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Polystyrene foam (PSF), has been used widely in oyster farming in Taiwan and is responsible for generate approximately 120,000 – 200,000 pieces floating PSF waste every year, this causes some issues related to its treatment, including, clogging during incineration, lack of economic benefits, and carcinogenic, and non-biodegradable components, and it also a menace to the seashore due to becoming debris. In this study, PSF waste was treated via an atmospheric-pressure microwave plasma reactor to obtain methane (CH4) and hydrogen (H2). The using of nitrogen as the carrier gas and higher microwave power (1200 W) show greater results as compared to argon in the production of H2 at concentrations of 4739 ppm, while the results for CH4 were less than 300 ppm. Higher amounts of PSF waste (0.2 g) indicate the production of CH4 and H2 at concentrations of 19,657 ppm and 440 ppm, respectively. The results of SEM-EDX and XRD testing confirmed the transformation of the PSF structure and a reduction of carbon (C) in the final residue. The application of atmospheric-pressure microwave plasma not only treats PSF waste but produces H2 and CH4 that recycles PSF waste as energy gases. This research contributed to an understanding of how plasma technology can be used to treat solid waste and produce valuable gases.

Both the air quality index (AQI) and indicatory air pollutants of Anqing, Hefei, and Suzhou near central China from 2017 to 2019, and the impact of COVID-19 epidemic prevention and control actions on air quality were investigated. The combined data for the three cities from 2017 to 2019 indicated that the lowest AQI (averaged 78.1) occurred in the summer season, for which the AQI proportions for classes I, II, III, IV, V, and VI were 25.6%, 49.9%, 21.9%, 2.7%, 0%, and 0%, respectively. The highest (AQI average of 112.6) was in winter, for which the proportions were 7.4%, 39.5%, 33.3%, 12.5%, 7.2%, and 0.1%, respectively. PM2.5, PM10, and NO2 in order were the most important indicatory air pollutants for AQI classes IV, V, and VI, which all prevailed in winter and spring, while O3 was the indicatory air pollutant that occurred most in summer. The COVID-19 event, which triggered global attention, broke out at the end of 2019. This study also investigated and compared the air quality levels in the three cities from January to March 2017–2019 with those in 2020. The results showed that during February 2020, in the three cities, the average ambient air concentrations of PM2.5, PM10, SO2, CO, and NO2 were 41.9 µg m–3, 50.1 µg m–3, 2.18 ppb, 0.48 ppm, and 8.97 ppb, and were 46.5%, 48.9%, 52.5%, 36.2%, and 52.8%, respectively, lower than those in the same month in 2017–2019, respectively. However, the O3 average concentration (80.6 ppb) did not show significant fluctuations and even slightly increased by 3.6%. This is because a lower concentration of NO2 resulted in constraints on the reaction of NO + O3, so the O3 level could not be effectively further reduced. In addition, this study also analyzed and compared the five highest daily AQIs from February 2017–2019 with those of 2020 for the three cities. The mean AQI for the 5 days with the highest daily AQI (averaged 122.6) in February 2020 was 45.1% lower than that for February 2017–2019 (averaging 223.2), and the indicatory air pollutant was always PM2.5, which decreased by 46.7% (from 173.6 to 92.6 µg m–3). It is clear that during the COVID-19 epidemic prevention and control action periods, the air quality near central China improved significantly.

In early 2020, the COVID-19 epidemic spread globally. This study investigated the air quality of three cities in Hubei Province, Wuhan, Jingmen, and Enshi, central China, from January to March 2017–2020 to analyze the impact of the epidemic prevention and control actions on air quality. The results indicated that in the three cities, during February 2020, when the epidemic prevention and control actions were taken, the average concentrations of atmospheric PM2.5, PM10, SO2, CO, and NO2 in the three cities were 46.1 µg m–3, 50.8 µg m–3, 2.56 ppb, 0.60 ppm, and 6.70 ppb, and were 30.1%, 40.5%, 33.4%, 27.9%, and 61.4% lower than the levels in February 2017–2019, respectively. However, the average O3 concentration (23.1, 32.4, and 40.2 ppb) in 2020 did not show a significant decrease, and even increased by 12.7%, 14.3%, and 11.6% in January, February, and March, respectively. This is because a lower concentration of NO2 resulted in constraints on the NO + O3 reaction, and the O3 could not be effectively further depleted. In addition, the average air quality index (AQI) for the three cities in January, February, and March 2020 were 32.2%, 27.7%, and 14.9% lower than the levels in 2017–2019, respectively. Based on the AQIs for the three cities, the combined proportions of Class I and Class Ⅱ in January, February, and March 2020 increased by 27.9%, 24.8%, and 4.3%, respectively, while the combined proportion of AQI Classes III, IV, V, and VI was reduced from 34.8% to 15.8%. In addition, in the first three months of 2020, the indicatory air pollutants in the three cities for the AQIs were predominant in the following order: PM2.5 (72.0%), O3 (16.4%), PM10 (8.3%), NO2 (2.9%), and CO (0.4%). This study provides useful information for establishing a scientific air pollution control strategy and is a valuable reference for future research on improving urban air quality.

