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The review is based on the results of the operation of the system of total ozone (TO) monitoring over Russia and neighboring territories that functions in the operational mode at the Ceniral Aerological Observatory (CAO). The monitoring system uses data from the national network equipped with M-124 filter ozonometers being under the methodological supervision of the Main Geophysical Observatory. The quality of the entire system functioning is operationally controlled by the comparison with the observations obtained from the OMI satellite equipment (NASA, USA). Basic TO observation data are generalized for each month of the second quarter of 2019 and for the second quarter. Data of routine observations of surface ozone values in the Moscow region and Crimea are also considered.

espanolEn este trabajo se han analizado datos de la columna total deozono derivados de las mediciones realizadas por el Espectrometro de Mapeo deOzono Total de la Sonda de la Tierra (Eptoms) de la Administracion Nacionalde Aeronautica y del Espacio (NASA), valorando su idoneidad para la predicciondel indice ultravioleta (UV) para la ciudad de Puno (15.83 latitud Sur y 70.03longitud Oeste). Al realizarse un analisis por ano mediante ajustes de funcionessenoidal, se observa que el desfasaje varia de un ano a otro. Asimismo, duranteel periodo estudiado (2005-2017) se encontraron tres fechas en las cuales sepresentaron agujeros de ozono: el 5 de febrero de 2010 y el 29 de abril del 2016se presentaron valores de 218 unidades Dobson (UD); y el 17 de mayo de 2005se presento el valor de 219 UD. El comportamiento de columna de ozono porano ostenta una forma ciclica senoidal, como lo establece el ciclo estacional. EnglishData of the Total Ozone Column have been analyzed in this paper,which were derived from the measurements performed by the Earth Probe TotalOzone Mapping Spectrometer (EPTOMS) of the National Aeronautics andSpace Administration (NASA), by assessing its suitability for the predictionof the Ultraviolet (UV) Index for the city of Puno (15.83 south latitude and70.03° west longitude). After a one-year analysis was performed by means ofadjustments of sinusoidal functions, it is observed that the gap changes, fromone year to the next. Additionally, during the period studied (2005-2017), threedates were found in which ozone holes were presented: On February 5, 2010 andApril 29, 2016, values of 218 Dobson Units (DU) were presented, and on May17, 2005, a value of 219 DU was presented. The behavior of the ozone column,per year, displays a sinusoidal cyclical shape, as it is established in the seasonalcycle.

In this work, the impact of various factors on the total ozone column and erythemal UV radiation (Qery) in the territory of Northern Eurasia for the period from 1979 to 2059 based on the calculations of the chemical-climate model INM-RHSU is analyzed. The sensitivity of ozone recovery to the setting of different input data on sea surface temperature (SST) is estimated. Depending on the SST datasets, there are significant differences in ozone trends. A possible mechanism that explains the reasons for these differences is examined. The numerical experiment with the only change in ozone depleting substances according to Montreal protocol showed the ozone recovery and, as a result, Qery reduction, but this recovery is not linear. During the 2016-2020 period we estimated the 2-5% increase in Qery values relative to the baseline period (1979-1983) with about 6% maximum over Russian polar region. During the 2035-2039 period the Qery change against 1979-1983 period is about zero, during the 2055-2059 period we obtained the decrease of about 4-6% over Northern Asia and 6-8% over Northern Europe These changes corresponded to the noticeable boundary location shift of UV resources, which determine UV radiation impact on human health. The most significant changes will be observed in spring and summer: the UV deficiency zone will be expanded in the north and the UV excess zone over northern seas will be reduced in the south.

The review is compiled of the results of the total ozone (TO) monitoring in the CIS and Baltic countries that functions in the operational mode at the Central Aerological Observatory (CAO). The monitoring system uses data from the national net work equipped with M-124 filter ozonometers op er at -ing under the methodological supervision of the Main Geophysical Observatory. The quality of the functioning of the entire system is operation ally con trolled in CAO by the comparison with the observations obtained from the OMI satellite equipment (NASA, USA). Basic TO observation data are generalized for each month of the first quarter of 2019 and for the first quarter. Data of routine observations of surface ozone values in the Moscow region and Crimea are also considered.

A continuous online observation of ozone and its precursors (NOx, VOCs) was carried out in central urban Wuhan from September 2016 to August 2017. The concentration levels of ozone, NOx, VOCs and their variations in urban Wuhan were analyzed, as well as effects of VOCs on ozone photochemical generation and the main controlling factors for ozone production. During the observation period, the average concentrations of ozone and NOx in Wuhan was 22.63 and 30.14 ppbv, respectively, and the average concentration of VOCs was 32.61 ppbv (42.3% alkanes, 13.0% alkenes, 10.0% aromatics, 7.3% acetylene, 9.9% OVOCs, and 10.5% halohydrocarbons). Ozone concentration was higher in spring and summer as compared with autumn and winter, wheras VOCs and NOx concentratios were lower in spring and summer but higher in autumn and winter. Aromatics and alkenes, two of VOCs species, showed the highest contributions to ozone formation potential in Wuhan (35.7% alkenes, 35.4 aromatics, 17.5% alkanes, 8.6% OVOCs, 1.6% halogenated hydrocarbons, and 1.4% acetylene). Among all VOCs species, those with the highest contribution were ethylene, m-xylene, toluene, propylene and o-xylene. The contribution of these five compounds to the total ozone formation potential concentration was 43.90%. Ozone-controlling factors in Wuhan changed within one day; during the early morning hours (6:00–9:00), VOCs/NOx was low, and ozone generation followed a VOCs-limited regime. However, during the peak time of ozone concentration (12:00–16:00), the ratio of VOCs/NOx was relatively high, suggesting that ozone generation followed a NOx-limited regime.

