Research On PM_2.5 Concentration Distribution And Indoor-outdoor Correlation In Urban Residential Areas In Severe Cold Regions

In recent years,with the increasing of haze pollution in domestic cities,research on atmospheric particles has begun to receive more attention.Residential areas are one of the most frequently used places for urban residents.The air qualities in residential areas and indoor environments are closely related to human's health.Due to the unique climatic characteristics of cities in severe cold regions,their urban energy structure,underlying surface,and building form are different with cities in other climate regions to a certain degree,and these factors will affect the particle pollution in relevant scales.In general,studies on the diffusion and concentration distribution of particles in urban residential areas in severe cold regions are relatively lacking.In view of the above problems,we studied the particle diffusion process and concentration distribution in urban residential areas and between indoor and outdoor environments in severe cold regions combining with test,experiment and numerical modeling research methods,and their influencing factors were further analyzed by experimental design and other methods.Firstly,taking a typical urban residential area in severe cold regions as the research object.We collected air PM_2.5 by sampling at two typical indoor sampling sites,one outdoor sampling site and one heating source sampling site during the heating season,and we made mass concentration analysis,carbon analysis,and water-soluble ion analysis on the sampling results.Through the analysis and comparison of the sampling results at each sampling site,it was found that the increase in heat supply will lead to an increase in the concentration of PM_2.5 and related components in indoor and outdoor environments,and strong indoor-outdoor correlations of them were also found.However,due to impact of indoor human activities,there are significant differences in PM_2.5 concentration levels between two indoor sampling sites.In addition,based on the component analysis results,it was found that the secondary generated particles are important components in PM_2.5,and the average proportion of secondary generated particles in PM_2.5.5 in indoor and outdoor environment reached57.29%and 40.34%,respectively.Secondly,we studied the particle transmission process between indoor and outdoor environment and the dynamic characteristics of indoor particles by experiment method.In the experiment of indoor-outdoor particle transmission,the effects of indoor particle source emission and window opening on the concentration of PM_2.5 and particles in different size intervals in the room were mainly investigated.The results showed that the indoor source had different effects on the concentration levels of indoor particles in various size intervals,and the increase of the concentrations of particles in smaller particle size interval was more significant;opening the window for a short time after the source emission can usually accelerate the decrease of the indoor particle concentrations effectively,and for particles with larger particle size,the removal effect is more significant.The experiment on the deposition and coagulation of indoor particles mainly analyzed the effects of indoor air temperature and air mixing intensity on the deposition and coagulation process of particles.The results showed that the increase of indoor air temperature and the indoor air mixing intensity could both promote the deposition and coagulation process of particles,and with the decrease of indoor particle concentrations,the contribution of coagulation on particle concentrations could be ignored gradually due to the weakening of the collision among particles.Based on the previous sampling and experiment results,in order to systematically study the diffusion process of particles in urban residential areas and the concentration relationships between indoor and outdoor environments in severe cold regions,we established urban local-building scale particle diffusion model for severe cold region on the basis of the urban region thermal climate prediction model,and the accuracy of the model was verified by comparing with measurement and experimental results.The verification results show that the model can better grasp variation and distribution trend of particle concentrations in local scale and the impact of traffic and other factors on concentration level of particles,and reflected the change of indoor particle concentrations during indoor particle source emission and window opening accurately.Meanwhile,the calculation efficiency of the model can meet the long-term dynamic simulation of the particle diffusion in local scale and the particle transmission between indoor and outdoor environments.Finally,based on the established urban local-building scale particle diffusion model for severe cold regions,the numerical simulation of the PM_2.5 concentration distribution of PM_2.5 in a super-high-rise residential area and the indoor-outdoor PM_2.5 concentration relationship during the heating season were carried out.The simulation results showed that the distribution of PM_2.5 mass concentration in the canopy showed a trend of decreasing with height due to the influence of the ground particle source,and the PM_2.5 mass concentration at 1.5 m showed a good consistency with the traffic flow with time.In addition,the results of orthogonal test analysis showed that the traffic flow,building density,building layout and underlying surface composition of the residential area will have different effects on the concentration distribution of PM_2.5,and the traffic flow has the most significant impact.For the indoor-outdoor PM_2.5 mass concentration relationships,the simulation results showed that as the increase of the floors,the I/O ratios of PM_2.5 mass concentration also increased gradually due to the increase of the air exchange rates,and the increase of indoor/outdoor temperature difference and outdoor wind speed could increase the I/O ratios,while the increase in airtightness of external doors and windows could decrease the I/O ratios significantly.In addition,prolonged the indoor particle source emission duration and enhanced its emission intensity could significantly increase the effect lasting time of indoor sources on indoor PM_2.5 mass concentrations,although opening windows for a short time after indoor source emission can accelerate the decay of the indoor PM_2.5 mass concentrations,but did not significantly reduce the effect lasting time of indoor sources.This paper combined different research methods to systematically study the particle pollution in urban residential areas and indoor environments in severe cold regions,and found the influencing factors and distribution patterns of PM_2.5 mass concentrations in typical urban residential areas and the correlation characteristics of PM_2.5 mass concentration between indoor and outdoor environments in severe cold regions.This study provided a theoretical basis and technical support for further improving the air qualities of urban residential areas and indoors in severe cold regions,such as by optimizing the building layout and controlling pollution sources.