Catálogo de publicaciones - libros

The present work provides an overview of the transport and transformation processes occurred above the Mediterranean with emphasis in the Eastern basin. It summarises the results from several campaigns performed since the last decade. The measurements gave evidence of a remarkably high level of air pollution from the surface to the top of the troposphere up to 15 km altitude. The strongest anthropogenic influence was observed in the lower 4 km by pollutants originating from both Westand East Europe transported by the northerly flow. The sources are industrial activity, traffic, forest fires, agricultural and domestic burning. Trajectory analysis and model results suggest also an important influence by Asian pollution plum near the tropopause from the east.

Near the surface the air pollution has several undesirable consequences. First, the European Union eight-hourly air quality standard for ozone is exceeded throughout the summer in the entire Mediterranean region. Second, the concentrations of aerosols are high as well, affecting human health. The aerosols furthermore influence the Mediterranean atmospheric energy budget by scattering and absorbing solar radiation. During summer, they reduce solar radiation absorption by the sea by about 10% and they alter the heating profile of the lower troposphere. As a consequence, evaporation and moisture transport, in particular to North Africa and the Middle East, are suppressed.

In the free troposphere, pollution is largely determined by intercontinental transport, whereas upper tropospheric pollution from Asia can reach the stratosphere. These “crossroads” carry large pollution loads over the Mediterranean, and the negative effects extend far beyond the region. International efforts are called for to reduce these atmospheric environmental stresses and to further investigate the links between Mediterranean and global climate change.

Mineral dust is a major aerosol component over many regions of the world, especially arid areas. In satellite images dust is the most persistently visible aerosol component over the oceans. There is increased interest in dust because of its impact on climate and also because iron associated with dust is an essential micronutrient that can serve to enhance ocean primary productivity and, thus, impact the global carbon cycle. Africa is the world’s largest dust source. Great quantities of African dust are transported over large areas of the North Atlantic and the Mediterranean. In this report I review recent research on African dust transport and discuss some of the possible impacts that dust might have. A major concern is the future trend in African dust transport under climate change conditions. It is very difficult to predict future trends because of our lack of understanding of the factors that affect the activity of dust sources. North Africa can serve as the ideal laboratory in which to study these important processes.

The radiative and physiological effects of doubled atmospheric carbon dioxide concentration (CO) on climate are described using climate simulations. When CO was increased for vegetation only assuming no radiative effect, the response was a decrease in stomatal conductance followed by a temperature increase. This temperature increase was stronger when the vegetation physiological “down-regulation” was allowed in the model. The radiative forcing alone did not affect the global mean photosynthesis, however, some stimulation was observed in cold places. The interactions between the physiological and the radiative effects of doubled CO are not linearly “additive” and when acting together they tend to reduce the warming in the Mediterranean region.

The site of Mt. Cimone, located to the south of the Alps and the Po Valley and to the north of the Mediterranean Sea, is considered to be representative of European background conditions. At the site a number of atmospheric studies are carried out in the frame of different International Research Projects. Among these, continuous observations of climate altering gases are carried out and are here reported.

This manuscript is a written version of the talk presented at the NATO ARW. The paper is not designed as a general overview of gas-phase processes, rather the intention has been to try and highlight work that has been going on gas-phase processes which have possible important conesquences for the complex chemistry occurring in the Mediterranean atmosphere. The manuscript is constrained to chemical processes involved in the gas-phase photooxidation of volatile organic compounds (VOCs).

Around the Mediterranean sea, deserts and desert-like conditions can be found in close proximity to a very warm sea and thus to a marine airmass with a high moisture content, e.g., the coasts of Morocco, Algiers, Tunisia, Libya, and Almeria in Southeastern Spain. These regions were covered with vegetation in historical times, e.g., during the Roman Empire, and in the case of Almeria, just 150 years ago, before the forests were used to fuel lead mines. The question is: did forest removal cause them to run a feedback cycle towards desertification? The reanalysis of results from seventeen EC research projects (Section 5) suggests that this could be the case.

This work shows that the hydrological system in this region is very sensitive to land-use changes and, more recently, to air pollution effects as well. Both of these can combine to exceed critical threshold levels, e.g., the height of the cloud condensation levels with respect to the height of the coastal mountain ranges. This results in the loss of summer storms and tips the regional climate towards desertification and drought. The non-precipitated water vapour returns and accumulates over the Western Mediterranean Basin to heights reaching over 5000 m, for periods lasting from 3 to 10 days in summer.

The purpose of this work is to investigate the direct radiative forcing of aerosols on the supersite of Djougou (Northern Benin) during the AMMA (African Monsoon Multidisciplinary Analyses) dry season experiment (January 2006). We focus our simulations on the Top Of Atmosphere (TOA), Bottom Of Atmosphere (BOA), and ATMosphere (ATM) radiative forcings. During the period, Sun-photometric measurements indicate a rather turbid atmosphere with a mean Aerosol Optical Depth (AOD), for the overall period, about 0.90 ± 0.01 at 440 nm. The aerosol absorption coefficient at the surface was comprised between 2 and 90 Mm with a mean value of 19.2 Mm. In the same time, the scattering coefficient ranged between 50 and 400 Mm, with an averaged of 160 Mm. This leads to a Single Scattering Albedo (SSA) comprised between 0.75 and 0.95 with an average value of 0.90, indicating moderate absorbing aerosols. Differential mobility analyser measurements indicate a monomodal (nucleation mode) number size distribution, with a mean geometric diameter of 96.5 nm, associated with a geometric standard deviation of 1.87. The characteristics of the size distribution, associated with the refractive index of aerosols, have been used in the Mie theory for computing aerosol optical properties at different wavelengths. Associated with ground-based observations, the micro pulse lidar indicates the presence of two distinct aerosol layers, with a first one located between the surface and 500 m and a second one, characterized by aged biomass burning particles, located above (1500-3500 m). Based on surface and aircraft observations, sunphotometer measurements, Lidar profiles and MODIS sensor, an estimation of the daily direct radiative forcing has been estimated for the 17 to 24 January 2006 period, by using a discrete ordinate radiative transfer model. Simulations indicate that aerosols reduce significantly the solar energy reaching the surface (mean Δ F = -61.3 Wm) by reflection to space (mean Δ F = -19.0 Wm) but predominantly by absorption of the solar radiation into the atmosphere (mean Δ F = +42.3 W.m).

