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The Third Iberian Meeting on Aerosol Science and Technology (RICTA 2015) was held in the city of Elche (province of Alicante, Spain) from 29 June to 1 July 2015, at Centro de Congresos Ciutat d'Elx. This event was organized and hosted by the Statistical and Computational Physics Laboratory (SCOLAb) of Universidad Miguel Hernández under the auspices of AECyTA, the Spanish Association for Aerosol Science and Technology Research. As in previous editions, the participation of young researchers was especially welcome, with the organization of the VI Summer School on Aerosol Science and Technology and awards for the best poster and PhD thesis, in recognition of outstanding research or presentations focusing on aerosols, during the early stage of their scientific career.

RICTA 2015 aims to present the latest research and advances on the field of aerosols, as well as fostering interaction among the Portuguese and Spanish communities. The meeting gathered over 70 participants from 7 different countries, covering a wide range of aerosol science and technology. It included invited lectures, keynote talks, and several specialized sessions on different issues related to atmospheric aerosols, radiation, instrumentation, fundamental aerosol science, bioaerosols and health effects.

The editors would like to express their sincere gratitude to all the participants, in particular, those who contributed to this special issue by submitting their papers to convey the current science discussed at RICTA 2015. In this special issue a series of peer-reviewed papers that cover a wide range of topics are presented: aerosol formation, emission, as well as aerosol composition in terms of physical and optical properties, spatial/temporal distribution of aerosol parameters, aerosol modeling and atmospheric effects, as well as instrumentation devoted to aerosol measurements. Finally, we also thank the referees for their valuable revision of these papers.

All papers published in this volume of IOP Conference Series: Earth and Environmental Science have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The present work is a first approach to the study of the spatio-temporal variability of the submicrometer atmospheric aerosol in Spain. The aerosol measurements have been obtained simultaneously at seven monitoring stations that compose the REDMAAS network during two measurement campaigns corresponding to summer and winter seasons.

In both summer and winter periods those measurement stations with a direct influence of anthropogenic emissions recorded the highest concentrations of particle number. In the summer campaign, the average daily pattern of the aerosol size distribution in the traffic and background urban stations was conditioned by the traffic emissions and secondary aerosol formation through photochemical reactions (new particle formation events, NPF). However, the secondary aerosol had a higher contribution to the aerosol total number concentration in the rural background and high-altitude stations. In the winter campaign, in all sampling sites with the exception of Izaña station, the traffic and domestic activity emissions had a greater contribution than secondary aerosol formation on particle number total concentration.

New particle formation events were identified at all sites during the summer period, and at sites without direct influence of anthropogenic emissions during the winter campaign. Some aerosol shrinkage processes were also observed at the Madrid and El Arenosillo stations.

The observation of high aerosol hygroscopic growth in Madrid is mainly limited to specific atmospheric conditions, such as local stagnation episodes, which take place in winter time. One of these episodes was identified in December 2014 and the hygroscopic growth factor (GF) measurements obtained in such episode were analysed in order to know the influence of the meteorological conditions on aerosol hygroscopic properties.

The prevailing high atmospheric stability triggered an increase of the particle total concentration during the study period, with several peaks that exceeded 4.0 10⁴ particles cm^-3, as well as an increase in the inorganic fraction of the aerosol, the NO₃⁻ concentration, which in this case corresponded to 25% of the total PM₁ non-refractory composition.

The aerosol hygroscopic growth distribution was bimodal during the episode, with an average GF around 1.2 for the five dry particle sizes measured and an average GF spread ≥ 0.15. In addition, it is important to note that when a reduction in the concentrations of NO₃⁻ is observed, it coincides with a decrease of the GF and its spread. These data suggest, on the one hand, a high degree of external mixing state of the aerosol during the episode and, on the other hand, a notable association between the GF and the inorganic fraction of the aerosol.

Several experiments were performed in the European Photo-reactor - EUPHORE - for studying aerosol formation from organophosphorus pesticides such as diazinon, chlorpyrifos, chlorpyrifos-methyl and pirimiphos-methyl. The mass concentration yields obtained (Y) were in the range 5 - 44% for the photo-oxidation reactions in the presence and the absence of NOx. These results confirm the importance of studying pesticides as significant precursors of atmospheric particulate matter due to the serious risks associated to them.

The studies based on the use of EUPHORE photoreactor provide useful data about atmospheric degradation processes of organophosphorus pesticides to the atmosphere. Knowledge of the specific degradation products, including the formation of secondary particulate matter, could complete the assessment of their potential impact, since the formation of those degradation products plays a significant role in the atmospheric chemistry, global climate change, radiative force, and are related to health effects.

