High Concentrations Of Tropospheric Ozone Research Articles

Physicochemical characteristics of lodging susceptibility of rice cultivars in response to ozone exposure

High tropospheric ozone concentrations reduce rice yield and grain quality, which imposes a serious threat to food security in Asia. This study aimed at determining the effect of ozone on rice lodging, an unpredictable constraint for achieving high yield and good quality in rice production under climate change. Two rice cultivars with different ozone sensitivity were exposed to ozone concentration of 80 ppb (8 h per day) and control conditions (13 ppb) in natural-light fumigation chambers from tillering to maturity. The pushing resistance of intact plants and the lodging-related culm traits were examined. Ozone exposure significantly decreased the in-situ pushing resistance of intact plant or single culm in the ozone-sensitive cultivar YD6, but had no effects in the ozone-tolerant cultivar WYJ27. Ozone reduced breaking resistance and bending moment to a similar magnitude, resulting in no change of lodging index when averaged across all rice basal internodes. In general, WYJ27 was less responsive to ozone than YD6. Negative ozone effects on lodging-related culm traits of YD6 included reductions in the internode dry weight as well as the dry weight per unit internode length, decreases in internode diameter, cross section area and culm wall thickness of basal internodes, and reduced concentrations of soluble sugar and starch. Correlation analysis indicated that ozone-induced decrease in culm strength of YD6 was mainly attributed to the thinner internodes and the smaller culm density due to less nonstructural carbohydrate deposition. The ozone-sensitivity of YD6 was confirmed by its high yield reduction of 25 %, caused by an 11 % decrease in spikelet number per panicle and a 10 % decrease in fulfilled grain weight. The results suggested that rice ozone sensitivity in yield was in consistent with that in stem strength, which could result in no change of lodging index under greenhouse conditions. The realistic lodging susceptibility of these cultivars in response to ozone pollution in open paddy fields, where rice was often subjected to wind and rain during ripening stage, needs further investigation.

Trends in Summer-Time Tropospheric Ozone during COVID-19 Lockdown in Indian Cities Might Forecast a Higher Future Risk

High concentrations of tropospheric ozone (O3) is a serious concern in India. The generation and atmospheric dynamics of this trace gas depend on the availability of its precursors and meteorological variables. Like other parts of the world, the COVID-19 imposed lockdown and restrictions on major anthropogenic activities executed a positive impact on the ambient air quality with reduced primary pollutants/precursors load. In spite of this, several reports pointed towards a higher O3 in major Indian cities during the lockdown. The present study designed with 30 pan-Indian mega-, class I-, and class II-cities revealed critical and contrasting aspects of the geographical location, source, precursor, and meteorological variable dependency of the spatial and temporal O3 formation. This unexpected O3 increase in the major cities might forecast the probable future risks for the National Air Quality policies, especially O3 pollution management, in the Indian sub-continent. The results also pointed towards the severity of the north Indian air quality, followed by the western and eastern parts. We believe these results will definitely pave the way for researchers and policy-makers for predicting/framing regional and/or national O3 management strategies in the future.

The interaction of ozone and aerosol in a semi-arid region in the Middle East: Ozone formation and radiative forcing implications

Investigations on the variations in ozone concentration, aerosol properties, and ozone-aerosol interactions can help to better understand the atmospheric radiation budget and their effects on climate. In this study, the interaction of ozone and aerosol was analyzed over Zanjan, Iran. The seasonal cycle of total column ozone demonstrated that high ozone concentrations often occur in early spring and winter. However, the seasonal cycle of tropospheric ozone showed that high concentrations of tropospheric ozone often happen in the spring and summer. The high values of Aerosol Optical Depth (AOD), Particulate Matter (PM10) and Absorption Aerosol Optical Depth (AAOD) were observed in the spring and summer, whereas low values in the fall and winter. The results showed that tropospheric ozone and AOD were negatively correlated during the spring and summer seasons. Especially on dusty days, the aerosol has reduced the concentration of ozone in the atmosphere. The correlation coefficients between PM10 and ozone were negative during dusty days/months. Moreover, the relation of ozone with a fine mode fraction of AOD depicted negative correlations in the spring and summer and positive correlation in the fall and winter. A comprehensive study on the effects of the aerosol types on ozone concentration showed that anthropogenic fine mode aerosols such as urban/industrial had a positive impact on ozone production, contrary to the effect of dust, which reduced ozone. This study showed that coarse mode aerosols such as dust with higher AOD, reduced the sunlight to reach the earth's surface. As a result, aerosol radiative forcing (ARF) values were found to be more negative at the surface; thus, the photolysis rate decreased considerably, and the concentration of surface ozone was reduced significantly.

