochemical model driven with analysed meteorological data from the same time period as the measurements (March 1993): (2) are the CEPEX O3 data likely to be representative of the mean state of the regional atmosphere, or do they instead indicate the degree of variability in this region of the atmosphere; and (3) what causes the UT O3 minima? It is found that MATCH‐MPIC is not able to reproduce the soundings obtained during CEPEX on an individual basis; however, the model does reproduce some of the key features present in the observations, such as UT minima and mid‐tropospheric maxima similar to those observed during CEPEX. the UT O3 minima computed by the model are mainly due to convective pumping of low‐O3 marine boundary‐layer air, as is demonstrated by comparison with the results of a run in which convective transport of O3 is suppressed. the UT O3 minima simulated by MATCH‐MPIC (with O3 between 5 and 10 nmol mol‐1) are less intense than those observed (with O3 &lt; 5 nmol mol‐1), even at relatively high model spatial and temporal resolution, and with a convection scheme that would be expected to readily produce UT O3 minima via intense pumping of low‐O3 marine boundary‐layer air directly into the UT convective outflow regions. This may indicate that additional photochemical loss processes are involved, either in situ in the UT or, in particular, near the surface in the convective inflow regions. where the model tends to overestimate the observed O3 levels. In addition, although a significant temporal variability for O3 in this region is computed, it is still less than indicated by the observations in the UT. This high degree of variability implies that individual O3 soundings will often differ considerably from the mean over a longer period. For instance, 20‐50% less O3 in the UT during the CEPEX period is computed with MATCH‐MPIC than the average for March. Thus, the CEPEX expedition was perhaps fortunate in encountering extreme conditions which produced extensive UT O3 minima. which have helped to demonstrate one end of the large degree of variability of O3 in the tropical troposphere.

Measurements of nitrogen oxides and a simple model of NOy fate in the remote North Atlantic marine atmosphere

NO and NOy (total reactive oxidized nitrogen) were measured at a site in the Azores (27.322°W, 38.732°N, 1 km altitude) over a 3 week period in August and September 1993, during the first summer intensive of the North Atlantic Regional Experiment (NARE). These measurements were performed to determine background reactive nitrogen oxides levels and to assess the impact that long‐range transport of reactive nitrogen oxides associated with human activities have on these levels. Median NOy mixing ratios during background marine boundary layer (MBL) periods ranged from 59 to 93 parts per trillion by volume (pptv), with an overall median of 73 pptv. Analysis of back trajectories, low and uncorrelated CO and O3 levels, and low levels of MBL NOy indicate that the central North Atlantic region was not influenced by direct transport of anthropogenic emissions during the period of this study. Changes in NOy levels during two MBL periods with adjacent in and out‐of‐cloud events indicated that up to 45–47% of MBL NOy was scavenged by clouds. However, mean NOy levels during all in‐cloud periods (∼70 pptv) and all out‐of‐cloud periods (∼80 pptv) were not significantly different, apparently because of variability in MBL NOy levels. In addition to the MBL periods, there were two periods when the site was within the free troposphere (FT), as indicated by vertical soundings and weather conditions at the site. FT NOy mixing ratios were ≥280 pptv and ≥400 pptv during these two periods. The median clear‐sky FT NO level during the hour centered on solar noon was 16 pptv. A mass balance model considering FT/MBL exchange and MBL removal processes is used to find the NOy MBL effective first‐order loss lifetime (∼1.2 days) and the NOy, MBL e‐folding response time due to both effective first‐order loss processes and subsidence‐induced ventilation of the MBL (∼0.9 days). The apparent rapid loss of MBL NOy, implies that it will respond rapidly to changes in the overlying FT, but that correlations of NOy with trace gases with slower MBL removal, such as O3 and CO, will be degraded within the subsidence‐influenced MBL.

