Derivation of the correction factor needed for COSMOS observations at high mass concentrations of black carbon

COSMOS is a continuous soot monitoring system for long-term observation of the mass concentrations of black carbon (MBC) in the atmosphere. The system uses a heated inlet to volatilize non-refractory aerosol components, a dual photodetector setup, and filter tape to collect BC particles from the air. In environments with very high MBC, rapid accumulation of BC on the filter tape results in a rapid decrease of filter transmittance (Tr), leading to more frequent filter advances and instrument downtime for changing the filter rolls. Thus, a correction factor is needed to allow accurate determination of MBC values even after large decreases of Tr. Here, by using MBC measurements obtained simultaneously by two COSMOS systems, we characterized Tr and derived a correction factor that permits the derivation of MBC at very low Tr while maintaining reasonable accuracy.COSMOS是一套用于长期监测大气中黑碳质量浓度（Mass Concentration of Black Carbon, MBC）的连续炭黑监测系统。该系统采用加热进气口挥发非难熔气溶胶组分，搭配双光电探测器装置，并通过滤带采集空气中的黑碳颗粒。在MBC浓度极高的环境中，滤带上的黑碳会快速累积，导致滤光透过率（Tr）迅速下降，进而需要更频繁地推进滤带，且更换滤带卷时会造成仪器停机时间增加。因此，亟需引入校正因子，以在滤光透过率大幅降低后仍能准确测定MBC数值。本研究利用两套同步运行的COSMOS系统获取的MBC测量数据，对滤光透过率进行了表征，并推导得到校正因子，该因子可在极低滤光透过率条件下准确推导MBC数值，同时保证合理的测量精度。