Scooter emissions have attracted attention in recent years because of human exposure to their direct effects in urban areas. Trace toxics, such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) have thus become important in scooter emissions. In this work, ten Tier 5 and 6 scooters were tested using a 100-second model to analyze their PCDD/F and PCB emissions and compare the results with previous Tier 3 studies. Tier 5 and 6 scooters emitted 1.86–2.91 and 0.133–0.298 pg WHO-TEQ Nm-3 of PCDD/Fs and PCBs, respectively. It was interesting to find that the PCDD/Fs were reduced by 94.6–97.4% and 99.4–99.6% in Tier 5 and 6 motors, respectively. The congener profiles of PCDD/Fs were affected by improving the emission control. The domination of highly chlorinated congeners shown in Tier 3 was reduced in Tier 5 with increases in low chlorinated PCDFs. This showed that de novo synthesis occurred and could be inhibited by the OBD system in Tier 6. The tailpipe renews reduced 60.0–93.8% of PCDD/Fs and 85.3–97.7% of PCB emissions, but several cases would still exhibit a delay for stable operation of a catalytic converter. The annual emissions of PCDD/F TEQ was calculated based on the statistics in 2019 and tested as 1.63 g WHO-TEQ. It could be 99.7% reduced to 3.55 mg by replacing all scooters with Tier 6. Consequently, the improvement of electronic fuel injection and on-board diagnostics systems from a carburetor without feedback control not only reduced the regulated pollutants but effectively reduced PCDD/F emissions.

This study provides an investigation of atmospheric PM2.5, PM10, SO2, NO2, CO, and O3 in the period from 2015–2017 in the southwestern and central part of Taiwan. In addition, the seasonal distribution of six AQI classes and corresponding primary pollutants were further analyzed. The daily AQIs were 15–194 in 2015, 17–213 in 2016, and 16–184 in 2017, respectively. During the three year period, in the studied area, the mean proportions of levels with Grade I, II, III, IV, V, and VI were 3%–31%, 30%–57%, 17%–46%, 0%–12%, 0%–1% and 0% in spring; were 38%–76%, 21%–57%, 0%–10%, 0%–2%, 0% and 0% in summer; were 2%–45%, 34%–77%, 13%–36%, 0%–18%, 0% and 0% in fall, and were 0%–12%, 38%–67%, 24%–41%, 1%–22%, 0% and 0% in winter. Generally, it was found that summer has the best air quality and that winter has the worst, where spring and fall are similar in terms of air quality. PM2.5 was the typical primary air pollutant when the AQI classes were 51–200, followed by O3 in summer, spring and fall, and PM10 in winter. As for class 201–300, the primary air pollutant was O3 and the 300–500 class did not occur.

The object of this study is to investigate the emission characteristics of reclamation of refuse-derived fuel (RDF) to evaluate the feasibility of substitution of RDF for current fuels. The cutting oil collected from a canned-food factory was pretreated, mixed with wood dust and bentonite, and was remolded into pellet RDF. Input materials, including coal, wood dust, and remolded RDF, were reclaimed in a steam generation plant. The pollutant characteristics of bottom ash, fly ash, and flue gas were analyzed to evaluate the combustion performance of the tested fuels. The PCDD/F concentration of the flue gas in the runs without coal (19.6 and 21.9 ng I-TEQ Nm–3) was two orders higher than those in the runs with coal (0.226 and 0.017 ng I-TEQ Nm–3) due to partial smoldering. Except for coal, the substitution of RDF for wood dust also reduced the formation of PCDD/Fs. According to the monitoring data for CO, O2, and combustion efficiency, RDF further improved the combustion condition with the aid of coal. The results show that reclamation of RDF is a promising method to take both waste treatment and energy regeneration into consideration.

