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Atmospheric particulate matter smaller than 2.5 micron (PM2.5) was evaluated at four sites in the lower southern part of Thailand during 2019-2020. 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 PM2.5 emission sources were identified by Principal Components Analysis. The average mass concentrations of PM2.5 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. The average OC/EC ratio in PM2.5 was 2.7-3.8 during the normal period, suggesting mixed sources of both vehicle combustion and biomass burning, whereas during strong haze period, the ratio rose to 3.3-5.2 indicating that biomass burning was a dominant source. This was consistent with the PAH diagnostic ratios. The average total PAHs and BaP-TEQ of PM2.5 during strong haze period were ~1.3-1.7 and ~1.2-1.9 times higher than those the normal period. The effects of external sources, especially the transboundary haze from peatland fires, are quantitatively pronounced because the background air in the study locations was generally clean. The 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. Backward trajectory simulations confirmed that the sources of PM during haze period was dominated by peatland fire in Sumatra, Indonesia due to south-west wind.

Rapid economic growth has led to increasing air pollution in Southeast Asia (SEA). Urbanization, industrialization and open biomass burning all lead to deteriorating air quality. Recent advances allow recording, sampling and analyzing ultrafine particles, or nanoparticles, finer than the already extensively reported PM2.5 particles; these nanoparticles have been shown to be a potentially more significant health hazard – causing cardiovascular and respiratory diseases, since they can penetrate further into our bodies. Analysis of the collected particles allows, in turn, identifying sources. Although vehicle emissions generally dominate nanoparticles, biomass generates a significant proportion in the burning seasons. In Malaysia, the number of particles smaller than 50 nm dominate, but, by mass, PM0.1 accounts for ∼15% of PM2.5 in upper SEA, and ∼18% in lower SEA. Sampling compared normal periods, where ratios of organic to elemental carbon and char to soot elemental carbon indicated that vehicle exhaust dominates. However, in haze periods, increased char to soot elemental carbon ratios indicate strong contributions from biomass burning. In lower SEA severe haze periods, polycyclic aromatic hydrocarbon levels are 3–8 times higher than in normal periods, confirming the sources as peatland fires in Indonesia. Open biomass burning clearly contributes a significant portion of PM0.1 during SEA haze periods. Further PM0.1 studies are needed to better understand sources, transport and influences on human health to identify suitable measures to solve the problem sustainably.

Transboundary and domestic aerosol transport during 2018–2019 affecting Bangkok air quality has been investigated. Physicochemical characteristics of size-segregated ambient particles down to nano-particles collected during 2017 non-haze and 2018–2019 haze periods were analyzed. The average PM2.5 concentrations at KU and KMUTNB sites in Bangkok, Thailand during the haze periods were about 4 times higher than in non-haze periods. The highest average organic carbon and elemental carbon concentrations were 4.6 ± 2.1 µg/m3 and 1.0 ± 0.4 µg/m3, respectively, in PM0.5–1.0 range at KU site. The values of OC/EC and char-EC/soot-EC ratios in accumulation mode particles suggested the significant influence of biomass burning, while the nuclei and coarse mode particles were from mixed sources. PAH concentrations during 2018–2019 haze period at KU and KMUTNB were 3.4 ± 0.9 ng/m3 and 1.8 ± 0.2 ng/m3, respectively. The PAH diagnostic ratio of PM2.5 also suggested the main contributions were from biomass combustion. This is supported by the 48-hrs backward trajectory simulation. The higher PM2.5 concentrations during 2018–2019 haze period are also associated with the meteorological conditions that induce thermal inversions and weak winds in the morning and evening. Average values of benzo(a)pyrene toxic equivalency quotient during haze period were about 3–6 times higher than during non-haze period. This should raise a concern of potential human health risk in Bangkok and vicinity exposing to fine and ultrafine particulate matters in addition to regular exposure to traffic emission.

