Atmospheric Environment: X最新文献

Identifying and quantifying the sources and clarifying the impacts of ultrafine particles (UFP) in the complicated urban environments are important for particle pollution control and UFP-climate interaction understanding. The previous studies have made notable contributions to these aspects and it is necessary to review the achievements. Here, the characteristics of traffic emissions and new particle formation (NPF) events/processes and their effects on urban UFP are summarized mainly based on the latest progresses. The constantly improved techniques of measuring UFP have played a vital role for knowing the sources and impacts of UFP. Meanwhile, the emissions inventories, dispersion models, and receptor models generally perform better when working together and using high resolution input and corrected algorithms. Besides, the interaction between UFP and climate is discussed mainly by linking radiation, cloud condensation nuclei, particle deposition, and the environmental conditions required for nucleation processes. Although for urban UFP, there are consensuses that traffic emissions and nucleation processes are two main sources and UFP and climate interact mainly via radiation and cloud condensation nuclei (CCN), there are many other crucial tasks for future and this work lists seven of them. They involve, scientifically, how much other sources such as industrial and regional sources mix with traffic emissions and nucleation processes in source contributions and how primary pollutants collaborate with UFP (aerosols) in aerosol-climate interactions; and engineeringly, how to improve the integration of the instruments and the instrument customization services according to actual situations. These progresses and future perspectives would help in more accurately quantifying the contributions of emissions and nucleation processes to UFP and better evaluating the impacts of UFP. Despite our efforts, knowledge on the main sources and impacts of urban UFP is limited and detailed solutions for the future tasks are missing here, which need joint efforts from UFP and related fields.

The quantification of gas emissions from waste storage and treatment ponds is an important problem. The objective of this study was to better understand the use of micrometeorological techniques for this purpose. Methane emissions were estimated from a large tailings pond (surface area >11 km²) at an oil sands mine site using datasets collected by different groups over a nine-month period. Emissions were calculated with eddy-covariance (EC) and inverse dispersion modelling (IDM) techniques. Three different IDM calculations were made using methane concentrations measured with either fixed-point sensors (IDM-LGR), a long-path laser (IDM-GL), or an unmanned aerial vehicle (IDM-UAV). Emissions were also estimated from a flux-chamber (FC) survey. Although the temporal overlap between the different datasets was limited, the results indicate substantial differences in emission-rate estimates. During a summer interval the EC, IDM-LGR, and IDM-GL estimates were 19%, 41%, and 56% of the FC-estimated rate, respectively. The overall ordering was EC ≈ IDM-UAV < IDM-LGR < IDM-GL < FC. Differences in the emission estimates appear to be explained by the physical location of the measurement footprints. The EC and IDM-UAV footprints were comparably small and confined to lower emitting areas of the pond, while the larger IDM-LGR and IDM-GL footprints included higher emitting areas. It would seem sensible to prefer the larger footprint IDM approaches for this large pond. However, the large IDM footprints necessitated a complicated analysis to remove the influence of an adjacent methane source in the calculations. This study illustrates the importance of understanding the footprint of micrometeorological techniques when quantifying emissions and the complications that arise when the footprint does not match the source area.

Tracer flux ratio (TFR) methodology performed downwind of 15 active oil and natural gas production sites in Ohio County, West Virginia sought to quantify air pollutant emissions over two weeks in April 2018. In coordination with a production company, sites were randomly selected depending on wind forecasts and nearby road access. Methane (CH₄), ethane (C₂H₆), and tracer gas compounds (acetylene and nitrous oxide) were measured via tunable infrared direct absorption spectroscopy. Ion signals attributed to benzene (C₆H₆) and other volatile gases (e.g., C₇ – C₉ aromatics) were measured via proton-transfer reaction time-of-flight mass spectrometry. Short-term whole facility emission rates for 12 sites are reported. Results from TFR were systematically higher than the sum of concurrent on-site full flow sampler measurements, though not all sources were assessed on-site in most cases. In downwind plumes, the mode of the C₂H₆:CH₄ molar ratio distribution for all sites was 0.2, which agreed with spot sample analysis from the site operator. Distribution of C₆H₆:CH₄ ratios was skew but values between 1 and 5 pptv ppbv^-1 were common. Additionally, the aromatic profile has been attributed to condensate storage tank emissions. Average ratios of C₇ – C₉ to C₆H₆ were similar to other literature values reported for natural gas wells.

