Marino Navazo

Ozone Cycles in the Western Mediterranean Basin: Interpretation of Monitoring Data in Complex Coastal Terrain

Abstract In summer, the complex layout of the coasts and mountains surrounding the western Mediterranean basin favors the development of mesoscale atmospheric recirculations and the formation of ozone reservoir layers above the coastal areas and the sea. Tropospheric ozone cycles vary here according to location and exposure of the monitoring station in relation to the flows and reservoir layers, and large differences can be encountered within tens of kilometers. The basic premise for this work is that the representativeness of any station is determined by the (fore)knowledge of the processes affecting the site, at the proper timescales and space scales within its region. Thus, available data have been combined with mesoscale analysis and modeling to interpret the observed summer ozone cycles for the monitoring network at Castellon, on the Spanish east coast. The area is approximately 120 km by 120 km, is backed by coastal mountains, and includes the following: a conurbation, industries, and a densely trav...

Climatic feedbacks and desertification: The Mediterranean model

Abstract Mesometeorological information obtained in several research projects in southern Europe has been used to analyze perceived changes in the western Mediterranean summer storm regime. A procedure was developed to disaggregate daily precipitation data into three main components: frontal precipitation, summer storms, and Mediterranean cyclogenesis. Working hypotheses were derived on the likely processes involved. The results indicate that the precipitation regime in this Mediterranean region is very sensitive to variations in surface airmass temperature and moisture. Land-use perturbations that accumulated over historical time and greatly accelerated in the last 30 yr may have induced changes from an open, monsoon-type regime with frequent summer storms over the mountains inland to one dominated by closed vertical recirculations where feedback mechanisms favor the loss of storms over the coastal mountains and additional heating of the sea surface temperature during summer. This, in turn, favors Medite...

Transport of Tropospheric Ozone over the Bay of Biscay and the Eastern Cantabrian Coast of Spain

During the 1989 field campaigns of the European Commission’s Mesometeorological Cycles of Air Pollution in the Iberian Peninsula (MECAPIP) project (1988‐91), airborne data were obtained under typical summer synoptic weather conditions, that is, a ridge of the Azores high pressure system extending over the north coast of the Iberian Peninsula combined with a thermal low in the interior of the peninsula. This paper presents a detailed analysis of the flights over the coastal area of Bilbao and a high-resolution simulation of the trajectories of the polluted air masses to determine the mechanisms leading to the type of stratification observed. Over the Bay of Biscay, on the eastern Cantabrian coast, the data showed the presence of two distinct groups of atmospheric strata with high ozone concentrations. The higher layers contained older pollutants, trapped between an inversion at about 1200 m and a near-isothermal layer at about 2000 m, and were moving under persistent north to northeasterly winds. The lowest layers, close to the surface in the Bilbao area, contained recently emitted pollutants. Back trajectories computed by using the 3D wind field simulated by the Regional Atmospheric Modeling System (RAMS) have shown that the source of the pollutants in the upper layers, 36 h before, was within a region near the English Channel.

Automatic on-line monitoring of atmospheric volatile organic compounds: gas chromatography-mass spectrometry and gas chromatography-flame ionization detection as complementary systems.

Traditionally air quality networks have been carrying out the continuous, on-line measurement of volatile organic compounds (VOC) in ambient air with GC-FID. In this paper some identification and coelution problems observed while using this technique in long-term measurement campaigns are described. In order to solve these problems a GC-MS was set up and operated simultaneously with a GC-FID for C2-C11 VOCs measurement. There are few on-line, unattended, long term measurements of atmospheric VOCs performed with GC-MS. In this work such a system has been optimized for that purpose, achieving good repeatability, linearity, and detection limits of the order of the GC-FID ones, even smaller in some cases. VOC quantification has been made by using response factors, which is not frequent in on-line GC-MS. That way, the identification and coelution problems detected in the GC-FID, which may led to reporting erroneous data, could be corrected. The combination of GC-FID and GC-MS as complementary techniques for the measurement of speciated VOCs in ambient air at sub-ppbv levels is proposed. Some results of the measurements are presented, including concentration values for some compounds not found until now on public ambient air VOC databases, which were identified and quantified combining both techniques. Results may also help to correct previously published VOC data with wrongly identified compounds by reprocessing raw chromatographic data.

