Spatial And Temporal Distribution Of INDOOR PM_2.5 Based On Short-term Exposure Of Indoor Pollution Sources

Health is an inevitable requirement for promoting al-round human develo PMent and a basic condition for economic and social develo PMent.Fine particulate matter(PM_2.5)in the air is an important factor affecting indoor air quality and is closely related to human health.Indoor PM_2.5 sources are mainly divided into two categories:outdoor sources and indoor sources.Compared with outdoor sources,the emission of PM_2.5 from indoor sources is often transient,intermittent,and violently variable.Based on this characteristic,PM_2.5 released indoorswill cause the uneven distribution of PM_2.5 in space.This inhomogeneity will inevitably lead to great differences in the quality of PM_2.5inhaled by people at different locations in the room.Indoor air quality surveys generally assume that pollutants are uniformly distributed throughout the indoor space and do not accurately assess inhalation during short-term exposure（the entire period of the pollutant’s effect）.In view of the inaccurate problem in the process of short-term exposure assessment,this article will revolve around PM_2.5 indoor source,studing the phase of time scales,and the time-space distribution characteristics of PM_2.5 at this stage,aimed at understanding of indoor PM_2.5 pollution in the process of indoor distributed space-time distribution rule,and short-term exposure to indoor to make more accurate evaluation.Firstly,in view of the inhomogeneity in the room caused by the release of indoor PM_2.5 pollution sources,the mixing time theory is used to study when it is safe to use the complete mixing hypothesis.The influencing factors of indoor PM_2.5 mixing time were studied experimentally.In the experiment,19 experimental conditions were designed,including different air distribution（no ventilation,mixed ventilation,cabinet air conditioning）,emission time of pollution sources（0,1,10,30min）,ventilation times（5～10h-1）.The results show that the minimum mixing time is determined by the emission duration of pollution sources,and the time from the end of release to the complete mixing is determined by the air distribution.The greaterthe number of air change rates,the shorter the mixing time;The average wind speed of the room is the decisive factor affecting the length of time.Secondly,CFD simulation was used to study the indoor PM_2.5 transient diffusion process and the change of instantaneous concentration at various locations in the room.In the early stage of PM_2.5 diffusions,its diffusion mainly depends on the location of PM_2.5 sources.At the location of PM_2.5 sources,a large amount of PM_2.5 will accumulate.Then,with the diffusion of PM_2.5,the effect of air distribution determines its distribution in the room.After the flow field of the room is fixed,the diffusion speed and spread range of the pollution sources in the room have a great relationship with the location of the pollution sources.The flow field in the room and the location of pollution sources together determine the diffusion of particulate matter in the room.In addition,the total particulate matter mass left by the source at different locations in the room is also different.The closer the source is to the tuyere,the less the total particulate matter in the room is.However,when the release position of particulate matter source changed,the change of mixing time was very smal,which was mainly related to the wind speed at the release place of pollutant source.The greater the wind speed at the release place of pollutant source,the shorter the mixing time is.Finally,based on the spatial and temporal distribution of indoor PM_2.5,the inhalation volume was evaluated at the location of indoor breathing zone under different working conditions.The results show that,in the emission stage of pollution sources,the difference of inhalation amount at different locations in the breathing area reaches the maximum of2 to 3 times,and ventilation will aggravate the diffusion of PM_2.5,resulting in the average inhalation amount is greater than that in the non-ventilation condition.In the transition zone from the end of release to the complete mixing stage,the amount of inhalation at different locations in the respiratory zone varies according to the different uniformity of the air distribution.The PM_2.5 exposure model was improved according to the mixing time and PM_2.5 emission rules,and a more accurate indoor PM_2.5 short-term exposure model was proposed to assess inhalation volume.