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The implementation of roadside air purifiers has emerged as an effective active control measure to alleviate air pollution in urban street canyons. However, technical questions raised under real conditions remain challenging. In this study, we conducted a pilot-scale investigation involving seven units of self-designed roadside air purifiers in an urban street canyon in Hong Kong. The air cleaning effects were quantified with an air quality sensor network after rigorous quality control. The removal efficiencies of Nitrogen dioxide (NO2), Fine suspended particulates (PM2.5), Carbon monoxide (CO), and Nitric oxide (NO) were determined by comparing with simultaneously measured ambient concentrations, with hourly average efficiencies of 14.0 %–16.9 %, 3.5–10.0 %, 11.9 %–18.7 %, and 19.2 %–44.9 %, respectively. Generally, the purification effects presented variations depending on the ambient pollutants' levels. Higher ambient concentrations of NO2, PM2.5, CO correlated with increased purification effects, while NO presented the opposite trend. The influence of interval distance combined with spatial distribution indicated the operation of purifiers will induce local NO2 attenuation even at an interval distance of four meters. Statistical analysis delivered evidence the air cleaning ability exhibited optimal performance when relative humidity level is ranged from 70 % to 90 %, aligning with the prevailing conditions in Hong Kong. Additionally, improved purification effects were observed at the downwind direction, and their performance was enhanced when the wind speed exceeded 2.5 m/s. Moreover, we estimated the operational lifetime of the air purifiers to be approximately 130 days, offering crucial information regarding the filter replacement cycle. This work serves as a pioneering case study, showcasing the feasibility and deployment considerations of roadside air purifiers in effectively controlling air pollution in urban environments. © 2023 Elsevier B.V.

Air pollution is a major environmental issue in Hong Kong, and ozone (O3) is one of the most concerned pollutants because of its notable rising trend during the past three decades. Volatile organic compounds (VOCs) are the main precursors to O3 formation, but their characteristics over coastal water in Hong Kong were not well studied due to a lack of observations. We conducted sixteen cruise campaigns and collected 109 VOC canister samples over Hong Kong coastal water between August 2020 and July 2021. 95 VOC species were analyzed from the samples by a GC-MSD/ECD/FID system to investigate their concentration distributions, reactivities, and potential emission sources. The average concentrations of alkanes, alkenes, aromatics, alkynes, halocarbons, and alkyl nitrates over Hong Kong coastal water were 8.94 ± 5.64 ppbv, 1.18 ± 1.09 ppbv, 1.90 ± 1.48 ppbv, 1.05 ± 0.63 ppbv, 3.82 ± 1.23 ppbv, and 0.09 ± 0.04 ppbv, respectively. Source apportionment results from positive matrix factorization (PMF) analysis suggest that liquefied petroleum gas (LPG) usage (24.9%), biomass burning (19.4%), gasoline evaporation (16.2%), ship emissions (15.6%), solvent usage (14.8%), and aged air mass (9.1%) were main VOC sources over Hong Kong coastal water during the study period. Toluene, ethene and m + p-xylene were found to be the top contributors to the O3 formation over Hong Kong coastal water, while isoprene had less O3 formation contributions compared with land measurements. This study provides important insights into the reactivities and sources of VOCs over Hong Kong coastal water and serves as a stepping stone to understanding the VOC characteristics and O3 formation mechanisms in a complex coastal environment.

Tropospheric ozone (O3) is an important air pollutant with a significant impact on human health, agricultural crops, ecosystems, and global warming. In the Greater Bay Area (GBA), O3 pollution concentration has shown an increasing trend in the last decade. It has become crucial to gain a deeper understanding of the factors contributing to this phenomenon. This study deployed a sensor network with high spatial-temporal resolution measurement of O3 and its key precursors in mid-November 2022 during a severe O3 episode. The spatialtemporal characteristics and contributions of local generation and regional transport were analyzed based on clustering methodology. The regional distribution and possible sources were also discussed in combination with the NAQPMS model and the HYSPLIT model. The results indicated that the O3 episode was dominated by local generation while regional transport contributed to an average of 20 ppb in the GBA region, under the influence of sea-land winds and low-level anticyclones. Guangzhou showed the most severe O3 pollution, with a maximum hourly concentration near 120 ppb, followed by Zhongshan, Dongguan, etc. The O3 pollution of Hong Kong and Macau showed faster dispersion and less accumulation during the daytime. The O3 concentrations of Huizhou and Jiangmen were the lowest, but the nighttime O3 accumulation was close to 40 ppb during the episode. The study demonstrated ad-hoc deployment of high-density sensor networks is an effective tool to study the formation and transport of O3 during episodic days with synoptic approaches by ad-hoc high-density sensor network measurement and combination of modeling tools.

Air pollutants from traffic make an important contribution to human exposure, with pedestrians likely to experience rapid fluctuation and high concentrations on the pavements of busy streets. This monitoring campaign was on Hennessy Road in Hong Kong, a densely populated city with deep canyons, crowded footpaths and low wind speeds. Kerbside NOx concentrations were measured using electrochemical sensors with baseline correction and subsequently deconvoluted to determine concentrations at 1-s resolution to study the dispersion of exhaust gases within the first few metres of their on-road source. The pulses of NOx from passing vehicles were treated as segments of a Gaussian plume originating at the tailpipe. The concentration profiles in segments were fit to a simple analytical equation assuming a continuous line source with R2 > 0.92. Least squares fitting parameters could be attributed to vehicle speed and source strength, dispersion, and sensor position. The width of the plume was proportional to the inverse of vehicle speed. The source strength of NOx from passing vehicles could be interpreted in terms of individual emissions, with a median value of approximately 0.18 g/s, but this was sensitive to vehicle speed and exhaust pipe position. The current study improves understanding of rapid changes in pollutant concentration in the kerbside environment and suggests opportunities to establish the contribution from traffic flow to pedestrian exposure in a dynamic heavily occupied urban microenvironment.

Impressions of a place are partly formed by smell. The urban waterfronts often leave a rather poor impression due to odor pollution, resulting in recurring complaints. The nature of such complaints can be subjective and vague, so there is a growing interest in quantitative measurements of emissions to explore the causes of malodorous influence. In the present work, an air quality monitor with an H2S sensor was employed to continuously measure emissions of malodors at 1-min resolution. H2S is often considered to be the predominant odorous substance from sludge and water bodies as it is readily perceptible. The integrated means of concentration from in situ measurements were combined with the AERMOD dispersion model to reveal the spatial distribution of odor concentrations and estimate the extent of odor-prone areas at a daily time step. Year-long observations showed that the diurnal profile exhibits a positively skewed distribution. Meteorology plays a vital role in odor dispersion; the degree of dispersion was explored on a case-by-case basis. There is a greater likelihood of capturing the concentration peaks at night (21:00 to 6:00) as the air is more stable then with less tendency for vertical mixing but favors a horizontal spread. This study indicates that malodors are changeable in time and space and establishes a new approach to using H2S sensor data and resolves a long-standing question about odor in Hong Kong.Implications: this study establishes a new approach combining dispersion model with novel H2S sensor data to understand the characteristics and pattern of odor emanated from the urban waterfront in Hong Kong. The sensor has dynamic concentration range to detect the episodic level of H2S and low level at background conditions. It provides more complete information in relation to odor annoyance, as well as quantitative information useful for odor regulation

