直射太阳光差分吸收光谱（DS-DOAS）技术用于NO2等气体的垂直柱浓度长期监测，当仪器视场中有云时，云内颗粒对光的多次散射会导致此技术的测量结果存在较大误差。针对此问题，采用DS-DOAS技术中同步测量O4垂直柱浓度的方法，判断视场内是否有云，对NO2垂直柱浓度的监测结果进行修正。统计得到了晴朗天气下由反演误差、大气扰动等因素引起的O4垂直柱浓度测量值的变化幅度为6%。O4变化幅度大于6%时，认为视场内有云。采用此方法修正了4天NO2垂直柱浓度监测结果，证实了此方法可以有效地提高DS-DOAS技术的测量精度。

NO2 vertical column density (VCD) is measured by direct-sun differential optical absorption spectroscopy (DS-DOAS). When cloud exists in the field of view of instrument, measurement results of this technique are influenced by multiple scattering of particles in cloud. To solve this problem, a new method is proposed. Simultaneously inversing O4 VCD is used to determine whether there is cloud in the field of view or not. Then the NO2 VCD is corrected. Statistics show that the variation amplitude of O4 VCD is 6% due to inversion error and atmosphere disturbance in cloud-free sky. If the magnitude of relative variation of O4 VCD is larger than 6%, there is cloud in the field of view. This method is used to correct NO2 results from a four-day field measurement. It is proved that this method can effectively improve the measurement precision of DS-DOAS when clouds exist in the field of view.