Advancing air quality monitoring: A low-cost sensor network in motion - Part I.

In urban areas, high levels of air pollution pose significant risks to human health, emphasising the need for detailed air quality (AQ) monitoring. However, traditional AQ monitoring relies on the data from Reference Monitoring Stations, which are sparsely distributed and provide only hourly or daily data, failing to capture the spatial and temporal variability of air pollutant concentrations. Addressing this challenge, we introduce in this article the ExpoLIS system, an all-weather mobile AQ monitoring system that integrates various AQ low-cost sensors (LCSs), providing high spatio-temporal resolution data. This study demonstrates that the inclusion of an extended sampling device may mitigate the effect of the meteorological parameters and other disturbances on readings. At the same time, it did not reduce the quality of the data, both in static conditions and in motion, as we were able to maintain a certain level of agreement between the LCSs. In conclusion, the ExpoLIS system proves its versatility by enabling the collection of large quantities of accurate data, allowing a deeper understanding of the AQ dynamics in urban environments.

Integrated Human Exposure to Air Pollution: A Step Further.

Along with climate change, air pollution is one of the biggest environmental problems affecting everyone in the world today [...].

Microplastic contamination of lettuces grown in urban vegetable gardens in Lisbon (Portugal).

Urban vegetable gardens are very often a feature of cities that want to offer their citizens a more sustainable lifestyle by producing their own food products. However, cities can have significant pollution levels (or pollution hotspots) due to specific sources of pollution, such as traffic. Among the various pollutants, microplastics (MPs) are emerging as a consensual concern due to the awareness of the environmental contamination, their bioaccumulation potential and human intake, and, consequently unknown human health impacts. The present study compared the content of MPs in lettuce plants cultivated in Lisbon urban gardens with those cultivated in a rural area, as well as samples bought in supermarkets. Microplastics were detected in all washed leaves, with mean levels ranging from 6.3 ± 6.2 to 29.4 ± 18.2 MPs/g. Lettuce grown in urban gardens from areas with high traffic density showed higher MPs levels. Weak positive Spearman's rank correlations were found between MPs content and concentrations of Cu and S (determined by Particle Induced X-Ray Emission, PIXE), suggesting a possible role of traffic contribution to MPs levels, as both elements are considered traffic-source tracers. These results contribute to shed light on the MP contamination of vegetables grown in such urban environments, that may represent a potential MP exposure route through the dietary intake, corresponding to a 70% increase in annual MP intake compared to lettuces bought in supermarkets.

The Representativeness of Outdoor Particulate Matter Concentrations for Estimating Personal Dose and Health Risk Assessment of School Children in Lisbon.

This study investigated the suitability of outdoor particulate matter data obtained from a fixed monitoring station in estimating the personal deposited dose. Outdoor data were retrieved from a station located within the urban area of Lisbon and simulations were performed involving school children. Two scenarios were applied: one where only outdoor data were used assuming an outdoor exposure scenario, and a second one where an actual exposure scenario was adopted using the actual microenvironment during typical school days. Personal PM10 and PM2.5 dose (actual exposure scenario) was 23.4% and 20.2% higher than the ambient (outdoor exposure scenario) PM10 and PM2.5 doses, respectively. The incorporation of the hygroscopic growth in the calculations increased the ambient dose of PM10 and PM2.5 by 8.8% and 21.7%, respectively. Regression analysis between the ambient and personal dose showed no linearity with R2 at 0.07 for PM10 and 0.22 for PM2.5. On the other hand, linear regression between the ambient and school indoor dose showed no linearity (R2 = 0.01) for PM10 but moderate (R2 = 0.48) for PM2.5. These results demonstrate that ambient data must be used with caution for the representativeness of a realistic personal dose of PM2.5 while for PM10 the ambient data cannot be used as a surrogate of a realistic personal dose of school children.

An Educational Game to Teach Children about Air Quality Using Augmented Reality and Tangible Interaction with Sensors.

