Person: Diez, Sebastian
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Diez
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Sebastian
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Publication Study of the Suitability of a Personal Exposure Monitor to Assess Air Quality(2024) Aljofi, Halah E.; Bannan, Thomas J.; Flynn, Michael; Evans, James; Topping, David; Matthews, Emily; Diez, Sebastian; Edwards, Pete; Coe, Hugh; Brison, Daniel R.; Tongeren, Martie van; Johnstone, Edward D.; Povey, AndrewLow-cost personal exposure monitors (PEMs) to measure personal exposure to air pollution are potentially promising tools for health research. However, their adoption requires robust validation. This study evaluated the performance of twenty-one Plume Lab Flow2s (PLFs) by comparing its air pollutant measurements, particulate matter with a diameter of 2.5 μm or less (PM2.5), 10 μm or less (PM10), and nitrogen dioxide (NO2), against several high-quality air pollution monitors under field conditions (at indoor, outdoor, and roadside locations). Correlation and regression analysis were used to evaluate measurements obtained by different PLFs against reference instrumentation. For all measured pollutants, the overall correlation coefficient between the PLFs and the reference instruments was often weak (r < 0.4). Moderate correlation was observed for one PLF unit at the indoor location and two units at the roadside location when measuring PM2.5, but not for PM10 and NO2 concentration. During periods of particularly higher pollution, 11 PLF tools showed stronger regression results (R2 values > 0.5) with one-hour and 9 PLF units with one-minute time interval. Results show that the PLF cannot be used robustly to determine high and low exposure to poor air. Therefore, the use of PLFs in research studies should be approached with caution if data quality is important to the research outputs.Publication QUANT: a long-term multi-city commercial air sensor dataset for performance evaluation(2024) Diez, Sebastian; Lacy, Stuart; Urquiza, Josefina; Edwards, Petethe QUaNt study represents the most extensive open-access evaluation of commercial air quality sensor systems to date. This comprehensive study assessed 49 systems from 14 manufacturers across three urban sites in the UK over a three-year period. the resulting open-access dataset captures high time-resolution measurements of a variety of gasses (NO, NO2, O3, CO, CO2), particulate matter (PM1, PM2.5, PM10), and key meteorological parameters (humidity, temperature, atmospheric pressure). The quality and scope of the dataset is enhanced by reference monitors’ data and calibrated products from sensor manufacturers across the three sites. this publicly accessible dataset serves as a robust and transparent resource that details the methods used for data collection and procedures to ensure dataset integrity. It provides a valuable tool for a wide range of stakeholders to analyze the performance of air quality sensors in real-world settings. Policymakers can leverage this data to refine sensor deployment guidelines and develop standardized protocols, while manufacturers can utilize it as a benchmark for technological innovation and product certification. Moreover, the dataset has supported the development of a UK code of practice, and the certification of one of the participating companies, underscoring the dataset’s utility and reliabilityPublication Long-term evaluation of commercial air quality sensors: an overview from the QUANT (Quantification of Utility of Atmospheric Network Technologies) study(2024) Diez, Sebastian; Lacy, Stuart; Coe, Hugh; Urquiza, Josefina; Priestman, Max; Flynn, Michael; Marsden, Nicholas; Martin, Nicholas A.; Gillott, Stefan; Bannan, Thomas; Edwards, Pete M.In times of growing concern about the impacts of air pollution across the globe, lower-cost sensor technology is giving the first steps in helping to enhance our understanding and ability to manage air quality issues, particularly in regions without established monitoring networks. While the benefits of greater spatial coverage and real-time measurements that these systems offer are evident, challenges still need to be addressed regarding sensor reliability and data quality. Given the limitations imposed by intellectual property, commercial implementations are often “black boxes”, which represents an extra challenge as it limits end users' understanding of the data production process. In this paper we present an overview of the QUANT (Quantification of Utility of Atmospheric Network Technologies) study, a comprehensive 3-year assessment across a range of urban environments in the United Kingdom, evaluating 43 sensor devices, including 119 gas sensors and 118 particulate matter (PM) sensors, from multiple companies. QUANT stands out as one of the most comprehensive studies of commercial air quality sensor systems carried out to date, encompassing a wide variety of companies in a single evaluation and including two generations of sensor technologies. Integrated into an extensive dataset open to the public, it was designed to provide a long-term evaluation of the precision, accuracy and stability of commercially available sensor