Synoptic circulation patterns and local sources associated to high concentrations of tropospheric ozone in rural and suburban areas in southwestern Spain

In Extremadura, Southwest Spain, environmental conditions combined with a complex mixture of natural and anthropogenic precursors favour the appearance of episodes of high concentrations of tropospheric ozone, whose levels sometimes exceed legal thresholds. In this mainly rural region, no study has been carried out to identify and interpret regional ozone episodes, so this work aims to fill this gap. Ozone and precursor (nitrogen oxides and organic compounds) levels from six representative air quality monitoring stations located in suburban and rural areas have been used to investigate selected ozone episodes during 2014 and 2015. Air mass back-trajectories were used to assess the contribution of long-range transport, resulting in Europe, Mediterranean and Peninsular routes. The analysis of synoptic patterns revealed that high pressures with stationary character, which occur in different synoptic conditions, have an important role in the increment of the ozone values. Finally, the evaluation of the results showed that the daily ozone cycle is mainly regulated by the emissions of precursors in the surrounding environment, the high temperatures that occur during the day and the influence of atmospheric conditions on the low troposphere under anticyclonic conditions that promote ozone accumulation.

Tailpipe VOC Emissions from Late Model Gasoline Passenger Vehicles in the Japanese Market

High concentrations of tropospheric ozone remain a concern, and strategies to reduce the precursors of ozone, volatile organic compounds (VOCs) and nitrogen oxides, have been established in many countries. In this study, chassis dynamometer experiments were conducted for 25 late model gasoline passenger vehicles in the Japanese market to evaluate VOC emission trends. Tailpipe emissions were collected and analyzed using gas chromatography mass spectrometer and flame ionization detector, and liquid chromatography–mass spectrometry (LC-MS). Results showed that tailpipe VOC emissions increased linearly with vehicle mileage due to deterioration of the three-way catalysis converter used to purify the toxic components in vehicle emissions. Distance normalized total VOC emissions showed that port injection mini-sized vehicles were effective in decreasing tailpipe VOC emissions because of their low vehicle weight. The VOC composition of tailpipe emissions was dependent on the fuel type (regular or premium gasoline). VOC emissions from hybrid vehicles were similar to those of other vehicles because cooling of the three-way catalysis converter during battery operations sometimes tended to reduce catalyst effectiveness during engine operations. However, it can also be assumed that each manufacturer is aware of this phenomenon and is taking action. Further monitoring of hybrid vehicles is warranted to ensure that these vehicles remain an effective means of mitigating air pollution.

First defense mechanisms of ornamental species suitable for urban green spaces in China exposed to ozone

High concentrations of tropospheric ozone (O3) represent a serious problem in the Northern Hemisphere, especially in hot spots as urban areas of China. In this study, the first defense mechanisms (i.e., stomatal behavior and morphology, ascorbate regulations) of three widely-used ornamental plant species (Cotinus coggygria Scop., Rosa chinensis Jacq., Tagetes erecta L.) to O3 were evaluated to test the suitability of these species for utilization in urban green spaces (UGS). Seedlings were exposed to (i) ambient air (AA), (ii) AA + 60 ppb O3 (AA + 60), and (iii) AA + 120 ppb O3 (AA + 120) for 60 (C. coggygria and R. chinensis) or 32 days (T. erecta), 9 h d−1. Considering the different physiological responses and O3 sensitivity among the species, data of the present study reveal that: (i) O3-induced stomatal closure observed in the three species was not an avoidance-strategy given the lack of a significant relation between gs and O3 fluxes into the leaves, a feature that confirm the strong negative effects of O3 on the photosynthetic metabolism previously reported; and (ii) stomatal morphology, as well as ascorbate regulations, seem to play a pivotal role in the responses of the investigated species to O3”. Overall, our study highlights the importance of investigating the first defense mechanisms adopted by plants to cope with urban environmental stresses, in order to direct a correct management of UGS.

