G. Gangoiti

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...

Mesoscale circulations over complex terrain in the Valencia coastal region, Spain – Part 1: Simulation of diurnal circulation regimes

We collected ground-based and aircraft vertical profile measurements of meteorological parameters during a 2-week intensive campaign over the Valencia basin, in order to understand how mesoscale circulations develop over complex terrain and affect the atmospheric transport of tracers. A high-resolution version of the RAMS model was run to simulate the campaign and characterize the diurnal patterns of the flow regime: night-time katabatic drainage, morning sea-breeze development and its subsequent coupling with mountain up-slopes, and evening flow-veering under larger-scale interactions. An application of this mesoscale model to the transport of CO 2 is given in a companion paper. A careful evaluation of the model performances against diverse meteorological observations is carried out. Despite the complexity of the processes interacting with each other, and the uncertainties on modeled soil moisture boundary conditions and turbulence parameterizations, we show that it is possible to simulate faithfully the contrasted flow regimes during the course of one day, especially the inland progression and organization of the sea breeze. This gives confidence with respect to future applicability of mesoscale models to establish a reliable link between surface sources of tracers and their atmospheric concentration signals over complex terrain.

Study of the correlation between columnar aerosol burden, suspended matter at ground and chemical components in a background European environment

Although routinely monitored by ground based air quality networks, the particulate matter distribution could be eventually better described with remote sensing techniques. However, valid relationships between ground level and columnar ground based quantities should be known beforehand. In this study we have performed a comparison between particulate matter measurements at ground level at different cut sizes (10, 2.5 and 1.0 mm), and the aerosol optical depth obtained by means of a ground based sunphotometer during a multiinstrumental field campaign held in El Arenosillo (Huelva, Spain) from 28 June to 4 July 2006. All the PM fractions were very well correlated with AOD with correlation coefficients that ranged from 0.71 to 0.81 for PM10, PM2.5 and PM1. Furthermore, the influence of the mixing layer height in the correlations was explored. The improvement in the correlation when the vertical distribution is taken into account was significant for days with a homogeneous mixing layer. Moreover, the chemical analysis of the individual size fractions allowed us to study the origin of the particulate matter. Secondary components were the most abundant and also well correlated in the three size fractions; but for PM10 fraction, chemical species related to marine origin were best correlated. Finally, we obtained a relationship between MODIS L3 AOD from collection 5.1 and the three PM cut sizes. In spite of being a relatively clean environment, all the techniques were able to capture similar day to day variations during this field campaign.

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.

Characterization of a long range transport pollution episode affecting PM in SW Spain

A multidisciplinary study on aerosol characterization was performed at the regional background monitoring station of El Arenosillo, in SW Spain, between 28 June and 5 July 2006. The main aim of the Arenosillo aerosol measurement campaign 2006 was to compare the results of aerosol characterization obtained by different groups by measuring physical and chemical parameters using optical methods and in situ sampling. The campaign coincided with a long-range transport episode from Western Iberia, passing through the Gulf of Cadiz and the Straits of Gibraltar towards the study area. The results of the variability of PM levels and chemical composition of PM10, PM2.5 and PM1 at El Arenosillo and at three nearby regional and urban background sites were interpreted. Mean levels measured during the campaign reached 23, 15 and 12 microg m(-3) for PM10, PM2.5 and PM1, respectively, at El Arenosillo. PM during the Arenosillo campaign 2006 was dominated by the secondary inorganic aerosols (SIA, 24, 38 and 39% of PM10, PM2.5 and PM1 mass), carbonaceous aerosols (17, 21 and 23% of the mass), crustal material (13, 9 and 4%), and sea spray (10, 5 and 1%). These values are within the usual range of regional background sites of Southern Spain with the exception of the relatively low crustal load and the high SIA levels. Two major PM episodes were differentiated. The first one was characterized by high levels of Bi, As, Pb, Se, P and Zn, which are the main tracers of the industrial emissions near the town of Huelva. High concentrations of these elements were also recorded at the nearby sites. In the second episode, maximum levels of SO4(2-), V and coarse Cu as well as the bulk mass of PM1 were determined, tracing the polluted air mass transport from Western Iberia through the Straits of Gibraltar. These results underline the importance of the influence of long-range transport of pollutants on the levels and composition of regional background PM in SW Iberia, where local emissions may also play a role.

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.

