High heterogeneity and aging state of mineral particles in a slowly-moving dust plume on the southwestern coast of Japan

Aerosol particles in two size ranges, namely 0.18-1.4 μm (fine) and larger than 1.4 μm (coarse), were collected in the pre-dust, in-dust, and post-dust air during the passage of a slowly-moving dust event at a coastal site in southwestern Japan. We identified the composition and size of individual particles using a scanning electron microscope to investigate the variations during dust passage. The particles could be classified as mineral-seasalt mixtures, non-mixture minerals, sulfur-containing minerals, and seasalt particles, and the number fractions of these type particles in the two size ranges exhibited significant variation across the three periods. In the coarse size range, mixture particles accounted for 17.6 %, 26.8 %, and 37.8 % of the particles in the pre-dust, in-dust, and post-dust air, respectively. Non-mixture particles made up 36.8 %, 29.2 %, and 24.3 % in the same respective periods. In the in-dust air, the average relative ratio of sulfur content in sulfur-containing mineral particles in the coarse range was 5.5 %, whereas in the fine range, it was 17.2 %. The aging state of sea salt components, described by the Cl loss and reflecting the changes in particles due to chemical reactions, exhibited significant differences in the two size ranges. In the fine range, the aging of >90 % particles was predominantly influenced by sulfate formation in the in-dust air. In contrast, nitrate likely played a certain role in both the pre-dust and post-dust air. In the coarse range, the aging was independent of sulfate formation. These results indicate the close dependence of the aging of dust particles on their size and the notable variations of the aged states, underscoring the essentiality to treat dust particles properly according to time and space for a better understanding on their roles in the marine atmosphere.

Physiochemistry and sources of individual particles in response to intensified controls during the 2022 Winter Olympics in Beijing

To investigate the particle sources before, during, and after the 2022 Beijing Winter Olympic and Paralympic (WOP) in Beijing, ambient particles were passively collected from January to March 2022. The physicochemical properties including morphology, size, shape parameters, and elemental compositions were analyzed by the IntelliSEM EPAS (an advanced computer-controlled scanning electron microscopy [CCSEM] system). Using the user-defined classification rules, 37,174 individual particles were automatically classified into 27 major groups and further attributed to seven major sources based on the source-associated characteristics, including mineral dust, secondary aerosol, combustion/industry, carbonaceous particles, salt-related particles, biological particles, and fiber particles. Our results showed that mineral dust (66.5%), combustion/industry (12.6%), and secondary aerosol (6.3%) were the three major sources in a wide size range of 0.2-42.8 μm. During the Winter Olympic Games period, low emission of anthropogenic particles and favorable meteorological conditions contributed to significantly improved air quality. During the Winter Paralympic Games period, more particles sourced from the dust storm, secondary formed particles, and the adverse meteorological conditions resulted in relatively worse air quality. The secondary aerosol all decreased during the competition period, while increased during the non-competition period. Sulfate-related particles had explosive growth and further aggravate the pollution degree during the non-competition period, especially under adverse meteorological conditions. These results provide microscopic evidence revealing variations of physicochemical properties and sources in response to the control measures and meteorological conditions.

Computer-controlled scanning electron microscope: Methodologies and application scenarios in atmospheric particle research

Understanding the physicochemical properties of atmospheric particles and the refined source apportionment become a vital foundation for targeted control of air pollution. The rapid development of the computer-controlled scanning electron microscope (CCSEM) provides a new era for atmospheric particle research by improving the efficiency of individual particle analysis. This study summarized the methodologies for CCSEM-based individual particle analysis and introduced the principle, characteristics, and development of CCSEM. The application scenarios of CCSEM in the field of air quality assessment, health assessment, and climate effects of atmospheric particles were reviewed. CCSEM has a great application prospect in the refined particle source apportionment, health effect assessment, and particle source spectrum database establishment. Much attention should be paid to the establishment of a well-developed methodology system for CCSEM, including particle identification, classification method and standardization, quantitative source appointment method establishment, and analysis timeliness enhancement.

Capillary rise induced salt deterioration on ancient wall paintings at the Mogao Grottoes

Salt deterioration has been found to be a major threat to wall paintings at culture heritage sites in arid areas along the Silk Road. However, the routes of water migration that cause the efflorescence have not been identified, and consequently, effective preservation measures have not been developed. Our microanalysis, by interrogating 93,727 individual particles collected in a Mogao cave in Dunhuang, China, revealed that capillary rise of water in the earthen plasters drives the deterioration of wall paintings. The vertical distribution of chloride and sulfate particles in the salt efflorescence and their morphologies implied a migration of salts through capillary rise and subsequent crystal growth under environmental conditions exerts sufficient pressure to cause surface decay and loss. These results indicate that blocking the water capillary rise under the porous structures is likely the most effective route to prevent rapid deterioration of the ancient wall paintings. These salt transport and deterioration mechanisms in an arid environment, suggests that a wide range of management strategies and protective measures could be developed to effectively preserve heritage sites in arid regions, especially along the Silk Road.

