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An intense and long-lasting Saharan dust outbreak crossed the Iberian Peninsula (IP) from the southwest (SW) to the northeast (NE) from 25 March until 7 April 2021. This work aims to assess the optical and mass contribution of both fine and coarse dust particles along their transport. Five Iberian lidar stations were monitoring the transport and evolution of the Saharan dust particles, i.e. El Arenosillo/Huelva, Granada, Torrejon/Madrid and Barcelona in Spain, and evora in Portugal. The particular meteorological conditions determined the aerosol scenario along the overall dust event, differing in the first part of the event (25-31 March), in which the strongest dust incidence occurred on 29-31 March at the south and central stations and 1 April at Barcelona, from the second one (1-7 April). The use of the two-step POLIPHON algorithm showed the relevance of using polarized lidar measurements for separating the aerosol properties of dust fine and coarse particles as an added value. Both the fine dust (Df) and coarse dust (Dc) components of the total particle backscatter coefficient (total dust, DD = Dc + Df) were separately derived. The dust plume was well-mixed with height and no significant differences were found in the vertical structure of both the Dc and Df particle backscatter coefficients. From the beginning of the dust outbreak until 1 April, the vertical Df / DD mass ratio was nearly constant in time at each station and also in altitude with values of & SIM; 10 %. Moreover, the mean dust optical depth at 532 nm was decreasing along that dust pathway, reporting values from SW to NE stations of 0.34 at El Arenosillo/Huelva, 0.28 at Granada, 0.20 at evora, 0.28 at Torrejon/Madrid, and 0.14 at Barcelona, although its Df / DD ratio remained almost constant (28 %-30 %). A similar pattern was found for the total dust mass loading and its Df / DD ratio, i.e. mostly decreasing mean mass values were reported, being constant in its Df / DD ratio (& SIM; 10 %) along the SW-NE dust pathway. In addition, the episode-mean centre-of-mass height increased with latitude overall, showing a high variability, being greater than 0.5 km at the southern sites (El Arenosillo/Huelva, Granada, evora) and & SIM; 1.0 km at Torrejon/Madrid and Barcelona. However, despite the relatively high intensity of the dust intrusion, the expected ageing of the dust particles was hardly observed, by taking into account the minor changes found in the contribution and properties of the coarse and fine dust particles. This is on the basis that the IP is relatively close to the Saharan dust sources and then, under certain dust transport conditions, any potential ageing processes in the dust particles remained unappreciated. The following must be highlighted: the different relative contribution of the fine dust particles to the total dust found for their optical properties (& SIM; 30 %) associated with the radiative effect of dust, with respect to that for the mass features (& SIM; 10 %) linked to air quality issues, along the overall dust event by crossing the IP., Ministry of Science and Innovation, Spain (MICINN) Spanish Government PID2019-104205GB-C21/AEI/10.13039/501100011033

Megacities and other major population centres (MPCs) worldwide are major sources of air pollution, both locally as well as downwind. The overall assessment and prediction of the impact of MPC pollution on tropospheric chemistry are challenging. The present work provides an overview of the highlights of a major new contribution to the understanding of this issue based on the data and analysis of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) international project. EMeRGe focuses on atmospheric chemistry, dynamics, and transport of local and regional pollution originating in MPCs. Airborne measurements, taking advantage of the long range capabilities of the High Altitude and LOng Range Research Aircraft (HALO, https://www.halo-spp.de, last access: 22 March 2022), are a central part of the project. The synergistic use and consistent interpretation of observational data sets of different spatial and temporal resolution (e.g. from ground-based networks, airborne campaigns, and satellite measurements) supported by modelling within EMeRGe provide unique insight to test the current understanding of MPC pollution outflows. In order to obtain an adequate set of measurements at different spatial scales, two field experiments were positioned in time and space to contrast situations when the photochemical transformation of plumes emerging from MPCs is large. These experiments were conducted in summer 2017 over Europe and in the inter-monsoon period over Asia in spring 2018. The intensive observational periods (IOPs) involved HALO airborne measurements of ozone and its precursors, volatile organic compounds, aerosol particles, and related species as well as coordinated ground-based ancillary observations at different sites. Perfluorocarbon (PFC) tracer releases and model forecasts supported the flight planning, the identification of pollution plumes, and the analysis of chemical transformations during transport. This paper describes the experimental deployment and scientific questions of the IOP in Europe. The MPC targets - London (United Kingdom; UK), the Benelux/Ruhr area (Belgium, the Netherlands, Luxembourg and Germany), Paris (France), Rome and the Po Valley (Italy), and Madrid and Barcelona (Spain) - were investigated during seven HALO research flights with an aircraft base in Germany for a total of 53 flight hours. An in-flight comparison of HALO with the collaborating UK-airborne platform Facility for Airborne Atmospheric Measurements (FAAM) took place to assure accuracy and comparability of the instrumentation on board. Overall, EMeRGe unites measurements of near- and far-field emissions and hence deals with complex air masses of local and distant sources. Regional transport of several European MPC outflows was successfully identified and measured. Chemical processing of the MPC emissions was inferred from airborne observations of primary and secondary pollutants and the ratios between species having different chemical lifetimes. Photochemical processing of aerosol and secondary formation or organic acids was evident during the transport of MPC plumes. Urban plumes mix efficiently with natural sources as mineral dust and with biomass burning emissions from vegetation and forest fires. This confirms the importance of wildland fire emissions in Europe and indicates an important but discontinuous contribution to the European emission budget that might be of relevance in the design of efficient mitigation strategies. The present work provides an overview of the most salient results in the European context, with these being addressed in more detail within additional dedicated EMeRGe studies. The deployment and results obtained in Asia will be the subject of separate publications., The HALO deployment during EMeRGe was funded by a consortium comprising the German Research Foundation (DFG) Priority Program HALO-SPP 1294, the Institute of Atmospheric Physics of DLR, the Max Planck Society (MPG), and the Helmholtz Association. Flora Kluge, Benjamin Schreiner, and Klaus Pfeilsticker acknowledge the support given by the DFG through the project nos. PF 384-16, PF 384-17, and PG 385-19. Ralf Koppmann and Marc Krebsbach acknowledge DFG funding through project no. KR3861_1-1. Katja Bigge acknowledges additional funding from the Heidelberg Graduate School for Physics. Johannes Schneider, Katharina Kaiser, and Stephan Borrmann acknowledge funding through the DFG (project no. 316589531). Lisa Eirenschmalz and Hans Schlager acknowledge support by DFG through project MEPOLL (SCHL1857/4-1). Anna B. Kalisz Hedegaard would like to thank DAAD and DLR for a Research Fellowship. Hans Schlager acknowledge financial support by the DLR TraK (Transport and Climate) project. Michael Sicard acknowledges support from the EU (GA nos. 654109, 778349, 871115, and 101008004) and the Spanish Government (ref. nos. CGL2017-90884-REDT, PID2019-103886RB-I00, RTI2018-096548-B-I00, and MDM-2016-0600). Midhun George, Yangzhuoran Liu, M. Dolores Andrés Hernández, and John Phillip Burrows acknowledge financial support from the University of Bremen. FLEXPART simulations were performed on the HPC cluster Aether at the University of Bremen, financed by DFG within the scope of the Excellence Initiative. Anne-Marlene Blechschmidt was partly funded through the CAMS-84 project. Jennifer Wolf acknowledges support from the German Federal Ministry for Economic Affairs and Energy – BMWi (project Digitally optimized Engineering for Services – DoEfS; contract no. 20X1701B). Theresa Harlass thanks DLR VO-R for funding the young investigator research group “Greenhouse Gases”. Mariano Mertens, Patrick Jöckel, and Markus Kilian acknowledge resources of the Deutsches Klimarechenzentrum (DKRZ) granted by the WLA project ID bd0617 for the MECO(n) simulations and the financial support from the DLR projects TraK (Transport und Klima) and the Initiative and Networking Fund of the Helmholtz Association through the project “Advanced Earth System Modelling Capacity” (ESM). Bruna A. Holanda acknowledges the funding from Brazilian CNPq (process 200723/2015-4). The article processing charges for this open-access publication were covered by the University of Bremen.

