• Energy Research

Abstract. Aerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system.

Abstract. Accurate measurements of the horizontal and vertical distribution of atmospheric aerosol particle optical properties are key for a better understanding of their impact on the climate. Here we present the results of a measurement campaign based on instrumented flights over NE Spain. We measured vertical profiles of size segregated atmospheric particulate matter (PM) mass concentrations and multi-wavelength scattering and absorption coefficients in the Western Mediterranean Basin (WMB). The campaign took place during typical summer conditions, characterized by the development of a vertical multi-layer structure, under both summer regional pollution episodes (REG) and Saharan dust events (SDE). REG patterns in the region form under high insolation and scarce precipitation in summer, favoring layering of highly-aged fine PM strata in the lower few km a.s.l. The REG scenario prevailed during the entire measurement campaign. Additionally, African dust outbreaks and plumes from North African wildfires influenced the study area. The vertical profiles of climate relevant intensive optical parameters such as single scattering albedo (SSA), asymmetry parameter (g), scattering, absorption and SSA Angstrom exponents (SAE, AAE, SSAAE), and PM mas scattering and absorption cross sections (MSC and MAE) were derived from the measurements. Moreover, we compared the aircraft measurements with those performed at two GAW/ACTRIS surface measurement stations located in NE Spain, namely: Montseny (MSY; regional background) and Montsec d'Ares (MSA; remote site). Airborne in-situ measurements and ceilometer ground-based remote measurements identified aerosol air masses at altitude up to more than 3.5 km a.s.l. The vertical profiles of the optical properties markedly changed according to the prevailing atmospheric scenarios. During SDE the SAE was low along the profiles, reaching values 2.0 and the asymmetry parameter g was rather low (0.5–0.6) due to the prevalence of fine PM which were characterized by an AAE close to 1.0 suggesting a fossil fuel combustion origin. During REG, some of the layers featured larger AAE (> 1.5), relatively low SSA at 525 nm ( 9 m2 g−1) and were associated to the influence of PM from wildfires. Overall, the SSA and MSC near the ground ranged around 0.85 and 3 m2 g−1, respectively and increased at higher altitudes, reaching values above 0.95 and up to 9 m2 g−1. The PM, MSC and MAE were on average larger during REG compared to SDE due to the larger scattering and absorption efficiency of fine PM compared with dust. The SSA and MSC had quite similar vertical profiles and often both increased with height indicating the progressive shift toward PM with larger scattering efficiency with altitude. This study contributes to our understanding of regional aerosol vertical distribution and optical properties in the WMB and the results will be useful for improving future climate projections and remote sensing/satellite retrieval algorithms.

Abstract. In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.