Impact of lightning and convection on reactive nitrogen in the tropical free troposphere

Latitudinal distributions of NO, NOy, O3, CO, CH3I, and H2O mixing ratios at 8.9–12 km were obtained between 30°N and 10°S by DC‐8 aircraft measurements made in February 1994 during Pacific Exploratory Mission‐West B (PEM‐West B). Very low NOy mixing ratios with a median value of 51 parts per trillion by volume (pptv) were observed at 9.5–12 km at 1°N–14°N during two flights made within 3 days. A very low median O3 mixing ratio of 19 parts per billion by volume (ppbv) and high mixing ratios of H2O and CH3I were simultaneously observed, suggesting that the low NOy values were probably due to the convective transport of air from the tropical marine boundary layer to this altitude. The median NOy/O3 ratio being a factor of 2 smaller than in the air masses in the tropical marine boundary layer might suggest the possibility that the heterogeneous removal of HNO3 during convective transport further reduced NOy levels. In addition to the measurements between 9.5 and 12 km, low values of NOy and O3 were observed between 4 and 12 km at 1°N. Divergent wind fields at 200 and 1000 hPa and infrared (IR) cloud images show that there was large scale convection (&gt;1000 km × 1000 km) in the northeast of New Guinea Island centered around 0°S and 150°E as part of systematic convective activity of the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ). This type of large scale convection could have transported air with low levels of NOy and O3 to the middle and upper troposphere over a wide area in the tropics. On the other hand, NO mixing ratios of 50–200 pptv and high NOx/NOy ratios of 0.4–0.6 were observed at 9.5 km between 4°S and 10°S. High H2O mixing ratios of 600–1200 parts per million by volume (ppmv) and low CO mixing ratios of 65 ppbv observed in the air mass indicated that the high NO values were probably due to NO production by lightning. Satellite observations showed relatively frequent lightning flashes over the New Guinea Island for 3 days prior to the aircraft measurements. These results are considered to be consistent with the idea that, in general, marine convection is not accompanied by lightning activity, whereas convection over land is. Because of the large areal extent of the influences from these processes, the convective transport of low NOy air and NO production by lightning should play critical roles in controlling the abundance of reactive nitrogen in the equatorial region.

Seasonal changes in root and soil respiration of ozone‐exposed ponderosa pine (Pinus ponderosa) grown in different substrates

Exposure to ozone (O3 ) has been shown to decrease the allocation of carbon to tree roots. Decreased allocation of carbon to roots might disrupt root metabolism and rhizosphere organisms. The effects of soil type and shoot O3 exposure on below-ground respiration and soil microbial populations were investigated using container-grown ponderosa pine (Pinus ponderosa Laws.) growing in a low-nutrient soil, or a fertilizer-amended organic potting media, and exposed to one of three levels of O3 for two growing seasons in open-top exposure chambers. A closed system, designed to measure below-ground respiratory activity (CO2 production, O2 consumption and RQ-Respiration Quotient; (CO2 :02 ) of plants growing in pots, was used monthly to monitor below-ground respiration of 3-yr-old ponderosa pine. Although seasonal differences were detected, CO2 production (μmol h-1 g-1 total root d. wt), O2 consumption (μmol h-1 g-1 total root d. wt) and RQ (CO2 :O2 ) increased with increasing O3 exposure level. Seasonal patterns showed increased respiration rates during periods of rapid root growth in spring and early fall. Respiration quotient tended to decrease during known periods of active root growth in control seedlings, but a similar response was not observed in O3 -treated seedlings. Responses to O3 were greatest in the soil-grown plants, which had a lower fertility level than media-grown plants. Although root d. wt was decreased, root: shoot ratios did not change in response to O3 . Soil-grown plants had higher root-shoot ratios than media-grown plants, reflecting the lower fertility of the soil. Plant exposure to O3 was found to affect both active and total populations of soil organisms. In both organic potting media and in soil, biomass of active soil fungi, and the ratio of active-fungal to active-bacterial biomass increased with increasing plant exposure to O3 . The effect of O3 on total fungal and bacterial biomass was not linear: at low O3 levels, total fungal and bacterial biomass increased; at the high O3 level, total fungal and bacterial biomass decreased compared with those of controls. Our results show that O3 exposure to shoots significantly disrupts CO2 production and O2 consumption of soil and roots of ponderosa pine seedlings. Below-ground respiratory differences were thought to be a result of changes in respiratory substrates, carbon refixation within the plant and soil microbial activity. Ozone also changes below-ground RQ, suggesting that O3 substantially disrupts root metabolism and interactions with rhizosphere organisms. Ozone exposure of ponderosa pine grown in different soil types can disrupt below-ground respiration and influence populations of soil organisms without alteration of biomass partitioning between above- and below-ground plant components. Collectively, the effect of O3 on the below-ground system is of concern since it is likely that these changes are accompanied by a change in the ability of root systems to acquire nutrient and water resources and possibly to synthesize amino acids and proteins necessary for normal plant function.

