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- Author or Editor: Rumen D. Bojkov x
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Abstract
During the last few years, increases in tropospheric ozone concentration have been detected and the need for more study has been recognized. There is very little knowledge about surface ozone background concentrations prior to the advent of widespread gasoline combustion. Therefore, the aim of this study was to uncover any useful information from the nineteenth century, and to explore the feasibility of converting it to obtain an approximate level of ozone concentration. After discovering ozone, Schönbein promulgated a simple method using iodized starch paper for qualitatively assessing its amount present in the air. This method was implemented at a few hundred sites, and although vulnerable to influence by humidity and oxidants in the air, continued to be used into the early years of this century. In the search for the best method of converting the Schönbein data, the most useful data sources turned out to be the 31-year series of regular quantitative ozone concentration measurements at Montsouris Observatory and, in particular, one year of simultaneous measurements by two methods carried out there. The nonlinear dependence of the coloration of Schönbein test-paper on the humidity was also considered. The corrections needed to convert the Schönbein data are discussed. The results indicate that during the last 30 years of the 19th century in the Great Lakes area of North America the average daily maximum of the surface ozone partial pressure was approximately 1.9 ± 0.2 mPa. European measurements between the 1850s and 1900s indicate little scattering outside of the range 1.7 to 2.3 mPa. All of these values are only about half of the mean of the daily maximum values of precise surface ozone measurements taken in the same geographical regions during the last 10–15 years. The annual cycle of surface ozone had an April–June maximum and an October–December minimum, and it was similar to the cycle now registered at stations generally free from local contaminations in midlatitudes. In general, the differences in the ozone partial pressure between old converted data and present-day measurements is greater for the summer than for the winter months. A statistically significant tendency for a surface ozone increase is noted in the data for Montsouris; however, at some other stations the trend would not be statistically significant. Further verification of the conversion technique may allow information on the background surface ozone concentration to be expanded.
Abstract
During the last few years, increases in tropospheric ozone concentration have been detected and the need for more study has been recognized. There is very little knowledge about surface ozone background concentrations prior to the advent of widespread gasoline combustion. Therefore, the aim of this study was to uncover any useful information from the nineteenth century, and to explore the feasibility of converting it to obtain an approximate level of ozone concentration. After discovering ozone, Schönbein promulgated a simple method using iodized starch paper for qualitatively assessing its amount present in the air. This method was implemented at a few hundred sites, and although vulnerable to influence by humidity and oxidants in the air, continued to be used into the early years of this century. In the search for the best method of converting the Schönbein data, the most useful data sources turned out to be the 31-year series of regular quantitative ozone concentration measurements at Montsouris Observatory and, in particular, one year of simultaneous measurements by two methods carried out there. The nonlinear dependence of the coloration of Schönbein test-paper on the humidity was also considered. The corrections needed to convert the Schönbein data are discussed. The results indicate that during the last 30 years of the 19th century in the Great Lakes area of North America the average daily maximum of the surface ozone partial pressure was approximately 1.9 ± 0.2 mPa. European measurements between the 1850s and 1900s indicate little scattering outside of the range 1.7 to 2.3 mPa. All of these values are only about half of the mean of the daily maximum values of precise surface ozone measurements taken in the same geographical regions during the last 10–15 years. The annual cycle of surface ozone had an April–June maximum and an October–December minimum, and it was similar to the cycle now registered at stations generally free from local contaminations in midlatitudes. In general, the differences in the ozone partial pressure between old converted data and present-day measurements is greater for the summer than for the winter months. A statistically significant tendency for a surface ozone increase is noted in the data for Montsouris; however, at some other stations the trend would not be statistically significant. Further verification of the conversion technique may allow information on the background surface ozone concentration to be expanded.
Abstract
A method for computing vertical ozone profiles from known total ozone data based on about 8000 vertical ozone profiles taken by the Umkehr method at 30 stations around the world is presented. The computed correlation matrices give a comprehensive picture of the relationships between the simultaneous change of total ozone amount and the ozone content in nine atmospheric layers between 5 and 50 km along various latitudinal belts. The correlation coefficients have the highest positive values (R≈0.85±0.05) in the lower stratosphere, approximately twice as high as the values of the coefficients for upper troposheric ozone. Between 22-24 and 30-35 km there exists a layer with a transition regime of relatively small ozone concentration changes. Below this transition layer changes are caused largely by atmospheric circulation and dynamics; above it, the changes are photchemical. A pronounced latitudional effect shows up in the relationship between the variation of vertical ozone distribution and the total ozone. From middle latitudes equator-ward, an upward shifting of the region with largest correlation coefficients is observed, especially above the equatorial belt, where R>0.50 up to the top layer. Regression equations are deduced for six latitudinal belts and for seven groups based on total ozone. These equations make it possible to estimate the ozone profile corresponding to the known total ozone content. The representativeness and the applicability of this method is discussed. Deviations between observed and estimated vertical ozone distributions usually do not exceed 5% of the value of the ozone partial pressure in the layers involved.
