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Volatile organic compounds (VOCs) cause the major air pollution concern. In this study, a series of ZSM-5 supported transition metals were prepared by impregnation method. They were combined with vacuum UV (VUV) photo-oxidation in a continuous-flow packed-bed reactor and used for the degradation of benzene, a typical toxic VOCs. Compared with VUV photo-oxidation alone, the introduction of catalysts can greatly enhance benzene oxidation under the help of O 3 , the by-products from VUV irradiation, via ozone-assisted catalytic oxidation (OZCO). The catalytic activity of transition metals towards benzene oxidation followed the order: Mn > Co > Cu > Ni > Fe. Mn achieved the best catalytic activity due to the strongest capability for O 3 catalytic decomposition and utilization. Benzene and O 3 removal efficiency reached as high as 97% and 100% after 360 min, respectively. O 3 was catalytically decomposed, generating highly reactive oxidants such as OH and O for benzene oxidation. [ABSTRACT FROM AUTHOR]

The adverse effects of acidic ultrafine particles (AUFPs) have been widely recognized in scientific communities. Two methods have previously been developed to measure AUFPs, but there are certain drawbacks. Thus, the aim of the study was to develop an easier, more rapid and more accurate measurement system for semi-automatic measurement of AUFPs in the atmosphere. The new measurement system was developed by integrating a diffusion sampler (DS) with three quartz crystal microbalances (QCM), namely QCM + DS system. The QCM detectors were coated with a nano-film of metal (metal-QCM detectors) and then placed inside the DS at three sampling spots for collection and detection of ultrafine particles (UFPs). The frequency changes obtained from the metal-QCM detectors were converted into the weights of deposited particles and used to determine the proportions of AUFPs in UFPs through the removal process of non-AUFP particles. Prior to sampling, the sensitive response of the QCM system and collection efficiencies of the QCM + DS system were calibrated using standard acidic and non-acidic particles. Reactions between the AUFPs and nano-film of metal were guaranteed by confirming much lower than one-layer deposition of particles on the detectors based on theoretical calculation and experimental results. Finally, the QCM + DS system was validated in a field measurement by comparing the results with those obtained from the previously developed method and a commercial measurement system (i.e. SMPS). All the three methods showed good agreements in measuring AUFPs and UFPs concentrations, indicating the reliability of the QCM + DS system for the quantification of ambient UFPs and AUFPs. Image 1 • A semi-automatic method was developed for measuring ambient AUFPs by a QCM + DS system. • The QCM detector was altered by coating a nano-metal film on its surface to collect and identify AUFPs. • The sensitive response of the QCM and collection efficiencies of the QCM + DS system were calibrated. • The QCM + DS system was validated in a field measurement. [ABSTRACT FROM AUTHOR]

Due to the high health risks associated with indoor air pollutants and long‐term exposure, indoor air quality has received increasing attention. In this study, we put emphasis on the molecular composition, source emissions, and chemical aging of air pollutants in a residence with designed activities mimicking ordinary Hong Kong homes. More than 150 air pollutants were detected at molecular level, 87 of which were quantified at a time resolution of not less than 1 hour. The indoor‐to‐outdoor ratios were higher than 1 for most of the primary air pollutants, due to emissions of indoor activities and indoor backgrounds (especially for aldehydes). In contrast, many secondary air pollutants exhibited higher concentrations in outdoor air. Painting ranked first in aldehyde emissions, which also caused great enhancement of aromatics. Incense burning had the highest emissions of particle‐phase organics, with vanillic acid and syringic acid as markers. The other noteworthy fingerprints enabled by online measurements included linoleic acid, cholesterol, and oleic acid for cooking, 2,5‐dimethylfuran, stigmasterol, iso‐/anteiso‐alkanes, and fructose isomers for smoking, C28‐C34 even n‐alkanes for candle burning, and monoterpenes for the use of air freshener, cleaning agents, and camphor oil. We showed clear evidence of chemical aging of cooking emissions, giving a hint of indoor heterogeneous chemistry. This study highlights the value of organic molecules measured at high time resolutions in enhancing our knowledge on indoor air quality. [ABSTRACT FROM AUTHOR]