Ozone distribution and variation within the Planetary Boundary Layer (PBL) present challenges for air quality management. UAV-based ozone profile measurements offer advantages in terms of high vertical resolution throughout the PBL and flexibility. However, previous studies on vertical variation in the Pearl River Delta (PRD) region have rarely focused on measuring the vertical ozone variation during ozone pollution episodes. In this study, we integrated UAV-based monitoring, ground monitoring, and numerical modeling to investigate ozone variation, driving processes, and source regions of pollution episodic period. UAV-based observations during a 2021 ozone episode at rural areas in the PRD region revealed three ozone profiles: increasing, well-mixed, and decreasing with height. Morning profiles showed multiple layers influenced by meteorology, while peak ozone hours exhibited a well-mixed pattern. By integrating the validated numerical model, we found that chemical processes (CHEM) contributed positively to ozone episodes in both rural and urban scenarios, especially at the middle and upper PBL. Horizontal advection (HADV) significantly contributes to the episode in rural cases, while urban cases were significantly affected by vertical diffusion (VDIF). Backward trajectory and source apportionment analyses categorized PRD cities into upwind/non-upwind/local categories, showing ozone pollution originating from both upwind and non-upwind cities at different vertical levels. It is because wind shear influenced diverse source regions, and the transport channel for city-level ozone pollution exhibited daily and vertical changes. Moreover, it could also be contributed by the formed regional mixing ozone layer (ROM Layer) throughout the PBL during persistent ozone episodes, triggered by enhanced CHEM and significantly contributed by the VDIF. The ROM Layer at center cities, influencing ground-level ozone downwind through horizontal transport and vertical exchange. Conside

Over the years, vehicular emissions have been the main contributor to the deterioration of urban air quality. However, quantification of real-world vehicular emissions is quite limited in low- and middle-income countries like India. Developing real-world vehicle emission factors (EFs) using reference-grade instruments requires a significant amount of resources. This study aims to develop the individual and fleet vehicle EFs and the fraction of high-emitting vehicles using high-time resolution, low-cost sensors from near-road measurements – a first-of-its-kind study in India. Traffic and air pollutant measurements were conducted at the kerbside of a street canyon in Mumbai. The individual vehicle fuel-based EFCO and EFNOx were estimated using the plume-identification technique coupled with the information obtained from the vehicle registration number plates. The fleet mean (±SD) EFCO, EFNO, and EFNO2 were 6.30 (±3.16), 1.38 (±1.17), and 0.43 (±0.32) g/kg, respectively, while for EFPM1, EFPM2.5, EFPM2.5-10, and EFPM10 were 0.70 (±0.34), 1.19 (±0.57), 0.90 (±0.65), and 2.09 (±1.05) g/kg, respectively. The developed individual vehicle EFCO and EFNOx were greatly varied within each vehicle type due to differences in emission control technology, engine size, and the prevalence of “super-emitters”. There was no substantial difference in EFCO and EFNOx among the different BS emission standards across almost all vehicle types. The reconstructed fleet EFCO and EFNOx from the developed single-vehicle EFs were 1.4 and 1.9 times higher than the recorded fleet EFs. Approximately 14% of vehicles in the fleet were identified as super-emitters, responsible for 37–54% of total emissions, primarily from private passenger vehicles such as cars and two-wheelers. The EFCO and EFNOx from these high-emitters were 3–30 times greater than the laboratory-reported emissions. Our study suggests that improving emission standards alone is not enough to decrease tailpipe emissions from vehicles. P

This study presents a novel approach utilising helicopters as platforms for real-time monitoring of air pollutants and routine canister sampling to enhance our understanding of air pollution in the Greater Bay Area (GBA). By employing this method, local spatial and vertical distribution of various air pollutants (including CO, NO, NO2, O3, PM2.5 and VOCs) in Hong Kong could be obtained within hours for fast snapshots of air pollution. The investigation involved hovering ascent and descent operations above Tap Mun Island, revealing no indication of self-contamination from engine exhaust during the hovering process. The analysis of air pollutant spatial distribution in and around Hong Kong through multiple trips showed higher concentrations of Osub>3 and PM2.5 in the northern region on days with episodic pollution, while urban areas exhibited elevated levels of NO2 and CO concentration. In contrast, Tap Mun Island as the background area demonstrated relatively low pollutant concentrations. The vertical distribution of concentrations of VOC species with high ozone formation potential revealed minor variations at sampling altitudes of 500 ft and 1000 ft over the waters around Hong Kong. The novel monitoring protocol using helicopters as platforms proves to be an effective approach for pollution episode investigations, offering valuable insights in the formation mechanisms and transport pathways of O3. The findings of the heterogenous spatial distribution of O3 and its precursors underscore the significance of ongoing monitoring efforts and policy development to combat air pollution in the dynamic GBA and similar regions worldwide.

While the crucial roles of ozone (O3) transport in the planetary boundary layer (PBL) have been acknowledged for some time, there is currently limited knowledge about this aspect primarily due to the limited availability of measurements to determine the characteristics of the PBL. In this study, measurements from a wind Light Detection and Ranging (LiDAR) system were taken to monitor vertical profile of wind pattern at an urban site in Hong Kong in September 2022, a period when the city was frequently impacted by tropical cyclones and experienced severe O3 pollution levels. The PBL height was identified based on the vertical profile of wind speed shear. By combining information on the PBL height, vertical wind profile, and O3 concentration, we performed a cross-sectional analysis to explore the total horizontal flux (THF) of O3 across the PBL in Hong Kong. Throughout the entire study month, the THF of O3 exhibited a predominant easterly component. However, during the O3 pollution episodes, the THF of O3 exhibited a predominant westerly component, indicating an increased regional transport from Greater Bay Area (GBA). The westerly winds between 240° and 300° contributed 61.2% to the total flux of O3 in the PBL during these episodes. In addition, clockwise veering winds were observed from the ground to the top of the PBL, which can be attributed to the Ekman spiral. As a result, during the O3 pollution episodes, the wind with the peak O3 flux shifted from westerly to northwesterly as the height increased in the PBL. The northwesterly THF of O3 between 290° and 300° reached its peak at 600 m above ground level during these episodes. These findings enhance our understanding of the 3D pollutant transports for both long-term averages and short-term pollution episodes in the GBA and Hong Kong. © 2023 Elsevier Ltd

This research explores the influence of renewable fuels, including three kinds of biodiesel along with ethanol on the physical properties and structural characteristics of particulate matter (PM) emitted from a diesel engine in comparison with pure diesel. After adding 10 vol% of grape seed biodiesel, coffee biodiesel and eucalyptus oil into diesel, three biodiesel blended fuels (10% grape seed biodiesel (DGs10), 10% spent coffee ground biodiesel (DC10) and eucalyptus oil biodiesel (DEu10)) were produced and tested in this study. Besides, one ethanol blend containing 9 vol% of ethanol and 1 vol% of biodiesel (blend stabilizer) was also tested to do the comparison. In the present study, scanning transmission electron microscope (STEM) and scanning electron microscope (SEM) were employed for analyzing the microstructure, nanostructure and electron diffraction pattern of PM. Raman spectrometer (RS) was also used for the analysis of structural characterization of PM. In addition, several experimental instruments like microbalance, measuring cup, viscometer, oxygen bomb calorimeter and Gas Chromatography-Mass Spectrometer (GC-MS) were employed to detect the fuel properties, including density, heating value, viscosity, composition and cetane number. A conclusion can be drawn that both biodiesel blends and ethanol blend have a changing effect on the PM properties compared to pure diesel, where biodiesel blends have a slightly weaker influence than ethanol blend. Regarding the biodiesel blends, DGs10 has more impact than DC10 and DEu10 in changes of PM properties, particularly in the reduction of PM mass, making it a good candidate for renewable fuel for diesel engines.

Traffic-derived nitrogen oxides (NOx) is a major component of kerbside pollution in large cities and represent an important source of exposure and health risk to urban populations, especially during the use of roadside pave-ments. The ratio of ambient NO2/NOx (xNO(2)) varies widely in urban environments, influenced by relative source strengths, but also oxidation. Primary NO2 emissions have changed over the years, with changes in engine and exhaust controls. Over the years 1998/2021 the NO2 fraction in exhaust (f(NO2)) in Hong Kong has changed from 0.05 in the late 1990s to values similar to 0.2 in the years 2010/2015, and has fallen to similar to 0.08 in recent years. To better understand f(NO2) from individual on-road vehicles, this study monitored NO and NO2 at the kerb in a busy street canyon in Hong Kong, capturing the rapid concentration changes in response to vehicles passing by. The kerbside xNO(2) was much lower (similar to 0.2) than that at the roadside air quality monitoring station (similar to 0.5) whose inlet was elevated some 3 m above the road nearby. Output from pollution sensors was deconvoluted to explore rapidly changing concentrations in the plume segments from individually identifiable vehicles as they passed and enable to estimate of the NO2 fraction in the exhaust for individual vehicle. Each vehicle was assigned to a type, Euro emission class and year of manufacture. The f(NO2) from individual vehicles depends on emission class, increasing from Euro 4 to Euro 6, while f(NO2) decreases as vehicles get older. The estimates of f(NO2) made at the kerb were similar to those derived for the local air quality monitoring station, but not necessarily that of the city as a whole, where f(NO2) varies by a factor of two.

