Abstract: The budget analysis of nitrous acid (HONO) is one of the challenging and hot topics in atmospheric chemistry research. This study conducted observations of HONO and related pollutants in urban Beijing during the spring of 2021. A simulation study was carried out to investigate the source and loss processes of high HONO events and their impact on O3 formation during the observation period. The results showed that the average concentration of HONO during the observation period was 2.55 ± 1.34 ppb, with two high HONO events (defined as the hourly maximum concentration of HONO exceeded 4 ppb for two consecutive days) accompanied by high PM2.5 and O3 concentrations. Based on the photochemical box model (F0AM) and observational data, the main sources and formation pathways of HONO were explored by coupling an updated heterogeneous chemical mechanism on the basis of a chemical mechanism (MCM3.3.1). The results indicated that the main daytime sources of HONO were photolysis of nitrates, the homogeneous reaction between NO and OH, and the photochemically enhanced heterogeneous reaction of NO2 on aerosol surfaces, with average formation rates (contribution ratios) of 2.70(55.8%), 0.53(10.8%), and 0.05(10.6%) ppb h-1, respectively. During nighttime, the contribution of heterogeneous reactions gradually increased, including the heterogeneous reactions of NO2 on the ground surfaces and aerosol surfaces, as well as heterogeneous reactions related to the enhanced aerosol surface uptake of NO2 with NH3, with average formation rates (contribution ratios) of 0.07(41.3%), 0.03(20.3%), and 0.03(20.0%) ppb h-1. The primary removal pathway for HONO during the day was photolysis, while dry deposition was dominant at night. Further simulation analyses revealed that the incorporation of the new HONO mechanism significantly enhanced both the formation and loss rates of ozone (O3). The sensitivity of O3 generation was observed to transition from a VOC-dominated regime to a synergistic control regime involving both VOCs and NOx. Elevated HONO concentrations and their source-sink processes were found to not only accelerate O3 production but also modify its generation sensitivity through dynamic regulation of O3 precursor concentrations (VOCs/NOx). Therefore, for the prevention and control of springtime ozone pollution in Beijing, it is crucial to correctly understand the feedback mechanism of HONO chemistry on ozone formation.