The global ozone layer has been continuously depleted in the last few decades due to the anthropogenic emissions of the ozone depleting substances (ODSs). This has created major concern for the ecosystem as well as mankind. This points to the need to examine the influence of each individual ODS in order to estimate how this burden can change in the future. To that end, we have analysed 52 years (1965–2017) data of the ozone depleting substances using the Box-Jenkins model, and have predicted the future trend of the ODSs until the year 2030. On the basis of the relationship between the trend in variations of the ozone depleting substances and the total ozone column, we have established that how much of the recent ozone increment is attributable to the concentration of the ozone depleting substances. By using the above mentioned model, we have estimated that the present atmospheric abundance of chlorine and bromine is about 3325 and 14.3 parts per trillion (ppt) respectively and have calculated that the atmospheric abundance of these substances will reduce to values of 3217 ppt (∼3.2%) and 13.1 ppt (∼8.3%) respectively. We have also inferred that if the decreasing trend of ODSs continues with the same rate in the coming decades, the ozone column will increase by 9–10% and the ozone level will return to its pre-1980 level by the year 2030.

Ultraviolet-B radiation (UV-B, 280–315 nm) constitutes less than 1% of the total solar radiation that reaches the Earth's surface but has a disproportional impact on biological and ecological processes from the individual to the ecosystem level. Absorption of UV-B by ozone is also one of the primary heat sources to the stratosphere, so variations in UV-B have important relationships to the Earth's radiation budget. Yet despite its importance for understanding atmospheric and ecological processes, there is limited understanding about the changes in UV-B radiation in the geological past. This is because systematic measurements of total ozone and surface UV-B only exist since the 1970s, so biological or geochemical proxies from sediment archives are needed to reconstruct UV-B irradiance received at the Earth surface beyond the experimental record. Recent developments have shown that the quantification of UV-B-absorbing compounds in pollen and spores have the potential to provide a continuous record of the solar-ultraviolet radiation received by plants. There is increasing interest in developing this proxy in palaeoclimatic and palaeoecological research. However, differences in interpretation exist between palaeoecologists, who are beginning to apply the proxy under various geological settings, and UV-B ecologists, who question whether a causal dose–response relationship of pollen and spore chemistry to UV-B irradiance has really been established. Here, we use a proxy-system modelling approach to systematically assess components of the pollen- and spore-based UV-B-irradiance proxy to ask how these differences can be resolved. We identify key unknowns and uncertainties in making inferences about past UV-B irradiance, from the pollen sensor, the sedimentary archive, and through the laboratory and experimental procedures in order to target priority areas of future work. We argue that an interdisciplinary approach, modifying methods used by plant ecologists studying contemporary responses to solar-UV-B radiation specifically to suit the needs of palaeoecological analyses, provides a way forward in developing the most reliable reconstructions for the UV-B irradiance received by plants across a range of timescales. acceptedVersion

Evidence of an underlying trend in the dependence of erythema effective ultraviolet (UV) radiant exposure (Her) on changes in the total ozone, cloud cover and aerosol optical depth (AOD) has been studied using solar ultraviolet radiation measurements collected over a 25-year period (1991–2015) at Chilton in the south of England in the UK. The monthly mean datasets of these measures corrected for underlying seasonal variation were analysed. When a single linear trend was fitted over the whole study period between 1991 and 2015, the analyses revealed that the long-term variability of Her can be best characterised in two sub-periods (1991–2004 and 2004–2015), where the estimated linear trend was upward in the first period (1991–2004) but downward in the second period (2004–2015). Both cloud cover (CC) and total ozone (TO) were found to have a highly statistically significant influence on Her, but the influence of the AOD measure was very small. The radiation amplification factor (RAF) for the erythema action spectrum due to TO was −1.03 at constant levels of CC over the whole study period; that is, for a 1.0 % increase in TO, Her decreases by 1.03 %. Over the first period (1991–2004), the RAF related to CC was slightly higher at 0.97 compared to that for TO at 0.79. The proportion of the change in Her explained by the change in CC (47 %) was much greater than the proportion explained by changes in TO (8 %). For the second period (2004–2015), the pattern reversed, with the observed RAF related to TO being −1.25, almost double that of CC (−0.65). Furthermore, in this period the proportion of variation in Her explained by TO variation was 33 %, double that of CC at 16 %, while AOD changes had a negligible effect (1 %). When the data were examined separately for each season, for the first period (1991–2004) the greatest effect of TO and CC on Her (i.e. the largest RAF value) was found during spring. Spring was also the season during which TO and CC variation explained the greatest proportion of variability in Her (82 %). In the later period (2004–2015), the RAF and greatest influence of TO and CC were observed in winter (67 %) and the AOD effect explained a further 5 % variability in Her. This study provides evidence that both the increasing trend in Her for 1991–2004 and the decreasing trend in Her for 2004–2015 occur in response to variation in TO, which exhibits a small increasing tendency over these periods. CC plays a more important role in the increasing trend in Her for 1991–2004 than TO, whereas for 2004–2015, the decreasing trend in Her is less associated with changes in CC and AOD.

