湍流对天津颗粒物粒径谱分布的影响

Impact of Turbulence on Particle Size Distribution in Tianjin

大气颗粒物粒径谱分布不仅受到温度、湿度和风等气象因素影响,也与湍流等边界层特征密切相关。基于2018年11月同步观测的14.6~660.0 nm颗粒物粒径谱和相关气象数据,探讨不同气象因子,特别是湍流对颗粒物粒径谱分布的影响。研究结果表明:气温升高有利于促进核模态颗粒物总数浓度的增加,相对湿度升高可减少核模态和爱根模态颗粒物的总数浓度,同时增加积聚模态的颗粒物总数浓度。风速、湍流动能、摩擦速度、湍流强度等增加,对爱根模态和积聚模态的颗粒物起稀释、清除作用,但可促进核模态颗粒物总数浓度的增长。与湍流日变化相反,爱根模态和积聚模态的颗粒物总总数浓度的日变化呈现昼低夜高的变化趋势,清洁日核模态颗粒物总数浓度在午后持续增加,并在傍晚前达到峰值。核模态颗粒物总数浓度的增加相对于湍流的发展存在时间上的滞后性,当湍流发展3~5 h后,核模态颗粒物总数浓度开始明显增加。

The particle size distribution is not only affected by meteorological factors such as temperature,air humidity and wind,but also closely regulated by the boundary layer mixing such as turbulence.Based on the simultaneously observed meteorological factors and particle size distribution in the range of 14.6-660.0 nm in November 2018,the impact of different meteorological factors,especially turbulence,on the particle size distribution is investigated to further understand the roles of meteorological factors in haze development.The results show that the increased relative humidity can reduce the total particle number concentration(TPNC)in nuclear mode and Aitken mode,but raise the TPNC in accumulation mode.Warmed temperature can increase the TPNC in the nuclear mode.The increase of wind speed,turbulent kinetic energy,frictional velocity and turbulence intensity can dilute and remove the particles in the Aitken and accumulation modes,but enhance the TPNC in the nuclear mode.In contrast to the diurnal variation of turbulence,the TPNC in Aitken mode and accumulation mode is low in the daytime but higher in the nighttime.In clean days,the TPNC in the nuclear mode continues to rise in the afternoon and reaches a peak in the late afternoon.A time lag has been found in the nuclear mode TPNC increase in contrast to the turbulence development.After the turbulence develops for 3 to 5 hours,the TPNC in nuclear mode begins to increase significantly.