Host model uncertainties in aerosol radiative forcing estimates: results from the AeroCom Prescribed intercomparison study

Simulated multi-model “diversity” in aerosol direct radiative forcing estimates is often perceived as a measure of aerosol uncertainty. However, current models used for aerosol radiative forcing calculations vary considerably in model components relevant for forcing calculations and the associated “host-model uncertainties” are generally convoluted with the actual aerosol uncertainty. In this AeroCom Prescribed intercomparison study we systematically isolate and quantify host model uncertainties on aerosol forcing experiments through prescription of identical aerosol radiative properties in twelve participating models. Even with prescribed aerosol radiative properties, simulated clear-sky and all-sky aerosol radiative forcings show significant diversity. For a purely scattering case with globally constant optical depth of 0.2, the global-mean all-sky top-of-atmosphere radiative forcing is −4.47Wm−2 and the inter-model standard deviation is 0.55Wm−2, corresponding to a relative standard deviation of 12 %. For a case with partially absorbing aerosol with an aerosol optical depth of 0.2 and single scattering albedo of 0.8, the forcing changes to 1.04Wm−2, and the standard deviation increases to 1.01W−2, corresponding to a significant relative standard deviation of 97 %. However, the top-of-atmosphere forcing variability owing to absorption (subtracting the scattering case from the case with scattering and absorption) is low, with absolute (relative) standard deviations of 0.45Wm−2 (8 %) clear-sky and 0.62Wm−2 (11 %) all-sky. Scaling the forcing standard deviation for a purely scattering case to match the sulfate radiative forcing in the Aero- Com Direct Effect experiment demonstrates that host model uncertainties could explain about 36% of the overall sulfate forcing diversity of 0.11Wm−2 in the AeroCom Direct Radiative Effect experiment

Operational Dust Prediction

Over the last few years, numerical prediction of dust aerosol concentration has become prominent at several research and operational weather centres due to growing interest from diverse stakeholders, such as solar energy plant managers, health professionals, aviation and military authorities and policymakers. Dust prediction in numerical weather prediction-type models faces a number of challenges owing to the complexity of the system. At the centre of the problem is the vast range of scales required to fully account for all of the physical processes related to dust. Another limiting factor is the paucity of suitable dust observations available for model, evaluation and assimilation. This chapter discusses in detail numerical prediction of dust with examples from systems that are currently providing dust forecasts in near real-time or are part of international efforts to establish daily provision of dust forecasts based on multi-model ensembles. The various models are introduced and described along with an overview on the importance of dust prediction activities and a historical perspective. Assimilation and evaluation aspects in dust prediction are also discussed

Aerosol forcing in the Climate Model Intercomparison Project (CMIP5) simulations by HadGEM2-ES and the role of ammonium nitrate

The latest Hadley Centre climate model, HadGEM2-ES, includes Earth system components such as interactive chemistry and eight species of tropospheric aerosols. It has been run for the period 1860–2100 in support of the fifth phase of the Climate Model Intercomparison Project (CMIP5). Anthropogenic aerosol emissions peak between 1980 and 2020, resulting in a present-day all-sky top of the atmosphere aerosol forcing of −1.6 and −1.4 W m−2 with and without ammonium nitrate aerosols, respectively, for the sum of direct and first indirect aerosol forcings. Aerosol forcing becomes significantly weaker in the 21st century, being weaker than −0.5 W m−2 in 2100 without nitrate. However, nitrate aerosols become the dominant species in Europe and Asia and decelerate the decrease in global mean aerosol forcing. Considering nitrate aerosols makes aerosol radiative forcing 2–4 times stronger by 2100 depending on the representative concentration pathway, although this impact is lessened when changes in the oxidation properties of the atmosphere are accounted for. Anthropogenic aerosol residence times increase in the future in spite of increased precipitation, as cloud cover and aerosol-cloud interactions decrease in tropical and midlatitude regions. Deposition of fossil fuel black carbon onto snow and ice surfaces peaks during the 20th century in the Arctic and Europe but keeps increasing in the Himalayas until the middle of the 21st century. Results presented here confirm the importance of aerosols in influencing the Earth's climate, albeit with a reduced impact in the future, and suggest that nitrate aerosols will partially replace sulphate aerosols to become an important anthropogenic species in the remainder of the 21st century

Photochemical sensitivity to emissions and local meteorology in Bogotá, Santiago, and São Paulo: An analysis of the initial COVID-19 lockdowns

