Chemical and optical properties of atmospheric aerosol iron sources: coal fly ash and Icelandic dust

This thesis describes laboratory measurements of the chemical and physical properties of coal fly ash (CFA) and volcanic dust from Iceland which are important sources of atmospheric aerosol iron (Fe). These measurements are needed to determine the impacts of Fe-containing aerosols on the radiative balance and marine biogeochemistry and to reduce the uncertainty in model predictions. The spectral optical properties and size distribution of Icelandic dust were measured using the multi-instrument atmospheric simulation chamber CESAM (based at LISA CNRS, France). The Fe dissolution kinetics of CFA samples were determined by time-dependent leaching experiments that simulated atmospheric processing. A wide range of analytical techniques including X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) analysis, X-ray absorption near edge structure (XANES) analysis, and sequential extractions were used to determine the chemical and mineralogical composition in the samples with particular focus on the Fe mineralogy/speciation. Our laboratory measurements indicate that the high ionic strength in the atmospheric aerosol water can strongly influence the Fe dissolution rates of CFA during the atmospheric transport. Our results also suggest that the Fe speciation is a key factor in determining the Fe solubility of CFA which varied considerably in different types of CFA. We also showed that CFA dissolves faster (up to 7 times) than mineral dust at similar experimental conditions. Based on these results, we developed a new Fe release scheme for coal combustion sources which has been implemented into the global atmospheric chemical transport model IMPACT to estimate the deposition flux of aerosol dissolved Fe to the ocean. In addition, we built a new dataset on chemical composition, mineralogy, Fe solubility, size distribution, and optical properties of Icelandic dust and quantified the differences from typical low-latitude dust (e.g., from northern African and eastern Asian). Our results indicate that Icelandic dust could make a substantial contribution to dissolved Fe to the subpolar North Atlantic Ocean in particular in the Iceland Basin. Our results also suggest that in Icelandic dust magnetite is a major contribution to light absorption particularly between 660 and 950 nm, which can be 2-8 times higher than in low-latitude dust. This new dataset of chemical and physical parameters can be used in global models to estimate the deposition fluxes of aerosol dissolved Fe to the North Atlantic Ocean and to determine the radiative impact of Icelandic dust in the Arctic

Ambient air quality monitoring for healthcare settings

Key messages 1. Air quality monitoring at healthcare sites can help understand exposure levels, identify local pollution sources, and inform targeted actions to reduce staff and patient exposure to poor air quality. 2. Air pollutant levels may be measured using diffusion tubes (nitrogen dioxide) and air quality sensors (particulate matter). 3. Appropriate planning and technical support/expert advice for healthcare site monitoring can help ensure that the air quality data generated are useful and usable

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's 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 km2, >560 000 km2, and >240 000 km2, respectively. In the Arctic HLD region (≥60∘ N), land area with SI ≥0.5 is 5.5 % (1 035 059 km2), area with SI ≥0.7 is 2.3 % (440 804 km2), and area with SI ≥0.9 is 1.1 % (208 701 km2). 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

Health impacts of air pollution in Birmingham

WM Air Briefing Note B34-CS-2023-07, June 2023. Contact: https://wm-air.org.uk; @WMAir_UoB; [email protected] WM-Air - Clean Air Science for the West Midlands (wm-air.org.uk) is a NERC funded initiative, led by the University of Birmingham. The programme, in collaboration with over 20 cross sector partners, applies environmental science expertise to support improvement of air quality, health, environmental and economic benefits, in the West Midlands. Research conducted by WM-Air has quantified the impacts of air pollution in Birmingham on a range of health conditions – including asthma, heart disease, stroke, lung cancer and risk of early death. Calculations were performed using the Air Quality Life Assessment Tool (AQ-LAT) developed within the WM-Air programme. For a detailed description of methods and to download the tool visit https://wm-air.org.uk/project/health/

Complex refractive index and single scattering albedo of Icelandic dust in the shortwave part of the spectrum

Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering albedo (SSA) and the complex refractive index (mCombining double low linen-ik) of Icelandic dust from five major emission hotspots were retrieved between 370-950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca) coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured βabs and βsca increased from 0.90-0.94 at 370nm to 0.94-0.96 at 950nm in Icelandic dust from the different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive index (n(λ)) was found to be 1.60-1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was almost constant with wavelength and was found to be around 0.004 at 370nm and 0.002-0.003 at 950nm. The estimated complex refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing towards the near-infrared. In Icelandic dust, k(λ) between 660-950nm was 2-8 times higher than most of the dust samples sourced in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has not been accounted for in climate predictions

