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Ventilation improvement for effective protection of healthcare workers in negative pressure airborne infectious isolation room from viral aerosols
(2024-07-01)
Kaeophet, Thanchanok
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Dejchanchaiwong, Racha
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Tekasakul, Perapong
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Phonsahwat, Thongchai
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Khongprom, Parinya
A negative pressure airborne infectious isolation room (AIIR) is the primary healthcare air contamination control system used for the treatment of severe respiratory infectious patients. Effects of the ventilation system configuration and conditions on airflow pattern, aerosol distribution and ventilation performance were investigated using computational fluid dynamics (CFD). The field measurement by SARS-CoV-2 environmental surface test was also conducted. The cycle threshold values from transcription polymerase chain reaction (RT-PCR) method showed inverse relation to the simulated number of particles trapped on the surfaces indicating a good agreement. Modification of the present AIIR to have alignment between air inlet and outlet where the aspect ratio of the air outlet, Width (W): Height (H) = 1:1 (Improved case: IC#1) showed a 78 % reduction of aerosol concentration in healthcare workers (HCWs) zones. Aerosol concentrations were increased when the openings of the air outlet were enlarged. Addition of air outlet led to large swirling air, resulting in more aerosols being trapped and suspended in the air. Results suggested that AIIR with alignment air inlet on the ceiling and air outlet at the wall over the patient's head with W:H = 1:1 be the most suitable configuration to maximize the ventilation performance and minimize exposure risk to aerosolized viral infection for HCWs. Air change rate plays a more important role than the differential pressure on the removal efficiency. The differential pressure value should be at least −2.5 Pa and the air supply rate 12 ACH for effective protection of HCWs in the negative pressure AIIR.
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Energy and exergy analysis for fast drying of ribbed smoked sheets in a novel forced-convection rubber smoking room
(2024-06-01)
Inthararak, Pennung
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Dejchanchaiwong, Racha
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Palamanit, Arkom
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Morris, John
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Tekasakul, Perapong
Rubber sheet smoking rooms are widely used by small farmers in rubber growing regions: sheets of raw rubber latex are ‘smoked’ in them to remove moisture, preserve and prepare the rubber for transport. Energy and exergy for a novel forced-convection rubber sheet smoking room were analyzed. Inlet hot air velocity varied between 12 and 14 m/s and the fuel-wood moisture content was between 24–55 % dry basis. Thermal efficiency for drying ribbed smoked sheet (RSS) rubber was 13.4–16.7 %. The specific energy consumption (SEC) was between 13.5–16.9 MJ/kg of water evaporated. The highest thermal efficiency or lowest specific energy consumption was achieved when using the dry fuel-wood (inlet velocity 14 m/s, 53 % db fuel-wood), while the RSS quality was maximum (100 %). The overall second law (exergy) efficiency was from 2.2-5.8 %. The highest exergy efficiency was obtained for air at 12 m/s and 24 % db fuel-wood. However, in this condition, only 55 % of sheets showed good quality. The exergy efficiency for the most suitable condition (100 % high quality sheets) was 2.6 %. Compared to an earlier forced-convection smoking room, the new room reduced the drying time from 48 h to 36 h, while thermal efficiency increased from 14.3 % to 16.5 %. When compared to the original smoking room, 65 % fuel-wood and 50 % drying time were saved and the rubber sheet quality increased from ∼90 % to 100 %. Overall, our forced-convection room was more efficient, dried faster and produced better quality than all previous types.
