Seasonal variation and size distribution of inorganic and carbonaceous components, source identification of size-fractioned urban air particles in Kuala Lumpur, Malaysia

Seasonal variations and sources of atmospheric EPFRs in a megacity in severe cold region: Implications for the influence of strong coal and biomass combustion

Environmentally persistent free radicals (EPFRs) can pose exposure risks by inducing the generation of reactive oxygen species. As a new class of pollutants, EPFRs have been frequently detected in atmospheric particulate matters. In this study, the seasonal variations and sources of EPFRs in a severe cold region in Northeastern China were comprehensively investigated, especially for the high pollution events. The geomean concentration of EPFRs in the total suspended particle was 6.58 × 1013 spins/m3 and the mean level in winter was one order of magnitude higher than summer and autumn. The correlation network analysis showed that EPFRs had significantly positive correlation with carbon component, K+ and PAHs, indicating that EPFRs were primarily emitted from combustion and pyrolysis process. The source appointment by the Positive Matrix Factorization (PMF) model indicated that the dominant sources in the heating season were coal combustion (48.4%), vehicle emission (23.1%) and biomass burning (19.4%), while the top three sources in the non-heating season were others (41.4%), coal combustion (23.7%) and vehicle emissions (21.2%). It was found that the high EPFRs in cold season can be ascribed to the extensive use of fossil fuel for heating demand; while the high EPFRs occurred in early spring were caused by the large-scale opening combustion of biomass. In summary, this study provided important basic information for better understanding the pollution characteristics of EPFRs, which suggested that the implementation of energy transformation and straw utilization was benefit for the control of EPFRs in severe cold region.

Seasonal variation of mercury in cloud water at a mountaintop in subtropical Hong Kong: Influences of transboundary transport and sea-salt aerosol

Understanding the distribution and controlling factors of mercury (Hg) speciation in cloud water is crucial for predicting the fate of atmospheric Hg and assessing the environmental impacts of Hg in cloud water. In this study, we collected 85 cloud water samples during autumn and spring at a mountaintop (957 m a.s.l.) in Hong Kong, China. The concentrations of total Hg (THg) in cloud water varied from 3.6 to 225.3 ng L-1, with volume-weighted mean values of 32.1 ng L-1 in autumn and 24.4 ng L-1 in spring. Due to the strong acidic condition of the cloud water, dissolved Hg (DHg) contributed to two-thirds of THg, with Hg complexes by dissolved organic matter (DOM) and chloride being the predominant species of DHg according to chemical equilibrium modeling simulations. Moreover, the levels of Hg-DOM were significantly higher in autumn cloud water compared to spring, and the latter contained more Hg(II)-halide complexes. These differences could be attributed to the different air mass pathways and their emission sources. By combining backward trajectories and Positive Matrix Factorization (PMF) models, we found that air masses originating from the inland Pearl River Delta region, which were only present in autumn cloud water and strongly influenced by stationary coal combustion, were responsible for the highest concentrations of THg, DHg, particulate Hg (PHg) and Hg-DOM. Additionally, air masses originating from regions in China-Indochina Peninsula were only found in spring samples and were significantly influenced by stationary coal combustion, industrial and biogenic sources, contributing to elevated proportions of methylmercury (MeHg) and PHg. In contrast, marine air masses mainly from the western Pacific Ocean contributed to high levels of Hg(II)-halide complexes, especially in spring cloud water. The dissolution and conversion of Hg from sea salt aerosols played a significant role in the enhanced DHg levels observed during cloud processing.

The BioCascade-VIVAS system for collection and delivery of virus-laden size-fractionated airborne particles

The size of virus-laden particles determines whether aerosol or droplet transmission is dominant in the airborne transmission of pathogens. Determining dominant transmission pathways is critical to implementing effective exposure risk mitigation strategies. The aerobiology discipline greatly needs an air sampling system that can collect virus-laden airborne particles, separate them by particle diameter, and deliver them directly onto host cells without inactivating virus or killing cells. We report the use of a testing system that combines a BioAerosol Nebulizing Generator (BANG) to aerosolize Human coronavirus (HCoV)-OC43 (OC43) and an integrated air sampling system comprised of a BioCascade impactor (BC) and Viable Virus Aerosol Sampler (VIVAS), together referred to as BC-VIVAS, to deliver the aerosolized virus directly onto Vero E6 cells. Particles were collected into four stages according to their aerodynamic diameter (Stage 1: >9.43 μm, Stage 2: 3.81-9.43 μm, Stage 3: 1.41-3.81 μm and Stage 4: <1.41 μm). OC43 was detected by reverse-transcription quantitative polymerase chain reaction (RT-qPCR) analyses of samples from all BC-VIVAS stages. The calculated OC43 genome equivalent counts per cm3 of air ranged from 0.34±0.09 to 70.28±12.56, with the highest concentrations in stage 3 (1.41-3.81 μm) and stage 4 (<1.41 μm). Virus-induced cytopathic effects appeared only in cells exposed to particles collected in stages 3 and 4, demonstrating the presence of viable OC43 in particles <3.81 μm. This study demonstrates the dual utility of the BC-VIVAS as particle size-fractionating air sampler and a direct exposure system for aerosolized viruses. Such utility may help minimize conventional post-collection sample processing time required to assess the viability of airborne viruses and increase the understanding about transmission pathways for airborne pathogens.