Evaluation of El Niño-Southern Oscillation influence on 30 years of tropospheric ozone concentrations in Houston

Surface observations collected over the period 1980–2010 at three Continuous Ambient Monitoring Stations located in Houston, Texas were leveraged to create a long-term composite dataset of tropospheric ozone measurements. This dataset was used to evaluate large-scale influences and their relationship to exceedances of the 70 ppbv National Ambient Air Quality Standard for ozone. A linear regression fit to monthly mean daily peak 8-h concentrations for each month revealed a decreasing trend for the duration of the study period. After removal of this temporal trend, 8-h peak values averaged for each month featured peaks in springtime and late-summer with relative minima in mid-summer and winter. Stratification of the database by El Niño-Southern Oscillation phase using the Oceanic Niño Index revealed a statistically significant (α = 0.05) dependence of peak 8-h concentration on ENSO phase, with an enhancement of 5.8, 4.8, and 7.0 for March, April, and June during warm phase years, while cool phase years had statistically significant enhancements of 5.0, 4.0, and 3.6 ppbv in February, October, and December relative to neutral conditions. Importantly, relative to neutral conditions, “El Nino years” produce 26% more exceedences while “La Nina years” produce 23% fewer. The earlier onset of ozone seasons both in spring and late summer during El Nino years leads to more exposure to direct sunlight and more seasonal photochemical production, while the delayed late summer season during La Nina years leads to decreased sunlight and suppressed seasonal photochemical production relative to neutral years. Evaluation of the number of exceedances per month for each ENSO regime also suggests high tropospheric ozone concentrations in the fall and spring, with 4.4 and 6.8 exceedances per month in June and September, respectively for the warm phase. During cool phase conditions, Houston averaged 5.0 exceedances per month in September. Exceedances for neutral conditions ranged from zero exceedances in December to 2.2 exceedances in May and 5.0 in September. Analysis of exceedance data and mean values in light of parameters of the underlying distribution of daily peak 8-h data suggests that ENSO may influence the shape of those distributions, influencing both background ozone concentrations and the number of exceedances. Fast Fourier analysis indicated a common spectral signature for the ENSO and ozone spectra. This finding has implications for air quality mitigation strategies employed during warm phase and cool phase years.

On the interactions among tropospheric ozone levels and typical environmental stresses challenging Mediterranean crops.

The main environmental stresses of Italian croplands are discussed in relation to their interactions with ozone effects on crops. Water deficit and salinization are frequent in Mediterranean environments during spring-summer causing a decrease of soil water potential and water uptake by roots and consequently stomatal closure. These stresses also stimulate secondary metabolism and antioxidant accumulation, which also serves as a stress protection mechanism. High concentrations of tropospheric ozone are common all over Italy during the spring-summer season. Ozone injuries to vegetation are related to its penetration into plant tissues, mostly via stomatal uptake, rather than to tropospheric concentrations per se. In several crops, closure of stomata due to drought/salinization reduces ozone entering into leaf tissues and counteracts possible ozone damages. Furthermore, the stimulation of antioxidant synthesis as a response to environmental stresses can represent a further protection factor from ozone injuries for Mediterranean crops.The co-existence of stress-induced stomatal closure and high ozone levels during spring-summer in Mediterranean environments implies that models that do not take into account physiological responses of crops to drought and salinity stress may overestimate ozone damages when stress responses overlap with seasonal ozone peaks. The shift from concentration-based to flux-based approaches has improved the accuracy of models to assess ozone effects on agricultural crops. It is, however, necessary to further refine the flux concept with respect to the plant abiotic stress defense capacity that can differ among genotypes, climatic conditions, and physiological states.

On-line algorithm for ground-level ozone prediction with a mobile station

It is important to be able to predict high concentrations of tropospheric ozone and to inform the population about any violations of air-quality standards, as defined by international regulations. Although first-principle models that cover large geographical regions and different atmospheric layers are improving constantly, they typically still only cover geographical regions with a relatively low resolution. Such model predictions can be problematic for the micro-locations of a complex terrain, i.e., a terrain with a large geographical diversity or urban terrain. For such micro-locations, statistical models can be utilised. This paper presents a modelling and prediction algorithm that can be used in, or in accordance with, a mobile air-quality measurement station. Such a mobile station would enable the set-up of a statistical model and a relatively rapid access to the model's predictions for a specific geographical micro-location without a large quantity of historical of measurements. Uncertainty information about the model's predictions is also usually required. In addition, such a model can adapt to long-term changes, such as climate changes. In the paper we propose Gaussian-process models for the described modelling and prediction. In particular, we selected evolving Gaussian-process models that update on-line with the incoming measurement data. The proposed algorithm for the mobile air-quality measurement and the forecasting station is evaluated on measurements from five locations in Slovenia with different topographical and geographical properties. The obtained evaluation results confirm the feasibility of the concept.

