Comparison of long term tropospheric ozone trends measured by lidar and ECC ozonesondes from 1991 to 2010 in Southern France

International audienceECC (Electrochemical Concentration Cell) ozonesondes and UV DIAL (DIfferential Absorption Lidar) measurements have been carried out simultaneously at OHP (Observatoire de Haute Provence, 44°N, 6.7°E, 690 m) since 1991. A unique long-term trend assessment by two different instruments operated routinely at the same location is possible. Air mass trajectories have been calculated for all the ozone observations available at OHP. The bias between the seasonal mean calculated with lidar and ECC ozone vertical profiles for 4 time- periods of 5 years is 0.6 ppbv in the free troposphere (4-8 km). Larger differences (> 10 ppbv) are explained by the need for clear sky conditions during lidar observations. The measurements of both instruments have been combined to decrease the impact of short-term atmospheric variability on the trend estimate

On the relationship between Arctic ice clouds and polluted air masses over the North Slope of Alaska in April 2008

Recently, two Types of Ice Clouds (TICs) properties have been characterized using ISDAC airborne measurements (Alaska, April 2008). TIC-2B were characterized by fewer (110 μm) ice crystals, a larger ice supersaturation (>15%) and a fewer ice nuclei (IN) concentration (<2 order of magnitude) when compared to TIC-1/2A. It has been hypothesized that emissions of SO2 may reduce the ice nucleating properties of IN through acidification, resulting to a smaller concentration of larger ice crystals and leading to precipitation (e.g. cloud regime TIC-2B) because of the reduced competition for the same available moisture. Here, the origin of air masses forming the ISDAC TIC-1/2A (1 April 2008) and TIC-2B (15 April 2008) is investigated using trajectory tools and satellite data. Results show that the synoptic conditions favor air masses transport from the three potentials SO2 emission areas to Alaska: eastern China and Siberia where anthropogenic and biomass burning emission respectively are produced and the volcanic region from the Kamchatka/Aleutians. Weather conditions allow the accumulation of pollutants from eastern China/Siberia over Alaska, most probably with the contribution of acid volcanic aerosol during the TIC-2B period. OMI observations reveal that SO2 concentrations in air masses forming the TIC-2B were larger than in air masses forming the TIC-1/2A. Airborne measurements show high acidity near the TIC-2B flight where humidity was low. These results strongly support the hypothesis that acidic coating on IN are at the origin of the formation of TIC-2B

Anthropogenic and forest fire pollution aerosol transported to the Arctic: observations from the POLARCAT-France spring campaign

During the POLARCAT-France airborne measurement campaign in spring 2008, several pollution plumes transported from mid-latitude regions were encountered. The study presented here focuses on air masses from two different geographic origins (Europe and Asia) and from 2 different source types (anthropogenic pollution and forest fires). One case study analyses an European air mass, which was sampled during three consecutive day. Modelling of the aerosol particle ageing by coagulation suggests that coagulation cannot solely explain the evolution of the size distributions, which is particularly true for the accumulation mode. Analyses of the aerosol refractory size distributions indicate that the Aitken mode was mostly composed of volatile compounds, while accumulation mode particles desorbed to a refractory mode yielding a modal mean diameter evolving from 48 to 59 nm for the three consecutive days of sampling the same air mass. The single refractory mode suggests an internally mixed aerosol population which is supported from electron microscopy and subsequent EDX analyses of the accumulation mode particles. Another case study focuses on European air masses polluted by fire emissions and Asian air masses with contributions from both biomass burning and anthropogenic emissions. On the one hand, the aerosol size distributions of the European biomass burning plumes are almost mono-modal with most of the particles found in the aged accumulation mode which desorbed uniformly. On the other hand, Asian air masses were more complex because of the mixing of different source contributions related to more variable and multimodal ambient and refractory aerosol size distributions. Electron microscopy illustrated soot-like inclusions in several samples. Within samples attributed to forest fire sources, the chemical signature is highly associated with the presence of potassium, which is characteristic for biomass burning plumes. The particle images suggest an internal mixing of sampled aerosol particles

OH and RO 2 radicals at Dome C (East Antarctica): first observations and assessment of photochemical budget