Nitrogen dioxide (NO2) is a pollutant that directly harm the human respiratory system, lead to inflammation, as well as to form the secondary aerosol pollutants. The main NO2 sources, combustion or thermal processes, were well controlled. However, the metal etching operation in semiconductor industry emits flue gases with reddish-brown NO2 fume that leads to visibility reduction, acidic odor, as well as negative effects on human health. In this study, a stream of flue gases with low NO2 (230 ± 10 ppm) and NO (50 ppm) concentrations were conducted to pass through an activated carbon-packed fixed bed for analyzing the adsorptive conversion behavior of NO2 by the activated carbon (AC) at room temperature. The repeated adsorption test was carried out by washing the regenerated waste carbon with a caustic solution and water and drying. Results propose that at the beginning of adsorption, nitrogen dioxide combined with carbon to form NO and desorbed from carbon surface. The net adsorptive conversion removal capacity of NO2 by the virgin AC and regenerated AC was 224 and 155 mg g–1 AC, respectively. Regeneration restored around 70–75% of effective surface area, pore volume, and adsorptive conversion capacity of the virgin AC. Leached caustic solution obtained from the carbon regeneration contained only nitrate and the phenomena indicates the adsorbed -C2(ONO2) hydrolyzed following the Eq. (2) -C2(ONO2) + H2O → 3 -C* + -C(O) + 2 HNO3, where -C* denotes active site on the carbon surface.

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in fly ash may pose health threats to onsite workers due to their inevitable dispersion in the working environments during recycling and disposal of fly ash from Municipal Solid Waste Incinerators (MSWIs). Here, PCDD/Fs in fly ash from an MSWI in Southern Taiwan was analyzed from several perspectives. The results can be summarized as follows: (1) Through multiple comparison analyses, it was revealed that four types of congeners (OCDD, OCDF, 1,2,3,4,6,7,8-HpCDD and 1,2,3,4,6,7,8-HpCDF) have significantly higher concentrations than other species (p < 0.01). (2) 2,3,4,7,8-PeCDF represented the main contributor to the total toxic equivalent concentration (TEQ). The top three candidate indicators of total TEQ are OCDF, 1,2,3,4,6,7,8-HpCDF and 2,3,4,7,8-PeCDF, in which OCDF might be most powerful indicator of fly ash from similar sources. (3) It was indicated that all congeners correlated positively with each other (with R2 values in the range between 0.707–0.939); Meanwhile, the results of the cluster analysis unveiled the specific features of several congeners (such as 1,2,3,7,8,9-HxCDF, OCDD and OCDF). (4) Through assessing health risk with a Monte Carlo simulation, both the 95th percentile carcinogenic risk (CR) and non-carcinogenic risk (non-CR) for onsite workers exceeded the threshold limit and should be considered as significant risks for onsite workers. (5) The results of the sensitivity analysis suggested that concentration (CC) and exposure duration (ED) were the two most sensitive parameters in both the CR and non-CR assessment. The above findings could be useful for improving existing health risk mitigation/management strategies for onsite workers in waste incineration plants.

The emissions factors of PCDD/Fs from the stack flue gas, bottom ash and fly ash of a municipal solid waste incinerator (MSWI) were analyzed in this study. The congner profiles of PCDD/F mass were dominant in OCDD and OCDF; however, those of PCDD/Fs-TEQ were mainly 2,3,4,7,8-PeCDF and 1,2,3,7,8-PeCDD in all samples. The PCDD/F emission factors of MSWI per metric ton of waste incinerated from the stack flue gas, bottom ash and fly ash were at an averaged of 0.0919, 7.20 and 12.8 μg PCDD/Fs-WHO_(2005)-TEQ ton^(-1), respectively. Futhermore, the emission factor of MSWI in the unit of electricity produced averaged 0.185, 14.5 and 26.3 μg PCDD/Fs-WHO_(2005)-TEQ (MWh)^(-1), respectively. As the results shown in this study, the majority of total PCDD/Fs-WHO_(2005)-TEQ were mainly in both bottom ash and fly ashes. From long-term perspective, the disposal of both bottom and fly ashes should pay more attention to this issue. The results of this study provide useful information for both further studies and environmental control strategies aimed at persistent organic compounds (POPs).