The atmospheric particulate matter has a large impact on climate, biosphere behaviour and human health. Its study is complex because of large number of species are present at low concentrations and the continuous time evolution, being not easily separable from meteorology, and transport processes. Closed systems have been proposed by isolating specific reactions, pollutants or products and controlling the oxidizing environment. High volume simulation chambers, such as EUropean PHOtoREactor (EUPHORE), are an essential tool used to simulate atmospheric photochemical reactions. This communication describes the last results about the reactivity of prominent atmospheric pollutants and the subsequent particulate matter formation. Specific experiments focused on organic aerosols have been developed at the EUPHORE photo-reactor. The use of on-line instrumentation, supported by off-line techniques, has provided well-defined reaction profiles, physical properties, and up to 300 different species are determined in particulate matter. The application fields include the degradation of anthropogenic and biogenic pollutants, and pesticides under several atmospheric conditions, studying their contribution on the formation of secondary organic aerosols (SOA). The studies performed at the EUPHORE have improved the mechanistic studies of atmospheric degradation processes and the knowledge about the chemical and physical properties of atmospheric particulate matter formed during these processes.

During the day November 26, 2014, a scheduled cleanup of the woods took place around the GOA-UVa aerosol measurement station located at the campus of the University of Beira Interior (40° 16'30"N, 7°30'35"W, 704m a.s.l.), Covilhã, Portugal. This cleanup included excessive vegetation removal during the morning, using fossil fuel-burning machinery, and burning of the vegetation during the afternoon. In situ measurements of aerosol optical properties were made and this study aims the characterization of the evolution of aerosol properties during the day. The optical parameters were monitored using a 3-wavelength nephelometer and a 3-wavelength particle soot absorption photometer. Selective sampling/exclusion of the coarse particles was done each 5 minutes. The scattering and absorption Ångström exponents as well as the single scattering albedo were derived and fully analyzed. The scattering and absorption coefficients increased dramatically during the event, reaching values as high as 720.3 Mm^-1 and 181.9 Mm^-1, respectively, for the green wavelength and PM10 size fraction. The spectral behavior of these parameters also changed wildly along the day and an inversion of the slope from positive to negative in the case of the single scattering albedo was observed.

The present work aims at studying a very recent episode of desert dust transport that affected Iberia in mid May 2015. The dust aerosols were detected over Évora, where a varied set of instrumentation for aerosol measurements is installed, including: a CIMEL sunphotometer integrated in AERONET, a Raman Lidar and a TEOM monitor, as well as ceilometer and a microwave radiometer (profiler). The aerosol occurrence, detected using the columnar, vertically-resolved and in situ measurements, was characterized by a fairly high aerosol optical thickness that reached a value of 1.0 at 440 nm and showed mass concentration peaks at the surface of the order of 100 μg/m³. Subsequently, the tropospheric vertical profiles of humidity and temperature obtained with the passive microwave (MW) radiometer are analysed in order to distinguish possible modifications that can be connected with the transport of desert dust. Modelling results are also examined and the total, SW and LW radiative forcings are investigated, taking into account the different vertical profiles obtained during the desert dust occurrence. It is found that the differences in the atmospheric profiles mostly affect the LW radiative forcing, with an underestimation of about 30% when the actual vertical profile is not considered.

The UV irradiance is measured at Évora since several years, where a CIMEL sunphotometer integrated in AERONET is also installed. In the present work, measurements of UVA (315 - 400 nm) irradiances taken with Kipp&Zonen radiometers, as well as satellite data of ozone total column values, are used in combination with radiative transfer calculations, to estimate the aerosol optical thickness (AOT) in the UV. The retrieved UV AOT in Évora is compared with AERONET AOT (at 340 and 380 nm) and a fairly good agreement is found with a root mean square error of 0.05 (normalized root mean square error of 8.3%) and a mean absolute error of 0.04 (mean percentage error of 2.9%). The methodology is then used to estimate the UV AOT in Sines, an industrialized site on the Atlantic western coast, where the UV irradiance is monitored since 2013 but no aerosol information is available.

A simple analytical method using low volumes of solvent for determining selected PAHs and NPAHs in PM samples is presented. The proposed extraction method was compared with pressurized fluid (PFE) and microwave (MC) extraction techniques and intermediate precision associated to analytical measurements were estimated. Extraction by agitation with 8 mL of dichloromethane yielded recoveries above 80% compared to those obtained from PFE extraction. Regarding intermediate precision results, values between 10-20% were reached showing increases of dispersion for compounds with high volatility and low levels of concentration. Within the framework of the INTA/CIEMAT research agreement for the PM characterization in gas turbine exhaust, the method was applied for analysis of aluminum foil substrates and quartz filters with mass loading ranged from 0.02 to 2 mg per sample.