Socio-economic activities are rapidly increasing in many countries of Asia due to a population explosion. It is also suggested that greenhouse gases alter regional climate, causing changes in meteorological factors such as atmospheric circulation, precipitation, heat balance, and monsoon. These factors have potential impact on chemical transformation and long-range transport of air pollutants. To detect current and future changes in air quality, systematic observational networks with wide spatial and temporal coverage are highly required. In this work, ground-based measurement data of ozone and its precursors at ~20 remote sites from multiple monitoring networks including operational programs and collaborative research projects in East Asia are integrated. The idea and basis is that in-situ data are more accurate than satellite and sounding data, though its spatial coverage is limited. The intercomparisons of reference scales in each network make ambient data comparable to each other, and the integration of such traceable data allows us to cover wide latitudinal zones ranging from subtropical to boreal regions in the western Pacific within ~2% uncertainties. The data are further utilized to test multi-year simulations by a regional chemistry transport model (CMAQ). Interestingly, there are sizable interannual variations (and latitudinal dependences), suggesting that changes in regional meteorology (e.g., transport paths, patterns, and efficiency) and/or enhanced precursor emissions from biomass burning may have large contribution. Trends for 7 years are not visible at boundary layer sites, but are substantial at mountainous sites during continental outflow seasons, possibly due to increasing NOx emissions from East Asia. Implications to Meditteranean region are discussed in terms of emissions from biomass burning in present and expanding human activities in future.

Beirut is an interesting experimental environmental chamber for its a cross road for several meteorological phenomena. Hence, measurements of fine and coarse particles were carried out during a whole year between February 2004 and January 2005 in a congested place (BH) in Beirut, Lebanon. The ionic and elemental compositions of PM collected in BH were determined using ion chromatography and PIXE analysis, respectively. Other PM10 mass concentrations and chemical speciation were conducted in several urban places in Beirut for comparison purposes. BH results showed that crustal elements mainly Ca, Ti, Mn and Fe, which were typical products of the calcite and basaltic rocks specific to Lebanon, were higher than most reported values in the eastern Mediterranean region and constituted the main component of the coarse particles. In addition, coarse nitrate and sulfate ions resulted from the respective reactions of nitric and sulfuric acids with a relatively high amount of dust, i.e., calcium carbonate. In the fine particles, ammonium sulfate predominated with higher amounts determined in the summer. While nitrate was mainly due to local heavy traffic, sulfates were due to local and long-range transport phenomena. Chlorine levels were high when the wind originated from the sea and low during sand storms. In addition to sea salt, elevated levels of chloride were also attributed to waste mass burning in proximity to the site. Variability of the different elements seemed to be strongly dependent upon meteorological and atmospheric stability conditions and, in particular, wind regimes. Anthropogenic elements like Cu and Zn were generated from local industrial emission and vehicle exhausts whereas elevated levels of Pb were directly linked to a southerly wind originated from Egypt and Israel. The comparison of BH to other micro environmental sites in Beirut showed that high diurnal and seasonal variations in PM10 concentrations and ionic composition confirmed the dynamicity of the eastern Mediterranean environment. Nevertheless, higher PM10 levels seemed to correlate with congested areas. Considering the location in Beirut at the levant of the eastern Mediterranean region, its local atmospheric environment is highly affected by the regional pollution and the meteorological conditions.

Aerosols are chemically complex constituents of the troposphere. They affect human health, visibility, tropospheric chemistry, ecosystems and climate. They exert an opposite to greenhouse gases effect on the global atmospheric temperature by decelerating the warming of the climate. Global 3-dimensional models have to account for the atmospheric processes that affect aerosols in the atmosphere, namely emissions, nucleation, condensation, evaporation, coagulation, cloud processing, atmospheric transport, dry and wet deposition and chemistry/climate feedback mechanisms. To describe this complex atmospheric system, simplifications are requested that result in differences in the model simulations of the budgets and the properties of the tropospheric aerosols and of their climatic impact. Such differences are documented in the frame of the international aerosol model intercomparison exercise AEROCOM (AEROsol model inter COMparison project). A major factor of uncertainty in the model simulations is related to the water associated to the particulate phase that can equal or even exceed the dry aerosol mass. Secondary organic aerosols (SOA), chemically formed in the atmosphere, are another major source of uncertainties in the models. SOA modelling is in its infancy and is actually based on oversimplifications due to the gaps in our understanding of the SOA occurrence and fate in the atmosphere. European aerosol budgets and the contribution of the various aerosol components over the Mediterranean to the total aerosol mass have been computed by the 3-dimensional global chemistry-transport model TM in the frame of the EU funded project PHOENICS (Particles of Human Origin Extinguish Natural solar Irradiance in the Climate System). Natural contributions of dust, sea-salt and SOA to the total aerosol mass are shown to be significant over the Mediterranean. Biogenic SOA are computed to be more important during summer and are expected to increase more in the future atmosphere. Challenges for future research and chemistry/climate model development are highlighted.