The literature shows that information about the physical, chemical, and cell toxicity properties of particulate matter (PM) from diesel vehicles is not rich as the existence of a remarkable number of studies about the combustion, performance, and emissions of diesel vehicles using renewable liquid fuels, particularly biodiesels and alcohols. Also, the PM analyses from combustion of spent coffee ground biodiesel have not been comprehensively explored. Therefore, this research is presented. Pure diesel, 90% diesel + 10% biodiesel, and 90% diesel + 9% ethanol + 1% biodiesel, volume bases, were tested under a fast idle condition. STEM, SEM, EDS, Organic Carbon Analyzer, TGA/DSC, and Raman Spectrometer were employed for investigating the PM physical and chemical properties, and assays of cell viability, cellular reactive oxygen species, interleukin-6, and tumor necrosis factor-alpha were examined for investigating the PM cell toxicity properties. It is found that the application of both biodiesel and ethanol has the potential to change the PM properties, while the impact of ethanol is more than biodiesel on the changes. Regarding the important aspects, biodiesel can be effective for better human health (due to a decrease in cell death (−60.8%)) as well as good diesel particulate filter efficiency (due to lower activation energy (−7.6%) and frequency factor (−83.2%)). However, despite a higher impact of ethanol on the reductions in activation energy (−24.8%) and frequency factor (−99.0%), this fuel causes an increase in cell death (84.1%). Therefore, biodiesel can be an appropriate fuel to have a positive impact on human health, the environment, and emissions catalysts performance, simultaneously. © 2022 Elsevier B.V.

With growing urbanization and industrialization, problems such as poor disposal practices of solid waste and ensuing uncontrolled air pollution adjacent to landfill pose threats to human and environmental wellbeing. Ahmedabad is highly polluted urban city in India and unregulated burning of solid waste further aggravates already appalling situation caused by a large number of industries and vehicle fleets. The present work was carried out to understand sources of metals in ambient air surrounding a municipal landfill known as Pirana. For the study, surrounding area of the landfill was divided into 100 rectangular cells covering almost 5 km distance from its outer boundary. A location representing major land-use feature of each cell was classified. Sampling was carried out at these locations. A total of 100 PM5.0 samples were collected. Sampling was conducted for 3 h at each sampling location with samples collected on quartz filter paper. Measurements were performed over approximately 6 months from August to February, 2018. The filters were analyzed for metals using an Atomic Absorption Spectrometer. These measurements were used to identify pollution sources using positive matrix factorization technique and locate the hotspots of emission sources of heavy metals pollution. Five major sources namely, ferrous industry, nonferrous industry, vehicular emissions, re-suspended dust and solid waste burning/industrial coal combustion were identified and quantified. The average contributions of these sources to heavy metals were 20.7 ± 16.2, 18.4 ± 14.3, 19.9 ± 13.6, 21.4 ± 17.6, and 19.6 ± 10.6%, respectively. The average contribution from solid waste and industrial coal combustion is only 19.6% against the total from the combined remaining sources (~ 80.4), which means contribution from former will be lesser. Thus, solid waste burning is minor contributor for degradation of air quality; presence of many other sources around the site is actually the dominant cause

Hong Kong, a densely populated metropolis in Southeast Asia, has endured severe ozone pollution during last two decades. Volatile organic compounds (VOCs) are important for mitigating the ozone pollution as its major precursors. Numerous efforts have been made to investigate the ozone and its precursors in Hong Kong and surrounding Pearl River Delta region, while most previous studies relied on ground measurements. Supported by Hong Kong governments, we set up a 3-D monitoring framework to measure VOCs onboard airborne and seaborne platforms, as well as at multiple ground sites. Based on measurements of VOCs and critical pollutants (e.g., O3, NOx), we explored the distributions and characteristics of major VOC species, and assessed the contributions from emissions, transport, and photochemical reactions on ozone formation in Hong Kong. The results suggests the ozone productions were limited by VOC during episodes, while the relative incremental reactivity of aromatics and alkenes from solvent use and vehicle exhaust were substantial and warrants further consideration.

Photochemical regime for ozone (O3) formation is complicated in the sense that reducing emission of nitrogen oxides (NOx) may increase O3 concentration. The lockdown due to COVID-19 pandemic affords a unique opportunity to use real observations to explore the O3 formation regime and the effectiveness of NOx emission control strategies. In this study, observations from ground networks during the lockdowns were used to assess spatial disparity of the Ratio of Ozone Formation (ROF) for nitrogen dioxide (NO2) reduction in the Greater Bay Area (GBA) of China. The health risk model from Air Quality Health Index (AQHI) system in Hong Kong was adopted to evaluate the risk tradeoffs between NO2 and O3. Results show that the levels of O3 increase and NO2 reduction were comparable due to high ROF values in urban areas of central GBA. The ozone reactivity to NO2 reduction gradually declined outwards from central GBA. Despite the O3 increases, the NOx emission controls reduced the Integrated Health Risk (IHR) of NO2 and O3 in most regions of the GBA. When risk coefficients from the AQHI in Canada or the global review were adopted in the risk analyses, the results are extremely encouraging because the controls of NOx emission reduced the IHR of NO2 and O3 almost everywhere in the GBA. Our results underscore the importance of using a risk-based method to assess the effectiveness of emission control measures and the overall health benefit from NOx emission controls in the GBA. © 2022 Turkish National Committee for Air Pollution Research and Control

Traffic-related air pollution (TRAP) was monitored using a mobile sensor network on 125 urban taxis in Shanghai (November 2019/December 2020), which provide real-time patterns of air pollution at high spatial resolution. Each device determined concentrations of carbon monoxide (CO), nitrogen dioxide (NO2), and PM2.5, which characterised spatial and temporal patterns of on-road pollutants. A total of 80% road coverage (motorways, trunk, primary, and secondary roads) required 80-100 taxis, but only 25 on trunk roads. Higher CO concentrations were observed in the urban centre, NO2 higher in motorway concentrations, and PM2.5 lower in the west away from the city centre. During the COVID-19 lockdown, concentrations of CO, NO2, and PM2.5 in Shanghai decreased by 32, 31 and 41%, compared with the previous period. Local contribution related to traffic emissions changed slightly before and after COVID-19 restrictions, while changing background contributions relate to seasonal variation. Mobile networks are a real-time tool for air quality monitoring, with high spatial resolution (similar to 200 m) and robust against the loss of individual devices.