In this work, the effect of the aerosol vertical distribution on the local shortwave aerosol radiative forcing is studied. We computed the radiative forcing at the top and bottom of the atmosphere between 0.2 and 4 microns using the libRadTran package and compared the results with those provided by AERONET (AErosol RObotic NETwork). Lidar measurements were employed to characterize the aerosol vertical profile, and collocated AERONET measurements provided aerosol optical parameters required to calculate its radiative forcing. A good correlation between the calculated radiative forcings and those provide by AERONET, with differences smaller than 1 W m-2 (15% of estimated radiative forcing), is obtained when a gaussian vertical aerosol profile is assumed. Notwithstanding, when a measured aerosol profile is inserted into the model, differences between radiative forcings can vary up to 6.54Wm-2 (15%), with a mean of differences =-0.74±3.06W m-2 at BOA and -3.69Wm-2 (13%), with a mean of differences = -0.27±1.32Wm-2 at TOA due to multiple aerosol layers and aerosol types. These results indicate that accurate information about aerosol vertical distribution must be incorporated in the radiative forcing calculation in order to reduce its uncertainties. This research was funded by European Union’s Horizon 2020 research and innovation programme through project ACTRIS-2 (grant 654109), the Spanish Ministry of Economy and Competitivity (CRISOL, CGL2017-85344-R and ACTRIS-ESPAÑA, CGL2017-90884-REDT) and Madrid Regional Government (TIGAS-CM, Y2018/EMT-5177).

Ammonia emissions play an important role in the formation of secondary inorganic aerosols. Road traffic is considered to be one of the main sources of ammonia in urban environments, although other sources have been identified. An experimental study was carried out in a suburban area of Madrid (Spain), in which high time resolution measurements of ammonia concentrations were obtained using Cavity-Enhanced Laser Absorption Spectroscopy. Mean hourly ammonia concentration during the study period of December 2014 to January 2015 was 2.17 ± 1.70 μg m−3, with 9.3 μg m−3 being the maximum recorded value for a period of 10 min. Stagnant conditions dominated the measurement period and influenced the observed concentrations. Other gaseous and particulate matter parameters, including size-segregated mass concentration, particle number size distribution and aerosol chemical composition (non-refractory species) were monitored at the same site in order to support the data interpretation. No relationships with traffic-related pollutants were found, however, a nearby wastewater treatment plant was identified as the main source affecting the observed ambient concentrations of ammonia and aerosols. Ammonia emissions from wastewater treatment plants may be significant annual sources of ammonia in urban environments. High-resolution observations of air chemistry help to resolve emission inventories in urban environments, and improve the effectiveness of policy to reduce secondary inorganic aerosols.

Complex spatial and temporal patterns of ground-level O3 and NO2 concentrations have been revealed across an important southern European O3 exceedance area (Madrid Basin, central Spain). Data were obtained from 102 diffusion tube sites and 49 monitoring stations (25 urban/suburban, 12 urban/suburban-traffic, 7 remote, 3 rural, 2 urban-industrial) located through a wide area inside and beyond the city. This new, high-density database confirms that current locations of monitoring stations in the Madrid networks are well positioned to record representative levels of O3 across the area. Two air quality monitoring stations were identified as reference measurement points, based on their lower O3 and NO2 concentrations, and used as a proxy for regional and hemispheric background levels. Although a main regional contribution was evidenced, emissions of local precursors within the Madrid urban plume play a key role in the generation of O3 exceedances, which are higher and occur earlier near the city than at rural sites, where the effect of NO titration is lower. Despite the fact that weekend emissions of O3 precursors in Madrid are typically lower than on weekdays, mainly due to fewer road traffic emissions, there is little difference in average values of weekday and weekend O3. However, more subtle “weekend effect” differences are revealed by probability density analysis, with high O3 and low NO2 at the highest temperature range (30-35° C) at weekends reflecting lower NO titration. This analysis highlights the importance of NO timing with respect to the photochemical activity timing. The complexity of these O3 pollution patterns in and around the city is dependent on an ever-changing interplay between weather conditions, emission sources, and the timescale required for pollutant transport, chemical processing and recirculation in an evolving contaminated airmass.

A high number of aerosol particle shrinkage cases (70) have been identified and analyzed from an extensive and representative database of aerosol size distributions obtained between 2009 and 2015 at an urban background site in Madrid (Spain). A descriptive classification based on the process from which the shrinkage began is proposed according which shrinkage events were divided into three groups: (1) NPF + shrinkage (NPF + S) events, (2) aerosol particle growth process + shrinkage (G + S) events, and (3) pure shrinkage (S) events. The largest number of shrinkages corresponded to the S-type followed by NPF + S, while the G + S events were the least frequent group recorded. Duration of shrinkages varied widely from 0.75 to 8.5 h and SR from −1.0 to −11.1 nm h−1. These processes typically occurred in the afternoon, around 18:00 UTC, caused by two situations: i) a wind speed increase usually associated with a change in the wind direction (over 60% of the observations) and ii) the reduction of photochemical activity at the end of the day. All shrinkages were detected during the warm period, mainly between May and August, when local meteorological conditions (high solar irradiance and temperature and low relative humidity), atmospheric processes (high photochemical activity) and availability of aerosol-forming precursors were favorable for their development. As a consequence of these processes, the particles concentration corresponding to the Aitken mode decreased into the nucleation mode. The accumulation mode did not undergo significant changes during these processes. In some cases, a dilution of the particulate content in the ambient air was observed. This work, goes further than others works dealing with aerosol particles shrinkages, as it incorporates as a main novelty a classification methodology for studying these processes. Moreover, compared to other studies, it is supported by a high and representative number of observations. Thus, this study contributes to get a better understanding of this type of atmospheric aerosol transformations and its features.