Regressor selection for ozone prediction

Being able to predict high concentrations of tropospheric ozone is important because of its negative impact on human health. In this paper eight regressor-selection methods are utilised in a case study for ozone prediction in the city of Nova Gorica, Slovenia. The comparison of the selected methods proved to be useful for building models that successfully predict the ozone concentrations for the treated case. Different regressors are selected for different models, with different methods based on the validation procedure’s cost functions. Namely, for the model to predict the maximum daily ozone concentration, ten regressors are selected; for the average concentration of ozone between 8.00 and 20.00h, fifteen regressors are selected; and for the average daily concentration, ten regressors are selected. The result of the study is a regressor selection that is specific for a particular geographical location. Moreover, the study reveals that regressor selection, as well as the obtained models, differ depending on the kind of averaging interval of the ozone concentration.

Modelagem Simplificada da Formação de Ozônio Troposférico Considerando o Uso de Combustíveis Alternativos

Brazilian cities have been constantly exposed to air quality episodes of high ozone concentrations (O3). Known for not be emitted directly into the environment, O3 is a result of several chemical reactions of other pollutants emitted to atmosphere. The growth of vehicle fleet and government incentives for using alternative fuels like ethanol and Compressed Natural Gas (CNG) are changing the Brazilian Metropolitan Areas in terms of acetaldehyde and formaldehyde emissions, Volatile Organic Compounds (VOC's) present in the atmosphere and known to act on the kinetics of ozone. Driven by high concentrations of tropospheric ozone in urban/industry centers and its implications for environment and population health, the target of this work is understand the kinetics of ozone formation through the creation of a mathematical model in FORTRAN 90, describing a system of coupled ordinary differential equations able to represent a simplified mechanism of photochemical reactions in the Brazilian Metropolitan Area. Evaluating the concentration results of each pollutant were possible to observe the precursor’s influence on tropospheric ozone formation, which seasons were more conducive to this one and which are the influences of weather conditions on formation of photochemical smog.

Precipitation chemistry and ozone and sulfate concentrations in the ocean atmosphere observed by multi-year cruising in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September

A comprehensive study on the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere was carried out for the data sets in 1990’s. It is important to study the atmospheric situation over the past years as well as the latest, especially in the East Asian region where emission amount of anthropogenic air pollutants have increased year by year due to rapid economic growth. The survey was conducted for 5 years in East Asia and West Oceania (35°N–35°S, 100–135°E) in August and September in 1990’s. The purpose of the survey was to study and understand the chemistry of deposition and the concentration of tropospheric ozone and particulate sulfate in the ocean atmosphere comprehensively in one project. Rainfall over the ocean was insufficiently neutralized. Gas and aerosol over the ocean were mature, i.e., well-mixed, during the period of the transportation. The characteristic latitudinal dependence was observed in the tropospheric ozone concentration, namely, higher in the southern hemisphere and lower in the northern hemisphere (approximately 25 ppb in the 10–40°S region and 5–15 ppb in the 20–40°N region). On the other hand, high concentrations of tropospheric ozone of over 30 ppb were observed in the northern hemisphere, which was attributable to the long-range transportation. The TSP concentration was approximately under the level of 40 μg m−3 irrespectively of the latitude; in contrast, the nss-SO42- concentration showed a clear latitudinal dependence, i.e., higher in the northern hemisphere and lower in the southern hemisphere. The background levels of the nss-SO42- concentration were approximately 0.5 μg m−3 in the 10–40°S region and 2–3 μg m−3 and 4–5 μg m−3 in the 0–20°N and 20–40°N regions, respectively.

Evaluation of the WRF meteorological model results during a high ozone episode in SW Poland - the role of model initial conditions

In meteorological, as well as air quality, modelling, input data plays an important role in the accuracy of the results, next to the model configuration. There are many sources of meteorological data available, both global and regional, and they differ not only by spatial and temporal resolution, but also by the number of observations included in the reanalysis and method of data assimilation used. In this study, the performance of the weather research and forecasting (WRF) model with two global reanalyses (ERA-Interim and NCEP FNL) used as input datasets has been assessed for a period of high tropospheric ozone concentrations. Both WRF model runs are in good agreement with observations, with IOA statistic ranging from 0.78 for wind speed to 0.98 for surface pressure. The ERA-Interim simulation showed better results for surface pressure, temperature and wind speed, while the performance of both datasets for parameters related to atmospheric moisture (e.g., dew point temperature) was comparable.