International audienceMeasurements of OH and total peroxy RO 2 (HO 2 + organic peroxy) radicals were performed in December 2011/January 2012 at the Dome C Concordia station (East Antarctica, 75.1˚S / 123.3˚E) in the frame of the Oxi-dant Production over Antarctic Land and its Export (OPALE) project. The goal of these first on the East Antarctica plateau radical measurements was to estimate the oxidative capacity and assess the role of snow emissions on the radical budget in this part of Antarctica. The OH concentration levels were found to be in general similar to those observed at South Pole. However, based on the analysis of the OH sources and sinks derived from the available measurements of NO x , HONO, HCHO, H 2 O 2 and others, it has been concluded that, in contrast to South Pole, the photolysis of HONO is the major OH source at Dome C site. The role of HONO as the major source of OH is also supported by an excellent correlation of OH with the production rate of OH from the HONO photolysis. The observed diurnal profiles of OH and RO 2 are discussed in relation with boundary dynamics and the variability of photolysis and snow emissions rates

Source contributions to Northern Hemisphere CO and black carbon during spring and summer 2008 from POLARCAT and START08/preHIPPO observations and MOZART-4

International audienceAnthropogenic pollution and wildfires are main producers of carbon monoxide (CO) and black carbon (BC) in the Northern Hemisphere. High concentrations of these compounds are transported into the Arctic troposphere, influencing the ecosystem in high northern latitudes and the global climate. The global chemical transport model MOZART-4 is used to quantify the seasonal evolution of the contribution of CO and BC from different source regions in spring and summer 2008 by tagging their emissions. Aircraft observations from the POLARCAT experiments, in particular NASA ARCTAS, NOAA ARCPAC, POLARCAT-France, DLR GRACE and YAK-AEROSIB, as well as the NSF START08/preHIPPO experiments during Spring-Summer 2008 are combined to quantify the representation of simulated tracer characteristics in anthropogenic and fire plumes. In general, the model reproduces CO and BC well. Based on aircraft measurements and FLEXPART back-trajectories, the altitude contribution of emissions coming from different source regions is well captured in the model. Uncertainties of the MOZART-4 model are identified by comparing the data with model results on the flight tracks and using MOPITT satellite observations. Anthropogenic emissions are underestimated by about 10% in high northern latitudes in spring, and shortcomings exist in simulating fire plumes. The remote impact of East-Siberian fire emissions is underestimated for spring, whereas the impact of Southeast Asian fire emissions to mid-latitude CO values is overestimated by the model. In summer, mid-latitude CO values agree well between model and observations, whereas summer high latitude East-Siberian fire emissions in the model are overestimated by 20% in comparison to observations in the region. On the other hand, CO concentrations are underestimated by about 30% over Alaska and Canada at altitudes above 4 km. BC values are overestimated by the model at altitudes above 4 km in summer. Based on MOZART-4, with tagged CO and BC tracers, anthropogenic emissions of Asia, Europe and the US have the largest contribution to the CO and BC in mid- and high latitudes in spring and summer. Southeast Asian, Chinese and Indian fires have a large impact on CO pollution in spring in low latitudes with a maximum between 20° and 30°, whereas Siberian fires contribute largely to the pollution in high latitudes, up to 10% in spring and up to 30% in summer. The largest contributions to BC values in high latitudes are from anthropogenic emissions (about 70%). CO and BC have larger mass loadings in April than in July, as a result of photochemistry and dynamics

Updated trends of the stratospheric ozone vertical distribution in the 60° S–60° N latitude range based on the LOTUS regression model