Validation of optical remote sensing measurement strategies applied to industrial gas emissions

In May 2004 a field campaign was conducted at a power plant in Spain, aiming to validate the use of a miniaturized, fibre‐optic, ultraviolet, differential optical absorption spectrometer (mini‐DOAS) for sulfur dioxide (SO2) flux quantification. Emissions were determined by integrating the total number of molecules in a vertical cross‐section of the gas plume, and multiplying them by the wind component at plume height. Calculated wind data were compared with balloon soundings. Plume height, computed from a tomographic reconstruction of the plume, was compared with stereo‐photogrammetric methods and a plume rise model. Finally, SO2 fluxes were compared to emissions reported by the power station. Although the meteorological conditions during the field campaign were adverse, with large fluctuations in wind speed and wind direction, the optical measurements performed proved to be practically feasible and compared well with the techniques used for validation. SO2 fluxes derived by the mini‐DOAS were within 7% of those reported by the power station.

Daily precipitation in Northern Iberia: Understanding the recent changes after the circulation variability in the North Atlantic sector

Trends in the characteristics of daily precipitation over Northern Iberia (NIB) are analyzed after 14 daily records covering the last 40 years plus seven century-length time series. Results reveal an evolution to drier conditions with subregional variations: in western and central subregions, the decrease in both the occurrence and the intensity of wet days results in a statistically significant decline of total precipitation. Contrary to other regions in the Iberian Peninsula, the lack of correlation between the North Atlantic Oscillation (NAO) index and the observed rainfall anomalies within NIB suggests that the dominance of a positive NAO mode from the late 1970s to 2002 cannot explain the trends. The land-sea and mountain distribution creates sharp rainfall transitions depending on the pathways of the moisture-laden winds. Consequently, NIB and other mountainous regions in the margins of the European continental water divide are sensitive to small changes in the NAO pressure centers and can exhibit both positive and negative rainfall anomalies for each NAO mode. A novel methodology for identifying changes in the NAO modes, consistent with the observed pressure/precipitation anomalies at both continental and regional scales, is presented. After the disaggregation of each dominant NAO wet season into two categories, the main rainfall changes in the NIB region can be explained in the context of the NAO variability during the last decades. The reported (sub)regional rainfall differences stress the need of caution when using NAO reconstructions, based in site specific rainfall anomalies, for the interpretation of the past climate precipitation variability in areas of complex terrain.

On the origin of the highest ozone episodes in Spain

The 2000-2015 occurrences of the highest ozone (O3) pollution episodes in Spain were evaluated to investigate their origin. To this end, data series available for urban and regional background (UB and RB), traffic (TR) and industrial (IN) sites were analysed separately and intercompared. Results evidenced that during these 16years mean O3 levels in the RB sites did not change significantly, and remained constantly high. However, there is a clear increase at the TR and UB sites. Although sensitivity analysis is needed to interpret the cause of this increasing trend, this might be caused probably by the lower O3 titration intensity due to the preferential abatement of NO vs NO2, as supported from the neutral trend of OX (NO2+O3) at these sites. We found that the exceedances of the hourly information threshold for O3 (>180μg/m3) are recorded mostly at UB and IN sites located in seven areas of Spain (specific hotspots or at the tail end of large urban plumes), and that these increased during summer heatwaves (i.e. 2003 and 2015). Although the external contribution of regional-to-subcontinental transported O3 might be relevant during the highest O3 episodes in the Western Mediterranean, our results evidenced that in the above specific areas, regional-local O3 production decisively contributes to the exceedances of the information threshold. Also that the human protection threshold and the AOT40 are more frequently exceeded in the Central, Southern and Mediterranean sides of the Iberian Peninsula. The design of effective episode abatement measures is quite complex in those conditions, due to both the nonlinearity of the chemical processes of O3 formation and destruction, and to the interplay with the complex meteorological setting, causing frequent recirculation and in situ aging of air masses. However, the combination of meteorological forecasting of the main recirculation processes and sensitivity analysis of NOX/VOC emission abatement measures might be powerful tools to evaluate the effectiveness of potential O3 mitigation strategies. Finally we would like to highlight that the current UB, RB, IN and TR classification (somewhat subjective) is not adequate to interpret the origin of O3 exceedances in complex areas of Southern Europe. Thus, a UB station recording exceedances, and located in a small city in the tail end of an urban plume of a large city, receives not only the contribution from its own UB, but mainly from the specific high O3 RB caused by the urban plume transport.