Wet deposition is an important mechanism for removing air pollutants from the atmosphere. The total PCDD/Fs-WHO2005-TEQ wet deposition from 2018–2020 was investigated for Beijing and Tianjin City in this study. In addition, the gas-particle partitioning of wet deposition, the total PCDD/Fs-WHO2005-TEQ concentrations in the rain, the PM2.5-bound total PCDD/Fs-WHO2005-TEQ content, and the PM2.5 concentration were also studied for Beijing and Tianjin City, respectively. Between 2018 to 2020, as a whole, the average seasonal variations in PCDD/F wet deposition fluxes in spring, summer, fall, and winter were 50.50, 41.47, 23.03 and 16.76 pg WHO2005-TEQ m–2 month–1, respectively, while in Tianjin, they were 35.30, 42.40, 13.37, and 14.77 pg WHO2005-TEQ m–2 month–1, respectively. Because the two cities have more rainfall in spring and summer than they do in fall and winter, rainfall has a significant influence on the wet deposition flux. In regard to PCDD/Fs-WHO2005-TEQ in the rain, in Beijing, the average total PCDD/Fs-WHO2005-TEQ concentration in the rain in spring, summer, fall, and winter were 1.70, 0.39, 1.42, and 1.52 pg WHO2005-TEQ L–1, respectively, while those in Tianjin, were 1.73, 0.42, 1.35, and 1.88 pg WHO2005-TEQ L–1, respectively. The above results show that the total PCDD/Fs-WHO2005-TEQ concentrations in the rain are significantly lower in summer, which is mainly due to the fact that in summer, the total PCDD/Fs-WHO2005-TEQ concentrations in the air are lower, and the proportion of the gas phase is increased. When the total PCDD/Fs-WHO2005-TEQ concentrations in the air are washed away by a heavy rainfall, the PCDD/F concentrations are diluted.

The effects of eighteen precipitation (rain and snow) events in both Jinan and Qingdao cities in Shandong Province, China, on the air quality and dry deposition flux in PCDD/Fs were investigated. A total of fifteen precipitation events were positive for AQI reductions. In these events, the AQI ranged between 29 and 195 and averaged 79, and the PM2.5 concentration ranged between 10 and 146 µg m–3 and averaged 39 µg m–3. A comparison of the average of the fifteen events during and after the precipitation, respectively, with that before the precipitation, showed AQI reduction fractions of 23% and 32%, respectively, while those for the PM2.5 concentration were 27% and 42%, respectively; the PCDD/F dry deposition ranged between 145.7 and 1152 pg WHO2005-TEQ m–2 day–1 and averaged 476.7 pg WHO2005-TEQ m–2 day–1. A comparison of the above events after the precipitation showed that the reduction in the fraction of the PCDD/F dry deposition flux averaged 35%. However, the other three precipitation events demonstrated an elevation in the AQI, where the AQI ranged between 24 and 147 and averaged 91, and the PM2.5 concentration ranged between 4 and 112 µg m–3 and averaged 42 µg m–3. A comparison of the values during and after the precipitation, respectively with those before the precipitation, revealed increased AQI fractions of –18% and 28%, respectively, while those for the PM2.5 concentration were 16% and 51%, respectively. In the three AQI elevation events, the PCDD/F dry deposition flux ranged between 191.3 and 946.2 pg WHO2005-TEQ m–2 day–1 and averaged 473.0 pg WHO2005-TEQ m–2 day–1. A comparison of the period after the precipitation with that before the precipitation showed that the increase in the fraction of the PCDD dry deposition flux averaged 20%. The above results revealed that, in general, rain and snow did improve the air quality in the areas of interest. This was due to the fact that the particulates or dissolved gaseous pollutants were scavenged out of the air and carried the aerosols down to the ground. However, in some events, after rainy or snowy days, increases in the source emissions and reductions in the atmospheric vertical convection did result in an elevation in the AQI, PM2.5 concentrations, and PCDD/F dry deposition in the ambient air. The results of this study provided useful information contributing to air quality management.

