Reply on RC1

Abstract

Satellite and surface carbon monoxide (CO) observations have been widely used to investigate the sources and variabilities of atmospheric CO. However, comparative analyses to explore the effects of satellite and surface measurements on atmospheric CO assimilations are still lacking. Here we investigate the evolution of atmospheric CO over E. Asia in 2015–2020, via assimilating CO measurements from the Measurement of Pollution in the Troposphere (MOPITT) and China Ministry of Ecology and Environment (MEE) monitoring network. We find a possible inconsistency by assimilating satellite and surface measurements: the adjusted CO columns are about 3.29, 3.63 and 3.68 x 1018 molec/cm2 by assimilating surface CO measurements, in contrast to 2.80–2.93, 3.14–3.25 and 3.09–3.22 x 1018 molec/cm2 by assimilating MOPITT CO observations in 2015–2020 over E. China, North China Plain (NCP) and Yangtze River Delta (YRD), respectively. This inconsistency could be associated with possible representation errors due to differences between urban and regional CO backgrounds. Furthermore, assimilations of normalized surface CO measurements (to mitigate the influences of representation errors) indicate declines of CO columns by about 4.0, 4.5, and 4.0 x 1016 molec/cm2/y over E. China, South Korea and Japan in 2015–2020, respectively, in contrast to 1.7–2.1, 2.1–2.7, and 2.1–2.6 x 1016 molec/cm2/y by assimilating MOPITT CO measurements. This discrepancy reflects the different vertical sensitivities of satellite and surface observations in the lower and free troposphere. This work demonstrates the importance to integrate information from satellite and surface measurements to provide a more accurate evaluation for atmospheric CO changes.