An Analysis on the Relationship between Ground-Level Ozone and Particulate Matter in an Industrial Area in the Yangtze River Delta during Summer Time

Based on the data collected from May 15th to August 31st 2013 in an industrial area of Nanjing (a representative industrial area in the Yangtze River delta), characteristics of ozone (O₃), PM_2.5 and aerosol optical depth (AOD), and the relationships between O₃ and PM_2.5 and between O₃ and AOD were analyzed. The effect of AOD on ozone formation was evaluated by the application of a detailed chemical mechanism model (NCAR MM). The average concentration of PM_2.5 was 56.2±20.1 μg m^-3, and the average AOD (500 nm) and Angstrom exponent α (440-870 nm) were 1.4±0.9 and 1.0±0.3, respectively. PM_2.5 and O₃ exceeded NAAQS-Ⅱ (the National Ambient Air Quality Standard Ⅱ) by 20.2% and 10.1%, respectively. When PM_2.5 exceeded the NAAQS-Ⅱ, the average AOD (500 nm) and α (440-870 nm) increased by 14.7% and 23.91%, respectively, and O₃ fell by 12.3%. When O₃ exceeded the NAAQS-Ⅱ, the average AOD (500 nm) increased by 34.9%, and the average α (440-870 nm) did not vary significantly. There existed a significant linear correlation between daily ozone maximum concentration (y) and PM_2.5 concentration (x) under the condition of high temperature and low relative humidity. When the relative humidity was less than 60%, the linear regression function was y＝0.97x+43.96 R²＝0.60 (R² denotes the degree of fitting). When the temperature was over 32°C, the linear regression function was y＝1.24x+30.61 (R²＝0.64). There existed a negative correlation between daily ozone maximum concentration (y) and ground-observed AOD (x) in general. There existed a good negative correlation between simulated daily ozone maximum concentration (y) and ground-observed AOD (x), and the regression functions could be written as y＝－34.28x+181.62 (R²＝0.93) and/or y＝220.62·exp (－x/3.17)－19.50 (R²＝0.99).