Dobson and Brewer spectrophotometers are the primary, standard instruments for ground-based ozone measurements under the World Meteorological Organization's (WMO) Global Atmosphere Watch program. The accuracy of the data retrieval for both instruments depends on a knowledge of the ozone absorption coefficients and some assumptions underlying the data analysis. Instrumental stray light causes nonlinearity in the response of both the Brewer and Dobson to ozone at large ozone slant paths. In addition, it affects the effective ozone absorption coefficients and extraterrestrial constants that are both instrument-dependent. This effect has not been taken into account in the calculation of ozone absorption coefficients that are currently recommended by WMO for the Dobson network. The ozone absorption coefficients are calculated for each Brewer instrument individually, but in the current procedure the effect of stray light is not considered. This study documents the error caused by the effect of stray light in the Brewer and Dobson total ozone measurements using a physical model for each instrument. For the first time, new ozone absorption coefficients are calculated for the Brewer and Dobson instruments, taking into account the stray light effect. The analyses show that the differences detected between the total ozone amounts deduced from Dobson AD and CD pair wavelengths are related to the level of stray light within the instrument. The discrepancy introduced by the assumption of a fixed height for the ozone layer for ozone measurements at high latitude sites is also evaluated. The ozone data collected by two Dobson instruments during the period of December 2008 to December 2014 are compared with ozone data from a collocated double monochromator Brewer spectrophotometer (Mark III). The results illustrate the dependence of Dobson AD and CD pair measurements on stray light.

The variability of Arctic total ozone in the winter of 2015/2016 is studied using the data of the national network equipped with M-124 filter ozonometers and satellite monitoring. The first ozone mini-hole that emerged in the first half-year over the whole history of observations (developed at the end of January 2016) is analyzed. The reasons for the total ozone variability over Russia in the first quarter of 2016 are analyzed, and the comparison with the significant Arctic ozone anomalies in 1996/1997 and 2010/2011 is presented.

We investigated the characteristics of the total ozone column (TOC) around West Antarctica (near the Weddell Sea) compared with ambient meteorological factors. For this analysis, we used ground-based and satellite TOC measurements as well as meteorology (air temperature, potential vorticity and wind field) from reanalysis data. Long-term patterns of TOC show the large year-to-year variation (e.g., maximumly ∼200 DU at King Sejong) but a steady recovering trend recently. Despite a generally consistent pattern, the TOC around West Antarctica did not correlate well between high- and low-latitude regions during austral spring; this result implies that the ozone hole area had a spatial variation over West Antarctica. The TOC pattern around West Antarctica correlated well with air temperature but showed a vertical difference; high positive correlations appeared in the lower stratosphere (maximumly R > 0.9 at ∼50–100 hPa height) showing enhanced ozone depletion in colder conditions, but negative correlations appeared in the upper stratosphere (minimum R 0.9 at ∼500–600 K height) during the austral spring but a moderately negative correlation in the lower stratosphere (minimum R

This study analyses the variations of aerosol optical depth, total column ozone and water vapour, measured by a Microtops-II (MICRO-processor based Total Ozone Portable Spectrometer) ozonometer/sunphotometer over a coastal station in southwest peninsular India, Kochi. Observations of ozone and aerosols are analysed for a period, May 2012 to May 2013. Satellite data sets available over the region are also analysed, and a comparison is made with the in situ data. Sunphotometer measured 1020 nm aerosol optical depth (AOD) shows a temporal variability with an increase in AOD during the summer (high value of 0.35 in May 2012) and fewer values near 0.2 during the winter and the post-monsoon seasons. Satellite observations also show a similar pattern of variability with high AOD during the summer. Water vapour is maximum (near 3.5 cm) during the pre-monsoon and the summer monsoon and minimum (below 2 cm in January 2013) during the winter. Ozone shows seasonal variability with a minimum concentration during the winter (230 Dobson Unit (DU) in January 2013) and maximum (280 DU in May 2012) during the summer. OMI (Ozone measuring Instrument) onboard Aura satellite overestimates the column ozone by 10 DU in comparison with the Microtops ozonometer. However, the sunphotometer and satellite observations show a similar pattern of temporal variability with a small difference in magnitude during certain months. The zonal ozone distribution shows a seasonal variability with a reverse gradient between the summer and the winter.

In the present study, 3-D chemical transport model, MOZART-4 (Model for Ozone and Related chemical Tracers-Version-4) has been used to study the seasonal and spatial distribution of surface ozone (O3) over India. To illustrate the capabilities of model, the simulations are compared with the ground-based observations. The model reproduces the principal features present in ground-based observations. However, model is unable to simulate very low concentration of O3 during monsoon months. The model simulations are used to quantify the contribution of background ozone and Indian anthropogenic emissions to the variability of surface O3. The spatial distribution of total O3 (TO) shows maximum over Indo-Gangetic plains (IGP) and Eastern India while minimum over southern Indian region. The seasonal cycle of TO vary from 34.2 ± 7.6 to 51.9 ± 4.9 ppbv over the Indian landmass region due to changes in its topography and ozone lifetime. Annual mean total background O3 (TBO) over India shows highest during spring (29.3 ± 5.0 ppbv) and lowest during monsoon (19.6 ± 3.4 ppbv). Both Natural background O3 (NBO) and pollution background O3 (PBO) shows a minimum in summer which are essentially following the seasonal changes of total ozone. Significant variation of India pollution O3 (IPO) is found over India and the spatial variation of IPO follows the spatial variation of TO as well as spatial variation of emission of ozone precursors.

