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

Abstract

Black carbon (BC) reduces the photolysis coefficient by absorbing solar radiation, thereby affecting the concentration of ozone (O₃) near the ground. The influence of BC on O₃ 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 O₃ precursors in Nanjing in 2014, an EKMA curve is drawn, and the variations in O₃ concentration are further investigated using a zero-dimensional box mechanism model (NCAR MM). When O₃ precursors are unchanged, radiation and O₃ 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 O₃ first trends upward before decreasing. In the mixing process, the attenuation of BC to radiation and O₃ 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 PM_2.5 ratio increases to 5% in Nanjing, the radiation decreases by approximately 0.13%–3.71% while O₃ decreases by approximately 8.13%–13.11%. The radiative effect of BC not only reduces O₃ 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 NO_x to VOCs ratio decreases by 8.27%, and part of the original NO_x control area is transferred to the VOCs control area.

摘 要

黑碳(BC)通过吸收太阳辐射降低光解系数,从而影响地面附近臭氧(O₃)的浓度。BC对O₃的影响引起了广泛关注。本文利用Mie散射和对流层紫外可见光辐射(TUV)模型分析了BC光学特性对辐射的影响。结合2014年南京市O₃前体物数据,利用EKMA曲线和美国国家大气研究中心零维箱模型(NCAR MM对南京市O₃浓度变化进行了深入分析。研究表明:在O₃前体物浓度不变的情况下,辐射与O₃对BC光学性质变化的响应呈现高度相似的趋势(R=0.997)。随着模态半径的增大,新鲜BC对辐射和O₃浓度的衰减先呈上升趋势,后呈下降趋势。在混合过程中,BC对辐射和O₃浓度的衰减随相对湿度的增加呈上升趋势,但随BC涂层厚度的增加呈先快速下降后缓慢增加的趋势。同时,PM_2.5中BC质量浓度高低是另一个主要因素。当BC /PM_2.5浓度比值增加到5%时,辐射下降约0.13% ~ 3.71%,O₃浓度下降约8.13% ~ 13.11%。BC的辐射效应不仅降低了O₃浓度,而且改变了EKMA曲线中臭氧产生控制区。与NO_x控制区相比,辐射对VOCs控制区有显著影响。当气溶胶光学厚度(AOD)增加17.15%时,NO_x /VOCs比值降低8.27%,即原位于NO_x控制区的部分区域将向VOCs控制区转移。