Canteens are important places in our daily life, so it is of great significance for human health to investigate the inhalable particle concentration distributions inside them. In this work, the cooking particle concentrations in a typical university canteen with both enclosed and open style cooking units are measured by GRIMM1109, a particle measuring instrument. The results show that the enclosed or open-style cooking plays an important role in the concentration of particles. The particle number concentration is mainly contributed by the particles smaller than 1µm. For the mass concentration at the same place however, PM10 is the top contributor, while PM1 can be negligible. The particle number and mass concentrations decrease with increasing the distance from the cooking source. The mass concentration of PM10 in the open-style cafeteria can arrive at even 0.45mg/m3, which is 8.5 times as many as that in the traditional student canteen, and exceeds the maximum allowable concentration of 0.15mg/m3. In contrast, the traditional student canteen with the enclosed cooking units is superior to the open-style cafeteria. It is recommended to enhance the ventilation to reduce the harmful effect of particulate matters on human health in the open-style dining hall.

Air cleaners are expected to improve the indoor air quality by removing the gaseous contaminants and fine particles. In our former work, the effects of the air cleaner on removing the uniformly distributed particles were numerically investigated. Based on those results, this work further explores the performances of the air cleaner in the reduction of two nonuniform particle distributions generated by smoking and coughing. The Lagrangian discrete trajectory model combined with the Eulerian fluid method is employed to simulate the airflow pattern and particle transport in a room. In general, the results show that the particle fates have been resulted from the interaction between the emitting source and the air cleaner. And the position of the air cleaner is a key parameter affecting the particle concentration, for which a shorter distance between the air cleaner and the human body corresponds to a lower concentration. Besides, the air velocity emitted from the human mouth and the orientation of the air cleaner can also influence the transport of particles.

Particles emitted from vehicles can threaten human health. Therefore the investigations about the particle dispersion characteristics inside the street canyon are of significance. For the current work, the airflow fields and the particle movement inside an isolated street canyon with three aspect ratios under perpendicular wind direction and two typical wind speeds are studied numerically, for which the particle distributions are obtained by solving the drift-flux model. The conclusions demonstrate that the trees will result in the particles gathering. However, the particle deposition fluxes on the trees are so small which cannot effectively remove the particles from the ambient air. Besides, the vehicles tend to cluster particles around the street axis and slow down the dispersion to the curbside buildings. Therefore, the vehicles should not be ignored in the numerical models, especially for the cases in the wind direction of 90°. Moreover the cases with the aspect ratio of 0.5 are more sensitive to the effects of trees and vehicles. The shop vendors expose to the highest particle concentrations in most of the scenarios.

Air quality has increasingly been a great concern all over the world, and the good command of indoor and outdoor air qualities is of benefit to the air pollution alleviation by various measures. In this work, the indoor and outdoor particle concentration distributions of a typical meeting room during the haze and clear-sky days were measured. The results show that the mass concentrations of the indoor and outdoor PM1, PM2.5, PM10 in heavy haze days are 114±1.8, 135.5±3.2, 161.7±12.8 μg/m3 and 146.4±8.4, 192.3±10.2, 431.4±34.8 μg/m3 respectively, corresponding to 39.3±1.5, 58.5±2.5, 127.9±10.5 μg/m3 and 54.5±4.0, 77.8±6.0, 173.4±21.6 μg/m3 in clear-sky days. Both in the haze and clear-sky days, the number distribution of particles reaches its peak value at the diameter of 0.25 μm, but the particle number concentration in the haze day is two times greater than the clear-sky day. The indoor particle concentration is not uniform with the peak value at the corner, which can be effectively alleviated by the air cleaner. The in-situ measurements of particle concentrations in a meeting room are helpful for the indoor air quality control.