systems. To attain a nuanced understanding of sensor performance, we have complemented commonly used single-value metrics (e.g. coefficient of determination, R2; root mean square error, RMSE; mean absolute error, MAE) with visual tools. These include regression plots, relative expanded uncertainty (REU) plots and target plots, enhancing our analysis beyond traditional metrics. This overview discusses the assessment methodology and key findings showcasing the significance of the study. While more comprehensive analyses are reserved for future detailed publications, the results shown here highlight the significant variation between systems, the incidence of corrections made by manufacturers, the effects of relocation to different environments and the long-term behaviour of the systems. Additionally, the importance of accounting for uncertainties associated with reference instruments in sensor evaluations is emphasised. Practical considerations in the application of these sensors in real-world scenarios are also discussed, and potential solutions to end-user data challenges are presented. Offering key information about the sensor systems' capabilities, the QUANT study will serve as a valuable resource for those seeking to implement commercial solutions as complementary tools to tackle air pollution.Publication A framework for advancing independent air quality sensor measurements via transparent data generating process classification(2026) Diez, Sebastian; Bannan, Thomas; Chacón, Miriam; Edwards, Pete; Ferracci, Valerio; Kılıç, Doğuşhan; Lewis, Alastair; Malings, Carl; Martin, Nicholas; Popoola, Olalekan; Rosales, Colleen; Schmitz, Sean; Schneider, Philipp; Von Schneidemesser, ErikaWe propose operational definitions and a classification framework for air quality sensor-derived data, thereby aiding users in interpreting and selecting suitable data products for their applications. We focus on differentiating independent sensor measurements (ISM) from other data products, emphasizing transparency and traceability. Recommendations are provided for manufacturers, academia,andstandardizationbodiestoadoptthesedefinitions,fosteringdataproductdifferentiation and incentivizing the development of more robust, reliable sensor hardwarePublication Open Air Quality Data Platforms for Environmental Health Research and Action(2025) Marciel, Colleen; Bratburd, Jennifer; Diez, Sebastian; Duncan, Sara; Malings, Carl; Pant, PallaviPURPOSE OF REVIEW: Air pollution remains the greatest environmental threat to public health, and significantly impacts many aspects of human life. This review surveys digital platforms that provide data openly and make air quality data available for use and analysis by environmental health researchers for scientific research and to inform air quality action. RECENT FINDINGS: Successful programs that rely on different types of open air quality data have been observed and exist as models for regions that have yet to improve their air quality. However, disparities remain in the availability and granularity of generated air quality data in resource-rich and resource-poor regions. Even if air quality data are made available and open, their usability and actionability still remain challenging. Determinants of usability may include the user’s technical know-how and ability to deal with disparate data; compute capabilities; barriers in data sharing and data generation; and misuse and misclassification of data and levels and sources of exposure. However, the synthesis of different sources of data and advancements in modeling may help fill in spatiotemporal gaps in many areas of the world. In addition, the democratization of air quality data is facilitated by advancements in air quality data generation (e.g., data collection by open-source air sensors) and the ability to contribute to global, open-access, publicly available repositories that openly share data. Many open data platforms exist for sharing and accessing ground-based/in-situ data, satellite remote sensing data, and modeled or otherwise derived outputs. Online platforms that allow visualization and analysis without the need to download software are also now widely available. Despite wide availability, disparities in accessibility exist—expansion and support through interdisciplinary collaboration and continuous funding support for air quality data is essential for the continuous global benefit and community-specific action to address air quality as an environmental health issue.Publication Assessment of aerosol remote sensing uncertainty in urban centers of Latin America(2025) Urquiza, Josefina; Diez, Sebastian; Tames, María Florencia; Puliafito, SalvadorLa profundidad óptica de aerosoles (AOD) derivada de satélites es un indicador clave para ampliar la cobertura espacial en estudios de calidad del aire, particularmente para estimar concentraciones de PM2.5. Sin embargo, la validación de productos AOD de alta resolución sigue siendo limitada en entornos urbanos de América Latina, que se caracterizan por una dinámica compleja de aerosoles y una escasa cobertura de monitoreo terrestre. En este estudio, evaluamos el desempeño del producto MAIAC C6.1 AOD en seis ciudades latinoamericanas densamente