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Exploration of characteristics and synthesis gas suitability for heat generation of coffee biomass pellets produced by single and co-pelletization
(2023-12-01)
Palamanit, Arkom
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Kongto, Pumin
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Chaiprapat, Sumate
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Dejchanchaiwong, Racha
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Chungcharoen, Thatchapol
Production of coffee beans generates various types of biomass that can be applied as bioenergy for drying and roasting the beans. Thus, the aims of this study were to explore the characteristics of coffee biomass pellets (CBPs) produced from coffee cherry pulp (CCP), coffee parchment (CPM), and expired green coffee beans (ECB) by single and co-pelletization. The CBPs were then used to produce the synthesis gas in a downdraft gasifier, and the syngas properties were investigated for further heat applications. The results showed that single and co-pelletization of CCP and CPM performed well. The CBPs had good physiochemical properties in shape, size, and atomic ratios. The higher heating value and energy density of CBPs were 19.25-24.29 MJ/kg and 12.09-14.87 GJ/m3. The ash from CBPs was rich in K2O, CaO and MgO oxides, and the CPM ash had the lowest initial deformation temperature at 1136 °C. The ash samples from CBPs also had different slagging and fouling indexes. The syngas from CBPs mainly contained H2 (6.85-9.30%), CO (12.15-18.85%), and CO2 (10.85-13.75%). The heating value and tar concentration of syngas from CBPs were 3.24-4.32 MJ/m3 and 21.75-30.92 g/m3. The main chemical compounds in tar were styrene, phenol, caffeine, and pyrrole according to GC-MS. These results indicate that CCP and CPM have potential for pelletization and gasification to generate heat needed for coffee bean processing.
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Fine and ultrafine particle emission factors and new diagnostic ratios of PAHs for peat swamp forest fires
(2023-10-15)
Nim, Nobchonnee
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Morris, John
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Tekasakul, Perapong
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Dejchanchaiwong, Racha
Peatland fires are one of the major global sources of atmospheric particles. Emission factors for fine (PM<inf>1</inf> and PM<inf>2.5</inf>) and ultrafine (PM<inf>0.1</inf>) particles and particle-bound polycyclic aromatic hydrocarbons (PAHs) from plants in the peat swamp forest (PSF), including Melaleuca cajuputi leaves, M. cajuputi branches, M. cajuputi bark, Lepironia articulata (Retz.) Domin, forest leaf litter and peat were measured in a laboratory combustion chamber. From these measurements, new PAH diagnostic ratios for fine and ultrafine particles were proposed for identifying the forest burning source. The new emission factors for PM were PM<inf>0.1</inf>: 0.03–0.33, PM<inf>1</inf>: 0.69–2.11 and PM<inf>2.5</inf>: 1.12–4.18 g/kg; for PM-bound PAHs, the factors were PM<inf>0.1</inf>: 5.7–166.0, PM<inf>1</inf>: 31.5–1338.9 and PM<inf>2.5</inf>: 36.3–3641.1 μg/kg. The predominant PAHs for PSF burning were Pyr, BbF, DBA (in PM<inf>0.1</inf>), Flu, DBA, BghiPe (in PM<inf>1</inf>), and BbF, DBA and BghiPe (in PM<inf>2.5</inf>). We also presented new diagnostic ratios for PSF burning, including BaP/(BaP + Chr): 0.39–0.75, BaP/(BaP + BbF): 0.21–0.47 and BaA/(BaA + Chr): 0.36–0.53. Moreover, the physical and chemical characteristics of ambient fine and ultrafine particles in the Kuan Kreng forest during the 2019 forest fire (FF) and 2021 non-forest fire (NFF) periods were investigated. The mean PM<inf>0.1</inf>, PM<inf>1</inf> and PM<inf>2.5</inf> concentrations during the FF period were approximately 3.5–4.4 times as high as those during the 2021 NFF period. New PAH diagnostic ratios of BaP/(BaP + BbF) versus BaP/(BaP + Chr) were able to identify PAH burning sources in PM<inf>1</inf> and PM<inf>2.5</inf> but were less clear for PM<inf>0.1</inf>, which was dominated by a single source – M. cajuputi. Chemical mass balance studies identified peat forest burning emissions as the main source of fine and ultrafine particles during the FF period. This study suggests that the new PAH diagnostic ratios can be used to identify the burning source for more precise source apportionment.
