Pollution Characteristics of Volatile Organic Compounds and Analysis of Ozone Production Sensitivity in Hohhot during Summertime

To investigate the effect of Volatile Organic Compounds (VOCs) on ozone (O₃) formation during summertime—which is conducive to O₃ pollution—the chemical composition characteristics of VOCs and their sources were studied using high-resolution online monitoring data obtained in an urban site of Hohhot during the summer of 2021. Furthermore, the sensitivity of O₃ pollution days and the control strategy of its precursors were further analyzed using an observation-based model (OBM). Results revealed that the averaged total mixing ratio of VOCs was 21.10±9.38 ppb (1 ppb=10⁻⁹), with Oxygenated Volatile Organic Compounds (OVOCs) being the most abundant group (36.3%), followed by alkanes (23.8%), halogenated hydrocarbons (16.8%), alkynes (10.4%), aromatic hydrocarbons (6.6%), and alkenes (6.1%). According to the Positive Matrix Factorization (PMF) source analysis, the primary sources of VOCs in Hohhot are diesel tail-gas sources, gasoline tail-gas sources, solvent sources, natural gas and combustion sources, biological emission sources, and liquefied petroleum gas sources, with contribution rates of 19.8%, 18.2%, 17.6%, 16.3%, 15.4%, and 12.7%, respectively. According to the Relative Incremental Reactivity (RIR) and Empirical Kinetic Modeling Approach (EKMA) analysis, O₃ sensitivity was in the VOCs-limited regime during the O₃ pollution days in Hohhot, with greater RIR values from alkenes and aromatic hydrocarbons. Simulating precursor reduction scenarios from the various VOCs sources resolved by PMF revealed that reducing VOCs from motor vehicle-related sources is most beneficial to the control of O₃ during summertime.