Morphology and mineralogical composition of sandblasting dust particles from the Taklimakan Desert

The physicochemical characteristics of dust particles from the Taklimakan Desert are the fundamental basis for the assessment of particle variation during their long-distance transport and the subsequent environmental effects. In this study, 43,222 individual sandblasting dust particles, which were mobilised using a chamber with surface soils of sand dunes and Gobi (the two types of surfaces constituting the desert) were analysed to statistically quantify the shape and mineralogical composition of dust particles from the desert. The mode of the number-size distribution of particles from the sand dunes was 0.5-0.7 μm and that of particles from Gobi soils was approximately 1.0 μm. In contrast, the distributions of particle number fractions versus shape factors such as aspect ratio and roundness were similar, despite the irregular shape of the particles. Clay mineral particles were most frequently composed of chlorite and kaolinite, accounting for 66.74 ± 12.08% of the particles from both types of soils. Quartz and feldspar particles accounted for 9.57 ± 4.52% and 2.84 ± 1.28%, respectively. The mineralogical composition of particles smaller than 1.0 μm, in both soil types, was dominated by chlorite (Al-Si-O-Mg), kaolinite (Ai-Si-O), and quartz (SiO). Gypsum (CaS) and halite (NaCl) were the major salt components in particles from both soil types. Gypsum-containing particles existed in a wide size range and occupied 3.42%-8.98% of the particles from Gobi soils and 0.27%-2.18% of the particles from sand dunes. Most gypsum-containing particles were mixed with Si-containing minerals in the form of silicate or aluminosilicate; the remaining gypsum-containing particles were gypsum crystals or mixtures of gypsum and Ca-containing minerals. These results provide a comprehensive statistical profile of dust particles released by the sandblasting process from the Taklimakan Desert to the atmosphere.

Mineralogical similarities and differences of dust storm particles at Beijing from deserts in the north and northwest

Dust storm particles have been one of the important contributors to global aerosol loading, affecting human health and climate system. Beijing, a megapolitan city, experienced two severe dust storms in spring of 2015, with maximum hourly-mean PM₁₀ mass concentrations exceeding 1000 μg/m³. The first dust storm (Dust 1) was from east area of Gobi Desert about 850 km in the north of Beijing and the second (Dust 2) was from west area of Gobi Desert about 1500 km in the northwest of Beijing. Morphologies and elemental compositions of dust particles were identified using high-resolution electron microscopy. The statistical analysis showed that the number fractions of mineral dust particles during the two dust storm episodes were 85.3% and 95.4%, respectively. Clay minerals were the most abundant among mineral particles, with a number fraction larger than 50%, followed by quartz particles (17.3% and 14.8%) and feldspar. Feldspar and carbonate particles accounted for 14.8% and 3.4% of mineral particles in Dust 1, and 9.9% and 13.6% in Dust 2, with the difference due to the different source areas. When the dust storms directly migrated to Beijing, the occurrence of S-containing mineral particles and the relative weight ratio of S in individual mineral particles were extremely low, indicating limited production of sulfate on the dust-storm particles in the atmosphere, regardless of the differences of source areas, migration paths, and mineralogical components. After the peaks of dust storms passed, the occurrence of S on the mineral particles were much higher, although the relative weight ratios of S in the mineral particles was still very small. This result suggests that most of the mineral particles underwent heterogeneous reactions, but the reaction rates were low.

A scoping study of component-specific toxicity of mercury in urban road dusts from three international locations

This scoping study presents an investigation of the total and bioaccessible mercury concentrations in road dust (RD) from three international urban sites, where a one-off sampling campaign was conducted at each. This was done to address the hypothesis that the matrix in which mercury is found influences its ability to become accessible to the body once inhaled. For that purpose, the samples were analysed for total and pulmonary bioaccessible mercury and the data compared to the chemical structure of individual particles by SEM. The results obtained from this study suggest that a high mercury content does not necessarily equate to high bioaccessibility, a phenomenon which could be ascribed to the chemical character of the individual particles. It was found that the Manchester samples contained more pulmonary soluble mercury species (as determined by elemental associations of Hg and Cl) in comparison to the other two samples, Curitiba, Brazil, and Johannesburg, South Africa. This finding ultimately underlines the necessity to conduct a site-specific in-depth analysis of RD, to determine the concentration, chemical structure and molecular speciation of the materials within the complex matrix of RD. Therefore, rather than simply assuming that higher bulk concentrations equate to more significant potential human health concerns, the leaching potential of the metal/element in its specific form (for example as a mineral) should be ascertained. The importance of individual particle behaviour in the determination of human health risk is therefore highlighted.

