Reactive uptake of NO2 on volcanic particles: A possible source of HONO in the atmosphere.

The heterogeneous degradation of nitrogen dioxide (NO2) on five samples of natural Icelandic volcanic particles has been investigated. Laboratory experiments were carried out under simulated atmospheric conditions using a coated wall flow tube (CWFT). The CWFT reactor was coupled to a blue light nitrogen oxides analyzer (NOx analyzer), and a long path absorption photometer (LOPAP) to monitor in real time the concentrations of NO2, NO and HONO, respectively. Under dark and ambient relative humidity conditions, the steady state uptake coefficients of NO2 varied significantly between the volcanic samples probably due to differences in magma composition and morphological variation related with the density of surface OH groups. The irradiation of the surface with simulated sunlight enhanced the uptake coefficients by a factor of three indicating that photo-induced processes on the surface of the dust occur. Furthermore, the product yields of NO and HONO were determined under both dark and simulated sunlight conditions. The relative humidity was found to influence the distribution of gaseous products, promoting the formation of gaseous HONO. A detailed reaction mechanism is proposed that supports our experimental observations. Regarding the atmospheric implications, our results suggest that the NO2 degradation on volcanic particles and the corresponding formation of HONO is expected to be significant during volcanic dust storms or after a volcanic eruption.

Saharan, Aral-Caspian and Middle East dust travels to Finland (1980-2022).

Studies on atmospheric dust and long-range transport of mineral dust have been a focus of atmospheric science in recent years. With its wide range of direct and indirect effects, mineral dust is one of the most uncertain elements in the mechanisms of climate change, and a deeper understanding of its role is essential for understanding future processes. The aim of our research was to provide the first systematic data on the so far episodically documented northward transport mineral dust from arid-semiarid areas. So, in this paper, we present dust storm events from lower latitudes reaching the Finnish atmosphere, based on the MERRA-2 model Dust Column Mass Density data and after a multistep verification procedure using independent data source. In total, 86 long-range dust storm events were identified between 1980 and 2022, when air masses loaded with dust reached Finland. Based on backward-trajectories different sources were identified: 59 were Saharan, 22 were Aral-Caspian, and five were associated with Middle Eastern source areas. Considerable variation in inter-annual frequencies was observed among the source areas, which may be due to changes in circulation conditions and the effects of human activity (agriculture and land use changes in Aral Sea region). There is a clear maximum of dust events in spring (60%), followed by summer and autumn (where 10 of the 11 autumn episodes were from the Sahara). However, the number and proportion of scarce winter events have more than doubled since 2010 compared to the preceding 30 years, but no autumn events were registered during this period. This clear temporal variation coincides with changes in dust transport observed in other regions of Europe, driven by greater atmospheric meridionality associated with climate change and driven by reduced temperature difference between low and high latitudes due to enhanced temperature increases at Arctic regions.

Multi-sectoral impact assessment of an extreme African dust episode in the Eastern Mediterranean in March 2018.

In late March 2018, a large part of the Eastern Mediterranean experienced an extraordinary episode of African dust, one of the most intense in recent years, here referred to as the "Minoan Red" event. The episode mainly affected the Greek island of Crete, where the highest aerosol concentrations over the past 15 yeas were recorded, although impacts were also felt well beyond this core area. Our study fills a gap in dust research by assessing the multi-sectoral impacts of sand and dust storms and their socioeconomic implications. Specifically, we provide a multi-sectoral impact assessment of Crete during the occurrence of this exceptional African dust event. During the day of the occurrence of the maximum dust concentration in Crete, i.e. March 22nd, 2018, we identified impacts on meteorological conditions, agriculture, transport, energy, society (including closing of schools and cancellation of social events), and emergency response systems. As a result, the event led to a 3-fold increase in daily emergency responses compare to previous days associated with urban emergencies and wildfires, a 3.5-fold increase in hospital visits and admissions for Chronic Obstructive Pulmonary Disease (COPD) exacerbations and dyspnoea, a reduction of visibility causing aircraft traffic disruptions (eleven cancellations and seven delays), and a reduction of solar energy production. We estimate the cost of direct and indirect effects of the dust episode, considering the most affected socio-economic sectors (e.g. civil protection, aviation, health and solar energy production), to be between 3.4 and 3.8 million EUR for Crete. Since such desert dust transport episodes are natural, meteorology-driven and thus to a large extent unavoidable, we argue that the efficiency of actions to mitigate dust impacts depends on the accuracy of operational dust forecasting and the implementation of relevant early warning systems for social awareness.