The aim of this study is to analyze the effect of the water vapor content on the downward irradiance measured at the Earth's surface. For that purpose, downward irradiance values have been estimated with the radiative transfer model libRadtran in different spectral ranges: shortwave (SW: 285-2800 nm) and longwave (LW: 3500-50000 nm), and with different water vapor content in the column. These simulations have been made for Évora, Portugal, the August 4, 2012, a cloud-free day and with low aerosol optical depth.

The comparison between the simulated irradiance with different water vapor contents shows differences in both spectral ranges. For SW, the irradiance reaching the surface increases when the water vapor content decreases, obtaining an increase of up to 4%, 2% and 1%, corresponding the largest increases to the smallest values of water vapor. For LW, the behaviour is the opposite, the irradiance decreases when the water vapor content decreases, obtaining a decrease of up to 10%, 4% and 2%, corresponding the largest decreases to the smallest values of water vapor. The effect of water vapor in the aerosol radiative forcing (ARF) has also been analyzed, obtaining relative difference values of up to 2.5% for SW and 35% for LW.

This study is aimed at analyzing the performance of the radiative transfer models libRadtran and SBDART for estimating the shortwave (285-2800 nm) irradiance under different aerosol conditions. For that purpose, measurements of downward irradiance at the Earth s surface in Évora and the corresponding model simulations have been compared for six selected days (03-08-2003, 15-08-2004, 24-08-2004, 18-07-2005, 19-08-2007 and 17-05-2010). The comparison between measured and simulated values shows a highly significant correlation, with determination coefficient between 0.999 and 1 for both models and slope very close to unity (between 0.992±0.004 and 1.017±0.003 for libRadtran, and between 0.997±0.004 and 1.024±0.002 for SBDART), supporting the validity of the models in the estimation of irradiance in the shortwave spectral range. Relative differences between the simulated and measured irradiances with respect to the measured values have also been calculated, being most of the differences for the six days lower than 0.2%. These small differences could be associated with experimental errors in the measurements as well as uncertainties in the input values given to the models, particularly those related with the aerosol properties. Also, relative differences between models have been calculated, obtaining values lower than 0.1%. SBDART model slightly overestimates the libRadtran simulations. The notably good agreement between simulated and measured irradiances indicates that both models can be used to estimate irradiance, provided that the models are fed with highly reliable-quality data.

The long-term (2003-2013) variations in columnar aerosol properties at Lecce, a site representative of the central Mediterranean, have been analysed for trend assessment. The study focuses on aerosol optical thickness (AOT) at 340, 440, 500 and 1020 nm and Ångström exponent (AE) for the pair 440-870 nm, retrieved from a sun photometer operating within the Aerosol Robotic Network (AERONET). A non-parametric trend analysis of the monthly mean, median and upper and lower tails (90th and 10th percentiles) suggests that the aerosol load has decreased during the study period, while the mean particle size remained unchanged. The characteristic advections reaching the study site were found by clustering analysis of back trajectories at 500, 1500 and 3000 m. Despite the strong influence they have on aerosol load and particle size, neither of the trends in advection routes could explain the tendencies found in the columnar aerosol properties. However, trends in aerosol data by advection type allow understanding the overall trends. Aerosol properties under flows with high residence time over continental Europe present differences according to the specific residing area. More specifically, no trend is found when flows arrive from Ukraine and the Balkans, while under advections from north-western/central Europe there are downward trends in the background levels and a reduction of the fine fraction. Negative trends are also found under flows with high residence time over the Mediterranean and northern Africa, again with differences according to the residing area.

Control of particulate matter emissions by means of hybrid filter has been included in the experimental plan of a research project in the field of Mediterranean agro-forestry waste biomass combustion at medium scale. Application of hybrid filters to biomass combustion has not been thoroughly experimented so far. An identification of the most important parameters in particulate matter emissions control by means of a hybrid filter was undertaken. The filter involves two of the most significant technologies in fly ash emission control, electrostatic precipitation and fabric filtration A discussion of these parameters and principles of operation of said technologies is presented, as well as the final selection of parameters to be included in the experimental matrix of the project in regards to emissions control. A novel approach is proposed for testing of filtration velocity influence in fabric filter module without impacting on operation of electrostatic precipitation module.

Elastic lidars provide range-resolved information about the aerosol content in the atmosphere. Nevertheless, a number of pre-processing techniques need to be used before performing the inversion of the detected signal: range-correction, time-averaging, photoncounting channel dead-time correction, overlap correction, Rayleigh-fitting and gluing of both channels.