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This study presents a fit-for-purpose lab and field evaluation of commercially available portable sensor systems for PM, NO2, and/or BC. The main aim of the study is to identify portable sensor systems that are capable of reliably quantifying dynamic exposure gradients in urban environments. After an initial literature and market study resulting in 39 sensor systems, 10 sensor systems were ultimately purchased and benchmarked under laboratory and real-word conditions. We evaluated the comparability to reference analyzers, sensor precision, and sensitivity towards environmental confounders (temperature, humidity, and O3). Moreover, we evaluated if the sensor accuracy can be improved by applying a lab or field calibration. Because the targeted application of the sensor systems under evaluation is mobile monitoring, we conducted a mobile field test in an urban environment to evaluate the GPS accuracy and potential impacts from vibrations on the resulting sensor signals. Results of the considered sensor systems indicate that out-of-the-box performance is relatively good for PM (R2 = 0.68–0.9, Uexp = 16–66%, BSU = 0.1–0.7 µg/m3) and BC (R2 = 0.82–0.83), but maturity of the tested NO2 sensors is still low (R2 = 0.38–0.55, Uexp = 111–614%) and additional efforts are needed in terms of signal noise and calibration, as proven by the performance after multilinear calibration (R2 = 0.75–0.83, Uexp = 37–44%)). The horizontal accuracy of the built-in GPS was generally good, achieving <10 m accuracy for all sensor systems. More accurate and dynamic exposure assessments in contemporary urban environments are crucial to study real-world exposure of individuals and the resulting impacts on potential health endpoints. A greater availability of mobile monitoring systems capable of quantifying urban pollutant gradients will further boost this line of research. [ABSTRACT FROM AUTHOR]

Mobile monitoring is used as an additional tool to collect air quality data at a high spatial resolution and to complement data from fixed air quality stations. Citizens are interested in contributing to air quality monitoring, and while the availability of low-cost air quality sensors can create opportunities to measure the air quality at a high spatial resolution, the data are often of lower quality, and sensors that measure combustion-related aerosols (like black carbon) are not commonly available. Mobile monitoring using a mid-range instrument can fill this gap. We present the results of a mobile BC (black carbon) monitoring campaign performed by citizens in Mechelen as part of a local citizen observatory (CO), Meet Mee Mechelen, initiated as part of the European H2020 project, Ground Truth 2.0. The goal of the study was two-fold: (1) to propose and evaluate a mobile monitoring method (data collection and data processing) to construct pollution maps of BC concentrations and (2) to demonstrate how to organize community-based air quality monitoring to measure both the spatial and temporal variations in air pollution levels. Measurements were taken during peak hours in four campaigns characterized by different meteorological conditions: October–November 2017, February–March 2018, June–July 2018 and September 2018. The results show large spatial and temporal variabilities. Spatial variability is influenced by traffic volume, stop-and-go traffic and also the building environment and the distance of biking paths from road traffic. The four different campaigns show similar spatial patterns, but due to background and meteorological influences, the absolute concentrations differ between seasons. A rescaling method using data from fixed stations in the air quality monitoring network (AQMN) was presented to construct maps representative of longer periods. This paper shows that mobile measurements can be used by CO to assess the spatial variability of air quality in a city. The data can be used to evaluate mobility plans, carry out hot spot detection, evaluate the exposure of cyclists as a function of cycling infrastructure and perform model validation. However, it is important to use high-quality instruments and apply the correct measurement methodology (number of repetitions, season) to obtain meaningful data. [ABSTRACT FROM AUTHOR]

Herein, we present the formation of transient radical ion pairs (RIPs) by single‐electron transfer (SET) in phosphine−quinone systems and explore their potential for the activation of C−H bonds. PMes3 (Mes=2,4,6‐Me3C6H2) reacts with DDQ (2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone) with formation of the P−O bonded zwitterionic adduct Mes3P−DDQ (1), while the reaction with the sterically more crowded PTip3 (Tip=2,4,6‐iPr3C6H2) afforded C−H bond activation product Tip2P(H)(2‐[CMe2(DDQ)]‐4,6‐iPr2‐C6H2) (2). UV/Vis and EPR spectroscopic studies showed that the latter reaction proceeds via initial SET, forming RIP [PTip3]⋅+[DDQ]⋅−, and subsequent homolytic C−H bond activation, which was supported by DFT calculations. The isolation of analogous products, Tip2P(H)(2‐[CMe2{TCQ−B(C6F5)3}]‐4,6‐iPr2‐C6H2) (4, TCQ=tetrachloro‐1,4‐benzoquinone) and Tip2P(H)(2‐[CMe2{oQtBu−B(C6F5)3}]‐4,6‐iPr2‐C6H2) (8, oQtBu=3,5‐di‐tert‐butyl‐1,2‐benzoquinone), from reactions of PTip3 with Lewis‐acid activated quinones, TCQ−B(C6F5)3 and oQtBu−B(C6F5)3, respectively, further supports the proposed radical mechanism. As such, this study presents key mechanistic insights into the homolytic C−H bond activation by the synergistic action of radical ion pairs. [ABSTRACT FROM AUTHOR]

One of the most widely available technologies to clean the air in homes of particulate matter of less than 2.5 µm in diameter (PM2.5), known to have negative health impacts, are portable home air purifiers (HAPs). This paper presents research which (1) explored the effectiveness of HAPs in real-world conditions in 57 homes in three European cities; (2) examined if HAPs affect users' perceptions of the indoor air quality (IAQ) at home; and (3) considered the motivations for occupants' operation of HAPs. Results from this study found that PM2.5 concentrations in bedrooms were reduced by 45% to 69%; perceptions of IAQ were not correlated with measured high PM2.5 levels; occupants reported the HAPs to have a 'cooling' effect, which may explain why the predominant driver of HAP use was thermal comfort, rather than IAQ, in all three cities. The latter finding was supported by a statistically significant increase in the probability of HAP use with increasing indoor temperatures. If the operation of HAPs can be managed, or fully automated, to reflect indoor air pollution levels rather than thermal conditions, better pollutant reduction would be feasible and their use to reduce PM2.5 may help mitigate the negative health effects of exposure whilst at home. [ABSTRACT FROM AUTHOR]