This study delves into the photochemical atmospheric changes reported globally during the pandemic by analyzing the change in emissions from mobile sources and the contribution of local meteorology to ozone (O3) and particle formation in Bogotá (Colombia), Santiago (Chile), and São Paulo (Brazil). The impact of mobility reductions (50%–80%) produced by the early coronavirus-imposed lockdown was assessed through high-resolution vehicular emission inventories, surface measurements, aerosol optical depth and size, and satellite observations of tropospheric nitrogen dioxide (NO2) columns. A generalized additive model (GAM) technique was also used to separate the local meteorology and urban patterns from other drivers relevant for O3 and NO2 formation. Volatile organic compounds, nitrogen oxides (NOx), and fine particulate matter (PM2.5) decreased significantly due to motorized trip reductions. In situ nitrogen oxide median surface mixing ratios declined by 70%, 67%, and 67% in Bogotá, Santiago, and São Paulo, respectively. NO2 column medians from satellite observations decreased by 40%, 35%, and 47%, respectively, which was consistent with the changes in mobility and surface mixing ratio reductions of 34%, 25%, and 34%. However, the ambient NO2 to NOx ratio increased, denoting a shift of the O3 formation regime that led to a 51%, 36%, and 30% increase in the median O3 surface mixing ratios in the 3 respective cities. O3 showed high sensitivity to slight temperature changes during the pandemic lockdown period analyzed. However, the GAM results indicate that O3 increases were mainly caused by emission changes. The lockdown led to an increase in the median of the maximum daily 8-h average O3 of between 56% and 90% in these cities

Assimilation variationnelle d'observations satellitaires dans un modèle atmosphérique d'aérosols

Le lidar CALIOP (à bord du satellite CALIPSO) et le radiomètre MODIS (à bord du satellite AQUA) font partie de l'A-train . Ils fournissent des mesures simultanées en donnant une occasion unique d'améliorer notre connaissance sur les propriétés des aérosols et leur distribution spatiale. Nous étudions dans quelle mesure la distribution verticale du coefficient d'extinction des aérosols et leur distribution en taille peuvent être restituée par la synergie du signal lidar et des mesures spectrales de réflectance. À cet effet un schéma variationnel d'inversion basé sur un modèle de transfert radiatif a été développé. Ce schéma prend en compte le profil de rétrodiffusion atténué du signal lidar à deux longueurs d'onde et la réflectance à six longueurs d'onde. Notre méthode vise à minimiser une fonction coût qui mesure le départ de la solution aux observations et à une ébauche donnée. La méthode de l'adjoint a été appliquée pour trouver le gradient de la fonction coût par rapport aux paramètres d'entrée. Le schéma d'inversion a été examiné d'abord sous des observations synthétiques et puis avec de vraies mesures prises pendant la campagne FRENCH. La restitution des profils de coefficient d'extinction pour les modes fins et grossiers a une meilleure performance quand les aérosols fins dominent. Si les particules grossières dominent, le schéma trouve le profil total du coefficient d'extinction avec une confiance plus élevée que celui du mode fin. Les résultats indiquent également qu'il y a une certaine perspective pour l'amélioration de la qualité de l'inversion en incluant d'autres sources d'information indépendantes telles que les mesures POLDER.LILLE1-BU (590092102) / SudocSudocFranceF

Soccer games and record-breaking PM 2.5 pollution events in Santiago, Chile

International audienceIn wintertime, high concentrations of atmospheric fine particulate matter (PM 2.5) are commonly observed in the metropolitan area of Santiago, Chile. Hourly peaks can be very strong, up to 10 times above average levels, but have barely been studied so far. Based on atmospheric composition measurements and chemistry-transport modeling (WRF-CHIMERE), the chemical signature of sporadic skyrocket-ing wintertime PM 2.5 peaks is analyzed. This signature and the timing of such extreme events trace their origin back to massive barbecue cooking by Santiago's inhabitants during international soccer games. The peaks end up evacuated outside Santiago after a few hours but trigger emergency plans for the next day. Decontamination plans in Santiago focus on decreasing emissions from traffic, industry, and residential heating. Thanks to the air quality network of Santiago, this study shows that cultural habits such as barbecue cooking also need to be taken into account. For short-term forecast and emergency management, cultural events such as soccer games seem a good proxy to prognose possible PM 2.5 peak events. Not only can this result have an informative value for the Chilean authorities but also a similar methodology could be reproduced for other cases throughout the world in order to estimate the burden on air quality of cultural habits

Deep winter intrusions of urban black carbon into a canyon near Santiago, Chile:a pathway towards Andean glaciers