In the framework of the LIFE MINOx-STREET European project (co-financed by the EU), a commercial photocatalytic product consisting of a TiO2-based water solution was implemented and tested on the bituminous asphalt of a main road of the municipality of Alcobendas (Community of Madrid, Spain), covering an area of approximately one thousand square meters both ways. This coating material was selected after rigorous laboratory assays carried out on a variety of commercial photocatalytic products. An expressly-designed experimental system has allowed to evaluate during 41 days the NOx depolluting ability of the photocatalytic material in that urban scenario. NOx ambient concentrations were monitored at several points located along the longitudinal axis of the road, both inside and outside the area treated with the photocatalytic material. Moreover, meteorological and ambient parameters at building's roof height were monitored to document the boundary conditions in the experimental area. Even though the selected photocatalytic material showed a remarkable surface deposition velocity (7.2 10−3 m s−1) in laboratory tests and although the experimental deployment was carefully designed and implemented to robustly compare control and test scenarios with a high time and spatial resolution, when analyzing average NOx concentrations under filtered optimal ambient conditions to guarantee the photocatalytic effect to be maximum, no clear trend were observed in the ambient NOx levels that could be unequivocally associated with the sink effect induced by the photocatalytic material. The results have shown that the NOx gradients formed along the road were quite large even without photocatalytic coating, reflecting a complex atmospheric reality far from a homogeneous behaviour along the street, which made extremely difficult to observe the weak NOx sink effect existing. In fact, taking into account the precision of the experimental system, the potential environmental NOx purification capacity, if it had existed, would have had to be greater than 3% to be observed under the experimental conditions. This finding agrees with the estimates made by means of a simple but consistent first-order kinetic calculation for which an environmental reduction of NOx of less than 1% was obtained. All the collected data have given detailed valuable information for evaluating the results provided by a mathematical model capable of simulating the dispersion of air pollutants at urban street scale. As it is presented in the Part II of this study, these simulations have permitted to estimate accurately the impact on air quality of the use of this remediation technology not only under the actual experimental conditions but also in other urban scenarios.

Photocatalytic materials are proposed as a mitigation strategy of urban air pollution because of its deposition feature. This study aims at evaluating their effect on NO2 concentrations in an urban environment under real atmospheric conditions through Computational Fluid Dynamics (CFD) simulations. A comprehensive study is performed to determine the potential of photocatalytic materials to remove NO2 at pedestrian level taking into account the variability of wind speed, traffic emissions and the photoactive area in an urban environment. The deposition velocity used to model the sink effect of a photoactive surface is derived from laboratory data and its applicability to outdoor conditions is proved through microscale simulations. The CFD simulation performed to assess the impact of a photocatalytic material on ambient pollutants in a real urban scenario is evaluated against the measurements presented in Part I (Fernandez-Pampillon et al., 2020). Results show that the application of photocatalytic materials in an urban environment yield a minimal reduction in NO2 concentrations below 1 % under the studied atmospheric conditions. In a hypothetical scenario, in which the photoactive area is extended to an entire neighbourhood, small decrease of NO2 concentrations below 2 % is obtained under the daytime prevailing atmospheric conditions of the area of interest. Finally, the reduction of NO2 under several atmospheric conditions results to be mainly dominated by wind flow and NOx emissions in the study street.

The research leading to these results has received funding from the H2020 program from the European Union (grant agreement no. 654109, 778349) and also from the Spanish Ministry of Industry, Economy and Competitiviness (MINECO, ref. CGL2013-45410-R, CGL2016-81092-R, CGL2017-85344-R, TEC2015-63832-P), the Spanish Ministry of Science, Innovation and Universities (ref. CGL2017-90884-REDT); the CommSensLab "Maria de Maeztu" Unity of Excellence (ref. MDM-2016-0600) financed by the Spanish Agencia Estatal de Investigación. Co-funding was also provided by the European Union through the European Regional Development Fund (ref. POCI-01-0145-FEDER-007690, ALT20-03-0145-FEDER-000004, ALT20-03-0145-FEDER-000011); by the Andalusia Regional Government (ref. P12-RNM-2409); by the Madrid Regional Government (projects TIGAS-CM, ref. Y2018/EMT-5177 and AIRTEC-CM, ref. P2018/EMT4329); by the University of Granada through “Plan Propio. Programa 9 Convocatoria 2013” and by the Portuguese Foundation for Science and Technology and national funding (ref. SFRH/BSAB/143164/2019). The BSC-DREAM8b and NNMB/BSC-Dust (now NMMB-MONARCH) model simulations were performed by the Mare Nostrum supercomputer hosted by the Barcelona Supercomputer Center (BSC). S. Basart acknowledges the AXA Research Fund for supporting aerosol research at the BSC through the AXA Chair on Sand and Dust Storms Fund, as well as the InDust project (COST Action CA16202). The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.ready.noaa.gov) used in this publication., An unprecedented extreme Saharan dust event was registered in winter time from 20 to 23 February 2017 over the Iberian Peninsula (IP). We report on aerosol optical properties observed under this extreme dust intrusion through passive and active remote sensing techniques. For that, AERONET (AErosol RObotic NETwork) and EARLINET (European Aerosol Research LIdar NETwork) databases are used. The sites considered are: Barcelona (41.38°N, 2.17°E), Burjassot (39.51°N, 0.42°W), Cabo da Roca (38.78°N, 9.50°W), Évora (38.57°N, 7.91°W), Granada (37.16°N, 3.61°W) and Madrid (40.45°N, 3.72°W). Large aerosol optical depths (AOD) and low Ångström exponents (AE) are observed. An AOD of 2.0 at 675 nm is reached in several stations. A maximum peak of 2.5 is registered in Évora. During and around the peak of AOD, AEs close to 0 and even slightly negative are measured. With regard to vertically-resolved aerosol optical properties, particle backscatter coefficients as high as 15 Mm−1 sr−1 at 355 nm are recorded at the lidar stations. Layer-mean lidar ratios are found in the range 40–55 sr at 355 nm and 34–61 sr at 532 nm during the event. The particle depolarization ratios are found to be constant inside the dust layer, and consistent from one site to another. Layer-mean values vary in the range 0.19–0.31. Another remarkable aspect of the event is the limited vertical distribution of the dust plume which never exceeds 5 km. The extreme aspect of the event also presented a nice case for testing the ability of two dust forecast models, BSC-DREAM8b and NMMB/BSC-Dust, to reproduce the arrival, the vertical distribution and the intensity of the dust plume over a long-range transport region. In the particular case of the February 2017 dust event, we found a large underestimation in the forecast of the extinction coefficient provided by BSC-DREAM8b at all heights independently of the site. In contrast NMMB/BSC-Dust forecasts presented a better agreement with the observations, especially in southwestern part of the IP. With regard to the forecast skill as a function of lead time, no clear degradation of the prognostic is appreciated at 24, 48 and 72 h for Évora and Granada stations (South). However the prognostic does degrade (bias increases and/or correlation decreases) for Barcelona (North), which is attributed to the fact that Barcelona is at a greater distance from the source region and to the singularity of the event., Funding from the H2020 program from the European Union (grant agreement no. 654109, 778349), Spanish Ministry of Industry, Economy and Competitiviness (MINECO, ref. CGL2013-45410-R, CGL2016-81092-R, CGL2017-85344-R, TEC2015-63832-P), Spanish Ministry of Science, Innovation and Universities (ref. CGL2017-90884-REDT), CommSensLab "Maria de Maeztu" Unity of Excellence (ref. MDM-2016-0600) financed by the Spanish Agencia Estatal de Investigación, Co-funding was also provided by the European Union through the European Regional Development Fund (ref. POCI-01-0145-FEDER-007690, ALT20-03-0145-FEDER-000004, ALT20-03-0145-FEDER-000011), Andalusia Regional Government (ref. P12-RNM-2409); by the Madrid Regional Government (projects TIGAS-CM, ref. Y2018/EMT-5177 and AIRTEC-CM, ref. P2018/EMT4329), Portuguese Foundation for Science and Technology and national funding (ref. SFRH/BSAB/143164/2019)