Short-term effects of ambient oxidant exposure on mortality: a combined analysis within the APHEA project. Air Pollution and Health: a European Approach.

The Air Pollution and Health: a European Approach (APHEA) project is a coordinated study of the short-term effects of air pollution on mortality and hospital admissions using data from 15 European cities, with a wide range of geographic, sociodemographic, climatic, and air quality patterns. The objective of this paper is to summarize the results of the short-term effects of ambient oxidants on daily deaths from all causes (excluding accidents). Within the APHEA project, six cities spanning Central and Western Europe provided data on daily deaths and NO2 and/or O3 levels. The data were analyzed by each center separately following a standardized methodology to ensure comparability of results. Poisson autoregressive models allowing for overdispersion were fitted. Fixed effects models were used to pool the individual regression coefficients when there was no evidence of heterogeneity among the cities and random effects models otherwise. Factors possibly correlated with heterogeneity were also investigated. Significant positive associations were found between daily deaths and both NO2 and O3. Increases of 50 micrograms/m3 in NO2 (1-hour maximum) or O3 (1-hour maximum) were associated with a 1.3% (95% confidence interval 0.9-1.8) and 2.9% (95% confidence interval 1.0-4.9) increase in the daily number of deaths, respectively. Stratified analysis of NO2 effects by low and high levels of black smoke or O3 showed no significant evidence for an interaction within each city. However, there was a tendency for larger effects of NO2 in cities with higher levels of black smoke. The pooled estimate for the O3 effect was only slightly reduced, whereas the one for NO2 was almost halved (although it remained significant) when two pollutant models including black smoke were applied. The internal validity (consistency across cities) as well as the external validity (similarities with other published studies) of our results on the O3 effect support the hypothesis of a causal relation between O3 and all cause daily mortality. However, the short-term effects of NO2 on mortality may be confounded by other vehicle-derived pollutants. Thus, the issue of independent NO2 effects requires additional investigation.

Ozone‐induced oxidative stress: Mechanisms of action and reaction

In this review we explore several models which might explain ozone (O3)‐induced injury to plant foliage. Ozone enters the cell through the wall and plasma membrane where active oxygen species are generated. If the concentration of O3 is very high, unregulated cell death will occur. Alternatively, the active oxygen species, or succeeding reaction products, may serve as elicitors of regulated plant responses. These regulated responses include the induction of ethylene which could serve as a primary signal for—or a facilitator of—subsequent responses. The role of regulated suppression of photosynthetic genes and induction of chitinases and β‐1,3‐glucanase in programmed cell death is explored. Induction of antioxidants, enzymes of lignification and glutathione‐S‐transferase are discussed in the context of O3‐induced cell repair or cell protection. A second model is postulated to explain induction of accelerated foliar senescence by low levels of O3. The notion that O3‐induced elicitation of responses in the nucleus might lead to increased oxidative stress in the chloroplast is considered as a mechanism for accelerating the rate of degradation of ribulose‐1,5‐bisphosphate car‐boxylase/oxygenase (Rubisco). The mechanisms by which O3 induces loss of Rubisco, and the relationship to accelerated foliar senescence are discussed.