Abstract
A method for computing vertical ozone profiles from known total ozone data based on about 8000 vertical ozone profiles taken by the Umkehr method at 30 stations around the world is presented. The computed correlation matrices give a comprehensive picture of the relationships between the simultaneous change of total ozone amount and the ozone content in nine atmospheric layers between 5 and 50 km along various latitudinal belts. The correlation coefficients have the highest positive values (R≈0.85±0.05) in the lower stratosphere, approximately twice as high as the values of the coefficients for upper troposheric ozone. Between 22-24 and 30-35 km there exists a layer with a transition regime of relatively small ozone concentration changes. Below this transition layer changes are caused largely by atmospheric circulation and dynamics; above it, the changes are photchemical. A pronounced latitudional effect shows up in the relationship between the variation of vertical ozone distribution and the total ozone. From middle latitudes equator-ward, an upward shifting of the region with largest correlation coefficients is observed, especially above the equatorial belt, where R>0.50 up to the top layer. Regression equations are deduced for six latitudinal belts and for seven groups based on total ozone. These equations make it possible to estimate the ozone profile corresponding to the known total ozone content. The representativeness and the applicability of this method is discussed. Deviations between observed and estimated vertical ozone distributions usually do not exceed 5% of the value of the ozone partial pressure in the layers involved.
Abstract
This paper reviews the results of the first systematic parallel measurements with a Dobson-type spectrophotometer and an M-83 filter ozonometer. Measurements were performed at the University of Sofia during a period of one full year. The M-83 is a working instrument in about one-third of the world's ozone network, and is predominantly used in the U.S.S.R.
Observations taken every 15 min on clear sunny days, as well as the monthly and seasonal values, show that the filter ozonometer gives a reading of about 6% less ozone than the Dobson when observations are taken at sun zenith angles <57° (relative path length of sunlight through the atmosphere μ < 1.5). When the sun zenith angle is greater than 60° (μ > 2.0) the filter ozonometer readings are 20–30% higher than the Dobson readings. When visibility is limited (V ≤ 5 km), the filter ozonometer readings of ozone are 9–14% higher than the Dobson readings.
Differences in the monthly ozone values between adjacent pairs of nearby stations using filter or Dobson instruments give results which agree with those from the simultaneous observations in Sofia.
A nomogram is presented giving values of μ as a function of the latitude and the time of the year. Using this nomogram and applying the results of the study it can be concluded that the ozone reported from filter ozonometers stations north of ∼40N would be ∼20% higher than the actual ozone content during the autumn-winter period. During the summer, up to about 70N, the filter data show less ozone.
The causes of the significant differences shown by the filter ozonometer M-83 are probably due to the use of filters with a very wide transmission band (>400 Å). The range of error could be partially decreased if measurements with the filter ozonometer were taken only symmetrically around noon and only when the sun's zenith angle is between 50° and 30° (1.3 < μ < 2.0). It is concluded that the ozone diagrams used for the filter ozonometer should be recomputed, including greater detail on the influence of changes of the effective wavelength (and corresponding changes of the ozone absorption coefficients) as functions of the sun's zenith angle.
Abstract
This paper reviews the results of the first systematic parallel measurements with a Dobson-type spectrophotometer and an M-83 filter ozonometer. Measurements were performed at the University of Sofia during a period of one full year. The M-83 is a working instrument in about one-third of the world's ozone network, and is predominantly used in the U.S.S.R.
Observations taken every 15 min on clear sunny days, as well as the monthly and seasonal values, show that the filter ozonometer gives a reading of about 6% less ozone than the Dobson when observations are taken at sun zenith angles <57° (relative path length of sunlight through the atmosphere μ < 1.5). When the sun zenith angle is greater than 60° (μ > 2.0) the filter ozonometer readings are 20–30% higher than the Dobson readings. When visibility is limited (V ≤ 5 km), the filter ozonometer readings of ozone are 9–14% higher than the Dobson readings.
