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Abstract People spend nearly 90% of their time daily in various indoors, hence indoor environment is important for mortal survival and activity, which affected human health directly. Indoor particulate pollution has become an issue of increasing concern for human beings. Personnel walking behavior and ventilation mode will significantly affect the transfer characteristics of indoor particles. This paper analyzes the effect of walking process on indoor particle resuspension, and different ventilation modes (ceiling exhaust and slit exhaust) on the removal of indoor particulate concentration in experimental and theoretical models. The results show that the particle diffusion model under walking is in good agreement with the experimental results. The particles with different sizes have different diffusion characteristics during walking due to the surface deposition and resuspension rate. Particles of 1.0–3.0 μm have the fastest velocity and the largest amount in suspension, while the smallest for 0.5–1.0 μm particles. Different ventilation modes have different effects on the removal of indoor particles. The particles attenuation index is higher under slit exhaust mode, therefore the ventilation effect is higher than ceiling ventilation mode. Highlights • The effect of human walking process on indoor particle resuspension and removal was analysed. • Different size particles have different diffusion characteristics during the walking process. • Different ventilation methods have different effects on the indoor particulate matter removal. [ABSTRACT FROM AUTHOR]

Abstract People typically spend many hours a day inside their homes. Outdoor PM2.5, indoor décor, and the activities of residents worsen indoor air quality. Natural ventilation, natural ventilation with a portable air cleaner (PAC), and mechanical ventilation are some of the main ventilation modes. However, limited data are available on the actual performance of different ventilation modes. We conducted a one-year on-site program of measurement in six apartments in Tianjin, China. The results showed that indoor air quality was affected by both outdoor particle concentration and indoor activities (walking, cooking, etc.). Natural ventilation alone cannot guarantee indoor air quality. A mechanical ventilation system could reduce the duration of high indoor particulate pollution periods to some extent; however, whole year monitoring revealed that it was not effective in increasing healthy time ratios. Reduction in CO 2 concentrations above the standard levels through mechanical ventilation is 22.3% more than that through natural ventilation dwellings. Natural ventilation with a portable air cleaner can remove mass particulate pollution rapidly and maintain good indoor air quality with long-time operation. This study is expected to contribute towards the improvement of indoor air quality and the health of residents. Highlights • One-year on-site measurement in six apartments in Tianjin. • Natural ventilation alone cannot guarantee indoor air quality. • Mechanical ventilation system does little to increase healthy time ratios. • Natural ventilation with portable air cleaner can create good indoor air quality. [ABSTRACT FROM AUTHOR]

Healthy indoor air quality (IAQ) is essential to the productivity and wellbeing of building occupants. In order to study the indoor air quality in residential buildings in Xi'an in the cold climate zone, this study selected seven natural ventilation (NV) and three mechanical ventilation (MV) samples to evaluate the levels of fine particulate matter (PM2.5) and carbon dioxide (CO 2) through long-term monitoring. The results showed that it is worth studying the ventilation options in January with the lowest outdoor temperature of −0.78 °C, and the highest PM2.5 pollution of 149 μg/m3. The monthly average operation duration of the MV showed an obvious seasonal distribution, which was consistent with the degree of outdoor pollution. Compared with NV, the short-term operation of MV cannot significantly improve indoor air quality, but better results can be achieved after increasing the operation duration. When outdoor pollution is serious, the mean daily operation duration of MV recommended in this study is greater than 9 h. The probability of excessive CO 2 concentration (above 1000 ppm) of MV was 26%, which is higher than that of NV (9%). The CO 2 concentration increased with the increase in the MV operation duration, and the indoor CO 2 concentration was proportional to the temperature difference between indoor and outdoor. The control and operation of the MV system should consider the influence of PM2.5 and CO 2 simultaneously. Long-term operation of the MV system combined with short-term NV may be a ventilation strategy suitable for IAQ control of residential buildings in Xi'an. • Xi'an suffered from the most serious outdoor PM2.5 pollution in January (149 μg/m3). • Summer needs to control the production of indoor PM2.5 and the secondary diffusion caused by NV. MV operation duration of more than 9 hours can reduce the negative impact of PM2.5. • Excessive CO 2 occurred when indoor and outdoor temperature difference was 9–12 °C. • Long-time operation MV with intermittent use of NV can simultaneously control PM2.5 and CO 2. [ABSTRACT FROM AUTHOR]