Distribution and origin of ozone in the eastern Mediterranean free troposphere during MINOS (August 2001)

International audienceA coupled tropospheric chemistry ? climate model is used to reproduce and analyze tropospheric ozone distributions observed during the MINOS campaign in the eastern Mediterranean region (August, 2001). Generally, regional atmospheric dynamics in summer are strongly influenced by the occurrence of an upper tropospheric anti-cyclone, associated with the Asian summer monsoon and centered over the Tibetan Plateau. The anti-cyclone affects the chemical composition of the upper troposphere, where ozone concentrations of about 50 ppbv were measured, through advection of boundary layer air from South-East Asia. A layer between 4?6 km thickness and containing up to 120 ppbv of ozone was present beneath. Ozone from stratospheric origin and from lightning NOx contributed to this layer. Additionally, pollutant ozone from North America was mixed in. Ozone in the lower troposphere originated mainly from the European continent. Modeled ozone profiles are in reasonable agreement with the observations. The stratospheric influence is sometimes overestimated by the model due to too strong vertical diffusion associated with the relatively coarse vertical resolution of the model, and specific convective events are not reproduced realistically. The modeled tropospheric ozone column over the eastern Mediterranean is ~50 DU in summer, to which ozone from recent stratospheric origin contributes about 30%, ozone from lightning 13%, and from South-East Asia, North America and Europe about 7%, 8% and 14%, respectively, adding to a long-term hemispheric background of 25% of the column

Transport and build-up of tropospheric trace gases during the MINOS campaign: comparision of GOME, in situ aircraft measurements and MATCH-MPIC-data

The MINOS (Mediterranean INtensive Oxidant Study) campaign was an international, multi-platform field campaign to measure long-range transport of air-pollution and aerosols from South East Asia and Europe towards the Mediterranean basin during August 2001. High pollution events were observed during this campaign. For the Mediterranean region enhanced tropospheric nitrogen dioxide (NO₂) and formaldehyde (HCHO), which are precursors of tropospheric ozone (O₃), were detected by the satellite based GOME (Global Ozone Monitoring Experiment) instrument and compared with airborne in situ measurements as well as with the output from the global 3D photochemistry-transport model MATCH-MPIC (Model of Atmospheric Transport and CHemistry - Max Planck Institute for Chemistry). The increase of pollution in that region leads to severe air quality degradation with regional and global implications

On the interpretation of in situ HONO observations via photochemical steady state

A substantial body of recent literature has shown that boundary layer HONO levels are higher than can be explained by simple, established gas-phase chemistry, to an extent that implies that additional HONO sources represent a major, or the dominant, precursor to OH radicals in such environments. This conclusion may be reached by analysis of point observations of (for example) OH, NO and HONO, alongside photochemical parameters; however both NO and HONO have non-negligible atmospheric lifetimes, so these approaches may be problematic if substantial spatial heterogeneity exists. We report a new dataset of HONO, NOx and HOx observations recorded at an urban background location, which support the existence of additional HONO sources as determined elsewhere. We qualitatively evaluate the possible impacts of local heterogeneity using a series of idealised numerical model simulations, building upon the work of Lee et al. (J. Geophys. Res., 2013, DOI: 10.1002/2013JD020341). The simulations illustrate the time required for photostationary state approaches to yield accurate results following substantial perturbations in the HOx/NOx/NOy chemistry, and the scope for bias to an inferred HONO source from NOx and VOC emissions in either a positive or negative sense, depending upon the air mass age following emission. To assess the extent to which these impacts may be present in actual measurements, we present exploratory spatially resolved measurements of HONO and NOx abundance obtained using a mobile instrumented laboratory. Measurements of the spatial variability of HONO in urban, suburban and rural environments show pronounced changes in abundance are found in proximity to major roads within urban areas, indicating that photo-stationary steady state (PSS) analyses in such areas are likely to be problematic. The measurements also show areas of very homogeneous HONO and NOx abundance in rural, and some suburban, regions, where the PSS approach is likely to be valid. Implications for future exploration of HONO production mechanisms are discussed

Evaluation of the MOCAGE Chemistry Transport Model during the ICARTT/ITOP Experiment

We evaluate the Meteo-France global chemistry transport 3D model MOCAGE (MOdele de Chimie Atmospherique a Grande Echelle) using the important set of aircraft measurements collected during the ICARRT/ITOP experiment. This experiment took place between US and Europe during summer 2004 (July 15-August 15). Four aircraft were involved in this experiment providing a wealth of chemical data in a large area including the North East of US and western Europe. The model outputs are compared to the following species of which concentration is measured by the aircraft: OH, H2O2, CO, NO, NO2, PAN, HNO3, isoprene, ethane, HCHO and O3. Moreover, to complete this evaluation at larger scale, we used also satellite data such as SCIAMACHY NO2 and MOPITT CO. Interestingly, the comprehensive dataset allowed us to evaluate separately the model representation of emissions, transport and chemical processes. Using a daily emission source of biomass burning, we obtain a very good agreement for CO while the evaluation of NO2 points out incertainties resulting from inaccurate ratio of emission factors of NOx/CO. Moreover, the chemical behavior of O3 is satisfactory as discussed in the paper

FTIS remote sensing of flare emissions

Increasing regulatory standards for the limitation of greenhouse gas and other pollutant emissions from industrial facilities require new environmental control strategies and innovative and cost- effective measurement techniques. Elevated flare stacks present a difficult measurement challenge, because it is extremely difficult to determine concentration in the post-combustion gas of operational flares by sampling techniques. A remote sensing measurement system has to be used, therefore. Fourier-Transform-Infrared-Spectroscopy (FTIS) measurements were realized using a mobile environmental laboratory which is equipped with a high resolution K300 spectrometer. A Multi-component Air Pollution Software (MAPS) was used to determine CO2, CH4, CO and NO concentrations. It is based on radiative transfer line-by-line calculations and least-square fit procedures. The paper focuses on the results of FTIS flare emissions measurements at natural gas production facilities. Different types offlares have been investigated under varying operational conditions. Emission rates and combustion efficiencies are calculated which indicate that the environmental impact of methane emissions from flares is rather small

Comportement alimentaire au cours du changement d'habitat lié à l'émergence chez le saumon atlantique Salmo salar L. et la truite commune Salmo trutta L., en conditions semi-naturelles

Les premiers comportements alimentaires après l'éclosion de jeunes larves de saumon Atlantique et de truite commune ont été analysés par examen de leurs contenus stomacaux. Les échantillons de larves provenaient de paniers grillagés contenant au départ 50 oeufs, de l'une ou l'autre espèce, mélangés à des graviers et introduits dans le substrat de ruisseaux artificiels extérieurs, alimentés par un cours d'eau naturel. Dans deux cages plus grandes, munies d'un piège de dévalaison, une centaine d'oeufs de chaque espèce constituait le témoin de développement. L'analyse simultanée du déroulement de l'émergence, du degré de résorption de la vésicule, de la croissance des larves et de leurs contenus stomacaux a permis de mettre en évidence que la prise alimentaire est postérieure à l'émergence et démarre, avec la perte de poids de l'alevin, avant la fin de la résorption de la vésicule pour les 2 espèces. Le comportement alimentaire est un peu plus précoce chez les truites. Chez les saumons, la capture des proies est précédée par une phase d'ingestion de débris végétaux liée au positionnement benthique des alevins