An unprecedented extreme Saharan dust event was registered in winter time from 20 to 23 February 2017 over the Iberian Peninsula (IP). We report on aerosol optical properties observed under this extreme dust outbreak through remote sensing (active and passive) techniques. For that, EARLINET (European Aerosol Research LIdar NETwork) lidar and AERONET (AErosol RObotic NETwork) Sun-photometer Cimel CE 318 measurements are used. The sites considered are: Barcelona (41.38º N, 2.17º E), Burjassot (39.51º N, 0.42º W), Cabo da Roca (38.78º N, 9.50º W), Évora (38.57º N, 7.91º W), Granada (37.16º N, 3.61º W) and Madrid (40.45º N, 3.72º W). In general, large aerosol optical depths (AOD) and low Ångström exponents (AE) are observed. An AOD of 2.0 at 675 nm is reached in several stations. Maximum values of AOD675 of 2.5 are registered in Évora. During and around the peak of AOD675, AEs close to 0 are measured. With regard to vertically-resolved aerosol optical properties, particle backscatter coefficients as high as 1.5∙10−5 m−1 sr−1 at 355 nm are recorded at every lidar stations. Mean lidar ratios are found in the range 40–55 sr at 355 nm and 34–61 sr at 532 nm during the event inside the dust layer. Mean particle and volume depolarization ratios are found to be very consistent between lidar stations. They range 0.19–0.31 and 0.12–0.26 respectively. The optical properties are also found very stable with height in the dust layer. Another remarkable aspect of the event is the limited height of the dust transport which is found between the ground and 5 km. Our vertically-resolved aerosol properties are also used to estimate the performances of two dust models, namely BSC-DREAM8b and NMMB/BSC-Dust, in order to evaluate their forecast skills in such intense dust outbreaks. We found that forecasts provided by the NMMB/BSC-Dust show a better agreement with observations than the ones from BSC-DREAM8b. The BSC-DREAM8b forecasts (24 h) present a large underestimation during the event. No clear degradation of the prognostics is appreciated in 24, 48, 72 h except for the Barcelona station.

This article presents a study of aerosol optical and microphysical properties under different relative humidity (RH) but well mixed layer conditions using optical and microphysical aerosol properties from multi-wavelength (MW) Raman lidar and in-situ aerosol observations collected at the Cabauw Experimental Site for Atmospheric Research (CESAR). Two hygroscopic events are described through 3 backscatter (β) and 2 extinction (α) coefficients which in turn provide intensive parameters such as the backscatter-related Ångström exponent (åβ) and the lidar ratio (LR). Along with it, profiles of RH were inferred from Raman lidar observations and therefore, as a result of varying humidity conditions, a shift on the aerosol optical properties can be described. Thus, it is observed that as RH increases, aerosols uptake water vapour, augment their size and consequently the åβ diminishes whereas the LR increases. The enhancement factor based on the backscatter coefficient at 532 nm, which characterizes the aerosol from hygroscopic standpoint, is also estimated. Finally, microphysical properties that are necessary for aerosol radiative forcing estimates - such as volume, effective radii, refractive index and size distribution, all vertically resolved - are retrieved using the inversion with regularization. Using this method, two hygroscopic events are described in detail. © 2015 Elsevier Ltd.

The aim of the study is to evaluate the influence of the use of oxygenates as additives to diesel fuel on the combustion process, the specific fuel consumption, effective efficiency and emissions, especially particle emissions in the range 5.6–560 nm in size distribution and number of a diesel engine. The oxygenate compounds used were EtilTerbutilEter (ETBE) and Diglyme which were added to Commercial Diesel (7% FAME). Engine bench tests were performed with 7 additive/CD blends in different proportions, 5%, 10% and 15% of oxygenated additive added to the base Commercial Diesel fuel. The tests were performed on a 2.0 TDI diesel engine VW Euro 4, in 9 stationary operating conditions (1500, 2250 and 3000 min−1 to 15%, 30%, 45% load). Experimental results show that the mixing ratio additive/diesel is the parameter that has the greatest influence on the particle emission. NOx emission compared to CD increases or remains constant depending on the amount of additive in the mixture, engine speed and load condition. Furthermore, there is a dramatic decrease in the total particle concentration with the addition of oxygenated additives, especially when the ratio reaches 15%. The geometric mean diameter (GMD) of the particles of the blends, presents consistent trends with load and speed variation. Blends with 15% additive at all engine operating conditions are maintained in smaller sizes than the CD. The GMD does not show a clear dependence on the type of additive used, however the proportion of additive has significant influence on GMD. A higher proportion of additive, lower GMD.

On 27 August 2012, a wildfire occurred in the western zone of the Madrid region. Consequently, a significant release of smoke and aerosols was injected into the free troposphere and advected by the synoptic circulation in trajectories that passed over the capital. This event was detected by the Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas (CIEMAT; Research Centre for Energy, Environment and Technology), Madrid lidar station at about 5 km height. While the main aerosol plume did not pass over the lidar station, the eastern portion of the dispersed emissions did. No aerosol layers were detected by lidar in the free-troposphere for the next few days. Since few observations of fresh biomass burning aerosol have been carried out by lidar so far, this study contributes to previous studies on biomass burning aerosols, in particular regarding the first stages of the smoke transport.This article studies the optical and microphysical properties of the smoke aerosols retrieved by the lidar ...

A comparison of columnar versus ground-level measurements of aerosol size distribution is presented. The purpose was to understand what atmospheric conditions are most suitable for closure between: 1) ground-based remote sensing instruments measuring vertical column-integrated optical and microphysical properties and 2) ground-based in-situ aerosol instruments measuring microphysical properties at the surface scaled to height using aerosol backscatter profiles from lidar measurements. Measurements were taken during the SPALI10 (SPAin Lidar Intercomparison 2010) field campaign at Madrid from 18 October to 5 November 2010 within the frame of the EARLINET-ASOS project. Monitoring included aerosol measurements of size distribution as well as chemical composition. Both combined Scanning Mobility Particle Sizer and Optical Particle Counters were used for determining aerosol size distribution ranging from 15 nm to 10 μm. Additionally, the column-integrated characterization of the atmospheric aerosol was provided by a sun tracking photometer using a methodology based on non-spherical particles. Two different synoptic situations were analyzed: a stagnation scenario with growing pollution concentrations and a clean atmosphere with low aerosol particle load. The shape of the ground-level aerosol size distribution matches with the column-integrated in both scenarios but absolute values disagree, particularly with stagnation. Better agreement was found for clean atmospheric situations when the mixing layer reaches higher altitudes and the aerosol concentration within the atmosphere follows an exponential decay profile with height.