Transboundary haze from biomass burning is one of the most important air pollutions in Southeast Asia. The most recent serious haze episode occurred in 2015. Southern Thailand was affected by the haze during September to October when the particulate matter concentration hit a record high. We investigated physical and chemical characteristics of aerosols, including concentration and aerosol size distribution down to sub-micron sizes during haze episodes in 2013 and 2015 and, for reference, an insignificant haze period in 2017. The highest total suspended particulates and PM10 levels in Hat Yai city were 340.1 and 322.5 µg/m3. The mass fractions were nanoparticles (< 100 nm) 3.1%-14.8% and fine particles (< 1 µm) 54.6%-59.1%. Polycyclic aromatic hydrocarbon size distributions in haze periods peaked at 0.75 µm and the concentrations are 2-30 times higher than the normal period. High molecular weight (4-6 ring) PAHs during the haze episode contribute to about 56.7%-88.0% for nanoparticles. The average values of benzo(a)pyrene toxic equivalency quotient were 3.34±2.54ng/m3 in the 2015 haze period but only 0.89±0.17 ng/m3 in 2017. It is clear that particles smaller than 1 µm, were highly toxic. Nanoparticles contributed 19.4%-26.0% of total BaP-TEQ, whereas the mass fraction is 13.1%-14.8%. Thus the nanoparticles were more carcinogenic and can cause greater health effect than larger particles. The fraction of BaP-TEQ for nanoparticles during 2017 non-haze period was nearly the same, while the mass fraction was lower. This indicates that nanoparticles are the significant source of carcinogenic aerosols both during haze and non-haze periods.

A cyclone was modified by inserting a stainless steel filter to enhance efficiency in collecting fine particles. Velocity and pressure distributions in the combined cyclone-filter were computed by ...

Distribution of PM

Background Kidney dysfunction is considered a cardiovascular risk factor. However, few longitudinal studies have examined the effects of air pollution on kidney function. We evaluated associations between long-term air pollution exposure and estimated glomerular filtration rate (eGFR) using data from a cohort of the Electricity Generating Authority of Thailand (EGAT) study in Bangkok Metropolitan Region, Thailand. Methods This longitudinal study included 1839 subjects (aged 52–71 years in 2002) from the EGAT1 cohort study during 2002–2012. eGFR, based on creatinine, was measured in 2002, 2007, and 2012. Annual mean concentrations of air pollutants (i.e., particulate matter with an aerodynamic diameter ≤10 μm (PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO)) prior to a measurement of creatinine were assessed with the ordinary kriging method. Mixed-effect linear regression models were used to assess associations between air pollutants and eGFR, while controlling for potential covariates. eGFR values are expressed as percent change per interquartile range (IQR) increments of each pollutant. Results Lower eGFR was associated with higher concentrations of PM10 (−1.99%, 95% confidence interval (CI): −3.33, −0.63), SO2 (−4.89%, 95%CI: −6.69, −3.07), and CO (−0.97%, 95%CI: −1.96, 0.03). However, after adjusting for temperature, relative humidity, PM10, and SO2, no significant association was observed between CO and eGFR. Conclusions Our findings support the hypothesis that long-term exposure to high concentrations of PM10 and SO2 is associated with the progression of kidney dysfunction in subjects of the EGAT cohort study.

A modified rubber sheet smoking room was designed, constructed and tested, with uniform hot air flow inside in it, so that the temperature difference between any plane was less than 7 °C. This room can dry up to 1500 sheets in 72 h. Specific fuelwood consumption was 0.42 kg/kg of dried rubber. It consumed 67% less fuelwood and increased the fraction of good quality rubber sheets by 8.5% when compared to a conventional rubber smoking room. Thermal efficiency also increased from 6.9% to 15.7%. Moreover, the modified smoking room can save 1414 USD/year with payback period of 5.7 years. Therefore, the modified design can be recommended to rubber cooperatives for a better return.