Extreme value modeling for the analysis and prediction of time series of extreme tropospheric ozone levels: A case study

The occurrence of high concentrations of tropospheric ozone is considered as one of the most important issues of air management programs. The prediction of dangerous ozone levels for the public health and the environment, along with the assessment of air quality control programs aimed at reducing their severity, is of considerable interest to the scientific community and to policy makers. The chemical mechanisms of tropospheric ozone formation are complex, and highly variable meteorological conditions contribute additionally to difficulties in accurate study and prediction of high levels of ozone. Statistical methods offer an effective approach to understand the problem and eventually improve the ability to predict maximum levels of ozone. In this paper, an extreme value model is developed to study data sets that consist of periodically collected maxima of tropospheric ozone concentrations and meteorological variables. The methods are applied to daily tropospheric ozone maxima in Guadalajara City, Mexico, for the period January 1997 to December 2006. The model adjusts the daily rate of change in ozone for concurrent impacts of seasonality and present and past meteorological conditions, which include surface temperature, wind speed, wind direction, relative humidity, and ozone. The results indicate that trend, annual effects, and key meteorological variables along with some interactions explain the variation in daily ozone maxima. Prediction performance assessments yield reasonably good results. Implications This paper develops a statistical approach to both analyzing and forecasting daily meteorologically adjusted tropospheric ozone maxima in the presence of seasonality and trend. The methods are applied to a 10-year follow-up of daily maxima of ozone levels for the metropolitan area of Guadalajara. One-day-lagged and present meteorological variables, 1- and 2-day-lagged tropospheric ozone maxima, seasonality, and a curvilinear trend are important predictors of the daily tropospheric ozone maximum in Guadalajara. The method provides a reliable tool to predict ozone levels exceeding a relevant threshold.

Ozone deposition to an orange orchard: Partitioning between stomatal and non-stomatal sinks

Orange trees are widely cultivated in regions with high concentrations of tropospheric ozone. Citrus absorb ozone through their stomata and emit volatile organic compounds (VOC), which, together with soil emissions of NO, contribute to non-stomatal ozone removal. In a Valencia orange orchard in Exeter, California, we used fast sensors and eddy covariance to characterize water and ozone fluxes. We also measured meteorological parameters necessary to model other important sinks of ozone deposition. We present changes in magnitude of these ozone deposition sinks over the year in response to environmental parameters. Within the plant canopy, the orchard constitutes a sink for ozone, with non-stomatal ozone deposition larger than stomatal uptake. In particular, soil deposition and reactions between ozone, VOC and NO represented the major sinks of ozone. This research aims to help the development of metrics for ozone-risk assessment and advance our understanding of citrus in biosphere-atmosphere exchange.

Episodes of extremely high concentrations of tropospheric ozone in the urban environment in Bor - Serbia

Abstract This paper presents results of measuring episodes of extremely high ozone concentrations in urban area of the town of Bor in Serbia. The measured ozone concentration of 3000 μgm −3 in two episodes, which lasted 3–5 days in November 2010, has not been recorded in the literature in this field. Sensitivity of generated ozone to the NOx was determined, since the concentrations of NOx in the same period were also high. In the morning when working hours start, episodes of increased NOx concentrations appear after several hours, leading to episodes of increased ozone concentrations reaching up to twenty times more than the threshold value, defined as harmful to vegetation and human health.

Increasing springtime ozone mixing ratios in the free troposphere over western North America

