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Aerosol interference with open-path eddy covariance measurement in a lake environment
Agricultural and Forest Meteorology ( IF 5.6 ) Pub Date : 2024-06-17 , DOI: 10.1016/j.agrformet.2024.110104 Lei Jia , Mi Zhang , Wei Xiao , Yini Pu , Zhen Zhang , Hengxin Bao , Pei Ge , Jie Shi , Yang He , Fuyu Yang , Kelly Aho , Peter Raymond , Xuhui Lee
Agricultural and Forest Meteorology ( IF 5.6 ) Pub Date : 2024-06-17 , DOI: 10.1016/j.agrformet.2024.110104 Lei Jia , Mi Zhang , Wei Xiao , Yini Pu , Zhen Zhang , Hengxin Bao , Pei Ge , Jie Shi , Yang He , Fuyu Yang , Kelly Aho , Peter Raymond , Xuhui Lee
Open-path eddy covariance (OPEC) is widely used for measuring trace gas fluxes between the surface and the atmosphere. At a lake in Eastern China (Lake Taihu), the CO flux measured with OPEC was often negative at night (with values as low as 22.1 μmol m s) and was coherent across the whole lake, as if the lake were a large sink of atmospheric CO. The purpose of this study is to investigate the cause of this negative flux phenomenon. In addition to OPEC, we also used closed-path eddy covariance (CPEC) and the transfer coefficient (TC) method to measure the flux. The results show that the persistent negative CO flux phenomenon was observed with OPEC but not with CPEC or TC. Because air drawn into the CPEC analyzer was filtered but the OPEC analyzer was influenced by aerosol contamination, the most logical explanation was that particles deposited on the optical lens of the OPEC analyzer changed its cross-sensitivity to water vapor. The direct evidence of this interference was a strong positive correlation between the OPEC analyzer's signal strength and the CO mixing ratio observed at 10 Hz. We suggest that it is possible to perform post-field correction to this negative flux bias using the 10 Hz signal strength data. In comparison, an OPEC system at a nearby land site did not experience aerosol interference due to low water vapor flux at night and lack of hygroscopic growth of particles on the optical lens in low humidity conditions. The type of aerosol interference reported here may also occur in high humidity and high pollution conditions elsewhere.
更新日期：2024-06-17
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