Exposure measurement error is an important source of bias in epidemiological studies. We assessed the validity of employing ambient (outdoor) measurements as proxies of personal exposures at individual levels focusing on fine particles (PM2.5) and black carbon (BC)/elemental carbon (EC) on a global scale. We conducted a systematic review and meta-analysis and searched databases (ISI Web of Science, Scopus, PubMed, Ovid MEDLINE®, Ovid Embase, and Ovid BIOSIS) to retrieve observational studies in English language published from 1 January 2006 until 5 May 2021. Correlation coefficients (r) between paired ambient (outdoor) concentration and personal exposure for PM2.5 or BC/EC were standardized as effect size. We used random-effects meta-analyses to pool the correlation coefficients and investigated the causes of heterogeneity and publication bias. Furthermore, we employed subgroup and meta-regression analyses to evaluate the modification of pooled estimates by potential mediators. This systematic review identified thirty-two observational studies involving 1744 subjects from ten countries, with 28 studies for PM2.5 and 11 studies for BC/EC. Personal PM2.5 exposure is more strongly correlated with ambient (outdoor) concentrations (0.63, 95% confidence interval [CI]: 0.57–0.68) than personal BC/EC exposure (0.49, 95% CI: 0.38–0.59), with significant differences in ṝ (0.14, 95% CI: 0.03–0.25; p < 0.05). The results demonstrated that the health status of participants was a significant modifier of pooled correlations. In addition, the personal to ambient (P/A) ratio for PM2.5 and average ambient BC/EC levels were potential effect moderators of the pooled ṝ. The funnel plots and Egger's regression test indicated inevident publication bias. The pooled estimates were robust through sensitivity analyses. The results support the growing consensus that the validity coefficient of proxy measures should be addressed when interpreting results from epidemiological studies to bette

The literature shows that information about the physical, chemical, and cell toxicity properties of particulate matter (PM) from diesel vehicles is not rich as the existence of a remarkable number of studies about the combustion, performance, and emissions of diesel vehicles using renewable liquid fuels, particularly biodiesels and alcohols. Also, the PM analyses from combustion of spent coffee ground biodiesel have not been comprehensively explored. Therefore, this research is presented. Pure diesel, 90% diesel + 10% biodiesel, and 90% diesel + 9% ethanol + 1% biodiesel, volume bases, were tested under a fast idle condition. STEM, SEM, EDS, Organic Carbon Analyzer, TGA/DSC, and Raman Spectrometer were employed for investigating the PM physical and chemical properties, and assays of cell viability, cellular reactive oxygen species, interleukin-6, and tumor necrosis factor-alpha were examined for investigating the PM cell toxicity properties. It is found that the application of both biodiesel and ethanol has the potential to change the PM properties, while the impact of ethanol is more than biodiesel on the changes. Regarding the important aspects, biodiesel can be effective for better human health (due to a decrease in cell death (−60.8%)) as well as good diesel particulate filter efficiency (due to lower activation energy (−7.6%) and frequency factor (−83.2%)). However, despite a higher impact of ethanol on the reductions in activation energy (−24.8%) and frequency factor (−99.0%), this fuel causes an increase in cell death (84.1%). Therefore, biodiesel can be an appropriate fuel to have a positive impact on human health, the environment, and emissions catalysts performance, simultaneously. © 2022 Elsevier B.V.

With growing urbanization and industrialization, problems such as poor disposal practices of solid waste and ensuing uncontrolled air pollution adjacent to landfill pose threats to human and environmental wellbeing. Ahmedabad is highly polluted urban city in India and unregulated burning of solid waste further aggravates already appalling situation caused by a large number of industries and vehicle fleets. The present work was carried out to understand sources of metals in ambient air surrounding a municipal landfill known as Pirana. For the study, surrounding area of the landfill was divided into 100 rectangular cells covering almost 5 km distance from its outer boundary. A location representing major land-use feature of each cell was classified. Sampling was carried out at these locations. A total of 100 PM5.0 samples were collected. Sampling was conducted for 3 h at each sampling location with samples collected on quartz filter paper. Measurements were performed over approximately 6 months from August to February, 2018. The filters were analyzed for metals using an Atomic Absorption Spectrometer. These measurements were used to identify pollution sources using positive matrix factorization technique and locate the hotspots of emission sources of heavy metals pollution. Five major sources namely, ferrous industry, nonferrous industry, vehicular emissions, re-suspended dust and solid waste burning/industrial coal combustion were identified and quantified. The average contributions of these sources to heavy metals were 20.7 ± 16.2, 18.4 ± 14.3, 19.9 ± 13.6, 21.4 ± 17.6, and 19.6 ± 10.6%, respectively. The average contribution from solid waste and industrial coal combustion is only 19.6% against the total from the combined remaining sources (~ 80.4), which means contribution from former will be lesser. Thus, solid waste burning is minor contributor for degradation of air quality; presence of many other sources around the site is actually the dominant cause

With the influence of global climate change, cities are facing more environmental challenges including Urban Heat Island effect and urban flooding. Urban Green Infrastructure (UGI) has been demonstrated to be a cost-effective nature-based solution that offers multiple ecosystem services to mitigate urban problems. However, few studies have explored the spatial organization of UGI on a city scale to maximize its benefits of heat mitigation in urban renewal. There is also a lack of studies that aim at quantifying and elucidating UGI benefits in runoff control for high-density subtropical cities. This thesis is constituted by two studies that address the above gaps respectively. In the first study, we developed a spatial optimization method that combines an urban cooling model and genetic algorithm to study the optimal geographical arrangement of roof greening in Kowloon, Hong Kong. It was found that with different planning objectives, the priorities of the buildings to implement green roofs vary. In the second study, we simulated different UGI implementations in a catchment of Kowloon for various rainfall events using the EPA Storm Water Management Model and compare their runoff reduction effects. The result shows that under a designed full-scale LID implementation scenario, the total runoff reduction can achieve 35%-45% and peak runoff reduction can achieve 30%-45%. The two studies help to further the understanding of UGI values and provide references for UGI planning in Hong Kong. In the end, the thesis proposes the possible incorporation of the two studies and explores the direction to maximize the synergy benefits of UGI planning for heat and runoff mitigation.

SO2 is among the major atmospheric pollutants, and the marine sector is an essential SO2 emission contributor. The International Maritime Organization (IMO) is banning oversea going vessels (OGV) from consuming fuels with sulphur content (FSC) over 0.50% to promote the air quality in coastal areas. Our team has developed a microsensor system (MSS) to measure FSCs at high efficiency and at a low cost. In this study, calibrations and experiments are carried out to verify the performance of the MSS and the calculation process of FSC. An integral method is the recommended way to calculate FSCs, introducing a linear correction coefficient of 1.657 with an error of 51.1%. After the verification, the MSS is applied to measure FSCs for OGVs in Hong Kong water. One hundred twenty-two ships are tested, with 102 having valid results. The average OGV FSC in Hong Kong water is 0.15±0.07%.

The use of air sensor technology is increasing worldwide for a variety of applications, however, with significant variability in data quality. The United States Environmental Protection Agency held a workshop in July 2019 to deliberate possible performance targets for air sensors measuring particles with aerodynamic diameters of 10 μm or less (PM10), nitrogen dioxide (NO2), carbon monoxide (CO), and sulfur dioxide (SO2). These performance targets were discussed from the perspective of non-regulatory applications and with the sensors operating primarily in a stationary mode in outdoor environments. Attendees included representatives from multiple levels of government organizations, sensor developers, environmental nonprofits, international organizations, and academia. The workshop addressed the current lack of sensor technology requirements, discussed fit-for-purpose data quality needs, and debated transparency issues. This paper highlights the purpose and key outcomes of the workshop. While more information on performance and applications of sensors is available than in past years, the performance metrics, or parameters used to describe data quality, vary among the studies reports and there is a need for more clear and consistent approaches for evaluating sensor performance. Organizations worldwide are increasingly considering, or are in the process of developing, sensor performance targets and testing protocols. Workshop participants suggested that these new guidelines are highly desirable, would help improve data quality, and would give users more confidence in their data. Given the wide variety of uses for sensors and user backgrounds, as well as varied sensor design features (e.g., communication approaches, data tools, processing/adjustment algorithms and calibration procedures), the need for transparency was a key workshop theme. Suggestions for increasing transparency included documenting and sharing testing and performance data, detailing best practices, and

Low-cost air quality sensors for air pollution monitoring have shown huge potential in enhancing the spatial and temporal resolution of much needed pollution data at a lower cost, greater flexibility in use with less maintenance than air quality monitoring stations. Air quality sensors provide opportunities to extend a range of existing air pollution monitoring capabilities and provide ideas for new monitoring applications. The widespread data sources combined with sensors improve people’s understanding of air quality research areas. However, severe gaps existed between the guarantee of sensor data quality and derivation of meaningful information from sensor applications in air quality monitoring. This study provides avenues from sensor calibration to applications in urban air quality monitoring. Three steps were divided as follows: Firstly, the air quality sensors were tested in the laboratory-controlled environment to understand the sensor performance and influence factors. The ambient factor influence was identified and quantified to build correction algorithms. Based on the understanding of the sensor working principle, a principle-based correction algorithm was built. The new algorithm proves the sensor sensitivity variation trend during different seasons. Meanwhile, compared with commonly used correction models, it shows the best performance and spatial representativeness in the sensor network. Secondly, a mobile sensor network was deployed in Hong Kong to monitor traffic-related air pollutants (TRAP) along bus routes. To estimate local and background contributions, a robust baseline extraction algorithm was developed and evaluated. The result indicates NO and NO2 are locally dominated air pollutants and varied within roads. Background concentrations primarily arose from CO and PM2.5 and decreased during summertime. The regional transport pollution is the primary contributor during high pollution episodes. For the traffic induced local co

