Characteristics and sources of VOCs and the O₃-NO_x-VOCs relationships in the central plain city, China

Abstract. Volatile organic compounds (VOCs) are important precursors of ozone (O₃) generation. Understanding the characteristics, and emission sources of VOCs, and the relationship between VOCs and O₃ during O₃ pollution are of great significance for O₃ pollution control. This study investigated the characteristics, sources, and effects of VOCs on O₃ formation in Zhengzhou, Henan Province from 1^st to 30^th June 2023, and provided recommendations for O₃ emission reduction strategies. Two O₃ pollution events occurred during the observation period. During the observation period, the concentration of Total VOCs (TVOCs) varied from 9.9 to 60.3 ppbv, with an average of 22.8 ± 8.3 ppbv. The average concentration of TVOCs in the two pollution events were higher than that on the clean days. Six major VOCs sources were identified by using the Positive Matrix Factorization model. Vehicular exhaust (28 %), solvent usage (27 %), and industrial production (22 %) were the main sources. An observation-based mode was applied to explore the O₃-precursors relationship and observation-oriented O₃ control strategies. The results of relative incremental reactivity (RIR) and empirical kinetics modeling approach showed that the O₃ formation in Zhengzhou in June was in anthropogenic VOCs (AVOCs)-limited regimes. VOCs with the largest RIR values, while NO_x had a negative RIR value. It was worth noting that the sensitivity of O₃ generation to biogenic VOCs (BVOCs) was greater than that of AVOCs. From the perspective of the reduction effect, the reduction ratios of AVOCs/NO_x should be no less than 3:1, which was conducive to the reduction of O₃ formation.