A sampling campaign was conducted at an urban roadside site in Hong Kong from Nov. to Dec. in 2017 using a suite of state-of-the-art instruments to monitor compositions of non-refractory sub-micron particulate matter (NR-PM 1) and gaseous pollutants. Results showed that the average NR-PM 1 concentration was 26.1 ± 0.7 μg/m3 (average ± 95% confidence interval) and organic aerosol (OA) contributed the most to NR-PM 1 with a proportion of 57.7 ± 0.2%. The aerosol size distributions of bulk composition of NR-PM 1 presented a peak at ~600 nm with internal mixtures of the organic and inorganic components, while there were a larger proportion of primary organic particles at < 200 nm, indicating intensive emissions of primary organics at this site. Positive matrix factorization (PMF) analysis was applied to the measurement data and four OA components were identified, including a hydrocarbon-like OA (HOA) factor, a cooking organic aerosol (COA) factor and two oxygenated OA (OOA) factors of different oxidation levels: less oxidized OOA (LO-OOA) and more oxidized OOA (MO-OOA). Strikingly, the contribution of MO-OOA was the highest (30.9 ± 0.4%), suggesting high oxidation degree and/or high regional background in the roadside environment. Moreover, the proportion of COA reached 25.4 ± 0.3% at this roadside site with heavy traffic fleet, which was even higher than the percentage of HOA (p < 0.01). The average ratio of C 3 H 3 O + / C 3 H 5 O + (2.01 ± 0.01) and the opposite pattern of C 3 H 3 O + / C 3 H 5 O + to O x during daytime hours suggested that the COA was oxidized to some extent when transported to the site. The findings implied that cooking activities are a significant source of organic aerosols in Hong Kong, even at a busy road. Control measures should focus on both cooking and traffic emissions in Hong Kong. [Display omitted] • The proportion of COA in NR-PM 1 was higher than HOA at this traffic-busy site. • The pattern of C 3 H 3 O + / C 3 H 5 O + ratio was opposite to the trend of O x during daytime hours. • Cooking activities are a significant source of organic aerosols in Hong Kong. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) irradiation was used to improve photocatalytic degradation of gaseous benzene. A multi-functional photocatalyst of 0.1%Mn/TiO 2 /ZSM-5 was developed by a modified sol-gel method for the elimination and utilization of O 3 , the by-product generated from VUV irradiation. O 3 was completely removed and efficiently used to enhance catalytic oxidation of benzene via ozone-assisted catalytic oxidation (OZCO). Under VUV irradiation, benzene removal efficiency was stably kept at 100% over 0.1%Mn/TiO 2 /ZSM-5, however, it was only about 50% and much O 3 was residual over commercial TiO 2 (P25). 0.1%Mn/TiO 2 /ZSM-5 perfectly synergized with VUV irradiation. It provides more efficient pathways besides photocatalytic oxidation, for benzene degradation. The possible mechanism of benzene degradation over 0.1%Mn/TiO 2 /ZSM-5 with VUV irradiation was proposed. This is the first report of an efficient photocatalyst with superior performance for O 3 elimination and utilization. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) present a great risk to the atmospheric environmental as well as the public health and safety. In this study, a series of TiO 2 /zeolites catalysts were synthesized by sol-gel method. They showed much better photocatalytic activity for benzene degradation under UV irradiation compared with commercial TiO 2 (P25), which suffered from typical catalyst deactivation. Vacuum ultraviolet (VUV) irradiation was used to further enhance photocatalytic oxidation of benzene. The VUV-PCO process obtained much higher benzene removal efficiency (nearly 100%) than conventional UV-PCO (less than 10%). Besides photocatalytic oxidation, photolysis and ozone-assisted catalytic oxidation was also involved in the VUV-PCO process and they contributed much to benzene degradation. Most of the removed benzene was oxidized into CO 2 . Among the prepared photocatalysts, TiO 2 /ZSM-5 with Si/Al ratio of 200 obtained the best catalytic activity due to its appropriate porous structure and framework, which led to superior capacity for benzene absorption and ozone decomposition. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) photolysis is a simple way to destroy volatile organic compounds (VOCs). However, its application is greatly limited by the formation of O 3 byproduct and the low degradation capacity. In this study, we are the first combining an efficient Mn/ZSM-5 catalyst with VUV photolysis to eliminate O 3 and improve VOC degradation efficiency via ozone-assisted catalytic oxidation (OZCO). Results indicate that the benzene removal efficiency is only 48% with 83 ppm residual O 3 in the VUV photolysis process. However, both benzene and O 3 were completely removed after the adoption of the Mn/ZSM-5 catalyst. O 3 can be efficiently decomposed by Mn/ZSM-5 and used for benzene degradation through the OZCO. The possible degradation pathways and mechanism in such a novel VUV-OZCO process was proposed according to the identified products and intermediates. This study provides an efficient and promising process and unique insights for the degradation of VOCs. [ABSTRACT FROM AUTHOR]

The operation of laser printers can lead to the emission of high numbers of ultrafine particles. Evidence on the toxicology and adverse health effects of these particles has been mounting, however few studies have investigated the complexity of these particles in terms of their volatility, hygroscopicity and mixing state. This study utilized a Volatility Hygroscopic Tandem Differential Mobility Analyzer (VH-TDMA) to explore the internal and external mixing states of printer-generated particles. Up to 6.0 × 105 particles. cm−3 were observed during the operation of the laser printer, and these ultrafine particles could be classified into three groups, each with its own particular volatility (i.e., gradually shrinkable, suddenly shrinkable and expandable), owing to the different internal mixing states. In particular, we propose shell-core structures to explain the special volatility of these particles. In addition, whilst the majority of the generated particles were initially hydrophobic at 90% relative humidity (RH), it was observed that there were a very small number of volatilized particles (less than 5%) that shrank (i.e., decreased in size) after humidification. This study can be used as a model for investigating the complex particle formation processes in relation to secondary organic aerosols from other sources. Furthermore, our results shed light on the complexity of indoor aerosols, which should be investigated further in future indoor air quality studies. [Display omitted] • Mixing state of printer-generated particles was measured for the first time. • Three different types of particles were identified in the printer emissions. • Physical models were developed for particle formation and ageing under different printing scenarios. [ABSTRACT FROM AUTHOR]