Numerical Simulation For Impact Of Entrainment On Ozone Concentration In The Rural Atmospheric Boundary Layer In Hong Kong

Entrainment is an important way for the exchange of heat,water and air pollutants between the atmospheric boundary layer and the free atmosphere.Comparing ozone sounding data(WOUDC)and three ground stations(CW,TC and TM)in EPD in Hong Kong from 2002 to 2016 and using some statistical analysis methods to study the spatial and temporal characteristics of ozone in Hong Kong during the past 15 years.At the same time,A zero-order model,Chemistry,Land-surface,Atmosphere,and Soil Slab(CLASS)model was used to quantify the impact of entrainment influence on O3 concentration in the atmospheric boundary layer and to compare its contribution with that of chemical reactions at a rural site.A series of observational data including O3,NOx,boundary layer height,and potential temperature as well as reanalyzed data are used to evaluate the simulations.The results were showed as follows:(1)Ozone mixing ratios overall present a trend of slow growth from 2002 to 2016 and the lowest levels of ozone appeared in February and July,with the high values in April and October.(2)Ozone mixing ratios of upper-level(6-12km)show a decrease in the past 15 years,but the lower two levels increased,with slightly grow in middle-level(2-6km)and higher increase in boundary layer(0-2km).(3)The CLASS model was able to capture the temporal variations in the atmospheric boundary layer height,surface temperature,O3,and other chemical species.The entrainment has a competitive impact on O3 in the PBL as compared to chemical reactions.(4)The numerical experiments further showed that the relative.contribution of entrainment increased with increasing O3 jumps.The entrainment exerted an important impact on the control effectiveness of emission reduction of nitrogen oxides(NOx)and volatile organic compounds(VOC)and even totally counteracted the emission reduction effect in spring.But in autumn it is totally opposite and the O3 jump is below zero.With the decreasing O3 jumps;the diurnal O3 concentration decreases so it will enhance the effect in releasing of the pollution.The study provides scientific evidence that entrainment must be considered in order to control surface O3 concentrations effectively while the emissions were reduced.