A Case Study of Ozone Diurnal Variation in the Planetary Boundary Layer in Southeast United States using Multiple Observations and Large-Eddy Simulation

We investigate the ozone diurnal variation on September 6^th, 2013 under midsize urban environment using multiple in-situ and remote sensing measurements and large-eddy simulation (LES) model coupled with a chemical module. Our study area is in Huntsville AL USA, a typical midsize city in the southeast United States. The ozone variation in the convective boundary layer (CBL) is majorly caused by local emissions and photochemical productions due to the weather condition controlled by an anticyclonic system on that day. The local chemical production contributes over 2/3 ozone enhancement in the CBL and the dynamical processes, including ozone transport from the free troposphere (FT) to CBL through entrainment processes, contribute the rest. The numerical experiments by LES model show good agreement with our ozone DIAL observations. However, our simulations results and ozone DIAL observations fail to reproduce a decline trend of surface ozone measured by an EPA surface monitoring station that is 6km south to our facilities, very likely due to the large ozone horizontal variation and the diurnal variation of ozone dry deposition under urban environment. This study indicates that a need of fine 3 dimension ozone observations with high temporal and spatial resolutions for fine scale air quality studies in urban and smaller scales.