Morphology and composition of particles emitted from a port fuel injection gasoline vehicle under real-world driving test cycles

Traffic vehicles, many of which are powered by port fuel injection (PFI) engines, are major sources of particulate matter in the urban atmosphere. We studied particles from the emission of a commercial PFI-engine vehicle when it was running under the states of cold start, hot start, hot stabilized running, idle and acceleration, using a transmission electron microscope and an energy-dispersive X-ray detector. Results showed that the particles were mainly composed of organic, soot, and Ca-rich particles, with a small amount of S-rich and metal-containing particles, and displayed a unimodal size distribution with the peak at 600 nm. The emissions were highest under the cold start running state, followed by the hot start, hot stabilized, acceleration, and idle running states. Organic particles under the hot start and hot stabilized running states were higher than those of other running states. Soot particles were highest under the cold start running state. Under the idle running state, the relative number fraction of Ca-rich particles was high although their absolute number was low. These results indicate that PFI-engine vehicles emit substantial primary particles, which favor the formation of secondary aerosols via providing reaction sites and reaction catalysts, as well as supplying soot, organic, mineral and metal particles in the size range of the accumulation mode. In addition, the contents of Ca, P, and Zn in organic particles may serve as fingerprints for source apportionment of particles from PFI-engine vehicles.

Individual particle SEM-EDS analysis of atmospheric aerosols in rural, urban, and industrial sites of Central Italy

PM10 samples were collected simultaneously at three representative areas (urban, industrial, and rural areas). Their morphology and elemental composition were determined by scanning electron microscopy coupled with energy-dispersive analysis (SEM-EDS). Twenty-four chemical parameters (C, O, Na, Mg, Al, Si, P, Cd, Cl, K, Ca, S, Sn, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, W, and Pb) were determined and three morphological parameters (area, roundness, and fractal dimension) were measured by Image Pro Analyzer 6.3. The particles were classified into ten groups based on morphology and elemental composition: Ca-rich and metal particles, soot aggregates, cenosphere, alumosilicates, sea salt, calcium sulfate, spherical particles of iron, biological carbonaceous particles, and various. Particles of natural origin were predominantly found in the coarse size fraction and particles of anthropogenic origin in the fine size fraction. The greatest contribution to particulate matter belonged to aluminum-silicates and calcium-rich particles. The cenosphere were recognized only in the coastal urban site, while all the other particles were present in each site. The coastal industrial site was characterized by the prevalence of alumosilicates and Ca-rich particles, due to construction activity in this site during the sampling period (movement of vehicles, transport of terrigenous materials, and use of construction products). The coastal urban site was characterized by a higher amount of soot and by the presence of cenosphere, due to the presence of vehicular traffic.

Morphologies and elemental compositions of local biomass burning particles at urban and glacier sites in southeastern Tibetan Plateau: Results from an expedition in 2010

Many studies indicate that the atmospheric environment over the southern part of the Tibetan Plateau is influenced by aged biomass burning particles that are transported over long distances from South Asia. However, our knowledge of the particles emitted locally (within the plateau region) is poor. We collected aerosol particles at four urban sites and one remote glacier site during a scientific expedition to the southeastern Tibetan Plateau in spring 2010. Weather and backward trajectory analyses indicated that the particles we collected were more likely dominated by particles emitted within the plateau. The particles were examined using an electron microscope and identified according to their sizes, shapes and elemental compositions. At three urban sites where the anthropogenic particles were produced mainly by the burning of firewood, soot aggregates were in the majority and made up >40% of the particles by number. At Lhasa, the largest city on the Tibetan Plateau, tar balls and mineral particles were also frequently observed because of the use of coal and natural gas, in addition to biofuel. In contrast, at the glacier site, large numbers of chain-like soot aggregates (~25% by number) were noted. The morphologies of these aggregates were similar to those of freshly emitted ones at the urban sites; moreover, physically or chemically processed ageing was rarely confirmed. These limited observations suggest that the biomass burning particles age slowly in the cold, dry plateau air. Anthropogenic particles emitted locally within the elevated plateau region may thus affect the environment within glaciated areas in Tibet differently than anthropogenic particles transported from South Asia.