pobladas (São Paulo, Santiago, Buenos Aires, Medellín, La Paz y Ciudad de México) entre 2015 y 2022, utilizando como referencia la red AERONET. El desempeño de MAIAC C6.1 también se comparó con su versión anterior (C6.0) y con MODIS DT, para analizar diferencias en la resolución espacial y evaluar mejoras en el rendimiento. Se observó una falta de datos AOD a nivel de superficie, especialmente en Medellín y São Paulo, junto con niveles promedio bajos (AOD < 0.2) en La Paz y Buenos Aires. El rendimiento de MAIAC C6.1 mostró una variabilidad notable según el tamaño de la ventana espacial, aunque la ventana temporal no tuvo un impacto considerable. Se identificaron dos grupos de sitios: (i) La Paz y Buenos Aires, con menores niveles de AOD, menor desempeño y sesgo positivo; y (ii) São Paulo, Santiago y Ciudad de México, con mayores niveles de AOD, mejor desempeño y sesgo negativo. MAIAC C6.1 mostró una mejora en la reducción del sesgo, aunque sin cambios significativos en R2 o RMSE respecto de C6.0. En comparación con MODIS DT, MAIAC C6.1 presentó mayor precisión y menor sesgo, ya que MODIS sobreestimó la AOD en todos los sitios. A pesar de los avances en productos de alta resolución, persisten limitaciones en la cobertura de datos e incertidumbres, especialmente en áreas urbanas de América Latina. Satellite-derived aerosol optical depth (AOD) is a key indicator for expanding spatial coverage in air quality studies, particularly for estimating PM2.5 concentrations. However, validation of high-resolution AOD products remains limited in Latin American urban environments, which are characterized by complex aerosol dynamics and sparse ground-based monitoring. In this study, we evaluated the performance of MAIAC C6.1 AOD in six densely populated Latin American cities (São Paulo, Santiago, Buenos Aires, Medellín, La Paz, and Mexico City) from 2015 to 2022, using the AERONET network as a reference. MAIAC C6.1 performance was also compared with the previous version (C6.0) and MODIS DT to analyze differences in spatial resolution and assess performance improvements. A lack of ground-level AOD was observed, especially in Medellín and São Paulo, along with low average levels (AOD < 0.2) in La Paz and Buenos Aires. MAIAC C6.1 performance showed notable variability depending on the spatial window size, although no considerable impact was seen in the temporal window. Two site groups were identified: (i) La Paz and Buenos Aires, with lower AOD levels, lower performance, and positive bias; and (ii) São Paulo, Santiago, and Mexico City, with higher AOD levels, better performance, and negative bias. MAIAC C6.1 showed improvement in bias reduction, but no significant changes in R2 or RMSE compared to C6.0. Compared to MODIS DT, MAIAC C6.1 exhibited greater accuracy and lower bias, with MODIS overestimating AOD across all sites. Despite advances with high-resolution products, limitations in data coverage and uncertainty persist, especially in urban Latin American areas.Publication A new generation of Early Career Researchers in atmospheric chemistry: Navigating a globalized scientific landscape(2025) Desservettaz, Maximilien; Ramacher, Martin; Thirstrup, Simone; Barbosa, Cybelli; Diez, Sebastian; Bryant, Hannah; Hamilton, Tamryn; Schneider, Stephanie; Vohra, Karn; Li, Yuanzhe; Mishra, Sachin; Abdul, Nor; Uz Zaman, Shahid; Brown, Flossie; John, Shyno; Tiwari, Pravash; Apondo, William; Matthews, EmilyAs the International Global Atmospheric Chemistry (IGAC) project marks its 35th anniversary,this paper examines the multifaceted experiences of Early Career Researchers (ECRs) navigating the increasingly globalized landscape of atmospheric chemistry. Drawing upon collective insights from the ECR Scientific Steering Committee and quantitative data from a survey of 180 ECRs across 40 countries, we investigate their primary motivations, challenges, and opportunities. Key obstacles identified include systemic difficulties in securing funding and resources, achieving sustainable work–life balance, and uncertainty around long-term career prospects, often compounded by precarious employment conditions. While globalization offers significant avenues for international collaboration, data sharing, and knowledge exchange, it concurrently presents challenges such as heightened competition, visa restrictions, regional disparities, and the risk of inequitable research practices. Despite these hurdles, ECRs are driven by a strong interest in their field, a desire to make a tangible impact on societal concerns, and the appeal of a supportive community. This perspective paper offers actionable insights focused on 4 key pillars: (i) strengthening mentoring programs; (ii) reforming funding mechanisms for improved accessibility and equity; (iii) providing targeted skill development workshops; and (iv) promoting equitable collaborations and advancing the decolonization of research practices. To foster a supportive, inclusive, and sustainable environment for the next generation of atmospheric scientists, this work underscores the urgent need for systemic change and sustained collaborative action by networks such as IGAC, as well as by senior researchers, academic institutions, and funding agencies.