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To investigate the pollution characteristics and formation mechanisms of ozone episodes in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) during autumn, ozone (O3) concentrations and emission characteristics of volatile organic compounds (VOCs) were analyzed during three ozone episodesin Hong Kong.Observational data combined withobservation-based model(OBM) and the empirical kinetics modeling approach (EKMA) wasemployed to assess the impact of VOCs on O3 formation sensitivity mechanisms and contribution to O3 formation. The peak O3 values recorded during the three episodes were 382.65, 302.67, and 301.76μg/m3, with corresponding concentrations of VOCs measuring 23.6×10-9, 25.4×10-9, and 32.1×10-9, respectively. Oxygenated volatile organic compounds (OVOCs)were the most dominant of the observed species, with methanol, formaldehyde, and acetone being the three most prevalent by volume fraction. EKMA curves confirmedthat the nonlinear relationship among O3-nitrogen oxides (NOx)-VOCs depends ontheir instantaneous concentrations. The morning hours were characterized as VOC-limited regimes, while the afternoon hourswerethe transitional regime. The photochemical initial concentration (PIC) was 8.2×10-9 higher than measured concentration, indicating that neglecting photochemically VOCs consumption may lead to an underestimation of the contribution of local VOCs photochemical reactions to O3 formation. Furthermore, differences in the types and concentrations of O3 precursors and radicals resulted in varying O3 formation and loss rates, confirming the promoting effect of VOCs as precursors on net O3 formation. Based on O3 formation potential (OFP) and OH loss rate (LOH) calculations, the VOCs with the highest contribution to the OFP were OVOCs (68.9%), alkenes (17.5%), and aromatics (13.6%). Formaldehyde and isoprene were the dominant species driving O3 formation and hydroxyl radical (OH) consumption in the autumn in Hong Kong, respectively. The OFP of formaldehyde ranged from 42.1 to 73.1μg/m3, and the LOH of isoprene varied from 1.35 to 2.12s-1. Backward trajectory cluster analysis revealed that Hong Kong’s background site was primarily influenced by three air mass types driven by northeasterly winds: long-range transport (52%), short-range transport (28%), and local sources (20%). Results reveal that the photochemical reactions of VOCs, the response characteristics of different VOCs to the sensitivity of O3 formation, and the synergistic effect of regional transport and local emissions have a significant impact on the O3 pollution in Hong Kong during autumn.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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