Differences in the monthly ozone values between adjacent pairs of nearby stations using filter or Dobson instruments give results which agree with those from the simultaneous observations in Sofia.
A nomogram is presented giving values of μ as a function of the latitude and the time of the year. Using this nomogram and applying the results of the study it can be concluded that the ozone reported from filter ozonometers stations north of ∼40N would be ∼20% higher than the actual ozone content during the autumn-winter period. During the summer, up to about 70N, the filter data show less ozone.
The causes of the significant differences shown by the filter ozonometer M-83 are probably due to the use of filters with a very wide transmission band (>400 Å). The range of error could be partially decreased if measurements with the filter ozonometer were taken only symmetrically around noon and only when the sun's zenith angle is between 50° and 30° (1.3 < μ < 2.0). It is concluded that the ozone diagrams used for the filter ozonometer should be recomputed, including greater detail on the influence of changes of the effective wavelength (and corresponding changes of the ozone absorption coefficients) as functions of the sun's zenith angle.
Abstract
This study is devoted to a comparison between the vertical ozone distribution profiles obtained using indirect Umkehr and direct ozonesonde methods. In the three year period 1963–1965, there were 17 days with simultaneous Umkehr and ozonesonde profiles at 53N, 60W, predominantly in the winter-spring season. The mean ozone profiles indicate that the greatest differences occur at or about the level of the ozone maximum. The ozonesonde profile shows two maxima with the predominant one at about 20 km and a secondary one between 13 and 14 km, whereas the Umkehr profile shows only one maximum near 22 km. The center of gravity of the Umkehr profile is close to 21 km, and is about 1 km above that of the mean ozonesonde profile. Generally, the vertical ozone distribution obtained by both methods shows an approximately similar percentage distribution of the ozone amount. Only within the 15–24 km layer in all cases do the sondes give 9 per cent (of the total amount) more ozone content than the Umkehr method. Above 24 km the ozone partial pressure given from Umkehr is higher than it is from sondes. In this region the Umkehr profile gives 6 per cent (of the total amount) more ozone than the sondes. The correlation between the simultaneous changes in the integrated ozone within a given layer, estimated by alternative sampling methods, is high (≥0.80) between 10 and 19 km. Little relationship is found between them in the troposphere and above 24 km. The study suggests that direct comparisons of profiles taken by Umkehr and ozonesonde methods cannot be useful for the study of short-period and small-scale features.
Abstract
This study is devoted to a comparison between the vertical ozone distribution profiles obtained using indirect Umkehr and direct ozonesonde methods. In the three year period 1963–1965, there were 17 days with simultaneous Umkehr and ozonesonde profiles at 53N, 60W, predominantly in the winter-spring season. The mean ozone profiles indicate that the greatest differences occur at or about the level of the ozone maximum. The ozonesonde profile shows two maxima with the predominant one at about 20 km and a secondary one between 13 and 14 km, whereas the Umkehr profile shows only one maximum near 22 km. The center of gravity of the Umkehr profile is close to 21 km, and is about 1 km above that of the mean ozonesonde profile. Generally, the vertical ozone distribution obtained by both methods shows an approximately similar percentage distribution of the ozone amount. Only within the 15–24 km layer in all cases do the sondes give 9 per cent (of the total amount) more ozone content than the Umkehr method. Above 24 km the ozone partial pressure given from Umkehr is higher than it is from sondes. In this region the Umkehr profile gives 6 per cent (of the total amount) more ozone than the sondes. The correlation between the simultaneous changes in the integrated ozone within a given layer, estimated by alternative sampling methods, is high (≥0.80) between 10 and 19 km. Little relationship is found between them in the troposphere and above 24 km. The study suggests that direct comparisons of profiles taken by Umkehr and ozonesonde methods cannot be useful for the study of short-period and small-scale features.
Abstract
Studies of the amount of total ozone at many observatories show that the negative 1983 deviation from the long-term average exceeded 2σ, and was the greatest in magnitude for an annual deviation in their entire record., the total ozone in December 1982 and first few months of 1983 decreased by more than 10% below its normal amount. Only during late 1983 did the total ozone recover to near normal values. It remained close to normal during most of 1984 but decreased sharply again in February–April in the Northern Hemisphere, and in June–September 1985 in the Southern Hemisphere. Only toward the end of 1985 and in 1986 did the total ozone recover to its long-term average amount. These ozone changes are confirmed by satellite observations to be truly global events, although with some time lag between different latitudes.
