光腔衰荡光谱法走航连续观测海表大气中CH4

以基于高精度光腔衰荡光谱法(Cavity Ring-Down Spectroscopy,CRDS)的Picarro G2301型分析仪为核心,自主设计、组装,建立了适用于船载走航连续观测大气CH4的系统.采用可溯源至世界气象组织全球大气观测网(WMO-GAW)的标准气序列开展多次测试,并建立了外标法线性校正方程.测试表明,该系统对CH4响应精密度优于0.5 ×l0-9,准确度优于0.1％,5个月内漂移小于0.3 ×l0-9.同时,结合船载走航连续观测的特点,优化建立了观测数据处理与质量控制方法,以保证所获数据的高质量和国际可比性.分别于2011年7月和2012年5月,率先在北黄海及渤海海峡区域开展了海表大气CH4的走航连续观测.实践证明,该系统操作简便,运行稳定,适用于船载走航连续海表大气CH4的研究,可获取高精度高时空分辨的观测数据.其中,2011年7月观测到的CH4浓度范围为1823.8×10-9～2020.7×10-9,2012年5月为1887.2×10-9～ 2136.2×10-9,均呈渤海海峡区域浓度高,北黄海中部区域浓度低的分布特征.

High-resolution measurement of CH4 in sea surface air based on cavity ring-down spectroscopy technique: the first trial in China Seas

For the purpose of high-resolution measurement of CH₄ in sea surface air, a low drift, high-precision cavity ring-down analyzer (model: Picarro G2301) is integrated into a continuously sampling system. A set of ship-based protocols for system operation and data processing are also developed. Briefly, air is pumped from a bow intake installed 10~15 m above the sea surface to avoid contamination from the ship. With an air cleaning unit and an airflow regulator, CH₄ concentrations in the sea surface air are continuously determined. This is the first trial in China Seas. Using four WMO-GAW traceable gas standards, the underway measuring system is calibrated and carefully tested over the concentration range of atmospheric methane of 1601×10^-9~2317×10^-9(dry volume ratio, the same below). The results verify the fact that the cavity ring-down analyzer has a typical precision of 0.5×10^-9 and a low drift of 0.3×10^-9in 5 months. In July 2011 and May 2012, the newly-developed measuring system has been applied to field surveys in the Northern Yellow Sea and the Bohai Strait. Results show that the underway measuring system can easily obtain high-quality CH₄ data with the relative error of less than 0.1%. The concentration ranges of atmospheric CH₄ in the regions under survey are revealed at 1823.8×10^-9~2020.7×10^-9 in July 2011 and 1887.2×10^-9~2136.2×10^-9 in May 2012, respectively. The two surveys show similar distribution pattern of atmospheric CH₄ that the concentration of CH₄ in sea surface air above the region of Bohai Strait is significantly higher than that above the central area of the Northern Yellow Sea.