The Effect of Outdoor Fungal Spore Concentrations on Daily Asthma Severity

The relationship between day-to-day changes in asthma severity and combined exposures to community air pollutants and aeroallergens remains to be clearly defined. We examined the effects of outdoor air pollutants, fungi, and pollen on asthma. Twenty-two asthmatics ages 9-46 years were followed for 8 weeks (9 May-3 July 1994) in a semirural Southern California community around the air inversion base elevation (1,200 ft). Daily diary responses included asthma symptom severity (6 levels), morning and evening peak expiratory flow rates (PEFR), and as-needed beta-agonist inhaler use. Exposures included 24-hr outdoor concentrations of fungi, pollen, and particulate matter with a diameter < 10 microns (PM10; maximum = 51 micrograms/m3) and 12-hour day-time personal ozone (O3) measurements (90th percentile = 38 ppb). Random effects longitudinal regression models controlled for autocorrelation and weather. Higher temperatures were strongly protective, probably due to air conditioning use and diminished indoor allergens during hot, dry periods. Controlling for weather, total fungal spore concentrations were associated with all outcomes: per minimum to 90th percentile increase of nearly 4,000 spores/m3, asthma symptom scores increased 0.36 (95% CI, 0.16-0.56), inhaler use increased 0.33 puffs (95% CI, -0.02-0.69), and evening PEFR decreased 12.1 l/min (95% CI, -1.8-22.3). These associations were greatly enhanced by examining certain fungal types (e.g., Alternaria, basidiospores, and hyphal fragments) and stratifying on 16 asthmatics allergic to tested deuteromycete fungi. There were no significant associations to low levels of pollen or O3, but inhaler use was associated with PM10 (0.15 inhaler puffs/10 micrograms/m3; p < 0.02). These findings suggest that exposure to fungal spores can adversely effect the daily respiratory status of some asthmatics.

The effect of outdoor fungal spore concentrations on daily asthma severity.

The relationship between day-to-day changes in asthma severity and combined exposures to community air pollutants and aeroallergens remains to be clearly defined. We examined the effects of outdoor air pollutants, fungi, and pollen on asthma. Twenty-two asthmatics ages 9-46 years were followed for 8 weeks (9 May-3 July 1994) in a semirural Southern California community around the air inversion base elevation (1,200 ft). Daily diary responses included asthma symptom severity (6 levels), morning and evening peak expiratory flow rates (PEFR), and as-needed beta-agonist inhaler use. Exposures included 24-hr outdoor concentrations of fungi, pollen, and particulate matter with a diameter < 10 microns (PM10; maximum = 51 micrograms/m3) and 12-hour day-time personal ozone (O3) measurements (90th percentile = 38 ppb). Random effects longitudinal regression models controlled for autocorrelation and weather. Higher temperatures were strongly protective, probably due to air conditioning use and diminished indoor allergens during hot, dry periods. Controlling for weather, total fungal spore concentrations were associated with all outcomes: per minimum to 90th percentile increase of nearly 4,000 spores/m3, asthma symptom scores increased 0.36 (95% CI, 0.16-0.56), inhaler use increased 0.33 puffs (95% CI, -0.02-0.69), and evening PEFR decreased 12.1 l/min (95% CI, -1.8-22.3). These associations were greatly enhanced by examining certain fungal types (e.g., Alternaria, basidiospores, and hyphal fragments) and stratifying on 16 asthmatics allergic to tested deuteromycete fungi. There were no significant associations to low levels of pollen or O3, but inhaler use was associated with PM10 (0.15 inhaler puffs/10 micrograms/m3; p < 0.02). These findings suggest that exposure to fungal spores can adversely effect the daily respiratory status of some asthmatics.