Aerosol measurements at two AERONET (AErosol RObotic NETwork) sites of the Iberian Peninsula: Madrid (40??.45N, 3.72W) and La Coru??a (43??.36N, 8??.42W) have been analyzed for the period 2012???2015 to assess aerosol optical properties (intensive and extensive) throughout the atmospheric column and their radiative forcing (RF) and radiative forcing efficiency (RFeff) estimates at the Bottom and Top Of Atmosphere (BOA and TOA respectively). Specific conditions as dust-free and African dust have been considered for the study. Unprecedented, this work uses the quantification of the African dust aerosol at ground level which allows us to study such AERONET products at different intensity levels of African events: Low (L), High (H) and very high (VH). The statistical difference between dust-free and African dust conditions on the aforementioned parameters, quantified by means of the non-parametric Kolmogorov-Smirnov test, is quite clear in Madrid, however it is not in La Coru??a. Scattering Angstrom Exponent (SAE) and Absorption Angstrom Exponent (AAE) were found to be 1.64 ?? 0.29 and 1.14 ?? 0.23 respectively in Madrid for dust-free conditions because typical aerosol sources are traffic emissions and residential heating, and black carbon is an important compound in this aerosol kind. On the other hand, SAE and AAE were 0.96 ?? 0.60 and 1.44 ?? 0.51 for African dust conditions in this location. RF (at shortwave radiation) seems to decrease as the African dust contribution at ground level is larger which indicates the cooling effect of African dust aerosol in Madrid. We have also proved the potential of a 2D-cluster analysis based on AAE and SAE to differentiate both situations in Madrid. Conversely, it is suggested that aerosols observed in La Coru??a under dust-free conditions might come from different sources. Then, SAE and AAE are not good enough indicators to distinguish between dust-free and African dust conditions. Besides, as La Coru??a is at a further distance than Madrid from the African dust source it is believed that aerosol optical properties might significantly change due to some deposition and aging/coating process and therefore the cooling effect (RF decreases as the African dust contribution at ground level is larger) is not observed.

Concerns about high levels of air pollutants, together with the observed differences between the vehicle emission running under normal operating conditions and the limits specified in the homologation tests, has encouraged to conduct in Spain a study to meet the actual emissions of the circulating vehicle fleet. For this purpose Madrid metropolitan area was selected to carry on this study, considering that the characteristics of its circulating park can be extrapolated to the rest of the country fleet. The measuring technology used was optical remote sensing that allows to measure the emissions in terms of ratios of each emitted pollutant versus CO2 in the exhaust plume. Some of the most relevant results are the high levels of NO/CO2 registered for euro 5 and euro 6 diesel vehicles, and the big differences among the emissions when they are evaluated comparing the results of brands of the Spanish fleet.

The Surface Processes and Ecosystem Changes Through Response Analysis (SPECTRA) Barrax Campaigns were validation campaigns developed in the framework of the SPECTRA mission in order to verify that the geophysical data products provided by satellite imagery are consistent with the measurements made by independent means. Two campaigns took place in Barrax, Spain, during the summers of 2003 and 2004. This paper presents the results of the characterization of the atmospheric composition from solar radiation, radiosoundings, and lidar measurements. Several potentially interesting situations involving atmospheric layers with different types of aerosols and water content are discussed. The presence of a residual layer capping the mixing layer during some days of the 2003 campaign and the arrival of a dust-rich air mass from the Sahara on the last two days of the 2004 campaign provide some relevant aerosol vertical profiles to test atmospheric correction algorithms. The study of the effects of these atmospheric situations on radiative transfer calculations is required in the development and validation of advanced atmospheric correction codes for the new generation of Earth Observation Systems. © 2007 IEEE.

In this paper we present the results corresponding to on-road traffic emissions measurements obtained during two field campaigns developed in the Madrid region (Spain) during 2014 and 2015 in the framework of the CORETRA project. The experimental strategy was based on the use of a RSD 4600 remote sensor in interurban roads. These measurements have produced a global database of > 190,000 vehicles with their associated emission data (NO/CO 2 , HC/CO 2 and CO/CO 2 ), which can be considered representative of the current Spanish circulating fleet. The results of M1 vehicles were analysed according to their distribution by Euro Standard and engine model. One of the relevant findings is that, despite the progressive introduction of increasingly stringent standards, no NO emission reduction is observed for diesel vehicles with time, although this behavior shows significative differences among brands and engine models. We have also investigated the presence of “high emitter” (HE) vehicles in the Spanish M1 circulating fleet and most of the HE detected corresponded to diesel vehicles with very high NO/CO 2 values. With these results at hand, we strongly propose the future incorporation of the “high emitter vehicle” definition into the European environmental legislation, as well as the establishment of specific strategies in each country/region in order to identify these anomalous vehicles. Identification and repair of HE vehicles within the European circulating fleets, although are not easy tasks, should be considered very important for the improvement of air quality in the EU. The use of non-intrusive optical technologies (i.e. RSD) is an excellent option to provide instantaneous real emission data of each individual vehicle without disturbing traffic and for on-road fleet monitoring. In summary, it is a good strategy to obtain valuable information about the long term surveillance of real vehicle emission trends, specially after the introduction of new standard.

A seasonal comparison of aerosol secondary inorganic component (SIC) patterns on annual, weekly and daily timescales has been performed at urban Madrid and London and at rural sites in the central Iberian Peninsula and south-eastern UK alongside data for precursor gases. A database from winter 2004 to summer 2011 has been analysed. Results show the dominant processes affecting the formation and evolution of nitrate (NO3−) and sulphate (SO42−) in both regions. In Madrid, photochemistry dominates formation of nitrate, which is mostly locally-generated. Strong thermal decomposition results in very low concentrations in summer. In contrast, in London high nocturnal values suggest the importance of heterogeneous formation processes as well as nitrate condensation at lower temperatures. The seasonal nitrate maximum in the UK is found in late winter-early spring, when the region typically receives the highest input of pollutants transported from mainland Europe. Daily evolution of nitrate in both cities is heavily influenced by meteorological factors. Seasonal sulphate patterns show no obvious trend, except at the Spanish rural site in summer where photochemical formation was apparent. In Madrid, daily SO2 and sulphate patterns exhibiting maximum concentrations at noon were found in winter. In previous studies this phenomenon was observed for SO2 in London, where it was explained by the entrainment of pollutants from aloft into the mixing layer. SIC weekend reductions were investigated at the urban background sites of Madrid and London, and in both cities statistically significant fine nitrate reductions of around 20% are found in summer. These values are consistent with the annual reductions observed by researchers in the US. Weekend sulphate reductions occurred in winter, reflecting a clear impact of anthropogenic sulphate in urban environments, in spite of the large reductions in sulphur emissions in Europe in the last decade. Ratios of nitrate and sulphate to oxidant gases and to one another have been calculated for Madrid, and are consistent with a contribution of local formation to sulphate in winter, while in summer a regional background unrelated to urban SO2 is observed. The strong differences in the behaviour seen in London and Madrid (and the rural sites) emphasises the need to study cities individually and not to extrapolate conclusions drawn in one city to others in different climate/topographic situations.

A novel on-board system was tested to characterize size-resolved particle number emission patterns under real-world driving conditions, running in a EURO4 diesel vehicle and in a typical urban circuit in Madrid (Spain). Emission profiles were determined as a function of driving conditions. Source apportionment by Positive Matrix Factorization (PMF) was carried out to interpret the real-world driving conditions. Three emission patterns were identified: (F1) cruise conditions, with medium-high speeds, contributing in this circuit with 60% of total particle number and a particle size distribution dominated by particles >52 nm and around 60 nm; (f2) transient conditions, stop-and-go conditions at medium-high speed, contributing with 25% of the particle number and mainly emitting particles in the nucleation mode; and (F3) creep-idle conditions, representing traffic congestion and frequent idling periods, contributing with 14% to the total particle number and with particles in the nucleation mode (

Particle emissions from diesel engine cars depend firstly on exhaust aftertreatment systems but the use of the vehicle becomes also crucial. In urban areas, this use depends on: transport demand, route choices, traffic density, street conditions, weather, driver behaviour and topographical characteristics of the roads. Nowadays, most diesel vehicles in urban areas across Europe are equipped with exhaust aftertreatment systems aiming to reduce the total mass of emitted particles. In comparison to earlier aftertreatment systems, the implementation of modern procedures is causing a reduction in the size of the emitted particles up to a nanometric range. The main goal of this work is the characterization of particle size and number distribution in the submicrometric range from a modern diesel vehicle emission in real traffic conditions in the city of Madrid with the purpose of assessing the actual weight of the different city parameters influencing the particle emission. In order to accomplish this objective, up to 12 on board emission measurement experiments have been performed with a Euro IV Diesel passenger car driving along a single urban circuit in Madrid City. To cover the main external factors, stretch, traffic conditions and driving directions have been considered as independent variables for this study. Assuming a proper car operating conditions, the results show that street characteristics, vehicle density and topographic features are the main factors conditioning the particle emission. Extrapolating our results, a diesel standard passenger car circulating across a city like Madrid can emit more nanoparticles per kilometre (up to 114% more in this study) at peak hour than at off peak hour. Moreover, the driving direction can also influence dramatically the emission of nanoparticles per second. This difference in the emission rate depends on the street but in our study it can be higher than 110% depending on the driving direction.

In April and May 2010 the eruption of the Eyjafjallajokull volcano disrupted air traffic across Europe. The vast economic impact of this event has stirred interest on accurate plume dispersion estimation and detailed ash characterization, in order to establish a more precise threshold for safe aircraft operation. In this work we study the physical and chemical properties of volcanogenic aerosol detected at ground level at several locations over the Iberian Peninsula, nearly 3000 km away from the Icelandic volcano. Between 4 and 14 May, the volcanogenic plume was detected at ground level, identified by an increase in sulfur dioxide, particle mass concentrations, and particulate sulfate concentration, at most EMEP stations as well as at the CIEMAT site (for the sulfate concentration in PM). At the CIEMAT site, the synergic use of Raman lidar and on-site instruments provided relevant information on the evolution and properties of the plume over the central part of the Iberian Peninsula. Aerosol extinction coefficient profiles provided by the lidar station show the presence of remarkable aerosol layers between 6 May and 15 May. Provenance studies using FLEXTRA backtrajectories confirmed that most of the aerosol layers originated in the Eyjafjallajokull eruption. The large suite of semi-continuous instruments present in the latter site allowed a better characterization of the aerosol properties. Size distribution and chemical composition were continuously monitored during the event, revealing a large increase in the aerosol fine mode, in coincidence with increases in ambient sulfate concentration, while the coarse mode remained almost unaltered. These results show that the plume carried mainly fine particles, with sizes between 0.1 and 0.7 μm in diameter, in contrast with studies of the plume that affected Central Europe in April, where particles with diameters larger than 20 μm were present in the ash layers. A possible explanation for this can be related to the long distance transport suffered by the plume and by the secondary formation of particulate sulfate from the gaseous sulfur dioxide. The information on volcanic aerosol characteristics after long-range transport provided by this study might contribute to better assess the type of aerosol that reach distant locations.

In this work we examine the possibility of using satellite remote sensors for the detection of air traffic emissions produced during the en-route segment of flight in the Upper Troposphere/Lower Stratosphere region (8000–12,000 m). NO 2 has been considered as the tracer of aircraft plumes with highest possibility of being successfully detected from space. An analysis of the technical potential of the current orbital sensors capable of measuring NO 2 in the proximity of the tropopause has been conducted. In order to estimate an upper bound for the NO 2 column related to aircraft emissions, the Canary Islands Corridor has been selected for conducting a simple emission calculation exercise based on real air traffic and operational data, assuming an ideal atmospheric scenario. The results obtained in this approximation have been compared to the actual information retrieved from space sensors. An in-depth inspection of the NO 2 column data for two particular areas (Canary Islands Corridor and North Atlantic Flight Corridor) obtained in recent years by SCIAMACHY and OMI has also been carried out. The general conclusions of this viability study are not optimistic. The estimated maximum NO 2 column value attributable to aircraft emissions at cruise altitudes were lower than the detection limits associated with SCIAMACHY and OMI for NO 2 column measurements. As a result, detecting and quantifying the actual NO 2 levels in aircraft corridors by space remote sensing is a very challenging task.

This paper analyzes the mass size distribution of some inorganic species present in the atmospheric aerosol from a field campaign carried out in Madrid throughout a complete year (February 2007–February 2008). Samplings were performed by means of a micro-orifice uniform deposit impactor (MOUDI). Ambient air was sampled during consecutive nocturnal and diurnal periods, and diurnal/nocturnal behaviors were compared for the twenty night-day sampling pairs that were gathered. Annual and seasonal averages were obtained, and some case studies under specific atmospheric conditions are discussed in the paper. Results have shown that the sulfate and ammonium mass was concentrated in the accumulation mode, between 0.18 and 0.56 μm, so that gas-phase and condensation processes for secondary aerosol formation prevailed during the sampling periods in this area. An exception to this behavior was found during a fog event when distributions for these two species were centered in the 0.56–1 and 1–1.8 μm size stages, corresponding to the droplet mode. In most of the samples, the ammonium mass measured in these size ranges was enough or almost enough to neutralize inorganic acidity by formation of ammonium sulfate and nitrate. However, a significant sulfate mass not neutralized by ammonium was found in the impactor backup quartz filter (aerodynamic diameter Regarding the nitrate concentration, it was found higher in the coarse mode than in the accumulation mode on an annual basis. The highest concentrations were measured in winter episodic situations. The marked seasonal variability shown in the accumulation mode by this species is related to the volatility of ammonium nitrate. Among all the studied ions, nitrate also presented the highest differences between the diurnal and nocturnal concentrations in all size ranges. This is probably related to the short time scale required for its formation from gaseous precursors.

The ambient particle number concentration and size distribution have been measured in an urban background site in Madrid, a continental Mediterranean area, over more than two years (Oct 2006–Dec 2008). The objective was to study the sources and processes affecting or contributing to fine and ultrafine particles in this area. They have been measured with a TSI–SMPS (15–600 nm) instrument and with a modified Vienna type DMA (3–80 nm) and a CPC 3025 (TSI) during 6 months. The average particle number concentration was lower than in other sites as it is an urban background site and because of its location in the Mediterranean area. The particle number concentrations have shown a clear seasonal influence: maximum values were observed every year in the period November–January, coinciding with atmospheric stagnant conditions and pollution episodes, while minimum values were measured in springtime, a period in which wind speed produced high atmospheric dilution. The Aitken and accumulation modes have shown similar seasonal behavior, with two maxima related to vehicle emissions. The nucleation mode had a third maximum observed at noon during spring and summer. The size distributions were bimodal during most of the time: the first mode was centered on 20–50 nm and was associated with fresh particles related to vehicle exhaust emission; the second mode, between 50 and 160 nm, mainly corresponded to the evolution of the first mode. The evolution of the size distributions reveals a marked annual cycle related to the season, with an increase of median diameters during summer and a decrease during winter. Different evolutions of particle size distribution corresponding to different meteorological and seasonal scenarios were identified. The influence of higher wind speeds on particle size distribution has been confirmed to cause a decrease in the particle number concentration and in the size distribution mode. Particle nucleation is not a frequent phenomenon in this measurement site, where 63 events per year have been observed. They mainly occurred during spring and summer periods, with the minimum number during winter. This suggests that insolation and temperature are important variables in nucleation. Class Ia nucleation events mainly occurred during spring and summer. High wind speeds were important during class II events, as the particles suffered low growth or lost their semivolatile compounds.

This work has focused on the development and evaluation of an experimental set-up to measure in real time and with on-board equipments the particle emissions of diesel vehicle minimizing the uncertainties associated to dilution ratio, the length of the transfer line and the sampling point in the engine exhaust pipe. Its suitability has been verified by ensuring the repeatability of the results in dynamometer tests reproducing standard circuits, as well as in closed circuits and in real urban traffic in Madrid, Spain. The experience derived from this work has been very useful, contributing to the advance in the measurement of particle number and size distribution in real time using on-board equipment and bringing us closer to understanding the relationship between the physical characteristics of the particles emitted by a diesel engine and its operation in real urban traffic conditions. The proposed on-board system has provided very satisfactory results.

—A group of eight Spanish lidars was formed in order to extend the European Aerosol Research Lidar Network–Advanced Sustainable Observation System (EARLINET-ASOS)project. This study presents intercomparisons at the hardware and software levels. Results of the system intercomparisons are based on range-square-corrected signals in cases where the lidars viewed the same atmospheres. Comparisons were also made for aeros backscatter coefficients at 1064 nm (2 systems) and 532 nm (all systems), and for extinction coefficients at 532 nm (2 systems). In total, three field campaigns were carried out between 2006 and 2007. Comparisons were limited to the highest layer found before the free troposphere, i.e., either the atmospheric boundary layer or the aerosol layer just above it. Some groups did not pass the quality assurance criterion on the first attempt. Following modification and improvement to these systems, all systems met the quality criterion. The backscatter algorithm intercomparison consisted of processing lidar signal profiles simulated for two types of atmospheric conditions. Three stages with increasing knowledge of the input parameters were considered. The results showed that all algorithms work well when all inputs are known. They also showed the necessity to perform, when possible, additional measurements to attain better estimation of the lidar ratio, which is the most critical unknown in the elastic lidar inversion.

After urban sources, mineral dust in Madrid is the second biggest contributor to PM10, making up 40% on average, of total emissions. Approximately, 50% of the days on which the daily limit of 50 μg m−3 marked by the European Directive, are ascribable to Saharan outbreaks. The present study has focused on individual particle characterization of North African dust over Madrid by SEM/EDX, since no previous works on this type of characterization have been found in the region. More than 30,000 particles from 6 different samples have been measured to characterize 4 African episodes with very different meteorological scenarios, transport processes and source origins. Different samples from the same episode have also been characterized to evaluate homogeneity of dust characteristics over time. Silicates, mainly composed of clay minerals, are the main component, with abundances ranging from 65 to 85% by particle volume. Chemical cluster distribution of silicates has been linked to the major topsoil mineralogical composition in the origin of the episodes. Aspect Ratio (AR) has been used to compare particle morphology between episodes. AR values from samples taken under the same scenarios are statistically equal. For all the samples and size ranges AR values are found to be in the same order: ARsulphates > ARsilicates > ARcarbonates. Particles not only maintained morphology during the episode, but also chemical composition, since clusters turned out to be very similar in samples taken on the same day and different days. Similarities and differences in particle chemical composition and morphology between the different transport patterns are discussed in detail throughout the paper.

During the 2002 summer, the VELETA 2002 field campaign has been carried out at the Sierra Nevada Massif, close to Granada in South-Eastern Spain. During the campaign, CIMEL CE-318 robotic radiometer has been one of the key instruments in the characterization of the atmospheric aerosol columnar properties. This kind of radiometers have been operated at Motril, a coastal location at sea level, Pitres (1200 m a.s.l.), located in the South slope of Sierra Nevada Massif, Las Sabinas (2200m a.s.l.), located on the north slope of the mountain range, and Armilla (680m a.s.l.), located in the valley. The principal feature of the locations is that they provide a strong altitudinal gradient. This work presents the evolution of changes followed by the atmospheric aerosol in the vertical column. Columnar aerosol properties have been derived from the CIMEL CE-318 measurements obtained at the four stations. In this sense, the combination of solar direct measurements and sky radiances were used to retrieve the aerosol columnar size distributions by means of Nakajima's code. Marked changes in the atmospheric aerosol along the campaign have been explained in terms of the synoptic conditions. A detailed study of the columnar properties at the different places has been done. Changes in the spectral dependence of the single scattering albedo under the influence of different air masses have been discussed. The size distributions have been fitted to a bimodal lognormal distribution function model, and the associated parameters have been correlated with aerosol optical depth or Angstrom exponent. In some cases, it has been necessary to develop different correlations for cases affected or non-affected by the arrival of Saharan dust. In the case of Armilla (680 m a.s.l.) and Las Sabinas (2200 m a.s.l.), the small horizontal distance allow us to consider that both stations are representative of the same atmospheric column, a fact that has been used to analyse the daily evolution of the mixing layer in the north slope. (C) 2007 Elsevier Ltd. All rights reserved.

