Characteristics and Photochemical Formation Mechanisms of Summertime Ozone Pollution in Suburban Shanghai

Abstract

To characterize summertime ozone (O3) pollution at the Dianshan Lake suburban site, hourly surface observations and 15 min ozone-lidar profiles were collected during June–August 2022. Monthly mean O3 increased progressively from June through August (89.0 ± 47.4 to 102.1 ± 59.3 μg/m3), while VOCs averaged 33.9 ± 22.4 μg/m3, dominated by alkanes (53.1%), followed by aromatics (30.3%), alkenes (14.4%) and alkynes (2.3%). A representative high-O3 episode revealed NO + HO2 as the dominant production pathway (60.0%), whereas O3 loss was dominated by the NO2 + OH pathway forming HNO3 (75.9%). Sensitivity analysis supported a VOC-limited response during the modeled 9–14 August episode; the transition in the tested joint-reduction scenarios occurred near a VOCs/NOx ratio of 0.80 but was model-sensitive. Integrating concentrations, ozone formation potential (OFP), and OH Loss Rates (LOH) prioritized isoprene, propylene, ethylene, m/p-xylene, toluene, and i-pentane for control. The reproduced five-factor PMF solution attributed 25.7% to gasoline vehicle exhaust, 24.6% to LPG/NG use, 21.2% to biogenic emissions, 15.1% to solvent use, and 13.4% to diesel vehicle exhaust.