Studies On The Distributions And Sea-to-air Fluxes Of Volatile Halocarbons In The Bohai Sea And The Yellow Sea

Volatile halocarbons （VHCs） are important atmospheric trace greenhouse gasesand take part in the catalytic ozone-destroying reactions, making it play significantroles in the global warming and atmospheric chemistry. The ocean is a massivereservoir of the VHCs that have natural and anthropogenic sources in the marineenvironments. Ocean interface layer is an important place of gases exchange betweenseawater and atmosphere. On the global scale, ocean may be the source or the sink ofVHCs in atmosphere. In the specific areas, especially in the coastal areas, the situationmay become more complex. Therefore, it is of great significance to investigate VHCsentirely and estimate the contribution of oceanic emission to the atmospheric VHCson the global scale.In the present dissertation, the concentration distributions, temporal and spatialvariations and sea-to-air fluxes of VHCs are studied systematically in the Bohai Sea（BS） and the Yellow Sea （YS） in spring and autumn. The main research results are asfollows:（1） Distributions and sea-to-air fluxes of6kinds of VHCs are studied in the BSand NYS （the North Yellow Sea） during Jun,2011and Nov-Dec,2011. The resultsshow that the average concentrations of CHCl₃, CH₃CCl₃, C₂HCl₃, C₂Cl₄, CHBrCl₂and CHBr₂Cl in the surface seawater of the BS are12.77（2.80³2.44）,17.51（0.28⁶9.52）,12.33（3.44³4.91）,5.20（2.12⁸.88）,5.33（0.66¹2.65） and7.79（0.56⁴3.40） pmol/L in spring and8.75（0.21²0.91）,14.94（7.07²9.58）,9.23（2.85¹9.71）,4.99（2.35¹0.26）,5.18（0.17¹6.37） and4.33（0.17¹7.79） pmol/L inautumn, respectively. The surface concentrations of6kinds of VHCs in the NYS are19.01（8.02²8.06）,11.12（2.73²2.32）,17.22（0.57³4.10）,7.90（2.59²6.82）,5.19（0.50⁵6.74） and7.10（0.12²4.28） pmol/L in spring and16.20（0.38³6.48）,9.91（2.72³1.73）,7.79（1.51¹2.65）,5.01（1.51¹0.90）,4.89（0.13¹1.93） and3.11 （0.97⁷.49） pmol/L in autumn, respectively, suggesting that the concentrations inspring are higher than those in autumn both in the BS and the NYS. There is a goodcorrelation between CHBrCl₂and CHBr₂Cl and there are no obvious correlationamong other compounds and the enviromental parameters. Depth profiles of6VHCsat transect S in spring show near surface and bottom maxima owing to in situproduction and the minima appear in the middle-layer of the water column, while inautumn the concentration gradient is small in vertical distribution because of thestrong vertical mixing. The sea-to-air fluxes of6VHCs in the BS are5.75（-73.6⁶8.5）,78.96（-3.7⁴14.3）,41.46（3.7¹47.4）,15.14（0.5⁶9.6）,20.18（0.5⁶7.2）,17.36（-0.06¹61.0） pmol/m²·d in spring and27.36（-12.5²9.1）,50.30（3.7¹40.6）,34.00（5.35⁹2.20）,8.19（1.07⁴8.66）,9.85（-1.5¹41.0）,4.19（-1.7⁴7.7） pmol/m²·d in autumn, respectively. The sea-to-air fluxes of6VHCs in theNYS are28.24（-0.2⁸5.8）,19.12（1.2⁶7.9）,29.36（0.1⁹1.1）,12.69（0.6⁵4.2）,7.26（-0.2²7.7）,10.65（-0.32⁴3.0） pmol/m²·d in spring and13.77（-79.4¹48.6）,74.98（0.02³69.6）,80.79（0.03³34.5）,13.74（-0.09⁵3.36）,16.64（-1.0⁵5.7）,7.30（-0.08³3.2） pmol/m²·d in autumn, respectively. The results of sea-to-air fluxes of6VHCs elucidate that the investigated area appear to be the source of atmosphericCHCl₃, CH₃CCl₃, C₂HCl₃, C₂Cl₄, CHBrCl₂and CHBr₂Cl during the study time.（2） Distributions and sea-to-air fluxes of6kinds of VHCs are determined in theSYS （the South Yellow Sea） during Jun,2011and Nov-Dec,2011. The surface waterconcentrations of CHCl₃, CH₃CCl₃, C₂HCl₃, C₂Cl₄, CHBrCl₂and CHBr₂Cl are7.92（1.22²5.69）,10.24（2.29⁶1.97）,18.86（3.13³8.76）,5.70（0.89¹4.96）,9.30（0.38²8.87） and13.45（4.46²6.85） pmol/L in spring and15.56（2.15⁸2.33）,28.04（3.10⁷4.57）,14.20（1.94²4.37）,5.21（1.69¹1.04）,6.17（0.92¹6.09） and3.77（1.20¹0.76） pmol/L in autumn, respectively. The sea-to-air fluxes of6VHCs in theSYS are1.42（-17.3⁴6.6）,14.22（0.01¹99.2）,31.14（0.08¹38.7）,8.63（-0.09⁴3.1）,11.56（-0.004⁴8.0）,17.87（0.04⁶7.0） pmol/m²·d in spring and18.96（-27.6¹43.4）,72.02（0.3²29.5）,38.02（1.8¹28.4）,8.36（-0.2²7.8）,14.97（0.09⁷0.5）,6.18（0.5³1.4） pmol/m²·d in autumn, respectively. Additionally, the sea-to-air fluxes of6 VHCs are impacted by wind speed remarkably.（3） The concentrations of6VHCs in surface seawater are varied in differentareas. In spring, the concentrations of CHCl₃and CH₃CCl₃are lowest in the SYS andthose of C₂HCl₃and C₂Cl₄are lowest in the BS. The concentrations of CHBrCl₂andCHBr₂Cl are highest in the SYS and lowest in the NYS. The spatial variation of6VHCs in autumn are similar, with maximum concentrations of CH₃CCl₃, C₂HCl₃,C₂Cl₄and CHBrCl₂in the SYS and minimum concentrations of CH₃CCl₃, C₂HCl₃,CHBrCl₂and CHBr₂Cl in the NYS. The concentrations of VHCs except for CHCl₃and CH₃CCl₃are higher in spring than those in autumn. The sea-to-air fluxes of6VHCs also show temporal and spatial variation. The fluxes of CH₃CCl₃, C₂HCl₃,C₂Cl₄and CHBrCl₂are highest in the BS in spring while those are highest in the NYSin autumn. The fluxes of VHCs in the YS are in marked contrast with those in the BSwhich appear to be higher in spring than that in autumn.