Investigation of the Exposure of Schoolchildren to Ultrafine Particles (PM0.1) during the COVID-19 Pandemic in a Medium-Sized City in Indonesia

The health risk of schoolchildren who were exposed to airborne fine and ultrafine particles (PM0.1) during the COVID-19 pandemic in the Jambi City (a medium-sized city in Sumatra Island), Indonesia was examined. A questionnaire survey was used to collect information on schoolchildren from selected schools and involved information on personal profiles; living conditions; daily activities and health status. Size-segregated ambient particulate matter (PM) in school environments was collected over a period of 24 h on weekdays and the weekend. The personal exposure of PM of eight selected schoolchildren from five schools was evaluated for a 12-h period during the daytime using a personal air sampler for PM0.1 particles. The schoolchildren spent their time mostly indoors (~88%), while the remaining ~12% was spent in traveling and outdoor activities. The average exposure level was 1.5~7.6 times higher than the outdoor level and it was particularly high for the PM0.1 fraction (4.8~7.6 times). Cooking was shown to be a key parameter that explains such a large increase in the exposure level. The PM0.1 had the largest total respiratory deposition doses (RDDs), particularly during light exercise. The high level of PM0.1 exposure by indoor sources potentially associated with health risks was shown to be important.

Carbon and Trace Element Compositions of Total Suspended Particles (TSP) and Nanoparticles (PM0.1) in Ambient Air of Southern Thailand and Characterization of Their Sources

The concentration of total suspended particles (TSP) and nanoparticles (PM0.1) over Hat Yai city, Songkhla province, southern Thailand was measured in 2019. Organic carbon (OC) and elemental carbon (EC) were evaluated by carbon aerosol analyzer (IMPROVE-TOR) method. Thirteen trace elements including Al, Ba, K, Cu, Cr, Fe, Mg, Mn, Na, Ni, Ti, Pb, and Zn were evaluated by ICP-OES. Annual average TSP and PM0.1 mass concentrations were determined to be 58.3 ± 7.8 and 10.4 ± 1.2 µg/m3, respectively. The highest levels of PM occurred in the wet season with the corresponding values for the dry seasons being lower. The averaged OC/EC ratio ranged from 3.8–4.2 (TSP) and 2.5–2.7 (PM0.1). The char to soot ratios were constantly less than 1.0 for both TSP and PM0.1, indicating that land transportation is the main emission source. A principal component analysis (PCA) revealed that road transportation, industry, and biomass burning are the key sources of these particles. However, PM arising from Indonesian peatland fires causes an increase in the carbon and trace element concentrations in southern Thailand. The findings make useful information for air quality management and strategies for controlling this problem, based on a source apportionment analysis.

Characteristics of trace elements bound to ambient nanoparticles (PM0.1) and a health risk assessment in southern Thailand

Ambient nanoparticles, or PM_0.1 and thirteen trace elements (Al, Ba, K, Fe, Cr, Cu, Ni, Na, Mn, Mg, Ti, Pb, and Zn) were studied in Hat Yai, Thailand during the year 2018. The annual average PM_0.1 mass concentration was 8.45 ± 1.93 µg/m³. The PM_0.1 levels in Hat Yai were similar to those in large cities in South East Asia, such as Hanoi and North Sumatra, but lower than other cities in Thailand. The sum of thirteen trace elements was 207.83 ± 17.06 ng/m³ and was dominated by Na, Zn, K, Mg, and Al. The highest concentration of elements occurred in the pre-monsoon season followed by the dry and monsoon seasons. A principal component analysis (PCA) indicated that PM_0.1 comes from motor vehicles, crustal dust, industrial and biomass burning. The PM_0.1 was dominated in the pre-monsoon season, suggesting that biomass burning from the southwest direction could cause an increase in the levels of Cr, Ti, and Ni. The total cancer risk from all the carcinogenic elements was 1.98 × 10^-6 in adults, indicating that the carcinogenic risk is in a tolerable risk assessment range. The increasing levels of PM_0.1 during transboundary haze pollution and local source emissions are a concern.