Distributions of volatile halocarbons in seawater and atmosphere in the East China Sea during spring

Volatile halocarbons (VHCs) are important greenhouse gases and ozone depleting substances in the atmosphere.The concentrations of CFC-11 (CC1₃F), CFC-12 (CC1₂F₂), CFC-113 (CC1₂FCC1F₂) and CH₃I in the seawater and marine atmosphere of the East China Sea were measured in May 2017.The spatial distribution of the four kinds of VHCs, their influencing factors and sea-to-air flux were investigated.The mean concentrations of CFC-11, CFC-12, CFC-113 and CH₃I were (8.1±5.1), (3.9±1.6), (10.4±2.3) and (6.3±2.7) pmol/L, respectively.The elevated concentrations of VHCs in the surface water were observed in the northeast of East China Sea as well as on the Fujian and Zhejiang coast area.The results indicated that the distributions of the four kinds of VHCs were influenced by the water mass, biological activities as well as human activities.A positive correlation was found between the concentrations of CH₃I and Chl a in seawater (r=0.403, p < 0.01).The result implied the influence of the production by phytoplankton to concentration distributions of CH₃I in the study area.The mean concentrations of CFC-11, CFC-12, CFC-113 and CH₃I in marine atmosphere were (9.8±1.0), (21.1±2.4), (3.0±0.9) and (0.2±0.2) pmol/L, respectively.Combined with meteorological parameters such as wind velocity and wind direction and back trajectory simulations, the transfer of air terrestrial pollutants from China land, the diffusion of offshore air masses and the exchange of VHCs between sea and air were important factors influencing the concentration distribution of VHCs in the atmosphere.The sea-air flux demonstrated that the East China Sea acted as a sink for atmospheric CFC-11 and CFC-12 in the study area, whilst a source for CH₃I in the air during spring.