Episodes of extremely low ozone columns were observed over the territory of Russia in the Arctic winter of 2015/2016 and the beginning of spring 2016. We compare total ozone columns (TOC) obtained using different remote sensing techniques (satellite and ground-based observations) and results of numerical modelling over the territory of the Urals and Siberia for the above period. We demonstrate that the provided monitoring systems (including new Russian Fourier- spectrometer IKFS-2) and modern 3-dimensional models are able to capture the observed TOC anomalies. However, the results of observations and modelling show discrepancies of up to 20–30 % in TOC measurements. Analysis of the role of chemical and dynamical processes demonstrates that it is unlikely that observed short-term TOC variability may be a result of local photochemical destruction initiated by heterogeneous halogen activation on particles of polar stratospheric clouds that formed under low temperatures in the mid-winter.

Solar ultraviolet (UV) irradiances were measured with NILU-UV multichannel radiometers at Ushuaia (54◦ S) and Marambio (64◦ S) between 2000 and 2013. The measurements were part of the Antarctic NILU-UV network, which was started in cooperation between Spain, Argentina and Finland. The erythemally weighted UV irradiance time series of both stations were analysed for the first time. The quality assurance procedures included a travelling reference instrument to transfer the irradiance scale to the stations. The time series were homogenized and high quality measurements were available for the period 2000–2010. During this period UV indices of 11 or more were measured on 5 and 35 days at Marambio and Ushuaia, respectively. At Marambio, the peak daily maximum UV index of 12 and daily doses of around 7 kJ m−2 were measured in November 2007. The highest UV daily doses at both stations were typically around 6 kJ m−2 and occurred when the stations were inside the polar vortex, resulting in very low total ozone amount. At both stations, daily doses in late November could even exceed those in the summer. At Marambio, in some years, also daily doses in October can be as high as those during the summer. At Ushuaia, the peak daily maximum UV index of 13 was measured twice: in November 2003 and 2009. Also during those days, the station of Ushuaia was inside the polar vortex. The Academy of Finland has given financial support for this work through projects FARPOCC and SAARA. The MAR Project was financed by the National R+D Plan of the Spanish Ministry of Science and Technology (National Research Program in the Antarctic) under contract REN2000-0245-C02-01.

In this paper we investigate response of the total ozone column to energetic electron precipitation (EEP) observed by bremsstrahlung effect. The list of EEP events was prepared by members of the balloon experiments of the Lebedev Physical Institute. Here we used superposed epoch analysis and the days with EEP events are registered during winter (November–February) and summer (June–August) months from 1970 to 2012 were chosen as key dates. This period corresponds approximately to three solar cycles. Data of the total ozone column were collected by single coherent total ozone dataset, called the Multi Sensor Reanalysis (MSR). A long series of data of the total ozone column is allowed us to study the response of ozone content to 90 winter and 103 summer EEP events. The obtained ozone sensitivity to the events of energetic electron precipitation is clearly pronounced during local winters in the high latitudes of the Northern and Southern Hemispheres (60–80 NH and 60–80 SH). In the high latitudes of the Northern Hemisphere, during winter months, the total ozone content can be reduced by up to 10 DU after energetic electron precipitation with minimum observed on the first day after EEP events. Response of the total ozone, over high latitudes of the Northern Hemisphere, to EEP events can be opposite during summer months.

The ground-based ozone observation instrument, Brewer spectrophotometer (Brewer), was used to evaluate the quality of the total ozone column (TOC) produced by multiple polar-orbit satellite measurements at three stations in Antarctica (King Sejong, Jang Bogo, and Zhongshan stations). While all satellite TOCs showed high correlations with Brewer TOCs (R = ~0.8 to 0.9), there are some TOC differences among satellite data in austral spring, which is mainly attributed to the bias of Atmospheric Infrared Sounder (AIRS) TOC. The quality of satellite TOCs is consistent between Level 2 and 3 data, implying that “which satellite TOC is used” can induce larger uncertainty than “which spatial resolution is used” for the investigation of the Antarctic TOC pattern. Additionally, the quality of satellite TOC is regionally different (e.g., OMI TOC is a little higher at the King Sejong station, but lower at the Zhongshan station than the Brewer TOC). Thus, it seems necessary to consider the difference of multiple satellite data for better assessing the spatiotemporal pattern of Antarctic TOC.