We developed a theoretical model for the transport phenomena affected by shrinkage in rubber sheet drying. The conjugate approach involving the simultaneous transfer of momentum, heat and mass in the drying chamber and rubber sheet was investigated by computational fluid dynamics. An isotropic, linear elastic model was assumed, and the shrinkage was correlated with the moisture content evolution in the rubber sheet. The Arbitrary Lagrangian-Eulerian (ALE) method was used to solve the two-dimensional problem accounting for shrinkage. The shrinkage across the rubber sheet thickness was estimated at 9.1% and the moisture content was reduced from 0.4 to 0.05 kg-water/kg-dried sheet at an average holding relative humidity of 60% within 46 h. Simulations and experiments showed good agreement (R2 values for moisture content and shrinkage were 0.9809 and 0.9991, while RMSE were 0.0196 and 0.0091). The derived model can be used as a quality index evaluation for rubber sheet and for drying process optimization. Water activity can also identify regions that may be prone to microbial spoilage. The drying time was lower than for traditional sun drying of air dried sheets (as high as 152 h) or drying in a natural flow chamber (72 h).

A forced-convection rubber smoking room aimed to reduce time and save energy on natural rubber sheet drying. Exhaust hot air is recirculated to reduce heat losses and improve thermal efficiency of drying system. Moisture content (% dry basis); thermal efficiency; specific fuelwood, electricity and energy consumption are evaluated for half and full load conditions. Economic benefits were also investigated. The rubber smoking room can dry up to 1500 sheets in 48 h by fuelwood combustion with 0.88 kg/s inlet mass flow rate reduction from conventional drying time of 72 h. Specific fuelwood and electricity consumption were 0.56 kg and 0.075 kWh per kg of dried rubber sheet, respectively. Air flow in the rubber smoking room was uniform with maximum variation of 6.75 °C and the dried products are of high quality. The saving of fuelwood consumption is 55.5% as compare to conventional rubber smoking room. Thermal efficiency of the rubber smoking room is 14.3% under full load condition. The net present value, internal rate of return, and payback period of the smoking room were estimated to be 28,773 USD, 24.6% and 4.0 years. Therefore, new design represents not only a good financial return but also better rubber sheet quality.

A new design of a rubber smoking room for fast drying based on conventional rubber smoking room was tested. Effects of the operating parameters for the fast drying of rubber in a forced-convection rubber smoking room were investigated. Temperature distribution, moisture content, thermal efficiency, specific fuelwood, electricity and energy consumption were evaluated for drying of 1,500 rubber sheets. The suitable operating condition from the experiment is 60°C and 12 m/s for the temperature and velocity. The rubber sheet moisture content was reduced to 0.4% db within 36 hours, i.e. 36 hours less than conventional smoke drying. The variation temperature inside the rubber smoking room was near uniform with a maximum of 8.0°C. The temperatures ranges were 38.9-64.6°C at the front plane, 40.4-65.0°C at the middle plane, and 36.7-62.9°C at the rear plane. A new rubber smoking room can save up to 49.3% in fuelwood consumption as compared to conventional rubber smoking room. Hence, the new rubber smoke drying system is capable of enhancing thermal efficiency and saving energy compared to existing rubber smoking room.

A nanoparticles real-time sensor in the present study was designed using corona discharge integrated with quartz crystal microbalance (QCM) or Nano-QCM detector. We investigated the following factors affecting the measurement accuracy of the detector; needle to plate distance, flow rate, and number of particles on QCM. DC high voltage power supply of 7 kV was used to maintain the positive corona voltages difference in the charger. The mass sensitivity of 10 MHz AT-cut QCMs coated by plate rigid gold film were investigated. The monodisperse aerosol particles smaller than 300 nm were initially used for the testing of the system. They were charged with negative corona voltages and then deposited on the surface of QCM electrode. Sauerbrey equation was used to describe the frequency-mass relationship at the QCM surface. Results show that the above factors significantly affect the accuracy of the detector measurement. The particles can be collected on a QCM electrode using the partial breakdown high voltage (reach to breakdown points) in terms of needle-to-plate corona discharge. The optimal needle-to-plate distance is 6 mm with maximum mass change (frequency shift) on QCM electrode of 0.607μg/min. The QCM collection efficiency of nanoparticles on the QCM electrode surface using corona discharge technique can be as high as 95% of total particles. Collection efficiency of PM0.1 is under investigation.