The 1983 and 1995 changes in total ozone are also examined by analyzing the deviations of ozone partial pressure at different altitudes. This analysis reveals the times and the layers of the changes, as well as their net contributions to the total ozone deviations. It is concluded that periods of total ozone deficiency were mainly due to changes in ozone amount in the lower and middle stratosphere, which suggests that circulation effects were dominant. The appearance of different partial contributions by the lower vs middle stratospheric layer is noted. Looking at the past 20-yr record in perspective, an important finding emerges that the observed ozone deficiencies are consequences of the quasi-biennial oscillation (QBO) in combination with the very pronounced circulation changes during the 1982/83 El Nino–Southern Oscillation (ENSO) event. The physical and photochemical processes triggered by the April 1982 El Chichóeruption, leading to partial ozone depletion, are also recognized and critically asessed. However, the results of the analysis suggest that the QBO, as has happened many times before, has “set the stage” for major ozone deficiencies both in 1983 and in 1985, and the ENSO and El Chichóevents only served to augment the effect in the 1982/83 episode.
Abstract
Studies of the amount of total ozone at many observatories show that the negative 1983 deviation from the long-term average exceeded 2σ, and was the greatest in magnitude for an annual deviation in their entire record., the total ozone in December 1982 and first few months of 1983 decreased by more than 10% below its normal amount. Only during late 1983 did the total ozone recover to near normal values. It remained close to normal during most of 1984 but decreased sharply again in February–April in the Northern Hemisphere, and in June–September 1985 in the Southern Hemisphere. Only toward the end of 1985 and in 1986 did the total ozone recover to its long-term average amount. These ozone changes are confirmed by satellite observations to be truly global events, although with some time lag between different latitudes.
The 1983 and 1995 changes in total ozone are also examined by analyzing the deviations of ozone partial pressure at different altitudes. This analysis reveals the times and the layers of the changes, as well as their net contributions to the total ozone deviations. It is concluded that periods of total ozone deficiency were mainly due to changes in ozone amount in the lower and middle stratosphere, which suggests that circulation effects were dominant. The appearance of different partial contributions by the lower vs middle stratospheric layer is noted. Looking at the past 20-yr record in perspective, an important finding emerges that the observed ozone deficiencies are consequences of the quasi-biennial oscillation (QBO) in combination with the very pronounced circulation changes during the 1982/83 El Nino–Southern Oscillation (ENSO) event. The physical and photochemical processes triggered by the April 1982 El Chichóeruption, leading to partial ozone depletion, are also recognized and critically asessed. However, the results of the analysis suggest that the QBO, as has happened many times before, has “set the stage” for major ozone deficiencies both in 1983 and in 1985, and the ENSO and El Chichóevents only served to augment the effect in the 1982/83 episode.
Abstract
Seasonal ozone profiles, representative of the autumn and winter-spring periods, are computed from 20 ascents, made using electro-chemical sensors in sondes, for Christchurch, New Zealand. The seasonal changes between the autumn and winter-spring seasons are discussed in terms of changes in successive layers at different levels of the atmosphere, and are qualitatively similar to the well authenticated changes in midlatitudes in the Northern Hemisphere.
The seasonal profiles at Christchurch (43S) are compared with the corresponding vertical ozone distributions in the Northern Hemisphere, and the results interpreted as suggesting that the vertical mass exchange processes are more effective in the middle stratosphere in the Southern Hemisphere during the spring ozone build up, but the trans-tropopause exchange is greater in the Northern Hemisphere.
A sequence of profiles between 14 and 23 June is used to estimate vertical velocities using an appropriate ozone continuity equation and the results compared for consistency with vertical motion inferred from the thermal profiles.
Abstract
Seasonal ozone profiles, representative of the autumn and winter-spring periods, are computed from 20 ascents, made using electro-chemical sensors in sondes, for Christchurch, New Zealand. The seasonal changes between the autumn and winter-spring seasons are discussed in terms of changes in successive layers at different levels of the atmosphere, and are qualitatively similar to the well authenticated changes in midlatitudes in the Northern Hemisphere.
The seasonal profiles at Christchurch (43S) are compared with the corresponding vertical ozone distributions in the Northern Hemisphere, and the results interpreted as suggesting that the vertical mass exchange processes are more effective in the middle stratosphere in the Southern Hemisphere during the spring ozone build up, but the trans-tropopause exchange is greater in the Northern Hemisphere.
A sequence of profiles between 14 and 23 June is used to estimate vertical velocities using an appropriate ozone continuity equation and the results compared for consistency with vertical motion inferred from the thermal profiles.