In the 2019/2020 measurement campaign at Hohenpeißenberg (Germany) and Davos (Switzerland) we compared the well-established Dobson and Brewer spectrometers (single and double monochromator Brewer) with newer BTS array spectroradiometer based systems in terms of total ozone column (TOC) determination. The aim of this study is to validate the BTS performance in a longer-term TOC analysis over more than one year with seasonal and weather influences. Two different BTS setups have been used. A fibre coupled entrance optic version by PMOD/WRC called Koherent and a diffusor optic which proved to be simpler in terms of calibration from Gigahertz-Optik GmbH called BTS Solar. The array-spectrometer based BTS systems have been traceable calibrated to National Metrology Institutes (NMI) and the used TOC retrieval algorithms are based on spectral measurements in the range of 305 nm and 350 nm instead of single wavelength measurements as for Brewer or Dobson. The two BTS based systems, however, used fundamentally different retrieval algorithms for the TOC assessment, whereby the retrieval of the BTS solar turned out to achieve significantly smaller seasonal drifts. The intercomparison showed a deviation of the BTS Solar to Brewers of < 0.1 % with an expanded standard deviation of < 1.5 % within the whole measurement campaign. Koherent showed a deviation of 1.7 % with an expanded standard deviation of 2.7 % mostly given by a significant seasonal drift. Resulting, the BTS Solar performance is comparable to Brewers at the comparison in Hohenpeißenberg. The slant path slope is in-between double monochromator and single monochromator Brewer. Koherent shows a strong seasonal variation in Davos due to the sensitivity of its ozone retrieval algorithm to stratospheric temperature similar to the Dobson results.

In this work we present the validation results of the daily observations of the Total Ozone Column (TOC) obtained by the TROpospheric Monitoring Instrument (TROPOMI), and the Dobson spectrophotometer No. 118 located in Athens, Greece, (WOUDC Station ID: 293) during the period November 2017 to February 2021. Simultaneous observations of both instruments are used for this validation.The increased spatial resolution of TROPOMI observations in relation to the push-broom configuration (non-scanning) of the instrument (swath width of ~2600 km) offers the opportunity to study the spatial analysis of the observed differences in a large area around the ground-based station. By using the ground-based station in Athens we attempt to analyze spatial and temporal behavior of the TOC differences between Dobson and TROPOMI data in an area enclosed by a 500 km radius during the period from August 2019 to February 2021.

Brewer spectrophotometers are one of the most widely used instruments for measuring the Total Ozone Column (TOC) in the world, which is obtained by measuring solar radiance at a set of UV sensible wavelengths. To date, the value of the uncertainty in these measures has not been obtained quantitatively. With this work, we have carried out an exhaustive study of the uncertainties that have affected the measure of TOC with data obtained during the first ATMOZ field campaign carried out between 12-25 September 2016 at the Izaña Atmospheric Observatory, Canary Islands, Spain at 2373 m.a.s.l., organized by the Spanish Meteorological Agency (AEMET) and the World Radiation Center (PMOD/WRC). For this, we have differentiated between three uncertainty components: related to the measure (dead time, filters, etc), model components (cross sections, etc) and atmospheric components (effective temperatures and heights, etc). The total uncertainty has been obtained through the propagation of errors of the different parameters, and the cross-correlations between the model and atmospheric components, using two different data sets. With the standard algorithm we have obtained the expected 2σ-uncertainty, around 2.4% for the three RBCC-E Triad Brewer double-monochromator spectrophotometers studied (Br157, Br183 and Br185) at noon and using the Extra-Terrestrial Constant (ETC) Langley calibration. On the other hand, for these same spectrophotometers, and using an updated algorithm the 2σ-uncertainty are reduced to values around 1.3 % in the TOC measurement. In first approximation, ignoring the cross-correlations the ozone absorption coefficient covers the most of total ozone uncertainty in both algorithms, followed by the ozone optical mass, the ETC and the measurement uncertainties.

Weather forecast based on extrapolation methods is gathering a lot of attention due to the advance of artificial intelligence. Recent works on deep neural networks (CNN, RNN, LSTM, etc.) are enabling the development of spatiotemporal prediction models based on the analysis of historical time-series, images, and satellite data. In this paper, we focus on the use of deep learning for the forecast of stratospheric Ozone ( $$O_3$$ ), especially in the cases of exchanges between the polar vortex and mid-latitudes known as Ozone Secondary Events (OSE). Secondary effects of the Antarctic Ozone Hole are regularly observed above populated zones on South America, south of Africa, and New Zealand, resulting in abrupt reductions in the total ozone column of more than 10% and a consequent increase in UV radiation in densely populated areas. We study different OSE events from the literature, comparing real data with predictions from our model. We obtained interesting results and insights that may lead to accurate and fast prediction models to forecast stratospheric Ozone and the occurrence of OSE.

Measurements by the Dobson ozone spectrophotometer at the British Antarctic Survey’s (BAS) Halley research station form a record of Antarctic total column ozone that dates back to 1956. Due to its location, length, and completeness, the record has been, and continues to be, uniquely important for studies of long-term changes in Antarctic ozone. However, a crack in the ice shelf on which it resides forced the station to abruptly close for eight months and [SC-UB1] led to a gap in its historic record. We develop and test a method for filling in the record of Halley total ozone by combining and bias-correcting overpass data from a range of different satellite instruments. Tests suggest that our method reproduces the monthly ground-based Dobson total ozone values to within 20 Dobson units. We show that our approach improves on the overall performance as compared to simply using the raw satellite average or an individual instrument. The method also provides a check on the consistency of the automated Dobson used at Halley after 2018 compared to earlier manual Dobson data, and suggests a significant difference between the two. The filled Halley dataset provides further support that the Antarctic ozone hole is healing not only during September, but also in January.