Traffic-related air pollutants are major contributors to deteriorating urban air quality and pose a serious threat to pedestrians. From both a scientific and a regulatory standpoint, it is important and challenging to understand the contributions of local and non-local sources to accurately apportion specific sources such as traffic emissions contribution to on-road and near-road microenvironment air quality. In this study, we deployed mobile sensors on-board buses to monitor NO, NO2, CO and PM2.5 along ten important routes in Hong Kong. The measurements include two seasons: April 2017 and July 2017. Two types of baseline extraction methods were evaluated and applied to separate local and background concentrations. The results show NO and NO2 are locally dominated air pollutants in spring, constituting 72%–84% and 58%–71%, respectively, with large inter-road variation. PM2.5 and CO largely arise from background sources, which contribute 55%–65% and 73%–79% respectively. PM2.5 displays a homogeneous spatial pattern, and the contributions show seasonal change, decreasing during summer. Regional transport pollution is the primary contributor during high pollution episodes. Isolated vehicle plumes show highly skewed concentration distributions. There are characteristic polluted segments on routes and they are most evident at rush hours. The most polluted road segments (top 10%) cluster at tunnel entrances and congested points. Some of these polluted locations were observed in Hong Kong's Low Emission Zones and suggest limitations to the existing control strategies, which only address larger buses. Our work gives new insights in the importance of regional cooperation to improve background air pollution combined with local control strategies to improve roadside air quality in Hong Kong. © 2021 Elsevier Ltd

Although fossil-based plastic products have many attractive characteristics, their production has led to severe environmental burdens that require immediate solutions. Despite these plastics being non-natural chemical compounds, they can be degraded and metabolized by some microorganisms, which suggests the potential application of biotechnologies based on the mechanism of plastic biodegradation. In this context, microbe-based strategies for the degradation, recycling, and valorization of plastic waste offer a feasible approach for alleviating environmental challenges created by the accumulation of plastic waste. This Minireview highlights recent advances in the biotechnology-based biodegradation of both traditional polymers and bio-based plastics, focusing on the mechanisms of biodegradation. From an application perspective, this Minireview also summarizes recent progress in the recycling and valorization of plastic waste, which are feasible solutions for tackling the plastic waste dilemma. © 2021 Wiley-VCH GmbH

Despite the improvement in technologies for the production of alternative fuels (AFs), and the needs for using more AFs for motor vehicles for the reductions in air pollution and greenhouse gases, the number of alternative fuel vehicles (AFVs) in the global transportation sector has not been increasing significantly (there are even small drops for adapting some AFs through the projections) in recent years and even in the near future with projections to 2050. And gasoline and diesel fuels will remain as the main energy sources for motor vehicles. After reviewing the latest advantages and disadvantages of AFVs, including flexible-fuel, gas, electric, hybrid electric, and fuel cell electric vehicles, it is found that the higher price of AFVs, compared to that of gasoline and diesel vehicles, might be one of the main barriers for their wider adoption. But on the other hand, there is the “chicken and egg” problem. Because people mostly do not select AFVs due to their higher price and sometimes their less infrastructure availability compared to those of gasoline and diesel vehicles, however, governments and AFVs manufacturers claim that the insignificant demand volume and less interest by people to purchase them, is one of the main reasons for a higher price and less infrastructure availability of AFVs. So, what should we do for adopting AFVs? This review shows that there are two very important and fundamental points that might cause a rise in the demand and usage of AFVs, rather than waiting for the reduction in AFVs prices. Those points are car salespeople's and people's knowledge about AFVs and the environmental issues, and their encouragement to accept and use AFVs. Although the AFVs are available on the market for many years, many people around the world have no/less/old/wrong knowledge about the current AFVs. Thus, most of these people reject these vehicles for usage, even when their important parameters such as purchase price, operating cost, driving range, and fue

Sensor technology has enabled the development of portable low-cost monitoring kits that might supplement many applications in conventional monitoring stations. Despite the sensitivity of electrochemical gas sensors to environmental change, they are increasingly important in monitoring polluted microenvironments. The performance of a compact diffusion-based Personal Exposure Kit (PEK) was assessed for real-time gaseous pollutant measurement (CO, O3, and NO2 ) under typical environmental conditions encountered in the subtropical city of Hong Kong. A dynamic baseline tracking method and a range of calibration protocols to address system performance were explored under practical scenarios to assess the performance of the PEK in reducing the impact of rapid changes in the ambient environment in personal exposure assessment applications. The results show that the accuracy and stability of the ppb level gas measurement is enhanced even in heterogeneous environments, thus avoiding the need for data post-processing with mathematical algorithms, such as multi-linear regression. This establishes the potential for use in personal exposure monitoring, which has been difficult in the past, and for reporting more accurate and reliable data in real-time to support personal exposure assessment and portable air quality monitoring applications.

Long-term ozone lidar routine measurements are sparse in China. In this study, we used one year of continuous ozone lidar measurements to systematically investigate the effects of synoptic patterns on the vertical structure of ozone during high ozone episodes in Hong Kong. The height of the near-surface ozone layer was identified and compared with that of the mixing layer. The results showed that Hong Kong was greatly affected by ozone transport from the Pearl River Delta region when a tropical cyclone (“C” pattern) or a trough (“T” pattern) existed. When a high-pressure center was located to the north (“H” pattern) or when both a high-pressure system and a tropical cyclone existed (“CH” pattern), Hong Kong was affected by ozone transport from southeastern or southern China. Substantial amounts of ozone were transported within a layer near the ground with an average height of 0.83, 0.75, 0.94, and 0.85 km under the C, H, CH, and T synoptic patterns, respectively. Variation in the near-surface ozone layer height was consistent with that of the mixing layer height. Weak vertical mixing resulted in a shallow near-surface ozone layer under the C and H synoptic patterns. Due to the combined effect of near-surface transport and suppressed vertical mixing, the ozone concentrations were extremely high near the ground but rapidly declined with height under the C synoptic pattern. Our investigations of the vertical structure of ozone contribute to filling the knowledge gap between synoptic patterns and the evolution of high surface ozone episodes.

The literature reveals that fossil fuels will continue to be the main energy source for transportation fleets up to 2050, despite their non-renewability and the emissions of pollutants resulting from their use. Until the full adoption of non-fossil and zero-emission vehicles (e.g., electric vehicles), the application of renewable liquid fuels could be the best choice due to the latter's positive effects such as reduced consumption of fossil fuels and reduced emissions of pollutants. Alcohols, among others, have been widely tested as alternative fuels in diesel engines, however, there is no comprehensive information about their impacts on particulate matter (PM) which has a direct influence on human health, the environment, and emission catalyst's efficiency. This review comprehensively explores the impact of lower/higher alcohols, from methanol to decanol, in dual-fuel mode on the PM physicochemical properties emitted from diesel engines under different alcohol ratios and operating conditions. It is observed that alcohols change the PM physical properties by reducing primary particle size/number, radius of gyration, fractal dimension, and fringe length and increasing fringe separation distance and tortuosity compared to those of diesel PM. Regarding the chemical properties, alcohols reduce polycyclic aromatic hydrocarbons, benzo[a]pyrene equivalent, organic carbon (OC), elemental carbon (EC), ions, and soot ignition temperature and increase OC/EC ratio and soot oxidation reactivity. Thus, each 10% of alcohol, by volume, has the potential to reduce PM mass, number, and size by about 17, 20, and 10%, while lower alcohols and blended mode have more impact than higher alcohols and fumigation mode, respectively. © 2021 Elsevier Ltd

