Study On Temporal & Spatial Distribution Of Indoor PM2.5 And Monitoring Data Correction Method

In 2013,"smog"became the annual key word.Its main component is fine particulate matter（PM2.5）,that is,particulate matter with an aerodynamic diameter of less than 2.5 microns that can enter the human lungs.Today,indoor PM2.5 has become one of the important factors affecting indoor air quality（IAQ）.How to properly monitor indoor PM2.5 is an issue that needs to be discussed and resolved urgently.At present,the sampling method is generally used to determine the indoor PM2.5 concentration.The relevant standards require that the indoor PM2.5 sampling time be at least 8 hours,and the sampling detection method takes a long time,resulting in the HVAC system cannot respond in real time,so real-time monitoring is an inevitable choice.However,at present,there is no scientific and reasonable uniform provision for the selection of monitoring points.Indoor environmental monitoring is a long-term behavior,closely integrated with indoor personnel activities.It is not possible to arrange multiple measuring points evenly in the height of the indoor breathing zone like sampling and testing,but a small number of measuring points should be arranged on the walls,ceilings,etc.that do not affect the activities of personnel.Therefore,it is very necessary to optimize indoor PM2.5 monitoring points and monitoring data.This article will focus on indoor environment,combining experimental research and CFD numerical simulation.By analyzing the spatial and temporal distribution characteristics of indoor PM2.5,to find out the relationship between the monitoring data at the wall monitoring point and the concentration level of the breathing zone.This article first summarizes domestic and foreign standards and specifications for indoor PM2.5 concentration detection and monitoring,and points out the deficiencies of existing monitoring methods in combination with standardized testing guidelines.At the same time,literature review on indoor PM2.5 diffusion and distribution are carried out.Secondly,using CFD numerical simulation,combined with orthogonal test design method,discussed the influence of six factors of air flow organizations,room aspect ratio,room area,intensity of pollution source,location of pollution source,number of air changes on the uniformity of PM2.5 mass concentration distribution in indoor environment.The study found that the airflow organization form is the most critical factor affecting indoor PM2.5 distribution,and then selected the four airflow organization modes of up supply with up return air,up supply with down return air,displacement ventilation and under floor air distribution as the primary factors for experimental analysis.Then,based on the PM2.5 mass conservation equation of the ventilated room,through experimental research,the PM2.5 emission rate of the pollution source in the experimental environment was obtained and the relationship（tending to power function）between the average PM2.5 mass concentration in the breathing zone and the PM2.5concentration under the supply air.Therefore,the diffusion and attenuation law of PM.5concentration respiratory area（C）with time（t）under the conditions of up supply with up return air,up supply with back return air and under floor air distribution are predicted.The basic form of the diffusion equation is C=t（at^β+yt+δ）+ε,and the basic form of the decay equation is C=(α+e^{-b（ε+λt）1}/b.Finally,taking the laboratory monitoring data as the main body and combining the actual indoor environment monitoring situation,the correction equations and correction coefficients of the 12 monitoring points of the side wall are obtained.Among them,the PM2.5 mass concentration at the monitoring point （C_M） under each air flow organization has a linear relationship with the mean of the respiratory zone （C_R）.The modified equation is C_R=β₂C_M+α₂.