Identification and characterization of natural aerosols over the Arctic

Le réchauffement climatique est l'un des défis les plus graves auxquels nous sommes confrontés aujourd'hui. L'Arctique est particulièrement vulnérable à ses effets. Les aérosols jouent un rôle clé en termes d'effets de forçage radiatif (à la fois directement et indirectement en termes d'influence sur les nuages). Par conséquent, ils sont l'une des plus grandes sources d'incertitude dans la modélisation du climat dans la mesure où leurs caractéristiques microphysiques, chimiques et optiques ne sont pas bien comprises. Les aérosols arctiques peuvent être classés selon deux catégories: les aérosols anthropiques et les aérosols naturels. Les aérosols naturels comprennent le carbone noir et le carbone brun (BC et BrC), la poussière, le sel de mer, les sulfates volcaniques et les cendres ainsi que les nuages stratosphériques polaires de niveau Ib (PSC). Le but ultime du projet de recherche était de caractériser les propriétés optiques et microphysiques des aérosols naturels dans les contraintes de pouvoir capturer des événements d'opportunité spécifiques. Bien que nous ayons enquêté sur de nombreux événements d'aérosols naturels dans l'Arctique, nous nous sommes finalement concentrés sur deux événements extraordinaires. Dans le premier article, nous avons utilisé la photométrie solaire au sol, les récupérations au sol FTIR (Fourier Transform IR), les profils lidar, la télédétection par satellite et la modélisation des aérosols pour analyser un événement de fumée extrême en août 2017 sur Eureka, entraîné par le incendies pyrocb (convection extrême) près de Prince George, en Colombie-Britannique. Selon nous, cet article a été une contribution innovante et originale à divers égards: d'abord en termes d'événements d’aérosols ainsi que l'infrastructure instrumentale et l'expertise que nous avons développées et apportées au fil des années sur Eureka. L’article était également original en termes de production d'une climatologie des fumées f (profondeur optique en mode fin) sur 10 ans qui excluait les événements confondants tels que les intrusions stratosphériques de sulfates en mode fin de Kasatochi et Sarychev de 2008 et 2009. Une contrainte originale sur l'étiquetage des événements f en tant qu'événements de fumée était la corrélation entre f et l'abondance de CO récupérée par FTIR (le CO étant un produit de fumée classique). Pour démontrer la nature extrême de l'événement, nous avons utilisé une analyse ‘‘pic au-dessus du seuil’’ (Peak Over Threshold, POT) des pics f individuels au cours de notre période d'échantillonnage de 10 ans. Le deuxième article était sans doute la contribution la plus importante et la plus originale de ce projet. Elle impliquait la réussite de l’application de techniques de télédétection pour détecter un panache de poussière à basse altitude et dans l'Extrême-Arctique (81 °N) au-dessus du lac Hazen (Ellesmere Island) en utilisant plusieurs techniques de télédétection passives et actives par satellite. Nous n'avons connaissance d'aucune publication traitant de la télédétection de la poussière locale de l'Arctique effectuée sur la surface complexe de neige, de glace et de poussière telle que présente au lac Hazen. Nous avons exploité les capacités d'imagerie multiangles et multispectrales (imagerie MISR et MODIS) ainsi que les capacités de profilage dépendantes de la taille des particules des capteurs actifs (le CALIOP lidar et le radar CloudSat) pour identifier et caractériser les propriétés physiques et optiques clés du panache de poussière. Cela a été accompli malgré le fait que les algorithmes de télédétection de tous ces capteurs n'étaient pas adaptés aux conditions arctiques. Nous avons réussi à caractériser l'épaisseur du panache supérieur (la région du signal comportant le bruit le plus élevé) en termes d’épaisseur optique à 532 nm (~ 0.7) et le rayon effectif des particules du panache (entre 18 et 25 µm de rayon; ce que les spécialistes du domaine qualifient de particules de poussière ‘‘géantes’’).Abstract: Global warming is one of the most serious challenges that we face today. The Arctic is particularly vulnerable to its effects. Aerosols play a key role in terms of their radiative forcing effects (both directly and indirectly in terms of their influence on clouds). They are, accordingly, one of the greatest uncertainty sources in climate modelling inasmuch as their microphysical, chemical and optical characteristics are not well understood. Arctic aerosols can be categorized into anthropogenic and natural aerosols. Natural aerosols include black and brown carbon (BC and BrC), dust, sea-salt, volcanic sulphates and ash as well as level Ib polar stratospheric clouds (PSCs). The ultimate goal of the research project was to characterize the optical and microphysical properties of natural aerosols within the constraints of being able to capture specific events of opportunity. While we investigated numerous natural aerosol events over the Arctic, we eventually focussed on two extraordinary events. In Paper 1, we employed ground-based sunphotometry, ground-based FTIR (Fourier Transform IR) retrievals, lidar profiles, satellite remote sensing and aerosol modelling to analyze an extreme, August-2017 smoke event over Eureka that was driven by pyrocb (extreme convection) fires near Prince George, BC. This paper was, we believe, an innovative and original contribution on various levels: first and foremost, in terms of the event as well as the instrumental infrastructure and expertise that we developed and brought to bear over many years at Eureka. It was also original in terms of the production of a 10-year f (fine mode optical depth) smoke climatology that excluded confounding events such as the 2008 and 2009 Kasatochi and Sarychev stratospheric intrusions of fine mode sulphates. An original constraint on the labelling of f events as smoke events was the correlation between f and FTIR-retrieved CO abundance (CO being a classical smoke product). To demonstrate the extreme nature of the event we employed a "peak over threshold" (POT) analysis of individual f peaks during our 10-year sampling period. Paper 2 was arguably the most significant and original contribution. It involved the successful application of remote sensing techniques to detect a low-altitude, high-Arctic (81 °N) dust plume over Lake Hazen (Ellesmere Island) using a diverse array of passive and active, satellite-based remote sensing techniques. We are not aware of any published remote sensing investigations of local Arctic dust carried out over the complex surface of snow, ice and dust that was encountered in the Lake Hazen case. We exploited multi-angle and multi-spectral imaging capabilities (MISR and MODIS imagery) as well as the particle size dependant profiling capabilities of active sensors (the CALIOP lidar and the CloudSat radar) to identify and characterize the key physical and optical properties of the dust plume. This was accomplished in spite of the fact that the remote sensing algorithms of all these sensors were not adapted to Arctic conditions. We succeeded in characterizing the upper plume thickness (the region of highest signal-to-noise) in terms of 532 nm optical depth (~ 0.7) and the effective radius of the plume particles (between 18 and 25 µm in radius; what the dust community characterize as “giant” dust particles)

Newly identified climatically and environmentally significant high-latitude dust sources

Peer reviewe

Newly identified climatically and environmentally significant high-latitude dust sources

Dust particles from high latitudes have a potentially large local, regional, and global significance to climate and the environment as short-lived climate forcers, air pollutants, and nutrient sources. Identifying the locations of local dust sources and their emission, transport, and deposition processes is important for understanding the multiple impacts of high-latitude dust (HLD) on the Earth\u27s systems. Here, we identify, describe, and quantify the source intensity (SI) values, which show the potential of soil surfaces for dust emission scaled to values 0 to 1 concerning globally best productive sources, using the Global Sand and Dust Storms Source Base Map (G-SDS-SBM). This includes 64 HLD sources in our collection for the northern (Alaska, Canada, Denmark, Greenland, Iceland, Svalbard, Sweden, and Russia) and southern (Antarctica and Patagonia) high latitudes. Activity from most of these HLD sources shows seasonal character. It is estimated that high-latitude land areas with higher (SI ≥0.5), very high (SI ≥0.7), and the highest potential (SI ≥0.9) for dust emission cover >1 670 000 km$^{2}$, >560 000 km$^{2}$, and >240 000 km$^{2}$, respectively. In the Arctic HLD region (≥60$^{∘}$ N), land area with SI ≥0.5 is 5.5 % (1 035 059 km$^{2}$), area with SI ≥0.7 is 2.3 % (440 804 km$^{2}$), and area with SI ≥0.9 is 1.1 % (208 701 km$^{2}$). Minimum SI values in the northern HLD region are about 3 orders of magnitude smaller, indicating that the dust sources of this region greatly depend on weather conditions. Our spatial dust source distribution analysis modeling results showed evidence supporting a northern HLD belt, defined as the area north of 50$^{∘}$ N, with a “transitional HLD-source area” extending at latitudes 50–58∘ N in Eurasia and 50–55$^{∘}$ N in Canada and a “cold HLD-source area” including areas north of 60$^{∘}$ N in Eurasia and north of 58$^{∘}$ N in Canada, with currently “no dust source” area between the HLD and low-latitude dust (LLD) dust belt, except for British Columbia. Using the global atmospheric transport model SILAM, we estimated that 1.0 % of the global dust emission originated from the high-latitude regions. About 57 % of the dust deposition in snow- and ice-covered Arctic regions was from HLD sources. In the southern HLD region, soil surface conditions are favorable for dust emission during the whole year. Climate change can cause a decrease in the duration of snow cover, retreat of glaciers, and an increase in drought, heatwave intensity, and frequency, leading to the increasing frequency of topsoil conditions favorable for dust emission, which increases the probability of dust storms. Our study provides a step forward to improve the representation of HLD in models and to monitor, quantify, and assess the environmental and climate significance of HLD

What may encourage or deter health services utilization by people living with or at the risk of HIV/AIDS in special health centers? Qualitative evidence from a stigmatized community

Abstract Background Behavioral Diseases Counseling Centers (BDCCs) and Vulnerable Women’s Counseling Centers (VWCCs) in Iran are the main peripheral centers that offer educational, counseling, diagnostic, preventive, curative and protective services to individuals living with or at high risk of contracting HIV/AIDS and female sex workers respectively. Due to the social stigma surrounding HIV in Iran, this study aims to identify the factors that may hinder or encourage HIV/AIDS patients and women with risky sexual behaviors from visiting these centers. Methods Conducted in 2023, this qualitative study involved individuals visiting BDCCs and VWCCs in two western provinces of Iran, Ilam and Kermanshah. The study participants included 21 health staff members working in BDCCs and VWCCs and 20 HIV/AIDS patients and vulnerable women with unsafe sexual behaviors referring to these centers. Purposive, snowball and maximum variation sampling techniques were applied to interview the participants. Interviews were conducted between January 5th and May 21st, 2023, using a semi-structure guideline. Interviews were transcribed and content analysis approach was applied to analyze data using MAXQDA20 software. Results According to the findings, the barriers and facilitators of visiting specialized centers for HIV/AIDS patients and vulnerable women were categorized into three main categories, 10 subcategories and 35 sub-subcategories including: Medical and operational processes (4 subcategories and 12 sub-subcategories), mutual interactions between the personnel and visitors (people living with and at the risk of getting HIV/AIDS) (3 subcategory and 13 sub-subcategories), and physical characteristics of the centers (3 subcategories and 10 sub-subcategories). Conclusions To improve the performance of BDCCs and VWCCs and encourage people living with and at the risk of contracting HIV/AIDS to visit these centers regularly, health policy makers should consider modifying clinical processes, physical features, personnel behaviors and visitors’ concerns raised by the interviewees and the issues identified in this study

Newly identified climatically and environmentally significant high-latitude dust sources

Peer reviewe