Upper limit for the generation of N2O from reaction of O2(A3Σu+) and N2

Evidence from several sources suggest possible in situ production of N 2 O in the stratosphere. Considering that solar photoabsorption provides a large stratospheric source of O 2 (A 3 Σ u + ), and since vibrational levels of v6 are primarily removed by N 2 , the O 2 (A 3 Σ u + )+N 2 system is studied to determine whether it is an atmospherically significant N 2 O source. Using 243–250 nm photoexcitation to produce vibrationally excited O 2 (A 3 Σ u + , v=7–10), and frequency modulation diode laser spectroscopy as the detector of N 2 O, we examine the products generated in a closed cell. We thereby set an upper limit of 0.002% on the N 2 O yield for the process, and conclude that stratospheric N 2 O production by this route is not significant compared to existing ground-based sources. The stability of N 2 O in an N 2 O–O 3 –N 2 mixture subjected to prolonged 245 nm radiation is also studied. For low levels of O 3 (10 ppm) and N 2 O (40–90 ppb), no loss of N 2 O is observed.

EFFECTS OF REPEATED EXPOSURES OF GERIATRIC RATS TO OZONE AND PARTICLE-CONTAINING ATMOSPHERES: AN ANALYSIS OF BRONCHOALVEOLAR LAVAG E AND PLASMA PROTEINS

Inhalation of ozone (O3) and airborne particles less than 10 m (PM-10) in mass median aerodynamic diameter (MMAD) is associated with adverse health effects in sensitive human populations, and pulmonary injury in laboratory animals. In order to simulate environmental exposures of sensitive individuals, such as the elderly, geriatric rats were exposed to O and particulate mixtures. This pilot study determined whether the pul3 monary effects of higher O3 concentrations reported in earlier studies are also seen after repeated exposures to lower O3 concentration used in this study, whether the O3 effects are modified by PM-10 components, and whether plasma biomarkers can be developed as noninvasive tests of pulmonary injury. Male Fischer 344 rats, 22-24 mo old, were exposed 4 h/ day, 3 days/wk for 4 wk to (a) purified air, (b) O3 (0.2 ppm), (c) low-level mixture of carbon (C, 50 g/ m3) plus ammonium bisulfate (ABS, 70 g/m3) plus O3, and (d) high-level mixture of C (100 g/m3) plus ABS (140 g/m3) plus O3. Twenty-four hours after the last exposure, groups of rats were prepared for measurement of protein and albumin concentrations in bronchoalveolar lavage (BAL) as markers of airways permeability, and blood was drawn for analysis of plasma immunoreactive prolyl 4-hydroxylase and fibronectin. Exposures to O3 and O3 /particle mixtures did not produce a consistent, significant change in the BAL markers of permeability. Nonsignificant changes represented individual animal variations. On the other hand, a significant increase in plasma fibronectin was observed in the group exposed to O3, but not in the rats exposed to O3/particle combinations. Such an effect was not observed for plasma immunoreactive prolyl 4- hydroxylase. The inability of low-level O3 and O3/particle combinations to produce intra pulmonary effects suggests potential utility of plasma biomarkers for the evaluation of pulmonary toxicity. These results also suggest modification of O3 effects upon its combination with PM-10.

Ground‐based measurements of NOx and total reactive oxidized nitrogen (NOy) at Sable Island, Nova Scotia, during the NARE 1993 summer intensive

