The MS addressed an important topic in viewing the variation of ambient HCHO by satellite. And the authors answered most of the comments raised by the two reviewers. I still have problem with the methods that the authors sperating the primary and secondary sources of HCHO, by using simple linear regression. I double that secondary HCHO had different temporal variation with primary ones, so the linear regression of total HCHO would tend to correlated better with primary sources, but this did not mean less contribution of secondary sources, especially during photochemical reactive time period. I suggest that the authors seek a more reliable approaches to the apportion by more literature review in this regard.