In this study, the atmospheric total-PCDD/Fs-WHO2005-TEQ concentrations, gas-particle partitioning, PM2.5 concentration, PM2.5-bound total PCDD/Fs-WHO2005-TEQ content and dry deposition flux in Shanghai and Nanjing were investigated from 2018-2020. In Shanghai, the total PCDD/Fs-WHO2005-TEQ concentration dropped from 0.0291 pg-WHO2005-TEQ m–3 from 2018–2019 to 0.0250 pg-WHO2005-TEQ m–3 in 2020, while in Nanjing, it dropped from 0.0423 pg-WHO2005-TEQ m–3 to 0.0338 pg-WHO2005-TEQ m–3. The average concentrations of PCDD/Fs-WHO2005-TEQ in spring and winter in Shanghai and Nanjing were 47.6% and 53.8% higher than those in summer, respectively. From 2018-2019, the average particle phase fractions of total-PCDD/Fs-WHO2005-TEQ in Shanghai and Nanjing were 50.3% and 57.5%, respectively, while in 2020, they were 47.8% and 55.1%, respectively. From 2018-2019, the average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content was 0.342 and 0.493 ng-WHO2005-TEQ g–1 in Shanghai and Nanjing, respectively, while in 2020, it was 0.312 and 0.489 ng-WHO2005-TEQ g–1, respectively. In Shanghai and Nanjing, the average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content in spring and winter was 77.5% and 73.2% higher than that in summer, respectively. From 2018–2019, the dry deposition flux of total-PCDD/Fs-WHO2005-TEQ was 316.3 and 460.5 pg WHO2005-TEQ m–2 month–1 in Shanghai and Nanjing, respectively, while in 2020, it was 272.5 and 368.4 pg WHO2005-TEQ m–2 month–1, respectively. The average dry deposition flux of total-PCDD/Fs-WHO2005-TEQ in spring and winter was 47.6% and 53.8% higher than that summer in Shanghai and Nanjing, respectively. The above results indicate that COVID-19 in 2020 had a positive effect on air quality improvement in PCDD/Fs. On average, more than 98.88% of the total PCDD/Fs-WHO2005-TEQ dry deposition flux was primarily contributed by the particle phase. This was attributed to the fact that dry deposition of particle phase PCDD/Fs was mainly due to gravitational settling accompanied by higher dry deposition velocities, while the gas phase PCDD/Fs were deposited mostly by diffusion at a lower dry deposition velocity. © The Author(s).

This study mainly involved conducting an atmospheric sensitivity analysis of the dry deposition and PM2.5-bound content of total PCDD/Fs-WHO2005-TEQ, respectively. The results for Fuzhou and Xiamen cities showed that the total PCDD/F mass concentration was the factor most positively correlated to the dry deposition flux: When Delta P/P ranged from -50% to 0%, Delta S/S ranged from -66.0% to 0%, but when Delta P/P increased from 0% to +50%, Delta S/S increased from 0% to +66.0%, respectively. The second factor positively correlated with the deposition flux was the PM2.5 concentration: When Delta P/P ranged from -50% to 0%, Delta S/S ranged from -63.3% to 0%;when Delta P/P increased from 0% to +50% and +100%, Delta S/S ranged from 0% to +20.8 and -0.9%, respectively. Ambient air temperature was found to be less sensitive to dry deposition fluxes in total PCDD/Fs-WHO2005-TEQ: When Delta P/P ranged from -50% to -17% and 0%, Delta S/S ranged from -17.0% to +5.6% and 0%;when Delta P/P increased from 0% to +50%, Delta S/S increased from 0% to -84.5%, respectively. The sensitivity analysis for PM2.5-bound total PCDD/Fs-WHO2005-TEQ content had similar results to those for dry deposition flux. In addition, in 2018, 2019, and 2020, the annual average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content at Fuzhou and Xiamen was 0.430, 0.127, 0.303, and 0.426 ng-WHO2005-TEQ g(-1) in the spring, summer, autumn and winter, respectively, which showed that summer had the lowest content, while spring and winter had the highest. The results of this study provided useful information for gaining a deeper understanding of both dry deposition and particle-bound of PCDD/Fs in the ambient air.