Measurements of NO, NO2, and total reactive oxidized nitrogen (NOy) were added to ongoing measurements of aerosols, CO, and O3 at Sable Island (43°55′N, 60°01′W), Nova Scotia, during the North Atlantic Regional Experiment (NARE) 1993 summer intensive. Ambient levels of NOx and NOy were found to be highly variable, and elevated levels can be attributed to the transport of polluted continental air or presumably to relatively fresh emissions from sources upwind (e.g., ship traffic). The median values for NOx and NOy are 98 and 266 parts per trillion by volume (pptv), respectively. A multiday pollution episode occurred during which elevated NOx and NOy were observed with enhanced levels of O3, CO, and condensation nuclei. Air masses of recent tropical marine origin characterized by low and constant levels of O3 and CO were sampled after Hurricane Emily. The correlation between ozone and CO is reasonably good, although the relation is driven by the single pollution episode observed during the study. The correlation of O3 with NOy and with NOy‐NOx is complicated by the presumed NOy removal processes in the marine boundary layer. Examination of the radiosonde data and comparisons of the surface data with those obtained on the overflying aircraft provide clear indications of vertical stratification above the site.

Ozone Adaptation in Rats after Chronic Exposure to a Simulated Urban Profile of Ozone

Ozone Adaptation in Rats after Chronic Exposure to a Simulated Urban Profile of Ozone. Wiester, M. J., Tepper, J. S., Doerfler, D. L., and Costa, D. L. (1995). Fundam. Appl. Toxicol.24, 42-51.Studies in both humans and rats have indicated that certain pulmonary responses induced by exposure to an acute provocative concentration of ozone (O3) will eventually attenuate if the exposure is repeated on a daily basis. This phenomenon is commonly referred to as O3 adaptation. Whether or not a "state" of adaptation develops due to long-term low level O3 exposure is unknown. Two human studies have reported adaptation in subjects living in Los Angeles during periods when ambient O3 concentrations have been relatively high. At present, however, we are not aware of comparable information from rats. This study assessed O3 adaptation in rats following chronic (12 or 18 months) exposure and after a 4-month recovery period. A chronic exposure pattern, similar to that found in an urban area during the summer (0.06 ppm O3 for 13 hr/day, 7 days/week; Monday-Friday, peak to 0.25 ppm O3, over 9 hr), was used. To assess whether adaptation had occurred and/or persisted, awake rats were challenged with high provocative concentrations of O3 for up to 2 hr. During a challenge, rats were monitored for typical O3-induced alterations in spontaneous breathing parameters (e.g., increase in breathing frequency and decrease in tidal volume). Adaptation was defined as attenuation of breathing response during the challenge in rats chronically exposed to O3 as compared to that in "control" rats (chronically exposed to air). Adaptation was found in the rats within 8 hr following the chronic O3 exposure but not after the 4-month recovery period. Spontaneous breathing parameters that were significantly attenuated in the chronically exposed rats were breathing frequency, tidal volume, inspiratory and expiratory times, and maximum expiratory flow. We conclude that rats demonstrated adaptation to O3 after long-term exposure to an urban-type O3 profile and that the adaptation was not seen 4 months postexposure. These results suggest that exposure to environmental O3 in Los Angeles air may have been responsible for the adaptation found in residential subjects.

Ozone Adaptation in Rats after Chronic Exposure to a Simulated Urban Profile of Ozone

Studies in both humans and rats have indicated that certain pulmonary responses induced by exposure to an acute provocative concentration of ozone (O3) will eventually attenuate if the exposure is repeated on a daily basis. This phenomenon is commonly referred to as O3 adaptation. Whether or not a “state” of adaptation develops due to long-term low level O3 exposure is unknown. Two human studies have reported adaptation in subjects living in Los Angeles during periods when ambient O3 concentrations have been relatively high. At present, however, we are not aware of comparable information from rats. This study assessed O3 adaptation in rats following chronic (12 or 18 months) exposure and after a 4-month recovery period. A chronic exposure pattern, similar to that found in an urban area during the summer (0.06 ppm O3 for 13 hr/day, 7 days/week; Monday–Friday, peak to 0.25 ppm O3, over 9 hr), was used. To assess whether adaptation had occurred and/or persisted, awake rats were challenged with high provocative concentrations of O3 for up to 2 hr. During a challenge, rats were monitored for typical O3-induced alterations in spontaneous breathing parameters (e.g., increase in breathing frequency and decrease in tidal volume). Adaptation was defined as attenuation of breathing response during the challenge in rats chronically exposed to O3 as compared to that in “control” rats (chronically exposed to air). Adaptation was found in the rats within 8 hr following the chronic O3 exposure but not after the 4-month recovery period. Spontaneous breathing parameters that were significantly attenuated in the chronically exposed rats were breathing frequency, tidal volume, inspiratory and expiratory times, and maximum expiratory flow. We conclude that rats demonstrated adaptation to O3 after long-term exposure to an urban-type O3 profile and that the adaptation was not seen 4 months postexpo-sure. These results suggest that exposure to environmental O3 in Los Angeles air may have been responsible for the adaptation found in residential subjects.