This study investigated the variation of particle number (PN), morphological features and nano structural parameters of particulate matter (PM) from a China Ⅵ GDI engine under different working conditions, oxidation temperatures, and aerodynamic diameters. The results showed that, particles with a diameter less than 10 nm or 23 nm accounted for 40–65% and 68–94% of total PN respectively. Engine speed has a larger effect on PN emissions with the diameter less than 10 nm. PM emitted from the GDI engine were mainly consisted of primary particles with a diameter of 12–72 nm. Primary particles were composed of numerous graphite fringes with a length of 0.1–1.8 nm, tortuosity of 1.10–2.65, and separation distance of 0.2–1.6 nm. The boundaries of primary particles became vague, the fringe tortuosity and separation distance decreased with the progress of oxidation. Particles in larger aerodynamic diameters were more likely to form cluster-like PM in micromorphology. PM accumulated by particles with an aerodynamic diameter of 52.1 nm had larger fractal dimension, smaller fringe length, higher fringe tortuosity, and greater fringe separation distance, and was more easily be oxidized.

Fused filament fabrication (FFF) is a material extrusion-based technique often used in desktop 3D printers. Polymeric filaments are melted and are extruded through a heated nozzle to form a 3D object in layers. The extruder temperature is therefore a key parameter for a successful print job but also one of the main emission driving factors as harmful pollutants (e.g., ultrafine particles) are formed by thermal polymer degradation. The awareness of potential health risks has increased the number of emission studies in the past years. However, studies usually refer their calculated emission data to the printer set extruder temperature for comparison purposes. In this study, we used a thermocouple and an infrared camera to measure the actual extruder temperature and found significant temperature deviations to the displayed set temperature among printer models. Our result shows that printing the same filament feedstocks with three different printer models and with identical printer set temperature resulted in a variation in particle emission of around two orders of magnitude. A temperature adjustment has reduced the variation to approx. one order of magnitude. Thus, it is necessary to refer the measured emission data to the actual extruder temperature as it poses a more accurate comparison parameter for evaluation of the indoor air quality in user scenarios or for health risk assessments.

Polyoxymethylene Dimethyl Ether (PODE_n) is a promising diesel additive that can reduce particulate matter (PM) emission effectively, yet the changes in chemical and physical characteristics of PM emissions due to the application of PODE_n-diesel blended fuel remain largely unexplored. This laboratory study investigates the effects of PODE₃–diesel blended fuels (10, 20, and 30 vol% of PODE₃ mixed with diesel, denoted as P10, P20, and P30, respectively) on diesel engine emissions at 30% and 60% engine loads. Black carbon (BC) and organic aerosol (OA) were characterized in real time by a combination of a soot-particle aerosol mass spectrometer (SP-AMS) and a seven-wavelength aethalometer. Our results show that PODE₃ can significantly reduce both OA and BC emissions at both engine loads, with P20 producing the largest total PM mass reductions (>84%). The changes in the contribution of refractory oxygenated fragments to BC mass (i.e., C₃O₂⁺/C₃⁺ and C₃O⁺/C₃⁺) indicate that PODE₃ can reduce the functionality of soot surface/nanostructure. This is the first work showing that PODE₃ can affect the mixing state of BC and OA in diesel engine exhaust. Increasing PODE₃ blended volume can reduce the total fraction contribution of particle types that were composed of notably amounts of BC by mass. Furthermore, clustering analysis of single-particle data can identify two OA-dominated particle classes that were dominated by hydrocarbon fragments (C_xH_y⁺), and one of them had higher signal contribution from high molecular weight compounds. Lastly, the absorption Ångström exponent of BC (AAE_BC) can be enhanced with PODE₃ blended volume for both engine loads, and brown carbon (i.e., a light absorbing fraction of OA) can contribute up to ∼5% to the total aerosol absorption at the wavelength of 370 nm. Overall, this work provides insights into the potential impacts of PODE_n blended fuel application on the chemical and optical properties of BC and OA emitted from diesel engine combustion.

Non-exhaust particulate matter (PM) emissions deriving from transports are steadily increasing over last years. Nevertheless, there is a proven lack of up-to-date emission inventory guidelines, as well as a lack of related research studies. Rail transportation such as trains and subways contribute to non-exhaust PM emissions from different phenomena and specifically from braking events, during which PM of different dimensions can be emitted from both mechanical processes and high temperature processes. This study reports the development and application of an experimental procedure for the investigation of particulate matter PM₁₀, PM_2.5 and PM₁ emissions in the atmosphere produced by brake pads for railway vehicles. Two different test programs composed of several brake events each were conducted on a dynamometer test bench to simulate the brake performance of a railway vehicle during typical routes. PM emission levels were measured with an Electrical Low-Pressure Impactor at the exhaust air channel of the dynamometer. The tests were performed on an innovative sintered material and two commercial organic materials. For both test simulation routes, the three brake pads exhibited very similar friction performances and very similar average maximum temperature profiles. On the other hand, the innovative sintered material revealed a considerably better behavior in terms of wear resistance compared to the organic materials. Relationships between wear rate, train speed, applied forces and particle concentrations were detected in the wear processes occurring in the braking materials. PM concentrations produced by the sintered brake pad during both simulation tests were substantially lower than the organic pads and the differences were more pronounced for fine particles (PM_2.5) and ultrafine particles (PM₁). The shape of particle size distributions was similar for the three materials, with the maximum mass concentration of particles measured in the coarse particle region and two other modes in the fine and ultrafine particle regions. An increase in the production of ultrafine particles was observed for an increase in the temperature of the disk, while the production of coarse and fine particles remains substantially unaffected. The experimental results provided in this work can furnish the basis for developing the optimal formulations of brake pad materials with low environmental impact and for setting specific measures on train brake pads composition and production for the mitigation of non-exhaust emissions.

Mountain observatories at high altitudes, far from local anthropogenic emission sources, are considered ideal for monitoring temporal variations of tropospheric air pollutants. During August 17–21 in 2013, we measured sulfur dioxide and nitric acid concentrations in the free troposphere at the top (3776 m a.s.l.) of Mt. Fuji, Japan. A parallel plate wet denuder-ion chromatographic system was used for the online measurement with 15 min temporal resolution. The continuous observations were successfully achieved without any problems. Of the samples collected, 97.8% of sulfur dioxide and 75.7% of nitric acid were above the limits of quantification. The average gas concentrations ± standard deviation (n = 408) were 0.106 ± 0.377 ppbv for sulfur dioxide and 0.015 ± 0.014 ppbv for nitric acid, respectively. Episodic elevations of sulfur dioxide concentration were recorded from August 20 to 21. Backward trajectory analyses indicated that the high-temporal resolution monitor detected the volcanic sulfur dioxide from Mt. Sakurajima, located 857 km from the sampling point. High-time-resolved observations in the free troposphere proved useful for source identification of air pollutants.

Ethylene oxide (EtO) is a hazardous air pollutant that can be emitted from a variety of difficult to measure industrial sources, such as fugitive leaks, wastewater handling, and episodic releases. Emerging next generation emission measurement (NGEM) approaches capable of time-resolved, low parts per billion by volume (ppbv) method detection limits (MDLs) can help facilities understand and reduce EtO and other air pollutant emissions from these sources yielding a range of environmental and public health benefits. In October 2021, a first of its kind 4-day observational study was conducted at an EtO chemical facility in the midwestern United States. The study had dual objectives to both improve understanding of EtO emission sources within the facility and advance NGEM methods. Using cavity ring-down spectroscopy (CRDS) instruments, a combination of mobile surveys and stationary multipoint process unit monitoring assessed EtO concentrations in and near facility operations, while testing and comparing measurement methods. The study concluded that four main areas of EtO source emissions existed within the facility, each possessing unique emission characteristics. Episodic EtO emissions from supply railcar switchovers and batch reactor washouts, lasting seconds to minutes in duration, produced EtO concentrations exceeding 500 ppbv inside the process unit in some cases. In one instance, EtO at ∼30 ppbv was briefly observed hundreds of meters from the process unit. Lower level but more sustained EtO concentrations were observed near an EtO transfer pump and wastewater tank outfall and drain system. Overall, 4.6% of mobile survey data were above the 1.2 ppbv mobile test MDL while the nine stationary sampling locations ranged from 17.7% to 82.8% of data above the 1.0 ppbv multipoint test MDL. This paper describes the EtO emissions observed in and near the four defined source areas within the facility and provides details of the NGEM method development advances accomplished as part of the study.

This study coupled a meteorological model with explicit bulk lightning and chemical transport models to investigate the impacts of lightning-induced nitrogen oxides (LNO_x) on nitrogen monoxide (NO), nitrogen dioxide (NO₂), and total reactive nitrogen oxide (NO_y) measured on August 22, 2017, at the top of Mt. Fuji, Japan. Our simulation results indicated that the LNO_x emitted around Wakasa Bay in the windward area of Mt. Fuji largely contributed to the NO_y content measured at the top of Mt. Fuji. Furthermore, sensitivity experiments regarding the height of LNO_x emissions indicated that the NO_y content measured atop Mt. Fuji originated from LNO_x emitted below 6 km. Our simulation assumed that a two-mode vertical distribution of LNO_x emissions was more consistent with measured NO_y at Mt. Fuji than a single-mode structure assumption in this case. A comparison of simulated NO_x (= NO + NO₂) and measured NO_x at Mt. Fuji indicated that the reaction rates of the NO and NO₂ cycles were well reproduced in our model; however, the ratio of NO_z (NO_y species other than NO_x) to NO_y estimated by the model were lower than the observed value, implying that the model either underestimated the reaction rate of LNO_x or overestimated the wet removal of lightning-induced NO_z. Finally, our results also suggest that the simultaneous observation of NO_y and NO_x is important for understanding LNO_x emissions, subsequent atmospheric chemical reactions, and removal processes, as well as validating chemical transport models.