Air pollution is known to be one of the main causes of injuries to the respiratory system and even premature death. Gases, particles, and biological compounds affect not only the air we breathe outdoors, but also indoors. Children are highly affected by the poor quality of the air they breathe because their organs and immune systems are still in the developmental stages. To contribute to raising children's awareness to these concerns, this article presents the design, implementation, and experimental validation of an serious augmented reality game for children to playfully learn about air quality by interacting with physical sensor nodes. The game presents visual representations of the pollutants measured by the sensor node, rendering tangible the invisible. Causal knowledge is elicited by stimulating the children to expose real-life objects (e.g., candles) to the sensor node. The playful experience is amplified by letting children play in pairs. The game was evaluated using the Wizard of Oz method in a sample of 27 children aged between 7 and 11 years. The results show that the proposed game, in addition to improving children's knowledge about indoor air pollution, is also perceived by them as easy to use and a useful learning tool that they would like to continue using, even in other educational contexts.

A Low-Cost Sensor System Installed in Buses to Monitor Air Quality in Cities.

Air pollution is an important source of morbidity and mortality. It is essential to understand to what levels of air pollution citizens are exposed, especially in urban areas. Low-cost sensors are an easy-to-use option to obtain real-time air quality (AQ) data, provided that they go through specific quality control procedures. This paper evaluates the reliability of the ExpoLIS system. This system is composed of sensor nodes installed in buses, and a Health Optimal Routing Service App to inform the commuters about their exposure, dose, and the transport's emissions. A sensor node, including a particulate matter (PM) sensor (Alphasense OPC-N3), was evaluated in laboratory conditions and at an AQ monitoring station. In laboratory conditions (approximately constant temperature and humidity conditions), the PM sensor obtained excellent correlations (R2≈1) against the reference equipment. At the monitoring station, the OPC-N3 showed considerable data dispersion. After several corrections based on the k-Köhler theory and Multiple Regression Analysis, the deviation was reduced and the correlation with the reference improved. Finally, the ExpoLIS system was installed, leading to the production of AQ maps with high spatial and temporal resolution, and to the demonstration of the Health Optimal Routing Service App as a valuable tool.

Source apportionment of PM2.5 before and after COVID-19 lockdown in an urban-industrial area of the Lisbon metropolitan area, Portugal.

The lockdowns held due to the COVID-19 pandemic conducted to changes in air quality. This study aimed to understand the variability of PM2.5 levels and composition in an urban-industrial area of the Lisbon Metropolitan Area and to identify the contribution of the different sources. The composition of PM2.5 was assessed for 24 elements (by PIXE), secondary inorganic ions and black carbon. The PM2.5 mean concentration for the period (December 2019 to November 2020) was 13 ± 11 µg.m-3. The most abundant species in PM2.5 were BC (19.9%), SO4 2- (15.4%), NO3 - (11.6%) and NH4 + (5.3%). The impact of the restrictions imposed by the COVID-19 pandemic on the PM levels was found by comparison with the previous six years. The concentrations of all the PM2.5 components, except Al, Ba, Ca, Si and SO4 2-, were significantly higher in the winter/pre-confinement than in post-confinement period. A total of seven sources were identified by Positive Matrix Factorisation (PMF): soil, secondary sulphate, fuel-oil combustion, sea, vehicle non-exhaust, vehicle exhaust, and industry. Sources were greatly influenced by the restrictions imposed by the COVID-19 pandemic, with vehicle exhaust showing the sharpest decrease. Secondary sulphate predominated in summer/post-confinement. PM2.5 levels and composition also varied with the types of air mass trajectories.

Citizens' Perception on Air Quality in Portugal-How Concern Motivates Awareness.

This study aimed to understand the knowledge of Portuguese citizens about air quality and the extent to which the concerns about specific environmental problems can motivate their acquaintance of information. Moreover, this study also allowed to understand which information about air quality needs further dissemination to provide the citizens with all the available tools and the correct knowledge. For this, a national online survey about air quality perception was conducted, where 1131 answers were obtained and two different populations were compared: the general population and a sub-population from an urban-industrial area of Lisbon metropolitan area that had experienced frequent air pollution events in the past. Air pollution was considered the environmental topic of higher concern among this sub-population (61.4%), while in the general population it ranked thirdly (27.4%). Generally, the sub-population showed higher knowledge about air quality than the general population, with 61% being able to identify at least one air pollutant. The perception of the local air quality was also very different between populations, with 61% of the sub-population considering it poor or very poor, while only 14% of the general population had the same perception, which highlights the different levels of concern between populations. A weak knowledge about air pollutants (50% of the general population could not identify any air pollutant) and an erroneous perception of the contribution of the different pollution sources to air quality levels were found. More than 50% of the respondents of both populations were considered to not have enough information regarding the air quality in their area of residence, with the national air quality database being unknown to almost everyone. Overall, strong efforts should be made to increase the awareness about the importance of air quality, which may promote a higher acceptance of the implementation of future actions to improve air quality.

Source apportionment of children daily exposure to particulate matter.

The present study aims to investigate the sources of particulate pollution in indoor and outdoor environments, with focus on determining their contribution to the exposure of children to airborne particulate matter (PM). To this end, parallel indoor and outdoor measurements were carried out for a selection of 40 homes and 5 schools between September 2017 and October 2018. PM2.5 and PM2.5-10 samples were collected during five days in each microenvironment (ME) and analysed by X-Ray Fluorescence (XRF), for the determination of elements, and by a thermal-optical technique, for the measurement of organic and elemental carbon. The source apportionment analysis of the PM composition data, by means of the receptor model SoFi (Source Finder) 8 Pro, resulted in the identification of nine sources: exhaust and non-exhaust emissions from traffic, secondary particles, heavy oil combustion, industry, sea salt, soil, city dust, and an indoor source characterized by high levels of organic carbon. Integrated daily exposure to PM2.5 was on average 21 µg/m3. The organic matter, resulting from cleaning, cooking, smoking and biological material, was the major source contributing by 31% to the PM2.5 exposure. The source city dust, which was highly influenced by the resuspension of dust in classrooms, was the second main source (26%), followed by traffic (24%). The major sources affecting the integrated exposure to PM10, which was on average 33 µg/m3, were the city dust (39%), indoor organics (24%) and traffic (16%). This study provides important information for the design of measures to reduce the exposure of children to PM.

Spatial Distribution of Air Pollution, Hotspots and Sources in an Urban-Industrial Area in the Lisbon Metropolitan Area, Portugal-A Biomonitoring Approach.

This study aimed to understand the influence of industries (including steelworks, lime factories, and industry of metal waste management and treatment) on the air quality of the urban-industrial area of Seixal (Portugal), where the local population has often expressed concerns regarding the air quality. The adopted strategy was based on biomonitoring of air pollution using transplanted lichens distributed over a grid to cover the study area. Moreover, the study was conducted during the first period of national lockdown due to COVID-19, whereas local industries kept their normal working schedule. Using a set of different statistical analysis approaches (such as enrichment and contamination factors, Spearman correlations, and evaluation of spatial patterns) to the chemical content of the exposed transplanted lichens, it was possible to assess hotspots of air pollution and to identify five sources affecting the local air quality: (i) a soil source of natural origin (based on Al, Si, and Ti), (ii) a soil source of natural and anthropogenic origins (based on Fe and Mg), (iii) a source from the local industrial activity, namely steelworks (based on Co, Cr, Mn, Pb, and Zn); (iv) a source from the road traffic (based on Cr, Cu, and Zn), and (v) a source of biomass burning (based on Br and K). The impact of the industries located in the study area on the local air quality was identified (namely, the steelworks), confirming the concerns of the local population. This valuable information is essential to improve future planning and optimize the assessment of particulate matter levels by reference methods, which will allow a quantitative analysis of the issue, based on national and European legislation, and to define the quantitative contribution of pollution sources and to design target mitigation measures to improve local air quality.

[Modelling the Contribution of Factors Influencing the Risk of SARS-CoV-2 Infection in Indoor Environments].

INTRODUCTION: This study estimates the risk of aerosol infection by SARS-CoV-2 in indoor environments where high density of occupation results in an increased probability of infection, such as schools, offices, supermarkets, restaurants and gyms. MATERIAL AND METHODS: In each type of building use, several conditions were simulated, such as the use and effectiveness of masks, ventilation, use of equipment that allows air asepsis using HEPA filters, the density of occupancy and the length of stay in the spaces, using a model based on the dispersion of aerosol particles in indoor spaces and on the accumulation and inhalation of these particles over time. RESULTS: The results showed that the replacement of social masks by masks with FFP2 classification decreased the risk of infection by 90% in schools. In schools with natural ventilation, the complete opening of windows reduced the risk of infection by 64% in comparison with the scenario with closed windows. In spaces where mechanical ventilation is normally used, the probability of infection decreased significantly when the regulatory fresh air flow rates were doubled (reduction of 32% in offices, 42% in restaurants, 24% in supermarkets and 46% in gyms). The filtration of air with HEPA filters allowed the reduction of the probability of infection by 72% in schools, offices, and restaurants and 61% in gyms. The length of stay in the spaces was also a relevant factor in the variation of the probability of infection, especially in schools where it was found that shorter classes with a higher number of intervals reduced the risk of infection. DISCUSSION: The results show the importance of adequate ventilation in indoor environments, especially in places where the density of occupation and the staying times are longer, making the introduction of outside air inside the spaces essential, either through natural or mechanical means. It is expected that the infection risk estimates presented are undervalued because the model only considers transmission by particles smaller than 10 µm and does not include the short-range transmission by assuming social distancing. Vaccination was not considered in the model since it was not yet available when the study was carried out. CONCLUSION: The present study contributes to the identification of measures that decrease the risk of viral transmission, and consequently provide greater security in indoor spaces.

Introdução: O presente trabalho estima o risco de infeção por SARS-CoV-2 em ambientes interiores onde a elevada densidade de ocupação resulta numa probabilidade acrescida de contágio, como escolas, escritórios, supermercados, restaurantes e ginásios.Material e Métodos: Foram testadas várias condições nos espaços interiores, tais como a utilização e eficácia de máscaras, a ventilação, a utilização de equipamentos que permitem uma assepsia do ar recorrendo a filtros HEPA, a densidade de ocupação e o tempo de permanência nos espaços, tendo sido utilizado um modelo baseado na dispersão de partículas de aerossóis em espaços fechados e na acumulação e inalação destas partículas ao longo do tempo.Resultados: Os resultados mostraram que a substituição de máscaras sociais por máscaras com classificação FFP2 diminuiu o risco de infeção em 90% nas escolas. Em escolas com ventilação natural, a abertura das janelas na sua totalidade reduziu o risco de infeção em 64% comparativamente com o cenário de janelas fechadas. Nos espaços onde a ventilação mecânica é normalmente utilizada, a probabilidade de infeção reduziu significativamente quando os caudais de ar novo regulamentares foram duplicados (redução de 32% nos escritórios, 42% nos restaurantes, 24% nos supermercados e 46% nos ginásios). A filtragem de ar com filtros HEPA permitiu a redução da probabilidade de infeção em 72% nas escolas, escritórios e restaurantes e 61% nos ginásios. O tempo de permanência nos espaços foi também um fator relevante na variação da probabilidade de infeção, principalmente nas escolas onde se verificou que aulas mais curtas e com um maior número de intervalos reduzem o risco de infeção.Discussão: Os resultados evidenciam a importância de uma adequada ventilação em ambientes fechados, principalmente em locais onde a densidade de ocupação e os tempos de permanência são mais longos, sendo essencial a introdução de ar exterior no interior dos espaços, seja através de meios naturais ou mecânicos. É expectável que os valores de risco de infeção apresentados ao longo do trabalho estejam subvalorizados pelo facto do modelo utilizado apenas considerar a transmissão por partículas inferiores a 10 µm e por, ao assumir o distanciamento social, não incluir a transmissão de curto alcance. A vacinação não foi considerada no modelo pelo facto de ainda não estar disponível quando o trabalho foi realizado.Conclusão: Este estudo vem contribuir para a identificação de medidas que permitem um menor risco de transmissão viral, e consequentemente, uma maior segurança no interior dos espaços fechados.

Lung-deposited dose of particulate matter from residential exposure to smoke from wood burning.

Residential settings are of utmost importance for human exposure, as it is where people spend most of their time. Residential wood combustion is a widespread practice known as a source of indoor particulate matter (PM). Nevertheless, research on the risks of exposure associated with this source is scarce, and a better understanding of respiratory deposition of smoke particles is needed. The dosimetry model ExDoM2 was applied to determine the deposited dose of inhalable particulate matter (PM10) from residential biomass combustion in the human respiratory tract (HRT) of adults and children. The dose was estimated using PM10 exposure concentrations obtained from a field campaign carried out in two households during the operation of an open fireplace and a woodstove. Simultaneously, PM10 levels were monitored outside to investigate the outdoor dose in a rural area strongly impacted by biomass burning emissions. Indoors, the 8-h average PM10 concentrations ranged from 88.3 to 489 µg m-3 and from 69.4 to 122 µg m-3 for the operation of the fireplace and the woodstove, respectively, while outdoor average PM10 concentrations ranged from 17.3 to 94.2 µg m-3. The highest amount of the deposited particles was recorded in the extrathoracic region (68-79%), whereas the deposition was much lower in the tracheobronchial tree (5-6%) and alveolar-interstitial region (16-21%). The total dose received while using the fireplace was more than twofold the one received in the room with a woodstove and more than 10 times higher than in the absence of the source. Overall, indoor doses were higher than the ones received by a subject exposed outdoors, especially at the alveolar-interstitial region. After 24 h of exposure, it was estimated that approximately 35 to 37% of the particles deposited in the HRT were transferred to the gastrointestinal tract, while approximately 2.0-2.5% were absorbed into the blood. The results from exposure and dose of indoor particles gathered in this work suggest that homeowners should be encouraged to upgrade the wood burning technology to reduce the PM levels inside their residences. This study also provides biologically relevant results on the lung deposition of particles from residential biomass burning that can be used as a reference for future research.

Analysis of spatial factors, time-activity and infiltration on outdoor generated PM2.5 exposures of school children in five European cities.

Atmospheric particles are a major environmental health risk. Assessments of air pollution related health burden are often based on outdoor concentrations estimated at residential locations, ignoring spatial mobility, time-activity patterns, and indoor exposures. The aim of this work is to quantify impacts of these factors on outdoor-originated fine particle exposures of school children. We apply nested WRF-CAMx modelling of PM2.5 concentrations, gridded population, and school location data. Infiltration and enrichment factors were collected and applied to Athens, Kuopio, Lisbon, Porto, and Treviso. Exposures of school children were calculated for residential and school outdoor and indoor, other indoor, and traffic microenvironments. Combined with time-activity patterns six exposure models were created. Model complexity was increased incrementally starting from residential and school outdoor exposures. Even though levels in traffic and outdoors were considerably higher, 80-84% of the exposure to outdoor particles occurred in indoor environments. The simplest and also commonly used approach of using residential outdoor concentrations as population exposure descriptor (model 1), led on average to 26% higher estimates (15.7 µg/m3) compared with the most complex model (# 6) including home and school outdoor and indoor, other indoor and traffic microenvironments (12.5 µg/m3). These results emphasize the importance of including spatial mobility, time-activity and infiltration to reduce bias in exposure estimates.

Integrated Human Exposure to Air Pollution.

Air pollution is one of the major environmental health problems that people face nowadays, affecting everyone in the world [...].

A methodology to empower citizens towards a low-carbon economy. The potential of schools and sustainability indicators.

Environmental empowering to control resource consumption and environmental impacts is critical to engage citizens to adopt more sustainable habits. This study demonstrates the potential benefits of innovative approaches based on sustainability indicators towards a low-carbon economy. A methodology to measure and promote sustainability in schools has been proposed and evaluated, aiming at showing the environmental performance and informing of potential environmental savings. The methodology, titled ClimACT, has two main purposes: measuring the environmental performance of schools through a school sustainability index based on measurable indicators in the areas of transport, procurement, green spaces, indoor air quality, energy, water and waste; and encouraging students, teachers and families towards an energy-efficient and low-carbon pathway through a structural procedure based on roles, activities and progress evaluation. The approach, applied to 39 pilot schools from Portugal, Spain, France and Gibraltar, achieved promising and encouraging results. All schools deployed the methodology successfully, achieving measurable environmental benefits in 95% of cases, with an average improvement of 10% in the global performance of schools after one year. Moreover, the 5112 surveys applied to school communities, before and after the methodology implementation, highlighted how the sustainable indicators had a significant influence on the daily lives of families, leading to improvements of their behaviour, with an average increase of 20% in indicators regarding good practices in transport, energy, water, waste and citizenship. The environmental empowering through measurable indicators is a step forward a low-carbon economy. This methodology is open and adaptable to all sectors and requirements.

Bioburden in sleeping environments from Portuguese dwellings.

A wider characterization of indoor air quality during sleep is still lacking in the literature. This study intends to assess bioburden before and after sleeping periods in Portuguese dwellings through active methods (air sampling) coupled with passive methods, such as electrostatic dust cloths (EDC); and investigate associations between before and after sleeping and bioburden. In addition, and driven by the lack of information regarding fungi azole-resistance in Portuguese dwellings, a screening with supplemented media was also performed. The most prevalent genera of airborne bacteria identified in the indoor air of the bedrooms were Micrococcus (41%), Staphylococcus (15%) and Neisseria (9%). The major indoor bacterial species isolated in all ten studied bedrooms were Micrococcus luteus (30%), Staphylococcus aureus (13%) and Micrococcus varians (11%). Our results highlight that our bodies are the source of the majority of the bacteria found in the indoor air of our homes. Regarding air fungal contamination, Chrysosporium spp. presented the highest prevalence both in after the sleeping period (40.8%) and before the sleeping period (28.8%) followed by Penicillium spp. (23.47% morning; 23.6% night) and Chrysonilia spp. (12.4% morning; 20.3% night). Several Aspergillus sections were identified in air and EDC samples. However, none of the fungal species/strains (Aspergillus sections Fumigati, Flavi, Nidulantes and Circumdati) were amplified by qPCR in the analyzed EDC. The correlations observed suggest reduced susceptibility to antifungal drugs of some fungal species found in sleeping environments. Toxigenic fungal species and indicators of harmful fungal contamination were observed in sleeping environments.

Chemical characterisation of particulate matter in urban transport modes.

Traffic is a main source of air pollutants in urban areas and consequently daily peak exposures tend to occur during commuting. Personal exposure to particulate matter (PM) was monitored while cycling and travelling by bus, car and metro along an assigned route in Lisbon (Portugal), focusing on PM2.5 and PM10 (PM with aerodynamic diameter <2.5 and 10 µm, respectively) mass concentrations and their chemical composition. In vehicles, the indoor-outdoor interplay was also evaluated. The PM2.5 mean concentrations were 28 ± 5, 31 ± 9, 34 ± 9 and 38 ± 21 µg/m3 for bus, bicycle, car and metro modes, respectively. Black carbon concentrations when travelling by car were 1.4 to 2.0 times higher than in the other transport modes due to the closer proximity to exhaust emissions. There are marked differences in PM chemical composition depending on transport mode. In particular, Fe was the most abundant component of metro PM, derived from abrasion of rail-wheel-brake interfaces. Enhanced concentrations of Zn and Cu in cars and buses were related with brake and tyre wear particles, which can penetrate into the vehicles. In the motorised transport modes, Fe, Zn, Cu, Ni and K were correlated, evidencing their common traffic-related source. On average, the highest inhaled dose of PM2.5 was observed while cycling (55 µg), and the lowest in car travels (17 µg). Cyclists inhaled higher doses of PM2.5 due to both higher inhalation rates and longer journey times, with a clear enrichment in mineral elements. The presented results evidence the importance of considering the transport mode in exposure assessment studies.

Long-Term Assessment of Air Quality and Identification of Aerosol Sources at Setúbal, Portugal.

Understanding air pollution in urban areas is crucial to identify mitigation actions that may improve air quality and, consequently, minimize human exposure to air pollutants and their impact. This study aimed to assess the temporal evolution of the air quality in the city of Setúbal (Portugal) during a time period of 10 years (2003-2012), by evaluating seasonal trends of air pollutants (PM10, PM2.5, O3, NO, NO2 and NOx) measured in nine monitoring stations. In order to identify emission sources of particulate matter, PM2.5 and PM2.5-10 were characterized in two different areas (urban traffic and industrial) in winter and summer and, afterwards, source apportionment was performed by means of Positive Matrix Factorization. Overall, the air quality has been improving over the years with a decreasing trend of air pollutant concentration, with the exception of O3. Despite this improvement, levels of PM10, O3 and nitrogen oxides still do not fully comply with the requirements of European legislation, as well as with the guideline values of the World Health Organization (WHO). The main anthropogenic sources contributing to local PM levels were traffic, industry and wood burning, which should be addressed by specific mitigation measures in order to minimize their impact on the local air quality.

Fine Particulate Matter and Gaseous Compounds in Kitchens and Outdoor Air of Different Dwellings.

Passive diffusion tubes for volatile organic compounds (VOCs) and carbonyls and low volume particulate matter (PM2.5) samplers were used simultaneously in kitchens and outdoor air of four dwellings. PM2.5 filters were analysed for their carbonaceous content (organic and elemental carbon, OC and EC) by a thermo-optical technique and for polycyclic aromatic hydrocarbon (PAHs) and plasticisers by GC-MS. The morphology and chemical composition of selected PM2.5 samples were characterised by SEM-EDS. The mean indoor PM2.5 concentrations ranged from 14 µg m-3 to 30 µg m-3, while the outdoor levels varied from 18 µg m-3 to 30 µg m-3. Total carbon represented up to 40% of the PM2.5 mass. In general, the indoor OC/EC ratios were higher than the outdoor values. Indoor-to-outdoor ratios higher than 1 were observed for VOCs, carbonyls and plasticisers. PAH levels were much higher in the outdoor air. The particulate material was mainly composed of soot aggregates, fly ashes and mineral particles. The hazard quotients associated with VOC inhalation suggested a low probability of non-cancer effects, while the cancer risk was found to be low, but not negligible. Residential exposure to PAHs was dominated by benzo[a]pyrene and has shown to pose an insignificant cancer risk.

Modelling air quality levels of regulated metals: limitations and challenges.

Toxic metals as arsenic (As), cadmium (Cd), nickel (Ni), and lead (Pb) exist in the atmosphere as particulate matter components. Their concentration levels in the European Union (EU) are regulated by European legislation, which sets target and limit values as annual means, and by the World Health Organization (WHO) that defines guidelines and reference values for those metal elements. Modelling tools are recommended to support air quality assessment regarding the toxic metals; however, few studies have been performed and those assessments rely on discrete measurements or field campaigns. This study aims to evaluate the capability of air quality modelling tools to verify the legislation compliance concerning the atmospheric levels of toxic elements and to identify the main challenges and limitations of using a modelling assessment approach for regulatory purposes, as a complement to monitoring. The CAMx air quality model was adapted and applied over Porto and Lisbon urban regions in Portugal at 5 × 5-km2 and 1 × 1-km2 horizontal resolution for the year 2015, and the results were analysed and compared with the few measurements available in three locations. The comparison between modelled and measured data revealed an overestimation of the model, although annual averages are much lower than the regulated standards. The comparison of the 5-km and 1-km resolutions' results indicates that a higher resolution does not necessarily imply a better performance, pointing out uncertainties in emissions and the need to better describe the magnitude and spatial allocation of toxic metal emissions. This work highlighted that an increase of the spatial and temporal coverage of monitoring sites would allow to improve the model design, contribute to a better knowledge on toxic metals atmospheric emission sources and to increase the capacity of models to simulate atmospheric particulate species of health concern.