Iron from coal combustion particles dissolves much faster than mineral dust under simulated atmospheric acid conditions

Mineral dust is the largest source of aerosol iron (Fe) to the offshore global ocean, but acidic processing of coal fly ash (CFA) in the atmosphere may result in a disproportionally higher contribution of bioavailable Fe. Here, we determined the Fe speciation and dissolution kinetics of CFA from Aberthaw (United Kingdom), Krakow (Poland), and Shandong (China) in solutions which simulate atmospheric acidic processing. In CFA-PM10 fractions, 8 %–21.5 % of the total Fe was as hematite and goethite (dithionite extracted Fe), 2 %–6.5  % as amorphous Fe (ascorbate extracted Fe), while magnetite (oxalate extracted Fe) varied from 3 %–22 %. The remaining 50 %–87  % of Fe was associated with aluminosilicates. High concentration of ammonium sulphate ((NH4)2SO4), often found in wet aerosols, increased Fe solubility of CFA up to 7 times at low pH (2–3). Our results showed a large variability in the effects of oxalate on the Fe dissolution rates at pH 2, from no impact in Shandong ash to doubled dissolution in Krakow ash. However, this enhancement was suppressed in the presence of high concentration of (NH4)2SO4. Dissolution of highly reactive Fe was insufficient to explain the high Fe solubility at low pH in CFA, and the modelled dissolution kinetics suggests that other Fe phases such as magnetite may also dissolve rapidly under acidic conditions. Overall, Fe in CFA dissolved up to 7 times faster than in Saharan dust samples at pH 2. Based on these laboratory data, we developed a new scheme for the proton- and oxalate- promoted Fe dissolution of CFA, which was implemented into the global atmospheric chemical transport model IMPACT. The revised model showed a better agreement with observations of surface concentration of dissolved Fe in aerosol particles over the Bay of Bengal, due to the rapid Fe release at the initial stage at highly acidic conditions. The improved model also enabled us to predict sensitivity to a more dynamic range of pH changes, particularly between anthropogenic combustion and biomass burning aerosols

Variability in sediment particle size, mineralogy, and Fe mode of occurrence across dust-source inland drainage basins:the case of the lower Drâa Valley, Morocco

The effects of desert dust upon climate and ecosystems depend strongly on its particle size and size-resolved mineralogical composition. However, there is very limited quantitative knowledge on the particle size and composition of the parent sediments along with their variability within dust-source regions, particularly in dust emission hotspots. The lower Drâa Valley, an inland drainage basin and dust hotspot region located in the Moroccan Sahara, was chosen for a comprehensive analysis of sediment particle size and mineralogy. Different sediment type samples (n=42) were collected, including paleo-sediments, paved surfaces, crusts, and dunes, and analysed for particle-size distribution (minimally and fully dispersed samples) and mineralogy. Furthermore, Fe sequential wet extraction was carried out to characterise the modes of occurrence of Fe, including Fe in Fe (oxyhydr)oxides, mainly from goethite and hematite, which are key to dust radiative effects; the poorly crystalline pool of Fe (readily exchangeable ionic Fe and Fe in nano-Fe oxides), relevant to dust impacts upon ocean biogeochemistry; and structural Fe. Results yield a conceptual model where both particle size and mineralogy are segregated by transport and deposition of sediments during runoff of water across the basin and by the precipitation of salts, which causes a sedimentary fractionation. The proportion of coarser particles enriched in quartz is higher in the highlands, while that of finer particles rich in clay, carbonates, and Fe oxides is higher in the lowland dust emission hotspots. There, when water ponds and evaporates, secondary carbonates and salts precipitate, and the clays are enriched in readily exchangeable ionic Fe, due to sorption of dissolved Fe by illite. The results differ from currently available mineralogical atlases and highlight the need for observationally constrained global high-resolution mineralogical data for mineral-speciated dust modelling. The dataset obtained represents an important resource for future evaluation of surface mineralogy retrievals from spaceborne spectroscopy.</p

Newly identified climatically and environmentally significant high-latitude dust sources

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