The total ozone column (TOC) is retrieved using multiple optical satellite instrumentation (including TOMS, OMI, TROPOMI, GOME, GOME-2, and SCIAMACHY, to name a few). The spatial resolution of total ozone satellite measurements is quite low (e.g., 7x3.5km for TROPOMI, 13x24km for OMI, and 30x60km for SCIAMACHY). In some cases (say, close to the ozone hole boundary) it is of importance to have information on the total ozone at a higher spatial resolution. In this work we propose the use of multiple optical instruments performing the measurements in the ozone Chappuis ozone bands (400-650nm) for the total ozone column determination. This makes it possible to extend the number of instruments, which can be used for the total ozone determination (say, also using current/historic measurements by MODIS/Aqua&Terra, S-GLI/SCOM-C, VIIRS/Suomi-NPP, MSI/S-2, OLCI/S-3, MERIS/ENVISAT). In particular, MERIS and SCIAMACHY have been operated from the same satellite platform and had similar swaths (960km for SCIAMACHY and 1150km for MERIS). This means the method of total ozone retrieval based on combination of SCIAMACHY (30x60km) and MERIS (0.3x0.3km) observations over highly reflective ground (say, in Antarctica, where the ozone hole is located) is of value. The total ozone retrievals using Chappuis ozone bands is based on the fact that the top-of-atmosphere reflectance observed over a highly reflective ground (say, snow) has a minimum in the visible located around 600nm. This feature is due to due to the absorption of light by the atmospheric ozone (Gorshelev et al., 2014). The contribution of both ground and atmospheric light scattering to the top-of-atmosphere (TOA) does not have extrema in the vicinity of 600nm. Therefore, there is a possibility to remove both atmospheric and ground light scattering effects to the TOA reflectance over highly reflective underlying surface and derive the atmospheric transmittance due to the ozone absorption effects, which can be used for the TOC determination. Such a method has been explored using MERIS/ENVISAT (Jolivet et al., 2016) and OLCI/S-3 (Kokhanovsky et al., 2020) in the past. This paper is aimed at further improvement of the technique as applied to OLCI/S-3A,B. We have performed intercomparisons of OLCI TOC retrievals with TOC derived from ground and other satellite (e.g., OMI, TROPOMI, GOME-2) measurements. The TOC retrievals using OLCI have been performed over entire Antarctica allowing the generation of TOC at various spatial resolutions including standard 1x1 degree resolution.Gorshelev, V., et al., 2014: High spectral resolution ozone absorption cross-sections – Part 1: Measurements, data analysis and comparison with previous measurements around 293 K, Atmos. Meas. Tech., 7, 609–624, https://doi.org/10.5194/amt-7-609-2014.Jolivet D., et al., 2016: TORMS : total ozone retrieval from MERIS in view of application to Sentinel-3, Living Planet Symposium, Proceedings of the conference held 9-13 May 2016 in Prague, Czech Republic. Edited by L. Ouwehand. ESA-SP Volume 740, ISBN: 978-92-9221-305-3, p.358Kokhanovsky, A. A., et al., 2020: Retrieval of total ozone over Antarctica using Sentinel -3 Ocean and Land Colour Instrument, JQSRT, 2020, 251, https://doi.org/10.1016/j.jqsrt.2020.107045.

10 pags., 4 figs., Many Chemistry-Climate Models (CCMs) include a simplified treatment of brominated very short-lived (VSL) species by assuming CHBr as a surrogate for VSL. However, neglecting a comprehensive treatment of VSL in CCMs may yield an unrealistic representation of the associated impacts. Here, we use the Community Atmospheric Model with Chemistry (CAM-Chem) CCM to quantify the tropospheric and stratospheric changes between various VSL chemical approaches with increasing degrees of complexity (i.e., surrogate, explicit, and full). Our CAM-Chem results highlight the improved accuracy achieved by considering a detailed treatment of VSL photochemistry, including sea-salt aerosol dehalogenation and heterogeneous recycling on ice-crystals. Differences between the full and surrogate schemes maximize in the lowermost stratosphere and midlatitude free troposphere, resulting in a latitudinally dependent reduction of ∼1–7 DU in total ozone column and a ∼5%–15% decrease of the OH/HO ratio. We encourage all CCMs to include a complete chemical treatment of VSL in the troposphere and stratosphere., This study has been funded by the European Union's Horizon 2020 Re-search and Innovation program (Project ‘ERC-2016-COG 726349 CLIMAHAL’), and supported by the Consejo Superior de Investigaciones Científicas of Spain. Computing resources and support are provided by the Computational and Information System Laboratory (CISL,2017). R. P. Fernandez would like to thank financial support from CONICET, ANPCyT (PICT 2015-0714), UNCuyo (SeCTyP M032/3853) and UTN (PID 4920-194/2018). NCAR is sponsored by NSF under grant number 1852977. R. J. Salawitch appreciates support from the NASA (grant ACMP 80NSSC19K0983). The authors thank two anonymous reviewers for their constructive comments