Saharan dust and giant quartz particle transport towards Iceland.

Mineral dust emissions from Saharan sources have an impact on the atmospheric environment and sedimentary units in distant regions. Here, we present the first systematic observations of long-range Saharan dust transport towards Iceland. Fifteen Saharan dust episodes were identified to have occurred between 2008 and 2020 based on aerosol optical depth data, backward trajectories and numerical models. Icelandic samples from the local dust sources were compared with deposited dust from two severe Saharan dust events in terms of their granulometric and mineralogical characteristics. The episodes were associated with enhanced meridional atmospheric flow patterns driven by unusual meandering jets. Strong winds were able to carry large Saharan quartz particles (> 100 µm) towards Iceland. Our results confirm the atmospheric pathways of Saharan dust towards the Arctic, and identify new northward meridional long-ranged transport of giant dust particles from the Sahara, including the first evidence of their deposition in Iceland as previously predicted by models.

Vertical distribution of aerosols in dust storms during the Arctic winter.

High Latitude Dust (HLD) contributes 5% to the global dust budget, but HLD measurements are sparse. Dust observations from Iceland provide dust aerosol distributions during the Arctic winter for the first time, profiling dust storms as well as clean air conditions. Five winter dust storms were captured during harsh conditions. Mean number concentrations during the non-dust flights were <5 particles cm-3 for the particles 0.2-100 µm in diameter and >40 particles cm-3 during dust storms. A moderate dust storm with >250 particles cm-3 (2 km altitude) was captured on 10th January 2016 as a result of sediments suspended from glacial outburst flood Skaftahlaup in 2015. Similar concentrations were reported previously in the Saharan air layer. Detected particle sizes were up to 20 µm close to the surface, up to 10 µm at 900 m altitude, up to 5 µm at 5 km altitude, and submicron at altitudes >6 km. Dust sources in the Arctic are active during the winter and produce large amounts of particulate matter dispersed over long distances and high altitudes. HLD contributes to Arctic air pollution and has the potential to influence ice nucleation in mixed-phase clouds and Arctic amplification.

Long-term dust aerosol production from natural sources in Iceland.

Iceland is a volcanic island in the North Atlantic Ocean with maritime climate. In spite of moist climate, large areas are with limited vegetation cover where >40% of Iceland is classified with considerable to very severe erosion and 21% of Iceland is volcanic sandy deserts. Not only do natural emissions from these sources influenced by strong winds affect regional air quality in Iceland ("Reykjavik haze"), but dust particles are transported over the Atlantic ocean and Arctic Ocean >1000 km at times. The aim of this paper is to place Icelandic dust production area into international perspective, present long-term frequency of dust storm events in northeast Iceland, and estimate dust aerosol concentrations during reported dust events. Meteorological observations with dust presence codes and related visibility were used to identify the frequency and the long-term changes in dust production in northeast Iceland. There were annually 16.4 days on average with reported dust observations on weather stations within the northeastern erosion area, indicating extreme dust plume activity and erosion within the northeastern deserts, even though the area is covered with snow during the major part of winter. During the 2000s the highest occurrence of dust events in six decades was reported. We have measured saltation and Aeolian transport during dust/volcanic ash storms in Iceland, which give some of the most intense wind erosion events ever measured. Icelandic dust affects the ecosystems over much of Iceland and causes regional haze. It is likely to affect the ecosystems of the oceans around Iceland, and it brings dust that lowers the albedo of the Icelandic glaciers, increasing melt-off due to global warming. The study indicates that Icelandic dust may contribute to the Arctic air pollution. IMPLICATIONS: Long-term records of meteorological dust observations from Northeast Iceland indicate the frequency of dust events from Icelandic deserts. The research involves a 60-year period and provides a unique perspective of the dust aerosol production from natural sources in the sub-Arctic Iceland. The amounts are staggering, and with this paper, it is clear that Icelandic dust sources need to be considered among major global dust sources. This paper presents the dust events directly affecting the air quality in the Arctic region.