In the lowermost layer of the atmosphere-the troposphere-ozone is an important source of the hydroxyl radical, an oxidant that breaks down most pollutants and some greenhouse gases. High concentrations of tropospheric ozone are toxic, however, and have a detrimental effect on human health and ecosystem productivity. Moreover, tropospheric ozone itself acts as an effective greenhouse gas. Much of the present tropospheric ozone burden is a consequence of anthropogenic emissions of ozone precursors resulting in widespread increases in ozone concentrations since the late 1800s. At present, east Asia has the fastest-growing ozone precursor emissions. Much of the springtime east Asian pollution is exported eastwards towards western North America. Despite evidence that the exported Asian pollution produces ozone, no previous study has found a significant increase in free tropospheric ozone concentrations above the western USA since measurements began in the late 1970s. Here we compile springtime ozone measurements from many different platforms across western North America. We show a strong increase in springtime ozone mixing ratios during 1995-2008 and we have some additional evidence that a similar rate of increase in ozone mixing ratio has occurred since 1984. We find that the rate of increase in ozone mixing ratio is greatest when measurements are more heavily influenced by direct transport from Asia. Our result agrees with previous modelling studies, which indicate that global ozone concentrations should be increasing during the early part of the twenty-first century as a result of increasing precursor emissions, especially at northern mid-latitudes, with western North America being particularly sensitive to rising Asian emissions. We suggest that the observed increase in springtime background ozone mixing ratio may hinder the USA's compliance with its ozone air quality standard.

Performance assessment of a long-term photochemical modelling system

Modelling systems can represent suitable tools to study photochemical pollution and to analyse and assess appropriate emissions reduction strategies. Since high tropospheric ozone concentrations are quite usual in Mediterranean areas, causing adverse effects on human health, materials and ecosystems, an integrated photochemical pollution modelling system has been developed and applied to Italian regions; seasonal simulations have been performed to estimate useful indicators of ozone exposure, as AOT indexes. A particular integrated system, including a 3D meteorological model (CALMET), a flexible emission evaluation model (POEM) and two photochemical transport models (CALGRID and STEM-FCM), has been applied to a Northern Italy domain including the whole Regione Lombardia, characterised by complex terrain, high urban and industrial emissions and a close road network. The simulation period was the sunny season May–July 1996. The model skill in simulating the long-term dynamics of pollutants in the atmosphere has been assessed by means of performance indicators and graphical tools, estimated for a restricted number of monitoring stations, selected as representative of different orographic and emissive features. A performance assessment and comparison referred to ozone estimates are presented for the two photochemical models taken into account.

Experiment probes elevated ozone levels over the tropical south Atlantic Ocean

Until late 1992, the atmosphere off the west coast of southern Africa was one of the least studied regions of the planet. From a meteorological point of view, the area is devoid of any interesting weather features, including tropical storm formation and monsoonal circulations. It is dominated by a vast center of subtropical high pressure that inhibits the formation of any convective activity.However, from an atmospheric chemistry point of view, an interesting feature was discovered in 1990 when satellite data revealed a region of enhanced tropospheric ozone off southern Africa's west coast that was at least as large as the smog plumes emanating from North America, Europe, and Asia [Fishman et al., 1990; Figure 1]. While the Northern Hemisphere high tropospheric ozone concentrations were most pronounced in the summer, the feature in the southern subtropics was highest during austral spring.

Vertical distribution of tropospheric ozone in Antarctica and in the European Arctic

Ozone soundings performed since 1988 on the Antarctic Peninsula at Marambio (64.2°S, 57.7°W) and in the European Arctic at Sodankyla (67.4°N, 26.6°E), Bear Island (74.5°N, 19.0°E) and Ny Alesund (78.9°N, 11.9°E) have been studied. Regular ozone soundings have never been made at these locations. A comparison of monthly mean tropospheric ozone profiles at high southern and northern latitudes has been made. In midwinter, differences between the monthly means in the northern and southern hemispheres are small, i.e. < 1 mPa. The general photochemical activation in springtime leads to larger differences: the partial pressures decrease in Antarctica whereas in the Arctic, pronounced production of ozone is seen. In spring and summer, the hemispheric differences are about 3 mPa. Exceptionally high and low partial pressures at Sodankyla and Marambio have been studied using 3-dimensional trajectories based on the ECMWF analyses. Episodes of upper tropospheric ozone loss at Marambio have been observed during the stratospheric ozone depletion period in spring. The only cause for especially high tropospheric ozone concentrations in Antarctica has been stratospheric intrusions. Low partial pressures in the boundary layer have been connected with advection of marine airmasses to Marambio. At Sodankyla, low boundary layer values have been observed during an advection from the Northern sea areas and also during the transport of airmasses from industrial source areas of Eastern Europe. Especially strong stratospheric ozone intrusion into the middle troposphere was observed at Sodankyla in September 1989. Partial pressures exceeding 7 mPa in the lower troposphere have been observed at Sodankyla during the summer in connection with the long-range transport of NO x /HC-containing air from Western Europe to Northern Scandinavia. DOI: 10.1034/j.1600-0889.1993.t01-1-00003.x