Black carbon transport from the Santiago Metropolitan Area, Chile, up to the adjacent Andes Cordillera and its glaciers is of major concern. Its deposition accelerates the melting of the snowpack, which could lead to stress on water supply in addition to climate feedback. A proposed pathway for this transport is the channelling through the network of canyons that connect the urban basin to the elevated summits, as suggested by modelling studies, although no observations have validated this hypothesis so far. In this work, atmospheric measurements from a dedicated field campaign conducted in winter 2015, under severe urban pollution conditions, in Santiago and the Maipo canyon, southeast of Santiago, are analysed. Wind (speed and direction) and particulate matter concentrations measured at the surface and along vertical profiles, demonstrate intrusions of thick layers (up to 600 m above ground) of urban black carbon deep into the canyon on several occasions. Transport of PM down-valley occurs mostly through shallow layers at the surface except in connection with deep valley intrusions, when a secondary layer in altitude with return flow (down-valley) at night is observed. The transported particulate matter is mostly from the vicinity of the entrance to the canyon and uncorrelated to concentrations observed in downtown Santiago. Reanalyses data show that for 10% of the wintertime days, deep intrusions into the Maipo canyon are prevented by easterly winds advecting air pollutants away from the Andes. Also, in 23% of the cases, intrusions proceed towards a secondary north-eastward branch of the Maipo canyon, leaving 67% of the cases with favourable conditions for deep penetrations into the main Maipo canyon. Reanalyses show that the wind directions associated to the 33% anomalous cases are related to thick cloud cover and/or the development of coastal lows

Evaluation of atmospheric dust prediction models using ground-based observations

Póster presentado en: EGU General Assembly celebrada del 7 al 12 de abril de 2013 en Viena, Austria.An important step in numerical prediction of mineral dust is the model evaluation aimed lo assess its performance to forecast the atmospheric dust content and to lead to new directions in model development and improvement. This work presents the use of different ground-based observing systems for the evaluation of dust models in the Regional Center for Northern Africa, Middle East and Europe of the WMO Sand and Dust Storm Warning Advisory and Assessment System (SDS-WAS, http://sds-was.aemet.es). The dust optical depth al 550 nm forecast by different models is regularly compared with the AERONET measurements of Aerosol Optical Depth (AOD) for 40 selected stations. This variable integrales the contribution of different aerosol types, but may be complemented with spectral information that enables hypotheses about the nature of the particles. Comparison is restricted lo cases with low Angstr6m exponent values in arder lo ensure that coarse mineral dust is the dominant aerosol type

Impacto de la calefacción residencial en la calidad del aire en las ciudades del centro y sur de Chile a través de simulación numérica

Las ciudades de centro y sur de Chile experimentan todos los inviernos intensos episodios de contaminación por material particulado (MP), específicamente MP2.5, con superación episódica de los límites fijados en la normativa ambiental nacional y con concentraciones horarias que a veces exceden los 800 mg/m3. Altos niveles de MP pueden causar daño a los pulmones, el sistema respiratorio y el sistema cardiovascular, lo que puede llevar a una mayor cantidad de consultas hospitalarias, menos productividad y muerte prematura. Además del impacto en la salud, la absorción de MP, como el carbón negro, puede perturbar el ciclo hidrológico a través del impacto en la capa de nieve. La deposición de BC sobre la nieve reduce su albedo y hace que la capa de nieve se derrita más pronto en la temporada de primavera.Un sistema de modelación capaz de simular la dispersión de contaminantes gaseosos y MP en la zona centro de Chile ha sido implementado (Mazzeo et al., 2018). Este sistema está compuesto por el modelo meteorológico WRF y el modelo de transporte químico CHIMERE. Adicionalmente, un inventario de emisiones geo-referenciado que incluye emisiones residenciales de quema de biomasa ha sido desarrollado. Este sistema de modelación será aplicado para simular la calidad de aire en las ciudades del centro y sur de Chile. En el presente trabajo se presentarán resultados preliminares de su aplicación en estas ciudades y de la capacidad de este modelo de reproducir las concentraciones observadas por las estaciones de monitoreo del Ministerio del Medio Ambiente. A través de estudios de sensibilidad se evaluará el impacto de las emisiones residenciales en la calidad de cada ciudad.ReferenciasMazzeo, A., et al. (2018). Impact of residential combustion and transport emissions on air pollution in Santiago during winter. Atmospheric Environment, 190, 195–208. http://doi.org/https://doi.org/10.1016/j.atmosenv.2018.06.043