Resumo Este estudo apresenta a segunda etapa da avaliação espaço-temporal das tendências a longo prazo nos valores da Coluna Total de Ozônio (CTO) sobre o Nordeste Brasileiro (NEB) durante a atuação do modo de variabilidade atmosférica El Niño - Oscilação Sul (ENOS), com foco na fase La Niña (modalidades Canônica e Modoki). O objetivo é analisar a variação anual e os efeitos desse fenômeno na região de estudo no período entre 1997 e 2018. Os dados utilizados são provenientes de sensoriamento remoto, gerados pelos sensores Total Ozone Mapping Spectrometer (TOMS) e Ozone Monitoring Instrument (OMI), disponibilizados pela National Aeronautics and Space Administration (NASA), e analisados através de médias, valores de anomalias e diagramas hovmoller. Foi constatado que eventos La Niña provocam, predominantemente, aumento na concentração de ozônio sobre o NEB. Nos períodos de atuação desse modo de variabilidade a desaceleração da Circulação Brewer-Dobson (CBD) é causada pela intensificação dos ventos alísios gerando acúmulo de ozônio na região tropical. Entre as duas modalidades, fenômenos Modoki apresentam esse efeito mais intensificado. O maior (+6,5) e menor (-3,0) valor médio mensal de anomalia obtidos ocorreram durante sua atuação, registrados na região norte do NEB em julho e setembro, respectivamente. Abstract This study presents a second stage of the spatio-temporal assessment of long-term trends in ozone concentrations in Northeast Brazil (NEB) under the influence of the El Niño - South Oscillation (ENSO) with emphasis on the La Niña phase (Canonical and Modoki). The objective is to analyze the annual variation and the effects of this phenomenon in the Total Ozone Column (TOC) over the NEB, between 1997 and 2018. The data come from remote sensing, generated by the Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instrument (OMI) sensors, made available by National Aeronautics and Space Administration (NASA), and analyzed using mean, anomaly values and hovmoller diagrams. It was found that La Niña events cause, predominantly, an increase in the concentration of ozone over the NEB. During periods of action of this mode of variability, the deceleration of Brewer-Dobson circulation (CBD) is caused by the intensification of trade winds, generating ozone accumulation in the tropical region. Between the two modalities, Modoki show this effect more intensified. The highest (+6.5) and lowest (-3.0) average monthly anomaly values obtained occurred during his performance, recorded in the northern region of NEB in July and September, respectively.

International audience; We proposed a simple algorithm to retrieve the total ozone column and snow properties (spectral albedo and effective light absorption path) using the high spatial resolution single–view MSI/S-2 measurements over Antarctica. In addition, the algorithm allows the retrieval of the snow grain size on a scale of 10–20 m. This algorithm should be useful for the understanding of intra-pixel total ozone and snow albedo variability in complement to satellite observations performed on a much coarser spatial resolution scale (0.3–1 km and even larger spatial scales)

The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. The S5P is a Sun-synchronous polar-orbiting satellite providing global daily coverage. The TROPOMI swath is 2600 km wide, and the ground resolution for most data products is 7.2×3.5 km2 (5.6×3.5 km2 since 6 August 2019) at nadir. The Finnish Meteorological Institute (FMI) is responsible for the development of the TROPOMI UV algorithm and the processing of the TROPOMI surface ultraviolet (UV) radiation product which includes 36 UV parameters in total. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and Antarctic areas were used for validation of the TROPOMI overpass irradiance at 305, 310, 324 and 380 nm, overpass erythemally weighted dose rate/UV index, and erythemally weighted daily dose for the period from 1 January 2018 to 31 August 2019. The validation results showed that for most sites 60 %–80 % of TROPOMI data was within ±20 % of ground-based data for snow-free surface conditions. The median relative differences to ground-based measurements of TROPOMI snow-free surface daily doses were within ±10 % and ±5 % at two-thirds and at half of the sites, respectively. At several sites more than 90 % of cloud-free TROPOMI data was within ±20 % of ground-based measurements. Generally median relative differences between TROPOMI data and ground-based measurements were a little biased towards negative values (i.e. satellite data < ground-based measurement), but at high latitudes where non-homogeneous topography and albedo or snow conditions occurred, the negative bias was exceptionally high: from −30 % to −65 %. Positive biases of 10 %–15 % were also found for mountainous sites due to challenging topography. The TROPOMI surface UV radiation product includes quality flags to detect increased uncertainties in the data due to heterogeneous surface albedo and rough terrain, which can be used to filter the data retrieved under challenging conditions.

An accurate characterization of spatial-temporal emission patterns and speciation of volatile organic compounds (VOCs) for multiple chemical mechanisms is important to improving the air quality ensemble modeling. In this study, we developed a 2017-based high-resolution (3 km × 3 km) model-ready emission inventory for Guangdong Province (GD) by updating estimation methods, emission factors, activity data, and allocation profiles. In particular, a full-localized speciation profile dataset mapped to five chemical mechanisms was developed to promote the determination of VOC speciation, and two dynamic approaches based on big data were used to improve the estimation of ship emissions and open fire biomass burning (OFBB). Compared with previous emissions, more VOC emissions were classified as oxygenated volatile organic compound (OVOC) species, and their contributions to the total ozone formation potential (OFP) in the Pearl River Delta (PRD) region increased by 17%. Formaldehyde became the largest OFP species in GD, accounting for 11.6% of the total OFP, indicating that the model-ready emission inventory developed in this study is more reactive. The high spatial-temporal variability of ship sources and OFBB, which were previously underestimated, was also captured by using big data. Ship emissions during typhoon days and holidays decreased by 23–55%. 95% of OFBB emissions were concentrated in 9% of the GD area and 31% of the days in 2017, demonstrating their strong spatial-temporal variability. In addition, this study revealed that GD emissions have changed rapidly in recent years due to the leap-forward control measures implemented, and thus, they needed to be updated regularly. All of these updates led to a 5–17% decrease in the emission uncertainty for most pollutants. The results of this study provide a reference for how to reduce uncertainties in developing model-ready emission inventories.

