• Energy Research

Knowledge gaps in the optical properties of carbonaceous aerosols account for a significant fraction of the uncertainty of aerosol - light interactions in climate models. Both black carbon (BC) and brown carbon (BrC) can display a range of optical properties in ambient aerosol due to different sources and chemical transformation pathways. This study investigates the optical absorption properties of BC and BrC at an urban and a rural site in the Po Valley (Italy), a known European pollution hot spot. We observed spatial and seasonal variability of aerosol absorption coefficients, with the highest values measured in winter at the urban site of Milan (12 Mm-1 on average) and the lowest values in summer at the rural site of Motta Visconti (3 Mm-1 on average). The average aerosol Absorption Å ngström Exponent (AAE) measured during the two experiments across the 370-880 nm wavelength range was 1.1 and 1.2 at the urban and the rural site, respectively. The observed AAE values in winter (the average AAE during the two winter campaigns was 1.2) are consistent with the contribution of wood burning BrC, as confirmed by macro-tracer analysis. The BC mass absorption cross section (MACBC) did not show a specific seasonal or spatial variability across the two sites and maintained an average value of 10 ± 5 m2 g-1 at 880 nm. The optical properties of BrC, investigated off-line after extraction of organic aerosol (OA) indicate that wood burning was the dominant BrC source in winter, while secondary organic aerosol (SOA) from other anthropogenic emissions was the main source of BrC in summer.

We analysed the variability of equivalent black carbon (BC) and ozone (O3) at the global WMO/GAW station Nepal Climate Observatory-Pyramid (NCO-P, 5079 m a.s.l.) in the southern Himalayas, for evaluating the possible contribution of open vegetation fires to the variability of these short-lived climate forcers/pollutants (SLCF/SLCP) in the Himalayan region. We found that 162 days (9% of the data-set) were characterised by acute pollution events with enhanced BC and O3 in respect to the climatological values. By using satellite observations (MODIS fire products and the USGS Land Use Cover Characterization) and air mass back-trajectories, we deduced that 56% of these events were likely to be affected by emissions from open fires along the Himalayas foothills, the Indian Subcontinent and the Northern Indo-Gangetic Plain. These results suggest that open fire emissions are likely to play an important role in modulating seasonal and inter-annual BC and O3 variability over south Himalayas.

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.

This paper presents a detailed review of atmospheric pollution observed in the Hindu Kush-Himalaya (HKH) region and its implications for regional climate. Data from in situ measurements made at high-altitude stations in the HKH region, observations from satellite-based instruments, and global climate modeling study results are discussed. Experimental observations discussed include both atmospheric measurements and data from snow and ice core sampling from different glaciers in the HKH region. The paper focuses on the atmospheric brown cloud loadings over the Himalayas, particularly black carbon (BC) and ozone, which have links to regional climate and air-pollution-related impacts. Studies show elevated levels of anthropogenic ozone and BC over the Himalayas during the pre-monsoon season with concentrations sometimes similar to those observed over an average urban environment. The elevated concentration observed over the Himalayas is thought to come from the lowlands, especially the highly populated areas of the Indo-Gangetic Plains. The implications of high BC loading in the Himalayan atmosphere as well as elevated BC deposition on snow and ice surfaces for regional climate, hydrological cycle, and glacial melt are discussed.

Abstract. For the last 25 years, CO-PDD (Cézeaux-Aulnat-Opme-puy de Dôme) has evolved to become a full instrumented platform for atmospheric research. It has received credentials as a national observing platform in France and is internationally recognized as a global station in the GAW (Global Atmosphere Watch) network. It is a reference site of European and national research infrastructures ACTRIS (Aerosol Cloud and Trace gases Research Infrastructure) and ICOS (Integrated Carbon Observing System). The site located on top of the puy de Dôme mountain (1465 m a.s.l.) is completed by additional sites located at lower altitudes and adding the vertical dimension to the atmospheric observations: Opme (660 m a.s.l.), Cézeaux (410 m), and Aulnat (330 m). The integration of different sites offers a unique combination of in situ and remote sensing measurements capturing and documenting the variability of particulate and gaseous atmospheric composition, but also the optical, biochemical, and physical properties of aerosol particles, clouds, and precipitations. Given its location far away from any major emission sources, its altitude, and the mountain orography, the puy de Dôme station is ideally located to sample different air masses in the boundary layer or in the free troposphere depending on time of day and seasons. It is also an ideal place to study cloud properties with frequent presence of clouds at the top in fall and winter. As a result of the natural conditions prevailing at the site and of the very exhaustive instrumental deployment, scientific studies at the puy de Dôme strongly contribute to improving knowledge in atmospheric sciences, including the characterization of trends and variability, the understanding of complex and interconnected processes (microphysical, chemical, biological, chemical and dynamical), and the provision of reference information for climate/chemistry models. In this context, CO-PDD is a pilot site to conduct instrumental development inside its wind tunnel for testing liquid and ice cloud probes in natural conditions, or in situ systems to collect aerosol and cloud. This paper reviews 25 years (1995–2020) of atmospheric observation at the station and related scientific research contributing to atmospheric and climate science.