Résumé. Les particules d'aérosol sont des constituants essentiels de l'atmosphère terrestre, ayant un impact direct sur l'équilibre du rayonnement terrestre en diffusant et en absorbant le rayonnement solaire, et indirectement en agissant comme des noyaux de condensation des nuages. Contrairement à la plupart des gaz à effet de serre, les particules d'aérosol ont des temps de résidence atmosphériques courts, ce qui entraîne une distribution très hétérogène dans l'espace et le temps. Il est clairement nécessaire de documenter cette variabilité à l'échelle régionale à travers des observations impliquant, en particulier, le segment in situ près de la surface du système d'observation atmosphérique. Cet article fournira le plus grand effort jusqu'à présent pour documenter la variabilité des propriétés des aérosols in situ pertinentes pour le climat (à savoir les coefficients de diffusion et d'absorption de la lumière des particules dépendant de la longueur d'onde, la concentration en nombre de particules et la distribution granulométrique) de tous les sites connectés au réseau Global Atmosphere Watch. Des données de haute qualité provenant de près de 90 stations dans le monde ont été collectées et contrôlées pour la qualité et sont rapportées pour une année de référence en 2017, fournissant une vue très étendue et robuste de la variabilité de ces variables dans le monde. La gamme de variabilité observée dans le monde entier pour les coefficients de diffusion et d'absorption de la lumière, l'albédo à diffusion unique et la concentration en nombre de particules est présentée avec des informations préliminaires sur leurs tendances à long terme et une comparaison avec la simulation par modèle pour les différentes stations. La portée du présent document est également de fournir la suite nécessaire d'informations, y compris les procédures de fourniture de données, le contrôle et l'analyse de la qualité, la politique de données et l'utilisation du réseau de mesure des aérosols au sol. Il fournit aux utilisateurs du Centre mondial de données sur les aérosols la confiance requise dans les produits de données sous la forme d'une chaîne de valeur entièrement caractérisée, y compris l'estimation de l'incertitude et les exigences pour contribuer au système mondial de surveillance du climat. Resumen. Las partículas de aerosol son constituyentes esenciales de la atmósfera terrestre, impactando el equilibrio de la radiación terrestre directamente al dispersar y absorber la radiación solar, e indirectamente al actuar como núcleos de condensación de nubes. A diferencia de la mayoría de los gases de efecto invernadero, las partículas de aerosol tienen tiempos de residencia atmosférica cortos, lo que resulta en una distribución altamente heterogénea en el espacio y el tiempo. Existe una clara necesidad de documentar esta variabilidad a escala regional a través de estudios que involucren, en particular, el segmento cercano a la superficie in situ del sistema de observación atmosférica. Este documento proporcionará el mayor esfuerzo hasta el momento para documentar la variabilidad de las propiedades de los aerosoles in situ relevantes para el clima (es decir, la dispersión de la luz de partículas y los coeficientes de absorción dependientes de la longitud de onda, la concentración del número de partículas y la distribución del tamaño del número de partículas) de todos los sitios conectados a la red de Vigilancia de la Atmósfera Global. Se han recopilado y controlado datos de alta calidad de casi 90 estaciones en todo el mundo y se informan para un año de referencia en 2017, lo que proporciona una visión muy amplia y sólida de la variabilidad de estas variables en todo el mundo. El rango de variabilidad observado en todo el mundo para los coeficientes de dispersión y absorción de la luz, el albedo de dispersión única y la concentración del número de partículas se presentan junto con información preliminar sobre sus tendencias a largo plazo y la comparación con la simulación del modelo para las diferentes estaciones. El alcance del presente documento también es proporcionar el conjunto de información necesario, incluidos los procedimientos de suministro de datos, el control y análisis de calidad, la política de datos y el uso de la red de medición de aerosoles terrestre. Ofrece a los usuarios del Centro Mundial de Datos sobre Aerosoles la confianza requerida en los productos de datos en forma de una cadena de valor completamente caracterizada, incluida la estimación de la incertidumbre y los requisitos para contribuir al sistema de vigilancia del clima mundial. Abstract. Aerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system. الخلاصة: جسيمات الهباء الجوي هي مكونات أساسية للغلاف الجوي للأرض، وتؤثر على توازن إشعاع الأرض بشكل مباشر عن طريق تشتت وامتصاص الإشعاع الشمسي، وبشكل غير مباشر عن طريق العمل كنوى تكثيف السحب. على النقيض من معظم غازات الدفيئة، فإن جزيئات الهباء الجوي لها أوقات بقاء قصيرة في الغلاف الجوي، مما يؤدي إلى توزيع غير متجانس للغاية في المكان والزمان. هناك حاجة واضحة لتوثيق هذا التباين على المستوى الإقليمي من خلال عمليات الرصد التي تشمل، على وجه الخصوص، الجزء القريب من السطح في الموقع من نظام مراقبة الغلاف الجوي. ستوفر هذه الورقة أوسع جهد حتى الآن لتوثيق تقلب خصائص الهباء الجوي الموضعي ذات الصلة بالمناخ (أي معاملات تشتت وامتصاص ضوء الجسيمات المعتمدة على الطول الموجي وتركيز رقم الجسيمات وتوزيع حجم رقم الجسيمات) من جميع المواقع المتصلة بشبكة مراقبة الغلاف الجوي العالمية. تم جمع بيانات عالية الجودة من حوالي 90 محطة في جميع أنحاء العالم والتحكم فيها من أجل الجودة ويتم الإبلاغ عنها لسنة مرجعية في عام 2017، مما يوفر رؤية موسعة وقوية للغاية لتباين هذه المتغيرات في جميع أنحاء العالم. يتم تقديم نطاق التباين الملحوظ في جميع أنحاء العالم لمعاملات تشتت الضوء وامتصاصه، والبياض أحادي التشتت، وتركيز عدد الجسيمات مع معلومات أولية عن اتجاهاتها طويلة الأجل ومقارنتها بمحاكاة النموذج للمحطات المختلفة. يتمثل نطاق هذه الورقة أيضًا في توفير مجموعة المعلومات اللازمة، بما في ذلك إجراءات توفير البيانات، ومراقبة الجودة وتحليلها، وسياسة البيانات، واستخدام شبكة قياس الهباء الجوي الأرضية. وهي توفر لمستخدمي مركز البيانات العالمي المعني بالهباء الجوي الثقة المطلوبة في منتجات البيانات في شكل سلسلة قيمة مميزة بالكامل، بما في ذلك تقدير عدم اليقين ومتطلبات المساهمة في نظام مراقبة المناخ العالمي.