A new rubber smoking room has been designed, constructed and tested for natural rubber sheet smoke drying for better air temperature and flow distributions. Three-dimensional numerical model of rubber sheet drying using a conjugate approach is investigated by a computational fluid dynamics simulation. The optimal 2.5 m × 6.0 m × 3.5 m rubber smoking room contains 40 63.5 mm diameter hot gas supply ducts on the floor and four 0.2 m × 0.2 m and one 0.5 m × 0.5 m ventilating lids on the roof. Velocity and temperature of the drying air, and temperature and moisture content of rubber sheets have been predicted. The experimental and simulation results are in good agreement in terms of statistical parameters. R2 for temperature and moisture content are 0.980–0.987 and 0.972, respectively, while RMSE are 5.73–6.99 and 2.20. The drying time is significantly reduced from 72 h in a conventional natural-flow smoking room to 48 h in this new design room.

Smallholder rubber producers typically dry rubber in the open air, a process that takes about seven days, allowing the rubber to deteriorate and thus decreasing the price obtained by the producers. Solar dryers decrease the drying time by 2–3 days, thereby yielding a higher quality product. In this study, performances of mixed-mode and indirect solar drying systems have been investigated for 30 natural rubber sheets. Drying efficiency of the mixed-mode dyer is 15.4% which is higher than the indirect solar dryer (13.3%). The moisture contents of rubber sheets are reduced from 32.3 to 2.0% and 29.4 to 8.0% on a wet basis for mixed-mode and indirect solar drying, respectively, in 4 days. Hii et al. model is the combination of the Page and Two-term drying model. This model is found to best describe the natural rubber sheet drying behavior in both mixed-mode and indirect solar dryers. Coefficient of determination and root mean square error for mixed-mode and indirect solar drying of natural rubber are 0.998 & 0.0096 and 0.996 & 0.0109, respectively. Performance of the mixed-mode dryer is superior to the indirect solar dryer. Therefore, mixed-mode solar dryers are recommended for natural rubber sheet drying to smallholders.

This study investigated the yields and characteristics of bio-oil, biochar and pyrolysis gas obtained from pyrolysis and co-pyrolysis of rubber wood sawdust (RWS) and oil palm trunk (OPT) by using an agitated bed pyrolysis reactor. Co-pyrolysis of RWS and OPT was performed at the mixing ratio of 50:50 (wt.). The biomass samples were pyrolyzed at temperatures of 400, 450, and 500 °C under specific conditions. The results indicated that the yields of the bio-oil, biochar and pyrolysis gas were in the ranges of 38.5-46.5, 22.27-28.68 and 30.1-36.9 wt.%, respectively. Pyrolysis of RWS at 500 °C provided the most bio-oil. Co-pyrolysis of RWS and OPT could improve the product yield and quality. The bio-oil had relatively high water content, while its pH was low. The main compounds of bio-oil were oxygenated compounds such as acetic acid, phenols and 2-Propanone, 1-hydroxy-, determined by GC-MS. The higher heating value (HHV) of bio-oil ranged from 16.1 to 20.36 MJ/kg. The biochar had high carbon content and low oxygen content in proximate and ultimate analysis, and based on FTIR. The HHV of biochar was in the range from 26.35 to 29.6 MJ/kg. The biochar also was highly porous, which was revealed by SEM and BET. The pyrolysis gas mainly contained CO, CO2, H2 and CH4, and its heating value was in the range from 3.23 to 6.7 MJ/m3. Based on these results, the RWS and OPT are alternative and challenging biomasses for conversion to biofuels and value-added products via pyrolysis.