Non‐methane hydrocarbons (NMHCs) play an important role in atmospheric chemistry and the ocean is a source of NMHCs in the atmosphere. Here, we investigated the annual variations of NMHCs concentrations and fluxes (i.e., ethane, ethylene, propane, propylene, and isoprene) in the semi‐enclosed shallow waters of Jiaozhou Bay from September 2016 to August 2017. Ethylene is the most abundant NMHCs, with an annual average concentration of 487.7 ± 239.3 pmol L−1. The concentrations of other NMHCs were lower; the average concentrations for ethane, propane, propylene, and isoprene were 87.0 ± 49.0, 65.7 ± 22.9, 127.4 ± 77.8, and 60.5 ± 47.1 pmol L−1, respectively. NMHCs concentrations varied largely between seasons and higher abundance were observed in summer. The correlations between NMHCs and environmental variables such as chlorophyll a (Chl‐a), dissolved organic carbon (DOC) were ambiguous, and principal component analysis (PCA) suggested nutrients contributed significantly to total variation. These results indicated that the control of NMHCs could be more complex in dynamic and anthropogenically impacted estuarine systems, which could be a result of multiple processes involving phytoplankton release, photochemical production, riverine input, and so forth. The average annual sea‐to‐air fluxes of ethane, ethylene, propane, propylene, and isoprene were 105.9–298.3, 583.5–1,337.0, 36.7–95.2, 85.2–389.6, and 25.2–182.4 nmol m−2 d−1, respectively. Although coastal and estuarine environments only account for a minor fraction of the global ocean (0.26%–0.39%), NMHC emissions from these areas could influence regional atmospheric chemistry and may be relatively important for global budgets (ethane, 1.70%; ethylene, 1.54%; propane, 1.29%; propylene, 0.87%; isoprene, 3.17%).

Methanol is one of the most abundant oxygenated volatile organic compounds in the atmosphere and plays an important role in atmospheric chemistry and ocean ecology (Heikes et al., 2002;Singh et al., 2001;Zhuang et al., 2018). Due to the variability of methanol concentrations and sea-air exchange fluxes between locations, uncertainty remains as to whether the ocean is a source or sink of atmospheric methanol. For example, Beale et al. ( 2013) observed methanol exchange in both directions in the Atlantic Ocean with a net oceanic emission of 12 Tg yr −1 , while Yang et al. ( 2013) reported a global extrapolation of −42 Tg yr −1 based on the atmospheric deposition of methanol over the Atlantic Ocean. In situ methanol production is often observed in oceanic waters (Dixon, Beale, et al., 2013) and phytoplankton could be a key methanol producer (Mincer & Aicher, 2016). However, methanol concentrations are maintained in the nanomolar range due to rapid consumption by marine microorganisms (