Rise of moist plumes from tall stacks in turbulent and stratified atmospheres

Abstract This paper, developed as a part of the European project RECAPMA (REgional Cycles of Air Pollution in the Mediterranean Area), presents a plume rise model capable of dealing with complex atmospheric profiles-wind shear and thermal stratification-since it performs a numerical integration, along the plume trajectory, of a set of differential equations derived from the balance of mass, momentum and energy in the plume. The classical parametrization for entrainment of air into plume due to self-generated turbulence has been completed with entrainment-detrainment processes in turbulent winds. The model deals with a mixture of four components-dry combustion gas, dry air, water vapor and liquid water-to allow for condensation and/or re-evaporation within the plume. Profile shapes of temperature and velocity of the plume cross sections are assumed to have axisymmetrical distributions and they can vary with the longitudinal distance to stack. Twenty field observations of plume trajectories and final rise in two power plants were compared to the numerical model predictions and a set of classical formulations used for regulatory models: effects like plume merger in a multiple source, condensation and re-evaporation, rise in turbulent winds, rise in light winds and in stratified atmosphere with wind shear, are discussed and tested separately. The results show that much of the scatter between classical model prediction and experimental results is due to the presence of complexities not allowed for in that formulation: some of the discrepancies are favorable because models underestimate plume rise, but caution has to be exercised, especially under negative wind shear-wind decreasing with height-combined with the presence of high inversions since plume rise is systematically overestimated. Our numerical model performs better under all those circumstances and can be used to calculate impacts downwind, by using the three-dimensional trajectories coupled with a dispersion model for the pollutant to be traced. A case study is presented in which impacts at long distances in turbulent winds and in a quasi-adiabatic atmosphere can be explained by using a model of uniform vertical distribution of pollutants under a subsidence inversion.

Online Hourly Determination of 62 VOCs in Ambient Air: System Evaluation and Comparison with Another Two Analytical Techniques

Abstract This paper presents results of the processing and validation of data collected by an automatic gas chromato-graph (AGC). This system was used to monitor 62 volatile organic compounds (VOCs) in urban air in the Basque Country, Spain. The nonpolar compounds (C2–C10) identified—paraffins, olefins, aromatics, and chlorinated compounds—accounted for 88% of the mass of total non-methane hydrocarbons (TNMHCs) in ambient air. The evaluation of linearity, precision, detection limits (DLs), and stability of retention times (RTs) indicates that the equipment is suitable for measuring ambient air automatically for prolonged periods (6 months). The calibration of the equipment using response factors calculated on the basis of the effective carbon number (ECN) showed variations of over 10% for acetylene, isoprene, and n-hexane. The results provided by the automatic chromatograph correlated significantly with simultaneous results from other widely used techniques for determining VOCs in ambient air: (1) portable GC, equipped with photoionization detector (PID), and (2) active adsorption on Tenax-TA followed by thermal des-orption and chromatographic analysis.

Determination of volatile organic compounds in the atmosphere using two complementary analysis techniques

During a preliminary field campaign of volatile organic compound (VOC) measurements carried out in an urban area, two complementary analysis techniques were applied to establish the technical and scientific bases for a strategy to monitor and control VOCs and photochemical oxidants in the Autonomous Community of the Basque Country. Integrated sampling was conducted using Tenax sorbent tubes and laboratory analysis by gas chromatography, and grab sampling and in situ analysis also were conducted using a portable gas chromatograph. With the first technique, monocyclic aromatic hydrocarbons appeared as the compounds with the higher mean concentrations. The second technique allowed the systematic analysis of eight chlorinated and aromatic hydrocarbons. Results of comparing both techniques, as well as the additional information obtained with the second technique, are included.

