Analysis of the Effect of Optical Properties of Black Carbon on Ozone in an Urban Environment at the Yangtze River Delta, China

Black carbon (BC) reduces the photolysis coefficient by absorbing solar radiation, thereby affecting the concentration of ozone (O-3) near the ground. The influence of BC on O-3 has thus received much attention. In this study, Mie scattering and the tropospheric Ultraviolet and Visible radiation model are used to analyze the effect of BC optical properties on radiation. Combined with data of O-3 precursors in Nanjing in 2014, an EKMA curve is drawn, and the variations in O-3 concentration are further investigated using a zero-dimensional box mechanism model (NCAR MM). When O-3 precursors are unchanged, radiation and O-3 show a highly similar tendency in response to changing BC optical properties (R=0.997). With the increase of modal radius, the attenuation of fresh BC to radiation and O-3 first trends upward before decreasing. In the mixing process, the attenuation of BC to radiation and O-3 presents an upward tendency with the increase of relative humidity but decreases rapidly before increasing slowly with increasing thickness of coating. In addition, mass concentration is another major factor. When the BC to PM2.5 ratio increases to 5% in Nanjing, the radiation decreases by approximately 0.13%-3.71% while O-3 decreases by approximately 8.13%-13.11%. The radiative effect of BC not only reduces O-3 concentration but also changes the EKMA curve. Compared with the NOx control area, radiation has a significant influence on the VOCs control area. When aerosol optical depth (AOD) increases by 17.15%, the NOx to VOCs ratio decreases by 8.27%, and part of the original NOx control area is transferred to the VOCs control area.

Automated summary

The study has shown that black carbon has a significant impact on ground-level O-3 concentration. With the increase of modal radius, as well as changes in relative humidity and coating thickness, the attenuation of black carbon to radiation and O-3 exhibits different trends.