Analysis of the Vertical Distribution of Ozone and Its Precursors and Ozone Sensitivity in Hangzhou, China

This study utilizes NO2, HCHO, and O3 data of Hangzhou obtained from the Air-pollution Hyperspectral Scanning Analyzer (AHSA) from September 2022, to August 2023, to analyze the characteristics of these pollutants on both temporal and vertical scales, and also examines the sensitivity of O3 generation using the HCHO/NO2 ratio method. The results of this paper are as follows: (2) The volume fractions of NO 2 and HCHO are highest near the ground, with elevated levels primarily concentrated below 500 m and 1 000 m. Due to photochemical reactions, meteorological conditions, and traffic peaks, NO2 volume fraction are highest in winter (10.08×10–9± 9.14×10–9), while HCHO volume fraction peak in summer (4.67×10–9±1.37×10–9). (2) O3 pollution levels are highest in summer (51.87×10–9 ±41.36×10–9), followed by spring (44.59×10–9± 31.65×10–9), autumn (40.37×10–9±31.18×10–9), and winter (27.56×10–9±20.25×10–9). The diurnal O3 peak occurs primarily between 12:00 and 16:00. During summer, sustained high volume fraction are observed around 600 m, while in spring and autumn, higher volume fraction are observed above 600 m. In winter, O3 volume fraction increases with altitude. (3) O3 formation in Hangzhou is primarily controlled by VOCs. However, in summer, the frequency of NO x–controlled and VOCs–NOx mixed-controlled periods increases significantly compared to other seasons. Vertically, VOCs control dominates within the 0–200 m range (62.63%), but its proportion decreases with altitude. Conversely, the proportions of VOCs–NOx mixed control and NOx control gradually increase, accounting for 41.64% and 20.91%, respectively, within the 800~1000 m range.