The Effect of Pre-Exposure to 0.12 ppm of Ozone on Exercise-Induced Asthma

Ozone (O3) is a common air pollutant that has been associated with a dose-dependent increased bronchial responsiveness and airway inflammation. Previous investigations have shown increased airway responsiveness to allergens in asthmatics pre-exposed to 0.12 ppm of O3 for 1 h. In the present study, we investigated whether inhalation of relatively low levels of O3 would modify the degree of exercise-induced bronchoconstriction. We studied 15 "never smokers" with mild stable asthma (7 male and 8 female) (mean age [+/- SD] 25.6 +/- 6.8 years) who had exhibited a fall in FEV1 > 15 percent after a standard 6-min treadmill exercise challenge test on the screening day. This was a double-blind, placebo-controlled study. The patients were randomized to receive either O3 or air (placebo) before performing the exercise challenge again. The average highest 1-h daily O3 concentrations in Toronto during O3 days and air days were 0.017 +/- 0.017 and 0.014 +/- 0.005 ppm, respectively. The O3 concentration inside the chamber averaged 0.122 +/- 0.005 ppm on O3 days and 0.002 +/- 0.001 on placebo days. Partial and complete flow volume curves were done before and after this exposure, and also 5, 10, 15, 20, 30, and 60 min postexercise. The percent fall in FEV1 on the O3 chamber day and on the air chamber day was the same (F = 0.67, p = 0.67, NS) as well as the percent fall in V40p (F = 0.91, p = 0.49, NS). A repeated measures analysis of variance to test the effects of exposure on the time course of the airway response after exercise showed no significant difference between the 2 days. There was also no significant difference in maximal percentage fall in FEV1 (25.6 +/- 8.6) or V40p (62.2+18.6) following O3 exposure, and FEV1 (26.8 +/- 9.4)(p = 0.64) or V40p (65.3+4.31)(p = 0.60) following air. Our data indicate that previous exposure at rest to a concentration of O3 that has previously been shown to augment the bronchoconstriction response to allergens did not increase the bronchoconstriction response to subsequent exercise nor did it change the time course of such bronchoconstriction.

Effects of Atmospheric O3 on Azolla-Anabaena Symbiosis

Cultures of water fern Azolla pinnata R. Br. exposed for 1 week to either 30, 50 or 80 nl l-1 O3 showed significant reductions in rates of growth and N2 fixation, and had fewer heterocysts. Although the levels of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) activity were decreased by low concentrations of O3 exposures (30 or 50 nl l-1), significant increases in levels of the same enzymes were caused by higher concentrations of O3 (80 nl l-1). Increased levels of total protein, polyamines (putrescine and spermidine), and the xanthophyll-cycle precursor of abscisic acid (ABA), violaxanthin, were also found with higher levels of O3 (80 nl l-1). Levels of ABA itself were significantly increased by low level O3 fumigation (30 nl l-1) but significantly decreased by exposure to 80 nl l-1 O3. This may indicate that higher levels of atmospheric O3 inhibit the final stages of ABA biosynthesis from violaxanthin.