Atmospheric semi-volatile organic compounds (SVOCs) are complex in their chemical and toxicological characteristics with sources from both primary combustion emissions and secondary oxygenated aerosol formation processes. In this study, thermal desorption of PM2.5 in association with online measurement of reactive oxygen species (ROS) was carried out to study the role of SVOCs in its gas-particle partitioning. The mass concentrations of PM2.5, black carbon (BC) and p-PAHs downstream of a thermodenuder were measured online at different temperature settings (25, 50, 100, and 200 °C) to characterize PM physico-chemical properties. While the mass concentrations of PM2.5 and p-PAHs reduced to ∼34% at 200 °C compared to that in ambient temperature, BC mass concentration has decreased by 30% at the highest temperature. Furthermore, the submicron particle size distribution showed reduced particle number concentration in Aitken mode at 200 °C heating. The ROS, measured by Particle-into-Nitroxide-Quencher, also showed reduction and followed a similar trend with PM measurements, where the total ROS decreased by 12%, 31%, and 53% at 50 °C, 100 °C, and 200 °C, respectively, compared to the ambient sample. When a HEPA filter was included in the upstream of samples, 39% of gas phase ROS reduction was observed at 200 °C. This provided a good estimate of the contribution of SVOCs in ROS production in PM2.5, where decreased SVOCs concentration at 200 °C increased the percentage of particle surface area. This concludes that the surface chemistry of these organic coatings on the particles is important for assessing the health impacts of PM.

With growing concerns over air quality in many countries around the world, metal–organic frameworks are now being widely researched for its application in developing air filtration technology for PM2.5 removal. Our study reports the successful fabrication of a polyacrylic acid @zeolitic imidazolate framework-8 (PAA@ZIF-8) membrane using electrospinning technology which shows great promise for PM2.5 filtration. Our PAA@ZIF-8 membrane had a small pore size at 0.5 µm with a porosity of 89.4%, and after modification by ZIF-8, the PAA@ZIF-8 membrane gained porous rough nanofibers, positive surface zeta potential, and high tensile strength. Our tests confirmed the PAA@ZIF-8 membrane’s high potential for PM2.5 filtration over commercial PVDF and electrospun PAA membranes, recording a PM2.5 retention rate of 99.6%. Besides its small pore size, the PAA@ZIF-8 membrane’s rough and porous nanofiber structure created a high BET surface area (344.9 m2/g) which physically adsorbs the PM2.5 particles. Additionally, we found that the positive surface zeta potential (67.3 mV at PH = 7) of the ZIF-8-coated nanofibers attracts negatively charged PM2.5 particles combined in air moisture, thereby further improving the PM2.5 filtration rate.

Busy street canyons can have a large flow of vehicles and reduced air exchange and wind speeds at street level, exposing pedestrians to high pollutant concentrations. The airflow tended to move with vehicles along the canyon and the 1-s concentrations of NO, NO2 and CO were highly skewed close to the road and more normally distributed at sensors some metres above the road. The pollutants were more autocorrelated at these elevated sensors, suggesting a less variable concentration away from traffic in the areas of low turbulence. The kerbside concentrations also showed cyclic changes approximating nearby traffic signal timing. The cross-correlation between the concentration measurements suggested that the variation moved at vehicle speed along the canyon, but slower vertically. The concentrations of NOx and CO were slightly higher at wind speeds of under a metre per second. The local ozone concentrations had little effect on the proportion of NOx present as NO2 . Pedestrians on the roadside would be unlikely to exceed the USEPA hourly guideline value for NO2 of 100 ppb. Across the campaign period, 100 individual minutes exceeded the guidelines, though the effect of short-term, high-concentration exposures is not well understood. Tram stops at the carriageway divider are places where longer exposures to higher levels of traffic-associated pollutants are possible. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Busy street canyons can have a large flow of vehicles and reduced air exchange and wind speeds at street level, exposing pedestrians to high pollutant concentrations. The airflow tended to move with vehicles along the canyon and the 1-s concentrations of NO, NO2 and CO were highly skewed close to the road and more normally distributed at sensors some metres above the road. The pollutants were more autocorrelated at these elevated sensors, suggesting a less variable concentration away from traffic in the areas of low turbulence. The kerbside concentrations also showed cyclic changes approximating nearby traffic signal timing. The cross-correlation between the concentration measurements suggested that the variation moved at vehicle speed along the canyon, but slower vertically. The concentrations of NOx and CO were slightly higher at wind speeds of under a metre per second. The local ozone concentrations had little effect on the proportion of NOx present as NO2 . Pedestrians on the roadside would be unlikely to exceed the USEPA hourly guideline value for NO2 of 100 ppb. Across the campaign period, 100 individual minutes exceeded the guidelines, though the effect of short-term, high-concentration exposures is not well understood. Tram stops at the carriageway divider are places where longer exposures to higher levels of traffic-associated pollutants are possible. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Long-term ozone lidar routine measurements are sparse in China. In this study, we used one year of continuous ozone lidar measurements to systematically investigate the effects of synoptic patterns on the vertical structure of ozone during high ozone episodes in Hong Kong. The height of the near-surface ozone layer was identified and compared with that of the mixing layer. The results showed that Hong Kong was greatly affected by ozone transport from the Pearl River Delta region when a tropical cyclone (“C” pattern) or a trough (“T” pattern) existed. When a high-pressure center was located to the north (“H” pattern) or when both a high-pressure system and a tropical cyclone existed (“CH” pattern), Hong Kong was affected by ozone transport from southeastern or southern China. Substantial amounts of ozone were transported within a layer near the ground with an average height of 0.83, 0.75, 0.94, and 0.85 km under the C, H, CH, and T synoptic patterns, respectively. Variation in the near-surface ozone layer height was consistent with that of the mixing layer height. Weak vertical mixing resulted in a shallow near-surface ozone layer under the C and H synoptic patterns. Due to the combined effect of near-surface transport and suppressed vertical mixing, the ozone concentrations were extremely high near the ground but rapidly declined with height under the C synoptic pattern. Our investigations of the vertical structure of ozone contribute to filling the knowledge gap between synoptic patterns and the evolution of high surface ozone episodes.

Traffic-related air pollutants are major contributors to deteriorating urban air quality and pose a serious threat to pedestrians. From both a scientific and a regulatory standpoint, it is important and challenging to understand the contributions of local and non-local sources to accurately apportion specific sources such as traffic emissions contribution to on-road and near-road microenvironment air quality. In this study, we deployed mobile sensors on-board buses to monitor NO, NO2, CO and PM2.5 along ten important routes in Hong Kong. The measurements include two seasons: April 2017 and July 2017. Two types of baseline extraction methods were evaluated and applied to separate local and background concentrations. The results show NO and NO2 are locally dominated air pollutants in spring, constituting 72%–84% and 58%–71%, respectively, with large inter-road variation. PM2.5 and CO largely arise from background sources, which contribute 55%–65% and 73%–79% respectively. PM2.5 displays a homogeneous spatial pattern, and the contributions show seasonal change, decreasing during summer. Regional transport pollution is the primary contributor during high pollution episodes. Isolated vehicle plumes show highly skewed concentration distributions. There are characteristic polluted segments on routes and they are most evident at rush hours. The most polluted road segments (top 10%) cluster at tunnel entrances and congested points. Some of these polluted locations were observed in Hong Kong's Low Emission Zones and suggest limitations to the existing control strategies, which only address larger buses. Our work gives new insights in the importance of regional cooperation to improve background air pollution combined with local control strategies to improve roadside air quality in Hong Kong. © 2021 Elsevier Ltd