The fibrous media with elliptical cross sections may improve the filtration performance, however, current researches mainly focus on the capture mechanisms of a single elliptical fiber, and the fibrous media with randomly distributed fibers are rarely involved. In this work, a 2D numerical model was developed to predict the pressure drop and particle penetration for the fibrous filter composed of randomly distributed elliptical fibers. The results show that a big solid volume fraction of filter increases the effective collision area, and enhances the capture at a low face velocity. The particle penetrations through the fibers with the diameter of 5 mu m are conspicuously weaker than those with the diameter of 10 mu m, especially at big solid volume fractions and high face velocities. The blunt elliptical fibers restrain the penetration more effectively than the circle ones when the solid volume fraction is high. Though the blunt fibers lead to a large drag force, the increased pressure drop cannot improve the filtration performance at low solid volume fractions. In most cases, the slim elliptical fibers can enhance the filtration performance. A bigger aspect ratio of elliptical fibers leads to a low quality factor, showing the capture efficiency increases with the penalty of a high pressure drop. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Ultrafine particles originating from vehicle exhausts may deteriorate the air quality inside the street canyon, so it is of importance for the air quality control to clarify the formation and dispersion characteristics of ultrafine particles. In this study, the population balance model considering the nucleation, condensation and evaporation, as well as the species transport and RNG k-ε turbulent models were employed, and the sensitivities of the dispersion of ultrafine particles to the wind direction, emission rates of H2SO4 vapor and organic compounds, traffic flow and ambient temperature inside an isolated street canyon were analyzed. The results show that the wind direction is a key issue to the particle number concentration. The emission rates of H2SO4 vapor and organic compounds play dominant roles in the formation and growth of particles, so should be strictly controlled to reduce the air pollution. Restricting the use of private vehicles based on the even-and-odd number licensed trip can conspicuously lower the ultrafine particle concentrations by more than one order of magnitude. More powerful nucleation among the vehicle exhausts will be triggered in a cold environment, therefore the haze pollution may break out in winter more easily.

As a major source of air pollution in urban areas, the motor vehicle exhaust has attracted more and more attention due to its growing amount and serious harm to human health. It is of benefit to the pollutant control to make clear the transportation characteristics of vehicle exhausts. In this paper, the transportation characteristics of vehicle exhaust pollutants are investigated by means of the on-site measurement based on a typical Beijing expressway-Badaling expressway (G6 state expressway). The concentrations of CO, NO x , SO2 and particles near the expressway were obtained, by which the variations of the particle number and mass concentrations, as well as the gas pollutant volume concentrations in the vicinity of the roadways with the distance from the expressway were fitted. The results show that the gas pollutant concentrations and particle concentrations decrease almost exponentially with the distance from the expressway, which is helpful for the air pollutant database establishment and future pollution control in big cities.

Single-sided natural ventilation has been common in multi-family residential buildings. Current research usually presumes that the outdoor air is clean, which is not realistic under the outdoor pollution situations. In this study, the particle transport and airflow pattern in an isolated living room with the single-sided natural ventilation are numerically investigated by means of Eulerian drift-flux model combined with the Eulerian fluid method. The results indicate that larger wind speed does not necessarily achieve better ventilation effect and higher air change rate (ACH). At high wind speeds, the effect of wind direction on the room average concentration becomes more conspicuous. Small particles tend to disperse in the room more uniformly while large particles exhibit stratified distributions. The results would be useful for optimizing single-sided natural ventilation in buildings.

The particles emitted from vehicles will pose a significant threat to the indoor air quality for the buildings next to the road, so it is of benefit to the indoor air quality to reveal the particle transport characteristics in the micro-environment near the roadway. In this work, the particle transport and airflow pattern near a typical highway at various barriers and meteorological conditions are numerically investigated by means of the drift-flux model combined with Eulerian fluid method. The results show that the wind speed plays a significant role in the dispersion of the vehicle emitted particles. The higher the wind speed is, the lower the indoor particle concentration exhibits. The noise barriers can effectively block the incoming flow and restrict the transporting downstream of vehicle emitted particles under most of the meteorological conditions. On the contrary, the vegetation canopies along the roadsides cannot confine the dispersion of the particles. The trees in front of the building facade tend to slow down the air velocity and result in the particle gathering near the windows, which will lead to higher indoor particle concentrations. The indoor particle concentration varies widely with the positions and leaf area density distributions of the trees in the wind direction of 90°, yet, varies little in the wind direction of 45°. The indoor air quality can be improved by increasing the particle deposition velocity on trees and keeping windows closed.

Air cleaner is one of the viable options for particle removal in the indoor environment. Therefore, it is vital to understand the performances of air cleaners under various working conditions. In this work, the models for airflow pattern and particle transport in a room with an air cleaner were developed by combining the Lagrangian discrete trajectory model with the Eulerian fluid method. The effects of the operating conditions of the air cleaner on the particle transport characteristics were numerically investigated, including the volumetric flow rate and positioning of the air cleaner as well as the ejection orientation of the outlet air. The results show that the volumetric flow rate of the air cleaner is a key parameter affecting the particle concentration in the indoor environment. At low volumetric flow rates, the location of the air cleaner plays a significant role in the air cleaner performance. There is little difference in the removal processes of airborne particles between the horizontal and upward ejections of the air cleaner, but they are both superior to that with the downward ejection.