This study presents an updated evaluation of stratospheric ozone profile trends in the 60° S–60° N latitude range over the 2000–2020 period using an updated version of the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) regression model that was used to evaluate such trends up to 2016 for the last WMO Ozone Assessment (2018). In addition to the derivation of detailed trends as a function of latitude and vertical coordinates, the regressions are performed with the datasets averaged over broad latitude bands, i.e. 60–35° S, 20° S–20° N and 35–60° N. The same methodology as in the last assessment is applied to combine trends in these broad latitude bands in order to compare the results with the previous studies. Longitudinally resolved merged satellite records are also considered in order to provide a better comparison with trends retrieved from ground-based records, e.g. lidar, ozonesondes, Umkehr, microwave and Fourier transform infrared (FTIR) spectrometers at selected stations where long-term time series are available. The study includes a comparison with trends derived from the REF-C2 simulations of the Chemistry Climate Model Initiative (CCMI-1). This work confirms past results showing an ozone increase in the upper stratosphere, which is now significant in the three broad latitude bands. The increase is largest in the Northern and Southern Hemisphere midlatitudes, with ∼2.2 ± 0.7 % per decade at ∼2.1 hPa and ∼2.1 ± 0.6 % per decade at ∼3.2 hPa respectively compared to ∼1.6 ± 0.6 % per decade at ∼2.6 hPa in the tropics. New trend signals have emerged from the records, such as a significant decrease in ozone in the tropics around 35 hPa and a non-significant increase in ozone in the southern midlatitudes at about 20 hPa. Non-significant negative ozone trends are derived in the lowermost stratosphere, with the most pronounced trends in the tropics. While a very good agreement is obtained between trends from merged satellite records and the CCMI-1 REF-C2 simulation in the upper stratosphere, observed negative trends in the lower stratosphere are not reproduced by models at southern and, in particular, at northern midlatitudes, where models report an ozone increase. However, the lower-stratospheric trend uncertainties are quite large, for both measured and modelled trends. Finally, 2000–2020 stratospheric ozone trends derived from the ground-based and longitudinally resolved satellite records are in reasonable agreement over the European Alpine and tropical regions, while at the Lauder station in the Southern Hemisphere midlatitudes they show some differences

Updated trends of the stratospheric ozone vertical distribution in the 60° S–60° N latitude range based on the LOTUS regression model

peer reviewedAbstract. This study presents an updated evaluation of stratospheric ozone profile trends in the 60∘ S–60º N latitude range over the 2000–2020 period using an updated version of the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) regression model that was used to evaluate such trends up to 2016 for the last WMO Ozone Assessment (2018). In addition to the derivation of detailed trends as a function of latitude and vertical coordinates, the regressions are performed with the datasets averaged over broad latitude bands, i.e. 60–35º S, 20º S–20º N and 35–60º N. The same methodology as in the last assessment is applied to combine trends in these broad latitude bands in order to compare the results with the previous studies. Longitudinally resolved merged satellite records are also considered in order to provide a better comparison with trends retrieved from ground-based records, e.g. lidar, ozonesondes, Umkehr, microwave and Fourier transform infrared (FTIR) spectrometers at selected stations where long-term time series are available. The study includes a comparison with trends derived from the REF-C2 simulations of the Chemistry Climate Model Initiative (CCMI-1). This work confirms past results showing an ozone increase in the upper stratosphere, which is now significant in the three broad latitude bands. The increase is largest in the Northern and Southern Hemisphere midlatitudes, with ∼2.2 ± 0.7 % per decade at ∼2.1 hPa and ∼2.1 ± 0.6 % per decade at ∼3.2 hPa respectively compared to ∼1.6 ± 0.6 % per decade at ∼2.6 hPa in the tropics. New trend signals have emerged from the records, such as a significant decrease in ozone in the tropics around 35 hPa and a non-significant increase in ozone in the southern midlatitudes at about 20 hPa. Non-significant negative ozone trends are derived in the lowermost stratosphere, with the most pronounced trends in the tropics. While a very good agreement is obtained between trends from merged satellite records and the CCMI-1 REF-C2 simulation in the upper stratosphere, observed negative trends in the lower stratosphere are not reproduced by models at southern and, in particular, at northern midlatitudes, where models report an ozone increase. However, the lower-stratospheric trend uncertainties are quite large, for both measured and modelled trends. Finally, 2000–2020 stratospheric ozone trends derived from the ground-based and longitudinally resolved satellite records are in reasonable agreement over the European Alpine and tropical regions, while at the Lauder station in the Southern Hemisphere midlatitudes they show some differences

Variabilité inter-annuelle de 20 ans de mesure de l'ozone troposphérique par lidar et sondes électrochimiques à l'Observatoire de Haute Provence (OHP)