Bulk material handling can be a significant source of particles in harbor areas. The atmospheric impact of a number of loading/unloading activities of diverse raw materials has been assessed from continuous measurements of ambient particle concentrations recorded close to the emission sources. Two experimental campaigns have been carried out in the Tarragona port to document the impact of specific handling operations and bulk materials. Dusty bulk materials such as silica–manganese powder, tapioca, coal, clinker and lucerne were dealt with during the experiments. The highest impacts on ambient particle concentrations were recorded during handling of clinker. For this material and silica–manganese powder, high concentrations were recorded in the fine grain size (

The objective of this paper is to show the methodology developed to estimate particle emissions from several typical activities of bulk handling in harbours. It is based on several field experiments carried out in the Harbour of Tarragona, where high time resolution monitors were deployed close to different areas of bulk solids handling operations. Monitors recorded particle concentrations and meteorological variables. A high-resolution dispersion model is used to estimate the emission rates that best fits the observations. Results were comparable to those obtained with the AP-42 (EPA). The new emission estimates are used as input for an emission model called EMIPORT. The model also employs AP-42 (EPA) emission factors as a complement. This work is one of the activities of the LIFE project called HADA (Herramienta Automatica de Diagnostico Ambiental or in English Automatic Tool for Environmental Diagnostic).

During the course of one year (March 2004–March 2005), PM2.5 particulate nitrate concentrations were semi-continuously measured every 10 min at a Madrid suburban site using the Rupprecht and Patashnick Series 8400N Ambient Particulate Nitrate Monitor (8400N). Gaseous pollutants (NO, NO2, O3, HCHO, HNO2) were simultaneously measured with a DOAS spectrometer (OPSIS AR-500) and complementary meteorological information was obtained by a permanent tower. The particulate nitrate concentrations ranged from the instrumental detection limit of around 0.2 μg m−3, up to a maximum of about 25 μg m−3. The minimum monthly average was reached during August (0.32 μg m−3) and the maximum during November (3.0 μg m−3). Due to the semi-volatile nature of ammonium nitrate, peaks were hardly present during summer air pollution episodes. A typical pattern during days with low dispersive conditions was characterized by a steep rise of particulate nitrate in the morning, reaching maximum values between 9 and 14 UTC, followed by a decrease during the evening. On some occasions a light increase was observed at nighttime. During spring episodes, brief diurnal nitrate peaks were recorded, while during the autumn and winter episodes, later and broader nitrate peaks were registered. Analysis of particulate nitrate and related gaseous species indicated the photo-chemical origin of the morning maxima, delayed with respect to NO and closely associated with secondary NO2 maximum values. The reverse evolution of nitrate and nitrous acid was observed after sunrise, suggesting a major contribution from HNO2 photolysis to OH formation at this time of the day, which would rapidly produce nitrate in both gaseous and particulate phase. Some nocturnal nitrate maxima appeared under high humidity conditions, and a discussion about their origin involving different possible mechanisms is presented, i.e. the possibility that these nocturnal maximum values could be related to the heterogeneous formation of nitrous and nitric acid by the hydrolysis of NO2 on wet aerosols.

This work presents for the first time a classification of shrinkage events based on the aerosol processes that precede them. To this end, 3.5 years of continuous measurements (from 2009 to 2012) of aerosol size distributions, obtained with a Scanning Mobility Particle Sizer (SMPS) at an urban background site in Southern Europe, have been interpreted. 48 shrinkage events were identified and analysed, all occurring during spring and summer when the atmospheric conditions are more favourable for their development. In this study the shrinkage events took place mostly towards the end of the day, and their occurrence could be associated to atmospheric dilution conditions and a reduction in photochemical activity. The shrinkage rate (SR) varied between −1.0 and −11.1 nm h−1 (average value of −4.7 ± 2.6 nm h−1). Changes in particle concentrations corresponding to the nucleation and Aitken modes were detected, whereby an increase in the number of particles in the nucleation mode often coincided with a reduction in the Aitken mode. The accumulation mode did not undergo significant changes during these processes. In addition, in some cases, a dilution of the total particle number concentration in the ambient air was observed. Following the proposed methodology, three groups of events have been identified: Group I (NPF + shrinkage), Group II (aerosol growth process + shrinkage) and Group III (pure shrinkage events). The largest number of shrinkage events has been observed in the absence of prior processes, i.e. pure shrinkage events, followed by Group I events and finally Group II events. Although this analysis has confirmed that the triggering of shrinkage events is clearly linked to the atmospheric situation and the characteristics of the measurement area, this classification may contribute to a better understanding of the processes involved and the features that characterize shrinkage events.

An analysis of hourly measurements of gaseous pollutants and fine carbonaceous aerosol (PM2.5) divided into two fractions, elemental and organic carbon (EC and OC), in a suburban Madrid metropolitan area site is presented. Data were obtained using a semi-continuous thermal analyser for two periods of time during the summer and late autumn–early winter of 2003. In the summer period, correlation between EC and OC was poor (r=0.46), and high OC/EC ratios were usually found. In contrast, during the late autumn–early winter period the two carbonaceous aerosol fractions showed a high degree of correlation (r=0.94). Coincident peaks of OC and secondary gases (NO2+O3) were observed during summer episodes and also on some winter episodic days, suggesting a significant non-primary contribution to OC in fine aerosol, linked to photochemical oxidation of gaseous pollutants. OC apportionment between primary and secondary origins has been attempted for the two measuring periods using the EC tracer model. In the summer period, the results of this apportionment were very dependent on the y-intercept value (considered as the non-combustion OC background concentration) of selected linear regressions. Calculation of the secondary contribution to the OC fraction during polluted days gave diurnal maximum hourly estimations in a range from 35% to 55% and daily estimations averaged during the 10–19 h period ranging from 25% to 45%. Thus, this would confirm a daily urban photochemical origin for the secondary organic aerosol, although biogenic contribution to both the OC background and the SOA formation may be significant in the area during summer. During late autumn–early winter episodes primary contribution to OC was more prevailing, although the model also estimated maximum hourly values of secondary OC in the order of 35% of the measured OC.

The results of a field study carried out in September–October 2000 near Madrid, regarding Quercus ilex and Pinus pinea monoterpene emission and its relation to ambient and physiological parameters, are presented in this paper. The major compounds in diurnal Q. ilex emission were limonene, α-pinene and β-pinene. Emission rates during warm days fitted reasonably well to the temperature and light-dependent model of Guenther (ES=13.4 μg gDW−1 h−1). However, during hot days at mid-day and afternoon hours, dramatic decreases of monoterpene emission, photosynthetic activity and stomatal conductance were observed. The poor soil–water availability combined with low relative humidity and high temperature is likely to be responsible for the observed emission drop. A parameterisation of emission, based on ambient atmospheric water vapour pressure deficit (WVPD), has been attempted in this study. Monoterpene diurnal emission from P. pinea was lower than that of Mediterranean oak (ES=1.5 μg gDW−1 h−1). A reduction in the total emission during the hottest hours of the day was not observed in this monoterpene storing species. Limonene emission rates, accounting on average for nearly half of the emission, were well described by the temperature-dependent model of Tingey. The rest of the emission was comprised of several compounds (cineole, myrcene, α-pinene, linalool) and was reduced at high WVPD values.