Trichloroethylene, tetrachloroethylene and carbon tetrachloride in an urban atmosphere: mixing ratios and temporal patterns

The measurement of halogenated hydrocarbons in the atmosphere is a matter of great interest owing to their adverse effects on the human health and the environment. This work is focused on the measurement of three toxic chlorinated hydrocarbons: trichloroethylene (TCE), tetrachloroethylene (PCE), and carbon tetrachloride (CTC). Moreover, CTC is a greenhouse gas and an ozone depleting gas, restricted under the Montreal Protocol. Owing to their low reactivity, the target chlorinated hydrocarbons are considered to be persistent and, thus, many measurements only address their mean mixing ratios (a concentration measure expressed as mol/mol). Consequently, most of the reported data have low temporal resolution as daily, seasonal or yearly mean mixing ratios, obtained with few measurements. In the study reported in this paper hourly measurements were performed for a long period of time: almost two years for TCE and PCE, and one year for CTC. The main objective was to study the temporal variability of the chlorinated hydrocarbons with high temporal resolution in order to identify their main sources and to enhance the understanding of their atmospheric processes. During the measurement period, March 2007–February 2008 with N = 3290 valid data, CTC showed a mean mixing ratio of 0.16 ppbv (SD = 0.13) with lower temporal variability than the majority of non-methane hydrocarbons (NMHCs), being very well mixed in the urban atmosphere owing to its long lifetime. TCE and PCE mean mixing ratios for the May 2006–February 2008 period, were 0.13 ppbv (SD = 0.42, N = 4601) and 0.25 ppbv (SD = 0.54, N = 4709) respectively, with a larger temporal variability. The study of the sources of TCE and PCE reveals that both compounds have industrial and/or commercial origin, but with different main sources.

Meso-Meteorological Analysis of Air Pollution Cycles in Spain

Three years of field measurements in the coastal area of Bilbao in Northern Spain show that most episodic conditions in this area occur as a result of: (a) anticyclonic stagnation over Central, Europe and (b) pollutants being trapped in local recirculating flows. In general, the dispersion behaviour in this area of complex terrain can be classified into several well defined patterns, which correspond to certain meteorological conditions. Results to date show that complex re-entry cycles occur and that synoptically different flows may be undistinguishable by wind sensors at ground level (affected by channelling), and yet result in totally different observed pollution levels by a fixed monitoring network (affected by topographical effects). A hitherto undocumented phenomenon occurs during the summer as the result of the diurnal formation of the Iberian thermal low. It can form every day over the central plateau and forces an inward flow of coastal emissions which can spiral inland over successive days. This inflow can originate episodic conditions in Madrid at the end of the summer when local emissions are at their lowest.

Atmospheric carbon tetrachloride in rural background and industry surrounded urban areas in Northern Iberian Peninsula: Mixing ratios, trends, and potential sources

Latest investigations on atmospheric carbon tetrachloride (CTC) are focused on its ozone depleting potential, adverse effects on the human health, and radiative efficiency and Global Warming Potential as a greenhouse gas. CTC mixing ratios have been thoroughly studied since its restriction under the Montreal Protocol, mostly in remote areas with the aim of reporting long-term trends after its banning. The observed decrease of the CTC background mixing ratio, however, was not as strong as expected. In order to explain this behavior CTC lifetime should be adjusted by estimating the relative significance of its sinks and by identifying ongoing potential sources. Looking for possible sources, CTC was measured with high-time resolution in two sites in Northern Spain, using auto-GC systems and specifically developed acquisition and processing methodologies. The first site, Bilbao, is an urban area influenced by the surrounding industry, where measurements were performed with GC-MSD for a one-year period (2007-2008). The second site, at Valderejo Natural Park (VNP), is a rural background area where measurements were carried out with GC-FID and covering CTC data a nonsuccessive five-year period (2003-2005, 2010-2011, and 2014-2015years). Median yearly CTC mixing ratios were slightly higher in the urban area (120pptv) than in VNP (80-100pptv). CTC was reported to be well mixed in the atmosphere and no sources were noticed to impact the rural site. The observed long-term trend in VNP was in agreement with the estimated global CTC emissions. In the urban site, apart from industrial and commercial CTC sources, chlorine-bleach products used as cleaning agents were reported as promotors of indoor sources.