An evaluation of the interaction of morning residual layer ozone and mixing layer ozone in rural areas of the North China Plain

Profiles of the ozone (O3) concentration and meteorological parameters were measured with tethered balloons at two rural sites (the Zhuozhou and Gucheng stations) in the summer of 2012 and 2013 to investigate the interaction of morning residual layer (RL) O3 and mixing layer (ML) O3. Results revealed that O3 from the previous day or surrounding transport will be stored in the RL and made significant impact on surface O3 via downward mixing during transition hours (06:00 LT-10:00 LT). More O3 was stored in the RL, the higher base concentration for O3 pollution was existed. Generally, the downward mixing and photochemical reaction jointly contribute to the surface O3 variation and horizontal transport of O3 will further enhance this impact. Sometimes, even though the meteorological condition is unchanged, surface O3 concentration could still be gradually accumulated via O3 carried over from the preceding day. Impact of this downward mixing process was usually the greatest from 8: 00-10: 00 LT. Concentration of the O3 carried over from the previous day can be as high as 76.8 ppb. Compared with local photochemical production, the RL O3 could contribute more than 50% to the surface O3 during transition hours. As a result, morning RL O3 significantly influence the ML O3 in rural areas of the North China Plain. Understanding of this mechanism will contribute to the experiment study and the improvement of air quality model.