Low-cost air quality sensors for air pollution monitoring have shown huge potential in enhancing the spatial and temporal resolution of much needed pollution data at a lower cost, greater flexibility in use with less maintenance than air quality monitoring stations. Air quality sensors provide opportunities to extend a range of existing air pollution monitoring capabilities and provide ideas for new monitoring applications. The widespread data sources combined with sensors improve people’s understanding of air quality research areas. However, severe gaps existed between the guarantee of sensor data quality and derivation of meaningful information from sensor applications in air quality monitoring. This study provides avenues from sensor calibration to applications in urban air quality monitoring. Three steps were divided as follows: Firstly, the air quality sensors were tested in the laboratory-controlled environment to understand the sensor performance and influence factors. The ambient factor influence was identified and quantified to build correction algorithms. Based on the understanding of the sensor working principle, a principle-based correction algorithm was built. The new algorithm proves the sensor sensitivity variation trend during different seasons. Meanwhile, compared with commonly used correction models, it shows the best performance and spatial representativeness in the sensor network. Secondly, a mobile sensor network was deployed in Hong Kong to monitor traffic-related air pollutants (TRAP) along bus routes. To estimate local and background contributions, a robust baseline extraction algorithm was developed and evaluated. The result indicates NO and NO2 are locally dominated air pollutants and varied within roads. Background concentrations primarily arose from CO and PM2.5 and decreased during summertime. The regional transport pollution is the primary contributor during high pollution episodes. For the traffic induced local co

Although fossil-based plastic products have many attractive characteristics, their production has led to severe environmental burdens that require immediate solutions. Despite these plastics being non-natural chemical compounds, they can be degraded and metabolized by some microorganisms, which suggests the potential application of biotechnologies based on the mechanism of plastic biodegradation. In this context, microbe-based strategies for the degradation, recycling, and valorization of plastic waste offer a feasible approach for alleviating environmental challenges created by the accumulation of plastic waste. This Minireview highlights recent advances in the biotechnology-based biodegradation of both traditional polymers and bio-based plastics, focusing on the mechanisms of biodegradation. From an application perspective, this Minireview also summarizes recent progress in the recycling and valorization of plastic waste, which are feasible solutions for tackling the plastic waste dilemma. © 2021 Wiley-VCH GmbH

Sensor technology has enabled the development of portable low-cost monitoring kits that might supplement many applications in conventional monitoring stations. Despite the sensitivity of electrochemical gas sensors to environmental change, they are increasingly important in monitoring polluted microenvironments. The performance of a compact diffusion-based Personal Exposure Kit (PEK) was assessed for real-time gaseous pollutant measurement (CO, O3, and NO2 ) under typical environmental conditions encountered in the subtropical city of Hong Kong. A dynamic baseline tracking method and a range of calibration protocols to address system performance were explored under practical scenarios to assess the performance of the PEK in reducing the impact of rapid changes in the ambient environment in personal exposure assessment applications. The results show that the accuracy and stability of the ppb level gas measurement is enhanced even in heterogeneous environments, thus avoiding the need for data post-processing with mathematical algorithms, such as multi-linear regression. This establishes the potential for use in personal exposure monitoring, which has been difficult in the past, and for reporting more accurate and reliable data in real-time to support personal exposure assessment and portable air quality monitoring applications.

The literature reveals that fossil fuels will continue to be the main energy source for transportation fleets up to 2050, despite their non-renewability and the emissions of pollutants resulting from their use. Until the full adoption of non-fossil and zero-emission vehicles (e.g., electric vehicles), the application of renewable liquid fuels could be the best choice due to the latter's positive effects such as reduced consumption of fossil fuels and reduced emissions of pollutants. Alcohols, among others, have been widely tested as alternative fuels in diesel engines, however, there is no comprehensive information about their impacts on particulate matter (PM) which has a direct influence on human health, the environment, and emission catalyst's efficiency. This review comprehensively explores the impact of lower/higher alcohols, from methanol to decanol, in dual-fuel mode on the PM physicochemical properties emitted from diesel engines under different alcohol ratios and operating conditions. It is observed that alcohols change the PM physical properties by reducing primary particle size/number, radius of gyration, fractal dimension, and fringe length and increasing fringe separation distance and tortuosity compared to those of diesel PM. Regarding the chemical properties, alcohols reduce polycyclic aromatic hydrocarbons, benzo[a]pyrene equivalent, organic carbon (OC), elemental carbon (EC), ions, and soot ignition temperature and increase OC/EC ratio and soot oxidation reactivity. Thus, each 10% of alcohol, by volume, has the potential to reduce PM mass, number, and size by about 17, 20, and 10%, while lower alcohols and blended mode have more impact than higher alcohols and fumigation mode, respectively. © 2021 Elsevier Ltd

Despite the improvement in technologies for the production of alternative fuels (AFs), and the needs for using more AFs for motor vehicles for the reductions in air pollution and greenhouse gases, the number of alternative fuel vehicles (AFVs) in the global transportation sector has not been increasing significantly (there are even small drops for adapting some AFs through the projections) in recent years and even in the near future with projections to 2050. And gasoline and diesel fuels will remain as the main energy sources for motor vehicles. After reviewing the latest advantages and disadvantages of AFVs, including flexible-fuel, gas, electric, hybrid electric, and fuel cell electric vehicles, it is found that the higher price of AFVs, compared to that of gasoline and diesel vehicles, might be one of the main barriers for their wider adoption. But on the other hand, there is the “chicken and egg” problem. Because people mostly do not select AFVs due to their higher price and sometimes their less infrastructure availability compared to those of gasoline and diesel vehicles, however, governments and AFVs manufacturers claim that the insignificant demand volume and less interest by people to purchase them, is one of the main reasons for a higher price and less infrastructure availability of AFVs. So, what should we do for adopting AFVs? This review shows that there are two very important and fundamental points that might cause a rise in the demand and usage of AFVs, rather than waiting for the reduction in AFVs prices. Those points are car salespeople's and people's knowledge about AFVs and the environmental issues, and their encouragement to accept and use AFVs. Although the AFVs are available on the market for many years, many people around the world have no/less/old/wrong knowledge about the current AFVs. Thus, most of these people reject these vehicles for usage, even when their important parameters such as purchase price, operating cost, driving range, and fue

With growing concerns over air quality in many countries around the world, metal–organic frameworks are now being widely researched for its application in developing air filtration technology for PM2.5 removal. Our study reports the successful fabrication of a polyacrylic acid @zeolitic imidazolate framework-8 (PAA@ZIF-8) membrane using electrospinning technology which shows great promise for PM2.5 filtration. Our PAA@ZIF-8 membrane had a small pore size at 0.5 µm with a porosity of 89.4%, and after modification by ZIF-8, the PAA@ZIF-8 membrane gained porous rough nanofibers, positive surface zeta potential, and high tensile strength. Our tests confirmed the PAA@ZIF-8 membrane’s high potential for PM2.5 filtration over commercial PVDF and electrospun PAA membranes, recording a PM2.5 retention rate of 99.6%. Besides its small pore size, the PAA@ZIF-8 membrane’s rough and porous nanofiber structure created a high BET surface area (344.9 m2/g) which physically adsorbs the PM2.5 particles. Additionally, we found that the positive surface zeta potential (67.3 mV at PH = 7) of the ZIF-8-coated nanofibers attracts negatively charged PM2.5 particles combined in air moisture, thereby further improving the PM2.5 filtration rate.

Atmospheric semi-volatile organic compounds (SVOCs) are complex in their chemical and toxicological characteristics with sources from both primary combustion emissions and secondary oxygenated aerosol formation processes. In this study, thermal desorption of PM2.5 in association with online measurement of reactive oxygen species (ROS) was carried out to study the role of SVOCs in its gas-particle partitioning. The mass concentrations of PM2.5, black carbon (BC) and p-PAHs downstream of a thermodenuder were measured online at different temperature settings (25, 50, 100, and 200 °C) to characterize PM physico-chemical properties. While the mass concentrations of PM2.5 and p-PAHs reduced to ∼34% at 200 °C compared to that in ambient temperature, BC mass concentration has decreased by 30% at the highest temperature. Furthermore, the submicron particle size distribution showed reduced particle number concentration in Aitken mode at 200 °C heating. The ROS, measured by Particle-into-Nitroxide-Quencher, also showed reduction and followed a similar trend with PM measurements, where the total ROS decreased by 12%, 31%, and 53% at 50 °C, 100 °C, and 200 °C, respectively, compared to the ambient sample. When a HEPA filter was included in the upstream of samples, 39% of gas phase ROS reduction was observed at 200 °C. This provided a good estimate of the contribution of SVOCs in ROS production in PM2.5, where decreased SVOCs concentration at 200 °C increased the percentage of particle surface area. This concludes that the surface chemistry of these organic coatings on the particles is important for assessing the health impacts of PM.