L ozone est un constituant minoritaire secondaire de l atmosphère. C est un gaz à effet de serre et un polluant nocif pour la biodiversité dans la troposphère. Il peut être transporté de la stratosphère ou de la couche limite vers la troposphère libre et parcourir de longues distances au-dessus des continents et des océans. L objectif de cette thèse est de contribuer à l analyse des tendances à long terme des concentrations d ozone dans la troposphère et à la compréhension des sources de cette variabilité temporelle. Pour cela, nous avons utilisé les mesures de deux instruments basés à l Observatoire de Haute Provence (OHP) dans le sud de la France (44 N, 6:7 E), des sondes ECC (Electro-chemical Concentration Cell) embarquées sous ballon et un lidar UV DIAL. Les travaux menés au cours de cette thèse ont montré qu il est indispensable de les combiner pour prendre en compte la diversité des conditions météorologiques. En effet, notre analyse montre un biais systématique d environ 1.3 ppb entre les moyennes saisonnières obtenues avec chacun des instruments qui est compatible avec les résultats des campagnes d inter-comparaison mais qui est beaucoup plus faible que les différences importantes (> 7 ppb) dues à la variabilité du transport du fait des différences d échantillonnage. En combinant les deux jeux de données, le lien entre la variabilité de l ozone et celle du transport (NAO, hauteur de la tropopause, origine des masses d air) a été étudié. Dans la haute et moyenne troposphère aucune tendance significative n est observée, malgré une corrélation significative avec la NAO et un changement pour la dernière décennie dans les apports d ozone à 500 hPa pour certains régimes de transport. En revanche, une tendance négative après 2000 est observée dans les basses couches. Elle peut être expliquée par une augmentation de la couche de mélange accompagnée d une augmentation des flux de sud et une diminution de l apport en ozone pour ces régimes de transport. La caractérisation des masses d air arrivant à l OHP avec d autres paramètres tels que l humidité spécifique, la vorticité potentielle et les aérosols a permis d expliquer certaines sources de variabilité des concentrations d ozone. L apport des mesures d aérosol issues de deux ans d observations du lidar spatial CALIOP reste cependant limité et d autres mesures d aérosols doivent être prises en compte.Tropospheric ozone is important both as an oxidant and as a greenhouse gas. It may have implications for human health and vegetation. It can be transported from the stratosphere or from the boundary layer into the free troposphere, and then it can be subjected to the long range transport over oceans and continents. The aim of this thesis is to contribute to the analysis of long term trends of the ozone concentrations in the troposphere and to the understanding of the sources of the temporal variability. We used measurements of two instruments based at the Observatoire de Haute Provence (OHP) in the south of France (44 N, 6.7 E), the ECC sondes (Electro-chemical Concentration Cell) and the UV DIAL lidar. Our study has shown that this is necessary to combine both data sets to take into account the different meteorology conditions. Our analysis shows a bias of about 1.3 ppb between the seasonal means of ozone measured by each instrument, which is consistent with the results of the inter- comparison campaign, but, which is much weaker than the strong differences (> 7 ppb) due to the variability of the transport because of the difference of sampling. In combining both data sets, the link between the ozone variability and the transport variability (NAO, tropopause height, air masses origin) has been studied. In the upper and the mid-troposphere, no significant trend is observed beside a significant correlation with the NAO index and a change for the last decade of the contribution in ozone of some transport regime at 500 hPa. However, a negative trend after 2000 is observed in the lower troposphere. It can be explained by an increase of the mixing layer height with an increase of the flux coming from the south and the decrease of the contribution in ozone of this transport regime. To characterize the air masses coming to OHP, we used other parameters like the specific humidity, the potential vorticity and the aerosols, which can explain some sources of ozone variability. However, the contribution of the aerosols measurements of the spatial lidar CALIOP during two years is still limited and more aerosols measurements must be taken into account.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Lidar measurements of ozone vertical profiles

International audienceAttention is given to the differential absorption lidar technique used in measuring the vertical ozone distribution of the troposphere and stratosphere. The basis of these measurements are UV wavelength range laser sources which encompass Nd:YAG pumped dye lasers and Exciplex lasers. High temporal and spatial resolution, together with measurement continuity, allow the observation of ozone variations at various time and space scales that are important in such areas of current interest as troposphere-stratosphere exchanges, long range transport, the global ozone budget, and correlations between ozone number densities and other atmospheric parameters

Etude du transport et de l'évolution physico-chimique de masses d'air européennes au-dessus de l'Atlantique Nord sous des conditions anticycloniques

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF