Recent advances in particle sensor technologies have led to an increased development and utilization of low-cost, compact, particulate matter (PM) monitors. These devices can be deployed in dense monitoring networks, enabling an improved characterization of the spatiotemporal variability in ambient levels and exposure. However, the reliability of their measurements is an important prerequisite, necessitating rigorous performance evaluation and calibration in comparison to reference-grade instrumentation. In this study, field evaluation of Purple Air PA-II devices (low-cost PM sensors) is performed in two urban environments and across three seasons in Greece, in comparison to different types of reference instruments. Measurements were conducted in Athens (the largest city in Greece with nearly four-million inhabitants) for five months spanning over the summer of 2019 and winter/spring of 2020 and in Ioannina, a medium-sized city in northwestern Greece (100,000 inhabitants) during winter/spring 2019–2020. The PM_2.5 sensor output correlates strongly with reference measurements (R² = 0.87 against a beta attenuation monitor and R² = 0.98 against an optical reference-grade monitor). Deviations in the sensor-reference agreement are identified as mainly related to elevated coarse particle concentrations and high ambient relative humidity. Simple and multiple regression models are tested to compensate for these biases, drastically improving the sensor’s response. Large decreases in sensor error are observed after implementation of models, leading to mean absolute percentage errors of 0.18 and 0.12 for the Athens and Ioannina datasets, respectively. Overall, a quality-controlled and robustly evaluated low-cost network can be an integral component for air quality monitoring in a smart city. Case studies are presented along this line, where a network of PA-II devices is used to monitor the air quality deterioration during a peri-urban forest fire event affecting the area of Athens and during extreme wintertime smog events in Ioannina, related to wood burning for residential heating.

Modern vehicles rely on data from a vast array of sensors such as radar and GPS equipment that can be shared with surrounding vehicles and other interested parties. Vehicle-to-everything (V2X) is the collection of systems that enable such communication. Although this data sharing has the potential to improve both the safety and efficiency of vehicles, ensuring that what is shared has not been altered, deleted, forged, leaked, or otherwise tampered with remains a challenging problem. Today, blockchain technology allows a system’s participants to come to an agreement (consensus) on the state of the system and its data in a decentralized, trustless manner. This new technology may be capable of securing V2X data, as well as enabling other useful V2X services such as payments. However, the V2X ecosystem poses several unique challenges that complicate the application of blockchain technology, not least of which is the vast number of communications that any proposed blockchain network will need to support. This paper gives an overview of V2X and blockchain technology, explores potential applications of blockchain within the V2X domain, and justifies its importance. It also reviews, analyzes, and discusses various blockchain architectures that could support V2X applications. Though there is a place for blockchain in the V2X environment, currently there is no robust or mature blockchain architecture available that could support the entire ecosystem’s needs. As such, this paper proposes novel directions for future research towards the creation of such a blockchain.

Atmospheric new particle formation (NPF) events taking place over large distances between locations, featuring similar characteristics, have been the focus of studies during the last decade. The exact mechanism which triggers NPF still remains indefinable, so are the circumstances under which simultaneous occurrence of such events take place in different environments, let alone in environments which are parted by over 1200 km. In this study, concurrent number size distribution measurements were conducted in the urban environments of Athens (Greece) and Amman (Jordan) as well as the regional background site of Finokalia, Crete, all located within a distance of almost 1300 km for a 6-month period (February–July 2017). During the study period Athens and Finokalia had similar occurrence of NPF (around 20%), while the occurrence in Amman was double. When focusing on the dynamic characteristics at each site, it occurs that formation and growth rates at Amman are similar to those at Finokalia, while lower values in Athens can be ascribed to a higher pre-existing particle number at this urban site. By comparing common NPF events there are 5 concomitant days between all three sites, highly related to air masses origin. Additionally, for another 19 days NPF takes place simultaneously between Finokalia and Amman, which also share common meteorological characteristics, adding to a total of 60% out of 41 NPF events observed at Finokalia, also simultaneously occurring in Amman.

Sisyfos is a modular and extensible platform for malware analysis; it addresses multiple operating systems, including critical infrastructure ones. Its purpose is to enable the development and evaluation of new tools as well as the evaluation of malware classifiers. Sisyfos has been developed based on open software for feature extraction and is available as a stand-alone tool with a web interface but can be integrated into an operational environment with a continuous sample feed. We present the structure and implementation of Sisyfos, which accommodates analysis for Windows, Linux and Android malware.

Many central banks are researching and piloting digital versions of fiat money, specifically retail central bank digital currencies (CBDCs). Core to many discussions revolving around these systems’ design is the ability to perform transactions even without network connectivity. While this approach is generally believed to provide additional degrees of freedom for user privacy, the lack of direct involvement of third parties in these offline transfers also interferes with key regulatory requirements that need to be accommodated in the financial space. This paper presents a compliance-by-design approach to evaluate technologies that can balance privacy with anti-money laundering and counter-terrorism financing (AML/CFT) measures. It classifies privacy design options and corresponding technical building blocks for offline CBDCs, along with their impact on AML/CFT measures, and outlines commonalities and differences between offline and online solutions. As such, it provides a conceptual framework for further techno-legal assessments and implementations.