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Source apportionment of PM2.5 in Thailand’s deep south by principal component analysis and impact of transboundary haze
(2023-08-01)
Chaisongkaew, Phatsarakorn
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Dejchanchaiwong, Racha
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Inerb, Muanfun
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Mahasakpan, Napawan
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Nim, Nobchonnee
Atmospheric particulate matter smaller than 2.5 micron (PM<inf>2.5</inf>) was evaluated at four sites in the lower southern part of Thailand during 2019–2020 to understand the impact of PM<inf>2.5</inf> transport from peatland fires in Indonesia on air quality during the southwest monsoon season. Mass concentration and chemical bound-PM, including carbon composition, e.g., organic carbon (OC) and elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs), and inorganic elements, were analyzed. The PM<inf>2.5</inf> emission sources were identified by principal components analysis (PCA). The average mass concentrations of PM<inf>2.5</inf> in the normal period, which represents clean background air, from four sites was 3.5–5.1 µg/m3, whereas during the haze period, it rose to 5.4–13.5 µg/m3. During the haze period, both OC and EC were 3.5 times as high as in the normal period. The average total PAHs and BaP-TEQ of PM<inf>2.5</inf> during the haze period were ~ 1.3–1.7 and ~ 1.2–1.9 times higher than those in the normal period. The K concentrations significantly increased during haze periods. SO<inf>4</inf>2− dominated throughout the year. The effects of external sources, especially the transboundary haze from peatland fires, were significantly enhanced, because the background air in the study locations was generally clean. PCA indicated that vehicle emission, local biomass burning, and secondary particles played a key role during normal period, whereas open biomass burning dominated during the haze phenomena. This was consistent with the OC/EC and PAH diagnostic ratios. Backward trajectories confirmed that the sources of PM during the haze period were predominantly peatland fires in Sumatra, Indonesia, due to southwest wind.
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Seasonal Field Calibration of Low-Cost PM2.5 Sensors in Different Locations with Different Sources in Thailand
(2023-03-01)
Dejchanchaiwong, Racha
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Tekasakul, Perapong
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Saejio, Apichat
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Limna, Thanathip
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Le, Thi Cuc
Low-cost sensors (LCS) have been increasingly deployed to monitor PM<inf>2.5</inf> concentrations. More than 1500 LCS have been installed in Thailand to increase public awareness of air quality. However, performance of these sensors has not been systematically investigated. In this study, PM<inf>2.5</inf> LCS were co-located next to a PM<inf>2.5</inf> federal equivalent method (FEM) reference instrument at three Thai locations—in the north, center and northeast. We evaluated the performance of a PM<inf>2.5</inf> LCS (PMS7003, Plantower) to understand the key factors affecting performance, including emission sources, relative humidity, temperature and PM<inf>2.5</inf> concentration. Low PM concentration and high humidity levels had a significant impact on performance. Sensors in a high traffic emission area showed low correlation. The unadjusted PM<inf>2.5</inf> LCS performance varied with locations. Errors were mainly observed at low concentrations. They significantly underestimated concentrations in congested urban environments. After calibration, accuracy was improved with multiple regression models. The performance of sensors only at Chiang Mai (CM) during the dry season and Ubon Ratchathani (URT) during the dry and wet seasons were acceptable with coefficient of variation: 5.8 ± 4.7–6.8 ± 5.0%, slope: 0.829–0.945, intercept: 1.12–5.49 µg/m3, R2: 0.880–0.934 and RMSE: 4.3–5.1 µg/m3. In the congested area in Bangkok (BKK), they underestimated concentrations of small particles.
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Transboundary haze from peatland fires and local source-derived PM2.5 in Southern Thailand
(2023-02-01)
Promsiri, Preyapon
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Tekasakul, Surajit
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Thongyen, Thunyapat
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Suwattiga, Panwadee
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Morris, John
This study characterizes impacts on PM<inf>2.5</inf> of transboundary haze from peatland fires in Indonesia and local emission sources during 2019–2020 to a large and densely populated city, Hat Yai in southern Thailand. Organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC), water soluble ions (WSI: Cl−, NO<inf>3</inf>−, SO<inf>4</inf>2− and NH<inf>4</inf>+), element tracers (K, Na, Mg and Ca), heavy metals (Cr, Co, Pb, Cd, Ni, Mn) and As, and 16 polycyclic aromatic hydrocarbon (PAHs) components from PM<inf>2.5</inf> samples (n = 18) were measured to identify local and regional emission sources using a chemical mass balance (CMB) model. We used a combination of air mass backward trajectories and CMB source apportionment to identify PM<inf>2.5</inf> sources. An increase of PM<inf>2.5</inf> and chemical component concentrations, during the transboundary haze period, were clearly influenced by aerosols from open biomass burning in Indonesia: PAH concentrations were 2 times higher and OC concentrations, 5 times higher. Secondary organic carbons were predominant during transboundary haze periods, accounting for 52–58% of total OC, indicating higher secondary organic aerosol formation. High K levels demonstrated that the dominant source during this period was biomass burning. Whereas a high level of Ca in the background air came from urban road dust, as well as local biomass burning. Moreover, the increased concentration of SO<inf>4</inf>2−, NH<inf>4</inf>+ and NO<inf>3</inf>− during the wet season, as well as transboundary haze periods, was mainly derived the secondary inorganic aerosol formation. Effect on PM<inf>2.5</inf> concentration from a volcanic eruption near the air mass trajectory during the sampling period was minimal. However, it may have contributed slightly to an increase of SO<inf>4</inf>2− concentration in PM<inf>2.5</inf>. Sources of PM<inf>2.5</inf> in Hat Yai were clearly influenced by local emission sources, e.g. diesel combustion and biomass burning (rubber wood and rice straw), transboundary haze and also secondary organic and inorganic aerosols.
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Estimation of Ultrafine Particulate Matter Emissions from Biomass Burning Using Satellite Imaging and Burn Severity
(2023-01-01)
Tekasakul, Perapong
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Nuthammachot, Narissara
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Malinee, Rachane
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Morris, John
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Dejchanchaiwong, Racha
Fine and ultrafine particles emitted from open biomass burning seriously affect air quality in many countries in Southeast Asia during haze episodes. In this study, PM<inf>0.1</inf> and PM<inf>2.5</inf> emissions were estimated for Thailand using agricultural residue burning. Data from Landsat-8 and Sentinel-2 satellites was obtained from 2016 to 2019. Burn severity was evaluated using NIR and SWIR bands. Results suggested agricultural residue burning as a significant contributor accounting for 82-90% of the total burned area, and the forest fires contributed the remainder. Further, the burned areas from agricultural waste during El Niño years were up to 2 times as high as those during La Niña years. Rice residue burning was the most significant contributor, followed by sugarcane and maize. Major burned areas of rice and sugarcane residue were in the northeast. Annual average PM<inf>2.5</inf> and PM<inf>0.1</inf> emissions from crop residue burning in Thailand were about 43.3 and 4.1 Gg/year, respectively. PM<inf>0.1</inf> emissions during El Niño years were also larger at 4.2-5.2 Gg/year compared to 3.7-3.4 Gg/year during La Niña. PM<inf>0.1</inf> emissions from crop residue burning were about 10% of PM<inf>2.5</inf>. These emissions affect local air quality in Thailand and neighboring countries due to long-range transport and vice versa. Annual mean PM<inf>0.1</inf> concentrations during the open biomass burning period ranged from 6.6 to 18.9 µg/m3. PM<inf>0.1</inf>-bound PAH concentrations were found to be 3-8 times higher than the background. The study highlights the estimation of fine and ultrafine particle emissions from open biomass burning useful for other researchers.

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