Atmospheric semi-volatile organic compounds (SVOCs) are complex in their chemical and toxicological characteristics with sources from both primary combustion emissions and secondary oxygenated aerosol formation processes. In this study, thermal desorption of PM2.5 in association with online measurement of reactive oxygen species (ROS) was carried out to study the role of SVOCs in its gas-particle partitioning. The mass concentrations of PM2.5, black carbon (BC) and p-PAHs downstream of a thermodenuder were measured online at different temperature settings (25, 50, 100, and 200 °C) to characterize PM physico-chemical properties. While the mass concentrations of PM2.5 and p-PAHs reduced to ∼34% at 200 °C compared to that in ambient temperature, BC mass concentration has decreased by 30% at the highest temperature. Furthermore, the submicron particle size distribution showed reduced particle number concentration in Aitken mode at 200 °C heating. The ROS, measured by Particle-into-Nitroxide-Quencher, also showed reduction and followed a similar trend with PM measurements, where the total ROS decreased by 12%, 31%, and 53% at 50 °C, 100 °C, and 200 °C, respectively, compared to the ambient sample. When a HEPA filter was included in the upstream of samples, 39% of gas phase ROS reduction was observed at 200 °C. This provided a good estimate of the contribution of SVOCs in ROS production in PM2.5, where decreased SVOCs concentration at 200 °C increased the percentage of particle surface area. This concludes that the surface chemistry of these organic coatings on the particles is important for assessing the health impacts of PM.

Sensor technology has enabled the development of portable low-cost monitoring kits that might supplement many applications in conventional monitoring stations. Despite the sensitivity of electrochemical gas sensors to environmental change, they are increasingly important in monitoring polluted microenvironments. The performance of a compact diffusion-based Personal Exposure Kit (PEK) was assessed for real-time gaseous pollutant measurement (CO, O3, and NO2 ) under typical environmental conditions encountered in the subtropical city of Hong Kong. A dynamic baseline tracking method and a range of calibration protocols to address system performance were explored under practical scenarios to assess the performance of the PEK in reducing the impact of rapid changes in the ambient environment in personal exposure assessment applications. The results show that the accuracy and stability of the ppb level gas measurement is enhanced even in heterogeneous environments, thus avoiding the need for data post-processing with mathematical algorithms, such as multi-linear regression. This establishes the potential for use in personal exposure monitoring, which has been difficult in the past, and for reporting more accurate and reliable data in real-time to support personal exposure assessment and portable air quality monitoring applications.

The literature reveals that fossil fuels will continue to be the main energy source for transportation fleets up to 2050, despite their non-renewability and the emissions of pollutants resulting from their use. Until the full adoption of non-fossil and zero-emission vehicles (e.g., electric vehicles), the application of renewable liquid fuels could be the best choice due to the latter's positive effects such as reduced consumption of fossil fuels and reduced emissions of pollutants. Alcohols, among others, have been widely tested as alternative fuels in diesel engines, however, there is no comprehensive information about their impacts on particulate matter (PM) which has a direct influence on human health, the environment, and emission catalyst's efficiency. This review comprehensively explores the impact of lower/higher alcohols, from methanol to decanol, in dual-fuel mode on the PM physicochemical properties emitted from diesel engines under different alcohol ratios and operating conditions. It is observed that alcohols change the PM physical properties by reducing primary particle size/number, radius of gyration, fractal dimension, and fringe length and increasing fringe separation distance and tortuosity compared to those of diesel PM. Regarding the chemical properties, alcohols reduce polycyclic aromatic hydrocarbons, benzo[a]pyrene equivalent, organic carbon (OC), elemental carbon (EC), ions, and soot ignition temperature and increase OC/EC ratio and soot oxidation reactivity. Thus, each 10% of alcohol, by volume, has the potential to reduce PM mass, number, and size by about 17, 20, and 10%, while lower alcohols and blended mode have more impact than higher alcohols and fumigation mode, respectively. © 2021 Elsevier Ltd

Despite the improvement in technologies for the production of alternative fuels (AFs), and the needs for using more AFs for motor vehicles for the reductions in air pollution and greenhouse gases, the number of alternative fuel vehicles (AFVs) in the global transportation sector has not been increasing significantly (there are even small drops for adapting some AFs through the projections) in recent years and even in the near future with projections to 2050. And gasoline and diesel fuels will remain as the main energy sources for motor vehicles. After reviewing the latest advantages and disadvantages of AFVs, including flexible-fuel, gas, electric, hybrid electric, and fuel cell electric vehicles, it is found that the higher price of AFVs, compared to that of gasoline and diesel vehicles, might be one of the main barriers for their wider adoption. But on the other hand, there is the “chicken and egg” problem. Because people mostly do not select AFVs due to their higher price and sometimes their less infrastructure availability compared to those of gasoline and diesel vehicles, however, governments and AFVs manufacturers claim that the insignificant demand volume and less interest by people to purchase them, is one of the main reasons for a higher price and less infrastructure availability of AFVs. So, what should we do for adopting AFVs? This review shows that there are two very important and fundamental points that might cause a rise in the demand and usage of AFVs, rather than waiting for the reduction in AFVs prices. Those points are car salespeople's and people's knowledge about AFVs and the environmental issues, and their encouragement to accept and use AFVs. Although the AFVs are available on the market for many years, many people around the world have no/less/old/wrong knowledge about the current AFVs. Thus, most of these people reject these vehicles for usage, even when their important parameters such as purchase price, operating cost, driving range, and fue

Although fossil-based plastic products have many attractive characteristics, their production has led to severe environmental burdens that require immediate solutions. Despite these plastics being non-natural chemical compounds, they can be degraded and metabolized by some microorganisms, which suggests the potential application of biotechnologies based on the mechanism of plastic biodegradation. In this context, microbe-based strategies for the degradation, recycling, and valorization of plastic waste offer a feasible approach for alleviating environmental challenges created by the accumulation of plastic waste. This Minireview highlights recent advances in the biotechnology-based biodegradation of both traditional polymers and bio-based plastics, focusing on the mechanisms of biodegradation. From an application perspective, this Minireview also summarizes recent progress in the recycling and valorization of plastic waste, which are feasible solutions for tackling the plastic waste dilemma. © 2021 Wiley-VCH GmbH

Atmospheric semi-volatile organic compounds (SVOCs) are complex in their chemical and toxicological characteristics with sources from both primary combustion emissions and secondary oxygenated aerosol formation processes. In this study, thermal desorption of PM2.5 in association with online measurement of reactive oxygen species (ROS) was carried out to study the role of SVOCs in its gas-particle partitioning. The mass concentrations of PM2.5, black carbon (BC) and p-PAHs downstream of a thermodenuder were measured online at different temperature settings (25, 50, 100, and 200 °C) to characterize PM physico-chemical properties. While the mass concentrations of PM2.5 and p-PAHs reduced to ∼34% at 200 °C compared to that in ambient temperature, BC mass concentration has decreased by 30% at the highest temperature. Furthermore, the submicron particle size distribution showed reduced particle number concentration in Aitken mode at 200 °C heating. The ROS, measured by Particle-into-Nitroxide-Quencher, also showed reduction and followed a similar trend with PM measurements, where the total ROS decreased by 12%, 31%, and 53% at 50 °C, 100 °C, and 200 °C, respectively, compared to the ambient sample. When a HEPA filter was included in the upstream of samples, 39% of gas phase ROS reduction was observed at 200 °C. This provided a good estimate of the contribution of SVOCs in ROS production in PM2.5, where decreased SVOCs concentration at 200 °C increased the percentage of particle surface area. This concludes that the surface chemistry of these organic coatings on the particles is important for assessing the health impacts of PM.