The ozonesonde is a small balloon-borne instrument that is attached to a standard radiosonde to measure profiles of ozone from the surface to 35 km with ∼100-m vertical resolution. Ozonesonde data constitute a mainstay of satellite calibration and are used for climatologies and analysis of trends, especially in the lower stratosphere where satellites are most uncertain. The electrochemical concentration cell (ECC) ozonesonde has been deployed at ∼100 stations worldwide since the 1960s, with changes over time in manufacture and procedures, including details of the cell chemical solution and data processing. As a consequence, there are biases among different stations and discontinuities in profile time series from individual site records. For 22 years the Jülich (Germany) Ozonesonde Intercomparison Experiment (JOSIE) has periodically tested ozonesondes in a simulation chamber designated the World Calibration Centre for Ozonesondes (WCCOS) by WMO. During October–November 2017 a JOSIE campaign evaluated the sondes and procedures used in Southern Hemisphere Additional Ozonesondes (SHADOZ), a 14-station sonde network operating in the tropics and subtropics. A distinctive feature of the 2017 JOSIE was that the tests were conducted by operators from eight SHADOZ stations. Experimental protocols for the SHADOZ sonde configurations, which represent most of those in use today, are described, along with preliminary results. SHADOZ stations that follow WMO-recommended protocols record total ozone within 3% of the JOSIE reference instrument. These results and prior JOSIEs demonstrate that regular testing is essential to maintain best practices in ozonesonde operations and to ensure high-quality data for the satellite and ozone assessment communities.

Plants rely on spectral cues present in their surroundings, generated by the constantly changing light environment, to guide their growth and reproduction. Photoreceptors mediate the capture of information by plants from the light environment over a wide range of wavelengths, but despite extensive evidence that plants respond to various light cues, only fragmentary data have been published showing patterns of diurnal, seasonal and geographical variation in the spectral composition of daylight. To illustrate patterns in spectral photon ratios, we measured time series of irradiance spectra at two distinct geographical and climatological locations, Helsinki, Finland and Gual Pahari, India. We investigated the drivers behind variation of the spectral photon ratios measured at these two locations, based on the analysis of over 400 000 recorded spectra. Differences in spectral irradiance were explained by different atmospheric factors identified through multiple regression model analysis and comparison to spectral irradiance at ground level simulated with a radiative transfer model. Local seasonal and diurnal changes in spectral photon ratios were related to solar elevation angle, atmospheric water-vapour content and total ozone column thickness and deviated from their long-term averages to an extent likely to affect plant photobiology. We suggest that future studies should investigate possible effects of varying photon ratios on terrestrial plants. Solar elevation angle especially affects the patterns of B:G and B:R ratios. Water vapour has a large effect on the R:FR photon ratio and modelled climate scenarios predict that increasing global temperatures will result in increased atmospheric water vapour. The development of proxy models, utilising available data from weather and climate models, for relevant photon ratios as a function of solar elevation angle and atmospheric factors would facilitate the interpretation of results from past, present and future field studies of plants and vegetation.

Characteristics of atmospheric VOCs (volatile organic compounds) have been extensively studied in megacities in China, however, they are scarcely investigated in medium/small-sized cities in North China Plain (NCP). A comprehensive research on possible sources of VOCs was conducted in a medium-sized city of NCP, from May to September 2019. A total of 143 canister samples of 8 sites in Xuchang city were collected, and 57 VOC species were detected. The average VOC concentrations were 42.6 ± 31.6 μg/m3, with 53.7 ± 31.0 μg/m3 and 32.1 ± 27. 8 μg/m3, in the morning and afternoon, respectively. Alkenes and aromatics contributed 80% of the total ozone formation potential (OFP). Aromatics accounted for more than 95% of secondary organic aerosol potential (SOAP). VOCs were dominated by the local emission with significant transport from the southeast direction. PMF analysis extracted 6 sources, which were combustion (33.1%), LPG usage (19.3%), vehicular exhaust & fuel evaporation (15.8%), solvent usage (15.2%), industrial (9.11%) and biogenic (7.51%), respectively and they contributed 33.4%, 17.6%, 12.9%, 18.6%, 9.28% and 8.22% to the OFP, respectively. Combustion and LPG usage were the dominant VOC sources; and combustion, solvent usage and LPG usage were the main sources of OFP in Xuchang city, which were different to megacities in China with a high contribution from vehicular exhaust, solvent usage and industry, suggesting specific control strategies on VOCs need to be implemented in medium-sized city such as Xuchang city.