The Transportation Of Atmospheric Particulate Matter In Hot And Humid Urban Atmosphere Environment

Particulate matter is one of the major pollutants in urban environment.In the urban living environment,extremely hot weather is a hazardous weather.The change of air temperature affects the evaporation of urban water body,and changes the air humidity.The process of water body evaporation absorbs heat,which regulates ambient temperature.Temperature and humidity have an effect on the particle transport.Therefore,it is a practical significance of controlling particulate matter pollution for studying the regularity and concentration distribution of particulate matter in hot and humid urban environment.A two-dimensional ideal model of near water buildings represents the hot and humid urban environment,which is a research object.Basing on the RNG k-?turbulence and Euler multiphase flow model,particles from motor vehicle exhaust emissions are set as sources of pollution,and vapor from water surface evaporation is the humidity condition.The numerical model is established for atmospheric particulate matter transporting in a high humidity environment.In order to verify the correctness and applicability of the calculation model,the distribution of particulate concentration is compared with the monitoring data of the Mock Urban Setting Trial(MUST),the relative error of the simulation result and MUST experiment is about5%,and the trend of curve is consistent.Therefore,the established numerical calculation model can be used to study the particulate matter transport in hot and humid urban environment and the effect of environmental factors(humidity,temperature and wind speed)on it.Richardson number is used to characterize the change of ambient temperature at four times a day.The results show that the temperature is expressed by the evaluation parameter Ri.When initial water vapor volume is same,the water vapor mass fraction is the largest at Ri=12.8 and the smallest at Ri=13.8 along the top of street canyon,but the concentration of particles reached the maximum at Ri=16.8and the minimum at Ri=3.98.With the wind speed increasing,the water vapor increases,the concentration of particles reached the maximum at u=2m/s and theminimum at u=1m/s.Therefore,with the wind speed increasing,the more particles are taken into the calculation domain,and the more particles were taken away from the calculation domain.The distribution characteristics of particulates concentration is studied in the three-dimensional street canyons in hot and humid environment.The results show that as the distance between the street canyon and the lake is larger,large amount of particulate matter accumulates below 20 m on the windward side of high-rise buildings,the minimum of particulate matter concentration is K=5.6×10-3 above 30 m.When there is an angle(65 °)between the low-rise building arrangement and the lake,the mass fraction of water vapor and particle concentration gradually decrease.When the building arrangement is parallel to the lake,particle concentration gradually decreases without building obstruction and its maximum is 6.72×10-2,the particle concentration of K is 2.5×10-3 with the building obstruction higher than the maximum of concentration without building obstruction.