Research On PM1.0 Dynamic And Dispersion Characteristics At Residential Underground Parking Lot In A Natural State

In recent years, most new residential communities are equipped with underground parking lots. PM1.0 exhausted from vehicles have been accepted as one of the main pollutants in the parking lot and the adverse health effect of those ultrafine particles is significant due to small size and high penetration rate in human body. However, characteristics of PM1.0 dynamic and dispersion at the near-wake region behind the vehicle and in the parking lot have not been fully understood yet. The paper focused on PM1.0 dynamic/dispersion in residential underground parking lot and the relationship between particle pollution and human health, presents a thorough study of size-resolved particle deposition and coaugltion from gasoline vehicle exhaust, PM1.0 dispersion trend and exposure level analysis in underground parking lot. The value of the paper is to reveal variation trend of particle concentration and exposure level in residential underground parking lot. The conclusion could not only be taken as the fundamental data of particle dynamic, epidemiological study and health risk assessment, but also be a guidance of ventilation design and particle pollution research in the enclosed en vironments like underground parking lot in the future.The paper concluded an appropriate theory when predicting PM1.0 dynamic and dispersion in a residential underground parking lot with natural state through the reference literature and indicated that deposition and coagulation are two main factors influencing PM1.0 dispersion. Meanwhile, the key parameters such as friction velocity, Hamaker constants and fractal dimension were determined to have important effect on PM1.0 deposition and coagulation, which dominated the particle dispersion in parking lot.Size-resolved ultrafine particle deposition and coagulation from gasoline vechile exhaust were evaluated using an environmental chamber experiment under the conditions of 12.24~25.22℃ and initial particle concentration in the range of 105~106 particles/cm3. A deposition theory with modified friction velocity and coagulation model with best-fitted Hamaker constant and fractal dimension were also employed to predict particle concentration decay during the experiment. The experiment results showed that best-fitted friction velocity, Hamaker constant and fractal dimension was 1.5~2.5cm/s, 20 k BT and 2.5~3, respectively. The contribution of coagulation during the first 1h of particle decay exceeded 60%.Characteristics of PM1.0 coagulation and half-time at the middle parking areas and moving vehicle condions were analyzed through a numerical simulation study combined with computational dynamic fluid(CFD), particle dispersion and coagulation. It could be found that PM1.0 coagulation was only significant at the narrow long region behind the tailpipe under different parking areas and vehicle moving conditions. Half-time due to PM1.0 coagulation in those narrow long regions was 1/4 of air exchange time under natural ventilation. PM1.0 coagulation in the region that is far from 0.2m along the centerline of tailpipe could be neglected under vehicle slowly moving conditions.A filed study on traffic-flow, PM1.0 concentration and environmental parameters in two different residential underground parking lots in Harbin, China were conducted and variation trends of measured parameters were extracted from logging data. The relationships between traffic-flow, environmental parameters at the entrance/exit and PM1.0 concentration were analyzed based on the theory of statistics. Logging data during the field study reflected that traffic-flow during the 12 h measurement in one day showed a U-shaped trend at both weekdays and weekends. Hourly PM1.0 concentration has essentially the same trend with trafficflow. The architectural structure of underground parking lot also influenced particle pollution level. PM1.0 concentration was dominated simultaneously by traffic-flow, temperature, relative humidty and wind velocity at the entrance/ exit. There was no leading factor observed when influencing PM1.0 concentration during field measurement.PM1.0 dispersion under transient vehicle exhaust conditions at the middle parking areas and near the entrance/exit was numerically simulated in the pa per. When a vehicle at the middl parking area exhausted lasting for 120 s,PM1.0 dispersion behind the vehicle could be treated as a “nearly static” process except for the area higher than 3m in the vertical direction. The spatial distribution of the vehicle plume, and PM1.0 concentration behind the vehicle could be simplified to be an exponential upward trend from the tailpipe. PM1.0 concentration with the distance after 0.5m behind the vehicle could be represented as a logarithmic decrease. After vehicle stopped exhasuting, PM1.0 diffused from upward to downward in the vertical direction. Outdoor air intake through the entrance of parking lot could mix parking concentration near the entrance uniformly.According to potential exposure dose and intake fraction, the paper evaluated PM1.0 exposure level in residential underground parking lot. The evaluation demonstated that total number/frequency of traffic-flow and outdoor air intake were two main factors influencing short-term potential exposure dose of PM1.0 in the parking lot. When analyzing PM1.0 exposure level under 2 vehicles exhausting for 120 s at the middle parking areas, PM1.0 intake fraction at respiratory region decreased logarithmically as exhaust time increased. PM1.0 potential exposure dose at respiratory region increased linearly during 300 s after as 2 vehicles stoppe d exhausting simultaneously.